Charging in parallel

[steve28]

I have a Astroflight charger for li pos , It'll do up to 8 Amps

Can I make a connector to connect 2 packs in parrallel and just double the charge rate .

If I had 2 6S packs at 4000 mAh could I connect them in parallel and turn the rate up to 8 Amps , this would still take an hour right ? and I would need a balancer on each pack

[SilverFoxCPF]

Hello Steve,

Yes you can... PROVIDED, you have a good solid connection between the two packs, and the voltage of each pack is about the same.

When you parallel LPo packs, there is an inrush of current as the packs equalize. This inrush of current is instantaneous and can exceed the charge rating of the pack.

For example, let's look at the worst case. You hook up one of your 6S packs that is fully charged, with the other one that is fully discharged.

A fully charged 6S pack has a voltage of 25.2 volts. A fully discharge pack is around 20.4 volts. If the internal resistance of each cell is 0.020 ohms, you would have an initial current of around 40 amps at the moment you make the connection.

That's a little high. 40 amps would be charging the empty pack at 10C.

If we look at a more reasonable example, we find that with a 1.0 volt difference in the two packs, the current is around 8 amps. This current rapidly drops off and the pack is able to handle higher charge currents when empty, so this is a reasonable target to shoot for.

With a 3S pack, you want the packs to be within 0.5 volts of each other.

The best procedure is to parallel the packs, then let them equalize for around 10 minutes before starting the charge.

Paralleling two packs will balance the two packs, but you still have to attend to the balance of the individual cells within each pack.

Tom

[Maxists The Baddist]

To parallel two packs, do you attach the parallel harness and just let them sit connected to or not connected to the charger?

[SilverFoxCPF]

Hello Maxist,

I connect the two packs together and let them equalize. Then I hook them up to the charger.

Tom

[steve28]

thanks thats some good info .