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A.K. Boomer
12-17-2016, 02:37 PM
Iv tried this along time ago - did not pan out but want to ask again.

have a new crank proto-type im testing on my bike dyno, crossed this bridge along time ago and settled on a solution that was acceptable as I tried the electronics alternative with no good results,,,

the goal is to stabilize the dyno voltage spikes that it goes through due to the pedaling forces being pulsating in bi-mechanical nature....

this is esp. important because all I have is a digi-meter and need to be able to read the last few digits with accuracy instead of them jumping all around - have tried the capacitor approach complete with diode and resistor combo's to just direct a "sample" of the voltage and filter it and then get a reading -- mixed success but generally not good enough, so I did what a mechanic would do - I built more of an electro-mechanical device and it actually worked very well, well enough to record down to 1/10th of a volt with stability...

Don't laugh but here's the unit below,,, this coupled with a heart rate monitor and my cadence meter and I have a pretty good dynamometer, it's just two perm mag tape deck motors and one is the motor and the other is the generator that's sole purpose is to power the volt meter,,, ends up being just a fraction of actual voltage but no worries as it does provide a stable guide - the real dyno gens power a ford taurus rad. fan that keeps me cool while testing - ambient air temp and all kinds of other factors are figured in...

Note the glued in heavy washer installed into the little gauge generator pulley for more stability...

http://i146.photobucket.com/albums/r249/AK_Boomer/DSC04153_zpsootpxeop.jpg (http://s146.photobucket.com/user/AK_Boomer/media/DSC04153_zpsootpxeop.jpg.html)

http://i146.photobucket.com/albums/r249/AK_Boomer/DSC04154_zps5wjnos50.jpg (http://s146.photobucket.com/user/AK_Boomer/media/DSC04154_zps5wjnos50.jpg.html)

Thing is - is this unit just shot craps --- I think it's been too much of a labor load for the motor, it got warm and I believe I either fuqued the brushes or the windings are shorting because my voltage is way low and not as stable...

here's the main dyno itself... http://i146.photobucket.com/albums/r249/AK_Boomer/DSC00032.jpg (http://s146.photobucket.com/user/AK_Boomer/media/DSC00032.jpg.html)

http://i146.photobucket.com/albums/r249/AK_Boomer/DSC00030.jpg (http://s146.photobucket.com/user/AK_Boomer/media/DSC00030.jpg.html)

Your mission - should you choose to accept - is to help me design a Cap system that will work because iv gutted out my last tape deck player and do not have any little 12 volt motors around,,, but what I do have is a couple old computers with the 110 to 12 volt power boxes,,, can something be done with them?

can I kinda isolate a Cap with a diode or two and then use a resistor to feed it and get the reading off of it?

How can I build a virtual mechanical "flywheel" in the electronics world, as you can tell not may area of expertise... thanks

darryl
12-17-2016, 02:51 PM
There is the electronic equivalent of a flywheel- it's an op amp that charges an output capacitor to the peak voltage on the input. You get to decide how long the charge on the output cap lasts- could be a fraction of a second or minutes. The circuit would be called a voltage follower or current amplifier, and would charge the cap through a diode. A resistor across the cap determines how fast the voltage decays. Make it longer than the integration time of a digital voltmeter and you should be able to get a workable reading. I'm guessing that you won't need to see variations second by second- probably more like 5 seconds or more.

A.K. Boomer
12-17-2016, 03:02 PM
I'm guessing that you won't need to see variations second by second- probably more like 5 seconds or more.

You guess very close,,, a mean average every 5 seconds would be just fine as my cadence meter is shorter intervals than that and if i kept watch on it most of the time like I do it means the voltage output and therefore "drag" is fairly stable too...

gutted out an old computer power converter, think there's enough variety in here to make it happen?

http://i146.photobucket.com/albums/r249/AK_Boomer/DSC04155_zpswo0ywxjn.jpg (http://s146.photobucket.com/user/AK_Boomer/media/DSC04155_zpswo0ywxjn.jpg.html)

The Artful Bodger
12-17-2016, 03:07 PM
I suppose if you powered a filament bulb from your dyno you could use a simple photo cell connected to your meter to read the brightness of the bulb which would vary with speed of the dyno. Hopefully the thermal inertia of the filament would smooth things out and all with few parts.

darryl
12-17-2016, 03:21 PM
Somehow it seems to me that you are over-complicating it. You have an output voltage from the dyno that you used to run the tape deck motor that runs another tape deck motor to give the voltmeter a reasonably stable input voltage. It seems that just putting the voltage from the dyno through a diode and into a capacitor would give a slowly enough varying voltage for the voltmeter to handle. Perhaps what is needed here is a current limiter in series with the output from the dyno so the peak voltage doesn't charge the capacitor as quickly. A current limiter that would work for this is very simple- one three terminal voltage regulator and one resistor. I'm guessing you won't care what the actual output voltage comes to be as long as it doesn't vary too quickly. If the output from the dyno is more than about 6 volts at any test speed, then this will work.

This circuit is so simple that I can describe it without needing a diagram, if you're interested in trying it. You can probably find a suitable resistor and capacitor in that old power supply, but you likely won't find a 317 regulator in there, which is what you'd need.

BCRider
12-17-2016, 03:33 PM
A diode and cap should do the trick. If the meter value was varying too much with that setup then it indicates that you didn't use a large enough value of capacitor. Or that your meter has a lower than optimum input resistance and it's bleeding down the voltage.

