Actually, while we are on the subject, I would have thought that it would be better to have the standard Greenpower circuit switching the +ve rather than the negative to the brake/horn/relay. This reduces the chances of shorts to the chassis (in case it is connected/used as -ve), but more importantly makes it easier to understand and test with a meter. Car and general electrical/electronic circuits have a common ground that is generally the -ve pole and switch the +ve side.

I would suggest on your comment of 60A+ fuse (F1) would be too low as many people have blown 100A multimeters and fuses when not using a motor controller as the motor can easily draw 80A+ on startup if people aren't careful.

mowicus is right
We have an ammeter on the steering wheel, and every time that you push the throttle, even if the car is doing 30mph, it draws 80, and if it is doing less than 20 it gets up to 100A.

A 60A breaker should be sufficient for any car as long as it's push started, it won't trip as soon as it reaches its rating, only if it's exceeded for a significant period of time; however it should trip instantly at the motor's stall current or if there is a short.

It's a similar situation with automotive Maxi fuses, the spec sheet below shows that a 60A fuse with handle 80A for 90 seconds, 105A for 10 seconds, and blow in under 0.1s at 130A (stall current). If a motor is drawing 80A for 90seconds it will be close to permanent damage.

http://www.aeroelectric.com/Mfgr_Data/Fuses_and_Current_Limiters/Bussman/MAXI_Specs.pdf

cookie
the Amps go down to about 27A when you have had your foot on the go pedal for about 50 secs

if youre drawing 100 while doing 20 theres something seriously wrong... or we havent calibrated it properly

Don't think new batteries will deliver anywhere near 100Amps. Am I correct ? Have reduced size of wiring to 50 amp max on new car hoping this will be sufficient.
Ashley

"Don't think new batteries will deliver anywhere near 100Amps."
Hmm, I dunno, if you short one of them, I would have thought you could get rather more than 100A.

SEC quote 1500A short circuit current.

With the quoted battery peak current of 1500A then we can calculate the batteries approximate internal resistance. This will be 12/1500=0.008 Ohms (V/I=R).
Two batteries in series would thus have a resistance of about 0.016 Ohms.
The motor has an internal resistance of about 0.18 Ohms. So the peak current that can flow will be 24 / (0.016 + 0.18) = 122 Amps (V/R=I). There is little difference from the old batteries as the motors resistance dominates.
However with a short there will be 24 / 0.016 = 1500Amps flowing. As andyfriar states if the fuse protecting the wiring is 70Amps then the wire it is protecting should be capable of handling 70 Amps continuous. It would have nearly 1500Amps flowing with a short (be a bit less due to the wires resistance to the short) and the wire needs to not get too hot before the fuse blows. This will be based on: the time for the fuse to blow, the resistance of the wire and the heat dissipation of the wire. There are some tables the IEE give for wire size versus current that could be used. I suspect that if the wiring is rated at 50 Amps continuous, it should be ok in the short lengths used in a Greenpower car but really it should be able to handle greater than 70 Amps (or whatever the fuse is) continuous to be fully safe.
I would use a minimum around 10mm^2. We use 16mm^2.

Of course, the point is, that irrespective of the size of the high current fuse, the low current wiring is not being protected by it, and hence there is a fire risk.

"the low current wiring is not being protected by it, and hence there is a fire risk."

True, we are getting rather off topic :D