Guys,

I have a battery that I'm testing, it needs to be charged and discharged at various currents. I already have a very nice computer controllable Lambda power supply that can do 0-130V and 0-141A? Is it possible to use the one power supply for both charging AND providing a variable load. E.g. I could wire the power supply to the battery via a DPDT contactor. In charge mode, + on the power supply goes to + on the battery. In discharge mode, + on the power supply goes to - on the battery, with a low ohm large wattage resistor in series. See my attached sketch. Would this scheme actually work in practice?

Thanks a lot,
FW

 

Well, yes... but it doesn't look like you are monitoring the charge current. If you are, then that's good.

Rather than a fixed resistance to discharge the battery, consider using a light bulb, or several light bulbs in parallel. Light bulbs have a much higher resistance when they are operating at their rated voltage. As the voltage across the bulb drops, the filament cools, and the resistance goes down. This helps to keep the rate of discharge more constant than if you used a simple resistive load.

 

Thanks for the response SgtWookie. Good idea on the light bulb load too.

 

You don't really need a DPDT relay/contactor. You could use a SPDT contactor on just the positive side.

 

How would the SPDT setup work exactly? Could you sketch a diagram?

 

Let me see if I can help, I'm working on something similar, to use a SPDT switch connect one end of the resistor and the negative terminal of the power supply to the negative battery terminal, and connect the positive end of the battery to the switch, then connect the power supply and resistor to the switch making it a selector switch, one way it charges and the other it discharges.

Some things to work out, you may need a relay heavy enough to open and close the contacts while under load.

There is no automatic shutoff to prevent overcharge and deep discharge, I have fallen asleep during a discharge (wooops)