The type of capacitor you use helps a little too. A solid tatalum cap will have a lower self leakage than a cheap electrolytic. But even so unless the electrolytic cap is a really bad one it should hold a charge without much of a drop for at least a while.

As a test try hooking the cap to the meter. Then touch a 9v battery set to the correct polarity to the cap leads to charge the cap. As the battery is pulled away watch the voltage on the cap with the meter. If it drops too rapidly for your needs then you need a better or larger value cap to work with the input resistance of that meter. Most likely a larger value. Testing this way totally isolates the meter and cap from any other issues and will tell you if the meter is bleeding off the charge fast enough to make the small numbers unusable.

A.K. Boomer
12-17-2016, 03:37 PM
Have not tried the three terminal regulator before - tried all kinds of combo's with diode resistor and cap...

You can see some pretty big caps in the power supply I took a pic of but those caps must be for the 110 side as they are rated 200volts

on the other side is a 3300 uf 16volt cap must be for the 12 volt supply, is this a good cap to start with? it's the biggest one there would it not provide the greatest buffer for saturation? I will look for a 317 reg. does it have 317 numbers on it? snowed in today - nothing better to do so thanks for the help Darryl U 2 BC

fixerdave
12-17-2016, 03:37 PM
Well, the modern way would be to feed the sample voltage into a micro-controller, read the voltage, apply whatever filtering you want programmatically, and then output said voltage.

That would cost you, oh about $4 for an Arduino. Now, if you wanted to dispense with using your voltmeter, you could put an LCD panel shield on said Arduino. That would be another $5 or so, though it would give you 2 lines and some buttons for whatever as well. Oh, probably need a wall transformer for power. That's another $2, shipping included.

In the end, you'd have a nice LCD readout you could mount on the handlebar that did whatever you managed to code around. Average power, peak, low, rate of climb, calories per hour, whatever. Once you get into the digital world, it's all just little bits of code, much of which is already written and freely available. You just have to figure out enough to tie it all together.

There is a learning curve, but compared to a lathe it's not that bad. And, it won't chop your fingers off if you mess up :)

David...

BCRider
12-17-2016, 04:06 PM
You shouldn't need anything like a 3300ufd cap for a voltage holding circuit. Something more around 100ufd should do just fine. A 3300ufd cap takes some serious current to charge it up. Mind you that in itself may aid in stabilizing the voltage. So it might be worth a try.

A resistor in series with the cap to slow down how fast it charges can work towards making the reading more steady. But the resistor by itself is enough of a current limiter. You don't need a voltage regulator as well. Also the regulator needs voltage to run so it'll also cause a voltage drop. And that might become an issue. Easier to just use a resistor to limit the current. That'll slow down the charging rate of the capacitor.

But at the same time the current limiting resistor also needs to be selected so it works with the input resistance of the meter that is leaking down the capacitor. MOST meters up way up around 10 or 20 Mohm input resisitance. But not all of them... if you're using a seriously cheap meter it may have a much lower input resistance value. You would want to read the manual to find out what the spec is.

You can get a feel for what resistor to use for an input current limit resistor. The RC time constant for a capacitor and resistor combination is given by R x C=t (greek "tau" actually). The value in ohms x farads. And for a series resistor and cap the time to reach up around 95% of the final value of the charge is 5t. Now you want a fairly long "t" so it stops the value rising too fast. Let's start with .5 seconds for "t". If you're using a 100ufd cap then the resistor you want to use with it would be .5/.0001=50K That combo would take 2.5 seconds to come up to a stable value. That seems a little too long to me. So perhaps start with more like 25K or 32K. And if the meter doesn't bleed it off too fast it'll hold that value to where you probably want to bleed it off with some other longer RC resistor. To avoid splitting away too much voltage you'll want to keep the bleed resistor up at 10 to 15x the value of the inflow limiting resistor so maybe 500K? Anything like a 470K to 560K should do the trick. You might need to play with these resistor values a little. But in the end you should be able to tune the values so that you have a fairly stable reading.

So you would end up with a diode and then the 25K resistor in series with the far end connected to the + of the cap. And across the cap in parallel you'd have the 470 to 560K bleed off resistor. That make sense? So fast but not TOO fast to charge up and quite slow to drop away the value.

PStechPaul
12-17-2016, 04:08 PM
What you may want is a simple R-C integrator, which is just a resistor in series with a capacitor. The time constant (in mSec) is simply the resistor (in kOhms) and the capacaitor (in uF). So for a 1 second TC a good combination might be 10 uF and 100 kOhms. You probably don't want to use a resistance much higher than that, maybe 500k maximum, and it would be best to use a "good" capacitor, perhaps ceramic (multilayer) or Mylar or polypropylene, or a tantalum electrolytic.

It seems you also have a problem with your dynamo. If it has brushes and a permanent magnet and generates DC, there will be commutating noise consisting of high voltage "spikes" of short (microseconds) duration. If these get to the voltmeter, they can cause erratic readings and possibly damage. Worn brushes and a dirty or pitted commutator can make the problem worse. If you are getting inconsistent and lower than normal output, I suspect such a problem, and it requires opening the device and repairing it by cleaning or resurfacing the commutator, and replacing or cleaning the brushes.

A small ceramic or film capacitor (with low impedance at high frequency) across the brushes can minimize the noise at its source. Locating it away from the motor/generator means the energy will travel along the wiring and possibly cause problems with radiated electromagnetic noise, which can couple into the meter even without leads attached.

