Overkill Solar (JBD) BMS and Short Circuit Protection

[HRTKD]

Not an "up in smoke" result but I said "WTF?" a lot. In rewiring my system for a new Multiplus inverter/charger I managed to switch the positive and negative cables at the inverter. Beats my why I did that, it's clearly labeled. In my defense, it's clearly labeled until you put cables on the incoming DC power studs. The cables then cover up the label.

The switch on the Multiplus was set to "Off" when I turned on the main system switch. The result was a bit underwhelming. Nothing, nada, zip, zilch. My multimeter told the tale, no power downstream of the BMS and the batteries were still good at 13.44 volts. The BMS app showed all cells balanced but a short circuit protection flag was set and the discharge was turned off. Hitting the discharge slider button would say that the operation was successful but it would immediately turn discharge off.

I switched the cables at the inverter to the correct positions and checked for power. Still nothing. I pulled the balance lead connector out of the BMS, waited 10 seconds and then reinserted it. I then had power, the inverter came online and all was right with the world (except for Russia invading Ukraine).

None of my fuses blew. My take is that the BMS is a lot more sensitive to bad wiring than the fuses are and reacted faster.

 

[Dynoman]

Not an "up in smoke" result but I said "WTF?" a lot. In rewiring my system for a new Multiplus inverter/charger I managed to switch the positive and negative cables at the inverter. Beats my why I did that, it's clearly labeled. In my defense, it's clearly labeled until you put cables on the incoming DC power studs. The cables then cover up the label.

The switch on the Multiplus was set to "Off" when I turned on the main system switch. The result was a bit underwhelming. Nothing, nada, zip, zilch. My multimeter told the tale, no power downstream of the BMS and the batteries were still good at 13.44 volts. The BMS app showed all cells balanced but a short circuit protection flag was set and the discharge was turned off. Hitting the discharge slider button would say that the operation was successful but it would immediately turn discharge off.

I switched the cables at the inverter to the correct positions and checked for power. Still nothing. I pulled the balance lead connector out of the BMS, waited 10 seconds and then reinserted it. I then had power, the inverter came online and all was right with the world (except for Russia invading Ukraine).

None of my fuses blew. My take is that the BMS is a lot more sensitive to bad wiring than the fuses are and reacted faster.

That's good information to know! I have 2 Overkill Solar BMS 8s 24VDC 100 amps. I have been using them now for 6 months or so and have been very happy with them. No problems at all.

I was sold on them after Wills video on the BMS and Overkill Solar saying if the BMS went bad they would replace them at no charge even if I fried them and it was my fault. It is good to see that kind of customer support still exists.

​

 

[DerpsyDoodler]

Not an "up in smoke" result but I said "WTF?" a lot. In rewiring my system for a new Multiplus inverter/charger I managed to switch the positive and negative cables at the inverter. Beats my why I did that, it's clearly labeled. In my defense, it's clearly labeled until you put cables on the incoming DC power studs. The cables then cover up the label.

The switch on the Multiplus was set to "Off" when I turned on the main system switch. The result was a bit underwhelming. Nothing, nada, zip, zilch. My multimeter told the tale, no power downstream of the BMS and the batteries were still good at 13.44 volts. The BMS app showed all cells balanced but a short circuit protection flag was set and the discharge was turned off. Hitting the discharge slider button would say that the operation was successful but it would immediately turn discharge off.

I switched the cables at the inverter to the correct positions and checked for power. Still nothing. I pulled the balance lead connector out of the BMS, waited 10 seconds and then reinserted it. I then had power, the inverter came online and all was right with the world (except for Russia invading Ukraine).

None of my fuses blew. My take is that the BMS is a lot more sensitive to bad wiring than the fuses are and reacted faster.

The multi-plus has reverse polarity protection, too, i'm sure (which likely also played a role in protecting everything). Check your manual.

 

[meetyg]

These BMSs have a short circuit protection in the magnitude of milliseconds (if I recall correctly from the app). That will act faster than any physical fuse or breaker, but should be used as the last act of defense.
I have shorted mine out a couple of times (not intentionally), fortunately no dramas... You have to remove any loads in order to enable discharge again.

 

[HRTKD]

These BMSs have a short circuit protection in the magnitude of milliseconds (if I recall correctly from the app). That will act faster than any physical fuse or breaker, but should be used as the last act of defense.
I have shorted mine out a couple of times (not intentionally), fortunately no dramas... You have to remove any loads in order to enable discharge again.

Once I opened the main switch there wouldn't have been any loads at all except for the shunt. Only after I pulled the balance cable connector did the fault clear.

 

[time2roll]

Never tested but in my head I knew the BMS should cut power from a direct short faster than the fuse. Thank you for the confirmation.
The fuse is there if the BMS fails.

