How to fully discharge 48v/280Ah pack ? (beyond inverter shutdown)

[msevestre]

Hi all

for BMS calibration purpose of my 48v 280Ah LiFePo4 DIY battery, I am asked by the BMS manufacturer to top charge and then discharge the battery down to 2.5v.

Yesterday, I successfully top charged (58.3v, with min cell was at 3,642v &max cell at 3,648v) with my inverter (EASun iGrid SV IV - similar to Voltronic InifiSolar V IV) then I drained the battery by charging my Tesla (still through the inverter).
-
Unfortunately, none of the battery bottom discharge stop points* were reached as my inverter shut downed before (while all cutoff/discharge/back to grid related settings were at the minimum).

Does anyone have an idea/solution that would allow me to continue discharging my battery after the inverter has shut down (what kind of easy to find and cheap 48v load can I use ??).

Thanks
Matthieu

* : two stop points exist in the BMS to reach the bottom calibration point:

• first cell to reach under voltage protection (2.5v)
• total battery reaching low voltage protection (43.3v).

 

[wpns]

Four 60W 12V car headlights in series should give you 5 amps…. That’ll take 2-3 days to discharge from full, but less time if it’s already partially discharged.

 

[msevestre]

Hi.

thanks.

I also have some old home filament bulb in my garage, normally for AC 220v (I'm based out France). I guess such legacy bulbs may work with DC, no ?

 

[wpns]

Hi.

thanks.

I also have some old home filament bulb in my garage, normally for AC 220v (I'm based out France). I guess such legacy bulbs may work with DC, no ?

Not sure how much current they’ll draw, but it won’t be much.

 

[msevestre]

It's 220v AC 60w filament bulbs. You're right, that's 0.3A... better to go with car headlights.

 

[wpns]

It's 220v AC 60w filament bulbs. You're right, that's 0.3A... better to go with car headlights.

While incandescent bulbs are to a first approximation constant current devices (anyone remember the mains-powered flashlight battery chargers with no transformers, a diode, and a 7W 120v bulb as a current limiter?) I’d measure the current, it’ll be higher because the filament will be cold. Maybe enough in parallel would work. Space heaters might work too but you’d want to find a way to keep the fan running or have an external fan.

 

[msevestre]

Hi

So I put in serie 4 12v 50w car bulb - tested fine with a loab power supply (48v, it was draining a bit more than 4A)

My battery is 47v right now.

I just tried to plug the bulbs on the battery terminals (the ones on the back) - BMS is raising a shortage protection alert.
Any clue why this happens ? Should I better put the bulbs directly on the terminals of the 16 cells (before/in parallel to BMS)

Thanks

 

[wpns]

Well, incandescent bulbs have an inrush, but it shouldn’t trigger a short circuit shutdown

 

[msevestre]

Short circuit when turning on the battery with bulb connected. But when battery is on, quickly connecting the second/last alligator clamp did it … now waiting with a low 4A drain.

Thanks for the help and advices !

 

[wpns]

Short circuit when turning on the battery with bulb connected. But when battery is on, quickly connecting the second/last alligator clamp did it … now waiting with a low 4A drain.

Thanks for the help and advices !

Ah, it checks the resistance of the load before it tries to power it up, and sees cold filaments, which have a very low resistance. makes sense, for some values of sense.