Overkill BMS connecting Inverter = short circuit! Help!!

[Kifo]

Here's how to build it into a switch:

Inverter Disconnect Switch with Precharge

To get the paper, click on the orange button at the top of this page. This circuit is designed as a disconnect switch that allows the user to pre-charge the inverter capacitors before turning the switch completely on. 26 June 2020 update: At...

diysolarforum.com

All you do with the light bulb is use it to complete circuit between cable terminal and stud. If light glows then slowly goes dim and goes out, time to put terminal on stud.

Sure, those resistors should work. What resistance values?

ok it 40 ohms and should i have the inverter in a off position please thanks.

 

[Hedges]

Does the inverter have a circuit breaker to turn it off? Or a low power switch.
(My Sunny Island has a circuit breaker which isolates its capacitor bank from input, so I would have to turn that breaker on before precharge.)

Ideally you precharge the capacitor before inverter starts operating. Because it might consume 25 to 50W no-load, which is 0.5A to 1.0A, would prevent complete precharge.

Try with the inverter off. Precharge, observe voltage riding with a meter (may be quick.) Then connect cable if voltage came up. Then turn on inverter.

50V / 40 ohms = 1.25A
1.25A x 50V = 60W

That is OK. If it gets too hot to touch during precharge, there is a short and you need to stop before overheating the resistor. (It is probably rated for 50W or 100W, but needs a heatsink to handle that continuously.)

A 120V 100W lightbulb has its advantages.

 

[Kifo]

Here's how to build it into a switch:

Inverter Disconnect Switch with Precharge

To get the paper, click on the orange button at the top of this page. This circuit is designed as a disconnect switch that allows the user to pre-charge the inverter capacitors before turning the switch completely on. 26 June 2020 update: At...

diysolarforum.com

All you do with the light bulb is use it to complete circuit between cable terminal and stud. If light glows then slowly goes dim and goes out, time to put terminal on stud.

Sure, those resistors should work. What resistance values?

ok do i have to keep battery breaker and bms off also ?

 

[Hedges]

You would turn battery & BMS on. So it supplies power through the resistor to precharge power.

It helps if you understand where current is flowing, and what components do.
I'm just winging it, don't even have a schematic of your circuit.

Why is solar so damn difficult?

I've found the lutron casetta stuff to be very reliable.(although not looking forward to the day I need to replace the batteries in all the remotes) Oh yeah. Battery replacement lol. But that's every 10 years though -so they say. I'm in the same boat. I've got a bunch of Bluetooth temperature...

diysolarforum.com

 

[Kifo]

tried all what you said but the light bulb never went off means there is a short on the inverter end.

 

[Levo]

This thread title seemed to fit, so hopefully a good place to start.

Just reinstalled my 280Ah LiFePO4 battery after winter storage, reading very close to 13v no load. Everything was still how I left it in October, SCC, B to B charger and 1600w LF inverter all connected to buss bars only. I tried to switch on the battery via overkill bluetooth, but no go. Just a red "short circuit" message. I tried a few times.


Decided to remove inverter connection from the buss bars; sure enough the battery powered up, house lights came on as did the SCC screen. At first my meter across the 12v +/- inverter connections showed "continuity". Then intermittently it went to reading "open circuit" and short again minutes later.

Now the inverter is on the bench and across the terminals it still reads open. I can't find anything loose to wiggle and bring back the short. This inverter has not skipped a beat since installation 2 years ago, and has seen no excessive loads or physical trauma.

What should the ohm meter read across the low voltage side? Would really appreciate a path forward if anyone has ideas. Thanks.

 

[ScrotusGobbleBottom]

That is needed for many lithium battery & inverter circuits.

I thought precharge was only to protect the battery/BMS from overcurrent tripping?

 

[Hedges]

Protects from overcurrent tripping, or blowing fuse or welding contacts or damaging capacitors.
Lots of things can get damaged by multi-thousand amps spikes.
Soft-start circuits are designed into many products, but few have the massive surge of these lithium batteries.

 

[Hedges]

What should the ohm meter read across the low voltage side? Would really appreciate a path forward if anyone has ideas. Thanks.

Try giving battery a recharge (With suitable CV/CC supply.)

 

[Levo]

Try giving battery a recharge (With suitable CV/CC supply.)

I don't have a CV/CC supply, just an old school charger for FLA. The battery is receiving solar charge from the SCC as we speak, so I should be able to see if bringing up the voltage helps. Thanks for the suggestion.

Also, just connected the inverter to a FLA deep cycle battery (showing 12.5v unloaded) and I have 115v at the output side. What the hell?

 

[Hedges]

FLA powered up the inverter, but LiFePO4 did not?
Sounds like cells or BMS dropped power to the inverter. ergo the suggestion to try charging.

BMS represents some standby drain. Don't know how many months/years a fully charged battery is expected to last. Nor the SoC when you put it away.

For cars, suggestion is to disconnect battery to eliminate parasitic drain when stored. (Unless electronics designed to lock up and need a code, e.g. stereo theft discouragement devices.)

 

[Levo]

I don't have a CV/CC supply, just an old school charger for FLA. The battery is receiving solar charge from the SCC as we speak, so I should be able to see if bringing up the voltage helps. Thanks for the suggestion.

Also, just connected the inverter to a FLA deep cycle battery (showing 12.5v unloaded) and I have 115v at the output side. What the hell?

Okay, I just let the SCC do it's job for a few hours and (per my friend's suggestion) restarted the phone and the overkill software. Well the inverter seems to switch on and off just fine, no errors or problems. I am of course happy to be up and running, but a little bewildered. I'll run the inverter on high power tomorrow just to ensure all is good.

 

[Quattrohead]

You just need a resistor or pencil to soft start the inverter by charging the capacitors.

 

[Levo]

FLA powered up the inverter, but LiFePO4 did not?
Sounds like cells or BMS dropped power to the inverter. ergo the suggestion to try charging.

BMS represents some standby drain. Don't know how many months/years a fully charged battery is expected to last. Nor the SoC when you put it away.

For cars, suggestion is to disconnect battery to eliminate parasitic drain when stored. (Unless electronics designed to lock up and need a code, e.g. stereo theft discouragement devices.)

First I tried charging up the battery to 13.32 volts, and tried the pre-charge using a resistor; (graphite pencil was all I had on hand, read 18 ohms), but made no difference. Still showed "short" on the overkill app as the BMS tried to start then switched off immediately. Then I replaced the Li battery with FLA, with all connected to the buss bars (incl. inverter). The system worked perfectly, proving there is no damn short in the inverter.

Finally, my lady wisely suggested updating the overkill control app (which I did) and I re-installed the Li battery. "Whale Oil Beef Hooked" every thing worked first try!

I was suspecting the uncharged capacitors (and therefore excessive draw) were triggering "short" on the BMS. Now I believe it was just a software problem. Anyway, now I'm a happy glamper, up and running since yesterday. *fingers crossed!* Thanks for tips and suggestions.