Another good way to deal with inductive spikes is to use a series inductor, such as the toroidal common mode choke in the power supply you show. You can use the windings in parallel or series on one lead from the generator to deal with "normal mode" noise rather than "common mode" for which the CMC is designed. The power supply also most likely will have some small chokes consisting of a bar or donut of ferrite with wires wrapped around it. One of these may be all you need.

It is really helpful, and perhaps necessary, to use a scope to diagnose and fix such problems. You can probably get a usable old analog scope on eBay for less than $100, or you can buy one of the cheap USB or AVR based digital storage scopes with color screen for $20-$50. You should get one with at least 1 MHz bandwidth, to see the narrow noise spikes.

Good luck!

darryl
12-17-2016, 04:10 PM
317- it will say LM317, or NE 317, or some other letter prefix before the number- but I can almost guarantee that you won't find one in that power supply.

3300 uf could be a bit large for this application, but then again it might smooth out the voltage variations enough for the circuit to be usable. You might find a 1000 uf in there- likely anything down to about 100 uf could be useful.

Short of finding a regulator ic, you could just use a series resistor. Your circuit would then be a resistor and diode in series, feeding a cap with its negative lead grounded, resistor in parallel with the cap. Meter reading taken across the cap. Dyno + voltage goes to the first resistor, and - voltage to the negative of the cap. As a guess I'll say the first resistor would be between 22 ohms and 100 ohms, the cap between 220 and 1000 uf, and the bleeder resistor across the cap between 470 and 2200 ohms. Pretty much all this could be found in that power supply.

PStechPaul
12-17-2016, 04:18 PM
The diode and capacitor will make a peak hold circuit, which may be useful but perhaps not what is wanted. With a bleeder resistor it would be a "fast attack slow decay" filter, which will give a long-time average of the peaks.

Adding a regulator may give a steady output from a varying input from the dyno, but I don't think that is what is wanted.

J Tiers
12-17-2016, 04:24 PM
Do you need any sort of calibration?

Do I understand that this dyno puts out a voltage?

If so, is it AC or DC? I'm not clear from the description, sounds like DC maybe

The basic thing is that for a resistor and cap system to get an average, there are two resistors.

one in series with the input, and usually one connected to discharge the capacitor.

The input one, along with capacitor value, sets the "charge time", the time it takes for the output to respond. when the input changes. The biigger the resistor and capacitor values, the longer. You can just multiply the values, resistor value times capacitor value. With megohms and microfarads, that comes out in seconds

The result is the time for the system to charge to 66% of the input voltage. That is called the "time constant" of the circuit.

The discharge one sets the time the system holds the value. Same equation.

If the input comes from a diode, you NEED the discharge resistor. If the input comes from a source that will accept current, such as a regular DC generator, you can use just the input resistor and it will average perfectly well.

From your comments, you may want a time constant of as much as 10 seconds. Maybe even more, if you want the meter to hold steady and change slowly.

With a DC source, no diodes, 10 seconds would be 1 megohm and 10 microfarads. Or 100k ohms and 100 microfarads. Charge and discharge time will be the same.

If it DOES come from a diode, you will need to change that somewhat. Charge and discharge will be diifferent. You may want to go with something more like 330K input, and 150k for the discharge, using 100 microfarads. That will change the voltage, but the effect will be the same.

BCRider
12-17-2016, 04:48 PM
Clearly from all the replies some of us are on the same page as to what the circuit should look like but there's some wildly varying suggestions as to the actual values for caps and resistors.

In the end it'll take a bit of trial and error to find the values that provide the limit on the input that slows down the charging and the value of the discharge resistor to slow the drop off.

I'd also suggest that for any regular digital multi meter used as a "speed gauge" that you consider the idea of masking off the last number. That one is always going to dither a lot.

Another option is to consider using a regular bicycle speedometer on some part of the arrangement. Programming these includes a step where you input the length of a wheel's circumference so the rotation time corresponds to the proper speed. And these speedometers have some suitable smoothing included so the readout doesn't wander badly. Doing this may require some additional pulley so that the wheel with the sensor magnet on it spins at some RPM that simulates a regular bicycle wheel in some sort of valid gear. Or you might be able to drive it off the pedal cranks directly if it'll take the equivalent value needed. I tend to think it'll need some form of gearing though. Otherwise you would need to input a circumference that would be suitable to an old style penny farthing bike. And I don't think the speedometers will let the circumference value go that high.

Note that this does not require a full size bicycle wheel. Just that you include the same sort of ratio you'd have in your most often used bicycle gearing.

A.K. Boomer
12-17-2016, 04:51 PM
So cool you guys seriously thanks for the help --- I just gutted the low voltage side of the board and I got a range of caps that should do the trick --- I been charging them like BC said with a 9 volt battery and then watching the state of decay whilst connected to the meter!

it's cool think im going to get it this time, check out all the caps and also got an adjustable variable resistor that says "102" on it but the board empty space it came off of says "vr 401"

http://i146.photobucket.com/albums/r249/AK_Boomer/DSC04156_zpsotmkc9hq.jpg (http://s146.photobucket.com/user/AK_Boomer/media/DSC04156_zpsotmkc9hq.jpg.html)

Im thinking if I use the right cap I won't have to use a bleed down resistor? just let the meter do that as it takes some consumption to run it??
and if I wire it right do I even need to use a diode?

this is actually very exciting to me because I don't know much about it so it's like a mad science experiment lol

J Tiers
12-17-2016, 05:02 PM
The meter, if it is a digital, may have an input resistance as high as 10 megohms. That's gonna be a long "hold time" unless the input source can accept a discharge back through the input resistor as I mentioned.

If you put your meter right on the dyno output, set to DC, do you get a reading when it is operating?

