BXProject

[smiffy]

Hello boys, any ideas on how easy or difficult it might be to rid myself of the fucking awfull rheostat affair on the ventilation fan, and put in the 4 position switch found on a ZX instead? Bearing in mind I have 2 scrap ZX vehicles so donor parts are not a problem, but my ineptitude is!

[Vanny]

for you, impossible i imagine.

Also, its not a rheostat, there is no coil, its just a variable resistor, if it was a rheostat it wouldn't wear out. Just clean the tracks, and then replace the bitron unit.

[Philhod]

Is that what we, in the model game call a Bob's board and servo? They are a waste of time, we have a little electronic thingy that replaces both the board and the servo and doesn't fail either.

[docchevron132]

for you, impossible i imagine.

Whats wrong with the standard set up J?

[Way2go]

Also, its not a rheostat, there is no coil, its just a variable resistor, if it was a rheostat it wouldn't wear out.

What's with all this keyboard warrior stuff lately? Don't know what your thinking about but a Rheostat is a variable resistor and is not a coil so Smiffy is not incorrect.

[mat_the_cat]

The way I understand it is that any variable resistor, or potentiometer can be connected as a rheostat just by using 2 of its teminals. What seems to be usually meant by a rheostat in my (limited!) experience is the wirewound (instead of the carbon track) type of variable resistors where you have a coil of resistive material and as the contact is moved it skips along the coils.
I should imagine that the ZX set up switches the current between a set of fixed value resistors, which on other vehicles I've worked on have been in the airflow from the heater blower to keep them cool.

But I agree, Vanny is being mean. Only the other day he tried to blackmail me! Or hang on a minute, maybe it's all a wind-up?

[Way2go]

Correct, it doesn't have to be a high power wire wound device like they used to use in theatre lighting before the days of DMX. The term applies whether it is light, average, or heavy power and whatever the resistance medium is.

Anyway if Smiffy looks at the circut of the blower board, Haynes Blue page 13 it looks reasonably easy to disconnect the existing control and replace it with a 4 position switch with 3 selected resistors connected together at one end especially as you are just controlling the transistor that is handling the fan current. The switch would have to be located aside from the existing control though as that wiould be significant redesign to get it in the same place.
Alternatively you could just connect a simple toggle switch to control the relay switching that bypasses the transistor and then you could quickly switch between a "comfort" setting on the existing dial and full speed.
But as Doc said, why would you want to, the existing design is functional?

[smiffy]

The reason for this out loud thought, is that sometimes when driving along, the fan changes speed all by itself, usually it ends up going slower but then comes back. you never seem to be able to get it to go on full speed......

[Bx Bandit]

/\ That be summat fucked then! Probably the doobery transistor jobby in the ducting!

[Way2go]

That sounds like dirty/worn wiper on the track. Apart from carefully cleaning it, if you apply the sorceror's mod to the board as shown on BXC then the high speed is switched directly on the knob and should be stable.

[Philhod]

You could use one of these electronik thingies like on our models.


Oh ! err .... no, then you would need a transmitter and............

Tell you what.....err..... give that a miss eh

[Way2go]

Tell you what.....err..... give that a miss eh

I take it you're enjoying a few bevvies there Phil!

[Philhod]

Err not had a drink for an hour now.....hadn't thought that through..... obviously need another

Enuff beer, I think I have some rum and coke lying at rest somewhere

[Vanny]

Also, its not a rheostat, there is no coil, its just a variable resistor, if it was a rheostat it wouldn't wear out.

What's with all this keyboard warrior stuff lately? Don't know what your thinking about but a Rheostat is a variable resistor and is not a coil so Smiffy is not incorrect.

Hang about, your calling me a keyboard warrior but you spend your days creating spin? Quite frankly thats a bit rude.

Regardless it's not about being a keyboard warrior it is about being correct. Rheostats have terroidal coils, its how they work, if it doesn't have a coil it isn't a rheostat, simplz. Potentiometers also have coils but are low current resistance, and your usual variable resistor has a resistive track. If Smiffy where to go buying a rheostat he would likely end up with something capable of high resistance and high current which isn't the requirement, so if the resistance range went low enough then there would be very little control between partial and max speed.

If the fan is dropping back at high speed thats probably an issue with the PMOS, i guess it could be vibration causing a dodgy contact, but it is more likely a result of the PMOS. Remember we have already changed that once and it is designed to back off at high speed (reduce the effect of ram air intake).

If you change the in car control to switches and the issue is with the PMOS then the problem will still be the same. You might with to measure the voltage out of the in car control and compare to the voltage at the fan over time

[docchevron132]

The fans been shite in the red car in all the years I've had it, I live with it!
If I want a really warm car, I just get the valver out.