Relay wiring question

[65 drop top]

I was talking to a car wiring guy the other day and he recommended that I wire my dual electric fans directly to the battery, and to wire the relays to the negative side of the fans. Does this sound correct?

[72BBSwinger]

Don't see any advantage to that.

[mmosley]

Same either way really. Power still flows through the wires, the relay is just completing the circuit. I do not see an advantage to one over the other.

[65 drop top]

He said that the relays will run cooler. I suppose that means lasts longer.

[H2Ogbodies]

That has nothing to do with anything-relays are rated in terms of switching cycles...cheapo Chinese relays are in the 20-25K range while TYCO are generally 100K or 250K. The better commercial grade relays (not the parts store ones either...)do have better contact metals which resist heat better to avoid arc-welding together from extreme spiking...but, rather than run off the battery its better to power the fan relays from a remote +12v junction which utilizes the alternators remote voltage sensing.

Aside from the actual fan power source, there are many ways to wire your dual fans using relays. I've designed a series relay setup for 2 speed operation and a resistored 3 speed harness as well.

[BonzoHansen]

I was talking to a car wiring guy the other day and he recommended that I wire my dual electric fans directly to the battery, and to wire the relays to the negative side of the fans. Does this sound correct?

Does any oe car maker do it that way? I've never seen it.

Here is how gm used three relays for two fans in f-bodies
http://img.photobucket.com/albums/v3...995_BOTTOM.jpg

[MrQuick]

Most after market relay kits set it up that way. IE: Derale. Also PCM controlled. 2 examples below.

The relay completes the grounding circuit. 87 to 30.

I run it this way too if a customer wants an illuminated fan switch since the over ride feeds a low amp ignition curcuit.

both fan circuits work fine. Just cat skinning.

[H2Ogbodies]

It also depends on what km and of fan you're using. For example, I run a 2010 F150 dual fan setup in my K10 short box which is rated @ nearly 6000 CFM. I run them @ 3 speeds in parallel instead of one on low, one on high.....that setup IMO is just not very efficient. With both fans running in parallel @ low speed, the fans rarely need to go any higher unless AC use is demanded. Everybody seems to do it differently but I always go as massive as possible with a cooling fan so minimal fan speed is required to keep engine temps stable.

[CanyonKiller]

Running relays on the ground side will not make them run cooler as the still have to handle the same amount of current that's on the positive side.

I's sure MRQuick has had good results with his wiring but I always look at things as what happens when it fails. Since the fan has constant power if the ground of the fan started chaffing and shorted somewhere the fan would remain on at all times.Also, I don't know where he also mounts his fuses but the further the fuse is form the battery can be a problem as a fuse will not open if there is a short before the fuse and will damage the battery and other sensitive electronics (PCM).

Running the relay on the positive side also limits the length of wire that will have constant power that can short out and cause a problem.