General electronics question
Discussion
Ok, so I'm not getting very far with my heater control and nobody seems to have any ideas on how to fix it. Are there any electronics guru's out there that can explain...
How does the motor know when to stop according to the current being passed through the pot? I think the problem I have may be due to a fault with the motor end but have no idea what's there and what could need replacing.
How does the motor know when to stop according to the current being passed through the pot? I think the problem I have may be due to a fault with the motor end but have no idea what's there and what could need replacing.
Hope this helps but it is based on a 92 4.3. Basically on the heater control valve is a geared motor which opens and shuts the valve. To limit the travel on this motor a micro switch is mounted each side to limit the movement for open and shut. A diode is inserted (an electronic one wayvalve) to control the switching. On mine the fact that microswitches were used was not evident as you could not really see them until the motorised valve was removed.
Dave
Dave
Joolz - you don't say what car it is, or what the problem is but as you mention the pot I'm guessing it is a 500. If so then basically the circuit works by balancing the current through both sides, i.e. if you move knob (ohh err missus) then there is an imbalance between either sides of the circuit, so the motor is energised to move - it moves until the circuit is in balance again.
I can't rememebr the circuitry (I sold my Griff 18 months ago), but that is basically how it works - I had to move my motor to stop heater working at all times, and ended up trashing the pot, so had to replace that - a real pain in the arse of a job.
Mike.
I can't rememebr the circuitry (I sold my Griff 18 months ago), but that is basically how it works - I had to move my motor to stop heater working at all times, and ended up trashing the pot, so had to replace that - a real pain in the arse of a job.
Mike.
Cheers chaps. It's a 97 500. I would guess then from what you've both said, that they replaced the micro switches that Rolfe talks about and now it's just the pot on the control panel that controls where the motor stops????
What it's doing at the moment is not moving to it's position and stopping - it will continuosly whirr away. I have found however, that it will stop in one particular position (when the pot's about 1/3rd way round).
You're right, it is a right pain in the arris job, I had given up from about a year ago and removed the fuse to it. So, I can't use any of the controls (some of which I'm not too bothered about) but some such as the fans would be good to have going. Now I've got my new dash I'd love to get it all up and running. The PCB is new from TVR and the parts are too, although I wrecked one pot and have ordered a replacement.
Forgot to say, when it stops in the position I mentioned above, it seems to go past, then reverse, then go back etc until it's happy, then stops. Don't know if that gives any more clues but would be really grateful for any help or advice as this is driving me potty (excuse the pun).
>> Edited by joolzb on Sunday 14th September 20:39
What it's doing at the moment is not moving to it's position and stopping - it will continuosly whirr away. I have found however, that it will stop in one particular position (when the pot's about 1/3rd way round).
You're right, it is a right pain in the arris job, I had given up from about a year ago and removed the fuse to it. So, I can't use any of the controls (some of which I'm not too bothered about) but some such as the fans would be good to have going. Now I've got my new dash I'd love to get it all up and running. The PCB is new from TVR and the parts are too, although I wrecked one pot and have ordered a replacement.
Forgot to say, when it stops in the position I mentioned above, it seems to go past, then reverse, then go back etc until it's happy, then stops. Don't know if that gives any more clues but would be really grateful for any help or advice as this is driving me potty (excuse the pun).
>> Edited by joolzb on Sunday 14th September 20:39
Joolz, I had a 400, then a 500 and the 400 is as Rolfe says and the 500 as you have summised. It sounds like it could well be the pot - I have some spare if you want one (I could only buy packs of 5 from RS and only needed one - and no, it's not like a "pack of three").
I'm trying to remember exactly what was the original problem with mine as I did get to a similar situation as you have at one stage, when it would only go one way, but I'm afraid I can't remember (was 2 years ago).
Let me know if you want one of the pots.
Cheers,
Mike.
I'm trying to remember exactly what was the original problem with mine as I did get to a similar situation as you have at one stage, when it would only go one way, but I'm afraid I can't remember (was 2 years ago).
