Lithium Battery Test Drive

[mythbuster88]

Here is a little experiment with two 100Ah LiFePO4.

The two fully charged Battle Borns in parallel were connected to a stock Airstream Brand X 1000 Watt inverter that in turn powered my wife's hair dryer. For about 90 minutes the batteries put out ~100 Amps taking them down to around 25% C.

A Victron BMV 712 was used to measure current and state of charge.

After a while I felt all cables and connections and was surprised that the cheap crimp-with-a-hammer tool crimp connections never got warm. But the fancy 300 Amp T type fuse did get warm.

The 4 gauge cable feeding the inverter got warm but not as much as the fancy fuse.

Then I turned off the inverter (to give Mom's hair dryer a break!) and charged the batteries with two 60 Amp Progressive Dynamics (lithium version) converters in parallel.

When charging, with the inverter off, neither PD converter operated at their rating. With one converter I got 40+ Amps and with two I got 80 Amps. Neither charger charged at over 14 Volts rather they were working at 13.7V. At some point late into the charging profile they moved up to 14.6 Volts but I never saw the max current I expected of 120 Amps.

Also while charging the batteries if I turned on the inverter it would rob the charging current going to the batteries. That was interesting.

Anyway about 30-40 feet from the trailer my phone with the Victron app is telling me:

State of charge is 100%
Voltage is 14.61V
Current is 0.4A

[rmkrum]

Impressive !

[mythbuster88]

Off the living room floor and everything is under the couch.
Still working it out!

[Wabbiteer]

Yeah, charge acceptance ramps down with rising SOC - I've seen it takes drawing lithium cells down to <5% SOC to allow comparatively ultra-high current inrush, then with slightly higher charge voltages, the current remains rock-solid to 50 or 60% SOC then tapers to near zero & hopefully BMS protection territory.

Fuses are fancy heaters - one Bussmann Class-T 'fast-acting' line graphs/charts out at five minutes melt time when conducting rated amperage... Littlefuse has a line labeled 'fast-acting' that takes 15+ minutes at 200% rated amperage...

It would be interesting to see what the voltage drop across your fuse reads, but remember each crimp/bolted connection inserts a resistance heating effect too... It's rare but some fuse makers publish the cold ohm resistance, when choosing the doomsday main fuse less waste heat is better as far as conservation is concerned, just not oversize it enough to make your 4awg glow in the dark before it lets loose...

http://www.cooperindustries.com/cont...S_1025_JJN.pdf

http://m.littelfuse.com/~/media/elec..._datasheet.pdf