Author Topic: Rebuilding a vintage 12v battery charger  (Read 8548 times)

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Offline bonneyman

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Rebuilding a vintage 12v battery charger
« on: June 21, 2011, 01:55:59 PM »
I read a post somewhere of a guy who rebuilt an old car battery charger. Was that on the old TT forum?
Anyway, I picked up this small charger made by Real Battery Charger Co, Chicago. The size of two packs of cigs. Very compact, made in USA. The transformer still puts out 16v AC, but no DC output. I'm guessing the rectifier circuit is bad? Anybody have any clues where to buy/make such a part? If I can get this thing working, I think it would be great to have on hand.
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Offline rusty

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Re: Rebuilding a vintage 12v battery charger
« Reply #1 on: June 21, 2011, 02:43:14 PM »

Depends how old it is, if it has selenium rectifiers, you are probably out of luck, i havn't seen one in 20 years. If it's earlier than that, it may have copper oxide rectifiers. good luck finding one of those ...

You could replace the rectifiers with a bridge rectifier from radio shack , if you can't see it it won't matter much, but, the voltage will be higher than it is supposed to be......

Before you go to all that trouble tho, check for a fuse or circuit breaker on the secondary side, some had them.....
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Offline Hm Wrench

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Re: Rebuilding a vintage 12v battery charger
« Reply #2 on: June 21, 2011, 03:25:05 PM »
If you want a selenium rectifier, here you go http://www.cougarelectronics.com/selenium.htm

For 1960's Honda motorcycles we use these from radio shack, i do not know if it would work on a battery charger though.

http://www.radioshack.com/product/index.jsp?productId=2062584

Thanks,
Kirk
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Offline bonneyman

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Re: Rebuilding a vintage 12v battery charger
« Reply #3 on: June 21, 2011, 06:52:30 PM »
Guess I should post a pic of the thing. Maybe you guys can tell me what diode it is.
I'm getting 15.6 v AC out of the transformer, so I know it's converting power. Just not getting DC. And I'm thinking the AC voltage is a bit high, as the rectifying process probably loses some power in the process (to get it down to 12-13 volts).
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lzenglish

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Re: Rebuilding a vintage 12v battery charger
« Reply #4 on: June 22, 2011, 06:02:05 AM »
Think of a diode as a "Check valve", allowing for current to only flow in one direction. A rectifier is made up of 4 diodes, to convert A/C volts, to DC volts. This is a very easy and do-able project George. Just go to Radio Shack and buy a full bridge rectifier that will handle the maximum current load that your little charger came with. These little componets like resisters, diodes, rectifiers, etc. are cheap, and are the ONLY things I still buy from Radio Shack, as their return policy SUCK'S !

Good Luck,

Wayne
« Last Edit: June 22, 2011, 06:04:20 AM by lzenglish »

Offline bonneyman

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Re: Rebuilding a vintage 12v battery charger
« Reply #5 on: June 22, 2011, 08:12:07 AM »
Here's the pics:




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lzenglish

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Re: Rebuilding a vintage 12v battery charger
« Reply #6 on: June 22, 2011, 10:12:01 AM »
That cute little trickle charger has more bells and whistles on it than a cadilac, so it must be an oldie?
I would give it a go at fixing it, if I were you! It is very rare you see a reset fuse in anything now days. And most of these little things are usually 12 volts only, "that I have seen"! IMO, etc. Lol

Wayne

PS. Here is another very basic schematic for you. The aluminum looking bracket on yours is probably a heat sink, and a good place to mount your new rectifier. I see you are shy the alligator clips, and wire leads, so you may want to see if this project will be cost effective after you buy all the parts.
« Last Edit: June 22, 2011, 12:36:46 PM by lzenglish »

Offline bonneyman

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Re: Rebuilding a vintage 12v battery charger
« Reply #7 on: June 22, 2011, 01:50:02 PM »
Made a visit to the local electronics parts supplier, and they said I have a selenium diode. The guy who knows said I could solder a 10 amp rated diode in place of the 2-wire diode I have now, and it would work fine. So I took it. For less than $4, I'm willing to try my hand at soldering.
Definitely going to leave the heat sink plate in there. Lets see if I can get some 12v DC out of this thing.
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Offline rusty

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Re: Rebuilding a vintage 12v battery charger
« Reply #8 on: June 22, 2011, 02:38:07 PM »
>and they said I have a selenium diode

Yup, single cell selenium diode, usually 20 volts or so, few amps with that size heat sink

>a 10 amp rated diode in place of the 2-wire diode

Should work fine...

It is not a very efficient design, but it should charge a battery...
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Offline bonneyman

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Re: Rebuilding a vintage 12v battery charger
« Reply #9 on: June 22, 2011, 06:49:42 PM »
>and they said I have a selenium diode

Yup, single cell selenium diode, usually 20 volts or so, few amps with that size heat sink

>a 10 amp rated diode in place of the 2-wire diode

Should work fine...

It is not a very efficient design, but it should charge a battery...

I have an email in to Cougar Electronics to see what they can come up with, and if it's cost-effective. Would really like to get this little antique humming again. I'll give it a good home!

Update: C.E. got back to me. They have such selenium cells in stock. If I send it in to them they'll analyze it for free and then repair it. Minimum repair cost is $50. Not cost effective.
« Last Edit: June 23, 2011, 04:26:23 PM by bonneyman »
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Offline bonneyman

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Re: Rebuilding a vintage 12v battery charger
« Reply #10 on: June 25, 2011, 10:15:24 AM »
OK, I'm going to do some soldering soon on this charger. And I have a set of new alligator clamps - with an in-line fuse port installed in the one side! I need to know what size to put in there.
The charger body says 1 amp - is that for 6 volts or 12? If you half the voltage, according to ohms law (everything else being equal), you double the amperage. I'm assuming (big) that the 1 amp is the max, which would indicate the 6volt setting.  So, the 12v would be .5 amp. But I'm not sure.
Don't want to blow a good car battery or start a fire. Any of you want to give me some advice?
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Offline rusty

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Re: Rebuilding a vintage 12v battery charger
« Reply #11 on: June 25, 2011, 11:00:30 AM »

A secondary fuse in that design primarily protects the rectifier/diode. The car battery won't care much, you can dump 20 amps into a car battery for hours without hurting it much.

The heat produced in the rectifier is determined almost entirely by current, the 6/12 volt setting won't change that, so select the fuse to protect the most expensive part, the diode.  (The amp rating for the charger is likely for either setting, as the reset/circuit breaker is set for that trip current)
Guessing a bit, but the transformer looks like it's good for several amps, as long as it has a primary fuse it will be ok. (if it doesn't, a 1/2 amp fuse to protect it may be a good idea, unprotected transformers start fires))  (Why this size is sorta complicated, theory would say smaller, but it will nuisence pop the fuse if the fuse isn't big enough to handle the inrush current when you plug it in. So, you go slightly bigger in this case, the short circuit current if the transformer fails will be much more than 1/2 amp))

As an aside, the rating is kinda funny, 4 amps at 117 volts is over 400 watts, but 1 amp at 12 volts is only 12 watts....are they implying this thing is that inefficient? LOL


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Offline bonneyman

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Re: Rebuilding a vintage 12v battery charger
« Reply #12 on: June 25, 2011, 01:38:56 PM »
Thanks for the info. The guy who sold me the diode said it was rated at 10 amps, so I don't really have to worry about over-amping it. I'll add an in-line fuse to the transformer in the line (input) side, just to be safe.
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