# High current fuse



## Tomaj (Oct 3, 2011)

I am converting Aprilia RS125. Setup consists of ME913, Kelly controller KHB12601 and A123 battery pack, total 130V.Wires are 95mm2.
Controller max. current for 1min is 600A.

Which fuse should I use? 500A or 600A?

Something like this...
http://www.discountfuse.com/A30QS600_4_Mersen_Ferraz_Shawmut_Amp_Trap_Fuse_p/a30qs600-4.htm


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## EVfun (Mar 14, 2010)

Or even something like this:
http://www.discountfuse.com/A15QS400_4_Mersen_Ferraz_Shawmut_Amp_Trap_Fuse_p/a15qs400-4.htm
There is no reason to go overkill on the voltage rating, are you expecting the peak pack voltage to exceed 150 volts?

If you look at the specs on that fuse it can hold 600 amps for 3 minutes, the controller can only hold it for 1 minute and has a 300 amp continuous rating. A 400 amp fuse should be sufficient. Plenty of cars powered with Curtis 1221 controller ran around with 250 amp fuses.


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## Tesseract (Sep 27, 2008)

Tomaj said:


> ...Wires are 95mm2.
> Controller max. current for 1min is 600A.
> 
> Which fuse should I use? 500A or 600A?...http://www.discountfuse.com/A30QS600_4_Mersen_Ferraz_Shawmut_Amp_Trap_Fuse_p/a30qs600-4.htm


Neither, for a couple of reasons. The first is because the maximum recommended current density for copper is 5A/mm², but the maximum allowed for any given real-world wire depends on the temperature rating of the insulation. A typical 90C or 105C rated insulation might let this size cable carry 280-320A (at 20-25C ambient). 

The second reason a 500-600A fuse won't be appropriate here is because fuses take a certain amount of time to blow, even at relatively high overcurrent. In the datasheet for the Mersen A30QS series fuses (an excellent choice for protecting the battery circuit wiring in an EV, btw) there is a chart that compares current vs. time for the different fuse amperage ratings. Note how a 500A fuse will take 40 seconds to blow at twice rated current? That's bad news for cable that is rated for ~300A continuous. A better choice would be a 300A or 350A fuse, though there is quite a big gap in the length of time they can tolerate 600A (~18 seconds and ~180 seconds, respectively).


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## Tomaj (Oct 3, 2011)

I have not bought the wires yet, but I think 95mm2 welding cable should hold max.current 600A and constant 150A. It is also rated for 200 degrees celzius.

It looks like 350A fuse should be enough, or maybe 300A. I am going to check some more graphs.

Thanks


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## Tesseract (Sep 27, 2008)

Tomaj said:


> I have not bought the wires yet, but I think 95mm2 welding cable should hold max.current 600A and constant 150A. It is also rated for 200 degrees celzius.


Oh, sure, I didn't say there was anything wrong with the size of the cable. 95mm² is approximately equal to AWG 3/0 which is way more than necessary for the battery side of even the most ambitiously rated Kelly controller.


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## Ziggythewiz (May 16, 2010)

Tesseract said:


> In the datasheet for the Mersen A30QS series fuses


Wow. That 3000A fuse is impressive. I'd love to drive a car that needs that.


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## obsecure (Oct 31, 2012)

Tomaj said:


> I am converting Aprilia RS125. Setup consists of ME913, Kelly controller KHB12601 and A123 battery pack, total 130V.Wires are 95mm2.
> Controller max. current for 1min is 600A.
> 
> Which fuse should I use? 500A or 600A?
> ...


 both fuse can work but in my opinion 600A is better for your ride


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## iop95 (Sep 4, 2012)

Fuses are designed to protect for shot-circuit events not for overload. Nominal current for a fuse must be egal or very little higher that maxim normal operating current in circuit. Fuse must protect for shot-circuit (current minim 10x of maxim normal operating currrent) cable, devices, etc. preventing blow-up or even fire / explosion. For overload (overcurrent) that mean currents in 1 to 10x range, there are other protection devices depending of circuit type / regulations / etc. In this case overcurrent sustained by controller it's limited internaly (maybe by thermal law/conditons) and for cables, an overcurrent in 1-5 times is supported in such amount of time depending of rated insulation, mounting / ventilation, ambient temperature, etc. If 600A is maxim normal operating current, should use a 600A nominal current fuse. Also, there are different curve response fuses that are suitable for protecting various devices (fast for semiconductors, slow for cables or similar).


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## Clarence (Oct 31, 2012)

I think some think is wrong in your engine and battery problem.If you look at the specs on that fuse it can hold 600 amps for 3 minutes, the controller can only hold it for 1 minute and has a 300 amp continuous rating.


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