Accessory fuse panel

[toofun]

Hey guys,

Got a question about adding an additional fuse panel without hacking into the factory one. The one I am looking at is from Painless wiring ( I know it can be done cheaper but with electrical I like to keep it simple since it is not my forte).

Question is with the MAIN FUSE BREAKER used to protect the entire circuit and fuse panel. In the drawing it shows several fuses rated at 20A and lower. The relay is rated for 40A and the main circuit breaker at the battery is rated for 50A.

Can someone explain to me why if you have 7 circuits with 20A fuses in them, why you only need a 40A relay and a 50A relay protecting the entire circuit? My non electrical brain would tell me you would need a much bigger relay and main circuit breaker if you had all 7 circuits working at the same time with those 20A circuit breakers in the panel.

As always appreciate the info. Here is the pic off the site.

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[dontlifttoshift]

If you run 20 amps through all 7 of those circuits, it won't work, you will trip the breaker. Are you going to run 20 amps through all 7 of those circuits?

I am assuming the relay feeds the 4 ignition circuits, if you exceed the relay rating with those 4 circuits you will trash the relay in short order.

You need to determine what you are powering, then wire and protect the wiring accordingly.

[boss_hoss]

Thats an excellent Question, I'm running that exact same auxiliary fuse block except mine is the Jegs version and hadn't even considered that. I'm using it predominately to run my EFI and a couple of other accessories so a pretty low draw overall. I think you're probably correct that running all the circuits at a high output would definitely blow the breaker so I wouldn't wire it up to anything like electric fans. If like me you're running an EFI unit, Vintage air and a radio or something you'll probably be fine.

I think they just put 20amp fuses in it as delivered because that is the maximum number of amps each circuit can handle, and they don't know exactly what you're using it for. You could/should probably swap out the 20A fuses for ones better suited to the amount of power each new accessory will be adding to the fuse block.

But like you this is my non-electrical brain talking so take of it what you will.

[toofun]

So I plan on running a dakota Digital Gauge set through this as well as an electric fan setup, and LED offroad light bars ( two in total). Everything else is already fused and protected. Just trying to understand and make sure I am protecting everything correctly. Info on the web is scattered at best.

Mark

[dhutton]

Running an electric fan setup through that block is a mistake imo. Electric fans are best run directly to the battery with appropriate sized fusible link or megafuses. I’m assuming you are running decent fans which will draw a lot of current.

[Vimes]

Maxi blade fuses will work as well, and is what GM is using on theirs now. The last set I installed was on a 2000 Silverado and it had spare maxi blade fuse slots on the factory fuse box so I used those for power.

Something like this would work for the fans, although I've never used this particular company so can't speak for quality.
https://ceautoelectricsupply.com/product/gep-dual-70a-relay-waterproof-pdc-kit/

I also thought I'd throw in a couple of diagrams that shows how GM runs their fans. One uses the computer high and low temp settings, the other uses engine sensors with different temp settings. Wiring them up this way will keep the fan noise down as it runs both fans in series (half speed) on low and in parallel (full speed) on high. The middle relay acts as the switch. For the AC, the computer commands it directly so no need for the 4th relay. If no computer, the fans will run on high when the AC is on. I've wired several up the computer way and it works well.

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217414

[dhutton]

I never want electric fans sharing a fuse block with any other devices due to high surge currents and transient spikes. Even when using a PWM controller with soft start. The spikes can be significant. Keep them direct to the battery with their own fuses or fusible link.

I also never want simple on/off fan control but that is a whole nother story. PWM control always….

[dhutton]

GM doesn’t use relay fan control anymore. PWM control for good reason….

[Vimes]

GM doesn’t use relay fan control anymore. PWM control for good reason….

Perhaps the newest models, but they were at least in the early 2000s.

[dhutton]

Perhaps the newest models, but they were at least in the early 2000s.
That was almost a quarter century ago… :)

[Vimes]

That was almost a quarter century ago… :)

Ouch, that hurt!