I often get asked to repair mobility scooters, most of the electrical faults are due to poor corroded contacts or broken wires, poor batteries or chargers that are dead but easily repaired. When I've repaired a charger it's ok to test IF I have the scooter and battery pack, often this is not the case. I am trying to find a circuit that will simulate a battery charging and discharging, ok I could use a real battery, but these scooters run on 12 or 24v SLA. has anyone any suggestions? As my forte is repairing power supplies, electronic loads, PSU's etc are available.

 

Ideally you need a sla battery, but you need to see what happens when you put a resistor, say 10 ohms, on the output of the charger, and if it's monitoring the voltage you need to feed a lower DC voltage back in, and gradually increase it to see if the charger stops.

 

Can you separate the power output cable from the battery voltage sense cable?
If so, connect the output to a past-its-best battery that you don't need any more, and connect the voltage sense to a power supply. Vary the power supply around the important battery voltages (absorption, float etc) and watch what happens to the output current.

 

DC buffer amplifier with a power resistor (or couple of rectifiers paralleled by a resistor) in series with the output? Feed the buffer a voltage that varies from 12v to 13v or so to simulate a battery charging. The buffer has to be able to sink the charging current. Or maybe it's easier to make a variable active power zener and have a pull‐up resistor to simulate battery voltage, instead of a power buffer.