Why is my SOK 206Ah BMS going into protect mode @ power on?

[corn18]

I installed a SOK 206 Ah LiFePO4 (LFP) a while back and it worked great. I had used cheapo cutoff switches and circuit breakers, so I swapped those out for the good stuff. Specifically, I replaced the generic battery cutoff switch and 100A circuit breaker coming from the battery with a Blue Sea 3 pole 250A circuit breaker that I also use as a switch.

The issue since the upgrade is that my LFP goes into protect mode when I flip on the breaker (nothing is on but the propane detector). The power comes on for a moment, and then cuts off and the battery is in protect mode. The only way to get it out of protect mode is to unhook the negative terminal from the battery and hook it back up. That's a pain. Interestingly, once I do that, everything works fine. I can flip the master breaker as many times as I want and the power cycles fine without the BMS going into protect mode.

If I leave the system off for a while and turn it back on with the breaker, the same thing happens again.

If I leave the system off for a while but disconnect the converter before I turn the system on (via its circuit breaker), the BMS does not go into protect mode. All works fine. I can turn it off and on without issue. The converter is a Progressive Dynamics 9160ALV made specifically for LFP duty. If I turn the converter on after I turn the main 250A breaker on, all works fine. Hmmmmm....

I cannot figure out what is causing the BMS to go into protect mode if the converter is connected.

Any ideas?

Here's my wiring diagram:

 

[MisterSandals]

Have you tried pre-charging the inverter caps to see if that resolves the issue? Just a guess.

 

[corn18]

Have you tried pre-charging the inverter caps to see if that resolves the issue? Just a guess.

How do I do that? The inverters are off when I power up the system.

 

[MisterSandals]

See post #19 video

Connecting a battery to the All-in-one controller

I recently purchased the PIP-2424LV-MSD charge controller and it seems I need to have a battery(s) (24v) connected to the battery input port on the controller before the controller will turn on. I just want to turn the controller on while it is sitting on my workbench, so I can hear how loud the...

diysolarforum.com

 

[mikefitz]

Mr S is pointing out that the inverters you have connected to the isolation switch output have input capacitors that take considerable current when connected to the battery. This is causing the battery BMS to shutdown on over current. The capacitors in the inverter will hold charge for some time, but if left disconnected from the battery, the charge will leak away via other system parts. When you are flipping the switch on and off quickly,, the charge does not have time to leak away and you have no issues, Leave things a while with the switch off, and the charge, the voltage, on the capacitors, drops. When you next switch on, the current flow to recharge the capacitors is in excess of the BMS protection limit.

Mike

 

[corn18]

Mr S is pointing out that the inverters you have connected to the isolation switch output have input capacitors that take considerable current when connected to the battery. This is causing the battery BMS to shutdown on over current. The capacitors in the inverter will hold charge for some time, but if left disconnected from the battery, the charge will leak away via other system parts. When you are flipping the switch on and off quickly,, the charge does not have time to leak away and you have no issues, Leave things a while with the switch off, and the charge, the voltage, on the capacitors, drops. When you next switch on, the current flow to recharge the capacitors is in excess of the BMS protection limit.

Mike

That makes sense. I wonder why all of this worked fine when I had a cheap 100A circuit breaker and cutoff switch installed? This just started happening after I replaced those two with the fancy Sea Power 3 pole 250A breaker/switch.

I do not have the second SOK 206Ah battery installed yet. It is on the way. I presume once I get that installed that the two batteries should be able to handle the inverter input capacitor inrush current?

I also don't have the solar panels hooked up yet. I assume those would keep the inverter caps charged all the time?

 

[MisterSandals]

I presume once I get that installed that the two batteries should be able to handle the inverter input capacitor inrush current?

This is VERY hard on your inverters.

 

[corn18]

This is VERY hard on your inverters.

What is the proper way to power up the inverters?

 

[MisterSandals]

See post #4

 

[corn18]

See post #4

Wow, did not know that. First reaction is what a PITA for a system that gets turned on and off a lot. Second reaction is trying to figure out how to implement this on an RV. Any thoughts?

