LocostBuilders - powered by XMB

Starter motor reverse fuse size??

woodsy144 - 20/8/23 at 12:01 PM

Hello all,
Been trying out my reverse system but keep popping the fuse.
My system has the starter motor engaging a gear attached to the engine sprocket, and then through the chain and diff.

My thinking is maybe the fuse is too small.
I'm curious to know what others are using?

Thanks.

obfripper - 20/8/23 at 12:41 PM

You need to allow for approximately 6x the running current of the starter, ie if it is 1.2kw rated, running current is 100a and peak current while going from standstill to normal operating rpm will be around 600a.

A running current rated fuse may be ok briefly above its rated capacity, but will blow with any continued high load. Moving the car means that the fuse blows if the motor doesn't get to speed quick enough, uprating the fuse to cover the peak current should cover this providing the wiring is sufficiently rated.
.

Dave

adithorp - 20/8/23 at 04:40 PM

All the ones I've delt with (removed) have been wired like most starter motors, ie. Un-fused feed to the starter.

Mr Whippy - 21/8/23 at 06:29 AM

quote:
Originally posted by adithorp
All the ones I've delt with (removed) have been wired like most starter motors, ie. Un-fused feed to the starter.

Speaking as someone who has a car with no fuses at all

I think adding a fuse to a large motor like that is a very good idea. It could be located some distance from the battery and so has potential for wiring damage (especially in a crash) and then rather an epic bit of meltdown going on. Tbh I'm sure there are fuses for the starter in modern cars, even my old Fiesta I think it is in the main fuse box like this. If you have a 3D printer there's a nice little housing to make to hold one

Description

coyoteboy - 21/8/23 at 10:12 AM

Get a slow-blow fuse rated for twice the running current, it will blow if the motor is stalled but ignore the initial start-up current.

Bear in mind, whatever fuse you get needs to be rated lower than the wiring you use - if you run a 600A fuse you need >600A capable wiring really, which is some beefy copper.

[Edited on 21/8/2023 by coyoteboy]

gremlin1234 - 21/8/23 at 10:55 AM

quote:
Originally posted by coyoteboy
Bear in mind, whatever fuse you get needs to be rated lower than the wiring you use - if you run a 600A fuse you need >600A capable wiring really, which is some beefy copper.

yep, the fuse is there to protect the wire.

woodsy144 - 21/8/23 at 11:03 AM

quote:
Originally posted by coyoteboy
Get a slow-blow fuse rated for twice the running current, it will blow if the motor is stalled but ignore the initial start-up current.

Bear in mind, whatever fuse you get needs to be rated lower than the wiring you use - if you run a 600A fuse you need >600A capable wiring really, which is some beefy copper.

[Edited on 21/8/2023 by coyoteboy]

Yeh that sounds like a plan.
My battery is mounted directly next to the starter motor to try and keep the run as short as possible.
Trying to find a slow burn high amp fuse is going to be the next challenge. I have seen slow burn small amperage fuses, but not big boys (ie around the 250 / 300 amp mark)

coyoteboy - 21/8/23 at 11:12 AM

These guys show time vs overcurrent rating data, and seem to do a 250A version. Resettable.

gremlin1234 - 21/8/23 at 11:40 AM

rs do a (huge) range
how about this one?
Littelfuse 400A Purple Time Delay Car Fuse, 32V dc
https://uk.rs-online.com/web/p/car-fuses/8781299?gb=b

woodsy144 - 24/8/23 at 11:09 AM

I have changed the fuse to 200amps and gave it a run.

https://youtu.be/Zcqo5ArfnYw

The battery was a bit low, so with a charged battery and a little move of a 'run up' Im hoping ill be able to get out of driveway (which has a slope).
It was noted that the cables did get a little warm. But I did try it 4 times one after another.

Mr Whippy - 24/8/23 at 11:33 AM

quote:
Originally posted by woodsy144
I have changed the fuse to 200amps and gave it a run.

https://youtu.be/Zcqo5ArfnYw

The battery was a bit low, so with a charged battery and a little move of a 'run up' Im hoping ill be able to get out of driveway (which has a slope).
It was noted that the cables did get a little warm. But I did try it 4 times one after another.

nice car

coyoteboy - 24/8/23 at 11:40 AM

Seems quite a high gearing, if it were lower it would help, but glad it is now working !

woodsy144 - 24/8/23 at 01:34 PM

quote:
Originally posted by coyoteboy
Seems quite a high gearing, if it were lower it would help, but glad it is now working !

I would love some lower gearing. Unfortunately I can not.
I have the largest sprocket I can fit at the engine sprocket and then relying on the chain gear/ final ratio. So I have 2 sets of reductions.
I can try and get some more teeth on the front great but might be pushing my luck.

woodsy144 - 11/9/23 at 04:26 AM

Just an update.
I managed to get one of these from a local store front and install.
It appears to work. No issues 'to date'. Will keep you informed.

https://www.altronics.com.au/p/s5897-300a-surface-mount-ip67-waterproof-circuit-breaker/

Mr Whippy - 11/9/23 at 06:24 AM

quote:
Originally posted by woodsy144
Just an update.
I managed to get one of these from a local store front and install.
It appears to work. No issues 'to date'. Will keep you informed.

https://www.altronics.com.au/p/s5897-300a-surface-mount-ip67-waterproof-circuit-breaker/

Looks great, wee bit pricey but if it's doing the job why not. I really need to put some breakers in the old car over the winter before it torches itself.