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diy solar

Recommend class t for 200ah lifepo4?

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uksuntimes

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I’m installing my system for a second time, and am horrified to have now learned about the massive AMP risk of lifepo4 batteries!

I had marine circuit breakers as recommended by Will as I basically built his 12v solar system that uses the renogy MPPT.

However I now believe it should also have a class T fuse between the battery and the system. Is that correct assumption?

If so here are some main stats:

Battery is 200ah 12v lifepo4 renogy Bluetooth smart battery

Goes to system via 35mm cables. 3meters in length. Rated for 240a.

My draw is generally a bunch of small LED items. The main draw is a 3000w inverter that is sometimes used to power an induction hob (up to 1800w).

I will still keep all my existing breakers and fuses etc but I believe adding a t class fuse between the battery and the system is smart.

I’m mostly worried about a short really.

From what I have read a 150a fuse would suffice. But are there different kinds? Does it need to be specifically for a 12v system?

One important note is that I want to add a second battery (same size, make etc) at some point to extend my capacity for longer camping trips. I would plan to fuse and isolate each one independently so if one goes bad I can isolate it safely. But would I then also want a bigger fuse on the main cables?

Part of the problem for me is finding the right size fuse and finding it for purchase in the UK.

Any help would be massively appreciated. :)

Wasn’t sure which category to post this, but as I’m mostly worried about my safety, I figured this may be a good spot.

Should I also get some rubber gloves for working on the system? :)
 
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3000W @ 12V is pulling 250A from battery bank. HF (High Frequency) inverter can do up to 6000W, LF (Low Frequency) can do up to 9000W. This surge handling is only possible for a few seconds and won't trip a breaker or blow a fuse in most usual cases.

Class-T fuses are great (quality brand only) but they are fragile & require a holder.
For under 36V, I suggest using an MRBF Fuse which are smaller, more robust and very good for smaller systems. A 250A fuse would suit just fine.

REF: These are readily available on ebay/amazon etc.

MRBF Terminal Fuse Block - 30 to 300A - Blue Sea Systems

Easily and economically satisfies ABYC 7 circuit protection rule by mounting on a 3/8 battery post, battery switch or bus bar.
www.bluesea.com www.bluesea.com
 
Thank you for the reply.

However my worry is a short rather than the load. I read of thousands of amps and resulting arcing with fuses. So it’s been said to use a class t to ensure if there is a short, it will catch it.

This is based on what I’ve read on this forum on similar posts. But perhaps I am misunderstanding?
 
I don't use Class-T's after I broke a couple (not hard to do). My system at the moment can dump 1200 Amps but in a short condition that can be 5x that... That is a serious ZOT and also why my powerhouse floor is 3cm thick rubber LOL... This ass does not get grounded hehehe... 1 lesson learned LONG ago and never repeated.

MRBF, Mega & Class-T's fuses will all catch it but at different points. The only fuses I use are for the battery packs directly, everything else is Polarized DC Breakers (except the master 250A breaker).

Photo of my MRBF's attached to Pike Industries Busbars with full proper covers. Also all batt terminals have covers as does everything else that is exposed and a possible contact source.

BusBar-closeup.jpgThe upper busbars is offset by 3/4"/19mm to allow the MRBF brackets to clear while allowing the cables to be "together" to reduce EMI.

I'm in a final reconfig mode now. All my battery packs are being reinstalled into new Steel cases which have their own DC Breakers but the existing MRBF's will remain as I am one to "play safe".
 
Your system sounds really interesting. And great idea with the floor.

Alas as mines in my camper car, I don’t have that option :)
 
uksuntimes said:
Your system sounds really interesting. And great idea with the floor.

Alas as mines in my camper car, I don’t have that option :)
Click to expand...
Look or "rubber horse matts". Typically made from recycled rubber and come in 4'x4' or 4'x6' formats... shop around though as some charge crazy prices while others don't. Farm Supply houses have the best deals on these usually.
 
Steve_S said:
Look or "rubber horse matts". Typically made from recycled rubber and come in 4'x4' or 4'x6' formats... shop around though as some charge crazy prices while others don't. Farm Supply houses have the best deals on these usually.
Click to expand...
That's a great thought. Thank you for taking the time to share :)

To clarify, the system is in a car, but I am generally in my awning / around the car. And have no space to start carrying mats :)

I am more worried about general shorts in use / when out in the field rather than only when installing :)

Thank you for all the ideas though.

I’m just after the right fuse knowledge :) haha
 
uksuntimes said:
The main draw is a 3000w inverter that is sometimes used to power an induction hob (up to 1800w).
Click to expand...
3000W @ 12vDC = 250A
uksuntimes said:
I will still keep all my existing breakers and fuses etc but I believe adding a t class fuse between the battery and the system is smart.
Click to expand...
not a bad idea. I always put a Class T between the Battery and {everything else} for just in case security. Use a proper shielded holder for the classT.
uksuntimes said:
I’m mostly worried about a short really.

