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Howto: Duovalve maintainance

Discussion in 'Engine, Drivetrain, Fuel and Exhaust' started by Parrot of Doom, Jun 8, 2006.

  1. Alex Crow

    Alex Crow Senior Member

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    they pulse very slowly malcolm. it is not really pulse width modulation at all, in so far as the valve is either open or closed and not held in an intermediate position.

    if you connect just a meter all will be revealed - no high speed capture needed. having said that i can't swear the same for eg the 220, but it definately goes for eg 124, 201, 202, 210 etc.

    i believe also that they are actually 12v as the unit would struggle to supply the current if it had to invert to 8v (or however it makes the 8v you suggest - pcb level electronics not my bag).
     
  2. television

    television Always remembered RIP

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    Owing to slow gate times on digital meters 8 volt could be roughly what would be displayed.

    I have remembered that I do have a CD with it all on somewhere
     
  3. Alex Crow

    Alex Crow Senior Member

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    would have to be blooming slow!! the go on/off no more than 1x per second, more like per 5 seconds.
     
  4. television

    television Always remembered RIP

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    Sorry not so, I work with them all day long,,a good metered instrument still has its place in electronics
     
  5. Alex Crow

    Alex Crow Senior Member

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    i think we are talking at cross purposes here malcolm, yes i know you work with meters, scopes and all sorts of other electronic voodoo/witchcraft.

    i just work with duo valves and mercs all day long, for the 124, 201, 126 etc age models the switching is NOT fast. come to think of it, yes the on time can be very short. but that will be versus a longish off time - so still slow hz wise but fast enough to fool a digital meter.

    i have among my armoury a wonderful avo meter. a very reliable and well made piece of history that is faster by far than my digimeter. sadly it just holds down a shelf as i very rarely find a use for it. now the star machine, that's another matter, hardly gets put down..................
     
  6. television

    television Always remembered RIP

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    Back in the days when these things came out we had interrupted DC, and that is probably what is used. with a spool resistance of around 16Ω that is very nearly 1.2 amps each making 2.4 amps in total, so not very high, but enough to require running in the cool mode for the semiconductors involved. the on time does have to be slow enough to allow for the out of phase voltage that is inverted back into the spool to die away or the max rise time could never be reached with the next on time. Any test in the unplugged mode are pointless.

    Once again looking via a scope it is all there, the time and voltage exactly. Once I can find the theoretical diagram all would be clear.
     
  7. television

    television Always remembered RIP

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    Talking of STAR the multiplexer, I have one in for repair, at least 100 of the soldered joints are suspect, but difficult due to the black stuff they paint on it that serves no real purpose
     

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  8. Alex Crow

    Alex Crow Senior Member

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    i make 16 ohms = 0.75 amps if v=ir, ie total current 1.5 amps. the next bit you posted is mainly in chineese? and the next bit, i test with the douvalve plugged in and use a 'power probe' or two to monitor the switching. i will test voltage on monday on probably one of the company 124s for reference. my money is that it uses vehicle voltage, ie typically 13.5v. the switching does not need to be all that fast as we are talking about the flow of water through a heater matrix influencing cabin temperature, high response times are not relevent. the control panel will calculate on times versus off times but the frequency is very low.

    i am surprised you would make a school boy error like mistaking a dmm value of 8v when it was a very quick 12v :lol: but i am impressed with your use of far eastern languages.
     
  9. Alex Crow

    Alex Crow Senior Member

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    ours rattles! it is just the heat gun glue they have used for no apparent reason. having said that it has endured 2 yrs of workshop use and abuse and i am amazed at the durability of this chinese imitation. you speak chinese don't you malc? ;)
     
  10. Number_Cruncher

    Number_Cruncher Senior Member

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    Owing to the inductance of the solenoid coil, after the voltage has been switched on by the controller the current cannot rise quickly - there is a bit more to it than V = I R.

    As there's a deep mathematical similarity between the equations which govern circuits with resistors, capacitors and inductors and mechanical circuits with dampers, springs, and masses, it's easy to imagine a mechanical analogy of this.

