Two Stage Fan Switch - Simple Solution?

Two Stage Fan Switch - Simple Solution?

Author
Discussion

v8s4me

Original Poster:

7,234 posts

218 months

Sunday 26th February 2017
quotequote all
This is TVR's idea of how to reduce the current and slow down the fan on the first speed setting...



Some marks for effort I suppose, even if it is a fire risk.

Would connecting THIS to the first stage do the trick?

Edited by v8s4me on Monday 27th February 10:20

Penelope Stopit

11,209 posts

108 months

Sunday 26th February 2017
quotequote all
Have TVR informed you that this is their work, I doubt they have
TVR didnt loop that wire to create a 1st speed, it would take many more meters of that size cable to create any sort of resistance, that is not resistive cable

No you can't fit that ballast resistor to create a 1st speed. You can't fit anything that gets hot inside the vehicle, you could engineer something so as to be able to fit a resistor inside the heater box so that the circulating air will cool it

You could fit a resistor in a heatsink box in the engine bay and wire it to the heater fan switch

You will need to work out what resistance is needed and also calculate for a suitable wattage rated resistor

v8s4me

Original Poster:

7,234 posts

218 months

Sunday 26th February 2017
quotequote all
Penelope Stopit said:
.... you could engineer something so as to be able to fit a resistor inside the heater box so that the circulating air will cool it....
I was planning to locate the resistor inside the heater air intake scoop for that very reason. Any suggestions as to what the resistance value might be though?

Wedg1e

26,760 posts

264 months

Monday 27th February 2017
quotequote all
Penelope Stopit said:
Have TVR informed you that this is their work, I doubt they have
TVR didnt loop that wire to create a 1st speed, it would take many more meters of that size cable to create any sort of resistance, that is not resistive cable

No you can't fit that ballast resistor to create a 1st speed. You can't fit anything that gets hot inside the vehicle, you could engineer something so as to be able to fit a resistor inside the heater box so that the circulating air will cool it

You could fit a resistor in a heatsink box in the engine bay and wire it to the heater fan switch

You will need to work out what resistance is needed and also calculate for a suitable wattage rated resistor
Unfortunately you're wrong on all counts; that is exactly how TVR did it. I had the 36th Tasmin built and that was done the same. It's actually a single-speed motor so they added the series resistance to slow it down for the 'slow' speed. Yes, a typical Blackpool bodge.
They did it the same way to give a dimmer for the instrument backlights. Later cars used the rheostat from the SD1 but that tends to burn out if you leave it near (but not at) the highest setting.

adam quantrill

11,535 posts

241 months

Monday 27th February 2017
quotequote all
Even later cars have a fan with 3 speed inputs, the wedge using only 2.

When my fast speed went (failed switch) I simply modes the corroding spade terminal for the slow speed to the fast speed at the fan end. Now the switch has failed completely I have a patch wire on there temporarily so I can run it during the winter. Sometime I'll get behind that centre console and sort it out - along with the clock.

Penelope Stopit

11,209 posts

108 months

Monday 27th February 2017
quotequote all
Wedg1e said:
Penelope Stopit said:
Have TVR informed you that this is their work, I doubt they have
TVR didnt loop that wire to create a 1st speed, it would take many more meters of that size cable to create any sort of resistance, that is not resistive cable

No you can't fit that ballast resistor to create a 1st speed. You can't fit anything that gets hot inside the vehicle, you could engineer something so as to be able to fit a resistor inside the heater box so that the circulating air will cool it

You could fit a resistor in a heatsink box in the engine bay and wire it to the heater fan switch

You will need to work out what resistance is needed and also calculate for a suitable wattage rated resistor
Unfortunately you're wrong on all counts; that is exactly how TVR did it. I had the 36th Tasmin built and that was done the same. It's actually a single-speed motor so they added the series resistance to slow it down for the 'slow' speed. Yes, a typical Blackpool bodge.
They did it the same way to give a dimmer for the instrument backlights. Later cars used the rheostat from the SD1 but that tends to burn out if you leave it near (but not at) the highest setting.
I don't find it unfortunate when I am wrong, I didn't know anything about electricity until I studied it, I am often learning something new
In this case I find it fortunate that I understand that there is no way a short length of coiled copper wire could possibly add a resistance value high enough to lower a blower motor speed
Now if that coiled wire was a resistive wire I understand how it would lower a blower motor speed but the wire in the above picture does seem to be copper as I can just about make out a copper colour where it terminates at the switch
If this circuit is genuine and does lower the blower motor speed by something like half, I would appreciate someone posting a diagram including this coiled copper wire
Copper wire is a very good conductor and far better than the one on my school bus

Penelope Stopit

11,209 posts

108 months

Monday 27th February 2017
quotequote all
v8s4me said:
I was planning to locate the resistor inside the heater air intake scoop for that very reason. Any suggestions as to what the resistance value might be though?
If and only you can check this.....the blower motor draws 10 amps at full speed, see below figures

12 volt 10 amp 120 watt 1.2 Ohm

Wiring a 120 watt 1.2 Ohm wire wound resistor in series with the blower motor will give you approximately half speed
When selecting the wattage of the resistor it is good to go higher than that calculated as a higher wattage resistor will be more robust

If your blower motor doesn't draw 10 amps at full speed you will need to calculate using the true full speed current draw figure

It is hardly worth doing all that work for a two speed motor, a three or four speed motor would be better and you could probably get away with using a blower resistor from some other vehicle that has three or four speeds



