dieselmo34

Hi all, I'm new here. I'm more of a mechanic than an electronics person, but I know some about electronics, I took 2 years of electronics tech in high school. Anyhow, I need to charge a 12v automotive style battery from power coming from a 32vdc generator. In case your wondering, I work on steam locomotives (the real things, not models), and they have 32v lighting. We use 12v VHF radios, and I'm trying to come up with a simple way to charge a 12v car battery to run the radio. Right now, we just charge the battery at night and hope it lasts all day. I saw this charger circuit you some of you were talking about:

http://www.uoguelph.ca/~antoon/gadgets/labc.htm

Can this charger take 32v input? Does it have any overcharge prevention? I would probably have the radio running off the battery at the same time the battery is charging. We use 50 watt motorola spectra radios. I can buy a dc to dc converter/13.8v power supply, but I'm afraid of overcharging the battery. How can I charge the battery without overcharging it? I'm handy with a soldering iron and thought it would be neat to build my own circuit if I could. Also, how can I make this (or other circuits) locomotive proof? Steam engines are hot, dirty, and wet, and they vibrate severely sometimes. Any help would be appreciated. Thanks

k7elp60

This charger can take the 32 volts as the input output differential of the LM350 is 35 volts. I would do two things.
1. Mount the LM350 on a big heat sink.
2. Change C1 to a 50V capacitor.
If you set the output voltage between 13.5 and 13.8 volts the battery will never overcharge.
The LM350 as internal current limiting so the maximum current the charger will supply is around 3A.

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dieselmo34

Sounds like I can just hook it right up to the power source I have. Should I mount it near the battery? Does it sense the temperature of the battery and reduce the voltage?

dieselmo34

Also, I've noticed some differences between what the parts list says and what the schematic says about the component values...which is right? The parts list says C1 is 63 volts...why would I need to change that to 50?

joecool85

I think he didn't read the list, on the schematic it says 35v. Either a 50v or 63v will do fine. Actually, even though I don't recommend it, a 35v should also be fine since you are doing 32v. The thing is, its better to have more "headroom" than the 3v you would have there, that way if there is a voltage flux that goes a little over 35v, you won't blow up your cap.

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dieselmo34

ok, so C1 is 10 or 100uf? I guess I should just ignore the list and obey the schematic...So, a 63 volt would be very safe...our steam-turbogenerators are know to occasionally surge to 37-38 volts when they are unloaded suddenly...so a little headroom wouldn't hurt I guess. Also, does it matter that the radio draws lots of current when it is transmitting? I suppose the battery would feed the draw so that the charger wouldn't burn up?

joecool85

I'd go with a 100uF cap personally. Also, the battery will take the hit when you need to pull a lot of amps, no worries there.

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dieselmo34

I keep thinking of more questions...What wattage should the standard resistors be? Also, I feel dumb for asking this, but what type are the standard resistors you buy at radioshack? Digikey lists all types of resistors, and I'm confused by what is what... Oh, and P1 is a pot I take it, what does 2k2 mean? 2k means 2000 ohms...what does the additional 2 mean? ops:

George L.

hello dieselmo34,

The standard resistor you buy at radioshack are 1/2 and 1/4 watt carbon film resistors, 5% tolerance. The 2K2 is just another way of saying 2.2K

2K + 200 ohms = 2.2K or 2K2
The colors are red, red, red.

I think using 1/2 watt would suffice, but I am not sure, ask an experienced member.

Yes, P1 is a pot.

George L.

dieselmo34

Thanks, I think I've gathered enough info that I can constrict this thing...it's been a while since I've built anything like this...

chemelec

If your going to use the LM350, I would Definately put a Fuse in the Line form your generator. Probably a 5 Amp One.

Should the Regulator FAIL, (Short Out) This will protect your battery and generator from Excessive Current.

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ip313

can someone help me to design charger for 12VDC 12A battery ?

aerobong

Hi im bong from dumaguete city phil anybody can give me idea if its ok to charge my 6V battery by the 12V battery charger

Nigel Goodwin

It's most probably NOT OK, it's likely to damage both the battery and charger.

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RODALCO

Put a 12 Volt lamp in series.
use a wattage which will correspond with the charging current.
(2 Amps 12V 21 W), (5 Amps 12 V 60W)

Bear in mind to check the charging current and time of charging, otherwise you can still overcharge the battery.

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