switched series and parallel connection

[fechter]

Looks good.

Again, the reason for the diode is if the packs are in series and only one BMS trips, the voltage across the BMS would be double what it was designed for and could cause failure. With more packs in series, this becomes more of an issue. If the FETs in the BMS are rated for more than the combined series voltage, you don't need the diodes.

[astrocloclo]

Hello all
is this schematical working correctly ?
i should be interested fo rmy own (2x48v / 15Ah vs 1x96v 8,5Ah with a Lyen controller)
Regards

[lazarus2405]

The question is what is the max current handling switch available to do this?

That's something I've been thinking about for a little bit. You really don't want to switch under load, so there isn't an arc to have to quench, so the voltage rating of the contacts shouldn't matter.

Finding DT relays rated for that sort of current is a pain, though, so I wonder if you could get away with using a few of those small 10a DPDT 12v relays ganged in parallel. It should work for smaller setups, but it doesn't exactly scale elegantly to Lyen 100v 100a controller. If they're rated for switching at 10a, what do you think they can take if they're only switched without a load?

A reversing contactor would be rated for the current and might work if you can sever one of the internal connections and run a lead to it. Otherwise you'll set yourself up for a spectacular dead short. Consider that awfully risky.

You could make your own knife switch for the Doc Brown look, but that might be a poor fit for handlebar mounting.

There's always the option to make a connector block of Andersons to swap between series/parallel. A few others have done it for charging. You wouldn't have any current issues then, but you'd have to physically unplug one thing and plug in another. It really looses out on elegance, though. I think the ideal would be a handlebar-mounted switch that you could just flick at a stop light or before letting a guest try out your bike.

Couldn't this be done with a couple of appropriately-specc'd FETs? What might that circuit look like?