Charging a Lithium (LiFePo4) battery in place

Community General Discussions
1

Hello,

Groucho’s (a wheelchair based robot) battery is a monster 90 lbs of battery (24v, 100 amp-hr).

I’m hoping to be able to just turn off the robot and then disconnect the load (the battery is connected to the power distribution system via an Anderson PowerPole) and hook it to the the charger.

Hopefully this is not risky.

What I want to eventually do is to have Groucho plug himself into the wall socket himself. For that I’d need a lot of things to happen in the right order, with testing. There would be relays in the power distribution system and tests that each step has worked before it goes to the next step.

  1. Groucho would plug the wire into the wall. This initially activates a power strip which turns on a 24v power supply to power the electronics and servos during charging.

  2. After the 24v supply is confirmed to be running properly, a relay would disconnect the battery from the power distribution system.

  3. After the battery is confirmed to have no load, another relay would connect the charger to the battery. Then yet another relay would turn on the charger, which is already plugged into the power strip.

  4. Once the charging is complete, the above steps would be repeated in reverse to get Groucho running on the battery again.

Does anybody see any problems with this? Have I over complicated it?

And does anybody know of any inexpensive source for good medium power (100 amp DC) DPDT relays. I’ve been looking and I see a lot that are lower than this, but not many that are both inexpensive and at least 100 amps.

Thanks in advance.

2

**Thank you.

Are there any**
Thank you.

Are there any recommendations you would make in the design of such a circuit? I have plenty of time for this because I will first build Groucho with manual recharging and that will take me a few months unless Lee comes up with new tasks for me.

And I’m hoping that the “dog poop cleaning” you mentioned in the SB was just hypothetical for now. Lee is pushing me to clean house so we can get another pair of dogs, so yet again, I’ll probably have that task again. And again. And again. :frowning:

3

I’ll work on the drawing.
My motors are wheelchair motors, so I’m assuming that the stall current is less than 10 amps per motor, but I will do my best to check. There is the electronics and servos, but my current estimate is around 20 amps total for that.

I’m also thinking of making two 12v batteries from the 24v one. That may make some things easier.