Fuse or Circuit Breaker for Alternator Feed

[TTimmy]

Howdy Folks,
I'm wondering what others have done for fuses or circuit breakers between the alternator and main wiring harness. Is there any downside to going with a resettable circuit breaker?

I didn't see any mention of this in the FFR documentation and it seems like it would be a good idea. (I also may have overlooked it.)

Thanks again for the guidance!

Tim

[edwardb]

Nothing in the instructions or RF wiring guide regarding some type of protection for the alternator circuit. I've used 150 - 200 AMP mega fuses on my builds. Depending on the output of the alternator. DD's typically use a fusible link, but haven't pursued anything like that. I suppose you could use a circuit breaker. But a fuse is a simple and easy installation.

[egchewy79]

Agree w/ Paul. I used a 175A megafuse and attached it to the top of my PS footbox in the engine bay.
The likelihood of blowing this fuse is low, so I didn't think a resettable fuse was necessary. I did install a low amp resettable fuse on a stay-alive circuit that circumvents my battery cutoff switch. this allows my EFI and clock to stay on despite removing the battery cutoff key, but if someone tries to start the car, the jump in current will blow the circuit.

[TTimmy]

Thanks for the input on this!

I will definitely do either the fuse or circuit breaker. I ordered each and will see what works out as I am semi-committed to locating it behind the dash given that I have already wired everything back from the alternator to the dash. I would hate to reengineer everything now that it has been dressed into the harness and wrapped. Thus, my concern is easy access to the fuse with tools etc. vs just reaching under and resetting a breaker. The breaker has the added benefit of acting as a security mechanism of sorts as I can manually "trip" it. While that alone would not prevent it from starting, they may not make it far.

[edwardb]

Thanks for the input on this!

I will definitely do either the fuse or circuit breaker. I ordered each and will see what works out as I am semi-committed to locating it behind the dash given that I have already wired everything back from the alternator to the dash. I would hate to reengineer everything now that it has been dressed into the harness and wrapped. Thus, my concern is easy access to the fuse with tools etc. vs just reaching under and resetting a breaker. The breaker has the added benefit of acting as a security mechanism of sorts as I can manually "trip" it. While that alone would not prevent it from starting, they may not make it far.

Don't overthink it. As alternator protection it will rarely if ever trip. Basically only if the alternator itself melts down and goes into a short situation. That's when you want the rest of the harness and vehicle protected. Sounds like you're deep into the wiring, but many would recommend against having high current cables, like this one, behind the dash. Better to keep them on the other side of the firewall or underneath the vehicle if the battery is in the back. We always say "build it the way you want" but I'd be a little cautious on the electrical side. And there are way better ways to do security. Like the ignition or fuel pump. Not trying to be negative, but trying to good advice. You can be the judge.

[TTimmy]

Thanks again for the input EdwardB. So the only high current bit behind the dash is the alternator feed to a bus bar. I was thinking of placing the fuse/breaker between the bus bar and where the alternator feed comes into the dash.

Am I better having the fuse on the outside of the dash - under the hood someplace?

[GT_Rich]

I recently made a video about how I handle the high current feeds in a build, including the alternator feed. I use a 150 amp fuse in the line between alternator and front power post. This is with a 3G 130 amp alt.

https://youtu.be/XjM86g-wN7Y

[edwardb]

Thanks again for the input EdwardB. So the only high current bit behind the dash is the alternator feed to a bus bar. I was thinking of placing the fuse/breaker between the bus bar and where the alternator feed comes into the dash.

Am I better having the fuse on the outside of the dash - under the hood someplace?

Not going to die on that hill -- if having the alternator line behind the dash is your best setup, then go with it. I've done it myself. But if given a choice, I try to keep it on the engine side of the firewall. Then the fuse in-line where I can get to it just in case. In 13 years of building, I've only blown one alternator fuse. And that was my fault for shorting the alternator leg with a wrench. Should have had the battery disconnected... I guess my main advice is don't try to make the fuse do something more than protect the car and wiring harness from a runaway alternator, overrev, high current draw, whatever.