Feedback wanted on a proposed large residential system

[jp4782]

G'day all

I'm hoping to get some feedback on a large system that I'm currently planning for.

I've included a rough schematic of the system - so basically it's 4 arrays of 6kw solar incoming (total 24kw). Batteries will probably be REPT or EVE 280 in a 4p17s config - total of 62kw. Battery busbars will be custom for the high amps (will limit to 300).

I'm going with the Batrium BMS due to the high amps - using NOARK circuit breakers with shunt trips. In case of a critical fault I want to simultaneously disconnect both battery and arrays - as I understand the batrium only has the ability to use 1 relay for a critical fault - which is just a pulse of 24v to the shunt in the circuit breaker - I'm hoping I can just parallel the power to the shunts to operate simultaneously.

Any feedback most welcome. And please excuse crappy diagram...

Thanks

 

[k490]

You will want solar panel disconnects don't use circuit breakers. If you disconnect under heavy load DC arc will not break and melt the thing. Lot of YT videos on that subject. Make sure you buy a quality shunt there is a thread in up in smoke guy burned up his DIY battery bank from a shunt that overheated melted. I'm no expert but if you plan on keeping that battery bank in your home I would in-close it something that won't burn down your home. Just saw new thread over there house burned down from a DIY battery bank.

 

[robbob2112]

Curiosity question rather than critique here - how you plan to connect things together with the Batrium BMS?

I am asking because the OP in this thread was using Batrium in what appears to be a recommended configuration and we think that design contributed to the fault which caused the fire. That along with using Mega verse class T fuses. Possibly long battery cable. DIY battery built 5ish years ago and missing some of the design ideas from the intervening years.

House burned down

So, after 4 to 5 years of working flawless, the 100 kwh lifepo4 battery caught fire at night and burned our house down. Luckily our family just made in out on time. Inspection of the fire expert revealed that a melt fuse melted, and created an arc between the 2 points wich ultimatly started the...

diysolarforum.com

Any other design/build methods you are using?

 

[robbob2112]

You will want solar panel disconnects don't use circuit breakers. If you disconnect under heavy load DC arc will not break and melt the thing. Lot of YT videos on that subject. Make sure you buy a quality shunt there is a thread in up in smoke guy burned up his DIY battery bank from a shunt that overheated melted. I'm no expert but if you plan on keeping that battery bank in your home I would in-close it something that won't burn down your home. Just saw new thread over there house burned down from a DIY battery bank.

Fire investigator says the fuse caused the issue, the speculation is with where the shunt was placed verse the shunt itself being at issue. We all doubt the fuse was the real issue, but might have been the spark

 

[k490]

Fire investigator says the fuse caused the issue, the speculation is with where the shunt was placed verse the shunt itself being at issue. We all doubt the fuse was the real issue, but might have been the spark

If the shunt, or fuse holder is made out of flammable material like plastic it can catch fire if it has a hot spot. I suppose that could even happen with a hot spot on a battery terminal. When you have low voltage and high currents hot spots are a problem. Lifepo4 has flammable liquids once it catches spreads the fire quickly. Also have the problem of flammable gas's.

Personally I'm going to treat DIY batteries as they will overheat someday and catch fire. I won't just rely on a fuse to save my home from burning down I will use Class T fuses. They will go inside a 300 lb steel box strong enough to withstand the heat and contain the fire.

The 100kw battery fire I suspect a battery shorted internally becuase he said there was no load, or charging going on at night. The battery charge was at peak charge. Have batteries that are sitting idle fully energised. Something failed inside a cell causing something to get hot and melt. I don't think local fire inspectors know enough about lithium battiers to really figure out what happened. DIY cells you don't have a company can go back and investigate most goverment investigators will go back to the manufacture to assist with the investigation.

 

[jp4782]

One thing to remember with fusing is not only correct sizing to suit the cable but the fuse/circuit breaker ultimate breaking capacity. That is at what point (ie amount of amps) does the fuse or CB simply get destroyed and become of no value in protection. I'm guessing with the house fire a massive bank of 100kw would require a massive fuse (ie with a huge breaking capacity) to protect it from a short.

I think circuit breakers correctly sized and installed offer proper protection - in my case a Noark 400 amp monster (it weighs in at over 5kg). There were many cases here in Oz of CBs melting due to the use of polarized CBs and electricians(!!) incorrectly installing them (confused by the CB markings) so the arc went in the wrong direction inside and with it lots of smoke and flame...