fuses, safety etc

backwoods

Solar Enthusiast
Joined
Apr 26, 2022
Messages
49
Greetings all, fng here. Forgoing the newcomers intro and just consolidating here.
I know enough about electric to be dangerous, yet enough to know there is a right way, not licensed though.
Anywhoo, I replaced my lead in the travel trailer for a 200 ah lifepo4.

I'm installing a class T Fuse, not sure on the size I need. Read a ton but most threads here, are dealing with
Solar coming in and 24v systems.
I'm just going to run a 12v system, with no solar as of yet. Down the road I will but I'll cross that bridge when I get there.
The trailer is your run of mill 30 amp service. The 200ah battery has a 100ah BMS.
I think a 125 amp Class T fuse should be plenty for this setup, or should I rate higher? lower?
I'm going with the stock power center in the trailer.
No plans on running heavy demand appliances off battery. Heaviest demand might be a coffee pot but I'd probably just go old school there.

Next question on safety,
What fire extinguishers are ppl recommending for lithiums? I was going to get a "purple K" extinguisher.
Some articles state the standard ABC extinguisher would work, obviously I don't want to find out the hard way.
Does anyone carry sand/soda ash in their trailers? I'd hate to add an extra 50 lbs of dead weight but rather be prepared.
Anyone stick their battery in a "fire bag" after seeing the recent post on the van battery letting out the magic pixies makes me shy
about sleeping over it. It wouldn't be completely sealed off obviously but it seems like it would be a good 1st defense?
How about using an automatic fire extinguisher that is listed for use in engine bays and electric panels?
My understand on those is they are more like a co2 extinguisher so I'm not really sure if it would work in this application.
May keep other flammable items from going up momentarily?
 

chrisski

Solar Boondocker
Joined
Aug 14, 2020
Messages
3,381
Your load will determine your fuse size which must be under the wire rating.

For a 3000 watt inverter, I have two 24 volt batteries in parallel, each with a 125 amp fuse. After they are paralleled, there’s a 200 amp fuse. All class T.

ClassT are huge fuses with a 6” fuse holders. Also my 200 amp fuse and 125 amp fuse uses a different sized holder. Not sure at what amperage the fuse changes size.
 
Joined
Nov 30, 2019
Messages
12,131
Greetings all, fng here. Forgoing the newcomers intro and just consolidating here.
I know enough about electric to be dangerous, yet enough to know there is a right way, not licensed though.
Anywhoo, I replaced my lead in the travel trailer for a 200 ah lifepo4.

I'm installing a class T Fuse, not sure on the size I need. Read a ton but most threads here, are dealing with
Solar coming in and 24v systems.
I'm just going to run a 12v system, with no solar as of yet. Down the road I will but I'll cross that bridge when I get there.
The trailer is your run of mill 30 amp service. The 200ah battery has a 100ah BMS.
I think a 125 amp Class T fuse should be plenty for this setup, or should I rate higher? lower?
Depends on the size of the wire.
What size wire are you using for the battery circuit?
Class t is the best fuse for LFP.
By my calculations its not absolutely necessary for a 12 volt system though.
For 12 volt systems I like these.
They fit in a very compact carrier that attaches directly to the battery terminal which just about prevents the possibility of an upstream short.

I'm going with the stock power center in the trailer.
The feeder circuit also needs to be fused.
The dc distribution panel can also be considered to be part of the feeder circuit and should be part of the fuse determination.
The feeder is usually 4 or 6 awg with no more than a 100amp fuse.
Depending on the round trip length of the circuit voltage drop may also be a consideration.
What size wire did you use?
What fuse?
What is the round trip length of the circuit?

No plans on running heavy demand appliances off battery. Heaviest demand might be a coffee pot but I'd probably just go old school there.
You have not mentioned an inverter.
Will you be using one?
Next question on safety,
What fire extinguishers are ppl recommending for lithiums? I was going to get a "purple K" extinguisher.
Good question.
 

backwoods

Solar Enthusiast
Joined
Apr 26, 2022
Messages
49
everything is stock, the power center/converter 32amp antique magnetek.
After reading lots of posts on updating/upgrading it, it seems like it's just best to leave it alone.
So no inverter per se, just the stock converter.
I thought about going with a mrbf, but the class t seemed more suited for lifepo4 especially with all the reading
and recommendations on using them on here.
I have 1/0 cable I can use but it's a bit overkill with such a short run,
the 6 awg spec seems good to continue using, I don't think there would be a noticeable volt drop in a short run.
I'm assuming the factory wires are 6awg, I haven't measured them or started to install anything yet. Just eyeballed them.

