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dvideo
08-17-2001, 03:51 AM
Home Power mag had an excellent article about a gentlemen in San Diego who did a "perfect situation" install. Took advantage of Energy Subsidies, sold power back to the utility during peak, and bought during off peak. Perfect, I think.

For shop use, you really have to look at what he did - and bend it to heat/cool/power a shop. Home use is more picky, I think.

I can undestand not liking to use a Diode. A good Schottky is a reasonable choice. You can also add "the right kind" of MOSFET in parallel, to get the benefits of low resistance. Same trick is used on high efficiency switchers for PCs.

--jerry

Evan
08-17-2001, 03:51 AM
This is a test

mofugly13
04-16-2004, 12:44 AM
I have the oppurtunity to purchase a Siemens solar panel, model SM50H, for $50. These are upwards of $300, new, so it looks like a good deal. What I don't know, is if it will work for my specific application.
Tis is the panel/specs:
http://www.fords-mtm.com/solar/sm50.htm

What I want to do is set up a CB base station, running from a deep cycle battery, at my hunting cabin. I want to be able to recharge the battery with solar power. Typically, I will use the CB on a weekend, and during the week or two that I am at home, the battery recharges. I have searched the net, and it seems that there are solar charge maintainers, but no actual chargers.My ??'s:

Can I use the panel to charge the battery?
What kind of monitoring device(s)/circuitry will I need?
How much CB usage can I expect per battery amp/hour?

I am an electrician, so circuits and wiring are no problem, once I have a schematic, or at least a good idea of how everything is supposed to work together.

------------------

sandman2234
04-16-2004, 01:21 AM
I used a small 12volt cooler(refridgerator?) in my T/T when I was running over the road. When I would get home, I would leave it on, which would drain the batteries after the 3rd day. I bought a battery charger/solar panel that put out .53watts and laid it on the skylight cover which kept it charging all the time. Plugged it into a cigerette lighter and left it. It would drain down all night, but charge back up during the day. That was just enough to allow me to leave it plugged in all the time, so I didn't have to unload it every time I came home.
Price was around $50. years ago. They offer larger units. This one is flexible, and will withstand water.
BoatsUSa or something like that.
David from jax

CCWKen
04-16-2004, 02:00 AM
Wow, that's one high powered solor cell. 3amps will maintain a battery and charge it if you have a way to limit the current. A group 24 "dead" battery (less than 11.3v) will draw over 12 amps at the start of charging. Sooooooo... you'll need a control circuit for it.

Put an AMP meter between your CB +lead and the battery. On standby, I don't think it will draw more than 1/4 - 1/2 amp depending on volume. On transmit, it may hit 4 amps. Use the Ah rating on your battery (not CCA) and divide that by your amp reading. That will get you close to the hours of use. Just a guess but I bet you'll get 20 hours on transmit and a week of just listening.

J Tiers
04-16-2004, 02:30 AM
<font face="Verdana, Arial" size="2">Originally posted by mofugly13:

Can I use the panel to charge the battery?
</font>

Yes, it will charge (maintain and/or re-charge) a 12V lead-acid battery.



<font face="Verdana, Arial" size="2">
What kind of monitoring device(s)/circuitry will I need?
</font>

Depending on the battery, nothing, maybe.
If you have a battery set of 200-300AH, that panel won't hurt it if it continuously charges. You will need to add water.

A charge controller may help somewhat, especially if
1) You discharge deeply (more than 20% of capacity on a larger battery)
2) Controller is one that incorporates a switchmode regulator which can increase the current into a discharged (and thus lower voltage) battery.


<font face="Verdana, Arial" size="2">
How much CB usage can I expect per battery amp/hour?
</font>

An Ampere-hour is just that, one ampere for an hour. If you have a 100 AH true deep-cycle battery, you can feasibly discharge about 10A for 7-8 hours regularly without damage (Capacity/10 rate).
Other lower currents for proportionately longer, higher currents for shorter times, but not proportionately.
That means 1A for 80 hours, but not 80A for 1 hour, more like 40A for 1 hour due to increased losses.

I dunno how much your CB draws on standby vs in use, so I can't comment on actual times.


Your issue is battery type and how much power you need, vs your recharge rate.

I would avoid the "marine deep cycle" because they aren't either one. They are trolling motor batteries, and are built like car batteries. They will crap out on deep discharges if repeated often. If you don't draw much, you could even use a car battery.

For deep discharge use, I would recommend Trojan T-105 Mileage-master golf cart batteries, a pair of 6V ones. More money, but worth it. They should last 10 years.

They are 220 AH, and will not be hurt by continuous charging at 3A if kept watered. I will assume use of these just for argument.

