1. Home
  2. Electronics Design
  3. Re: Can a 12 volt regulatred power supply be used to charge car batteries?

Re: Can a 12 volt regulatred power supply be used to charge car batteries?

>> Unlisted wrote in

>> news: snipped-for-privacy@4ax.com: >> >> > I have a 12volt regulated power supply that was probably made for >> > using automotive CB radios in a house. It's rated at 3 amps. Can >> > this be used to slow charge 12V car batteries? I have a big car >> > battery charger, which puts out 15 or 60 amps, but I want to >> > trickle charge a battery in severe cold weather. >> > >> > I'm more worried about damaging the power supply than the battery. >> > >> > >> >> If you can set the supply voltage to 13.6 volts under the supply's >> full rated load, then yes. >> >> The problem is not you needing to worry about the supply. The >> problem is that you could overcharge the battery and blow it up >> (lead acid). >> >> If you can ensure that you do not exceed the fully charged voltage >> and stop charging when that is attained. >> >> If you can't, you'd better find a way to monitor the battery's >> temperature, or have some other means to determine full charge state >> and turn OFF the charge device. > >Old car chargers had no cut-off when full, folk just unplugged them after a while. >You can do that if you don't make a habit of it. If you do it often, use a better cha >rger. Old unregulated chargers will kill batteries if you leave them on day after day.

I have an old charger, a small 6A model, which only has an over current cutout. No cut-off. I had it connected to my farm tractor last week, when we got a huge snowstorm. The tractor and charger were outdoors, but I had a cover over the charger. However, the plug was laying on the ground, connected to an extension cord. That cord is plugged into a GFI outlet on the barn. After the storm, I unplugged the charger, which had been connected for around 36 hours. However, the GFI had tripped from the cord being buried under the snow.

I soon found that battery was completely dead. (It was only halfway discharged when I applied the charger). The tractor ignition switch and lights were NOT turned on.

So, what drained the battery? It had to be the charger, which drained it after the GFI tripped. I did not think that current is supposed to go backwards on battery chargers, but I assume it did. With the ingition switch and lights turned off, there is nothing to drain the battery. (this is a simple OLD tractor, no radio or heaters or stuff).

I can only assume that the charger has a leaky diode...... I guess thats possible???? I am not quite sure how to check this???? I can only guess to hook my multimeter across the plus and minus clamps, then reverse it and see if there is low resistance both ways????

Or maybe I should just put new diodes in it. 6A rated diodes cant be too costly...

Reply to
tubeguy
Loading thread data ...

Put the charger on a good battery. Power it off. Put your current meter between the battery and charger to see how much current flow you get back into the charger.

If you are gonna replace the diodes, you should use the same technology. Very old chargers had selenium rectifiers.

Battery chargers are dirt cheap compared to the batteries they charge. Just get a smart one and be done with it.

Reply to
Mike

Minimal chargers are just transformer & diodes. Leaky diodes yet it works are unlikely, but as Mike says measure it & see.

NT

Reply to
tabbypurr

How are you going to simulate a 3 stage charge cycle? or deal with changes needed by temperature extremes? I don't think it can be done correctly with a (roughly) 12V 60A power supply. The 3A charger might work, but you'll need some kind of regulator and charge controller. Most CB radio power supplies that I've seen use linear regulators, which means that the unregulated voltage is probably about 15V. Rip out the linear regulator, install a lead-acid battery charger circuit, and you might have something that works. Something like this PCB: Or, just buy a battery maintainer and be done with the project.

Normally, I would suggest you run out and buy a proper battery charger. However, my luck hasn't been too good with some products. Six out of these seven charges died or went insane while charging fairly new lead-acid batteries. The seventh charger died a few months later after boiling the water out of 2 expensive batteries: I'll spare you the details, but basically these were an attempt to save money by not buying a proper charger. I donated my Statpower Xantrex 10A charger to the cause and had no further problems that required long drives to various mountain top sites:

You mention something about wanting to trickle charge a lead-acid car battery. That will not work. Automotive lead-acid batteries are NOT made for stationary use. Ask in any of the wind, solar, or alternative energy forums about how well car batteries work for stationary use. Car batteries were made to deliver a large amount of current quickly when starting a car and then recharge quickly.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558
Reply to
Jeff Liebermann

+1
Reply to
David Lesher

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.