fan relay

This is my first post,not sure how post diagram so I'll try verbally. This cooling fan is going in my Chevelle. !2v automotive cooling fan. Pulls approx 20amps at startup settles down to approx 10 amps. I'm using a standard 5 pin Relay. My hookup is as follows. #30   To the + terminal on the fan #85   Ground, using a temp switch to ground out at 180*       water temp to turn the fan on #86   Ignition key switch power #87a To ground #87   To direct battery power My question is when the fan is not energized, and it is freewheeling when traveling down the road at 60 mph, the voltage will feed back through #30 and out to #87a. Will the relay take this feedback or should I put a small lamp near the end of the 87a line. Thanks Playing the ultimate game every day

No need to connect anything to 87A.  All other connections are dead on.

Some use a grounded 87a to brake (stop) the fan motor - at least I assume that's the reason - I often see it provided for fan wiring.    But I see no reason reason for that... Besides, why create extra drag (hence less fuel efficiency) and reduce airflow through the radiator? IMO let the fan spin freely. (Not that I have specifically searched for reasons... Maybe I'll feel stupid if a find (an obvious) reason, though I suspect it will be another case of stupid ideas & ignorant hypotheticals. I await my embarrassment - feel free to take advantage. Hmmm - shii - stupid hypotheticals & ignorant ideas?

wysiwyg wrote: No need to connect anything to 87A.  All other connections are dead on.

Thanks for your help on verifying all the other connections. I forgot to mention there is an indicator lamp wired in on #85, to let you know when the fan is energized. I guess my initial thoughts are like yours, I was wondering why 87a is being used. RegardsPlaying the ultimate game every day

oldspark wrote: Some use a grounded 87a to brake (stop) the fan motor - at least I assume that's the reason - I often see it provided for fan wiring.    But I see no reason reason for that... Besides, why create extra drag (hence less fuel efficiency) and reduce airflow through the radiator? IMO let the fan spin freely. (Not that I have specifically searched for reasons... Maybe I'll feel stupid if a find (an obvious) reason, though I suspect it will be another case of stupid ideas & ignorant hypotheticals. I await my embarrassment - feel free to take advantage. Hmmm - shii - stupid hypotheticals & ignorant ideas?

Thanks... so your thinking 87a could or might act as a brake for the fan when the fan is not energized. I forgot to mention in my original post that there is a indicator on lamp wired in on #85 if that changes any thing. I going to try and mock up the wiring today on my work bench. These little relay cubes are just fascinating. RegardsPlaying the ultimate game every day

I thought you meant "indicator lamp to #86" until I realised that it's GND switched, ie, 85 is off or on, on being to GND. [ Hence the indicator light/LED is wired between 85 and +12V - but maybe not from 86; see below. ] But it could also be a grounded light/LED with its +12V to the fan (switched) +12V - though a LED might need spike protection... (which is not guaranteed even with 87a to GND). That would show when the fan is on. But if its fuse has blown... Nah - scrap that. I'd argue yes - as you suggested: lamp or LED -ve to 85. That then shows when the fan should be on. You can then hear the fan to confirm, else watch the temp gauge or steam rise if it isn't - eg, the fan's (relay's) +12V power fuse may have blown or the fan failed etc. Hence to why the indicator's +12V should be from a separate circuit - maybe the dash-meter's +12V, with 86 from another IGN-switched circuit. {Otherwise the fan can come on with IGN off. Though the coolant temp rises after engine stoppage, that is not a problem because the critical heat effected areas like the head gasket & chamber, pistons, valves etc are cooling down. Only if coolant boils might there be a desire a fan with the engine stopped (turn the IGN back on?), but it's that versus the risk of a switch or wire fault that leaves the fan running and flattens the battery...). Sorry for that last stuff, but I know many think that the post engine-stop temp gauge rise is a bad thing, while others run their indicator power from the same +12V as the relay coil (sometimes taken from the same +12V as the fan's +12V), and hence they don't get a light OR fan if 86's +12V fuse has blown. The other benefit - only the switch/85 need be extended into the cabin to the indicator's -ve side. (And grounded wires are "safer" in case of shorts etc.) The indicator +12V can be from any cabin IGN switched +12V whilst the relay's 86 gets its IGN 12V in the engine bay - preferably on different fuse to the indicator's IGN +12V. (And then the battery thru fuse to 30/87 to the grounded-fan's +12V.) As to 87a to GND, I wonder what that is for? Some say transient suppression, but so what? The fan's +12V isn't connected to anything. And the delay switching from 87 to 87a is enough to damage electronics, but the input +12V (to 30) should be from the battery which helps suppress spikes. Some say to prevent high voltages being generated by the wind turned fan. But again, so what (as before). And some say the fan can generate voltages higher than its winding insulation tolerance. What? Insulation is that exact, AND it can't tolerate the hundred(s) Volt spikes the fan generates upon power removal? Besides, a 12V fan might be lucky to generate even 50V at best (I think). Yep, it beats me. Maybe it's a pitch by fan or relay manufacturers to sell more through relay arcing or abrupt fan stoppages? Maybe one day I'll investigate further. But yeah, indicator light to 85, not the fan power side (eg, to 30, with its other side to GND). BTW - with no 87a connection, 30 & 87 are interchangeable. Usually 30 is the +12V input, but that's a trivial convention for SPST usage (ie, no 87a connection) - unlike 86 which should be +ve and 85 -ve (GND aka 0V) in case relays with internal spike-quenching diodes are used. Apols for my long windedness, but for possible clarification and peace of mind... As well as to provoke comment, correction, or endorsement...

Shut up Peter, too verbose. Poster, forget 87a, wire you pos leg of LED (set up as 12Volts pleas) to 30 and the neg side to ground.

Oh wow geez. I'm going to have to read all this a couple times to straighten it out in my head. Oldspark and HowieII thankyou. Gimme some time to sort this out in my head. I'm in my garage now, need to get a few things done. But I will be back. RegardsPlaying the ultimate game every day

Well I have the fan mocked up on my work bench. I have no idea what the intent is for grounding 87a, the fan appears to work properly with or without 87a, so why use it, it has no braking effect that I can tell on my fan My original thought of the indicator light in series on #85 does not work. I'm glad HowieII mentioned to tap into #30, and then to a ground which seems to work properly. RegardsPlaying the ultimate game every day

Not in series! In parallel, eg across the GND-switched 85 & 86 +12V. (Though preferably not from 86 - use another circuit as I discussed earlier.)