Question about Fuses

1408 Views 3 Replies 3 Participants Last post by Tesseract, Mar 2, 2011

Duncan

Discussion Starter · Mar 2, 2011

Hi Guys
I am starting to think about fuses
I had a look at the specs on type J -Time Delay and Type Tjs - Fast Blow

The results surprised me, I was expecting to be using a 500 or 600 amp fuse in the motor circuit to go with an OpenRevolt 500 amp controller

The specs seem to say
J -Type 200 Amp
Time to blow(sec) Current
0.01 ---------------2400
0.1 ----------------1800
1 ------------------1500
10 -----------------1100
100 ----------------500
300 ----------------400

Tjs -Type 200 Amp
Time to blow(sec) Current
0.01 ---------------2000
0.1 ----------------1300
1 ------------------1000
10 -----------------600
100 ----------------300
300 ----------------250

From this a 200 amp J Type would probably be OK for my motor - it would need 100 seconds on 500 amps to blow

The battery (100Ah TS) could be protected by a 200 amp fast blow Tjs Type as it would take 100 seconds at 3C to blow

Am I reading this correctly?

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major

· #2 · Mar 2, 2011

Duncan said:
I was expecting to be using a 500 or 600 amp fuse in the motor circuit to go with an OpenRevolt 500 amp controller

Hi Dunc,

I have never seen or heard of a fuse in the motor circuit. The fuse needs to be in the battery circuit.

major

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Duncan

Discussion Starter · #3 · Mar 2, 2011

Thanks Major

I was going to put fuses in both!

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Tesseract

· #4 · Mar 2, 2011

Duncan said:
From this a 200 amp J Type would probably be OK for my motor - it would need 100 seconds on 500 amps to blow

The battery (100Ah TS) could be protected by a 200 amp fast blow Tjs Type as it would take 100 seconds at 3C to blow

Am I reading this correctly?

I wouldn't put a fuse in the motor circuit - if it were to open up from high current then the motor's inductance will create a huge overvoltage spike (by jumping across the fuse terminals) to maintain current flow. Really a bad idea. It's why I don't like to see contactors in the motor circuit, either.

So you put the fuse on the battery side, and yes, it should be a fast-blow fuse (aka "Semiconductor" fuse, which I swear are named that because the semiconductors they are supposed to protect will almost always lay down their lives to protect the fuse instead...

)

We like to use Ferraz-Shawmut (now Mersen) Class-T fuses. The recommended current rating for the fuse technically depends on what the wiring can withstand - don't expect the fuse to blow before the controller or motor or batteries die a horrible death unless you are willing to use a very low current fuse (and deal with lots of nuisance faulting).

For example, we recommend - absent any other analysis - that one use a 400A fuse to protect 2/0 wiring in an EV installation. This would NOT be acceptable for a commercial wiring installation (ie - not "code approved") but it will give reasonable protection in a "machine wiring" application.

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