Schumacher SE 5212A Charger repair

[SteveRosenlund]

Hey there everyone.  Please help me with this repair.  I've searched for schematics for this particular charger, but can't find anything as of yet.  There's lots of schematics out there claiming to be of the SE 5212A but none actually appear to be. 

I'm a beginner but have plenty of diagnostics tools in my lab so far.  How would you go about troubleshooting this?

Symptoms:
No charging output. 
12.6VDC on output until i apply a load, then voltage drops to 0
Photos attached.  I'm just getting started on this, so any help is appreciated. 

Steve

[floobydust]

Resistor R6 looks burnt possibly was 47R. I would sketch a schematic of the little board, test the transistors on it.
The big triac? A17 might have failed. Not sure of its part number.
The high current rectifier diodes might be the part on the heatsink with two black wires going to it? The heatsink is used as a connection, hopefully it doesn't have cheeseball alternator-style diodes that are spring fit.

[TheMG]

The circuitry on the PCB, aside from the large rectifier, is responsible for the analog meter and LED indicators only.
Upon closer inspection it appears to have a relay to turn the output on/off, presumably upon sensing that the battery has reached fully charged voltage. Is this relay being energized appropriately when a discharged battery is connected to the charger, and then de-energizing the relay when no battery is connected? If yes, then this circuitry is doing what it should.

Otherwise, this charger is nothing more than a cheap and nasty unregulated unfiltered half-wave rectified power supply. The output from the transformer passes through a single rectifier diode, a thermal overload, and a current shunt.

More than likely you've got a bad connection somewhere, high resistance, so as soon as you put a load on it all the voltage drops across the bad connection.

It is also possible the bad connection is on the primary side, so check to see if the voltage to the primary taps on the transformer is proper.

Check for cracked solder joints, bad switch contacts, loose terminals. Use a DMM to determine where the voltage drop is occurring.

Do also check across the relay when it is energized, in case it has poor contacts.

[highpower]

More than likely you've got a bad connection somewhere, high resistance, so as soon as you put a load on it all the voltage drops across the bad connection.

 

Automotive battery chargers are notorious for breaking wires inside the insulation at the battery clips. Lot's of flexing happening there over the years.

[floobydust]

There's no relay, I see a thermal circuit-breaker on the output, after the ammeter.
This thing has regulated output voltage, my guess is with phase-control. Although they did it without any capacitors, small diodes or zener, or IC that I can see for a voltage reference.

The burn resistor R6 connects to the big guy on the heatsink, so I'd say it's failed.
A two-lead TO-3P seems odd, guessing a triac or SCR. I hate rivets and drill them out.

[picburner]

This device is a battery charger not a power supply.
If you apply a load (like a resistor), its circuit may not detect the presence of a minimum voltage at output and may deactivate considering this lack as an anomaly.
I recommend you try it on a real battery to check if it works or not.

A17 is definitely a thyristor (SCR) since no other rectifiers are seen in the pic.
R6 has been overloaded but does not seem completely burned, however it is better to check it.

[mikerj]

This thing has regulated output voltage, my guess is with phase-control. Although they did it without any capacitors, small diodes or zener, or IC that I can see for a voltage reference.

One of the TO-92 devices could be a TL431 or similar.

[SteveRosenlund]

THanks for the replies everyone.  I'll get into making a schematic of the board and testing all the components/connections asap. 

[TheMG]

There's no relay, I see a thermal circuit-breaker on the output, after the ammeter.

That's what I initially thought but if you have a really close look at the pictures, there are more than two wires going into that device.

A two-lead TO-3P seems odd, guessing a triac or SCR. I hate rivets and drill them out.

An SCR or TRIAC must have a gate pin, in this case there isn't, and if you follow the traces one of the pins is commoned to the heatsink which is not insulated from the tab of the device.

It has to be just a regular rectifier diode.

[bdunham7]

Clearly we need some better pictures to see what wires go where and if there are any part numbers, especially on the unknown semiconductor.

This isn't going to be a crude half-wave setup.  Based on my experience with Schumacher chargers and the pictures, this is a full-wave rectified setup with two rectifiers and a CT transformer.  The charging rates and levels are selected with primary taps and the primary system is completely isolated from any controls on the secondary side--this is standard and is also obvious from the pictures.  The big shiny plate is on insulated standoffs and is probably energized--the rectifier pair I have marked is connected to the outer leads of the CT transformer and the rectifier common goes to the plate. 

The only question on the controls is what the semiconductor is and what it does.  I marked an area that I think is not connected, although some have assumed that it is.  If that is connected, then I have no idea how that part of the unit works.  If it is not connected, it is either an SCR or a transistor and power comes in on the tab of the device, is controlled by the base or gate pin on the left and goes out on the right hand pin.

[SteveRosenlund]

Clearly we need some better pictures to see what wires go where and if there are any part numbers, especially on the unknown semiconductor.

This isn't going to be a crude half-wave setup.  Based on my experience with Schumacher chargers and the pictures, this is a full-wave rectified setup with two rectifiers and a CT transformer.  The charging rates and levels are selected with primary taps and the primary system is completely isolated from any controls on the secondary side--this is standard and is also obvious from the pictures.  The big shiny plate is on insulated standoffs and is probably energized--the rectifier pair I have marked is connected to the outer leads of the CT transformer and the rectifier common goes to the plate. 

The only question on the controls is what the semiconductor is and what it does.  I marked an area that I think is not connected, although some have assumed that it is.  If that is connected, then I have no idea how that part of the unit works.  If it is not connected, it is either an SCR or a transistor and power comes in on the tab of the device, is controlled by the base or gate pin on the left and goes out on the right hand pin.

