Running Duel radiator fans

[unknownmale]

My radiator fan has packed in, I was going to replace it, but the shroud is already too small as I fit a larger GTI rad last year. Anyhow I have a couple of 10" universal fans which fit perfectly so I thought i'd make a high low set up.

I initially thought about having both fans running in series, giving them both around 6v on the low setting, then switching to a parallel circuit for the high speed. I've since decided against that and gone for this:

Screen Shot 2016-02-17 at 01.30.23.png

So currently being shown is the low setting, then if needed I can hit the high side switch for both fans to operate. It would be nice to have the high side operated automatically, I considered using a temp sender as a resistor but figured that it would be too much load, maybe a second thermo switch in the mix for higher temps?

[unknownmale]

Just as a note, the top relay is a n/c 4 pin 30amp, but i would most likely be using a 5 pin changeover and a 4 pin as they're easier to get hold of. Also, I know OEM shrouds work best etc, but I have these fans already in the shed and I like making things.

[duggers]

Could you utilize a temp switch from something oe. I have oe twin fan set up on my daily mk4 Goof that has a temp switch for low and high setting to determine one or both fans coming on?

[unknownmale]

Yeah, but that would be computer controlled, This is an analogue circuit. I could use a temp sender, but it would be inline with the high amp side of the circuit and used as a variable resistor (The higher the temp, the less resistance would pass through the sender allowing more current to pass through which would increase the speed of the motor. But don't really want a 30amp circuit running like that.

[james butler]

Yeah, but that would be computer controlled, This is an analogue circuit. I could use a temp sender, but it would be inline with the high amp side of the circuit and used as a variable resistor (The higher the temp, the less resistance would pass through the sender allowing more current to pass through which would increase the speed of the motor. But don't really want a 30amp circuit running like that.

computer controlled?
i thought there was an anologue temp switch that did high and low fan speeds?
you could use this to turn on the one fan slow speed then relay the high speed to run both

[unknownmale]

Yeah, but that would be computer controlled, This is an analogue circuit. I could use a temp sender, but it would be inline with the high amp side of the circuit and used as a variable resistor (The higher the temp, the less resistance would pass through the sender allowing more current to pass through which would increase the speed of the motor. But don't really want a 30amp circuit running like that.

computer controlled?
i thought there was an anologue temp switch that did high and low fan speeds?
you could use this to turn on the one fan slow speed then relay the high speed to run both

I don't know for sure, but reckon the ecu would trigger the fans on a mk4.

Yeah, i'd like to put another temp switch in place of where I have the "High switch" but have it trigger at a higher temp but i'm not entirely sure how this would work. Do they close at a set temp or open? Would also need to know what temp the stock switch operates and try and find another switch for a higher temp?

Also considered using a VDO sender as a variable resistor, but the way I've figured it, I would need to have this inline on the high amp side which I wasn't sure about.

I Need to do more research I guess!

[james butler]

to be honest your probably better off just daisy chaining both of them together and running them off the standard single speed setup.
because you wont be using the origenal fan housing anymore the dynamics of how the air is drawn through the radiator has been changed.
so bringing both fans on full speed wont do any harm, if anything it may just cool it that little bit quicker and once the temperature is reduced enough the thermo switch will cut out any further cooling.
im using a dual fan setup but only the one fan is powered and the other runs off a belt connected to the first one.
the dual speed thing really is only for A/C applications where the radiator is exposed to more heat not only from the engine but from warm air being drawn through the condensor radiator first when the A/C is on.
so in a rocko i cant really see it being that much of a necessity to have both speeds.

[unknownmale]

The only reason I want the two speeds really is because both fans draw 30amps, thats why I first considered running them in series first to keep the load on the alternator down, and then if really needed I could switch to parallel to run both at full 12v.

I think you're right though, day to day both running at 6v should probably be enough, they cover the surface of the rad perfectly too. Will probably wire in an under the bonnet option to flick into parallel just incase its not enough. Removed my front fogs so can use that circuit to activate it. WIl see how it holds up

[Nate]

I thought you could get a 2 speed fan (3 pin temp switch) on some roccos as standard?

[unknownmale]

I thought you could get a 2 speed fan (3 pin temp switch) on some roccos as standard?

That would be handy, Only ever seen 2 pin one speed on previous cars though. Will have a look though!

[unknownmale]

Looks like this was on the mk1s - http://www.ebay.co.uk/itm/MK2-GOLF-Ther ... SwT6pV1Lrk

Doesn't say if its the 1/2 NPT, M10 etc. But i'd assume it would be the same?