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Too_Many_Tools
11-03-2009, 01:36 PM
I have access to a Schumacher wheeled battery charger that is 12 v
only.

I want to both use its boost feature (200+ amp) on 6 volt systems and to also charge 6 volt batteries.

Any suggestions as to how to make a mod where the charger will do both
12v and 6v?

I have looked and have not found any schematics for the Schumacher charger.

Thanks for any suggestions.

And any suggestions as to where else I could post this question?

Good electronic BBSes seem to be few and far between.

TMT

MrSleepy
11-03-2009, 03:21 PM
What type of battery are you designing for..the battery chemistry will have a major impact on the circuit.

Rob


okay..so assuming lead acid... for a 6v battery you will need 7.2v (or 2.4v a cell) ...in low power chargers..the charger circuit will probably have a reference zener diode that could be lowered in value..but without a circuit diagram itd be a guess.
If yours gives out 200amps it will be more akin to a welding set..with little more than a resistor to control the current..
If its a SLA battery charger it will be more complex to stop the battery overcharging and gassing.

If you have another 6v battery you can put them in series and not have to alter the charger at all.


there are some good datasheets and info on charging lead acids here...
www.unitrode.com/products/apps_prt.htm

Too_Many_Tools
11-04-2009, 01:32 AM
What type of battery are you designing for..the battery chemistry will have a major impact on the circuit.

Rob


okay..so assuming lead acid... for a 6v battery you will need 7.2v (or 2.4v a cell) ...in low power chargers..the charger circuit will probably have a reference zener diode that could be lowered in value..but without a circuit diagram itd be a guess.
If yours gives out 200amps it will be more akin to a welding set..with little more than a resistor to control the current..
If its a SLA battery charger it will be more complex to stop the battery overcharging and gassing.

If you have another 6v battery you can put them in series and not have to alter the charger at all.


there are some good datasheets and info on charging lead acids here...
www.unitrode.com/products/apps_prt.htm


Lead acid.

The charger I am discussing is a wheeled battery charger that is used to provide starting current for a vehicle that has a dead battery.

http://store.schumachermart.com/se-2352.html

So how does one make a 12v 200a charger into a 6v 200a (or 100a) charger?

TMT

MrSleepy
11-04-2009, 01:54 AM
Than definately looks like a basic transformer/rectifier version..it will not have much electronics in it ..if any....

If yours runs on 220v AC...it may be possible to run it off 110v to halve the rectifier output....but the tranformer impedance is designed to limit the current to the battery,so you may need an external resistor...

Also check if there are any taps to lower the transformer output to the rectifier..

Rob

Ernie
11-04-2009, 02:14 AM
I have a much less powerful battery charger but it will charge both 6 or 12 volt batteries by selecting a lower voltage tap on the transformer. The diodes and the filter capacitor are the same at either setting. As was suggested above, look for another lower voltage tap on the transformer. If not, see if there's room for another transformer in there with the lower output voltage. Otherwise, you'll need a resistor in series with the 6 volt battery to drop the excess 6 volts. If you plan to jump start something at 200 amps, that will be a hefty resistor. As was suggested above, the simplest way is to charge 2 batteries in series, each will drop 6 volts.
Ernie

andy_b
11-04-2009, 02:15 AM
So how does one make a 12v 200a charger into a 6v 200a (or 100a) charger?

TMT

not easily. :)

i'm guessing a REAL 12v/6v charger has different taps on the transformer to pull off the 12v or 6v. there are electronic circuits to alter DC voltages, but i doubt they would work at 100A (or at least not cheaply enough to be worth doing).

andy b.

MrSleepy
11-04-2009, 02:34 AM
not easily. :)

i'm guessing a REAL 12v/6v charger has different taps on the transformer to pull off the 12v or 6v. there are electronic circuits to alter DC voltages, but i doubt they would work at 100A (or at least not cheaply enough to be worth doing).

andy b.


they would definately use taps to switch between 12v/6v in such a crude charger..

but it would be possible to feed the rectifier output (after removing any capacitors) to an SCR and then use a phase angle delay trigger circuit to give 120hz controlled pulses to the battery.

1-200 amp SCRs arnt too expensive..

