Question for the electrical gurus.

Jamieg285 · August 07, 2014, 09:19:07 AM

Yes, I know you're out there

I'm running a dual fan setup, currently with a 2 relay setup, with fans running in parallel.

On dark rainy nights, I find that my alternator cannot keep up with the headlights (also relayed), wipers and rear defogger and then fans on top of that, with the voltage dropping below 12 on the dash guage (normally runs a healthy 13ish).

I've read about running the fans in series instead, where the aim is to make them run slower (combined with a more complicated circuit to also give them a high speed state). If I run then in series, with the voltage drop be less, i.e. will I avoid the state where I am asking too much of the alternator?

On a related note, there is a big surge when the fans first kick in. Will that be any worse, or better if the fans are in series?

art b · August 07, 2014, 07:01:17 PM

just thinking aloud ...

surely running fans slower will reduce the cooling..

does it need 2 fans ,

can they be wired to come on separately on thermostats [stats that fit in the pipework]
so one can kick in,later and for for less time than the other ?

Jamieg285 · August 08, 2014, 03:23:10 AM

Quoting: art b

surely running fans slower will reduce the cooling..

does it need 2 fans ,

can they be wired to come on separately on thermostats [stats that fit in the pipework]
so one can kick in,later and for for less time than the other ?

Yes, you're right on all of that.

I'm looking to see if I can do a low/high setup, by running them in series/parallel. Initially it would be low triggered by the temp sensor, with high being an optional manual override. If I think it's worth spending some more, I may get a 2nd, higher value temp sensor to auto trigger the high mode.

I just wanted to know what the draw implications would be when running the fans in series.

Roadkill · August 08, 2014, 04:44:20 AM

What size (diameter) are the fans ?

I was running 1 Spal on the Camaro, connected to an inline sensor.

I don't know about the wiring side but would suggest two is overkill . . . especially as one would be more efficient than the original belt-driven one, anyway.

Jamieg285 · August 08, 2014, 06:09:48 AM

Quoting: Roadkill

What size (diameter) are the fans ?

Pass. It's the fan setup that was originally cooling your LT1

It's a 4th gen dual fan, complete with original shroud.

AFAIK, originally it worked from the PCM which would fire up one based on water temp and the other if AC was on or it got really hot.

I could wire them individually, but I'd prefer both on at the same time.

BTW, 2 on full (in parallel) certainly works well.

Titsy · August 08, 2014, 08:13:32 AM

Does it not run a bit cold with two fans on? Serial connection is a no go. You will only have 6 to 7v across each fan. I'd get a dual fan thermostatic controller. You can get them where you press the thermostat into the rad fins and it brings on each fan as required based on the temperatures you have set. You should need a fan at all for normal running and it should only need to kick in for sat in traffic, mega hot day, or with aircon (which I'm guessing isn't fitted)...

Andy · August 08, 2014, 08:46:37 AM

Series setup is also a no go from the point of view that if you lose one, you lose both, having them wires in parrallel at least gives you some reassurance you're not about to lose all your cooling.

As said though, really it shouldn't be on at all unless stuck in traffic or it's incredibly hot, in which case I dare say you would be using your demisters at the same time.

That said, if you've stuck modern fans in an old car, maybe it is time to modernise the electric too. I would imagine a 2nd gen was designed to have an engine driven fan not an electric one, so using the rule of diversity, maybe the system just can't cope with what you're expecting of it?

Jamieg285 · August 08, 2014, 09:11:37 AM

Quoting: Titsy

Does it not run a bit cold with two fans on?

Only if you leave them on

Quoting: Titsy

Serial connection is a no go. You will only have 6 to 7v across each fan.

I got this idea from the 3rd gen forum, where they've talked about doing this with the LT1/LS1 fans, with some people that have done it. What's wrong with 6-7V at the fan?

Quoting: Titsy

I'd get a dual fan thermostatic controller...

Budget=£0. I can work with what I've got which is wires and relays. (Plus a temp sensor or 2).

Quoting: Titsy

You should need a fan at all for normal running and it should only need to kick in for sat in traffic, mega hot day, or with aircon (which I'm guessing isn't fitted)..

Correct. Currently it's setup in parallel, with both kicking in/out based on the temp sensor in the head. Works pretty well (or it did when the car was driveable

) There is also a manual override switch.

Quoting: Andy

Series setup is also a no go from the point of view that if you lose one, you lose both, having them wires in parallel at least gives you some reassurance you're not about to lose all your cooling.

Understood, but that's where the manual over-ride kicks in. The relay setup is set to switch between serial and parallel.

Quoting: Andy

That said, if you've stuck modern fans in an old car, maybe it is time to modernise the electric too. I would imagine a 2nd gen was designed to have an engine driven fan not an electric one, so using the rule of diversity, maybe the system just can't cope with what you're expecting of it?

Agree/disagree. There is a reasonable system and it works OK, I'm just looking for improvements.

Titsy · August 08, 2014, 09:59:45 AM

If the car needs two fans then really the alternator should be upgraded to cope. A dual fan controller could set you back as little as £30, but with zero budget I would wire one fan to the electronic stat switch and the second to manual override for the once in a blue moon event that it's actually required. I would suspect that one fan will easily cope with stationary running in hot weather, if not then I think there is a more deep seated problem with your cooling system...

Jamieg285 · August 08, 2014, 10:31:45 AM

Quoting: Titsy

If the car needs two fans then really the alternator should be upgraded to cope.

Fair comment. I don't know that it needs both, it's just I've always run them that way. I guess I need to do some testing when it's all back together.

I do have a 140 Amp Powermaster that gave up the ghost, and a rebuild kit in the garage somewhere. Been there for about 4 years now! I think I should dig it out and sort it. That said, I seem to remember the output at idle (i.e. when I'm stuck in traffic and temps are rising!) is quite low, and needs a bit of revs to perform more to it's potential.