because they don’t have the fault current rating necessary for LFP batteries.
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Ask offgridtec, they sell them for this purpose.
just a word of warning – those NH1 fuses and the respective holders are huge, about 20cm terminal to terminal. I use them myself, but today I’d probably look into Adler EF3 which have the same terminal spacing as Mega fuses but are rated for serious fault currents.
Also, while the NH1 fuses themselves are rather cheap (about 10€ for a 250A Siemens piece with datasheet values for DC), the holders are a bit pricey, and only seem to come in sets of 3.
Do they have datasheets with rated DC fault current? None that I could find quickly. And the Mega fuses where I found a datasheet specify 2000A of fault current, which is a third of what a 16S block of EVE 280’s can deliver.
I might skimp on some stuff, but not on fuses.
Here the BMS, wiring and fuse limits the current, not the battery
Otherwise we’re back to field one, the abb mcb with 10ka switching capacity.
The Siemens NH1 200A fuses have a current breaking rating of 40kA DC. Somewhat higher than the Megas.
The BMS has MOSFETs which tend to fail shorted (i.e. passing current and not turning it off), the wiring can withstand fault currents only for so long before the isolation melts.
It’s the fuse that first has to blow (which is the easy part if we’re talking short circuits) and then be able to extinguish the DC arc, which is why fuses for high fault currents are sand-filled and not open to the environment like those Mega fuses.
With an LFP battery, people have measured 5500A of short-circuit current and posted videos on youtube showing Mega fuses shooting molten metal all over the place. That’s what sand-filled fuses like NH or EF3 or T-class are designed to prevent.
That all will not matter if all you’re concerned about is a bit of overload from your Multis, but imagine you slip while attaching something to your busbars and suddenly there’s a solid piece of wrench welded to them. Ask any experienced automotive electrician about their horror stories of wrenches dropped across battery terminals.
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Absolutely. It’s not overload current I’m worried about. It’s the LFP battery short circuit current. I’ll stick with the NH fuse links.
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Thats what the disconnect switch is all about.
I still prefer the mcb, swich and fuse in one, all in one tight space. Nobody has space for a couple of nh fuses in an rv.
In my experience the mosfets save the fuses.
Series to increase voltage are 4 pole designs switching same time with common lever.
Fusing 230V AC, 48V Battery and 500V DC Moduls are completely diffrent matters.
The higher the voltage, the more loss is generated by a fuse. Therefore we have many diffrent fuse models on the market.
Another thing to consider for fuses is the breaking capacity. Midi/Mega fuses might be ok for old OPzS / OPzV cells but Lithium have considerable lower intrinsic resistance. Breaking capacities of 20kA or more are required for protection.
On the other hand, all BMS have build in Mosfet switches what should switch off faster than melting a fuse. Unfortunately, there are several cases, what will distroy any BMS discharge Mosfet. This is mainly a high inductivity between battery and load. At switch off moment, there is full voltage over drain-source but current through mosfet goes on because of the inductivity. For several microseconds the mosfet is hit by several kilowatts. Survival depends mainly from size of inductivity and start temperature of mosfet.
Specialists use SOA safe operating area diagramms to design reliable BMS switches. Therefore they have to specify maximum allowed inductivity for safe operation. As far as I know, no BMS shows such specification. To be honest: No user knows the inductivity of his installation. The only rule is to keep battery wires as short as possible. For this reason, a short circuit protection melting fuse is always recommendet for each battery. Nominal value can be much above average use current as overload protection is already done fine by the mosfet with shunt current meassurement.
To come back to the thread topic: Attached is a photo of NH00 160Amp DC and AC Fuses and sockets. Jean Mueller is specified for DC use up to 200V, ETI is only AC specified. Disconnect sockets sold by Rittal and Hager are produced by EFEN.
As you see, the 80V DC specified NH00 fuse with gBat characteristics has longer terminals as the normal gG/gL characteristics what is AC specified.
For Efen disconnectors, only AC fuses fit. For ETI disconnectors, AC and DC fit. For Jean Mueller, AC and DC fit also, but using AC model in DC disconnector is not recommended as the contacts are only covered partitially.
Benefit of DC spec 80V fuse for use with battery or Multiplus are 9 instead 12 Watt power dissipation for 160 Amp nominal current. Further, the DC NH00 fuses are available up to 800 Amp while the AC NH00 stops at 160 Amp with the greatest nominal value. Anyhow DC sockets above 160 Amps are special expensive models what consist of pure silver metal instead copper.
Unfortunately, discourse seems not uploading any jpg photos in this thread.
Photo link is here: Jpg upload test
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ABB XLP series NH fuse disconnects are rated DC-21B and from NH000 to NH1 available in single, double and triple variations.
The NH1 versions are HUUUUUGE, but as far as battery safety is concerned, I would say those are the best option.
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Hi,
I’m a bit late, but I can contribute something from my installation.
I have also used NH00 fuse-disconnectors to protect my multis and RS450/100.
For that I used the triple holders from Rittal. The charm is that you can isolate all 3 multis at the same time.
The NH00 from Simens have a switching capacity of 25 kA DC (IEC 60947-2) and range from 35A to 160A
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Thanks everyone for all the suggestions and advice. I’ve decided to go for the Jean Muller Keto NH 00 disconnectors and fuses. for the battery-inverter cablers. 160A is plenty for my installation as I’ll be running at a nominal 100A. I’ve chosen Mersen 38x10 1000V DC 15A PV fuses and holders for the PV cables.
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