Amps, Alterntors & Rad Fans

[450Nick]

ChimpOnGas said:

Yes the fans are staged Rich, the otter switch runs one and the ECU the other, I never actually measured the spike but it's eaten three relays in the last year so there's definitely an issue.

Edited by ChimpOnGas on Sunday 27th November 18:55

Issue or not, this is not the right way to do it; by switching on one fan and not the other, the running fan will pull hot air from the exhaust side through the non running fan in a circle so you won't get efficient cooling.

On my new GEMS build, I have put in a new otter switch from Land rover which has a two stage switch, one at 87 and one at 89 I believe, and via a couple of relays (I have the circuit diagram at home) it wires the fans in series for the first stage, or in parallel for the second. By doing this, it switches both fans on gently at half speed, and limits the current draw significantly for a soft start (they are also extremely quiet at half speed). Because they are already running, when full power is required, relatively little effort is needed to wind them up to full power so again, no big current draw is seen. I have noticed through doing this that half speed is all you need most of the time, and it is very rare that full power even engages.

Edit: just noticed that someone beat me to it!

[FoxTVR430]

450Nick said:

ChimpOnGas said:

Yes the fans are staged Rich, the otter switch runs one and the ECU the other, I never actually measured the spike but it's eaten three relays in the last year so there's definitely an issue.

Edited by ChimpOnGas on Sunday 27th November 18:55

Issue or not, this is not the right way to do it; by switching on one fan and not the other, the running fan will pull hot air from the exhaust side through the non running fan in a circle so you won't get efficient cooling.

On my new GEMS build, I have put in a new otter switch from Land rover which has a two stage switch, one at 87 and one at 89 I believe, and via a couple of relays (I have the circuit diagram at home) it wires the fans in series for the first stage, or in parallel for the second. By doing this, it switches both fans on gently at half speed, and limits the current draw significantly for a soft start (they are also extremely quiet at half speed). Because they are already running, when full power is required, relatively little effort is needed to wind them up to full power so again, no big current draw is seen. I have noticed through doing this that half speed is all you need most of the time, and it is very rare that full power even engages.

Edit: just noticed that someone beat me to it!

Do you have a part number for the relay, otter switch?
Is that all you need, or do you need something else.
cheers Simon

[Discopotatoes]

450Nick said:

ChimpOnGas said:

Yes the fans are staged Rich, the otter switch runs one and the ECU the other, I never actually measured the spike but it's eaten three relays in the last year so there's definitely an issue.

Edited by ChimpOnGas on Sunday 27th November 18:55

Issue or not, this is not the right way to do it; by switching on one fan and not the other, the running fan will pull hot air from the exhaust side through the non running fan in a circle so you won't get efficient cooling.

On my new GEMS build, I have put in a new otter switch from Land rover which has a two stage switch, one at 87 and one at 89 I believe, and via a couple of relays (I have the circuit diagram at home) it wires the fans in series for the first stage, or in parallel for the second. By doing this, it switches both fans on gently at half speed, and limits the current draw significantly for a soft start (they are also extremely quiet at half speed). Because they are already running, when full power is required, relatively little effort is needed to wind them up to full power so again, no big current draw is seen. I have noticed through doing this that half speed is all you need most of the time, and it is very rare that full power even engages.

Edit: just noticed that someone beat me to it!

I doubt it will draw that much in from the engine bay, as it will draw air with the least resistance I e straight through the rad as opposed to through the rad the wrong way then turn 180 degs and back through the rad. My original fan setup never had a cowling so there were large areas of rad exposed to the hot side, never had an issue.
Anyway I was referring to staging the start up of the rad to avoid current spikes all at the same time

[stevesprint]

FoxTVR430 said:

Do you have a part number for the relay, otter switch?
Is that all you need, or do you need something else.
cheers Simon

I used this thermostat switch off my old 205GTi, there are plently of other temperatures and connectors to choose from.
Valeo 819773 (Quinton Hazell XEFS40) 1st: 93-88, 2nd: 97-92 degree.


To run twin fans with 2 stages on my Precat I only fitted this one extra relay for the 2nd stage serial to parallel change over and left all the original TVR wiring, fuse and relay in place to bring on the 1st stage as normal.