Rob

fredf
11-04-2009, 05:10 PM
I have a much less powerful battery charger but it will charge both 6 or 12 volt batteries by selecting a lower voltage tap on the transformer. The diodes and the filter capacitor are the same at either setting. As was suggested above, look for another lower voltage tap on the transformer. If not, see if there's room for another transformer in there with the lower output voltage. Otherwise, you'll need a resistor in series with the 6 volt battery to drop the excess 6 volts. If you plan to jump start something at 200 amps, that will be a hefty resistor. As was suggested above, the simplest way is to charge 2 batteries in series, each will drop 6 volts.
Ernie
A hefty resistor would only work at one current. A diode drops a pretty constant .5 -.7 volts depending on type. for 200a you would need some beefy ones with heatsinks but a chain of 10-14 diodes would drop your voltage

boslab
11-04-2009, 05:58 PM
voltage divider, guess at 1.5 ohm resistor, metalclad high wattage but google it to confirm
mark

Too_Many_Tools
11-06-2009, 01:26 PM
Okay...I found a schematic of a similar charger sold by Sears.

Does this help explain the design?

TMT

http://www.searspartsdirect.com/partsdirect/getSubComp.pd?modelNumber=200.71230&productCategoryId=0405000&brandId=3206&modelName=BATTERY-CHARGER&diagramPageId=00001&documentId=P0305118&pop=flush

BudB
11-06-2009, 02:40 PM
I've been thinking about using a HF solar battery charger down at the farm. The only problem is the 12V output would be too much for my 6V '47 Farmall Super A. A resistor sounds like it would rob too much current. It would be nice to keep it charged for my monthly visit.

interrupted_cut
11-06-2009, 03:24 PM
I'm no electronics whiz, but how about switching a diode into the supply of the primary side of the transformer to make a half wave rectifier. It should reduce the input voltage amplitude by half, and the output should follow. For the solar Farmall charger, put several diodes in series between the PV array and the battery. You'll get a diode voltage drop accross each one. Measure the drop of one and determine how many diodes you need.

fredf
11-06-2009, 07:13 PM
I'm no electronics whiz, but how about switching a diode into the supply of the primary side of the transformer to make a half wave rectifier. It should reduce the input voltage amplitude by half, and the output should follow. .

transformers wont run on DC, which is what you'll have by using a diode in the primary. if it was a restive load it would work, not so for an inductive load.



For the solar Farmall charger, put several diodes in series between the PV array and the battery. You'll get a diode voltage drop accross each one. Measure the drop of one and determine how many diodes you need..

as for the diodes in series that will work as you are just dropping a dc voltage.

fred

darryl
11-06-2009, 09:13 PM
Best I can tell from that diagram is it's a 110vac unit. That means you can't simply make the change from what might have been a 220v input to a 110v input and thereby mostly solve the problem. I say mostly because what will happen is that even though the output voltage from the transformer will drop in half, the rectifiers will still be dropping the same voltage, so what you'd have on the output is considerably less than the full 200 amps.

At any rate, assuming you can't turn it into a 6v charger that way, next best might be to tap the secondary winding to a point where you're getting a little more than half the output voltage than the full winding gives. There won't be that many turns on the secondary, so my plan of attack would be- first make sure there's no short on the dc output, and no battery attached, unless the charger doesn't start up without one. Measure the ac voltage across the full secondary. Now make an educated guess at what might look to be about halfway on that winding. You'll probably have to poke through insulation to get a reading, so pick a spot to do this that won't matter if it's bared a little. Your aim is to find a point on the secondary winding where you can make a connection to it, and the voltage is about 1 volt higher than half the full voltage reading. You need that bit extra voltage to ensure that at 6v output, there will be enough current available to be somewhat near the capacity of the charger.

Assuming you find that point and can make a solid and permanent connection to it with another suitable gauge wire, the next step is to be able to switch between that wire and the original wire to give the 6v/12v output capability. That's going to require a high current switch, or the ability to do that job fairly easily from the front of the charger. You could mount a terminal strip that you make up yourself with three terminals, and then physically move a connecting bar between them to get the switching you need.

mcskipper
11-06-2009, 09:44 PM
If you wire the primary windings to work on 220V that will drop the output voltage.
Check that the cooling fan works @ the lower voltage.

The best way is if the secondary of the transformer has two sets of windings
don't fool w/ the input voltage. If there is two sets of output terminals there should be a short wire between the two inner lungs.
Remove that wire.
Then make up a set of jumper wires to connect X1 & X3 to one output wire then connect X2 & X4 to the other output wire.
You will have a 6V charge @ full current.
There are switches made to do this.
Install one then you will have both voltages at the flip of a switch.