But, if you deeply discharge, you will be sitting partly discharged for a long while as that little panel charges it back up. That can allow capacity loss due to what is usually termed "sulphation". It happens when the battery sits discharged for a long time, the lead sulphate becomes difficult to convert back to acid.

Your panel will recharge at a basic rate of 3 AH per hour of full sunlight exposure.

It will take about 90 hours of good light to recharge from zero (which you wouldn't want to have to do). Figure a 60% discharge max, which needs then about 60 hours of light to recharge (including charge losses of about 20%).

You get about 6 hours good light in the best location with a fixed panel (no sun-tracker) so that's 10 days of varying partial charge state for a 60% discharge. But then, that's for about 130 AH usage in one weekend, not accounting for recharge during daylight.

If you use less you would have excess capacity and no problem. One day you might need that, you can get light from it too, etc.

A smaller battery will need a charge controller to kep from boiling dry, but will charge up faster. In fact, the current-boost types mentioned above will charge any battery faster, as at low states and voltage you might get 5A charge (same power, lower voltage, = more possible current). That will cut re-charge times maybe 20%, and spend less time deeply discharged.

if you don't pull 100+ AH in a weekend, you won't take so long to charge back up.

I have a shed/garage with 440AH of batteries and a 6A panel setup. I pull large currents, but not for that long. Sometimes up to 100A for a few minutes, because out there I have a 2500W DC to 120AC inverter and various electric tools including air compressor. (lights are DC)

The setup has been running 10 years and is going strong. Usually 90+% charged. I do have a simple-minded charge limiter on them, left over from when I had smaller batteries. The panels were 10 years old when I got them (from the Carrizo solar power test plant).

CCWKen
04-16-2004, 03:18 AM
<font face="Verdana, Arial" size="2">Originally posted by J Tiers:
I would avoid the "marine deep cycle" because they aren't either one.</font>

Ditto there. I found out the hard way trying to cheat and use them 3x3 in a golf cart. Lasted one week. Fortunately, the store took them all back.

Evan
04-16-2004, 04:01 AM
The standard 5 watt CB draws around an amp on transmit and maybe 100ma on listen. I have one I put a 4 amp hour nicad pack on and it can be used all day.

One thing about solar panels is that if any part of the panel is shadowed the output falls to near zero. Also, you can't "overload" a solar panel. Shorting the output doesn't hurt it at all.

mofugly13
04-16-2004, 09:51 PM
Thank for all the good info, guys. I am leaving in about 10 min. to go up to my cabin, where I have the battery. It's a trojan, and quite large. I'll get a model# from it this weekend. Again, thanks to all who replied.

wierdscience
04-16-2004, 09:57 PM
Good point Evan,I have several "top off"chargers on various vehicles around here,they output 14.7 volts in full sun and drop off to 10 or 11 with clouds.Never had one dry a cell,not enough output for that.

Be aware thou not all solar chargers include one crucial part,a back up diode,without them I found out the solar panel will back radiate at night(drain battery).Found this to be the case on the top offs,$30.00 model has them and they work like a champ.$19.99 HF model doesn't,and boy do they suck till you add one.

CCWKen
04-16-2004, 10:06 PM
Evan, I wasn't aware that the panels could be shorted. That was the only reason I mentioned using a controler. I wouldn't want to fry a $300 cell. Good to know though. Thanks!

By the way, your CB must be one of those teeny-weennies. Or.... I think I "tweeked" mine a number of years ago. http://bbs.homeshopmachinist.net//biggrin.gif (Before adding the linear) http://bbs.homeshopmachinist.net//eek.gif

Oh yea, did you know they dropped the output from 5 to 4 watts a number of years ago? At least in the US.

[This message has been edited by CCWKen (edited 04-16-2004).]

J Tiers
04-17-2004, 01:08 AM
<font face="Verdana, Arial" size="2">Originally posted by wierdscience:
.

Be aware thou not all solar chargers include one crucial part,a back up diode,without them I found out the solar panel will back radiate at night(drain battery).Found this to be the case on the top offs,$30.00 model has them and they work like a champ.$19.99 HF model doesn't,and boy do they suck till you add one.</font>


A silicon solar panel WILL NOT allow back current. Most of them do include a diode in them. But even if they did not, the array is made up of 30+ silicon diodes, all oriented so as to block reverse current. Any current will be negligible.

They will NOT "re-radiate" in any case. They are not "reversible".

If you get into high voltage arrays, diodes make sense
But at low voltages, they are pretty much a net loss of power.

An "amorphous" array may have reverse current, its cells are not very good diodes. With them, a diode is a necessary evil. I suspect the "top-offs" are amorphous, as they are quite cheap. I have a couple of them.