 

[railcon56]

Not an "up in smoke" result but I said "WTF?" a lot. In rewiring my system for a new Multiplus inverter/charger I managed to switch the positive and negative cables at the inverter. Beats my why I did that, it's clearly labeled. In my defense, it's clearly labeled until you put cables on the incoming DC power studs. The cables then cover up the label.

A timely lesson I needed to see. I am very careful, but it reminds me to be extra careful and triple check things. Tomorow it will be warm enough to resume my install. I'll remember this.

 

[the_uglydog]

Once I opened the main switch there wouldn't have been any loads at all except for the shunt. Only after I pulled the balance cable connector did the fault clear.

I'm just curious. We were away and one of our employees shut the load off while our system was charging and all of the batteries charged up to 57 volts. All the batteries show idle when turned on and 53.2-53.5 volts, but as soon as the inverter is restarted they go to SCP Fault and everything shuts off. I don't see anything burned and I don't see a fuse either inside of them. Is this what you are talking about? Did you disconnect the balance connector while the battery is on or off? Thanks the dog.

 

[HRTKD]

I'm just curious. We were away and one of our employees shut the load off while our system was charging and all of the batteries charged up to 57 volts. All the batteries show idle when turned on and 53.2-53.5 volts, but as soon as the inverter is restarted they go to SCP Fault and everything shuts off. I don't see anything burned and I don't see a fuse either inside of them. Is this what you are talking about? Did you disconnect the balance connector while the battery is on or off? Thanks the dog.

If I understand your scenario, the inverter's DC side was disconnected, therefore the capacitors in the inverter were discharged. Now you're trying to recharge the capacitors. Normally the capacitors are charged when a DC current is present. The inverter doesn't have to be on for that to happen, but your inverter may be different.

In my case, the wiring fault caused the BMS to go into protect mode. It had nothing to do with the surge required to charge the capacitors.

 

[Pierre]

The caps in the inverter normally stay charged for a long time. (The discharge time is determined by the RC time constant) . The overload protection setting determines the trigger point and another setting determines wether the load must be disconnected or not. The capacitors should be pre-charged now in your case and by reconnecting the load you should be o.k. . If not you may have to disconnect the voltage sensing leads at the connector on the BMS. If it happens again you may have to pre-charge the caps in the inverter by placing a resistor ( about 20 Ohm ) in series at the DC input on the inverter for about 1- 2 sec. Now reconnect the DC leads to the inverter.

 

[JJJJ]

A humble reminder that even the most experienced user on a given day…

Thank you very much for sharing. Serves as a terrific reminder that double and triple checking demonstrates “best practices “ and is not a sign of OCD, or CDO alphabetic as it should be.

 

[Quattrohead]

I don't know about the 12/24v BMS, but the 48v version with the external contactor has the pre-charge resistor built in...and it works a treat.

 

[the_uglydog]

I'll try that with the inverter, I already have a new board for it but I would rather try doing that first and see what happens. Also the batteries, all of them, show standby at 53.2 to about 53.6v, but as soon as I turn on the breaker to each it shows a SCP fault. I connected the inverter to a bank of AGM batteries to see if it works. Even if I leave it connected it trips off saying that the battery voltage is too low, the AGM bank is at 50v, the inverter was set to shut off at 46v.

 

[Pierre]

Seems like the inverter got hurt. Do you have another type of load that you can test the battery banks with , instead of the inverter , to test the operation of the BMS (‘s) ? Say a load of 5 - 20 Ohm . Even an old 120v water heater element or bread toaster will work.

 

[the_uglydog]

Yes, I have 2 new boards for the inverter but I'm afraid to hook it up in case the batteries are damaged, I didn't want to damage it again. The batteries are 48v do I need a 48v DC load or will anything do? The company I bought the batteries from is shutdown right now there so much Covid in the city that everyone that works there is sick so I haven't been able to get any answers from them. I'm In The Philippines and here they don't have things we're used to in The US like water heater elements etc. Thanks for the great suggestion, it is GREATLY appreciated....the dog

 

[Pierre]

It becomes a bit more tricky to test batteries with higher voltages unless you are equipped or in the business of these things. You will have to use 4 x car headlight bulbs in series etc. Any resistive load of around 5 - 10 Ohms will work. I presume your mains supply is 230v ? Trying to work out a suitable load for you that may be available.

 

[the_uglydog]

Oh Yes! I never thought of headlight bulbs in series. Can't expect much from a dog anyway can you. That would work perfect i have lots of used halogen headlight bulbs laying around looking for a new job. I do all of my own building and repairs of everything, replacing control boards and all the testing, once I know what to do I can usually follow it pretty good. I can't find anyone who can repair any of it correctly here. You have no idea how much I appreciate the suggestion. In this part of PH we use the same split phase 220v as in the US except no one uses the 110v, everything is 220v. We have all split phase inverters and a complete 110v system since we brought many of our appliances from home in The US. the dog