[Trevor]

The following information although secured for another thread may be of use to those perusing this one

In an effort to find out exactly what is occurring in the resistor and solenoid circuits I hooked up my scope and had a look at things.

Unfortunately I was on my own so was unable to run the car in drive against the brakes as I had hoped to do. I admit being chicken as I was conscious of the garage wall and shelves containing valuable stuff in front of the car, as well as my own neck ! As a result the car was run in neutral and I could do no more than increase revs while checking the scope trace and taking measurements.

Static, all voltage measurements coincided with specifications.
The resistor measured 12.3 ohms and the solenoid 3.4 ohms.

With the engine running and the resistor in circuit the output from C7, i.e. before the resistor, showed a pulsed signal at a constant approximate 13.5 volts and at a rate of around 50 hertz. This was not in effect a square wave as the voltage fell to zero between pulses and the solenoid EMF was completely disrupted resulting in a substantial reverse spike. The frequency remained constant as did the voltage but the length of the pulses became shorter as the revs rose.

Tested as above, the output from C 8, i.e. the direct circuit to the solenoid, showed a similar signal but with shorter pulses. The pulse length did not vary with throttle opening and increased revs. Once again a significant negative spike was observed.

It was noted that the resistor ran extremely hot .

With the resistor open circuit, the same pattern was registered showing that feed back had not effected the individual circuit measurements.


N.B. Beav if you are looking,

It is hard to fathom how the system actually operates. One would expect the direct circuit to impart primary control and the resistor circuit to have some sort of auxiliary function, but who knows do you ? I now realise that I should have checked the relationship between the two signals. It could be that the two are in synchronism and one overrides the other and so lengthens each pulse, but this is a rather weird concept. I have designed systems involving the control of solenoid valves in industrial plant but have never seen or used anything similar.

Harvey has on several occasions stated that the signal from the resistor circuit is constant but at a varying voltage and is designed to provide a platform which prevents the solenoid from completely bottoming. On the basis of the above measurements this does not hold water.

Beav please throw in your $1000 dollars worth !

Regards Trevor. *<)