[450Nick]

I decided to rip out all of the wiring in my car and replaced it with the wiring diagram I drew above. I used a similar fan switch, then used a 70A DPDT relay from Farnell for the changeover and a single 70A relay for initial switch on. Works a treat!

http://www.ebay.co.uk/itm/Radiator-Fan-Switch-Visa... (fan switch)

Edited by 450Nick on Tuesday 29th November 09:49

[ChimpOnGas]

450Nick said:

I decided to rip out all of the wiring in my car and replaced it with the wiring diagram I drew above. I used a similar fan switch, then used a 70A DPDT relay from Farnell for the changeover and a single 70A relay for initial switch on. Works a treat!

http://www.ebay.co.uk/itm/Radiator-Fan-Switch-Visa... (fan switch)

Edited by 450Nick on Tuesday 29th November 09:49

Thanks Nick

Let me see if I've understood this correctly

Wired as shown your fans are in series for the first stage and in parallel for the second? Both fans initially come on gently at half speed which should significantly limit current draw on start up and mean they are quieter too, when they shift to full speed the current spike is also reduced because the fans are already running?

To make all this work I need a 70A DPDT changeover relay and a twin value otter switch?

I really like your setup for the following reasons:

1. It uses a proven, reliable and cheap to buy twin value otter switch

2. I get to free up my Canems ECU output that's currently controlling one fan so I can use it for something else

3. The fans soft start reducing the current spike we see on start up with the standard setup

4. The first speed is much quieter and should be sufficient to control coolant temps in most situations on its own without needing to resort full speed

5. In summer stop start traffic when full speed is required you still enjoy a greatly reduced current spike because your fans are already running at half speed

That adds up to five clear benefits, if I've understood your system correctly wiring the fans this way looks to me like the definitive setup

Thanks again, Dave.

[450Nick]

Yup, you're exactly right on all points. It's nice and simple and robust but does the job elegantly.

[stevesprint]

450Nick said:

Nick
Thanks, that's a brilliant & clear diagram.

Here’s a few M22 x 1.5mm sensors to choose from with some old Quinton Hazel and Intermotor part numbers.

QH Part   1stStage  2nd Stage                       Equiv  
XEFS202    95-90     100-95    4 Pin               FAE37960   50018   Escort 1.6/8 90-95 Mondeo 1.8D 
XEFS40     93-88      97-92    3 Std Spades        Intermotor 50102 205 1.6/9 83-90, pug/Cit 86-93 
XEFS86     92-87      97-92    3 Pin Junior Timer  Intermotor 50092 205 1.6/9 90-94, pug/Cit 87-96 
XEFS31     84-79      88-83    
           87-75      93-82    3 Pin VW plug       Intermotor 50025
LFS025     88-83      92-87    3 Std Spades        Intermotor 50091 or 50216

I like the idea of this one with the modern 3 way junior timer plug plus its temperatures are about right for the 14CUX, any cooler and the lambda probes won’t work correctly.


Dave
I like your summary, you could even add "6. Halves the wear as the fans run at half the speed".

What temperatures does your Canems ECU turn your fans on and off? For the last 20 years I’ve always used fan switch 92-87 97-92 and found the first stage perfect for most of the year, the second stage very rarely kicks in like on the hottest day of the year or on a rolling road.

[ChimpOnGas]

stevesprint said:

Nick
Thanks, that's a brilliant & clear diagram.

Here’s a few M22 x 1.5mm sensors to choose from with some old Quinton Hazel and Intermotor part numbers.

QH Part   1stStage  2nd Stage                       Equiv  
XEFS202    95-90     100-95    4 Pin               FAE37960   50018   Escort 1.6/8 90-95 Mondeo 1.8D 
XEFS40     93-88      97-92    3 Std Spades        Intermotor 50102 205 1.6/9 83-90, pug/Cit 86-93 
XEFS86     92-87      97-92    3 Pin Junior Timer  Intermotor 50092 205 1.6/9 90-94, pug/Cit 87-96 
XEFS31     84-79      88-83    
           87-75      93-82    3 Pin VW plug       Intermotor 50025
LFS025     88-83      92-87    3 Std Spades        Intermotor 50091 or 50216

I like the idea of this one with the modern 3 way junior timer plug plus its temperatures are about right for the 14CUX, any cooler and the lambda probes won’t work correctly.


Dave
I like your summary, you could even add "6. Halves the wear as the fans run at half the speed".

