High capacity DC breakers

Sea Change

Sea Change

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I'm soon going to be re-organising my lithium system, as I double it from two to four 280Ah batteries.
This seems like a good time to revisit a few things. At the moment, I have MRBF fuses on each battery, then a class T master fuse.

A few weeks ago WIll Prowse was singing the praises of DC breakers. This is the sort of thing he was talking about:
https://www.amazon.com/DIHOOL-Circuit-Breaker-Disconnect-Switch/dp/B0CJBB6J5D?ref_=ast_sto_dp&th=1

If the specs are to be believed, they could function as both a fuse and an isolator. I would maybe keep my class T master fuse in place as well.

These things are very chunky, but otherwise I'm not sure I see a reason not to use them? Unless they're actually Chinese rubbish and not to be trusted, of course.
 
Chinese but how would we know if they were rubbish? Dihool is a big company making lifts and lots of sophisticated engineering products established in 2019 from its parent company, a taxi firm!
 
Sea Change said:
I'm soon going to be re-organising my lithium system, as I double it from two to four 280Ah batteries.
This seems like a good time to revisit a few things. At the moment, I have MRBF fuses on each battery, then a class T master fuse.

A few weeks ago WIll Prowse was singing the praises of DC breakers. This is the sort of thing he was talking about:
https://www.amazon.com/DIHOOL-Circuit-Breaker-Disconnect-Switch/dp/B0CJBB6J5D?ref_=ast_sto_dp&th=1

If the specs are to be believed, they could function as both a fuse and an isolator. I would maybe keep my class T master fuse in place as well.

These things are very chunky, but otherwise I'm not sure I see a reason not to use them? Unless they're actually Chinese rubbish and not to be trusted, of course.
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How much current are you going to be taking through each breaker? Do you really need a 200 amp breaker(s)? Maybe have a lok at what's available in the solar worled. Look for PV circuit breakers, then if worried about reliability of the units, purchase from a good solar firm.
 
Alex_Blackwood said:
How much current are you going to be taking through each breaker? Do you really need a 200 amp breaker(s)? Maybe have a lok at what's available in the solar worled. Look for PV circuit breakers, then if worried about reliability of the units, purchase from a good solar firm.
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Each battery has a 200A BMS. I run a 300A master fuse.
The main load is the 3kvA inverter.
 
The look good to me but you would want to know they work as per the specs. Has Will Prowse (or other YT-ers) ram tests on them yet? Ideally someone like Blue Seas will start selling a trusted version.
That said, the thing I like about MRBF is that there is no part of the pos circuit that is unfused. With all the other fuse or breaker types you have that short tail between pos terminal and device that is unprotected (except by the BMS obvs).
 
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Sea Change said:
I take it you think these are unsuitable. That's all you had to say.
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Not just that they are unsuitable, it's the mindset that fitting things that are not suitable for LFP installs is OK. For instance, it is pretty much universally accepted that class t fuses or NH fuses are the best, you know this, but have fitted MRBF fuses to the batteries. Fred is now also promoting MRBF fuses too, at best they have half the recommended AIC rating.
 
PaulRainbow said:
Not just that they are unsuitable, it's the mindset that fitting things that are not suitable for LFP installs is OK. For instance, it is pretty much universally accepted that class t fuses or NH fuses are the best, you know this, but have fitted MRBF fuses to the batteries. Fred is now also promoting MRBF fuses too, at best they have half the recommended AIC rating.
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I want to find out if they are suitable, that's why I asked the question.
I get information from various sources. It was Will Prowse who first suggested them. I know his expertise isn't in marine systems, so I took his suggestion and asked it on here for clarification.

MRBFs are quite widely used as individual battery fuses in marine systems. You're absolutely correct that they're not as suitable as Class T or NH. They have some advantages in physical form, that you can fit them closer to the battery. I plan to upgrade mine to something with a higher AIC rating, hence this thread.

Returning to the original question, what makes the breakers unsuitable? Is the certification bogus? Are the materials not fit for the marine environment?
 
When you drill down in to the actual interrupt current likely with all the resistance in the way after the cells it's likely that many things will be just as good as ClassT - BUT then a bullet can be deflected by a cigarette case over the heart but I'd rather have a bunker!

Class T has dropped massively in price; the costs associated with doing it the recommended way and the way insurers are likely to demand is maybe £100 more than going with the cheapest and possibly / probably less safe set ups on a project that may cost hundreds if not thousands of pounds.

This is not a criticism of the OP for asking questions but in general, until new high quality options become available from trusted, certified sources, the wheel has been well and truly invented and we may as well all use it.

Many are happy with NH fuses too and these are available with breaker style holders so you can get two in one if you wish.I know the specs support NH and I don't disagree but personally I never use them for customers because the savings are small and the insurers like the Class T spec.
 
Sea Change said:
I want to find out if they are suitable, that's why I asked the question.
I get information from various sources. It was Will Prowse who first suggested them. I know his expertise isn't in marine systems, so I took his suggestion and asked it on here for clarification.

MRBFs are quite widely used as individual battery fuses in marine systems. You're absolutely correct that they're not as suitable as Class T or NH. They have some advantages in physical form, that you can fit them closer to the battery. I plan to upgrade mine to something with a higher AIC rating, hence this thread.

Returning to the original question, what makes the breakers unsuitable? Is the certification bogus? Are the materials not fit for the marine environment?
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Where would you fit them ? Fuses should be close to the batteries, but with these you'd need to reach over the batteries to turn them off, bad idea.

But, insurance companies like proven equipment and are happy with class T or NH fuses, so i see no reason to fit anything else.
 
Trident said:
When you drill down in to the actual interrupt current likely with all the resistance in the way after the cells it's likely that many things will be just as good as ClassT - BUT then a bullet can be deflected by a cigarette case over the heart but I'd rather have a bunker!

