Advice on how the sun blind works
 

How does the sun blind of a saloon detect it is all the way up or down?

As I now have a prized replacement motor and gear box thanks to directstep's generosity, I am worried about breaking it once fitted. As my blind will be down how do I know or how does the blind know, it's down and does not try to go down and therefore break?

macafee2

As far as I remember, it's a simple two motion motor. When you press the button it will only go thelsewhere way of least resistance ie up if it's already down. No need to panic once fitted. Good luck

what stops it? when I tested the motor without the blind and gearbox the motor just spun and spun

macafee2

That's a very intelligent question Ian. RAVE has the explanation:

"... the sun blind switch contains ... a controller circuit, a Field Effect Transistor (FET) and a current monitor. Each time the switch is pushed, the controller circuit modulates the FET for a timed period to produce the power outputs to the motor and gearbox. The current monitor limits the current draw of the outputs to the motor and gearbox."

You don't have to be an electronics wizard to get the gist of that. The timed period is 2.5 ± 0.1 seconds. The maximum current draw is 3.2 ± 0.1 amps for 500 ± 20 mS.

See how much technology and effort goes into the design of a toy. :D

Simon

Simon I should say thank you but sorry still don't understand. I've even done a Google search and am none the wiser.
I assume from the post the switch plays some part in this


macafee2

OK, no problem Ian.

The sun blind switch contains a sophisticated electronic circuit. When you push the button to raise your sun blind, this circuit sends a voltage to the motor. The motor then runs and raises the blind.

You asked how the blind knows that it is "all the way up or down". The answer is that it doesn't. The movement of the blind is stopped by the voltage being removed from the motor after it has run for two and a half seconds. It has been calaculated that this is the exact time required for the motor to drive the blind up or down. The voltage to the motor is switched on and off by the electronic circuit in the sun blind button. That's the answer to your later question: "what stops it?".

That's basically how it works. There's a safety mechanism to prevent the motor burning out if something goes wrong and that's the "current monitor". Please say so if you want to know more about that.

Is that any clearer? If not, it's no problem, just let me know which bits are confusing and I'll think of another way to explain it.

Simon :}

I will put it even more plainly from how I understand your explanation Simon, but I have a question also at the end.

The switch has a timer built in. Which is active for 2.5 seconds. :D




My question would be this. If you removed a blind whilst it was in the up position, with one that was in the down (closed) would the sun blind work? I am assuming the circuitry assumes press 1 is up press 2 is down, press 3 is up, press 4 .....etc Thinking on this, if the switch was pressed with the ign on, but the blind unplugged, could it upset the setting. The switch could be 'thinking' the blind needs to be pulled down when it is closed, reversing the polarity, that it needs to be, and so therefore the blind would appear to be faulty? (that could explain why my blind isnt working, although of course there are a number of other issues that it could be, including the broken magnet, that failed on the first motor ;) I am not going to get a chance to try this for a few weeks :duh:)

that's more to my level of understanding, thank you.
Next question, how does it know if to go up or down? I ask as mine went faulty and so I have pushed the button a number of times and so I have no idea if the last push was to go up or go down. Now fitting a replacement I am concerned that although the blind is down, the next push will try to send the blind down and damage it

sorry if these are elementary questions but I appreciate the help with understanding

macafee2

for what its worth, mine went I think went faulty when a tooth or more on the fibre gear broke off. the motor seems to work ok

macafee2

Looking at the illustration in RAVE of the blind's mechanics, it works on the same principle as windscreen wipers. That is, the motor always turns in the same direction but the hinged operating rods allow the blind, having reached its limit of travel, to reverse direction at the next push of the button. So ....
Yes.
'Assuming' is a very risky practice Alan. :D In fact, it doesn't work like that at all.

I hope the above explains that the button doesn't need to know the direction of travel. That is achieved by a simple, but clever mechanical linkage system.
If you have fitted an entire assembly (motor, blind and linkages) then there's no need for any concern. It won't be damaged.

Simon