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Fixing an old car century battery charger

chipdj

May 29, 2021
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I am trying to fix an old century battery charger-6v-10a/12v-2a/12v-10a/12v-55a start. the two button diodes are bad and I can't fined them any where the part number is M 1504t2e04. I was thinking maybe I could change it to bridge rectifier diode 50a. but the charger has a 55amp start setting. So would the 50amp rectifier be to low of an amp? or could I use two of them?
 

Kiwi

Jan 28, 2013
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I have done this before on old battery chargers.
You could parallel a couple of 50A bridge rectifiers to be safe.

The charger is probably just a 10A charger that will supply 55A for a short time to jump start an engine with a flat battery?
 

Bluejets

Oct 5, 2014
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Never seen these things capable of jump starting a car anyhow, especially when the current can reach upwards of 600A on the older style starter motors.

There was one exception, and it was O-L-D.
Tranny cooked itself and I had to rewind it.
Primary had wire gauge like fencing wire, secondary just short of 10sq. mm mains size. ( whatever gauge that is....can't remember offhand) just remember having one hell-of-a-time getting the windings to lay down. ;);)
 

chipdj

May 29, 2021
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OK thanks just ordered two 50A bridge rectifiers. I will try that. I can only fined 50 amp cheap and the charger says 55 start so I was not Shure if it would just cook it.
 

dave9

Mar 5, 2017
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Two buttons does not make a bridge. Of course you can wire the bridge rectifier to only go through one diode, or two in parallel but then with an unregulated design, could be the peak charge voltage goes higher than ideal so could start to boil off battery electrolyte if end of charge is not monitored. Depends on the design.

A 50A diode is going to have a higher, short duration peak current rating, should be fine as long as you're sensible at not cranking it all day long which would burn out the starter too, but it's not hard to find larger diodes at electronics suppliers... just have to heatsink them if you want them capable of anywhere near their rating.

Normally you can just mount them near where the button was, or if you need to add an extra piece of plate aluminum to spread the heat, that's do-able too. Extended charging at 10A is really more of a scenario where your heatsinking needs to keep up, not so much a few seconds cranking.
 

chipdj

May 29, 2021
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OK I bought this charger new about 30 or 35 years ago. The 55 amp is not great for starting but it does help a week battery.
Over the years I have changed the clamps, circuit breaker, and cleaned the diodes and plate about five times. The other day I was jumping my lawn mower and the positive clamp hit ground and I herd a pop. I guess I am getting old never did that before.
So I checked the diodes and one was cracked and I checked both for polarity and I get voltage in both directions.
I like this charger because there is no circuit boards. I wood like to fix it but I can't find button diodes over 55amp and the 25 amp are like $20. So I figured I would just upgrade it to two 50amp rectifiers If I can figure out how to hook it up.
I was thinking of getting the 25amp and adding four of them.
 

ghokans

Jun 21, 2021
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50A, 400v button diodes from plpbattery.com for $2.95 a pair. They also have 90A for a bit more
 

chipdj

May 29, 2021
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OK I just received my two 50A 1000V Metal Case Single Phases Diode Bridge Rectifier KBPC5010SNHV hm
Now I need to figure out how to hook them up. I was thinking plus to one of the hot wires on the transformer and the ac- to the plate and not use the two dc but I don't no if that is right
The transformer has two power wires and a ground. I am guessing that is a center tap.the center wire goes to the amp gauge then the other side of the gauge is where the ground
wire with clamp is connected. I attached a picture showing what I was thinking of doing
battery-charger-and-bridge.jpg
 

Harald Kapp

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Nov 17, 2011
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The 2 AC points are the input to the rectifier. '+' and '-' are the output:
upload_2021-7-2_7-30-44.png
Your picture is not clear enough to see all the connections. Try to draw a diagram of the connections and componnets.
 

chipdj

May 29, 2021
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How is this? Bad I no! the diodes are bad I want to change it to bridge rectifier. so would I connect the neg trans
digram.jpg
 

bertus

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Nov 8, 2019
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Hello,

If you want to have a similar arangement as in the old situation, use half the bridge:
old charger upgrade half bridge.png
Bertus
 

chipdj

May 29, 2021
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OK so ac pos out lines to d1 and d2 and should I use the dc pos out for the pos dc? d3
 

Harald Kapp

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should I use the dc pos out for the pos dc? d3
Huh? Sorry, I do not understand what you ean here.

D1...D4 are only placeholders for the diodes within the bridge rectifier. What you see on the retifer is the symbols
1 × '+'
1 × '-'
2 × '~'
You connect the two outer wires from the transformer to the two inputs of the rectifier labeled '~'. Connect the output labeled '+' to the charger. This will be your DC output. Leave the output labled '-' unused.
Just as @bertus has shown in his modification of my schematic.
 

bertus

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Nov 8, 2019
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Hello,

As @Harald Kapp said, the pins have symbols next to them.
( I see them printed on the side of the rectifier ).
The ~ pins are in inputs from the transformer.
The + pin is the positive output.
The - pin is not used.
kbpc50 pinout.png

Bertus
 

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