Class T has dropped massively in price; the costs associated with doing it the recommended way and the way insurers are likely to demand is maybe £100 more than going with the cheapest and possibly / probably less safe set ups on a project that may cost hundreds if not thousands of pounds.

This is not a criticism of the OP for asking questions but in general, until new high quality options become available from trusted, certified sources, the wheel has been well and truly invented and we may as well all use it.

Many are happy with NH fuses too and these are available with breaker style holders so you can get two in one if you wish.I know the specs support NH and I don't disagree but personally I never use them for customers because the savings are small and the insurers like the Class T spec.
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How much are you paying for a class T fuse? I've not seen any change in price over the past five years.
I did recently pick up a couple of Renogy class T fuses at only $20 a pop, but they turned out to be only 10kva AIC. Should have read the specs properly before buying!
My boat's currently in the US where I can't get a class T for under $50.
 
PaulRainbow said:
Where would you fit them ?
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I'm looking at completely rebuilding the system so that's all up for debate. It's likely that the batteries will go under a bunk and the breakers would then be mounted low down on the bulkhead, so easily accessible yet still only a few inches from the batteries.
 
Trident said:
When you drill down in to the actual interrupt current likely with all the resistance in the way after the cells it's likely that many things will be just as good as ClassT
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The only resistance will be in the main battery cable, after that it's down to smaller fuses.
 
PaulRainbow said:
The only resistance will be in the main battery cable, after that it's down to smaller fuses.
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There's resistance in the bus bars between cells, the BMS and BMS cables in and out and then the battery wire to the fuse holder , the fuse holder itself etc. Some tests have been done and found the quoted cell IRC is massively reduced by all of these factors. I don't want to confuse the issue however, and the take away should be use a class T fuse, full stop.
 
PaulRainbow said:
. Fred is now also promoting MRBF fuses too, at best they have half the recommended AIC rating.
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Not so much promoting them as saying I like the fact that they eliminate an un-fused length of cable between terminal and fuse. I fitted an MRBF to my 280ah battery after reading the CF thread below on AIC which suggests that MRBF are perfectly adequate for my setup. Unless I misunderstand what they’re saying a 280ah LiFePo battery will not exceed the AIC rating of my MRBF fuse.

https://www.cruisersforum.com/forums/f166/lithium-short-circuit-current-aic-298934.html

Edit: The thread above is a long one, so here’s part of the OP’s summary, based on tests he did:
…”For 12/24V systems up to 200Ah, AMI/MIDI, MRBF, ANL and class-T fuses are acceptable. Above 200Ah, only MRBF, ANL and class-T fuses are acceptable.

For 48V systems up to 200Ah, MRBF, ANL and class-T fuses are acceptable. Above 200Ah only ANL and class-T fuses are acceptable.”
 
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Sea Change said:
How much are you paying for a class T fuse? I've not seen any change in price over the past five years.
I did recently pick up a couple of Renogy class T fuses at only $20 a pop, but they turned out to be only 10kva AIC. Should have read the specs properly before buying!
My boat's currently in the US where I can't get a class T for under $50.
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In the UK I can get them , depending on size for well under £50 - up to 200 amp retail at £33 and up to 500a £49
BEP or BlueSeas holders at £30 each
For multi battery systems there are bulk discounts as well
Not sure with the US tariff situation now how de minimus would work but if you're happy with shipping costs I'm happy to get you some here and post them over if the figures work for you
 
fredrussell said:
Not so much promoting them as saying I like the fact that they eliminate an un-fused length of cable between terminal and fuse. I fitted an MRBF to my 280ah battery after reading the CF thread below on AIC which suggests that MRBF are perfectly adequate for my setup. Unless I misunderstand what they’re saying a 280ah LiFePo battery will not exceed the AIC rating of my MRBF fuse.

https://www.cruisersforum.com/forums/f166/lithium-short-circuit-current-aic-298934.html

Edit: The thread above is a long one, so here’s part of the OP’s summary, based on tests he did:
…”For 12/24V systems up to 200Ah, AMI/MIDI, MRBF, ANL and class-T fuses are acceptable. Above 200Ah, only MRBF, ANL and class-T fuses are acceptable.

For 48V systems up to 200Ah, MRBF, ANL and class-T fuses are acceptable. Above 200Ah only ANL and class-T fuses are acceptable.”
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But isn't that just a forum post by some random bloke ?

The general thinking is that Class T or NH fuses are best practice. Even the best midi fuses only have an AIC of 5000A with a max current of 200A. Again, it's stuff like this that makes insurance companies insist on pro installs.
 
PaulRainbow said:
But isn't that just a forum post by some random bloke ?

The general thinking is that Class T or NH fuses are best practice. Even the best midi fuses only have an AIC of 5000A with a max current of 200A. Again, it's stuff like this that makes insurance companies insist on pro installs.
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From all of the digging I've done on this, and working from memory, it goes something like:
NH: 20-50kvA
Class T: 10-20kvA
MRBF: 10kvA
ANL: 3-6kvA

Note the range of values within the same type of fuse. You can't just say 'fit a Class T', you still need to check the spec for that brand. And if I understand it correctly, the operating voltage affects it too. So if the AIC is quoted at 32v, you'll get a higher capacity at 12v. Happy to be corrected on that, I am not a professional.

The only instance I've come across where the incorrect fuse left to bridging and subsequent fire, was a case reported on the DIY Solar Forum where a very large 48v bank was fitted to a house and protected by a Mega fuse. The house was completely destroyed.
That's a fairly extreme example- high voltage, massive capacity compared to most boats, and an obviously inadequate fuse.
Does anybody have any other examples?
 
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