Gold and silver resistors

DerekS · 1st May 2017, 15:18

I see threads recently about problems with the fan resistors . ....overheating to the extent that they fail and sometimes with disastrous consequences .
The resistor is there to reduce the voltage supplied to the fan motor, and it has to be able to carry quite a high current . The heat generated by this resistance in a small component must be dissipated or the resistor will fail due to overheating .
I am wondering .... why not use two resistors in parallel, to reduce the individual current in each component , thus halving the heat each resistor has to dissipate ? The total heat will be the same , but spread over two instead of one , so reducing the temperature the resistor has to stand . Smaller current , higher value resistors should be cheaper than the
single heavy duty one required .
With so many high class, knowledgeable members , i wonder if this has been considered . I would be interested in their ideas .

T-Cut · 1st May 2017, 15:33

I've certainly considered doing that myself, but haven't gone any further. For a double unit, you'd need two 1ohm resistors, preferably rated 50watts minimum. Whether that would prevent resistor 'exploding' through water penetration or whatever the cause, is debatable. The main problem is fitting two resistors onto the fan guard. You'd have to organise a second mounting point which might be easier said than done. Of course anything's possible with enough effort. Realistically, the chance of anyone's fan exploding is pretty small, around (0.3%) according to Jules who's supplied more than anyone. My view is try to minimise the damage IF it happens.

So far I've simply changed the 80amp fuse to a 40amp to reduce the possibility of frying the harness if the motor is seized or something stops the fan from turning.

TC

oswestryalex · 1st May 2017, 19:26

YOu need to be careful with the 'effective resistance' of what you end up with, of course - so two in parallel will halve the value, thus that needs to be taken into account. Perhaps a set of 4 two in series, paralleled (if that makes sense?) might do it - but the mounting would be the main bugbear.

MarkS · 1st May 2017, 20:35

I am going to go for 2x 100W resistors in parallel, and a 40 amp fuse :

http://www.the75andztclub.co.uk/foru...2&postcount=34

(I don't fancy doing a Zafira!)
(Or should that be a Zafire ?)

T-Cut · 1st May 2017, 20:48

Quote:

Originally Posted by MarkS

I am going to go for 2x 100W resistors in parallel, and a 40 amp fuse

According to the theory as to why they 'explode', the twins in parallel approach is no less likely to blow than the standard system. They'll both get above 100C internally. The 40amp fuse is a wise move IMO. Let us know how you get along with the fitting. It'll be worth taking plenty of photos for a HowTo, so please do come back on this. They need to be 1ohm each of course.

TC

DerekS · 1st May 2017, 21:53

Well thats stirred up a bit of interest . Thank you all for your comments .
Can anyone answer MarkS question (elsewhere ) about the specification of the normal silver and gold resistors? ( amps and max temperature ) .
I havent had the 'pleasure '..yet... of fitting a resistor to the fan housing , but would it be possible to use a small metal plate to mount it on, and then fasten it to the housing ? .
I am just trying to reduce the temperature of the resistor, by the plate, and halving the current through each parallel resistor .
And best of luck to the experimentors . Be careful and get the calculations right .

Mike Trident · 1st May 2017, 23:11

if you could bolt the thing to a piece of sheet alloy to work as a heat sink it would help, but where could you put it?

Mine blew due to my fault. Like T-Cut says, some may blow from time to time, just like some tyres have punctures now and again. Like it has been said, the odds of one blowing is small. It's the possible damage to the wiring or even the whole car that is more of an issue. I would rather pop a 40 amp fuse now and again than watch my car go up in flames. At least the fuse is in a very easy place to get at, you don't need to remove the glovebox lol.

murphyv310 · 1st May 2017, 23:41

The gold resistor should be rated at 100 watts if I'm not mistaken, the OE silver one was lower rated at 50 as far as I can remember.
For one of these to go bang either there was a short in the motor or wiring or the fan was baulked.

MarkS · 2nd May 2017, 07:46

Can I recommend that everybody (that has had a resistor failure) check that the main fan fuse FL4
1) Has a 80 amp fuse fitted.
2) Remove FL4 and check that somebody hasn't bypassed the fuse with a piece of wire ( as has been known to happen to alternator fuses et al).
After all, we could be being led up a blind alley by idiots bypassing fuses!!!

murphyv310 · 2nd May 2017, 08:05

Even fitting a 40 amp fuse in a fault condition could still pop the resistor.
These resistors are used in many electronic items, power supplies and control circuitry the most common. They are usually bolted to metal framework or a chassis to aid cooling, not so in our case the air passing over the resistor does help though. The control of the fan should have really been done by PWM.

1st May 2017, 15:18	#1
DerekS Posted a thing or two Rover 75 Tourer Join Date: Nov 2006 Location: Malpas Posts: 1,526 Thanks: 34 Thanked 118 Times in 89 Posts	Gold and silver resistors I see threads recently about problems with the fan resistors . ....overheating to the extent that they fail and sometimes with disastrous consequences . The resistor is there to reduce the voltage supplied to the fan motor, and it has to be able to carry quite a high current . The heat generated by this resistance in a small component must be dissipated or the resistor will fail due to overheating . I am wondering .... why not use two resistors in parallel, to reduce the individual current in each component , thus halving the heat each resistor has to dissipate ? The total heat will be the same , but spread over two instead of one , so reducing the temperature the resistor has to stand . Smaller current , higher value resistors should be cheaper than the single heavy duty one required . With so many high class, knowledgeable members , i wonder if this has been considered . I would be interested in their ideas .

