30 amp relay fail- now what?

Guys:

I have an aftermarket electric fan installed in my truck, as I've deleted the mechanical. Whys and wherefores are unimportant- let's just say "my junk ain't stock"...

It's a two-speed electric fa, moves a ton of CFM. In operation, it draws 25A constant. Inrush is vicinity of 32A. I was using a standard 8730 relay, it lived fine for 2 years. This morning, I had a serious overheat situation in my engine (yay iron heads and block. Let it cool and don't sweat it). After addressing the ruptured hose caused by the overheat, I troubleshot my fan (it had never came on, leading to the problem in traffic).

Turns out, the relay failed. Hmm, 95 percent of rating, ya think?

I want to stay with a commonly-available relay, so if I have issues I can stop in at the nearest LAPS or Walmart and buy the problem away. Will putting two of these same 8730 relays in parallel be a reasonable way to solve the issue? Is there another relay available that is commonly available and doesn't cost $75 that will do it better?

Thanks!


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"Always listen to experts. They'll tell you what can't be done, and why. Then do it. - Robert A. Heinlein"

- or am I better off using something like this?
https://www.amazon.com/Vehicle-Black-Power-Relay-RTT7105/dp/B00GN7VJRW

RTT7105-12V. Rated 80A

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"Always listen to experts. They'll tell you what can't be done, and why. Then do it. - Robert A. Heinlein"

Yes use the relay in the second post.
A 30 amp relay can switch 60 amps for about 3 seconds, you might have another problem there.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

I think the biggest part of the problem is that it's bolted to the header right next to the hot tank of the rad- so it's definitely an abusive environment.

If I wasn't concerned about current-sensing on my alarm being triggered by the fans running while the truck was sitting unoccupied, I'd just delete the relay entirely. It's only supplying the mains current to the fan controller relay.

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"Always listen to experts. They'll tell you what can't be done, and why. Then do it. - Robert A. Heinlein"

Early designs never used a relay e.g. early Euro Fiesta, Renault 5 turbo, battery (fused) to fan, ground return via thermal (Otter) switch.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

or You could just Double up the relays.





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John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !

howie ll wrote:

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Early designs never used a relay e.g. early Euro Fiesta, Renault 5 turbo, battery (fused) to fan, ground return via thermal (Otter) switch.

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Early designs didn't have a microprocessor-controlled alarm which monitors the current draw of the vehicle's electrical system and goes off if it increases.

When I first built out the electric fans, I had them wired constant through a thermo, much as you describe (except lacking the switched ground). Worked fine, but wasn't compatible with the other projects.

I am using this not to switch the motor directly. For that, I'm using a Volvo dual-speed fan control (completely up to the job, running a Taurus fan, very commonly used). I am using this relay to switch supply to that one, in order to not have it not run while parked/armed.

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"Always listen to experts. They'll tell you what can't be done, and why. Then do it. - Robert A. Heinlein"

Only real answer seems to be to move the relay to a safer operating environment.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

The "Volvo Relay" has the B+ for the fan motor outputs common with the relay coils. So on a thermo-switched system, the relay coils stay energized until the thermo switch opens. While the Volvo relay is very popular in electric fan retrofits, it is not ideally suited for non-ECM controlled cooling fans. Unless you don't care about the fan running when IGN is off.

You're switching the B+ INPUT to the Volvo relay with an aux relay that is only energized with the IGN on to keep the fans from running with the key off. Why not switch the Volvo relay thermo switch inputs with the auxiliary relay(s) instead of the B+ input? Then your Volvo relay is doing the heavy current switching and load-carrying, not your aux relay. Your aux relay will never burn up again.

Or change-out the Volvo relay to two (Hi and Lo speed) 40A relays with segregated coil terminals, so the coils can be supplied from IGN source independent of the B+ source for the fans, solving the "fan runs with key off" problem with the least complexity and lowest component count.

hotwaterwizard wrote:

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or You could just Double up the relays.

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That was the original question, but it's not a proper solution. It'll get you by for a while- but so did the one relay, till it burned out.

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"Always listen to experts. They'll tell you what can't be done, and why. Then do it. - Robert A. Heinlein"

davep. wrote:

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Why not switch the Volvo relay thermo switch inputs with the auxiliary relay(s) instead of the B+ input? Then your Volvo relay is doing the heavy current switching and load-carrying, not your aux relay. Your aux relay will never burn up again.

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This is a distinct possibility. For now I'm going to go with the 80A relay to shut the entire system upon key off.

I agree that your proposed solution will work. But the easiest solution in my already-built rig is to upgrade the BATT cut relay. $9. Done.

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"Always listen to experts. They'll tell you what can't be done, and why. Then do it. - Robert A. Heinlein"