Hey there.  Thanks for the interest.  Let me answer your questions. 
The area you marked is NOT connected.
The transistor in questions is a Rectifier and the data sheet is located here: https://www.mouser.com/datasheet/2/389/CD00000672-249975.pdf
            I ordered in new ones for this repair a while back. 
All of the other transistors are either PNP or NPN ("P" marking=PNP, "N" marking=NPN)
           PNP transistors are these: https://www.onsemi.com/pdf/datasheet/2n4403-d.pdf
           NPN transistors are these: https://www.onsemi.com/pdf/datasheet/mmbt4401-d.pdf
I also ordered in a new circuit breaker.  I have resistors and the other transistors in stock.

Others have asked, but the r6 47ohm resistor tests at 47 ohms still. 

The transformer is outputting 2 sine waves @ 36VPP 180 degrees out of phase with each other.  Looks like this:


after going through the diodes, the two signals merge to form this rectified waveform which is present on the entire back plate, entering the board at two locations: the back of the rectifier and the top left pad that was rivetted to the plate. 

[bdunham7]

OK, the part is an SCR, which controls output current by turning on at different points in the cycle. You can test the main components--transformer, rectifiers, circuit breaker, ammeter--by simply bypassing it by connecting the plate or the rivet to the right side SCR pin, which is connected to the blue output wire.  If you connect a battery it should start charging it at full rate and it should show on the meter.  If all that works, then your issue is going to be on that board somewhere.  The first thing to do would be to check the gate drive with scope, which I see you have.

[SteveRosenlund]

Ok I've traced the board to the best of my ability.  Here's that drawing. 



All of the resistors and transistors test good.  Also, in my haste, I removed all the transistors and found one that was different after the fact.  I think it goes in the "R1" space.  It's a PNP with a diode across the emitter and collector.  Amplifier maybe?  Anyway i think it goes in the R1 space.  Here's how it tests compared to the rest of the PNP transistors.




Here's the rest of the PNP

[floobydust]

I drew a schematic for your review. It's not as bad as it looks, figuring it out.
R6 and R7 are not connected, to make sense. Not sure where the power on LED connects, it looks like at the heatsink.
I think part "R" must be a TL431 and would be the oddball part you tested as it has the extra diode.

When the output voltage is high (past the setpoint) "R" TL431 turns on which turns on P4, which turns on N2, which turns off N3, which turns off P2, which turns off the SCR. P1 and N1 are for some current-limiting. Not sure what P3 is doing, looks strange.

I would test the charger using a tail light bulb for a dummy load, like an #1157. Line trigger the scope, and poke around.
If R6 47R heats up smokes then the SCR is dead.

How do they rate this for "50A Car starting"? Ouch.

[SteveRosenlund]

Wow!  Thanks for that!  I can build a new board with that. The traces on the board are super thin and the pads are being damaged desoldering. After testing all the components, and finding them all within spec, I’m not sure where to go from here. First I gotta go through the board and check for continuity between the pads/terminals cause after reassembly, it doesn’t give any output.
Thanks again.

[bamboone]

Firstly, let me heap praise and thanks to the OP, and the people who have replied to this thread! Beautifully clear pictures, and backwards engineering including drawing up a schematic? Magnificent! My Schumacher SE-5212A had no voltage output, but my first round of following voltages caused me to find that there was no voltage getting from the heatsink (12vdc 'hot' plate), and the pcb with all the other components. The manufacturer had used a pop-rivet (just like in your post's pictures), but with a star washer on the component side of the pcb. I replaced the pop-rivet with machine screw (screw/star washer to pad on pcb/lock washer/nut), and all is well again. Thanks for all your help!

[m3vuv]

FFS,it says 50 amp engine start,what plannet are they on,looks like a piece of chineese junk,bet its a crappy ali wound transfo as well?.

[bdunham7]

FFS,it says 50 amp engine start,what plannet are they on,looks like a piece of chineese junk,bet its a crappy ali wound transfo as well?.

These are actually pretty good chargers.  50A is a boost mode where they overdrive the primary a bit. 10 seconds on and 3 minutes off as it says on the front.

[BlueFalcon]

Hey everyone, I apologize for asking the question here, but it seems like the best place for me to ask: I have the same model charger, and I managed to wear out/break the 3 position selector switch that allows you to switch between 2, 10 and "50" amp.

I cannot find an exact replacement to match. It's an 8 pin, 3-position variety. Is there an alternative switch I could purchase to make this work?

I'm a bit of a newbie when it comes to electronics and circuitry, but I'm willing to learn!

[bdunham7]

You are looking for a DP3T (Double Pole Triple Throw) slide switch with panel mounting.  Measure its dimensions carefully and then google the term "DP3T panel mount slide switch" and start looking at the results.  I don't have the dimensions, but my first guess would be:

https://www.mouser.com/ProductDetail/Switchcraft/46313LDRSX?qs=Mv7BduZupUj%2FDLUW%252BiYlvg%3D%3D&mgh=1&gclid=CjwKCAjw-rOaBhA9EiwAUkLV4g6EBEklSzVCC9ysgLVx5ykgKZTskdIA7JEpsTmorMOE7cgFWoOj1hoCJYEQAvD_BwE

[BobbyZ]

I am trying to diagnose my SE 5212A  charger, I am getting a voltage reading of 12.1 volts before power enters the PCB but I only read 9.6 volts on output of PCB where charge cable ties in to it. Any suggestions? I don't see any indication of burned reisitere, etc.

[floobydust]

The 5212A charger outputs pulsing DC (there are no filter capacitors). So the reading you are getting could be fine - it depends if the multimeter has true RMS or what it does measuring pulsed DC signals, it could read low.
If you connect the charger to a car light bulb as a load, see if it has some output current, and you can measure the output voltage with a capacitor (or battery) added to smooth out the DC. That would give a more accurate voltage measurement.