# High Amp Fuses



## evmetro (Apr 9, 2012)

I run shawmut 300 volt 500 amp fuses with all my 1238 controllers. I still don't know everything that I would like to know about fuses, but I see that this is a very popular main fuse.


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## Ivansgarage (Sep 3, 2011)

Caps18 said:


> So, I finally received my Nissan Leaf battery disconnect today, along with a fuse inside of it.
> 
> The question I have is how do I know what size or rating of fuse I should be using?
> 
> ...


Hi caps these breakers are at autoparts stores they come in 20-40-50 ect amps you can allso disconnect them with a push of a button for your 12v aux battery.

Why haven't you posted no pics of your truck?


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## frodus (Apr 12, 2008)

So best thing to do is to look at a datasheet for a particular fuse.

I get my fuses from www.discountfuse.com and usually get something in the A15QS line (150V). They also have 300V, 500V and 690V (A30QS, A50QS and A70QS respectively). They're great fuses and I think a pretty decent value. 

Just click on a fuse, like the 300A for instance:
http://www.discountfuse.com/A15QS300_4_Mersen_Ferraz_Shawmut_Amp_Trap_Fuse_p/a15qs300-4.htm

Then click "technical specs" tab, then click on the link for the PDF
http://www.discountfuse.com/v/vspfiles/downloadables/Ferraz/PDF/a15qs.pdf

If you look at page D6, there are some graphs with a time scale and amperage scale. Part of chosing a fuse has to do with not only current, but how long it takes to clear. Sometimes you'll want it to be able to hit 650A, but the continuous current is usually much less. So lets say you choose 650A and you want the fuse to clear after 1 minute at 650A (I doubt you'd use 650A on the curtis for longer than 10 seconds in most cases unless something is wrong). 

So go 650A and 1 minute on the graph, and look at that curve. I go up from 650A until I hit 60s on the side, and that line is associated with the 400A curve. So a 400A fuse would cover me for 1 minute at 650A, and clear other amperages according to that curve. 350A-450A is about right depending on application. Lighter car, go less amperage, heavier truck go 450A.


WRT the fuse on the DC-DC, Everything that taps off the high voltage should get its own fuse IMHO. You could tap off after, but that doesn't protect the wiring between the DC-DC and the High current fuse. I'd get a A150QS at the correct current for your DC-DC. That way the wires are protected. You can put this before or after the main fuse, but I'd definitely fuse the DC-DC.


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## evmetro (Apr 9, 2012)

This is a fantastic guide for the DIY level EV builder. I have navigated through fuse specification charts and felt overwhelmed...


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## Caps18 (Jun 8, 2008)

https://www.pecj.co.jp/en/fuse/ev/ev.html

This is the fuse that came with the Nissan Leaf battery disconnect. It is the 225A one. Looking at the current vs time chart, it looks like it can handle 450A without ever blowing, at 500A it takes 30 seconds, and at 650A it would take 8 seconds. If there is a short and the amperage gets to 2000A it would blow in 0.2 seconds. Did I read that right? Do those values sound like they would protect the wires, controller, and contactor?

Even though the 600A one would fit barely, I looked at the spec sheet and found that it didn't work the way I had thought. I had thought that at 601A it would have tripped. The 600A one could get 900A through it for 1000 seconds before it ever tripped. It might only blow in an extreme short situation, but everything else would be fried too if I am understanding the charts correctly.

Now...why didn't HPEVS, Nissan, or EVTV (or any other parts vendor) give me the right fuse or provide these spec sheets? Well I can't say that entirely. Most of the time people would use the fuse to go in the middle of the battery pack, so what I am doing might not be typical, but it still should be better explained...

Pictures and video of the build will be coming. I am working on getting all the parts here and a plan devised first.


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## frodus (Apr 12, 2008)

It will blow at 450, but its over 100seconds. Looks like its about right actually. The likelihood of you being at 650A+ for over 8seconds is low, but not unheard of. That fuse is probably fine for what you're using it for. Its there to stop current flow and prevent sustained arcing that would lead to fire.