If you get a reading, then if you try to read ohms across the output (not operating) do you get a low reading?

The averaging time you want should be one that gets you a stable reading at your slowest cadence. The dyno may have a low frequency output at your slowest cadence, which might lead to a good deal of meter bounce.

A.K. Boomer
12-17-2016, 05:10 PM
The meter, if it is a digital, may have an input resistance as high as 10 megohms. That's gonna be a long "hold time" unless the input source can accept a discharge back through the input resistor as I mentioned.

If you put your meter right on the dyno output, set to DC, do you get a reading when it is operating?

Yes anywhere from 6 to 12 volts depending how hard I pedal and in what gear...



If you get a reading, then if you try to read ohms across the output (not operating) do you get a low reading?
I would think I would get a reading - it would be like testing three perm. mag motors --- the generators and the fan no?


The averaging time you want should be one that gets you a stable reading at your slowest cadence. The dyno may have a low frequency output at your slowest cadence, which might lead to a good deal of meter bounce.


yes well said and that would be sprint mode not spin,,, standing up and torquing out instead of high rpm spinning - and that is where I seen the most fluctuation even with the little motor/gen set up

A.K. Boomer
12-17-2016, 05:16 PM
Just for the record - there is nothing wrong with my main dyno, it's putting out like crazy and the fan will blow stuff away that is not anchored down --- all this hoopla is to just stabilize the reading as I said before the human machine is a little herky-jerky power production wise in fact the typical pedal stoke is really a pulsation at best,,,

add to that the digi meter skipping around and even though I have an ample flywheel on the dyno side of the bike it still is too abrupt to get any quality readings off of

PStechPaul
12-17-2016, 05:50 PM
For your purposes, perhaps an analog meter would be better.

http://www.ebay.com/itm/New-Analog-Voltmeter-Panel-Pointer-Volt-Voltage-Meter-Gauge-85L1-AC-0-15V-/401244433879

http://i.ebayimg.com/images/g/uecAAOSw6DtYVNtR/s-l1600.jpg

A.K. Boomer
12-17-2016, 07:22 PM
Ok I think I got it - I had a resistor - a capacitor and a diode just in case I missed something --- all soldered up ready to be played with in the dyno room,

I tried my best to follow Darryls wiring advise but im sure i blew it severely as I really can't follow instructions well when it comes to electronic stuff. so went down there - hooked everything up - meters jumping all around no way I got it right.

tried another config. same deal - tried another - same... totally pissed that I can have something on the bench and test it like BC told me too - see it behave steady and then watch it go haywire when I try to connect it --- so - got discouraged - started drinking,,, when the going gets tough - the tough get drunk right? yeah kinda unless you really want to make some progress so caught myself and took one last stab at it - in my minds electronic eye which granted is best described as a distorted cyclops --- I was asking why such erratic behavior - i mean even more so than if I just connected the meter direct...

the answer lied in using the diode and then using it in the correct place and i'll tell you why, it's because during the "dead spots" in pedaling the generators are no longer generators and try to "bleed" anything with a higher value into them because at that point they want to become motors - so enter the cap discharging at a "spike rate" and really fluctuating the meter...

so - I thought i would just forgo the resistor as the diode actually has some of those values for "cap charging" and as far as discharge if the diode is in the right place then the discharge rate will be just meter induced,,, connected it all up and walla,,,
totally stable beyond believe! it's way better than my little motor gen set up ever was,,, it's got one quirk --- it's stable and reaches it's operating range quick - but takes off very gradually to higher values just in the 100ths of voltage rage --- it does level off,,, so it's not simply cap saturation mind you - again that happens very fast - there's a warming process of some kind in one of the components,,, i can live with this as like i said it seems to move up and then stabilize just after a few minutes...

anyways - thanks for all the help from all of you - i think you guys got me in the right cap range - what I went with was a 470uf 16 volt...

I can go twice as high or twice as low if i want but so far do not see the need

here's the simple config. that ended up working;
http://i146.photobucket.com/albums/r249/AK_Boomer/DSC04158_zpsw1maoowy.jpg (http://s146.photobucket.com/user/AK_Boomer/media/DSC04158_zpsw1maoowy.jpg.html)

http://i146.photobucket.com/albums/r249/AK_Boomer/DSC04157_zpstzue8dbc.jpg (http://s146.photobucket.com/user/AK_Boomer/media/DSC04157_zpstzue8dbc.jpg.html)

Swarfer
12-17-2016, 07:32 PM
Hi Boomer

Have you thought about trying some electronic circuit simulation software? It is fantastic when trying to understand the behaviour of circuits. It won't help you with reading your voltage, but it will help you understand things like how capacitors charge and discharge, because you can look at the curves with a virtual oscilloscope. I use NI Multisim, as I don't have an oscilloscope, something I really need to get...

A.K. Boomer
12-17-2016, 07:46 PM
Swarfer i have to admit it's a fascinating field for sure and am a little drawn to it if not just for at least to bettering my understanding about it some but main goal here was trying to build a better unit and also do it without leaving the house or ordering anything, knew i had a bunch of components in my junk/storage room that were in the voltage range and thought it all there just have to figure out a way of combining the right ingredients so to speak...

darryl
12-17-2016, 07:50 PM
Just to possibly belay any confusion as to my suggestion of using a regulator- it would be set up as a current regulator, not a voltage regulator which is its usual use. As a current regulator in series with the cap charging circuit, it behaves like a series resistor but with some benefits. The voltage generated by the dyno supplies a charge current to the cap, and if no series intervention was used, the voltage on the cap would quickly come up to what the dyno was putting out, minus the diode voltage drop. By limiting this charging current, the rise time of the voltage on the cap is lengthened, thus smoothing out the voltage changes on the cap. A series resistor would work this way as well, but with a less precise action. It may of course be totally good enough, and in this case it would just go in line with the lead going from the dyno to the diode. Worth checking this out regardless, as it's a very simple thing to add and might improve the results beyond what Boomer has achieved already.