From what I have read a 150a fuse would suffice.
Click to expand...
Fuses protect the Wire. If your wire can safely carry 250A, the job for the fuse is to cut energy flow if higher amperage than the wire can safely carry is flowing. The purpose of the Class-T vs other fuses is it's very high current breaking capacity.
uksuntimes said:
But are there different kinds?
Click to expand...
yes
uksuntimes said:
Does it need to be specifically for a 12v system?
Click to expand...
no
uksuntimes said:
One important note is that I want to add a second battery (same size, make etc) at some point to extend my capacity for longer camping trips. I would plan to fuse and isolate each one independently so if one goes bad I can isolate it safely. But would I then also want a bigger fuse on the main cables?
Click to expand...
The fuse protects the wire. If the wire size doesn't change, then the fuse size doesn't change.
uksuntimes said:
Part of the problem for me is finding the right size fuse and finding it for purchase in the UK.
Click to expand...
check on Amazon, or look for marine suppliers. In Canada I use a yacht supplier in Toronto for Class T fuses and holders, perhaps in UK you will find boating suppliers carry what you need locally.

edit: I cut and paste this from another thread on this forum: 'since you are in the UK consider the equivalent to class T, a HRC fuse. Look online at the major distributors, like Farnell. https://uk.farnell.com/c/circuit-protection/fuses-fuse-accessories/fuses/hrc-fuses'
 
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uksuntimes said:
Should I also get some rubber gloves for working on the system?
Click to expand...
IMHO that would make it hard to work on and more likely you drop a wrench or screwdriver where you don't want to.

Just remove or tape up rings and remove any other jewellery before working on a system. ?

With only 12V the danger is shorting with metal, not shock through body - body is too high resistance to carry significant current at 12V
 
SeaGal said:
Also could consider NH type fuses - NH00 for up to 125A, NH1 for 200A, NH2 for 250A+

Available widely in UK (with holders / disconnectors) including from Bimble or Jean-Muller...
e.g.

200A DC fuse, 250VDC for NH1 Fused Disconnect

www.bimblesolar.com www.bimblesolar.com

This guide may be useful too... (pages 33/34 re fuses)
Click to expand...
And just to double check, ANL fuses are not up to the task when it comes to potential lifePo4 shorting?
 
SeaGal said:
I didn't say that. I just said you could also consider NH fuses - see the Victron Guide, where IIRC it also mentions ANL.
Click to expand...
Apologies. I was in no way seeking to imply that you did.

It was an enquiry as I’ve seen posts saying they will arc / fail in a short, and you seem knowledgable so thought you may have a view on the matter :)

Whatever the case I appreciate your reply and I’m taking time to try and find a suitable holder for the type of fuses you have noted.

All the best.
 
NP - sorry, not familiar with ANL myself - I've only used NH and a 70V mega-fuse.
 
In my own set up, I have DIY batteries from 16s cells. At the suggestion of another member I have been using a fuse between cells #8 and #9 inside the pack. For the space in my cases the ANL fit well in this location. If a moderate overcurrent event takes place with a battery pack, I expect the ANL will break the pack into two 8s disconnected sets - hopefully stopping this overcurrent, and cutting the voltage in half in the process. The pack BMS has a 100A limit, the pack output has a 125A 2P breaker and the ANL 150A fuses between cells 8/9 in the packs. Multiple levels of disconnect protection.

All that said, for the connection of the ESS as a whole (at the moment 6 battery packs) I use 400A Class T fuses, with their higher current interrupting capacity, as a safeguard against some massive dead-short in the system (imagine dropping a spanner across the pos/neg poles in an accident) bassed on the reasoning this doesn't rely upon the ANL fuses (or their limited interrupting current) as my only line of defence.
 
SeaGal said:
Also could consider NH type fuses - NH00 for up to 125A, NH1 for 200A, NH2 for 250A+

Available widely in UK (with holders / disconnectors) including from Bimble or Jean-Muller...
e.g.

200A DC fuse, 250VDC for NH1 Fused Disconnect

www.bimblesolar.com www.bimblesolar.com

This guide may be useful too... (pages 33/34 re fuses)
Click to expand...
This is what I am using. A fraction of the cost of class T and similar or better AIC. EBay in the UK is full of NH00 fuses and holders
 
SeaGal said:
For fuses in particular, I'd recommend purchasing from a reputable supplier, rather some random selling on eBay.
Click to expand...
It's not the seller. If you buy Siba fuses and fuse holders, it's a reputable item. You aren't buying a car
 
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