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Selection of fuses for 600V+

1176 Views 6 Replies 6 Participants Last post by  csuich
Hi all,

long time diy-ev'er, working on an upgrade for an existing setup.
Going from 450V to 650 V(or higher) system and I have trouble finding the right fuses for the project.

Are there any known suitable 600+ volt fuses with 400A rating for EV's that do not resemble a counterweight or mass-damper? :eek:

I have included the carnage below from buying a fuse on ebay on mere voltage & current specs. (the fuse on the right is the old one I used for 450V)


1 - 7 of 7 Posts

· Registered
1,021 Posts
The Cooper-Bussman FWJ series is the best (only?) series that is rated for DC voltages above 600 VDC. But yeah, they are going to be big. There is no way around that.

Edit: yes, if you are going to only 650, then that FWP series would work, we usually go to 800 which does require the FWJ.

· Administrator
1,762 Posts
You could build your own, using a wire size calculator to do critical diameter.
That's called a "fusible link", and sometimes higher amperage devices have them too.

The fuse generally protects your wiring from being a fire hazard, not much else.

So if you're using wire that's 10 units thick, and you don't want it to melt in the event of a short, if you include a small section of wire that is 8 units thick, you know that in series, before the whole wiring system that is 10 units thick will become hot enough to melt, the thinner section that is 8 units thick will have already melted and broken the connection.

Wire doesn't melt itself to the point where it breaks at the same temperature that you'd want it to avoid reaching (you want to stop a few steps before it gets that hot, not right on the edge of it), so this means by choosing the right thickness of fusible link you can have the connection break before the heavier wire gets too hot. The bigger the difference between the two, the more safety room you give yourself.

After all, that's all a fuse is, a piece of wire that melts.

DC is particularly tough to snuff out, because the resistance of plasma in an arc is perhaps 2% the resistance of air. That means that even though a gap in the wire opens up, if power was already flowing, it may continue to flow through the plasma in the gap. In AC isn't not as bad because the power shuts off 120 times a second (for household AC).

Here's a short, fun video demo of that:

So DC fuses, and switches, have to be a lot better at snuffing out arcs. They'll be filled with different things (sand) to break the plasma arc and not just let it jump through air.


However, I wonder if you could just daisy-chain two of the smaller fuses in series. As long as the total arc gap can handle a given voltage, does it matter whether it's comprised of a single fuse or many?

· Registered
14 Posts
There is an interesting paper on fuses in parallel.

What is your max continuous operating current?

As I read and interpret the paper
Accounting for operating and temp deratings (Their paper assumed 85C)
I think you could use 2 600V/500A fuses in parallel for 400A operating current instead of a single 630A single fuse with the same deratings.
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