By the way, the marking 102 on that trimmer pot means it's 1000 ohms- 1,0, followed by 2 more zeros, or 1000. The number R 401 is just a circuit part number. It could be the same part, but called R 2 in some other circuit, or R 1205, or whatever. It's still 102, which is 1000 ohms.

Swarfer
12-17-2016, 07:53 PM
There is free software, and trial versions of multisim, and you don't have to leave your house, order anything, take anything apart, make a mess, or get dirty :)

J Tiers
12-17-2016, 07:55 PM
You probably do NOT need the diode, then. You already have DC, then, so what you need is a smoothed version of that.

A large value resistor and a substantial value capacitor will do for you. the meter will be fine as the discharge, because there will be discharge back into the source (the dyno).

As mentioned, a 100k ohm and a 100 microfarad capacitor should give a pretty smooth response. It's a place to start. Will take 10 seconds to come from zero to about 4 volts out of 6. And will also take that long to come DOWN 4 volts out of 6 if you stop pedaling entirely.

From what you say, you need a considerably higher resistor value than what you are using.

It is inherent in the "average" that when you stop, or slow down, that the output will decrease, "average" is defined over time, so any time with lower or zero output will reduce the reading.

A.K. Boomer
12-17-2016, 08:12 PM
You probably do NOT need the diode, then. You already have DC, then, so what you need is a smoothed version of that.



I have what is called "pulsating DC" and while not AC it kinda acts like it with a fully charged Cap from a power stroke that then goes to becoming a very small (and quickly drained) power source during the "dead spot"

so by totally isolating it from being able to "bleed back" (with the diode) then all's im at the mercy of is power spikes (which are also filtered through the diode as it's a resistor) and the bleeddown effect that the meter has on the cap (real slow)

as stated all is good! it's actually perfect - was just looking for the answer as to what causes the very slow and small increase in values AFTER the cap is fully charged --- is it the cap warming up or the diode warming up to operating temps? it totally stabilizes within a couple three minutes...

J Tiers
12-17-2016, 08:48 PM
If you get what you want, that's fine. You still don;t NEED the diode, it just acts as a "peak hold", which may work for what you want.

A small change? Could be anything. Diode forward voltage goes down with temp, so that would increase the voltage a few millivolts. Grease everywhere warms up, so the same pedaling effort might go a tad faster, raising the voltage.

How small is it? With all the variables, I'm a little surprised anything small is really see-able.

BCRider
12-17-2016, 08:48 PM
was just looking for the answer as to what causes the very slow and small increase in values AFTER the cap is fully charged --- is it the cap warming up or the diode warming up to operating temps? it totally stabilizes within a couple three minutes..

Depending on the values of the parts you are using it's likely that time constant thing again. The RxC thing mentioned by a couple of us. What occurs is that when the cap is very low in voltage it acts like a short circuit and the resistor controls the current to the cap. But as the current charges the cap the voltage at the cap rises and there's less difference voltage across the limiting resistor. Less voltage = less current so a slower charge.

Here's a page on RC networks that has a graph half way down showing the charge curve on the cap and the discharge curve.

http://www.electronics-tutorials.ws/rc/rc_1.html

In your case if you are using different value resistors for the input current limit and the bleed down resistors then each time constant for charge and discharge will be different.

But you can see how initially the voltage rises fairly fast. Then the last little bit takes a lot longer time. You're seeing this because of the numbers. In the days of analog meters that last needle's width or two went mostly unnoticed unless you had a really keen eye on it.

darryl
12-17-2016, 08:49 PM
It's probably the cap stabilizing after having not had voltage on it for some time. Many caps will be like that. It doesn't normally become a problem, but in the case of time-constant circuits (like what yours is) it can show these symptoms. Someone suggested a tantalum cap several posts ago- probably would be better but it may be hard to find in that value. You would have to change the resistor values to get the same time constant. Since you're using a digital meter and relying on it for the cap discharge, there will be a minimum capacitance level required to keep the circuit performing as you need it to.

With regards to your diode behaving like a resistor- it's really only dropping some voltage and not interfering with the charge current to any real extent. That looks like a 1N4000 series part- it does have a fairly low forward voltage drop, even at 1 amp of current. I'd be surprised if there is any peak current flowing through it in your application that's higher than a tenth of that. Irrelevant anyway, since you have it working to your satisfaction.

BCRider
12-17-2016, 08:52 PM
Since he's using half wave DC I sort of consider the diode to be required. Otherwise it's going to discharge during part of the cycle. ESPECIALLY if it's true half wave rectified where the missing half of the wave is 0 volts and if there's any way for the cap to bleed back out through the other circuitry.

If nothing else using the diode will smoothen the digital meter used to measure the cap voltage. And that was the point of the using this circuit in the first place so AKB can get a feel for how the numbers say he's working out. Without the diode it won't smooth out the variations as much.

