Slimline fans -wiring

[oneohtwo 8]

I've checked the resistance on the fan motor, and it's as follows:

Speed 1: 0.5 - 0.7 ohms

Speed 2: 0.1 - 0.2 ohms.

I double checked the multimeter against a resister with a known value of 0.66 (+/-5%) and it read 0.7 so should be correct.

Took a few readings which gave the range above. Speed 1 initially was 0.7 but then had more readings at 0.5-0.6 probably after I scraped some corrosion off the contacts.

 

 

 

[fla 9]

Thats great info, thanks

 

Hasan

[oneohtwo 8]

Right based on all this, I think a reasonable wiring diagram/loom could look like this:

Which I don't think would need any diodes - correct me if I am wrong. This pretty well reflects the Bentley diagram:

But with the take off to the second fan. I've added the colours and thicknesses of wire to the diagram for reference as well. Just need to decide what resistors are needed. I have shown the lower end of the readings I got, on the basis that at some point in the circuit the resistance was at those levels. The higher values could be due to gunk on the connectors.

I am not sure what power rating the resistors should have, not being all that familiar with electronics. I understand this is the power the resistor needs to dissipate and can be found y P=V^2/R where V is the voltage drop - but how do we find the voltage drop? I know this could be found by V = IR where I is the current, but I don't know the current. Any ideas?

Or just pick the resistor with the highest power rating for those resistances and hope that covers it?

 

 

[fla 9]

That seems to make sense. The power rating might be written on the fan but i guess a fair assumption would be a 15amp power draw tops. P=VI so 15x12 =180w resistor power rating.

 

[Dox 22]

Mk4s have a really poor unreliable slow speed fan set up, many years ago bigal did an external resistor fix, maybe worth a read?

 

https://uk-mkivs.net/topic/224371-mk4-golfbora-radiator-fan-fix/

 

id wire the earth side direct to the body to eliminate voltage drop from the oe wiring

[oneohtwo 8]

Yeah, those seem fair assumptions to give a worst case. (removed the nonsense about the alternator) Voltage drop won't be the full 12V and I read somewhere a rule of thumb was to use a resistor with twice the power rating so I think 180W would do the job, as the voltage drop on the first resistor will be about 6V with 15a. 

This is good! Think I am going to go with that. 

Edited February 25, 2021 by oneohtwo

[oneohtwo 8]

Thanks Dox, that is quite useful - I think d need those panel mounted resistors as well, in order to get the power rating. The inline ones don't go high enough from what I can see.  Will need some thought for where to locate them.

[Dox 22]

On the golf they mount them under the chassis leg underneath the battery in air flow for cooling

[fla 9]

Anywhere in the engine bay should be fine to allow sufficient cooling. As long as they're not too near any plastic. Some screws to hold the resistors in place might be easier than sticking them. It'll help with cooling too as well as being easier to replace if necessary

Edited February 25, 2021 by fla

[oneohtwo 8]

To add to this I have found the data sheet for the Revotec/Comex fans and the current is listed as 7.2A approx, with max 8.1A:

Revotec Instructions Template

Based on that 1 fan has a resistance of about 1.5Ohms. I have measured it and it is more like 1.8 Ohms, but a lower resistance gives a worst case at the resistor so We'll work with 1.5.

For Fan Speed 1 the circuit therefore looks like this:

Which gives the following values for

R1: P = 37.5 W, V = 3.9 V, I = 9.7 A

R2: P = 9.4 W, V = .97 V, I = 9.7 A

And for Fan Speed 2:

 R2: P = 20.4 W, V = 1.4 V, I = 14.3 A

(I have run these through some circuit builder software to get the values, so the values should be accurate although I have rounded. I got lost trying to do it by hand...)

So I think we just need a 75 W resistor for the R1 on the fan speed 1 circuit and 50 W for R2. Little bit less than initially thought, but should do the job.

 

 

 

[fla 9]

Wiring would be 14 swg which can handle about 8.5 amps or if you really felt like it you could do 12swg which will take about 13amps. But it would be harder to work with.

