What do our experts think of this of this?

[olley]

I have 90mm on my 3kw inverter, after 10mins running 2.5kw of heaters to test it the cables were warm.

 

[Raul]

Raul

so 125A DC breaker at home? i think i ordered a breaker a week or so ago, i just need to check what it is!

in the motorhome a 100A or 150A?

Yes all the 15kwh 16 cells I built with 125A breaker and 35mm2 cables. Yours, will have a poxy 400A mega inside near the bms. Leave that there and add the 125A outside, maybe in a box on the wall where is convenient for isolation as well.

 

[Raul]

or just up the cable to 50mm?

You are better of with 2x 35mm2, it will give better heat disipation as you get more surface area on 2x35 compared to 1x50.

 

[EuroTrotters]

Expensive

 

[MisterB]

https://www.amazon.co.uk/Renogy-Current-Construction-Vehicles-Caravans/dp/B0DS48KWCW/?tag=mhf04-21

this seems to meet the specs?

^{_{Subscribers  do not see these advertisements}}

 

[Raul]

https://www.amazon.co.uk/Renogy-Current-Construction-Vehicles-Caravans/dp/B0DS48KWCW/?tag=mhf04-21

this seems to meet the specs?

Don't touch it.

 

[MisterB]

Don't touch it.

is there a reason? its a 250A T class fuse?

 

[Raul]

This is another good choice, meets the existing regulation requirements for battery storage. You just need to find the suitable amps ratings for your application, as appropriate. I have used the 125A on 2 Seplos batteries.

Projoy 2 Pole Battery Isolator 125A 160V DC with Enclosure

Part No: PEBS-L-125A-160V-2PL-ENCL Storage Systems - Battery Fuse Holder This part is made up of the following items: 1 x PEBS-L-160V-125A-2P-DC Projoy Battery Isolator 160V 125A DC MCB 1 x PEBS-L-IP66-4P-ENCLOSURE Projoy DC MCB Weatherproof Empty Enclosure 4 Module PEBS-L Series DC...

electric-solar.co.uk

 

[Raul]

is there a reason? its a 250A T class fuse?

I don't see any testing or accreditation, mikey mouse.

 

[68c]

Can anyone explain how these fuses fail then reconnect?
Is the normal path through the fuse itself melting then reconnecting, possibly now at a higher fuse rating as it is a blob of metal rather than a thin strip? Very unlikely I think.
Or, is the plastic fuse base melting allowing the attachments to short out elsewhere?
This seems more likely so best to be carefully what you attach the fuse holder to.

^{_{Subscribers  do not see these advertisements}}

 

[Ray-Vic]

Can anyone explain how these fuses fail then reconnect?
Is the normal path through the fuse itself melting then reconnecting, possibly now at a higher fuse rating as it is a blob of metal rather than a thin strip? Very unlikely I think.
Or, is the plastic fuse base melting allowing the attachments to short out elsewhere?
This seems more likely so best to be carefully what you attach the fuse holder to.

They don't break and then reconnect in that sense, they break and the massive currents, depending on the type of fuse, can cause an arc between the bits that are left, which is fuelled by the vapour within the blown fuse. Class-T fuses still have fusible links within them, but they also have sand which acts as an arc suppressant inside.

 

[68c]

That makes more sense.

 

[Guigsy]

Won't a starter battery push a few hundred amps if it's shorted?

 

[Sewdhull]

A fuse is not to protect the Battery. It's to protect the cable.

You should not fuse anything based on the supply current.

You figure out the load, cable appropriately then fuse for the cable.

Also maybe think about going to 24v for the leisure batteries to reduce costs and the excitement of high current failures

 

[Ray-Vic]

Won't a starter battery push a few hundred amps if it's shorted?

Yes but lithium's can be many thousands.

^{_{Subscribers  do not see these advertisements}}

 

[Raul]

You should not fuse anything based on the supply current.