Evan
11-06-2009, 10:06 PM
Best I can tell from that diagram is it's a 110vac unit. That means you can't simply make the change from what might have been a 220v input to a 110v input and thereby mostly solve the problem. I say mostly because what will happen is that even though the output voltage from the transformer will drop in half, the rectifiers will still be dropping the same voltage, so what you'd have on the output is considerably less than the full 200 amps.



Tapping the secondary half way will produce the same result as cutting the input in half. The only way to maintain the total power output on 6 volts is for the main transformer to be wound with two 6 volt secondaries that can be series or parallel connected.

Without that capability the easy way to reduce the output is to install a buck transformer in series with the input. Use a 220 to 110 stepdown xformer with a rating of at least 5 amps, 10 is better.

Connect one side of the 110 ac line direct to one side of the 220vac input and to one side of the charger ac input. Connect the other side of the line to the other 220 transformer input and to one of the transformer 110 output wires. Do not connect the other 110 output wire to the charger yet. Apply power and carefully measure the output across the free 110 output wire and the wire connected to the charger. It's a 50/50 chance of being 55 volts higher or 55 volts lower. If it's higher reverse the 110 output side wire connection and then connect the free wire to the other input of the welder.

The stepdown transformer acts as a buck transformer and only needs to have sufficient capacity to handle the continuous primary side current draw on it's secondary winding. During battery boosting it may be somewhat overloaded but it can take that for a few minutes.

interrupted_cut
11-07-2009, 12:47 AM
fredf,
If you put a single diode in an AC circuit, it blocks 1/2 of the waveform. What you have left is a half sine, which is still an AC waveform to the transformer. So instead of this: ^v^v^v^v^, you get this: ^-^-^-^-^, which has half the amplitude(voltage). It's not as clean, but lead acid batteries like some ripple from their charging circuits anyway. At least that is what my EE friend at work says, and he helped design the uninterruptible power supplies that back up the US air traffic control system.

fredf
11-07-2009, 12:14 PM
as easy as 1-2-3

1) the dc pulses will saturate the transformer core if its not designed for a huge dc offset.

2) the saturated core will cause the transformer to start drawing current like crazy

3) smoke

Evan
11-07-2009, 12:40 PM
The use of a buck transformer is standard practice for reducing line voltage. You can buy boost/buck transformers for exactly that purpose. They tend to be expensive but any transformer designed to operate on 60 hz ac with sufficient current capacity will work including a pair of 110>24vac transformers with the secondaries phased in series. A good place to find a 48 vac secondary transformer or something close is in an old high power audio amplifier. The secondary amperage rating only needs to be reasonably close to the amperage rating of the primary of the charger.

This isn't theoretical. I use exactly this type of setup to reduce high line voltage for various purposes around here. It is exactly the same thing as a variac except it isn't adjustable.

MrSleepy
11-07-2009, 01:43 PM
This isn't theoretical. I use exactly this type of setup to reduce high line voltage for various purposes around here. It is exactly the same thing as a variac except it isn't adjustable.

Its quite common...we call the autotransformer's in the UK.. a single winding transformer ... I use them on my US made high power laser supplies where isolation isnt important ..

http://en.wikipedia.org/wiki/Autotransformer.


Rob

MrSleepy
11-07-2009, 01:49 PM
I've been thinking about using a HF solar battery charger down at the farm. The only problem is the 12V output would be too much for my 6V '47 Farmall Super A. A resistor sounds like it would rob too much current. It would be nice to keep it charged for my monthly visit.


The simplest way for you to proceed is to get another 6v battery and put it in series with the tractor battery..

there are 6v solar chargers on on US ebay going dirt cheap..
http://cgi.ebay.com/7-5V-260mA-Solar-Energy-Charger-Cell-Panel-6V-Battery-C_W0QQitemZ260491936510QQcmdZViewItemQQptZLH_Defau ltDomain_2?hash=item3ca68782fe

Rob

Evan
11-07-2009, 01:53 PM
Just use the 12 volt solar charger as is on the battery. It will be current limited by the solar cells themselves and it won't hurt the battery. I presume that the panel in question puts out less than an amp.

darryl
11-07-2009, 03:50 PM
Finding a way to tap into the secondary at an appropriate point should allow you to draw the same or nearly the same current, but of course at the reduced voltage. The total power output will drop by roughly half, of course, since (again roughly) 6v x 200 amps is 1200 watts, and 12v x 200 amps is 2400 watts. You don't have the problem of reduced capacity unless you're considering the total output. If you wanted that, you'd be looking for 400 amps at 6v. In that case I'd have to agree, you would need to use the whole secondary winding to achieve that.

topct
11-07-2009, 04:08 PM
If the power transformer is wired like the one in the Sears diagram it looks like there are 4 wires coming from the secondaries going to the rectifiers.