PStechPaul
12-17-2016, 10:02 PM
I think the pulsing DC is just a variation caused by the inconstant nature of pedaling and the resultant change in speed of the DC generators. I really doubt they are AC, but I am making an assumption. I am surprised that it varies so much, however, as "proper" pedaling technique uses "ankling (https://cyclingtips.com/2009/05/efficiency-of-pedal-stroke-ankling/)" to produce a relatively constant rotational speed and torque. For a conventional bicycle with a freewheel, the rider should always be exerting some force on the pedals and the ratchet should not operate. Because of the inertia of the bicycle and rider, with constant contact of the tires on the road, the speed does not change significantly. However, going up a steep hill might require more of a "pumping" action on the pedals, and resultant variations of speed.

BCRider
12-17-2016, 10:16 PM
Part of my user name refers to the fleet of bicycles I've got. Pedaling in circles instead of just up and down is the Holy Grail. The serious racers train and learn to do it automatically. And I can do it for some time until I stop thinking about it. I still do it to some extent but not as much or as smoothly as when I really concentrate.

On a trainer though? Nope, not happening. I'd be far more interested in what I'm thinking about to take my mind off the fact that I'm bloody well exercising and that there's no scenery flowing past... frankly I'd rather do home surgery on my own kidneys. But then out here the weather is such that I can ride year 'round for the most part if I bundle up for the colder months.

I guess it depends on what is being used as the generator. I don't think AK mentioned that. Or I missed it. Still, his goal was a steadier readout that he could read more easily. If that is due to half wave rectified AC then a diode would be real handy for that. If it's a DC generator and it's only for the twice per rev variation then I'd still say it will help to avoid deeper pulsations in the cap voltage.

A.K. Boomer
12-17-2016, 10:31 PM
Paul your not off track its the reasoning for the whole effort to smooth things out electronically - it's pulsating DC due to the bio mechanical's of the rider, and yes trying to "spin in circles" is key in fact we train to kick a dog in the teeth on the very top stroke and then scrape it's crap off our shoe on the bottom - blend it all together and you get a full cycle,,,

still keep in mind its a trainer with a minimal flywheel effect and it's not like you have your body (and the bikes) mass to keep pulsations in check --- plus half my dyno training is also for the all so critical "sprint mode" way slower cadence and WAY more pulsations...

as far as a mild AC effect - without the diode there may actually be one between "power strokes" as the super charged cap instantly discharges back into the slower spinning lower voltage generators - not amounting to anything but an unstable voltage reading at the meter which I had without the diode....

PStechPaul
12-18-2016, 12:18 AM
I haven't ridden a bike (other than stationary exercise types) for quite a few years, but when I rode regularly, I usually used the ankling technique, and I even do so to some extent on the trainer/exerciser. It seems that it has a considerable flywheel effect, and that is probably caused by an actual flywheel. But I wonder if it could be caused by the generators putting energy into large capacitors, such that if I slow down, the generators act as motors being driven by the capacitors.

Perhaps it would provide a better exercise/training experience to use generator/motors and capacitors large enough to act as an electronic flywheel? The problem might be that there would be little resistance when pedaling at constant speed. To change this, energy could be dissipated in a resistor, or used to charge a battery.

A good load for the continuous power that can be generated by an average human is about 200 watts or 1/4 HP. I think the maximum for a well conditioned athlete is about 1 HP (750 watts) for short sprints.

J Tiers
12-18-2016, 02:17 AM
If it is DC, then it will NOT MATTER if it is half wave or full wave.

What will change is the VALUE of the average voltage, period.

So long as the integration time is long compared to the pulsations, whatever their source, you will get a true average level. The longer the integration time, the smaller will be the residual effects of the pulsations.

The diode is not required, and it fundamentally changes the nature of the response, from averaging to peak detection (modified by discharge resistors, if any). Of course, there may already be diodes in the dyno, with an AC generator. We don't know, but AK suggests that current WILL go back in, which is suggesting it is a DC generator. But an AC generator with full wave rectifiers would be no conduction one way, and a near short the other, so unless measured both ways, we don;t know.

AK SEEMS to want an indicator that will allow him to maintain any desired cadence by watching the meter. Almost anything will do that, and he may not WANT a long term average, just because of the very slow response time.

There are several possible sources of the pulsations, varying in how the averaging treats them.

1) Variation as the generator unit spins and the various poles pass thru their maximum output during one revolution. Virtually ANY averaging should take care of this.

2) Variation as the pedals revolve, probably speeding up a little during a downstroke/upstroke when you have maximum leverage, and slowing a little as the pedals pass thru top/bottom center, and the leverage is not as good. Any averaging that is significantly longer than the period of one crank turn should reduce that to a small effect.

3) Longer term variations in speed of pedaling. This is probably what you want to see, so the ideal averaging system would NOT reduce these very much.


An averaging time in the 10 second area would likely be about right to let the #3 effect be seen. Much shorter, and the #2 effect will start to be visible, confusing the issue.

The #2 effect is probably NOT a concern, because when actually riding, your mass does a good job of "integrating out" that effect in all cases except maybe riding up a steepish hill. If you are really concerned about it, a shorter integrating time (time constant) will let it be seen. A switch could allow eitehr longer or shorter times, depending on whether you want to see how steady your rotation is, or how steady your average power output is on a longer term basis.

Ideally a rider is a constant torque machine, but I never achieved that performance.

So, maybe you could give a little more input in terms of the minimum and maximum rpm, And also what you are really looking to see and monitor.

darryl
12-18-2016, 06:25 AM
I don't pretend to speak for AK, but I believe that what he's looking for is the most output from the actual wheel for the least input from his body. That's what he is trying to achieve with his modified crank experiments. Putting the method of how to give a smooth voltage reading aside for a moment, let's look at what could actually be more informative. If you could provide a final number after a timed pedalling event, you'd be gauging the total achieved output for that time period. I'd assume you'd pedal your ass off for a duration that you're comfortable with, then repeat that 'pedalling event' for each modification you make. You don't look at a meter during the test, you look at it after the event and see a single number.

