# Battery disconnects and cut-off switches



## dragonsgate (May 19, 2012)

Check out high voltage turning it on turning it off thread. Here is a picture of my solution.


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## madderscience (Jun 28, 2008)

Such a disconnect is a critical safety feature on any EV, especially a DC motor powered one. 

Not only can you cut power under load (presuming the disconnect is located where you can reach it) but you can also conveniently disconnect the battery when working on things. 

Common solutions are the mechanical linkage disconnect applied to an anderson connector as in the prior post, and using a DC rated circuit breaker of the right size. These can be purchased from EV parts retailers, or depending on what it is, ebay and surplus electronics resellers. The circuit breaker solution is a bit more expensive (up to a couple hundred $ in most cases) but has the advantage that it will automatically break the connection, and is designed for more frequent cycling than an anderson plug.

a discussion of the solution I came up with for my car is at http://amphibike.org/blog/scion-xb-...xb-ev-battery-boxes-and-high-voltage-conduit/

If you go the circuit breaker route, make darn sure it is DC rated. an AC rated breaker may fail to open under load.


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## Matej (Dec 4, 2015)

Thank you for the information. Sorry for not searching better. I looked if such a thread already existed but I did not find it when I first searched.

Would the Leaf disconnect be alright for use in a DC motor application?
It is rated for 450V DC with a 225A fuse inside.
Not sure how reliable these numbers are, but apparently it can handle 110% Ampere load for 4+ hours, 200% for 5-100 seconds, 300% for 0.5-15 seconds, and 500% for 0-1 seconds, and it has a 2000A breaking capacity.
If anyone has experience with it, is it possible to potentially replace the fuse with a higher rated one?


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## madderscience (Jun 28, 2008)

All batteries are DC  The reason for DC motor powered conversions needing an extra layer of protection is if the controller shorts out the motor can run away. This cannot (as easily) happen in an AC motor powered conversion.

Depends on the specs of your build.

Obviously, for a leaf the specs are perfect.

If you are building a car with the same voltage battery and same kilowatt (horsepower) rating then it should work well.

If you are building a car with higher voltage battery, or higher amp pull (even if lower voltage) then it might not do the job.

If you just need a fuse (usually recommended to be in addition to a disconnect, as you can't manually disconnect a fuse) its easy enough to find appropriate fuses on places like ebay, so don't let that stop you)

Basically for fuses, you want a "semiconductor fuse" whose DC voltage rating meets or exceeds the max on charge voltag e of your pack, and whose amp rating is equal or slightly above the max expected amps to be pulled from your battery. To small, and it will pop when you simply step on the throttle; too large and it might as well not be there.


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## Duncan (Dec 8, 2008)

Hi Madder
I disagree about the size of the fuse,
Fuses have an over-current/time relationship - if you are just over-current they will take a looong time to blow
Most of us can only use max current for a few seconds so we can use a much lower rated fuse,
I can use over 800 battery amps - but my 400 amp fuse does not blow because I can only use 800 amps for a couple of seconds


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## bigmotherwhale (Apr 15, 2011)

duncan is spot on about the fuses, they are quenched using glass granules. I would take his recommendation.


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## jeffcoat (Apr 16, 2012)

I use the Leaf disconnect in one of our EV conversions, but since we draw up to 700A, we removed the fuse from inside the disconnect and replaced it with a copper bus bar. Opening it up and removing the fuse was easy; however, our replacement fuse would not fit inside. We put a separate 500A DC fuse in line with the disconnect, so that we still have a fuse in our pack as well. We use the disconnect strictly when performing maintenance on the vehicle, as it is inaccessible from inside the passenger compartment.


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