I would measure the voltage across each of what appears to be two pairs of taps.

Evan
11-07-2009, 07:37 PM
I can't tell how it is wired, the schematic isn't clear enough. I will say one thing, the Sears unit in the link isn't a 200 amp charger, not even close. It might put out 200 amps on a direct short at a couple of volts output but this is another case of "vacuum cleaner/air compressor" horsepower.

From the apparent size of the transformer I would say it is able to put out around 20 to 30 amps at most while charging a 12 volt battery.

Too_Many_Tools
11-10-2009, 04:00 PM
LOL...the 200 amp boost feature is for 5 seconds on and 240 seconds off.

The nameplate shows that the charger is using 40 amps on the input...while plugged into a 15amp rated service.

Evan
11-10-2009, 04:18 PM
If you use a buck transformer on the input it won't change any of the features. They must be switching to a very low turn count winding for the boost and relying on the fact that a 15 amp breaker won't trip instantly on that load.

If you buck it down to half voltage you will have half the voltage and half the current so the power will be 1/4 what it is at 12 volt operation. That means that the boost mode will be able to run 4 times as long or often (but not both at once).

BTW, if all you really need is the boost mode you might just try using it in 12 volt mode. If it charges a 12 volt battery at 30 amps max it will give about double that on a 6 volt battery. The time will have to be limited to prevent overheating in that case.

darryl
11-10-2009, 10:45 PM
Rated for 40 amps input, and the right plug for an ordinary wall socket? Well, I don't recall the numbers, but a 15 amp breaker is supposed to be able to pass 70 amps for some small period of time, 50 amps for a slightly longer time, 30 amps for an even longer time, etc. 20 amps for what is it- two minutes?

Too_Many_Tools
11-29-2009, 05:06 PM
Okay..the battery charger saga continues.

I now have a Dayton (Century made) battery charger that does 6v/12v/12vboost/24v wheeled charger that I am attempting to fix..the 24v feature did not work and that problem has been traced to a burned out switch element in the charger.

The charger switches the different leads on the primary side of the transformer to get the various 6/12/12boost/24 volt outputs.

The primary has four different leads that are connected in different ways to the 110 v input to invoke different combinations of turns on the primary side.

I can understand how and why they would switch in different number of turns on the primary side for the 6/12/24 volts but what would they be doing on the primary side to get a "12 boost" (I assume a higher amperage 12v output) on the secondary? Again the charger only allows various connections of the four different leads on the primary side of the transformer.

So has anyone looked at the design of multioutput battery chargers which switch the primary side of the transformer and understands how they are laid out?

I would love to be educated on this.

FYI...I looked long and hard on Google for some info on this subject..the Internet is becoming a wasteland for useful design info.

TMT





I have access to a Schumacher wheeled battery charger that is 12 v
only.

I want to both use its boost feature (200+ amp) on 6 volt systems and to also charge 6 volt batteries.

Any suggestions as to how to make a mod where the charger will do both
12v and 6v?

I have looked and have not found any schematics for the Schumacher charger.

Thanks for any suggestions.

And any suggestions as to where else I could post this question?

Good electronic BBSes seem to be few and far between.

TMT

topct
11-29-2009, 06:15 PM
You have answered your question.

A combination of primary taps.

JBL37
11-29-2009, 07:01 PM
The link below will give you a wiring diagram for the typical automotive battery charger. Hope this will be some some help to you. Jim

buy1.snapon.com/catalog/parts/pro_det.asp?Item_id=25972&group_id=5862

darryl
11-29-2009, 08:44 PM
There's a couple of basic possibilities- one is that a neutral wire on the primary never changes connections, with only the hot wire switching between multiple taps- the other is that the hot wire changes connections, but also the windings go from series to parallel. The first case makes it easy- all you're doing is changing the number of turns involved in the primary and hence the voltage produced in the secondary. The lower the number of turns tapped into of the primary, the higher the ratio is between the primary and secondary. That's pretty much a direct relationship to the output voltage.

