fuse or relay?
 

For a electric fan, I have a heavy duty relay.
The fan is controlled by the standalone that switches ground.
Power is from the fuse block under the hood.

What benefit is a relay over a heavy duty fuse or circuit breaker?

"I have a heavy duty relay. Power is from the fuse block under the hood."

Sounds like it's done right. The relay is the switch, and it's getting powered from a fused source.

Are you talking about using a relay and no fuse, or something else?

I want to know why I think I need a relay if I have it fused and its being switched with a ground?

Oh... Depends on if the ECU can handle that much of a load on that output. I know on my E6K I can use a switched output for a fan depending on temp, but I can't directly use the output to power the fan, I have to use a relay.

but the ECU switches ground, not power

this is why Im wondering why need to use the relay, less wires and less complications.
I was thinking of a circuit breaker or fuse instead.

Hmm, maybe someone else can chime in, as I'm no electrical expert. What does the ECU manufacturer say about using the ground switch as far as application goes?

The ground side of a circuit still carries electrical load. Electricity flows from negative to positive. Right now your relay carries all the load, and the ECU just has to deal with the very small amount of current needed to switch the relay. If you remove the relay, your ECU will see a lot more current.

switched grounds are usually very thin gauge wiring

This is not my thing, but I think of a amplifier, it has ground and fused or circuit breaker power, no relay.

Switched grounds meant to operate something like a relay can be small gauge, since relays only draw milliamps across the coil side. The ground wire on an amp should be the same gauge as the power wire, as it will be carrying the same amount of current. But the difference between an amp and an ECU is it's meant to carry a lot of current, and probably will have an internal relay anyhow. My SPAL fan controller is set up that way. It has 10 gauge power and ground wires & and internal relay. It gets a fuse wired in-line, but an extra relay isn't necessary.

Furthermore, an amp is an incomparable item, amps use many capacitors, which indicates and infact means that your ground wire should be LARGER than your power wire. You may only take in 40 amps into an amp, but you can discharge 60-80 at a time through the saved energy of a capacitor.

My $.02
 

Hey Rob-

Audio amps have an internal relay- the 'click' you hear when you turn on the amp is the sound of the relay switching.

The 'switch to ground' that you are referring to in your ECU/standalone is likely rated for milliamp currents, but I cannot be certain. It is likely not intended to carry a high amp load. When you consider an E-fan, the ground side of the circuit carries the same amperage as the current side. IOW, if your Taurus efan is consuming 25 amps, that circuit in your ecu MUST be capable of carrying ...25 amps.

The manufacturer of your standalone will be the only one that can tell you the capability.

That being said...on high current switching of dc motors what you can be certain is that the contacts will wear on the make and break. *Whatever* you use WILL wear out. Better a to wear out a $5 relay than a $1000 standalone.

My advice is to let the standalone activate the coil (milliamps!) of your relay.

And I am now convinced that a circuit breaker is a superior way to protect an efan from overcurrent.

Thanks guys, I understand it now.

So if the circuit breaker is better your saying to use that AND a relay?

Yes, exactly.


You must have something to protect the circuit for the fan. Your choices are either a fuse, fuseable link or a circuit breaker. I am using a fuse in the ABS location of my underhood fuse box. If I redo it, I will go with a circuit breaker.

The relay is the control for the circuit. The fuse/circuit breaker should be located closer to the source of the current than the relay. This way the relay is also protected.