DIY Car Battery Charger

[mike9h29]

Hi,

I want to build a 12v Car Battery Charger.

What I have so far is a 18V Transformer. Is this good? or Its better if I find a 12/14v Transformer?

Also, for the rectifier, is this good please? http://cgi.ebay.co.uk/ws/eBayISAPI.d...tchlink:top:en

I will also buy a Volt Meter and Amp Meter.

Any feedback is appreciated.

Thanks

Mario

[999999999]

It depends on what type of charger. If it's going to just trickle charge there's less to consider - just the trickle rate, but if it's going to float charge or use a termination method then you may have to account for the voltage drop across the regulation circuit.

Thus, the rest of the charger design needs worked out first. Either way, with all else being equal an 18V (VAC) transformer is a bit on the high side. You could make it work but a 12V to 14V would be more optimal. Presuming the transformer isn't capable of 50A, yes the bridge rectifier you linked would work, though many of us might be charging at a lower current within which we already had a spare bridge rectifier lying around that would handle it.

I have to wonder if it's a worthwhile project because by the time you buy all the components, including cables, clips or clamps, etc., let alone the time to build it, you could probably buy a complete ready to use charger with a charge termination circuit and meters built into it.

[larrymoencurly]

Yard sales? I haven't come across a car charger yet with a bad transformer, mostly bad cables (broken at battery clamp or case strain relief) or shorted SCR (typically rated 50A) in automatic charges.

[mike9h29]

Originally Posted by 999999999

It depends on what type of charger. If it's going to just trickle charge there's less to consider - just the trickle rate, but if it's going to float charge or use a termination method then you may have to account for the voltage drop across the regulation circuit.

Thus, the rest of the charger design needs worked out first. Either way, with all else being equal an 18V (VAC) transformer is a bit on the high side. You could make it work but a 12V to 14V would be more optimal. Presuming the transformer isn't capable of 50A, yes the bridge rectifier you linked would work, though many of us might be charging at a lower current within which we already had a spare bridge rectifier lying around that would handle it.

I have to wonder if it's a worthwhile project because by the time you buy all the components, including cables, clips or clamps, etc., let alone the time to build it, you could probably buy a complete ready to use charger with a charge termination circuit and meters built into it.

Hi,

Thanks for the useful reply.

I have a battery charger already, but I want to build something and decided to build a charger

I will search for a 12/14v transformer and use that.

Thanks again.

Mario

[kc8adu]

junk 12v ups transformer.
used one to repair a battery charger with a smoked transformer.iirc it was from an apc 650 with lightning damage.

[mike9h29]

Originally Posted by kc8adu

junk 12v ups transformer.
used one to repair a battery charger with a smoked transformer.iirc it was from an apc 650 with lightning damage.

I opened a UPS today to take the Transformer but it has 5 wires on the primary side and 3 wires at the secondary side.

Do you know which wires should I use please?

Thanks

Mario

[999999999]

^ look in the UPS to see where those wires went. You need to find (trace) from the AC mains/wall outlet input to the ups, which winding that is, and trace from the battery back through its charging circuit to the other winding for that. Remember there is also the opposite that you don't need, the battery to transformer circuit to produce the AC output for the gear the UPS is powering when the grid AC shuts off.

You might also see if there are markings on the transformer to help identify it, manufacturer and part #, or do a web search for the UPS model to see if anyone has discussed the parts internal to it, and of course, mention the UPS make and model here and provide some pictures.

[budm]

Or you can use the UPS batteries charging function if that section is still good for charging your batteries?

[999999999]

^ ha! The best answer, though with most UPS that circuit can only do a few hundred mA current AFAIK, Mario didn't mention the desired charge rate but it could be higher if he's considering a 50A bridge rectifier.

[Kiriakos GR]

I care for a true working Lead Acid battery desulfation - Pulse Generator.

If some one haves a good link just share it.

[kc8adu]

Originally Posted by Kiriakos GR

I care for a true working Lead Acid battery desulfation - Pulse Generator.

If some one haves a good link just share it.

http://leadacidbatterydesulfation.yu...y#.T7zrCcWJJuY

[kc8adu]

the apc iirc had standard white/black on its secondary which becomes primary.
the 2 very heavy leads go to your rectifiers.

[Kiriakos GR]

Originally Posted by kc8adu

http://leadacidbatterydesulfation.yu...y#.T7zrCcWJJuY

Thanks, I am aware about this page, what I wanted was to find one person in this forum who will have made his own project.
Like: tested & working !!

In the above website they change the schematic almost every month. (experimental project)