If the secondary is switched to different taps as well, it becomes more complicated.

Going from 12v position to 12v boost could be as simple as tapping the primary a few turns less than the normal 12v position. In other words, you'd be expecting say 14volts from the secondary instead of 12. That will give a higher charge current into a 12v battery.

Is all the switching being done on the primary?

Too_Many_Tools
12-01-2009, 07:49 PM
There's a couple of basic possibilities- one is that a neutral wire on the primary never changes connections, with only the hot wire switching between multiple taps- the other is that the hot wire changes connections, but also the windings go from series to parallel. The first case makes it easy- all you're doing is changing the number of turns involved in the primary and hence the voltage produced in the secondary. The lower the number of turns tapped into of the primary, the higher the ratio is between the primary and secondary. That's pretty much a direct relationship to the output voltage.

If the secondary is switched to different taps as well, it becomes more complicated.

Going from 12v position to 12v boost could be as simple as tapping the primary a few turns less than the normal 12v position. In other words, you'd be expecting say 14volts from the secondary instead of 12. That will give a higher charge current into a 12v battery.

Is all the switching being done on the primary?

Yes ...all the switching is occurring at the primary side.

If it is as you mention....a "12v" setting and a "12v boost" setting where one or both are not true 12 volts...that would make sense...but...the difference of a relatively small voltage difference would not seem to allow for a sizable current difference.

From what I am seeing in high current chargers, the switching is always on the primary side...lower currents mean cheaper switches can be used.

On the Century charger I am looking at now, it has four different primary leads it switches in and out...I can't tell if it is only one lead per voltage setting or more...the switch used has been fried.

TMT

darryl
12-01-2009, 10:18 PM
'the difference of a relatively small voltage difference would not seem to allow for a sizable current difference.'

It may seem that way, but consider this- you feed a 12v battery some current and it charges up. Gets to about 13.2 volts, measured after a rest period off the charger, and it's fully charged. Now feed it 13 volts- no juice will flow because the feed voltage is lower than the battery voltage. Increase the voltage to 14- now some juice will flow. It's gone from no current at 13v to definite current flow at 14v. There's a 'knee' point in there. If the battery behaved like a 'perfect' component, it would draw no current until the feed voltage rose to exactly and just past the batterys current voltage level. Raise the voltage a bit more and it tries to draw tons of current.

In practise it's not that cut and dried. If the battery is good, with low internal resistance, it will work more closely to that ideal than if the battery is old and maybe has dry or damaged cells.

Raising the output voltage of the transformer by one ac volt will add 1.4 peak volts to the charge voltage. That's enough to go from no charge to sizable charge. Adding one more ac volt is enough to raise the charge voltage and therefore the current quite a lot. The battery is going from taking what might be called a trickle charge, to taking what might be rated output current from the charger over that small range of feed voltage.

JBL37
12-01-2009, 10:33 PM
Most quality automotive battery chargers have essentially the same design.
The start with a transformer that has a multiple tap primary, and a center tapped secondary. Have worked inside many different brand over the years. They were always this way, from the five amp tote to the larger one on two wheels. The secondary outside leads are connected voltage rectifiers and the rectifiers' outputs are connected together together and connected to the positive clamp. the center tap is then connected to the negative clamp.
Now for the boost circuit. There is no boost circuit. Salesmen need a angle to persuade a customer to purchase a product. It's called giving the customer a reason to buy the product. Warranty, service, and 500 AMP BOOST..... Worked many times for me. The bigger the transformer in a battery charger means you can claim a larger boost amperage.
Boost amperage is the measure of maximum amperage measured when the output leads are connected together and the on switch is monetarily engaged.
JIm

davidfe
12-02-2009, 02:29 PM
I have access to a Schumacher wheeled battery charger that is 12 v
only.

I want to both use its boost feature (200+ amp) on 6 volt systems and to also charge 6 volt batteries.

Any suggestions as to how to make a mod where the charger will do both
12v and 6v?

I have looked and have not found any schematics for the Schumacher charger.

Thanks for any suggestions.

And any suggestions as to where else I could post this question?

Good electronic BBSes seem to be few and far between.

TMT

Did you ever open up the unit?

What is the model number?

Too_Many_Tools
12-02-2009, 11:10 PM
Did you ever open up the unit?

What is the model number?

No..it was not mine.

http://store.schumachermart.com/se-2352.html

TMT