All arrays are current limited by the amount of light hitting them, and their maximum efficiency. So shorting causes no damage at all.
Current is quite constant from the "peak power point" normally around 16 to 18 volts, to zero volts, as load resistance is reduced.

[This message has been edited by J Tiers (edited 04-17-2004).]

darryl
04-17-2004, 02:56 AM
A little mental exercise- if the battery's capacity is 90 ah, and the charge current from the solar array is 3 amps max, it will take 30 hrs of full sun to charge it from dead. Not from shorted, but from fully depleted. Add to that a factor of about 30% for losses in charging, that becomes 40 hrs or so. That charge rate also is less than the maximum continuous trickle charge rate, but it will use up some water. Other than that, no regulator should be needed, nor should a diode be needed. If anything, I would use a simple current cutoff set for 13.6 volts. That charge rate is so low that the battery will just slowly build in voltage until that supposed full charge level is achieved, which that voltage is supposed to represent. It's not like an alternator is driving it, where the voltage will rise to maybe 15 or 16 volts during the charge, which is a requirement for a fast charge. You can't fast charge a battery by feeding it from a 13.6 volt power source, even if the current capacity of the source is huge. So a simple current cutoff based on a voltage reading is all that's needed to reduce or prevent the slow water loss that you would have with a continued trickle charge. I figure that with a charge rate less than 1% of ah capacity, no regulation circuitry is needed, and for a rate of 1% to 5%, use the cutoff regulator set at 13.6 volts. For a faster charge rate, you'll have to set the limit higher, at 14.5 or so, but don't make it continuous.

Evan
04-17-2004, 04:57 AM
JT,

Even monocrystalline cells will allow a significant reverse current when not illuminated. Since most panels are composed of cells in parallel as well as series the reverse resistance is reduced. Polycrystalline cells are much worse and a blocking diode is mandatory. Amorphous cells are even worse. Solars cells as diodes have low reverse resistance.

I didn't mention it as most panels include a blocking diode. For maximum efficiency a shottky diode can be used, only around .3 volt forward drop.

Darryl, look up solar panels on the net, diodes are mandatory.

[This message has been edited by Evan (edited 04-17-2004).]

wierdscience
04-17-2004, 10:56 AM
Yep,thats right,they do need diodes,I didn't believe it until a buddy mentioned it to me and I also saw the same thing in a West Marine catalog,solar top off's are popular on boats.West had several large panels and all the descriptions said that they included backup diodes.

I still didn't believe it until my buddy said to look at the HF model after dark,sure enough it looked radioactive,had kind of a yellowish glow,not real bright,but you could tell it was there.

J Tiers
04-17-2004, 12:13 PM
<font face="Verdana, Arial" size="2">Originally posted by Evan:
JT,

Even monocrystalline cells will allow a significant reverse current when not illuminated. Since most panels are composed of cells in parallel as well as series the reverse resistance is reduced.
</font>

I have measured for this, and have found a very insignificant current flow in the silicon arrays I have. On the order of hundreds of micro-amperes, vs the 6A forward current in good sun at low temps.
I opted for no diode for many years, and have seen no increase of current with or without.
At least a couple other arrays I know about have or have had no diodes also. No light show, no problems of "draining" the battery.

If you don't mind a volt or so extra drop, put it in. I think more recent NEC requirements include the diode at least under certain conditions.

Mine are not mult-parallel cells, and are now at least 20 years old, with much previous abuse from use with a concentrator at the Carrizo plant (so I am told). If they were going to have increased leakage, it would have shown up by now.....


<font face="Verdana, Arial" size="2">
Polycrystalline cells are much worse and a blocking diode is mandatory. Amorphous cells are even worse. Solars cells as diodes have low reverse resistance.

I didn't mention it as most panels include a blocking diode. For maximum efficiency a shottky diode can be used, only around .3 volt forward drop.

Darryl, look up solar panels on the net, diodes are mandatory.

[This message has been edited by Evan (edited 04-17-2004).]</font>


It may be of interest that while schottky diodes DO have low forward voltage, they also typically have much MORE reverse leakage than silicon. There may be little advantage in using one, depending on the voltage and current rating of the schottky.

Amorphous arrays REQUIRE diodes as I mentioned, they DO leak nicely.

I have not seen the light show, but if you say so......I know some transistors will give off small amouts of light under certain conditions.

Use of an over-rated (current-wise) silicon diode will reduce forward voltage to the same area as a smalle schottky, without overly increasing leakage.