    Imagine a heavy mass connected to a fixed point by a viscous damper.

    If you suddenly apply a force to the mass, the mass will slowly accelerate until it reaches a speed where the reaction force from the damper matches the applied force - thereafter, the mass continues at constant speed.

    The suddenly applied force is the analogy of the voltage being switched on.

    The velocity of the mass is the analogy of the current in the circuit.

    The strength of the damper is the analogy of resistance - the force produced by the damper is proportional to the velocity.

    The mass is the analogy of the inductance of the circuit.

    Back to electrics, after the voltage is turned on, owing to the inductance, the current slowly builds until eventually, V=IR. As the magnetic field is proportional to the current, the magnetic field is also subject to this gradual increase [and decay] even though the voltage may be switched almost instantaneously.
     
  11. Alex Crow

    Alex Crow Senior Member

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    so N/C, you are saying that in this case current does not immediately reach the 0.75a, but takes time to reach it. i suppose what is happening is when the current initially flows it sets up a magnetic field in the coil. this field in turn produces it's own current which to some degree cancels out the flow of applied current. as this is dc we are talking about, and the electromagnetic effect in question only produces current with a change of magnetic field, the inductance effect will only make a difference momentarily when the current is turned on and off. i get the idea but, in the case of duovalves, this is not necessarily relevant. if you turn the dial to the coolest setting the power is on permanently for instance. most of the time they are either off or on for over a second.

    i would be interested to hear from anyone with a seemingly sticking duovalve that has done the impedance test.
     
  12. Number_Cruncher

    Number_Cruncher Senior Member

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    >>will only make a difference momentarily when the current is turned on and off. i get the idea but, in the case of duovalves, this is not necessarily relevant.

    Yes, I agree. I'm quite sure that MB have made sure that the time between switchings is long enough for the current to stabilise.

    I posted to add some extra information about how quickly the circuit works, and that in the case of any circuit that relies upon windings to produce a magnetic field, it's the current that matters.
     
  13. Alex Crow

    Alex Crow Senior Member

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    yes, it was stimulating food for thought, N/C, and something i always forget. you also mentioned the effect of capacitance? i note that when connecting a car battery the initial current draw is very large -please expand...................:)
     
  14. Number_Cruncher

    Number_Cruncher Senior Member

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    There's lots going on!

    But, broadly, while all the circuits which are effective inductors will be drawing less initial current, all the circuits which are effective capacitors will be drawing more.
     
  15. Alex Crow

    Alex Crow Senior Member

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    thought you might say that :D
     
  16. television

    television Always remembered RIP

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    Please do not try and tell what the black stuff is if you do not know,it is not heat gun glue, that is transparent, this black kind of paint I not serving much purpose other than to mess up the soldering iron,,I have removed more hot gun glue that you have had hot dinners, when it ages and messes up HP circuits

    Is all that you do not know Chinese .
     
  17. television

    television Always remembered RIP

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    Why do you post such stuff when you do not know,,do you have a degree in transformer design,,its total rubbish
     
  18. Number_Cruncher

    Number_Cruncher Senior Member

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    Go for it TV, I'm all ears.
     
  19. Alex Crow

    Alex Crow Senior Member

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    easy tiger. our multiplexer was full of hot glue gun glue on much of the boards and especially where the wires joined on. most of it came loose and one slow day i had a peek inside and spotted the cause.

    i did not presume to tell mr TV what he has on his board. however i can inform said person that my hot dinner intake has been considerable.

    sadly chinese is not the extent of all that i do not know. my urdu is a little shaky and the implications of the exclusion principle make my weary head spin - am looking after shrodinger's cat while he's on holiday, haven't looked in the box but there is a humming smell................
     
  20. television

    television Always remembered RIP

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    Changing you mind now are you I did not mention the output socket wires
    So anything that you do not understand you call Chinese,, at least I know your limits,,you could use the F word,,others do when they do not know
     

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