Re: Seat heater switches

[quk@isham-research.demon.co.uk (Phil Payne)]

In message <36166E3D.24567074@nh.ultranet.com> Huw Powell writes:

> > The seat heater switches in the ur-quattro are the thumbwheel type -
> > On/off when moving from 0 to 1, and then gradually more heat up to
> > a setting of 6.
> >
> > Anyone know the nominal resistance for each setting?
>
> The resistance of the heater wire?
>
> Because the switches like that that I have seen are just that -
> switches, with 7 positions.  They go to a pair of relays, then to the
> three heater wires.  The six settings are the different combinations of
> the three different resistance wires...
>
> hth a little?  I don't have any heated seats around so I can't answer
> the other half of the question.

No.  There is only _one_ heater wire - the backrest and squab are wired
in series, and there's only one circuit back to the controller.

I suspect the switch presents on/off and six different resistances
to the controller.  The controller applies a voltage to the switch
resistance and to the thermistor in the seat element.  All it would
have to do is amplify the delta current and apply it to a relay via
a diode.

At least, that's the only mode of operation I can deduce from the
paucity of physical circuits present.

--
 Phil Payne
 Phone: 0385 302803   Fax: 01536 723021
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