Evan
04-17-2004, 01:54 PM
JT,

I'm not making this up. It is the recommendation of nearly all panel manufacturers. They also either use or reccomend shottky diodes. A silcon solar cell has much lower reverse resistance than a normal silicon diode simply because of the huge junction area.

The panels you have probably have a blocking diode built in.

Try this link.

http://www.google.ca/search?q=solar+panel+blocking+diode&ie=UTF-8&oe=UTF-8&hl=en&meta=

darryl
04-17-2004, 06:27 PM
I hereby ammend any recommendations I have made to include the diode. My experience has been with single series connected cells, and not arrays. I agree that whatever the reverse leakage of a single strip will be multiplied by the number of strips in parallel, so be on the safe side with the diode. Ok. Now I have to go check the reverse leakage of some diodes, schottky and others, and of some of the solar cells I still have kicking around.

wierdscience
04-17-2004, 10:15 PM
By glow I mean in the dark of course,kinda reminds me of the way a tv screen glows after shutdown and the lights are off.

ibewgypsie
04-18-2004, 12:00 AM
A few years ago, Nuts and Volts did a fencepost type radio station that worked.

It had a solar array, and a battery, I'll look for the issue to see if it is handy.

David

J Tiers
04-18-2004, 11:10 AM
<font face="Verdana, Arial" size="2">Originally posted by Evan:
JT,

I'm not making this up. It is the recommendation of nearly all panel manufacturers. They also either use or reccomend shottky diodes. A silcon solar cell has much lower reverse resistance than a normal silicon diode simply because of the huge junction area.

The panels you have probably have a blocking diode built in.

</font>


Nope, no diode, but they are older ones. Older and less efficient cells probably have thicker depletion areas, and hence higher reverse voltage capability per cell.

Newer cells probably have a lower reverse voltage max per cell. That affects leakage and the need for separate blocking diodes.

The diode has always been *recommended*.....and I DO NOT recommend AGAINST it.

In fact my system at the moment HAS a high current diode in it. A diode can be a useful safety device.

However, all the silicon arrays (older) I have dealt with have not been such as to "fail instantly" or "drain batteries" if the diode is not included.

Amorphous arrays are leaky devils, use a diode for them.

The number of cells has been cut back in newer arrays, as the arrays and cells have been through the usual process of being "thinned and lightened".
Old arrays had OC voltages of 25V, and peak power points of 18V or so. Newer ones have OC volts around 20 or 21, and peak power points of only 16 volts or so.

Looks like a small difference, but can be bigger when charging a 12V battery which may reach nearly 15V in cold weather, or when under charge. The diode then becomes a serious power loss, limiting "equalizing" current, and affecting system performance.

Since some charge controllers (typically smaller ones for single arrays) have the diode built in, it pays to check and see if the diode is required outside the controller. If not, providing one will double the diode losses.

A newer array that a buddy of mine got has TWO diodes, since it can be connected as 6V or 12V. In 12V mode, the diodes would be in series, potentially giving three diode drops, if there is another in the controller.

With a potential drop of 1V-1.25V for a silicon diode at near rated current, or 0.6 to 0.7V for a schottky st rated current, that adds up. There could be a total diode voltage drop of up to 2 or 3 volts at max current.

Yes I know all about the 0.6V and 0.2V theoretical voltages. The rest is resistive losses at near max current, which is likely since diodes cost money, and manufacturers will use the cheapest, smallest possible part.

Check the data sheets for various diodes, you'll see what I mean. For an SMPS design, the assumed rectifier drop is ALWAYS taken at 1V, unless you know it's more.

Evan
04-18-2004, 10:03 PM
I agree, I live in an area where a large number of people use solar electric power. I have been considering it myself even though I am connected to the grid. We know how to conserve. It has been a way of life for us living in a rural area for most of our life.

I would guess that the panels you have are not typical, probably single crystal silicon, state of the art at the time they were amde.

Evan
04-20-2004, 03:05 PM
topic rescue

J Tiers
04-20-2004, 06:09 PM
<font face="Verdana, Arial" size="2">Originally posted by dvideo:
You can also add "the right kind" of MOSFET in parallel, to get the benefits of low resistance. Same trick is used on high efficiency switchers for PCs.

--jerry</font>


Quite so, active rectification. it does require some extra circuits.

