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Wiring up relays for 3 radiator fans - Engine/Ancilliaries - The Lotus Forums Jump to content
Jims

Wiring up relays for 3 radiator fans

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I just order some new spal fans and I keep reading that its a good idea to update the wiring and add  in relays.    I'm not quite sure how to wire this  correctly.

Would I run 3 wires to the  directly to the battery  then each wire would have a fuse that would go to the relays?

  And the wire from  the otter switch is what triggers the relays to come on?  

 

I get the concept but not sure if this is the correct way to do it?

Jim

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How hard do you want to make it?

The issue is the current surge to start the (larger) fans all at once. It can be pretty large and will eventually crisp the relay socket terminals if not the wiring. Unless you want to add a delay circuit of some kind on one or two of the fans, its best to upsize the conductors and relay. 

You could add one or two more battery fed relays to feed the fuse box fan supply BN wires in parallel to the existing one, fed with the same coil trigger wiring. This would retain your fan fail light function, but still uses the stock power wires to the fans. I'm not sure on the OE wire sizing, but at least there's one wire for each fan. My car is running large SPAL's on them so far, but many have doubted their capacity. Accessing the back of the fuse box to swap/spice the wires might be a pain, and you'll need to find room for the relay(s). You will need to go to the next fuse rating up if you are running the large SPALs.

Or you could just bypass all the OE wiring and put in a high power relay in the frunk feeding the new fans and just tap into the Otter switch (+A/C?) BO wire to get a trigger to run the coil. There's a positive battery terminal at the base of the right A pillar to get power.

Then splice the fan grounds so each fan has it's own ground wire. ( I don't know what Lotus was thinking with the 3 wires in 2 out method) I also added  a ground lug to the frame above the fan shroud so all the current was not trying to get back out through the crusty old connector.

Federal Radiator fans.jpg

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https://www.12voltplanet.co.uk/adjustable-delay-timer-relay-delay-on-or-off-12v-10a.html

 

My  friend suggested this relay.   What are your thoughts on it?

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Well it all depends on which SPAL you bought. I went with the largest option (057) as it was easy to mount to the OEM shroud, but it runs at 9-10 amps and the start surge is in excess of 15 amps. Smaller fans would be kinder to your wiring.

The first relay option would not directly have the current capacity but could control other relays.  The second looks good for a rewire option, although  the sensor might take some tweaking. I've put that sort of sensor on the outside of a metal pipe with some heat transfer paste and a wrap of metal tape. You could do that on the J-pipe above the existing otter switch if the wire is long enough. 

Delay module possibility-

http://www.casperselectronics.com/cart/index.php?route=product/product&product_id=498&search=delay+relay&description=true

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Delay module possibility-

http://www.casperselectronics.com/cart/index.php?route=product/product&product_id=498&search=delay+relay&description=true

Instructions-

http://www.installationinstructions.com/109086.pdf

 

You could use a better relay in the stock location to run one fan, then tap this delay module to the BO wire to trigger a heavy duty relay controlling the other two fans, or two delay modules could sequence each fans relay in turn.  So many options......

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Yep, that's the one I went with, three of those can surge 45 amps if called at the same time, a lot to ask of one relay in an old socket. 

A couple delay-on units to run two more relays so they come on 1-2 seconds apart after the first fan would seem ideal. 5-10 second delays seem a little long on a car I've already overheated.

Something like these to trip the #2&3 relay coils, a little bulky, but easier to set up than generic timer modules:

https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=372642079494&_sacat=0

 

Or if 3-5 seconds is OK, you could just add two relay sockets feeding the fuse block fan fuses and use two of these relays with integrated delay on timers. This is what I'm leaning towards on my car once I overcome the dread of getting to the back of the fuse block, and find a spot to mount the relays. 

https://www.ebay.com/itm/30A-Automotive-12V-5-Pin-Time-Delay-Relay-SPDT-10-second-ON-delay-relay-3/323877818904?hash=item4b689f5218:m:mVlGSJ15flnZBt1Vljq8m0g

 

 

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I ended up ordering the Davies Craig Digital Thermatic Fan Switch Kit.   I like the idea to be able to pick when the fans come on.  I live in Orlando and get stuck in traffic all the time.   With this kit I can dial in what works with my driving commute.

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