In this case it won't matter at all what the output from the dyno is doing, as long as you are gathering the voltage over time for the total time. There is a circuit for doing this, and it works by having the input voltage controlling a current source, which charges a capacitor from a separate power source. The higher the input voltage, the faster the capacitor charges, and the final voltage on the cap is a representation of the average input voltage for the total test time. The circuit is a peak hold circuit, requiring a high quality capacitor and a high impedance output buffer so the meter doesn't load the capacitor and drop the voltage as soon as you connect the leads. The circuit is not really complicated, but probably more than Boomer is comfortable creating. But I think it would give a better indication of performance improvement, both through the mechanical modifications that might be made, and of the result of body training.

If the indication needs to show the steadiness of the output, then the output from the dyno should show the variations directly. An analog meter is far better than a digital to show this, as someone already mentioned. I say it here again because this is true- digital meters simply can't replace analog in all applications.

And now we need to look at the dyno again to find out how steady the output voltage is at a steady rpm. Perhaps there are strong pulsations in output voltage, perhaps there aren't. If it's a dc motor with a high slot count armature it should be pretty steady- probably quite readable with a digital meter directly. You may need a capacitor across the output leads to smother the hash that might be riding the output voltage. If you use an analog meter you won't need the cap.

Looking at the picture again, I'm pretty sure that's a dc motor being used as a dyno, and it probably is a high slot count armature- probably the best thing that could have been used here.

PStechPaul
12-18-2016, 09:16 AM
There are inexpensive electronic instruments that take care of all the parameters you may want for testing bike pedals and techniques. For $10 you can read many parameters:
http://www.banggood.com/100V-10A-DC-Combo-Meter-Volt-Amp-Power-Watt-Capacity-Panel-Meter-Monitor-for-Oled-p-1044480.html?rmmds=search

http://img3.banggood.com/thumb/gallery/oaupload/banggood/images/25/4F/f9df8670-2e0a-4a87-fb8a-8cd774ba8213.jpg
You can also get a data logger shield for Arduino that can record voltage at a set interval and then you can import data into Excel to get a graph of voltage over time, as well as perhaps watts and total watt-hours. I made something similar using a PIC that sends voltage and current data for battery charge/discharge curves over a Bluetooth serial connection to a terminal program on my PC, and saves to a file that can be read by Excel.

http://www.banggood.com/Logging-Recorder-Shield-Data-Logger-Module-For-Arduino-UNO-SD-Card-p-929174.html?rmmds=search

A.K. Boomer
12-18-2016, 09:45 AM
Lot's of good stuff - the dyno generator's are perm mag motors --- DC with no diodes in themselves and Darryl is correct they are a high slot count no problems there even at lower RPMs

JT your summary about #2 not being a concern would be correct IF the unit was some how used on the road with no hills and all my body weight along with the bikes to "hold a constant"

but this is not the case - it's a stationary trainer/dyno and although Iv sped up the gearing and fitted it with as large a flywheel I could it falls short for keeping my meter "stable"

so actually as stated before this is all about #2, it's the only area Iv had a problem with...

I like the Digi-meter over analog because when I get it to stabilize I can call it to within 1/10 of a volt which suits me fine and there's no "guess work" with that, like "do I have the meter in the same position as the last test or am I looking at it from an angle?" also not fun to try to decipher when your heads bouncing up and down in sprint mode, or even maybe favoring the needle in one direction in "hopes" of a change, numbers don't lie, their staring right at me and im staring back at them, be it whatever angle or whatever chaos im going through or whatever "perceived intentions"

FWIW here's what I do - or at least what I did with the last proto-type, I have 3 tools to gauge my work effort and the "reward" there-of, for my work effort I have my heart rate monitor, for my work reward I have my dyno output, and to ensure things are matching up with the dyno numbers I have cadence - technically all I would really need is one or the other of the last two as long as I used the same gearing... get right down to it they are both one in the same, volts output under a predetermined load (the cooling fan) is the final say - but so is gearing under the same predetermined load if the cadence is held to the same number.
The latter two are simply there for cross checking each other, the variable then becomes heart rate,
My experimentals go to changing to box stock cranks in about 5 minutes for total comparison purposes,
The reason why I keep cadence and therefor volts as the constant and not the other way around is due to the fact that to get accurate testing results you want to keep your cadence Identical,,, this ensures that the "human machine" is functioning within the same testing realm for BOTH sets of circumstances...
The variable then becomes - ok - identical RPMs and voltage output - but how hard are you working to achieve this?

the old design broke even in the "spin cycle" but made about 3 or 4% in the much slower out of the seat sprint mode...