What temperatures does your Canems ECU turn your fans on and off? For the last 20 years I’ve always used fan switch 92-87 97-92 and found the first stage perfect for most of the year, the second stage very rarely kicks in like on the hottest day of the year or on a rolling road.

To answer your question I've configured my Canems system to turn on one fan at 89c and off at 87c, this is a very tight 2c on/off window because the otter switch controlled fan does most of the work and only needs the support of the Canems controlled fan very briefly.

I believe the rating I chose for my otter switch was 88c on and 83c off so the otter switch controlled fan always comes on first, the Canems controlled fan typically chimes in a few seconds later as the coolant hits 89c, it only stays on briefly while the other fan continues the work of getting the coolant below 83 degrees before that too shuts off.

With an 88 degree thermostat the car maintains coolant temps between 82 & 85 degrees while on the move depending on ambient temps, this means the fans are only ever used (and needed) when the car is at idle. The fans cycle on and off in a staggered way and never fire up at the exact same moment, this reduces the current drop associated with two fans starting in unison. Saying that one of my fans is sick so I'll be replacing it very soon with a new low amp brushless motor model from Spal with the soft start feature, clearly this will improve my system still further.

The otter switch controlled fan is on a permanent live while the Canems controlled one is running from a switched live just as TVR wired the original set up. This means when I switch the engine off the Canems fan will be stopped immediately but the otter switch controlled fan will continue to run until the coolant temperature falls to 83c, the permanent live circuit also runs a Davies Craig electric booster water pump so all the time that fan is running there's also a circulation of coolant around the engine even though it's been completely switched off and the mechanical water pump is no longer turning.

The system works well as coolant temps never exceed and absolute and momentary peak of 92c at idle as tested on the very hottest summer day this year in the South of France where ambient temps soured close to 100, under normal weather conditions the car will idle happily all day never exceeding an absolute maximum of 88c. Running temps also never exceed 85c with road speeds above a modest 15mph, and finally even with the engine completely switched off on a hot day there's still both air flow from one fan and water circulation from the electric booster pump, this system eliminates any risk of heat surge to the heads on switch off.

I still like the way Nick wired his fans though, and may well incorporate it as an enhancement to my current set up, but first I need to replace the sick fan that's causing its relay contacts to stick closed.

Edited by ChimpOnGas on Tuesday 6th December 19:05

[stevesprint]

Dave
Thanks for your detailed answer, I’m impressed with your attention to detail and fine tuned Canems fan output, you’re nearly as anal meticulous as me

The only advantage of a Chimmy compared to a Precat Griff is the Chimmy rad is upright where as the Precat Griff rad leans forward more than 45 deg and therefore requires more speed to keep the fans off.

My fans are wired the same as 450Nick's and I wouldn’t have them any other way, its the oldest trick in the book for twin motors, I've seen the same wiring trick on a kids battery powered car with two gears, it works a treat.

[ChimpOnGas]

stevesprint said:

Dave
Thanks for your detailed answer, I’m impressed with your attention to detail and fine tuned Canems fan output, you’re nearly as anal meticulous as me

The only advantage of a Chimmy compared to a Precat Griff is the Chimmy rad is upright where as the Precat Griff rad leans forward more than 45 deg and therefore requires more speed to keep the fans off.

My fans are wired the same as 450Nick's and I wouldn’t have them any other way, its the oldest trick in the book for twin motors, I've seen the same wiring trick on a kids battery powered car with two gears, it works a treat.

Your & 450Nick's system is very elegant, mine is more simple than I made it sound as its really just an otter switch controlling one fan more or less as normal and my ECU controlling the other which makes it easy to tune.

The slow speed of your & Nick's set up is something I don't have and is a really worthwhile addition, I'm keeping it simple with mine by just adding one of the newer soft start Spal fans.

Both system are proven to work well it seems but your & Nicks is the better of the two in my opinion, my electric water pump adds a nice line of defence against heat surge on switch off but I can't really present any proof its actually necessary. The pump is on the heater circuit as is my LPG vaporiser so for faster change overs to gas in cold weather I just flick it on to get some hot coolant around the vap a little sooner, works well to warm the car's interior too.

Having the electric pump run on with the fan after engine switch off really just came as a secondary idea, and was only implemented because I could.

Dave

Edited by ChimpOnGas on Tuesday 6th December 23:30