I'll try and get one made up soon and see how it goes and where it could be best located.

So in summary, 

0.1 ohm aluminium clad resistor 75 -100w

0.4 ohm aluminium clad resistor 50-75w

Length of wire approx 1m

Aluminium base plate heat sink

 

Oneohtwo is that about right?

 

Hasan

[oneohtwo 8]

Other way around on the resistors!

0.4 Ohm 75-100w

0.1 Ohm 50-75w

I couldn't find a panel mount resistor at 0.4 Ohm, nearest available was 0.47 Ohm which I was going to go for, and rerun the calcs to double check the power. 

I think you may need a higher current rating on the wire to be safe - Fan speed 2 is at 14.7A and on Fan Speed 3 without the resistors it would be just over 16A, for the shared part of the circuit. I was going to just try and copy the sizes for the existing cables: 2.5 mm2 for fan speed 1(red/white) , 4.0 mm2 for fan speed 2 (black/red) and 6.0 mm2 for fan speed 3 (red/green) and ground. I found these:

Tri Rated 6mm 53amp Automotive Cable (cablecuts.co.uk)

Tri Rated 4mm 41amp Automotive Cable (cablecuts.co.uk)

Tri Rated 2.5mm 30amp Automotive Cable (cablecuts.co.uk)

Which I was going to use, only downside is they are not thinwall. This place: CABLE (altecautomotive.co.uk) also looked promising for thinwall but they didn't have the 2.5mm wire but I expect you could use 3.0mm instead. Everywhere else seemed to be selling full drums of 10m+ length!

I was considering using the two holes in the slam panel for the plastic fan guard to mount the resister base two (resistors on the underside) as I didn't massively want to cut new holes in the bodywork. Or possibly my preferred is to have it fixed to the fan shroud coming out perpendicularly, at the the coolant pipe end. That way it's all together in one plug and play unit. What do you think?

 

[1xshaunx1 27]

I’d stick With 4mm for both and get a different colour if you really want them to be more identifiable. Very interested how you get on. 

[oneohtwo 8]

Got all the wire and clips ready to sort and had a shroud made for the new fans. My plan is to mount the resistors on a panel fixed to the side of the mount between the upper and lower hoses:

Where I have taken the shroud around under the bottom of the radiator it rests on the radiator cross member (where the green tape is, which is a bit annoying. Too late to change now, and if I cut the bottom flange off I don't think the shroud will have enough stiffness. I can't see it being a problem, but it just feels like it should be kept clear like the original?

Edited March 29, 2021 by oneohtwo

[oneohtwo 8]

Right, it all works!

On 3/10/2021 at 2:43 PM, 1xshaunx1 said:

I’d stick With 4mm for both and get a different colour if you really want them to be more identifiable. Very interested how you get on. 

You were right about this, I was going way overboard with 6mm wire, which wouldn't have fitted in all the connectors. i guess the original fan motor ran a much higher current. When I looked the actual ratings I found 1mm wire would be sufficient for fan speed 1. Anyway, this is what the finished wiring looked like:

Which is to this wiring diagram:

Essentially the same as the one at the top of the page but I have updated the wire thicknesses. Also I couldn't find Red/Green wire in 4mm so just used Red.

I used this wire:

Thin Wall Cable (autoelectricsupplies.co.uk)

And these connectors to splice the wires:

108961-000 Raychem - Te Connectivity, Butt Splice, Yellow, DuraSeal Series | Farnell

Which are Duraseal Yellow crimp butt connectors with heatshrink. These are nice because the heatshrink material gives a good seal around the wires at the connection. You need yellow (10-12AWG) for all connections I found. The Blue connectors (14-16 AWG) is just too small, even for the 1 and 2mm wire join, which approximately makes 13 AWG. You have to double over the end of the 2.0mm wire where it is on its own, but this is no big issue.

