Class T details and specs

[filippomasoni]

Be careful with that. NH is used a lot in industry and distribution cabinets, they need a special carrier that's bulky and not cheap (but real good). Also, the NH rated for DC and currents available on battery packs is extremely expensive - few hundred Euros per fuse.
HRC is good for solar lines and they have a nice carrier to them.
I believe the class t is the most suitable for our cells and smallest/cheapest option, even if you need to import them from US.

Recently I've ordered a couple Bussmann LMT fuses from eBay but didn't received them yet. They are the only alternative to class t I've found in Europe.

I found different fuse holders, some are really cheap like this one https://uk.rs-online.com/web/p/fuse-holders/7652942 and some are 10 times as much. Maybe because the 160A is thinner and when going up they need more copper. But I'm not really sure how to check for compatibility. It's industrial stuff and not very user-friendly, even the spec sheets have so much info it gets confusing. I was thinking of connecting it with it resting of the end of a copper bar and bolting a piece of copper on top so that the copper squeezes onto those fuse terminals. Once tighten it should have a good connection, but it's definitely too much of a hack and not worth the hustle and risk, so not going to use NH. The one I linked (only about 10 euro) is rated for DC with a breaking capacity of 25kA, which is on par if not more than blue seas T class.

Anyway, the other one I found, from another supplier, the same kind of industrial seller, is the Bussman BS88 180A LET series. From what I understand the LET series has a capacity from 25 to 180A and the LMT from 160-450A but should be of the same quality. It's about 20 euros and I might try that, 180A is enough for my system as I'm never going to go above 150A.

 

[zolee]

I found different fuse holders, some are really cheap like this one https://uk.rs-online.com/web/p/fuse-holders/7652942 and some are 10 times as much.

Yeah, that's one you choose when you don't plan for quick change and have a touch protection in front of it. Otherwise use the one with integrated disconnector.

was thinking of connecting it with it resting of the end of a copper bar and bolting a piece of copper on top so that the copper squeezes onto those fuse terminals. Once tighten it should have a good connection, but it's definitely too much of a hack and not worth the hustle and risk, so not going to use NH.

Don't do that! If you can't afford the proper holder just don't select this type of fuse.
Btw, the proper subtype of NH is aR - check the prices, the suitable holder costs pennies compared to the fuse.

The one I linked (only about 10 euro) is rated for DC with a breaking capacity of 25kA, which is on par if not more than blue seas T class.

Again, check NH aR - the proper one for our batteries.

Anyway, the other one I found, from another supplier, the same kind of industrial seller, is the Bussman BS88 180A LET series. From what I understand the LET series has a capacity from 25 to 180A and the LMT from 160-450A but should be of the same quality. It's about 20 euros and I might try that, 180A is enough for my system as I'm never going to go above 150A.

Aha, much cheaper and suitable. LET and LMT looking very similar to each other.

 

[filippomasoni]

Yeah, that's one you choose when you don't plan for quick change and have a touch protection in front of it. Otherwise use the one with integrated disconnector.

Don't do that! If you can't afford the proper holder just don't select this type of fuse.
Btw, the proper subtype of NH is aR - check the prices, the suitable holder costs pennies compared to the fuse.

Again, check NH aR - the proper one for our batteries.

Aha, much cheaper and suitable. LET and LMT looking very similar to each other.

In our case, we hopefully never need to change it, so no need for a quick change. I have no idea how those work, looks like it is retained with springs to make the connection, which is still much quicker to remove than a bolt like on the bussman.

I checked the NH aR and they are definitely made for bigger stuff, with a braking capacity of 30-50kA. I've also seen the gBat type specifically made for batteries and with braking of up to 150kA at 1500VDC. Insane stuff! I didn't even find prices, just spec sheets, haha. I guess these are used in battery power plants and industrial applications. Very interesting, but I don't think it's applicable to our case.
Also the more we go up with this stuff voltages also go up, because of course for efficiency in power distribution and industrial they go up in voltages. Stopping an arc at 200VDC is much harder than at 24VDC, so the breaking capacity at our voltages is definitely higher than the rated 20-25kA, so we should be fine with something like the Bussmann LET or LMT and not break the bank. Also, we need to consider we have to buy at least one spare, in the remote case we blow it.

