Engineering help - how does the charging circuit on this board work?

[repair-it]

This board attaches to 2 12v batteries in tandum (Black/Red squares). There is a 24v power supply that attaches at the 2 pin molex connector (circled in red). I need help to determine which components run the charging circuit in an effort to determine a point of failure. There are multiple via's, making it difficult to trace the circuit. Nothing appears to be shorted but I wasn't able to fully test as I do not have 2 12v batteries available. My assumption is that the micro controller (red question mark) determines when to turn the charging circuit on & off. I'm pretty sure a regulator and opamp are involved but this design is beyond my ability to figure out. All I have is the board, not the device it runs. If this is the wrong forum for this request - PLEASE tell me which is the proper group - thank you.

[eccerr0r]

You'll have to disclose the device this board belongs to (model, brand, etc.) at the very least else you will have to trace the vias. Not enough information here, ultimately people will also need to trace vias and not having the physical board makes it even tougher.

[sam_sam_sam]

We have to know what type of battery chemistry it is as well and if you hook everything back up and identify what wires are connected to the battery would help a lot

Is this tool battery charger if so what brand is it

Is it a 24 volt battery charger

[R_J]

seems to be a board from an Acorn stairlift 130 T700

[eccerr0r]

If that's the case it's AGM/SLA standard 12V 7Ah packs, so it could be cheap or elaborate...

[repair-it]

seems to be a board from an Acorn stairlift 130 T700

Yes, you are correct. It is powered by 2 12v lead-acid batteries. I have tried to trace the charging portion but not easily. I did discover that the microprocessor is involved as is the relay. Maybe the microcontroller went bad. Not sure if that's a possibility. I haven't encountered any faulty components along the way so far.

[sam_sam_sam]

Ok now that we know what type of battery cells we are dealing with do you have a 24 volt power supply that is capable of at least one amp of output if so use an M16 incandescent light bulb in series with the power supply and go from where you connect the battery power wires and see if you have power all the way back to the relay that is controlling the charging circuit then see if you can get the controller to take over the charging function if not then you have to trace out the voltage sensing circuit and see what type of circuit it is and show on the circuit board where it is in a picture so we go from there and how it is controlled

[eccerr0r]

I need to ask the question: what was the initial complaint of the circuit?
Was it that it doesn't charge, or the batteries don't last long?
Lead acid charger circuits tend to be robust and rarely fail. Lead acid batteries, however, fail all the time...

[petehall347]

some chargers wont work unless batteries with charge are connected

[sam_sam_sam]

some chargers wont work unless batteries with charge are connected

This is very true and probably this one might be same way

[repair-it]

I need to ask the question: what was the initial complaint of the circuit?
Was it that it doesn't charge, or the batteries don't last long?
Lead acid charger circuits tend to be robust and rarely fail. Lead acid batteries, however, fail all the time...

Thank you all for your replies. The issue was a fault code indicating the battery(s) were not charging. I am limited in how I can test these boards as I do not have 2 12v batteries available, I have monitored under a thermal camera and the only component getting hot is the voltage regular but the temp is within spec. The customer wanted all relays replaced as they tend to 'hang' and the supplier told him that the fix was to tap it with a hammer.🤣 I was hoping that someone who designs circuits could look at the way this board is laid out and maybe explain how the charging part of this board works, I have tried to trace the circuit from the molex connector back to the relay with a MM and testing voltages but so far all the components along the way tested good, The company made this board as an upgrade to another and it seems to have more issues than the board it's suppose to replace. On the older board, it was a simple smd fuse that went bad. The older board had an external power supply that was 15V AC. The newer boards use an external power supply of 24v DC. At some point soon, I am going to the customers shop to see how everything functions so I can get a better idea how the batteries should charge up. It goes w/o saying, I'll be bringing my meter.

[eccerr0r]

An open / broken battery can also trigger some charging circuits as not charging, so you need to do some system analysis with the whole circuit including batteries. Did you ask if they tried replacing the batteries before sending you the board?

You need a bigger relay and better snubbing if it's "hanging" or I assume they mean it gets stuck closed, probably due to arcing due to inductive kickback of the heavy electric motor...