[Pb Cruiser]

Hi all. First time poster here. I'm currently converting a '95 Geo. My first conversion and it's going well, no surprises so far. I'm probably 25% in to it and I have one of a thousand questions: I see circuit breakers used in conjunction with fuses. Is the breaker used to open the traction voltage pack for ease and safety regarding maintenance? If that is the case can't one of those 500 amp battery disconnects be used for the same purpose? They are much less expensive.

 

[Mr. Sharkey]

With the car standing still, there probably isn't a significant difference between the switch and a breaker. The breaker, though, is designed to interrupt the circuit under full load and do it without arcing or catching fire. The switch, on the other hand, would turn into a fireball if opened with more than a few dozen amperes going through it at EV traction pack voltages.

It all depends of what you expect to use it for. A switch could be a good safety item for use when working on the car, but a very poor circuit interrupter if needed to cut the power after a controller failure resulting in "full on" mode.

 

[Pb Cruiser]

I see. Should the rating of the circuit breaker be somewhat lower than the fuses but yet high enough to allow the controller to admit proper current to the motor through a variety of conditions?

 

[Nick Smith]

The circuit breakers most commonly available (Airpax) are rated at 250A continuous which is fine for most EV's. How they manage to work with higher amperages is because they have a trip delay which is relative the amount of overcurrent that is going through.

For example:
250A - all day no problem
300A - maybe 5min to trip.
350A - 2 min. to trip
400A - 20 sec.
500A - 1 sec
550a - pack fuses already blew at 500A!

 

[Greenflight]

I'm using a 250A breaker, and I've only had one nuisance blow. Works great. I got it off of ebay for about 60 bucks. I think there's a few others on there. Some names you can search on are Airpax, Xantrex, and Outback. You should be able to get one pretty cheap.

I also use a 450A delay fuse, in case the circuit breaker doesn't cut it for some reason.