[GuySmily]

Hi guys,

I'm interested in both repairing this thing and learning a little more about it. I'm an engineering major and have learned the physics behind electricity and magnetism, but I haven't yet taken circuits. All my knowledge is limited to projects I've done so far (populating PCBs, wiring car stereos, research on building an electric car, etc).

0) What is the device?
I've got an old (70s? 80s?) Schumacher SE-1275A battery charger that I want to fix.

It looks like the charger is still sold today. The graphics have changed, but the switches and meter are in the same locations and look exactly the same.
http://www.amazon.com/Schumacher-SE-1275A-Automatic-Onboard-Battery/dp/B000BO8TTY#productDetails

At the minimum, I'd like to use it to power an electrolysis bath. In other words, I don't mind losing the switch functionality as long as I can get power out of this thing.

1) What is the fault?
The problem is that it doesn't appear to work at 2A or 12A. When the charger is plugged in, the meter always points all the way to the left (not necessarily pegged, but within the "CHARGE" label).

I thought that maybe only the gauge was broken, but I've tried to charge dead batteries overnight and had no luck.

At 75A, it buzzes (as it always has) and it definitely puts out electricity as it makes my electrolysis bath bubble like crazy.

I measured voltage at the clamps at different switch positions and no load (no battery connected). Here's what I got:
Switch position: Voltage measured (+/- 1V)
2A: 8V
12A: 10V
75A: 12V
(Note that I did NOT measure amperage. Those are labels on the switch)

2) History of the fault
~10 years ago, when I first had this problem, I discovered that flicking the amperage switch back and forth would sometimes get me a reading on the meter. I tried to avoid flicking to 75A. After doing this a few times, flicking the switch stopped helping, and now it's always stuck at 100% with the "Full Charge" LED on.

3) Actions unspecified in the manual
I may have left this on 75A for too long, but nothing crazy (less than a minute). Flicking the switch probably wasn't good for the charger either.
It's never been reversed or shorted or anything like that.

4) Does anything look or smell burnt?
5) Do any components look "wrong"
See photos. Only the SCR(?) looks suspect, but I might just be seeing burned flux.

6) PHOTOS
These burned looking contacts belong to the SCR/thyristor. Only the two outer terminals are hooked up. The middle one is cut off and is not connected to anything.

I tested the thyristor using the procedure here (without desoldering it), and it seemed okay.
http://www.androiderode.com/how-to-check-a-scr-with-digital-multimeter/

Here's a couple shots of the circuit board:

Back of the Charge Rate switch:

Back of the meter (top) and battery chemistry switch (bottom). What does the meter do, anyway? Is it an ammeter that drops to 0 as voltage approaches 12v?:

Switch/meter connections (In this picture, you are looking at the front of the charger, but I have lifted/rotated the front panel up and back like a garage door):

Don't know what this is. It's attached to the floor of the charger.

It sounds like these are diodes? There are two of these bolted to the same plate (heatsink?) as the SCR. I don't understand how these work - it looks like both terminals on the diode connect to the same place on the charger. Does the electricity flow from one side, through the heatsink,and into the other (e.g. white -> heatsink -> blue)?

FYI, I have some basic electronics knowledge - I've fixed a couple TVs, assembled a few PCBs, etc, but I'm still taking my first circuits course at school (I'm a software engineering major).

For kicks, here's a shot of my electrolysis tank. Looking forward to getting this up and running!

 

[GuySmily]

Okay, I did some more thorough testing now that I have my own DMM here. Does this tell you anything?

 

[Bluejets]

The following is what it appears to be from your photos......
Yellow black orange plus perhaps a couple of others(bit hard to see).......... Transformer primary
Black coming off bottom of transformer ...........Secondary common (negative out)....goes through ammeter and then through current limiter (grey component 12v G20 35A) then out to negative lead.
White and blue pairs to diodes...??....no marking i can see but.... that could make the plate positive out to the regulator ( you say triac/scr) this component more than likely has tab connected to the plate therefore the centre lead cut.(not required)
Terminal marked "tab" is output to positive lead.
Digital multimeter for voltage readings may not give you the readings you expect, I tend to use analog as the output is rather choppy.
Check the usual, fuses, primary and secondary transformer circuit, diodes, (seems only explation for the 2 black devices), current limiter (usually they auto reset) all can be checked without powering up.
Trace and measure transformer secondary output...(AC)...lower black common first to blue, then to white

S2055W does indeed appear to be a fairly hefty SCR.(70A)
You can google how to test these with a multimeter..you said "burnt looking contacts" but I suspect it's just remnant flux.

 

[bttremblay]

Hi , I have the same problem and I wonder if you found the solution. if so what was it. thanks

 

[GuySmily]

Wow, blast from the past. I transferred schools and left this thing in my parents' garage, where it still sits to this day. Sadly, even after 5 years of education (I graduate this December), I still couldn't tell you how to fix this thing. But I would like to take another look someday.

 

[tec602]

Funny, I have the same old charge which failed with the exact symptoms, switching the CHARGE RATE switch a few times used to get it too work but it slowly got worse and would just stop in the middle of a charge.
These guys over here, https://www.eevblog.com/forum/repair/schumacher-se-5212a-charger-repair/ have dug deeper, very similar model. Right now I am finding loose connections in mine at the pcb rivet to heatsink and the black diode brass male tabs are intermittent. thank you all for your posts.

 

[noelmem6]

This is an old thread but a bro-in-law just handed me his unit telling me he accidentally connected the clips to the battery reversed .. he heard a click then claims it no longer works . The click came from the circuit breaker - the 2 terminal device riveted to the floor Shumacher 12v K31 35A - its a self resetting Circuit breaker after 5 cooling minutes .

If the charger only works at the 75A setting then the 3 position slide switch is worn out . The current rating output is determined by varying the input into the Taps of the Primary winding - the longest is for 2A , mid tap is for 12A , earliest tap is for 75A . But it seems your problem is not like this .

The secondary seems like 2 parallel windings but each winding goes into separate SCR ( the model at hand ) controlled by a voltage comparator. In Your model there are 2 dual Diodes into the heatsink , Heatsink to the SCR Cathode ( the Positive charger output ) you have only 1 SCR .

When Charging voltage reaches 14.7 (2A) - 15.75 (12A) it fires the CHARGED LED ( im using 112v ac input but the charger needs 120Vac so it will take more time for the unit to charge a battery) , once fired it cuts-off the charging current - SCRs OFF ...assuming the battery is still connected ...when the Battery voltage drops down to 13.3v , the CHARGED LED turns OFF and charging commences again and the cycle continues topping off the battery safely .

Now you said you like to use it as the PS for you electroplating - it may not work continuously because as the clip voltage reaches 14.7v/15.5v the charging voltage cuts off . As long as the electroplating electrodes maintains a voltage lower than 14.7/15.5 you have output, but cuts off above that , maybe you need to vary the electrodes' distance in the plating tub to get the Charger to just output charging voltage without reaching the "CHARGED" Voltage of 14.5v/15.5v . Must understand the charger must see a Battery and not a variable resistance load for it to output a charging voltage/current . It will be tricky to use it for electroplating while in the 2A 12A range . There is a warning that the 75A range be used only for 5sec then rest for 4 minutes.

Must check the voltage comparator components should the charger performs differently than normal charging cycle .