# Fuse



## onegreenev (May 18, 2012)

Been hunting for a small 1/2 amp 250volt DC ceramic or sand filled type fuse for my setup. Been using the glass type but would rather use something better. All I find in that amp rating are AC voltages and no DC voltages. That nice little video from EVWEST got me thinking I do really need a proper fuse. It is for full pack voltage but only 1/2 amp. It goes to the controller. Any ideas on where to find actual DC volt rated fuses of this amperage and ones that will actually break full pack voltage in the event of a short. Id hate to see the video replayed in my vehicle live. 

Pete


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## major (Apr 4, 2008)

onegreenev said:


> Been hunting for a small 1/2 amp 250volt DC ceramic or sand filled type fuse for my setup. Been using the glass type but would rather use something better. All I find in that amp rating are AC voltages and no DC voltages. That nice little video from EVWEST got me thinking I do really need a proper fuse. It is for full pack voltage but only 1/2 amp. It goes to the controller. Any ideas on where to find actual DC volt rated fuses of this amperage and ones that will actually break full pack voltage in the event of a short. Id hate to see the video replayed in my vehicle live.
> 
> Pete


http://www.ferrazshawmutsales.com/pdfs/CC4142227.pdf

or

http://www.ferrazshawmutsales.com/pdfs/DCT.pdf

As low as 2 or 5 Amps. Should work for you with #20 or 18 wire.


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## PThompson509 (Jul 9, 2009)

www.discountfuse.com sells those fuses among many others. I've been very happy with their people and their product.

Cheers!

P.S. Just a happy customer, not an employee of discountfuse.


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## onegreenev (May 18, 2012)

Thanks Major but 2 amps is still higher than the recommended 1/2 amp fuse. I'll sent this to them to see what they say. If given the OK then I will pursue these fuses.


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## favguy (May 2, 2008)

I wish EVWest had tested 250v AC ceramic fuses instead of just 12v automotive ones, although still not rated for DC use, I suspect they'd perform much better...

Come to think of it, I might just try one myself on my 144v system and see how it holds up ...


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## PhantomPholly (Aug 20, 2008)

Why not use a circuit breaker? They don't have to be replaced.

Didn't look very hard, so this one is 2amps not 500mAmps but I suppose they come in all sizes. 

On the other hand, my electronics guy once explained to me that "fuzes and circuit breakers don't protect your equipment - they only protect your wires." So if your wires can handle 2amps then this would be ok.


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## EVfun (Mar 14, 2010)

onegreenev said:


> Been hunting for a small 1/2 amp 250volt DC ceramic or sand filled type fuse for my setup. Been using the glass type but would rather use something better. All I find in that amp rating are AC voltages and no DC voltages. That nice little video from EVWEST got me thinking I do really need a proper fuse. It is for full pack voltage but only 1/2 amp. It goes to the controller. Any ideas on where to find actual DC volt rated fuses of this amperage and ones that will actually break full pack voltage in the event of a short. Id hate to see the video replayed in my vehicle live.
> 
> Pete


I don't know where to find one with a 250 volt DC rating, but in the common 1/4 inch by 1-1/4 inch size the ABC series fuse is a ceramic body fast blow fuse with a 125 volt DC rating. It would likely work, it would be a lot better bet than a glass body 1/4 by 1-1/4 fuse. If you wire that circuit up with a fair length of 20 gauge wire there shouldn't be 125 volts at the fuse at 1/10th its current interrupt rating. 

I've blown up common glass body fuses that tried to break excess DC voltage. I don't use them on EVs anymore.


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## palmer_md (Jul 22, 2011)

EVfun said:


> I've blown up common glass body fuses that tried to break excess DC voltage. I don't use them on EVs anymore.


Have you seen the video mentioned above? Start at 1 minute 29 seconds.

http://youtu.be/rzIvgC09ji8?t=1m29s


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## Tesseract (Sep 27, 2008)

onegreenev said:


> Thanks Major but 2 amps is still higher than the recommended 1/2 amp fuse. I'll sent this to them to see what they say. If given the OK then I will pursue these fuses.


Fuses are for protecting *wiring* from overheating, not the actual electronic device supplied by said wiring. In other words, one never relies on the fuse to protect an electronic device from failure. Either a 5A or 7.5A fuse is commonly used to protect 18AWG (1mm Ø)wiring with 90C rated insulation.



EVfun said:


> ..in the common 1/4 inch by 1-1/4 inch size the ABC series fuse is a ceramic body fast blow fuse with a 125 volt DC rating. It would likely work...


Energy goes up with the square of voltage, so no, you don't really want to push a fuse's voltage rating. 

That said, ABC series fuses are cheap, so if the device connected to the traction battery draws less than a couple amps then fault current can be limited by inserting a 1 ohm/10W wirewound resistor in series with the fuse. This will also help reduce the effect of controller ripple (if such a concern applies).


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## EVfun (Mar 14, 2010)

Tesseract said:


> Energy goes up with the square of voltage, so no, you don't really want to push a fuse's voltage rating.
> 
> That said, ABC series fuses are cheap, so if the device connected to the traction battery draws less than a couple amps then fault current can be limited by inserting a 1 ohm/10W wirewound resistor in series with the fuse. This will also help reduce the effect of controller ripple (if such a concern applies).


Wasn't that what I was suggesting with a length of 20 gauge wire? The idea was that a fuse that could interrupt 10,000 amps at 125 VDC could interrupt somewhat less than 2500 amps less at 250 VDC.

A 20 gauge wire has about 10 milliohms a foot. 10 feet of 20 gauge wire has about 0.1 ohms of resistance. That will limit the current at 250 volts to 2500 amps all by itself (and every connection, plus the fuse itself, add resistance.) So I would take a bet that if you wire for function you can set things up so that an ABC fuse can handle a 250 VDC system if the current is less than 1 amp.


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## Tesseract (Sep 27, 2008)

EVfun said:


> Wasn't that what I was suggesting with a length of 20 gauge wire? The idea was that a fuse that could interrupt 10,000 amps at 125 VDC could interrupt somewhat less than 2500 amps less at 250 VDC...


Fuse ratings don't quite work that way; the voltage rating of the fuse depends greatly on the distance an arc must travel, and above 125-150VDC rating a fuse pretty much needs to have some means of quenching the arc formed when the fusible link melts (such as filling the fuse cartridge with quartz "sand").

Also, right off the top of my head I don't think 20 awg wire will tolerate 2500A for even 10ms, which is generally the minimum time given for a fuse to blow. Yep... looks like 18 AWG is rated for 900A peak let-through for a half-cycle (~8-10ms), so #20 will be around half that. Let wires be wires, fuses be fuses and resistors be resistors...


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