Yes you should, you fuse with a man enough fuse, so it can chop the flow to protect the cable. How you do that? You find the max potential of the supply, and stick a fuse capable to cut the flow of that supply.
Short circuit capacity in kA

 

[Sewdhull]

Won't a starter battery push a few hundred amps if it's shorted?

It will. Most lithiums will too. If you find out the IR of you lithium you can approximate the short circuit current, 12.8/IR = the initial short circuit current, many hundreds/thousands of Amps. A BMS will cut the battery out at its cutoff, but if the mosfets fail shorted the current will keep going, for a little while at least.

 

[Raul]

Won't a starter battery push a few hundred amps if it's shorted?

Yes, probably double the CCA rating, imagine a lithium short what it can do.

 

[fishplug]

This is another good choice, meets the existing regulation requirements for battery storage. You just need to find the suitable amps ratings for your application, as appropriate. I have used the 125A on 2 Seplos batteries.

Projoy 2 Pole Battery Isolator 125A 160V DC with Enclosure

Part No: PEBS-L-125A-160V-2PL-ENCL Storage Systems - Battery Fuse Holder This part is made up of the following items: 1 x PEBS-L-160V-125A-2P-DC Projoy Battery Isolator 160V 125A DC MCB 1 x PEBS-L-IP66-4P-ENCLOSURE Projoy DC MCB Weatherproof Empty Enclosure 4 Module PEBS-L Series DC...

electric-solar.co.uk

I came to this thread off the back of the same video referenced by the OP.

I've got MCBs between my PV input and the MPPT, between the MPPT and the battery and between the battery and everything else.

Sounds like the prudent thing to do would be to add a Class T fuse on the battery - but are you suggesting that the battery isolator you linked to could be used instead of my current MCB (and Class T) Raul ? The 160v DC rating being the maximum it can take therefore 12v is fine?

I'm outside of my understanding here and trying to learn / stay safe.

I also winced at £100 for a fuse + holder initially, and then thought about the cost in both time and money of all the things it protects. When looked at from that viewpoint it's an inexpensive insurance policy IMO.

 

[Raul]

That breaker I suggested for MisterB is for a house battery 48v. He has a Seplos 48v. It will be an overkill for 12v applications, it will do the job, but it's just too big in the van, 2pole 3 modules.
You may want a smaller classT or even a MRBF for a smaller battery.
I have 700ah too much for an MRBF, and went with 10kA DC breakers from Outback. I could have fitted a classT, but, I have 3 batteries in parallel, and each has a breaker on it, that can be used as isolators. MRBF directly on the battery terminal is a good solution too.

^{_{Subscribers  do not see these advertisements}}

 

[Ray-Vic]

The Blue Sea MRBF's (which I believe are actually Bussman (Eaton)) have an interrupt rating of 10kA @ 14v, which should be perfectly adequate for most situations if installed correctly on each battery. See below specs.

As Raul notes, when you get up to multiple batteries and very large banks the class-T is probably the way to go if only using a single fuse as they can provide up to 200kA interrupt, and the way they work with effectively forming a glass shield against arcing is very safe. Below is a video from Victron about their Class-T power in module.

Victron Class-T power in.

I wish I had seen your previous information on this subject Raul as I would never have installed Mega fuses in place of my ANL ones. I am actually really happy with the MRBF's as they make a tidy job and I have a spare simply cable tied to the battery cable.

 

[fishplug]

Thanks Raul.

Mine's a single 300Ah Fogstar Drift.

The Max discharge current is rated at 150A so would I be correct in saying that I'd want a 175A MRBF for it? I appreciate you may prefer me to check with the manufacturer so please say if you're not comfortable offering that level of advice.

At £11 ish a piece I'd even stretch to carrying a spare!

 

[Raul]

The Blue Sea MRBF's (which I believe are actually Bussman (Eaton)) have an interrupt rating of 10kA @ 14v, which should be perfectly adequate for most situations

Thank you for posting the data, I vaguely knew they take 2kA at 58v, and that kA rating will increase as you lower the voltage, but, never knew for sure how high; 10kA is plenty for our 12v aplications.