Another thing, is a proper holder needed even for the bussmann? In my case it will probably go from a copper busbar on the positive terminal to the battery switch with precharge, very short and in free air. I've seen people wrapping it in clear shrink wrap. to not have any contacts exposed.

 

[zolee]

Insane stuff! I didn't even find prices, just spec sheets, haha.

For prices you can check farnell or tme. They start at xxx EUR

Stopping an arc at 200VDC is much harder than at 24VDC, so the breaking capacity at our voltages is definitely higher than the rated 20-25kA,

There's not much information on that, I didn't found any accept on forums. A 16S LFP should have a short circuit current around 10kA or more, depending on internal resistance and contact/cabling resistance. I would not count on just 10k.

so we should be fine with something like the Bussmann LET or LMT and not break the bank. Also, we need to consider we have to buy at least one spare, in the remote case we blow it.

I think we are fine. I've also ordered a set of LMTs.

Another thing, is a proper holder needed even for the bussmann?

Yes! Proper holding is necessary for any type of fuse.

In my case it will probably go from a copper busbar on the positive terminal to the battery switch with precharge, very short and in free air. I've seen people wrapping it in clear shrink wrap. to not have any contacts exposed.

I'll make my own, but I have access to pure copper bars, have a milling machine and can do nickel electroplating.
I'll make a base out of some thick electrical insulation material I have, then fix two copper bars (each with two studs) at the needed distance to fit the fuse body, then fix all that next to the BMS and connect with short jumpers.
The fuse body should not experience any force from the cables attached.

 

[filippomasoni]

I also have pure copper bars, but no milling machine or a way to electroplating them. Like many other do it diy I'm sure I can manage to make a few busbars and if the eventually oxidize a bit I'll do some maintenance and clean them.
What electrical insulation material are you using for the base? Anything we can diy ?
Of course there should be no force on the fuse, if the battery switch is properly secured that will act as strain relief, on the other end there will be a battery cell which is also secured since it's in the compression box.

 

[zolee]

I also have pure copper bars, but no milling machine or a way to electroplating them.

The milling machine is just making things easier and prettier. You can do most things without one. Machining electrical copper is hard and I prefer to minimise it.
Electroplating is easy. I learned it from some YouTube videos, all you need is pure nickel, vinegar and a small power supply (adjustable if possible). Then clean the copper really good and stick it in (I use fine steel wool and alcohol 99%). The higher the polish when you started the nicer is the finished plating.
Make sure the nickel is pure nickel. First time I tried it everything went black in seconds. The nickel I thought was pure was copper inside and that copper poisoned the solution.
Now that I have a prepared solution it is just a few minutes to connect the wires and start the process.

Like many other do it diy I'm sure I can manage to make a few busbars and if the eventually oxidize a bit I'll do some maintenance and clean them.

There is no clean copper or aluminium in air. After cleaning they oxidize very fast (in seconds). You can break the oxide layer and keep the air out, but that requires a nice flat mating surface between the copper piece and the cable lug. It's surface will tarnish over time but that is not a problem if the contact was prepared well. No need for cleaning.

What electrical insulation material are you using for the base? Anything we can diy ?

The material is leftovers from my cell cage, I used 4mm FR4 and something called Tekstolit TCF-5 in 18 mm thickness.

Of course there should be no force on the fuse, if the battery switch is properly secured that will act as strain relief,

It will still dangle in the breeze.

on the other end there will be a battery cell which is also secured since it's in the compression box.

Never "secure" anything to the cell terminals.
I will make my fuse holder by the following procedure:
- cut two pieces of suitable thickness copper bars
- drill two holes in each (for the studs),
- countersink and tap the holes.
- drill two more holes, this time smaller, to screw down the copper bars.
- clean, polish electroplate
- screw in the four studs from the countersunk side
- fix the copper to the textolit base.
- connect cell terminal with flexible jumper cable
- connect output cable
- install fuse