Mosfets do have one non-fatal problem for this use, in that they have an intrinsic reverse-poled diode in them which bypasses the active portion. So they conduct in the reverse directiomn.
You have to take that into account and use them in an appropriate polarity so that they will block reverse current.

mofugly13
04-20-2004, 08:06 PM
Thanks again for all the info, folks. And thank you Evan for rescuing my thread. My battery, by the way, is a little-used Trojan 807, it's quite large, and I might be able to pick up another for a bargain.

darryl
04-21-2004, 11:01 PM
Funny how things seem to come up surrounding a topic. A friend of mine showed up yesterday and we sat for a coffee. He showed me a catalogue with solar panels, inverters, etc. all the stuff. His hydro bill is 20 bucks for two months. He wants to get off hydro and into a solar system. I'm not a doctor and I don't have the gizmo for looking into his brain to see if anything's amiss.( I suppose I could just look for light coming through from the other side) Well, what can you do? Anyway, it looked to me like a 24 volt system with two batteries only, running a 600 watt continuous inverter, and using two solar panels in series would give him the cheapest setup to minimize the average current draw from the batteries, and keep things as efficient as possible. Maybe use just one panel and set up a series/parallel switch for charging. The reason his hydro bill is so low is that he's almost never home, and when he is, he watches tv, has a small light on, shaves in the morning, and leaves. No laundry, cooking, no power tools, etc. We figured his power draw to be 400 watts for 3 to 5 hours, once a day, and that's only when he's there. There isn't room for more than a couple of batteries, but the balcony area, which is never used, can handle two solar panels, which would also provide some shade where it's needed. My questions are a, is either one of us thinking straight, b, should I offer to pay his hydro bills for ten years, but take from him in a lump sum the cost of this system, and c, should I just be suggesting that maybe he should 'accidently' fall off the balcony and put an end to this insanity? Ok, main question, under what circumstances would any of you go with a 24 volt system?

wierdscience
04-21-2004, 11:20 PM
Would I go for a 24v system?Only if it were attached to a perfectly usable Hummvee http://bbs.homeshopmachinist.net//biggrin.gif

I like solar for backup,topping off batteries,power in remote locations,fence chargers and that sort of thing,but not as primary power.

Maybe you should ask him what he will do when its cloudy or overcast for a week at a time http://bbs.homeshopmachinist.net//biggrin.gif

J Tiers
04-22-2004, 12:19 AM
<font face="Verdana, Arial" size="2">Originally posted by darryl:
should I just be suggesting that maybe he should 'accidently' fall off the balcony and put an end to this insanity? Ok, main question, under what circumstances would any of you go with a 24 volt system?</font>


I wouldn't do any of it. its crazy.

The ampere hours used are about 67 per day, figuring 4 hours of your 400W.

That means he has to charge back about 80 AH each day.

First, that means he needs BIG panels, since he needs at least 12A just to keep up if he lives in Southern Arizona. For a normal area he needs more.

Second, the batteries do NOT come in 12V versions. Good batteries come in 6V, which means 4 big honkers for 24V.

Third, they will have 220 AH, or so, which means he has 3 days max and then they are dead discharged. So 3 to 4 days of clouds and he is a dead turkey electric-wise, since overcast typically drops you to about 15% to 20% output.

Fourth, all this to escape $20 per month? The investment will be something like 3 grand US. Payback is then way out there at 150 months.

Fifth, he does not have room for the system in any case, per your description.


I know folks who live on solar. They don't use a lot of electric. They are 8 miles down a logging road in outstate MO. It was going to cost $10,000 of their money to get power to them, as the power co wasn't covering it.

They paid $4700 for a big solar setup, 24V and 440AH (8 6V batteries), about 20A charging current, and it works for them. The array is about 8 x 14 feet, on a big post like a highway billboard, but much shorter. They have the large integrated Trace power panel, with one 3500W inverter and room for a second (except Trace is OOB, bought out along with Statpower, Heart, and all the other companies).

Solar works, but everyone starts by underestimating the size of the system they need.

dvideo
04-22-2004, 01:16 AM
There is a good place for it.... If you have to do it solely by yourself, you should probably spend on cutting power cost. Buy a $30 meter and see what is burning $$.

Check out.... http://www.learnaboutrobots.com/austin-solar.htm

-jr

Mike W
04-22-2004, 05:58 AM
I used to work on scada systems on a gas pipeline. There was a .....50 watt panel and a 12 volt, 100 amp hour battery. The 5 watt radio would transmit several times an hour for a few seconds. I don't recall any major problems with the batteries.

J Tiers
04-22-2004, 10:13 AM
<font face="Verdana, Arial" size="2">Originally posted by Mike W:
I used to work on scada systems on a gas pipeline. There was a .....50 watt panel and a 12 volt, 100 amp hour battery. The 5 watt radio would transmit several times an hour for a few seconds. I don't recall any major problems with the batteries. </font>

Perfect application...remote area, panel sized to support load even if overcast,etc.

Same with hiway work alert signs.

It is all in the sizing of panel and battery.