The resistors I used are:

HSC100R47J | TE Connectivity HSC100 Series Aluminium Housed Solder Lug Wire Wound Panel Mount Resistor, 470mΩ ±5% 100W | RS Components (rs-online.com)

For the fan speed 1 circuit. This is a 0.47 Ohm resistor as I couldn't find a 0.4 Ohm. Makes little difference though. Don't know if this is the best brand, but it seemed to have a better temperature stability.

And:

HSA50R10J | TE Connectivity HSA50 Series Aluminium Housed Solder Lug Wire Wound Panel Mount Resistor, 100mΩ ±5% 50W | RS Components (rs-online.com)

For fan speed 2.

At the end the resistances were about 0.7 Ohm for fan speed 1, 0.2 Ohm for fan speed 2 and 0.1 Ohm for fan speed 3. Little bit higher accounting for the extra resistances for the other circuit components, and possibly rounding due to my multimeter only going to 1 decimal place accuracy, but within the right original range.

You can also get the female connectors for the Comex slimline fans here:

2 Pin Plug Connector for Comex Fans from Merlin Motorsport

For straight plug and play. These (and the spade connectors on the Passat plug) are open barrel types so you will need the correct crimper tool. To get the existing wires out of the Passat spade connectors is a pain but doable. For the 2 larger connectors (Speed 3 and Ground) I found it was possible to hammer a small screwdriver (jewellery/watch type) down the back of the wire to open it up. Make sure the spade is held securely in a vice to stop it bending, and use pliers to hold the neck of the connector as well. For the smaller two it should be possible to pull the wires out with a pair of pliers, starting with one or two threads in the middle of the bunch. With the wires out you can just about open the metal enough to get the new wire in. Because you are reusing these I would solder as well as re-crimping them. I re-crimped and the seemed to be holding OK, but soldered as well as a back up. 

I then knocked up a bracket to mount the resistors on. Here is the finished setup:

Not my best wrapping! Thought I had ran out of the usual tape, and used the slightly furry stuff which doesn't look as neat, and then found the plain roll again. The panel for the resistors tucks around the side of the rad between the battery in the void behind the headlights, as my original plan of mounting the panel straight out clashed with the battery. This is it in the car:

The big downside with this is that you can't get the battery out without removing the fans as the plug is in the way...  Unfortunately I had no time to prototype this so  I had to live with it for the time being. I think it theoretically should be possible to slide the whole shroud out in one go to get the battery out but it's a pain, and I will need to try and remedy this longer term. In hindsight I should have kept the panel coming out perpendicularly but flipped so that the resistors are mounted in the fan slipstream; I may try and do this, although will have to try and find another Passat plug!

Anyway, I tested the three fan speeds with the battery prior to fitting and the all come on fine, and at different speeds (no reason why they shouldn't!) Since being on the car they do come on alright, although I can't really tell if all 3 speeds have been used yet. Not sure what temp speeds 2 and 3 come on and it's a bit hard to tell over the engine noise. 

Don't know if it was worth the hassle and expense yet, but the fans seem a bit quieter and on the initial slow (20-30mph), albeit, short driving runs the temp seems to have stayed about 90-100 degrees.

 

Edited April 17, 2021 by oneohtwo

[Cressa 44]

Absolute awesome write. I hope it benefits someone else another time, yet a great read for me anyway.👍

[fla 9]

Excellent work there oneohtwo!  I'll be making one of these and compare with the existing loom i have as to which is better - and quieter!

[1xshaunx1 27]

Excellent progress and brilliant write up. 
👍

[easypops 8]

Absolute brilliant, really nice work....... makes me realise I’m miles away in terms of quality, my setup looks like I’ve done it with boxing gloves on 🤣

I’ll have a good read soon and I’ll be ordering all the bits you’ve used. 
Again, superb work and help 😎

[oneohtwo 8]

No problem!

The biggest issue is working out where to fit the resistors, so take a bit of time on that one. You should also get some heat transfer compound to go under the resistors when you mount them.

It's a bit of a pain that I'll have to redo mine so you can get the battery out, but I should be able to do it at my leisure now, rather than rushing against the clock.

