Voltage delta?

[Stinsy]

You want the voltages to be as close as possible. The internal resistance is very small and the energy stored is very high so you risk damaging the cells. The resistance of your cable is what limits the current flow so that super-expensive 35mm² cable works against you and a busbar connection would be very dangerous indeed. A helix of 1mm² (maybe 2m) acting as a resistor will slow down the current transfer and keep it below 100A. Be careful, your resistor will get very hot, so you might want to connect for a few seconds at first, disconnect for a minute or two, then remeasure Voltages and hook up again for a bit longer.

Once you’re closer than 0.1V hook up without the resistor.

A 1V difference can mean a huuuge energy transfer, maybe as much as 30% of the rated kWh of the pack, all dumped as heat into your cells almost instantaneously.

[ALAN/ALAN D]

I have been using a 3 Kw immersion heater for balancing.
You just feel the heat in the element / check voltage.

[Lincs Robert]

Sorted.

I waited until the stack voltages were similar, within 200mV. Connected the two 0v together & then connected the positives via ammeter & “cable helix” - current was only about an amp. So I went for it, no sparks, cracks or other drama.

This will give me an additional 11.04kWh of storage. Am already talking to Fiona at Deriy about the next upgrade - which will almost certainly be a similar sized increment. The EVE 230 cells are currently priced at $63.20 each, plus shipping, so the next 11kWh step will cost about £950.

Rob

[Joeboy]

Sorted.

I waited until the stack voltages were similar, within 200mV. Connected the two 0v together & then connected the positives via ammeter & “cable helix” - current was only about an amp. So I went for it, no sparks, cracks or other drama.

This will give me an additional 11.04kWh of storage. Am already talking to Fiona at Deriy about the next upgrade - which will almost certainly be a similar sized increment. The EVE 230 cells are currently priced at $63.20 each, plus shipping, so the next 11kWh step will cost about £950.

Rob

That is brilliant Rob, I think i"ll be joining you in Spring.

[Lincs Robert]

I have been using a 3 Kw immersion heater for balancing.
You just feel the heat in the element / check voltage.

Hi Alan,

That’s an excellent prompt which reminded me that I have a spare immersion heater element which I pressed into service. Nice easily accessible terminals and a resistance of about 19 ohms. When connected to a stack draws roughly 2.7 amps from the 49 or so volts present at the time - enough to make the element nicely warm but not stupidly hot. It’s a long element so the 130 watts of heat is nicely distributed over the full length.

A useful tip methinks.

Rob