*And by the way:*
It's not HPEVS or anyone else's job to design your system for you and spec out every single part. Part of an EV involves disconnects, cables, batteries, BMS, FUSES, etc. which are completely up to you. None of these companies have any idea of what other devices you're using and it is not their job to integrate it for you. A fuse is tricky, because the Controller is just ONE of many loads connected to the batteries. 

EVTV gave you the pinout. Its a very simple hall effect that I figured out in 5 seconds after looking at it. 

You bought cells that were intended to be used in a Nissan vehicle where there is no expectation for someone to use them in a DIY vehicle, thus no reason to provide the general public any documentation. 

*I'm going to offer some useful advice:* Please don't blame everyone else for your lack of experience and knowledge. This is OEM level stuff you're purchasing as DIY components and a certain level of knowledge and ability are REQUIRED. That falls on you, not anyone else.


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## Caps18 (Jun 8, 2008)

I'll give you NISSAN wouldn't really know that I needed the spec sheets for their fuse since they would think that I am just replacing a part that they assembled. But the other EV component companies are based on selling parts to people who they should want to be successful. I'm kind of surprised they don't come up with a 'standard' kit that includes batteries and boxes if they want to expand the number of people doing this to sell more motors and stuff. I know I'm not an electrical engineer, but I think that some of these typical parts should be explained and shown how they get used in other people's builds.

And I knew it was a Hall effect throttle, and HPEVS did provide a good wiring diagram. But there was no pin out for the throttle pedal and I still don't know what the official connector is to get the wires out of it. I'm not 100% sure that the throttle pin out that I found is correct until I test it either. I did see something today on a website that I need to use sensor 1 instead of 2, since 2 starts at 4.5V and goes down when you press the pedal. That is why you have your drive wheels up in the air when you turn it on for the first time...


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## Tesseract (Sep 27, 2008)

Caps18 said:


> https://www.pecj.co.jp/en/fuse/ev/ev.html
> 
> This is the fuse that came with the Nissan Leaf battery disconnect. It is the 225A one. Looking at the current vs time chart, it looks like it can handle 450A without ever blowing, at 500A it takes 30 seconds, and at 650A it would take 8 seconds. If there is a short and the amperage gets to 2000A it would blow in 0.2 seconds. Did I read that right? Do those values sound like they would protect the wires, controller, and contactor?


First off, the only thing you should rely on a (properly specified) fuse to protect is overheating of the wiring. Even so-called "semiconductor" fuses will usually take longer to blow than the semiconductors they are supposed to protect. In other words, do not expect a fuse to protect a motor controller from a downstream load failure (e.g. - a turn-to-turn short in the stator windings). Not without having to use so low an amperage for the fuse that it will blow from normal operating conditions, anyway.

Secondly, the plot for the 225A fuse in the link you provided indicates it will blow in ~60s at ~450A, not carry that current indefinitely. It will carry 600A for 10s, a little over 1000A for 1s and ~2kA for 0.1s. I would use this fuse to protect (US) 2/0 wiring.



Caps18 said:


> Even though the 600A one would fit barely, I looked at the spec sheet and found that it didn't work the way I had thought. I had thought that at 601A it would have tripped.


601A is just 0.17% higher than 600A... not even an electronic circuit breaker is going to be that accurate, so definitely don't expect a glorified piece of wire (ie - a fuse) to be that accurate!



Caps18 said:


> Now...why didn't HPEVS, Nissan, or EVTV (or any other parts vendor) give me the right fuse or provide these spec sheets?


I agree with frodus that it is up to *you* to select the size of the fuse for the battery pack wiring. Think about it: if the parts vendor recommended, say, a 500A fuse but you used some leftover #8 THHN to wire up your battery pack that would just end in tears...


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## arklan (Dec 10, 2012)

just want to say that I found this thread to be extremely informative and helpful


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