# fuses: where and how many?



## halestorm (Apr 28, 2009)

I'm thinking I should add one or more of the HV/high current fuses like A30QS500-4 to my battery pack. Where should they go and how many should there be? Attached is a layout of my battery pack. Would it be sufficient to have one in line with either the most positive or most negative lead? Or perhaps one in each of the parallel lines between the front and rear packs? I don't want to sprinkle them around unnecessarily since they're $120 apiece. Thanks.


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## RIPPERTON (Jan 26, 2010)

Single fuse in the negative in cable where it joins from 2 into one.
What kind of cells are they, Chevy Volt?


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## halestorm (Apr 28, 2009)

RIPPERTON said:


> Single fuse in the negative in cable where it joins from 2 into one.


 Figures you'd say that, since that's where I have the least amount of space to install one of these monster fuses. I have more room in the front box. Why do you say the negative leg?




RIPPERTON said:


> What kind of cells are they, Chevy Volt?


yes


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## arklan (Dec 10, 2012)

i got my fuses for $30 each off ebay, they came from an american supplier of old parts, they came as a group of 3 and i put my fuse as close to the negative battery as i could, i had one in between my packs for a while but i took it out when that one blew


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## RIPPERTON (Jan 26, 2010)

halestorm said:


> Why do you say the negative leg?


Spacing the components out so they have room.
Usually the contactor is in the positive line.
they both should be in the engine bay so you can check them.
You could put it in the positive too.


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## EVfun (Mar 14, 2010)

Generally, one fuse in each battery box or right next to it. The idea is that if shorting occurs it most likely will be a cable that goes between battery boxes getting damaged and shorting to the chassis. If a second cable between battery boxes doing the same what could happen? You want to know that no matter which two that happens to the pack will not dump all its energy in a short circuit. Two undetected shorts are normally unlikely, but could happen in an instant in a traffic accident.


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## z_power (Dec 17, 2011)

I know these are "safe" chemistry but what if one or more cells get shorted inside? It could end up as two series strings connected in parallel, where one's OCV is for example 180V and another's 175V; large ballancing current flows trough interconnects without any fuse... I'd use individual fuse with 1/2 rating on each serial string.
PS had this happened with NiMH, caugt fire thanks to interconnecting cables insulation melting and shorting to sheetmetal.


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## skooler (Mar 26, 2011)

EVfun said:


> Generally, one fuse in each battery box or right next to it. The idea is that if shorting occurs it most likely will be a cable that goes between battery boxes getting damaged and shorting to the chassis. If a second cable between battery boxes doing the same what could happen? You want to know that no matter which two that happens to the pack will not dump all its energy in a short circuit. Two undetected shorts are normally unlikely, but could happen in an instant in a traffic accident.


+1 on this.

The uk spec asks for a fuse in each battery box and a fuse for the whole system.


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## dougingraham (Jul 26, 2011)

Best practice would be a fuse in each battery box. Fuses are there to protect the cables in the event of a short.

That is an odd way to do your batteries. I would tie the two boxes together with a single cable instead of trying to keep the strings separate.


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## bigmouse (Sep 28, 2008)

RIPPERTON said:


> Usually the contactor is in the positive line.
> they both should be in the engine bay so you can check them.
> You could put it in the positive too.


I would certainly advocate for using a contactor on each terminal. This is what the Chevy Volt and other EVs do. They do it so that you can remove the battery and not have voltage present on any external terminals. It's a good idea in a conversion as well because it allows you to work on motor controller connections without risk of HV being present.

A compromise would be to install a resistor across one of the contactors, close the other one to precharge, then the one with the resistor to drive.

As for fuses, definately fuse the parallel strings from each other. I would use a setup similar to what z_power described with the added safety of the same precautions taken in each battery box.

In your case, I'd put fuses on the positive terminals of banks 0 and 8, as well as 2 and 10 (especially if you're going to parallel mid-pack and bring one cable out between the two boxes). You could do it on the appropriate negative terminals instead if that's more convenient.


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