Homemade battery chargers.

[Julius Tangka]

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[hiker]

how many amps do you need??

[Julius Tangka]

My Battery has  50 Amp Hour rating and I have a 5 Amps and 230V supply.

[nack]

A transformer that can deliver 10A at 12VAC plus a rectifier.  After rectification, you will see about 17 volts DC with no load, and under a load it will drop to something closer to the rated secondary voltage.  Can and will overcharge if left unattended.  Truth is if you have to buy the parts new it is probably cheaper to just buy a 10A battery charger from an autoparts store.  Mouser's price for the transformer alone is more than I paid for a Schumaker 2/10/50A 6/12V battery charger/booster.

[Julius Tangka]

Thanks,  I will try to follow your steps to see what I will get. I am  in Cameroon, Africa. A ten Amps battery charger is not as easy to come by as you would think.

[nack]

If you have a transformer that can do about 150Watts but wrong secondary voltage, you might be able to rewind just the secondary for 11-12V.  Typical wire size for transformer winding is to allow minimum 300 circular mils (copper wire) per amp of current, although some people prefer to go as high as 500CM/amp.  If you want 10A secondary, I would use AWG16 or 1.5mm wire.  AWG16 = 3446CM = 1.491mm.  Wrap 10 turns first, and measure the voltage on that to get an approximation of volts per turn, then calculate total turns needed.

[(unknown)]

You say you have a 'supply' at 230v at 5 amps... I have to assume you mean 230 volts AC...? (Dangerous to assume) A simple, (SOoo simple!) effective, if not elegant nor fancy solution involves a light bulb as a dropping resistor and a diode of proper rating. As noted, can and will overcharge if left unattended. I don't know what light bulbs you can come by, so can not recomend one...(I am less familiar with 230v systems)

230vac X 5amps =1150 watts. 50 amphour batt @ 12 volts=600 watts... (50X12) So your 'supply' is plenty, IF you can convert it.

Generaly, charging is done on a 10 hour rate... so devide 50 by 10=5amps @ 12 (nominal, actual more like 13.8 to 14.2vdc for charging) So you need 5 amps at charging voltage for ten hours. Clear? (There are other charging rates, and some depend on type of battery, the 10 hour 'rule' is just a 'rule-of-thumb')  So, that's 71 watts, (at 14.2vdc) for 10 hours. A 1,079 watt lightbulb,(Is there even such a thing!? Try several real world bulbs in series)  plus your 'charger', should, in theory, leave zero... But in the real world, it's not really like that. But you get the idea, and I hope that gives you some ideas on how to get started.

I have seen old battery chargers, cheaper kinds, which used just this sort of method... It's wasteful, most of the energy goes into heating the bulb filiment, but if effeciency isn't primary concern, it can work. Measure, if you can, the voltage drop across the various bulbs you can find, and experiment with various bulbs, or combinations, to get what you need. Once you get about 14 to 15 volts, anywhere around that range, you have to account for diode forward voltage drop, plus drop due to load. (Volts will drop as amps are needed)

Measure actual voltages with load, if possible. Take care not to come into contact with the 230v ac! It can KILL you! (I know, you already knew that... But I ain't about to get sued for bad advice)

If this is TOO simple, or unworkable in your situation, write back and we can see what you have to work with... If there's power, there's a way!

Junkman