The distance is a very short run (10 feet round trip at best) It is shorter than the factory configuration with the battery on the tongue.
where I plan on installing this, is right next to the existing power center.
Just swapping batteries and wanting to add safety features, no extra inverters or controllers. just a stock travel trailer.
kind of boring compared to most posts here.
 
Joined
Nov 30, 2019
Messages
12,131
everything is stock, the power center/converter 32amp antique magnetek.
After reading lots of posts on updating/upgrading it, it seems like it's just best to leave it alone.
So no inverter per se, just the stock converter.
I thought about going with a mrbf, but the class t seemed more suited for lifepo4 especially with all the reading
and recommendations on using them on here.
I have 1/0 cable I can use but it's a bit overkill with such a short run,
the 6 awg spec seems good to continue using, I don't think there would be a noticeable volt drop in a short run.
I'm assuming the factory wires are 6awg, I haven't measured them or started to install anything yet. Just eyeballed them.

The distance is a very short run (10 feet round trip at best) It is shorter than the factory configuration with the battery on the tongue.
where I plan on installing this, is right next to the existing power center.
Just swapping batteries and wanting to add safety features, no extra inverters or controllers. just a stock travel trailer.
kind of boring compared to most posts here.
6 awg will be fine.
For an old magnatek distribution panel I suggest you keep the fuse rating to 50 amps.
You can't get a class-t that small.
MRBF has a breaking capacity of 10,000 amps at 14 volts.
I've done the math and had my figures peer reviewed.
The dead short ampacity of a 12 volt LFP battery will be well less than 10,000 amps.
I can share the spreadsheet if you are interested.
 

backwoods

Solar Enthusiast
Joined
Apr 26, 2022
Messages
49
No I have read a lot of your posts and believe you. If you feel a mrbf is plenty for a 200 ah lifepo4 I'll go with that.
it's less pesos for that than the class T so who doesn't like saving some money, just not at the cost of being safe.

Any thoughts on other safety gear, fire bag, fire blanket, sand?
One other thing of concern, my fresh water tank will share the same space.
Not only would the battery going up in smoke make for a bad day, that water would make it a worst day.
My thought for now on that is I have kaowool that I can wrap the tank side exposed to the battery with.
May not stop it from melting down but may buy enough time to prevent that.
 
Last edited:
Joined
Nov 30, 2019
Messages
12,131
Any thoughts on other safety gear, fire bag, fire blanket, sand?
You have reminded me that I need to update my own fire extinguishers and my plan.

I found this "Lithium-ion batteries are considered a Class B fire, so a standard ABC or dry chemical fire extinguisher should be used. Class B is the classification given to flammable liquids. Lithium-ion batteries contain liquid electrolytes that provide a conductive pathway, so the batteries receive a Class B fire classification." -- https://resources.impactfireservices.com/how-do-you-put-out-lithium-ion-battery-fire
 

backwoods

Solar Enthusiast
Joined
Apr 26, 2022
Messages
49
You have reminded me that I need to update my own fire extinguishers and my plan.

I found this "Lithium-ion batteries are considered a Class B fire, so a standard ABC or dry chemical fire extinguisher should be used. Class B is the classification given to flammable liquids. Lithium-ion batteries contain liquid electrolytes that provide a conductive pathway, so the batteries receive a Class B fire classification." -- https://resources.impactfireservices.com/how-do-you-put-out-lithium-ion-battery-fire
Right, which was why I was leaning to a purple K extinguisher they are rated B,C.
 

backwoods

Solar Enthusiast
Joined
Apr 26, 2022
Messages
49
So it appears there is a shortage of economical mrbf's mouser/waytek are backordred thru end of May/June.
Rather not pay blueseas markup.
So I found a class T a6t50 fuse.
My only concern is it isn't bolt down, would a push in fuse be in an issue with vibration or another issue I'm not considering right now?
These type fuses are not very easy to just pop out so I think vibration may not be much of an issue?
 
Joined
Nov 30, 2019
Messages
12,131
So it appears there is a shortage of economical mrbf's mouser/waytek are backordred thru end of May/June.
Rather not pay blueseas markup.
So I found a class T a6t50 fuse.
My only concern is it isn't bolt down, would a push in fuse be in an issue with vibration or another issue I'm not considering right now?
These type fuses are not very easy to just pop out so I think vibration may not be much of an issue?
Please provide a product link for the fuse.
 
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