Edited by Penelope Stopit on Monday 27th February 08:59

Rockettvr

1,804 posts

142 months

Monday 27th February 2017
quotequote all
As mentioned above copper is a very good conductor so for the coil above to work as a resistance it would have to be either extremely long or of a very small cross section - that coil looks neither.
Its not the best idea either as what is created is an electric heating element not great under the bonnet - even if its only low wattage ( fire up a 60w bulb and see how much heat is generated) - not if you want to avoid this

Penelope Stopit

11,209 posts

108 months

Monday 27th February 2017
quotequote all
Rockettvr said:
As mentioned above copper is a very good conductor so for the coil above to work as a resistance it would have to be either extremely long or of a very small cross section - that coil looks neither.
Its not the best idea either as what is created is an electric heating element not great under the bonnet - even if its only low wattage ( fire up a 60w bulb and see how much heat is generated) - not if you want to avoid this
Correct
It also looks like that coil of wire has each end of it connected or should I say rammed into the switch plug
How does this coil of wire get switched in series with the blower motor? That is the question

adam quantrill

11,535 posts

241 months

Monday 27th February 2017
quotequote all
Low speed is probably only 1/4 speed on a wedge, finger in the air 2A and 10V across the resistor, so only 20W, and 5 ohms. Maybe less of a fire risk than a 21W bulb operating.

THe switch has two poles - on fast it shorts out the resistor and gives full beans to the motor.

mrzigazaga

18,534 posts

164 months

Monday 27th February 2017
quotequote all
While we are on the subject has anyone found an alternative blower motor?...Im going to disconnect my heater matrix and look for something else...But what yet I know not...

mk1fan

10,507 posts

224 months

Monday 27th February 2017
quotequote all
Mark, Car Builder Solutions do a few heater matrix units with various numbers of outlets and sizes. Not original, but will work a lot more effectively.

Wedg1e

26,760 posts

264 months

Monday 27th February 2017
quotequote all
Penelope Stopit said:
I don't find it unfortunate when I am wrong, I didn't know anything about electricity until I studied it, I am often learning something new
In this case I find it fortunate that I understand that there is no way a short length of coiled copper wire could possibly add a resistance value high enough to lower a blower motor speed
Now if that coiled wire was a resistive wire I understand how it would lower a blower motor speed but the wire in the above picture does seem to be copper as I can just about make out a copper colour where it terminates at the switch
If this circuit is genuine and does lower the blower motor speed by something like half, I would appreciate someone posting a diagram including this coiled copper wire
Copper wire is a very good conductor and far better than the one on my school bus
I'm stuck in a hotel at the moment so don't have access to it but I'm sure someone could post the infamous 'all black' wiring diagram for the Tasmin which does indeed show it as a resistor, albeit of unspecified value or construction.
As far as I recall, uncoiled it was about 6 feet long. Cross-section unknown... but the motor was a poor wheezy Lucas thing that had less power than a mouse fart so wouldn't have taken much slowing.

adam quantrill

11,535 posts

241 months

Monday 27th February 2017
quotequote all
Mark, what have you got in there now? Does it have a 4-way terminal block under the dash on the passenger side?

mrzigazaga

18,534 posts

164 months

Monday 27th February 2017
quotequote all
mk1fan said:
Mark, Car Builder Solutions do a few heater matrix units with various numbers of outlets and sizes. Not original, but will work a lot more effectively.
Thanks mate,I did see that....

adam quantrill said:
Mark, what have you got in there now? Does it have a 4-way terminal block under the dash on the passenger side?
Not sure ...Ill have to have a look...It does work but its could do with being 10 times better....smile

v8s4me

Original Poster:

7,234 posts

218 months

Friday 3rd March 2017
quotequote all
v8s4me said:
....Would connecting THIS to the first stage do the trick?....
Yes it would!

Dead simple to connect and reduces the voltage to the fan effectively to give a real slow/fast.

Slow...



Fast....



The ballast resistor does get quite hot on the slow setting so the only real issue is where to mount it.


Edited by v8s4me on Friday 3rd March 21:46

phillpot

17,105 posts

182 months

Friday 3rd March 2017
quotequote all

My "Electrics" here, two in series would obviously reduce the voltage further but would two in parallel half the load (and therefore heat) but give same 7 volts?

Bearing in mind that those fine engineers at TVR put a pair in parallel just to do the dash lights on the S Series

v8s4me

Original Poster:

7,234 posts

218 months

Friday 3rd March 2017
quotequote all
I was thinking of getting another one for the instrument lights so I could try two in parallel to see how much cooler they are. Given how much effort it's taken so far to keep the rain out, not having to run wires through the bulkhead would be good.

adam quantrill

11,535 posts

241 months

Friday 3rd March 2017
quotequote all
v8s4me said:
The ballast resistor does get quite hot on the slow setting so the only real issue is where to mount it.
Looks like a good idea - how about putting it in the air path into the heater box? Then air will be drawn over it by the fan, cooling the resistor and warming the air into the bargain.

Then - when you have it on full in the summer to cool down, the resistor is shorted out and generates no heat.

phillpot

17,105 posts

182 months

Friday 3rd March 2017
quotequote all

Out of interest, did the resistor wire (in first photo) not work?


I have that set up on the Taimar (original as far as I know), works fine although the blower fan/motor is under the bonnet so the wire is not tucked away behind the dash or console.
I think those wires were Fords way of doing Ballast Coil rather than use the Lucas resistor.

Edited by phillpot on Friday 3rd March 19:53