Edited April 23, 2021 by oneohtwo

[ABV-VR6 12]

This as been quite an interesting read, nice projects and write ups.
This week, I took apart my rad shroud to get it ready for powder coating. I noticed the plastic rings around the fan blades all cracked up. It sucks because these are NLA and the rest is in very good condition. Anyways, long story short, I'm looking at alternatives and that's how I found this thread. So from this reading, it's making me realize that I'm probably not alone having issues as it looks like almost all of you already upgraded to a newer system with bigger & thinner fans... Is it worth it? Is it way better at cooling the engine? Cheers!

[oneohtwo 8]

It's a good question and to be honest - it's hard to say!  I did the fans at the same time as I did the engine rebuild so I haven't got a direct comparison on a fresh engine. They are the same size as the stock fans (11"); you might just be able to squeeze in 12" if you wanted to go bigger.

Currently my engine temp sits at about 100 C in slow moving traffic in this weather which is OK I think. To be honest I thought it would be a little bit better than that what with the engine rebuild, but I don't know what would be considered low and high temps; however, I'm sure you'd get this with a stock fans as well.  When I first got the car 10 years ago I am sure it ran fairly cool in traffic, around 90-100 (memory might be playing tricks there though!). I'm sure other people could confirm but 100 doesn't seem wildly low or beyond the realms of the OEM ones, but then who knows, if I had stuck with OEM fans I might be getting temps of 110 or so.

I did have issues with engine temps sitting in traffic for long periods in the couple of years before I started the rebuild, to the point where the engine would start to run badly, and be on the verge of cutting out. But that was with a tired old engine so not really a good comparison. 

I also need to do an engine flush as I think deposits have built up in the rad (the old pipes I took off were coated) which won't help, so the fans might be battling against that. 

For the moment I am a little bit sceptical about whether it was worth it: It was a bloody hassle to sort (although would be a lot easier now I've done it once and got a guide), it's not really that much lighter (if you were thinking of that - about 1kg less), and doesn't seem to be greatly cooler. Think they might be a little bit quieter. 

[1xshaunx1 27]

The slims aren’t massively better but quieter,  it’s also that with them being new they should be more reliable. 
As you know I have a turbo fitted and as such more heat in the bay and a big fat intercooler infront of the radiator doesn’t help either, the fans were coming on a fair bit. 
I read up on spal fans and their abilities and went for 12” fans the best slim and a very powerful not so slim. This set up really does draw a lot of air when both are on. My cooling is definitely better than before and hopefully because it’s new it won’t matter how often it comes on. If new OE fans were available off the shelf I might have stuck to stock but I think this set up works well for the heat I’ve got to get rid of in slow moving traffic on a hot day. 
Having said all that my previous Corrado was a stock set up and I never really had problems with that, over 20k miles but I did change the thermostat, housing and sensors early on and the correct coolant with not much water. But these days the fans are nearly 30 years old so it’s a problem you might have to solve one day anyway. 
My 12” set up when nearly finished. It does fit but that’s about as big as you can go. 

[ABV-VR6 12]

Thank you very much to you too for your time and comments. Much appreciated! Shaun that set-up you've put together is really looking good! 

I never thought of doing anything about my oem fans other than a powder coat but finding those broken plastic rings lead to a NLA part search. I'm not going turbo and I think the oem system is efficient enough but if I can't fix it, then what! And maybe this is good thing after all. It's true, those old parts would fail and with a new engine going on and knowing how VR6 runs hot, maybe it is a good thing to upgrade to spal fans. There's a kit I can buy here with the shroud, electrical and two 12" spals. I'm starting to think that maybe it would be a good thing to go for this, specially after noticing that many of you did the move already! 

Thanks for helping me out, you guys are the best! Cheers 

[fendervg 29]

It's worth doing a  search for those rings - they are out there, I got some new 2 years ago when replacing my radiator - I'll see if I can dig out the receipt and part# - as far as I remember they are not a Corrado specific part either, and used on other models.

One problem is that if the metal shroud is rusting, the holes that the rings clip into could be corroded and might not fit securely.