I was thinking:

Batt+ >>>> circuit breaker/switch >>>> 30ohm resistor >>>> + Bus bar. Before I flip on the main breaker, turn on this CB and precharge the inverters. Then flip on the main CB. Then flip off the precharge CB. Seems simple enough and will protect the BMS and inverters. What size wire and breakers do I need? Seems like it won't be a lot of amps with the resistor in there.

 

[MisterSandals]

Do a search on precharge. Lots of solutions.
And this download howto:

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

 

[corn18]

Went with the simple solution for now. I added a precharge circuit for the inverters. It's a 6 ohm 50W resistor wired to a momentary horn button between the + battery terminal and the + bus that feeds the inverters. Hooked it up. Pressed the horn button for 1 sec and flipped on the main breaker. Worked like a champ.

I'm sure there is a more elegant solution, but I need to go camping on Thurs. Looks silly having that 14ga wire running around all that 4/0 cable, doesn't it? I'll see what else is out there, but this works.

 

[MisterSandals]

I'm sure there is a more elegant solution, but

Looks just fine. I'd only add a colorful "press first" label as a reminder if i did anything.

I'd be wondering what is going on with the nails protruding from the other side of that wall above the cutout (which should have been cut out with a sharper axe). :*)

 

[corn18]

Looks just fine. I'd only add a colorful "press first" label as a reminder if i did anything.

I'd be wondering what is going on with the nails protruding from the other side of that wall above the cutout (which should have been cut out with a sharper axe). :*)

Those are the steps in my 5er. I was happy to find cigarrets in my basement behind the partition they put in. And a bunch of spare parts and a ton of sawdust. Wonderful workmanship, eh?

 

[corn18]

Kept the same design but made it look nicer. Mounted a nice momentary push button right next to the breaker switch. Also put the 6 ohm resistor in the same box. So it looks a lot better and the big red button right next to the breaker switch is a good reminder.

 

[DerpsyDoodler]

Kept the same design but made it look nicer. Mounted a nice momentary push button right next to the breaker switch. Also put the 6 ohm resistor in the same box. So it looks a lot better and the big red button right next to the breaker switch is a good reminder.

View attachment 66251

Nice. This is similar to my pre-charge circuit. Did you fuse it? An inline fuse would be an easy addition.

 

[corn18]

Hadn't considered a fuse but I should. The resistor has 18 ga wire so maybe a 10A fuse?

 

[PerryB67]

Here's my wiring diagram:
View attachment 65679

Where on the web did you draw this schematic? I'm looking for something simple. Does it exist?

Thanks,

Perry

 

[corn18]

Where on the web did you draw this schematic? I'm looking for something simple. Does it exist?

Thanks,

Perry

I used powerpoint. Not simple but I am a certified Powerpoint ranger.

 

[Sanwizard]

I installed a SOK 206 Ah LiFePO4 (LFP) a while back and it worked great. I had used cheapo cutoff switches and circuit breakers, so I swapped those out for the good stuff. Specifically, I replaced the generic battery cutoff switch and 100A circuit breaker coming from the battery with a Blue Sea 3 pole 250A circuit breaker that I also use as a switch.

The issue since the upgrade is that my LFP goes into protect mode when I flip on the breaker (nothing is on but the propane detector). The power comes on for a moment, and then cuts off and the battery is in protect mode. The only way to get it out of protect mode is to unhook the negative terminal from the battery and hook it back up. That's a pain. Interestingly, once I do that, everything works fine. I can flip the master breaker as many times as I want and the power cycles fine without the BMS going into protect mode.

If I leave the system off for a while and turn it back on with the breaker, the same thing happens again.

If I leave the system off for a while but disconnect the converter before I turn the system on (via its circuit breaker), the BMS does not go into protect mode. All works fine. I can turn it off and on without issue. The converter is a Progressive Dynamics 9160ALV made specifically for LFP duty. If I turn the converter on after I turn the main 250A breaker on, all works fine. Hmmmmm....

I cannot figure out what is causing the BMS to go into protect mode if the converter is connected.

Any ideas?

Here's my wiring diagram:
View attachment 65679try removing the ground on your shunt.