1st May 2017, 15:33	#2
T-Cut This is my second home Rover75 and Mreg Corsa. Join Date: Nov 2006 Location: Sumweer onat mote o'dust (Sagin) Posts: 21,752 Thanks: 341 Thanked 3,660 Times in 2,924 Posts	I've certainly considered doing that myself, but haven't gone any further. For a double unit, you'd need two 1ohm resistors, preferably rated 50watts minimum. Whether that would prevent resistor 'exploding' through water penetration or whatever the cause, is debatable. The main problem is fitting two resistors onto the fan guard. You'd have to organise a second mounting point which might be easier said than done. Of course anything's possible with enough effort. Realistically, the chance of anyone's fan exploding is pretty small, around (0.3%) according to Jules who's supplied more than anyone. My view is try to minimise the damage IF it happens. So far I've simply changed the 80amp fuse to a 40amp to reduce the possibility of frying the harness if the motor is seized or something stops the fan from turning. TC Last edited by T-Cut; 1st May 2017 at 15:39..

1st May 2017, 20:35	#4
MarkS Gets stuck in Rover 75 Diesel Tourer, called Perseverance Join Date: Nov 2011 Location: Bournemouth Posts: 664 Thanks: 189 Thanked 157 Times in 108 Posts	I am going to go for 2x 100W resistors in parallel, and a 40 amp fuse : http://www.the75andztclub.co.uk/foru...2&postcount=34 (I don't fancy doing a Zafira!) (Or should that be a Zafire ?) Last edited by MarkS; 1st May 2017 at 22:23..

1st May 2017, 23:41	#8
murphyv310 This is my second home Hyundai i10 998cc Join Date: Mar 2012 Location: Kilmarnock Posts: 6,602 Thanks: 2,088 Thanked 2,298 Times in 1,349 Posts	The gold resistor should be rated at 100 watts if I'm not mistaken, the OE silver one was lower rated at 50 as far as I can remember. For one of these to go bang either there was a short in the motor or wiring or the fan was baulked. __________________ Cheers from Trevor MM0KJJ

2nd May 2017, 08:05	#10
murphyv310 This is my second home Hyundai i10 998cc Join Date: Mar 2012 Location: Kilmarnock Posts: 6,602 Thanks: 2,088 Thanked 2,298 Times in 1,349 Posts	Even fitting a 40 amp fuse in a fault condition could still pop the resistor. These resistors are used in many electronic items, power supplies and control circuitry the most common. They are usually bolted to metal framework or a chassis to aid cooling, not so in our case the air passing over the resistor does help though. The control of the fan should have really been done by PWM. __________________ Cheers from Trevor MM0KJJ Last edited by murphyv310; 2nd May 2017 at 08:11..

1st May 2017, 19:26	#3
oswestryalex Loves to post Rover 75 1.8T connoisseur saloon 2003 in blue , MG ZT 190+ 2003 Join Date: Jul 2012 Location: Oswestry Posts: 308 Thanks: 159 Thanked 99 Times in 57 Posts	YOu need to be careful with the 'effective resistance' of what you end up with, of course - so two in parallel will halve the value, thus that needs to be taken into account. Perhaps a set of 4 two in series, paralleled (if that makes sense?) might do it - but the mounting would be the main bugbear.

1st May 2017, 21:53	#6
DerekS Posted a thing or two Rover 75 Tourer Join Date: Nov 2006 Location: Malpas Posts: 1,526 Thanks: 34 Thanked 118 Times in 89 Posts	Well thats stirred up a bit of interest . Thank you all for your comments . Can anyone answer MarkS question (elsewhere ) about the specification of the normal silver and gold resistors? ( amps and max temperature ) . I havent had the 'pleasure '..yet... of fitting a resistor to the fan housing , but would it be possible to use a small metal plate to mount it on, and then fasten it to the housing ? . I am just trying to reduce the temperature of the resistor, by the plate, and halving the current through each parallel resistor . And best of luck to the experimentors . Be careful and get the calculations right .

1st May 2017, 23:11	#7
Mike Trident Posted a thing or two Rover 75 CDTi Saloon & Citroen C1 Join Date: Jun 2016 Location: Oakenshaw, Near Bradford Posts: 1,622 Thanks: 385 Thanked 552 Times in 328 Posts	if you could bolt the thing to a piece of sheet alloy to work as a heat sink it would help, but where could you put it? Mine blew due to my fault. Like T-Cut says, some may blow from time to time, just like some tyres have punctures now and again. Like it has been said, the odds of one blowing is small. It's the possible damage to the wiring or even the whole car that is more of an issue. I would rather pop a 40 amp fuse now and again than watch my car go up in flames. At least the fuse is in a very easy place to get at, you don't need to remove the glovebox lol.

2nd May 2017, 07:46	#9
MarkS Gets stuck in Rover 75 Diesel Tourer, called Perseverance Join Date: Nov 2011 Location: Bournemouth Posts: 664 Thanks: 189 Thanked 157 Times in 108 Posts	Can I recommend that everybody (that has had a resistor failure) check that the main fan fuse FL4 1) Has a 80 amp fuse fitted. 2) Remove FL4 and check that somebody hasn't bypassed the fuse with a piece of wire ( as has been known to happen to alternator fuses et al). After all, we could be being led up a blind alley by idiots bypassing fuses!!!