Now things are not as simple as they used to be, my new design "changes gearing" it's not a 1:1 ratio that I can just use cadence and volts to match up, in fact I have to shift up a gear in the back to get close to what the stock cranks do, so it's a good thing I have two separate systems,

Now only cadence can be the constant,,, so as to not cheat the human machine, then both volts and heartrate will have to be gauged against each other - and then that deviation compared to the "other system"

Darryl I really like your idea of total output over a set time, thought about going that route but there's allot of variables involved and one of them is the human machine "getting stabilized"

what I do is tests for each mode and watch the meters closely --- esp. heart rate --- i then get into a comfort zone when my body accepts the workload given - the heart rate initially "peaks" and then comes back down some and sits there, after things stabilize I then just go into a zone and focus for the next 5 minutes on totally keeping the cadence spot on, and while doing that glances at HR and volts are noted --- they usually do not waver at all, if they do i did not allow enough time to stabilize... i just keep the two numbers in my head - cadence is a constant so don't have to remember that one just hold to it, as soon as im content on knowing nothing has changed for quite awhile i cool down and then write down the results... it's as close as I can come to being unbiased -

then a few days later do the same tests backwards in starting, so im not hitting one test "fresh" verses the other --- air temp has to be a constant also because after all my resistance is a fan, but usually no problem because dyno is in the basement in an isolated semi insulated room...


Paul that's allot more professional looking for sure, if it allows me to forgo the rinky dink electronics I just built to stabilize the volts then I just might order that thanks for bringing that up --- im excited because im testing today and will post the results later... might be good news but might be not so good - before I burnt out my other little apparatus to power the volt meter the testing was "inconclusive"...

boslab
12-18-2016, 10:23 AM
I remember having to use an old avo8 meter to get a reading where there was a lot of LF crap going on, the digital was all over the place, they are probably better now, assuming it was LF crap, I never found out, initially I thought it was the meter, so I went to the stores and got another one (they didn't like parting with them, made of gold I think)
Would AC generating be better?
Fascinating stuff this electrickery
Mark

J Tiers
12-18-2016, 11:20 AM
.....

JT your summary about #2 not being a concern would be correct IF the unit was some how used on the road with no hills and all my body weight along with the bikes to "hold a constant"

but this is not the case - it's a stationary trainer/dyno and although Iv sped up the gearing and fitted it with as large a flywheel I could it falls short for keeping my meter "stable"

so actually as stated before this is all about #2, it's the only area Iv had a problem with...

....

ALREADY HANDLED


.......

An averaging time in the 10 second area would likely be about right to let the #3 effect be seen. Much shorter, and the #2 effect will start to be visible, confusing the issue.

The #2 effect is probably NOT a concern, because when actually riding, your mass does a good job of "integrating out" that effect in all cases except maybe riding up a steepish hill. If you are really concerned about it, a shorter integrating time (time constant) will let it be seen. A switch could allow eitehr longer or shorter times, depending on whether you want to see how steady your rotation is, or how steady your average power output is on a longer term basis.
.....
.

AK, I KNOW what the unit is, I'm actually NOT THAT STUPID. And I have ridden thousands of miles on bicycles over time.

The problem was that we didn't know whether you were trying to train yourself to give steady force on rotation, or trying to hold a constant long term output. Kinda still do not. You may have tried to explain, but there has not really been clear statement of your goal, it seems to be mixed in with other things.

So, is the issue that you want to DETECT that variation and train to avoid it?

Or is the issue that you find that variation interferes with the reading on the meter? Sounds more like this is it, but.....

If the variation is just a nuisance, I already explained how to avoid it.

If you want to be able to observe it, I already explained how to do THAT too.

A.K. Boomer
12-18-2016, 11:41 AM
Or is the issue that you find that variation interferes with the reading on the meter? Sounds more like this is it, but.....




yes I will say that part again - this is all this has ever been about is to get a stable reading on the meter, in fact it's all but impossible to get a stable power stroke on a bicycle esp. in the sprint mode when your out of the saddle which is where half my testing takes place,,,

anyways please don't take offense was not trying to say what you said you weren't --- I know better than that and appreciate the input, im going down to test in about an hour or so... nap time first lol

The Artful Bodger
12-18-2016, 02:01 PM
I am sure someone has already suggested using a regular bicycle digital speedometer?

That would seem to be ideal for your purpose and not only would you have a steady digital speed reading you would also (depending on model) have peak and average speed read out at the end of your run.

You would need to arrange for the pickup to be on the layshaft (i.e. rear axle) to keep within range that the speedo has been designed for.

J Tiers
12-18-2016, 02:07 PM
yes I will say that part again - this is all this has ever been about is to get a stable reading on the meter, in fact it's all but impossible to get a stable power stroke on a bicycle esp. in the sprint mode when your out of the saddle which is where half my testing takes place,,,

anyways please don't take offense was not trying to say what you said you weren't --- I know better than that and appreciate the input, im going down to test in about an hour or so... nap time first lol

OK, so a LONGER integration time will fix that.

I'd GET RID of the diode, and experiment with resistors in place of it to get the response time you want.

Tell us what the capacitor value you are using is, and then there may be better suggestions for the resistor.

The diode is very low resistance in the conducting direction, so the reading will tend to jump up, then drift down according to the "discharge resistor", which may be the meter.

Yeah, the sprint mode always seemed to be about me trying to tear the handlebars off as I pulled up on them trying to force my feet down harder. I did actually bend one, which made me kinda worried about doing thet afterwards.

TR3driver
12-19-2016, 08:57 AM
I'd GET RID of the diode,
Ditto.
A big cap from that old power supply should do fine, but you'll probably need a divider network to keep the voltage well below the cap rating. So pick the time constant you want (I'm thinking about a second should do, longer will remove more noise but take longer for the reading to settle) and work backwards from the capacitor value to get an effective resistance (R = C / Tc with R in megohms, C in microfarad, Tc in seconds), then pick a pair of resistors to give that value when treated in parallel and the right ratio for the division you need when in series. The divider leg to ground will swamp any leakage in the cap, so a plain electrolytic cap will do fine (although variations in the actual capacitance may affect the actual time constant).