Let me know if you want one of the pots.
Cheers,
Mike.
Mike,
I'm not too sure what I should be replacing. I've got some on order for the control panel end from RS but couldn't find one with a push switch, so have decided to do without the heated mirrors(it looked like the only one that used the switch part of the pot). Could it be that the one on the motor end has packed up? I've not had a good look at the motor end as it's a right steward to get to.
cheers
Joolz
I'm not too sure what I should be replacing. I've got some on order for the control panel end from RS but couldn't find one with a push switch, so have decided to do without the heated mirrors(it looked like the only one that used the switch part of the pot). Could it be that the one on the motor end has packed up? I've not had a good look at the motor end as it's a right steward to get to.
cheers
Joolz
Be warned, this is a pure guess, but this is how I'd set it up ...
The valve position is probably measured by three devices: two microswitches (one for fully open and one for fully closed), and a potentiometer that measures all the intermediate positions between fully open and closed.
The switches do a pretty obvious job of turning the motor off so it doesn't knacker itself or the valve when the valve can move no further. The clever bit would be the potentiometer.
If the knob on the control panel is also a potentiometer then the simplest way of getting it to control the position of the valve would be to use a circuit called a "window comparator" with a bit of feedback.
A potentiometer is a "voltage divider". A pot's output (on a car) is going to be somewhere between 0V and 12V, depending on how far it has been turned.
A "comparator" works by comparing two input voltages and switching its output on or off depending on which of the two inputs has a higher voltage. A "window" comparator is made up of two comparators set to slightly different voltages so that they tell you when the two input voltages are within a certain range of each other.
One of these window comparator circuits will be driving the valve's motor until the voltage from the valve's pot is within the window set by the control panel's pot (plus some feedback dependent on the direction the motor is turning). The feedback and the window are used so that the motor doesn't try to be too precise and end up jigging backwards and forwards trying to fine tune the valve position pointlessly.
The circuit itself should be bomb proof, but the potentiometers themselves and the microswitches all contain moving parts that may get worn by use or corroded by damp.
The valve position is probably measured by three devices: two microswitches (one for fully open and one for fully closed), and a potentiometer that measures all the intermediate positions between fully open and closed.
The switches do a pretty obvious job of turning the motor off so it doesn't knacker itself or the valve when the valve can move no further. The clever bit would be the potentiometer.
If the knob on the control panel is also a potentiometer then the simplest way of getting it to control the position of the valve would be to use a circuit called a "window comparator" with a bit of feedback.
A potentiometer is a "voltage divider". A pot's output (on a car) is going to be somewhere between 0V and 12V, depending on how far it has been turned.
A "comparator" works by comparing two input voltages and switching its output on or off depending on which of the two inputs has a higher voltage. A "window" comparator is made up of two comparators set to slightly different voltages so that they tell you when the two input voltages are within a certain range of each other.
One of these window comparator circuits will be driving the valve's motor until the voltage from the valve's pot is within the window set by the control panel's pot (plus some feedback dependent on the direction the motor is turning). The feedback and the window are used so that the motor doesn't try to be too precise and end up jigging backwards and forwards trying to fine tune the valve position pointlessly.
The circuit itself should be bomb proof, but the potentiometers themselves and the microswitches all contain moving parts that may get worn by use or corroded by damp.
So could it be that one of the devices (the ones that control the upper and lower of the "window") has packed up, meaning that it will only stop in one particular position?
Please bear in mind I've got no idea what's connected to the motor and any idea of what I'm talking about. Mike mentions some pots at the motor end but this is way above my head.
Thanks to Dan by the way for posting to the other similar topic I had open, I closed that one off to try and keep the comments together.
Please bear in mind I've got no idea what's connected to the motor and any idea of what I'm talking about. Mike mentions some pots at the motor end but this is way above my head.
Thanks to Dan by the way for posting to the other similar topic I had open, I closed that one off to try and keep the comments together.
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