RV electrical system upgrade complete

[HammaMan]

"Also @Davexxxx you need a fuse capable of breaking a 80kva overload. LFP batts are capable of at least a 10x rated ah/current. 600x10x13.3=80kva. Requires a sand filled fuse to break the arc."

Had a big long write up, describing the various components, fuses and their ratings but the either ate it.

So, the short version ...

I'm listening but you're gonna have to give me more.

It looks like you've got a standard 12v fuse with visible link in it?

These are examples of the products you want / need. Your surge load of 200% is 360 amps so 400a fuse is the way to go.

https://www.westmarine.com/blue-sea...th-insulating-cover-225-to-400a-10093813.html

https://www.westmarine.com/blue-sea-systems-class-t-jjn-jlln-a3t-fuses-P009_273_004_003.html

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[Samson16]

I'm listening but you're gonna have to give me more.

I think he’s discussing the need for the dielectric strength of the gap to outpace the rising transient voltage in order to break the arc.

 

[Davexxxx]

In the pic, right over the batteries, is a Blue Sea holder with a 400a ANL. Inside of the Lynx distributer (a fancy buss bar system) every line pair has its own mega fuse and the chassis ground is 4/0, straight to the frame.

I'll be sleeping above this, so want to be safe but the mini qasar you described, seems highly unlikely.

I've seen LiFePO4s shot with guns and just give off a bit of smoke.

If such a catastrophic failure happened, burnt through the BMS, with its various disconnects, then the ANL, then the several fuses in the distribution busses and then on to the chassis ground, how long would it last?

 

[HammaMan]

LFPs just have far too many amps to use anything other than T class, especially at the amperage you have on hand. If that shorts, it's just going to arc across the air gap. T class fuses are full of a medium that physically blocks an arc. 600ah batteries need a 6,000 amp breaking capacity. Otherwise the fuse is potentially worthless for breaking the current due to the amount of short-circuit capacity behind those cells. It can turn the fuse element into plasma creating an arc channel that just keeps going. LFP cells themselves are one of the safest chemistries, bested only by LTO, but you need proper fusing in them. The current is such that it can short closed the FETs in the BMS. It's standard practice to use T class fuses on all lithium chemistries due to the exceptionally low resistance of the cells.

 

[Davexxxx]

I think he’s discussing the need for the dielectric strength of the gap to outpace the rising transient voltage in order to break the arc.

I gathered but each time it burns through something, it is weakened and I'm thinking for a burst failure of that magnitude, we're talking milliseconds in duration?

After the BMS, the fuses, the ground, the disconnect and then the cables themselves. Its gonna take time to have green flames of copper burning.

Not that it couldn't wreck a bunch of gear on the way ....

 

[Davexxxx]

LFPs just have far too many amps to use anything other than T class, especially at the amperage you have on hand. If that shorts, it's just going to arc across the air gap. T class fuses are full of a medium that physically blocks an arc. 600ah batteries need a 6,000 amp breaking capacity. Otherwise the fuse is potentially worthless for breaking the current due to the amount of short-circuit capacity behind those cells. It can turn the fuse element into plasma creating an arc channel that just keeps going. LFP cells themselves are one of the safest chemistries, bested only by LTO, but you need proper fusing in them. The current is such that it can short closed the FETs in the BMS. It's standard practice to use T class fuses on all lithium chemistries due to the exceptionally low resistance of the cells.

I'll explore it.

 

[Samson16]

I gathered but each time it burns through something, it is weakened and I'm thinking for a burst failure of that magnitude, we're talking milliseconds in duration?

After the BMS, the fuses, the ground, the disconnect and then the cables themselves. Its gonna take time to have green flames of copper burning.

Not that it couldn't wreck a bunch of gear on the way ....

I tend to agree. The difference of potential is so low it will end quickly lol

 

[Samson16]

Course if you ever have a coin get across the 9V battery in your pocket you’ll be surprised how fast you can strip those pants off

 

[HammaMan]

Course if you ever have a coin get across the 9V battery in your pocket you’ll be surprised how fast you can strip those pants off

9vs can start fires if stored improperly. If you got some loose ones, put tape over the prongs!

 

[Davexxxx]

This article agrees with Hammerman, preferring a class T fuse, for a LiFePO4 battery bank of my size.

Its for boats, so not sure it directly applies to RVs too but as I said, I'm listening.

https://marinehowto.com/battery-banks-over-current-protection/

 

[HammaMan]

This article agrees with Hammerman, preferring a class T fuse, for a LiFePO4 battery bank of my size.

Its for boats, so not sure it directly applies to RVs too but as I said, I'm listening.

https://marinehowto.com/battery-banks-over-current-protection/

Marine has stricter standards as a loss of vessel could very well result in loss of life. In an RV the standard is slightly lower because you're expected to exit as it burns down and being on the ground is okay. Just something to sleep on .

Something to think about, was watching something on the energy of fires and the average mattress contains "up to a megawatt of thermal energy".

 

[mflynndelta]

I don't have the complete total compiled yet, mainly, because there were some incidentals but it will come in around something over 5K plus another for the panels.

These are the batteries. and are, at this writing, still at the price I paid.

https://www.epochbatteries.com/products/12v-300ah-heated-bluetooth-lifepo4-battery-epoch-essentials

Most of the rest came from this kit.

https://shop.explorist.life/shop/al...d-camper-wiring-kit/#start-with-your-base-kit

I didn't choose everything in it. Had a couple things I wanted to do differently, or not at all.

By the way, just now confirmed, that if fully charged, this system will run the air conditioner for several hrs. at least.

Also confirmed that there is no conflict between this gear and the Powerboost 7.2KW running it.

thank you

 

[Davexxxx]

Nate also prefers the class T for battery bank fusing but as of a yr. ago, claims there was a severe shortage, though West Marine claims they're in stock.

 

[Samson16]

In the pic, right over the batteries, is a Blue Sea holder with a 400a ANL. Inside of the Lynx distributer (a fancy buss bar system) every line pair has its own mega fuse and the chassis ground is 4/0, straight to the frame.

I'll be sleeping above this, so want to be safe but the mini qasar you described, seems highly unlikely.

I've seen LiFePO4s shot with guns and just give off a bit of smoke.

If such a catastrophic failure happened, burnt through the BMS, with its various disconnects, then the ANL, then the several fuses in the distribution busses and then on to the chassis ground, how long would it last?

A, Incredible build out sir.

B, What kind of party was going on where shooting at batteries seemed like a good idea?

 

[Davexxxx]

A, Incredible build out sir.

B, What kind of party was going on where shooting at batteries seemed like a good idea?

It was a demo, illustrating the safety of LiFePO4, as opposed to other lithium formats, which can experience thermal runaway.

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