Killing relays in the fuse box

[ndragun]

I'm having a bit of a hard time with relays at the moment. The main relay in the fuse box has been on its last legs for a little while. I've brushed off the contacts and given it a bit of a tweak with a pair of needle nose pliers to get it to make better contact - and its doing semi-ok at the moment (but its still a bit dodgy from time to time).

However, recently I appear to have completely melted the cooling fan relay. The photo below might be hard to see, but for the eagle eyes, you can see the plastic on the left-hand side of the coil has all sagged, which is now holding the switch mechanism apart... So its dead and buried...

I'm wondering if this is 'normal', or have I melted this relay for an avoidable reason?

I have relatively recently replaced the stock fan with a SPAL cooling fan. I did read in passing that these fans pull more load than stock from the electrical system, but I haven't seen anything about changing relays to suit - the posts I did read was more about combining the wiring from the A/C fan and the rad fan...

Either way - I'm a relative novice with this stuff... any advice or comments appreciated.

Could well just all be co-incidence, and/or related to starting and stopping the car (and starting and stopping the cooling fan fairly frequently with A/C coming on and off) while we've been tuning.

[Magpie]

I'm running SPAL fans as well and only recently had a burnt out the relay, since it has been replaced no issues. However I do keep spare fuses/relays with me just in case.

If you are concerned consider replacing it with a solid state relay. This would allow ECU control of the fan

This is a link to the Haltech wiring, however it can be substituted to work on any ECU or wired in to replace the existing relay (on/off only).

http://www.haltech.com/wp-content/uploads/2011/01/Solid-State-Relay-HT030202.pdf

General use of a SSR http://www.autospeed.com/cms/article.html?&title=Using-Solid-State-Relays&A=112737

[Locutus]

That relay is rated at 10A. How much current does the fan require?

You can protect your next relay by installing a flyback diode.
https://learn.digilentinc.com/Documents/390

[Magpie]

My SPAL's are 1225 CFM 140 watt, this calculates to about 12 amps (each).

[ndragun]

That relay is rated at 10A. How much current does the fan require?

You can protect your next relay by installing a flyback diode.
https://learn.digilentinc.com/Documents/390

Perfect answer - thanks Locutus.

My fan is 1777CFM - and appears to require 20A after a bit of investigation... So - with a flyback diode as per the doc, is that sufficient or should I be looking at an alternate relay? Or more to the point, is the 'stock' wiring up to the job or should I be re-wiring somehow? I'd be hoping to avoid solid state relays and extensive re-wiring at this point... but if its gotta be done then its gotta be done.

It is an awesome fan for the record... albeit a bit noisy... at the expense of melting the electrics evidently!

[Locutus]

No, you need to replace the relay with one capable of switching a minimum of 20A. The flyback diode only protects the relay (and the rest of the circuit) from voltage spikes every time the fan is switched on or off. Given that your old relay failed due to being over dríven, you probably don't need flyback protection but it does provide very cheap insurance and will prolong the lifespan of your new relay.

Not sure if the stock wiring is up to the task.

[davekmoore]

The EFI relay in mine started failing after I uprated the fuel pump. Higher rated relay solved the issue. For safety's sake also had a qualified auto elec check all the wiring to and from the relay. Some was suffering from the relay being under rated.

Someone here also suggested, weirdly, that I check the wiring to the headlights. Even more weirdly, some of it had been overheating and had burnt the insulation enough for it to be shorting out. Dunno if the two issues were related. Seems unlikely.

[ndragun]

Awesome responses, thanks guys.
I already ordered like-for-like replacements for both the fan and main relays prior to posting, so will add the flyback diode and see how long they last, and then look at up-rating them after that.

For my interest though - and I don't have the wiring diagrams in front of me - the fan fuse from memory is a 30A... what's the mentality behind that? As in - to my uneducated brain, I would have blindly thought that the relay should be rated at the same amperage or higher as the fuse, rather than the other way around? I'm just asking from the point of view of learning...

[hks_kansei]

For my interest though - and I don't have the wiring diagrams in front of me - the fan fuse from memory is a 30A... what's the mentality behind that? As in - to my uneducated brain, I would have blindly thought that the relay should be rated at the same amperage or higher as the fuse, rather than the other way around? I'm just asking from the point of view of learning...

I would have assumed the same.

I'm no electrician by any means, but i've always thought you were supposed to make sure the fuse was the weakest point?

[taminga16]

While I am not up to speed with your fan set-up might I suggest that you install a heavier cable to run it. Less resistance equals less heat.
Greg.

[Locutus]

According to the NB wiring diagram (which doesn't show a fan fuse?), the following are on the same circuit
- main fan
- condenser fan
- A/C motor clutch
- cabin blower/fan

So the wiring in the main harness and fuse needs to be capable of having all of the above at max load. This doesn't mean that the wiring for the main fan alone is capable of sustaining all the load. A shared fuse is sufficient because a typical failure of the circuit (say, a short to the chassis) would cause a massive spike in current draw, quick enough to blow the fuse in a split second.

20A is a lot of current. If I were you (I am pedantic about not tinkering with factory wiring where possible) I would re-install the relays you've already purchased so that the factory circuit is back to normal, and then use the factory fan circuit to control a new relay which switches a new high current fused line to the fan. Perhaps use something like this and run power from the main fuse in the engine bay.

[ndragun]

If I were you (I am pedantic about not tinkering with factory wiring where possible) I would re-install the relays you've already purchased so that the factory circuit is back to normal, and then use the factory fan circuit to control a new relay which switches a new high current fused line to the fan. Perhaps use something like this and run power from the main fuse in the engine bay.

Yea - I think that's a perfect idea, so I'll give that a go. I had the same reservations about replacing the existing relay with something uprated, since it gets further and further away from the original wiring (although having said that, the wiring in mine is starting to go that way anyway...) So a relay driving another relay, and pulling power from the main fuse sounds like the right idea.

Thanks again for the help!