1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Howto: Duovalve maintainance

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

  1. television

    television Always remembered RIP

    Messages:
    164,074
    Likes Received:
    277
    Joined:
    Mar 14, 2005
    Location:
    Daventry
    Your Mercedes:
    2002 SL500, 216 CL500, all fully loaded
    I am pleased that you are digging a hole for yourself.. if you knew anything about inductance, even just simple basic stuff,,you would know that when a voltage is removed from an inductance, the magnetic field that collapses back into the coil is out of phase to any incoming voltage, and this voltage does not fall off rapidly, it slowly decays and would appose any incoming voltage from the next cycle. this effect limits the speed of the device, and when you have your digi meter connected what are you measuring,,I do not think that you know .


    Lets take a few lines of yours.

    so N/C, you are saying that in this case current does not immediately reach the 0.75a, but takes time to reach
    it.

    How much time do we have then, not forgetting that another pulse is following??



    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 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


    Why are you talking about current when that is a side effect of voltage and resistance,, impedance is the current set up in an AC circuit,,this is not AC it is interrupted DC

    Would you like to have a go and explain again please,, the middle part is backwards
     
  2. television

    television Always remembered RIP

    Messages:
    164,074
    Likes Received:
    277
    Joined:
    Mar 14, 2005
    Location:
    Daventry
    Your Mercedes:
    2002 SL500, 216 CL500, all fully loaded
    After reading you description of how these things work,,I now have my serious doubts of some of the other figures that you try and blind members with. Why do you post such things when you do not know anything about it,,the average member here could not care on toss
     
  3. television

    television Always remembered RIP

    Messages:
    164,074
    Likes Received:
    277
    Joined:
    Mar 14, 2005
    Location:
    Daventry
    Your Mercedes:
    2002 SL500, 216 CL500, all fully loaded
    Do you know what pulse width modulation is,,what the heck has that got to do with duo valves

    I did not say that the voltage was 8volt anywhere
     
  4. Alex Crow

    Alex Crow Senior Member

    Messages:
    10,677
    Likes Received:
    29
    Joined:
    Jul 9, 2009
    Location:
    Super Suffolk
    Your Mercedes:
    W169, W124, w202, W203, KTM 250 EXC, VW T25 camper and a Polo in a pear tree
    give it up malcolm. I WAS TALKING ABOUT OUR MULTIPLEXER, not yours.

    and why do suppose i may be inclined to swear when short of information? i do find, however, that you dear chap tend to just keep digging. i have read many posts of yours that have incorrect advice and information. on occasion i will place footnotes to your answers with the correct details. usually though i let it go, after all none of us know it all do we?

    i imagine from the contrasting nature of your posts through the day that something impairs your function a little in the evening? lets talk about it in the morning.
     
  5. television

    television Always remembered RIP

    Messages:
    164,074
    Likes Received:
    277
    Joined:
    Mar 14, 2005
    Location:
    Daventry
    Your Mercedes:
    2002 SL500, 216 CL500, all fully loaded
    Nothing wrong with my night time activities,it was just hard to take in all of the rubbish talked about electronics.

    You have also made mistakes,,and one today,, If I am wrong sometimes then fine point it out,,it is the OP that matters.

    I am not a MB engineer, and I have never set out to be, I just try and help people, OK I do fix some and 99% of my own cars faults.
     
  6. Number_Cruncher

    Number_Cruncher Senior Member

    Messages:
    1,806
    Likes Received:
    1
    Joined:
    Oct 10, 2007
    Your Mercedes:
    1995 W124 E300D TE
    For anyone interested, here's the maths of the situation.

    With a series circuit, of an inductance, L, the resistance of the winding, R, the applied emf, e, and the current, i.

    Applying Kirchoff's law and assuming the voltage is switched on at t=0, gives;

    e H(t) = L di/dt + iR

    where H(t) is the so-called Heaviside step function which describes the sudden switching on of the circuit, and di/dt is the differential of current with respect to time, t.

    Taking Laplace transforms gives;

    E(s) / s = I(s) (Ls+R)

    Where E(s) and I(s) are the transformed emf and current respectively.

    Re-arranging to give an expression for the transform of the current gives

    I(s) = E(s) / [s (Ls+R)]

    which can be further re-arranged to give

    I(s) = (E(s) / R) * ( (R/L) / [s (s+R/L)])

    this is a standard form which can be inverted easily to give

    i = (e/R) * (1-e^(-Rt/L))

    The first bit, i = (e/R) is the steady state, Ohm's law solution, while the (1-e^(-Rt/L)) term describes the transient behaviour which I have been talking about.

    The value L/R, the ratio of inductance divided by resistance is called the time constant of the circuit - after 1 time constant, the current reaches 63.2% of the final value, and after 5 time constants have passed, the current has reached 99% of the (e/R) value.

    Although I realise that was not an easy post to follow, I am happy to explain in more detail if anyone wants to know.
     
  7. television

    television Always remembered RIP

    Messages:
    164,074
    Likes Received:
    277
    Joined:
    Mar 14, 2005
    Location:
    Daventry
    Your Mercedes:
    2002 SL500, 216 CL500, all fully loaded
    Oh dear all that 2½ hours of searching,,had you looked up Lenz law it is explained so simply, that is simply

    " The induced emf will oppose the direction of the current that caused it when the circuit is switched on. the result is that the current in a circuit that contains an inductor, does not change instantly when a voltage is first applied. When the voltage is switched off, there is again a change of current, this time more rapid, because switching off is an abrupt change, the amount of change in the flux is more rapid, so that a large EMF is generated"

    This is what I have been trying to tell you, and was the missing part of yours and Alexanders so called theory



    Ohms law does not apply to inductance
     
  8. Number_Cruncher

    Number_Cruncher Senior Member

    Messages:
    1,806
    Likes Received:
    1
    Joined:
    Oct 10, 2007
    Your Mercedes:
    1995 W124 E300D TE
    >>Oh dear all that 2½ hours of searching

    No searching at all Malcolm.

    Lenz's law is just another way of looking at it, but, unfortunately Lenz's law doesn't offer anything of practical use during design.

    The general form of Ohm's law, V=IZ applies to any linear circuit, which may include inductance.
     
  9. television

    television Always remembered RIP

    Messages:
    164,074
    Likes Received:
    277
    Joined:
    Mar 14, 2005
    Location:
    Daventry
    Your Mercedes:
    2002 SL500, 216 CL500, all fully loaded
    No searching and you had it all in your head,,wow I wish I could do that

    Since when are we designing something here,,we are fixing a ready made item. Lenz law is much easier than what you posted,it explains what happens rather than bombarding people with a load of figures and equations that are meaning less to 99.9% of the readers here
     
  10. Number_Cruncher

    Number_Cruncher Senior Member

    Messages:
    1,806
    Likes Received:
    1
    Joined:
    Oct 10, 2007
    Your Mercedes:
    1995 W124 E300D TE
    Higher up in the thread, you asked about how long the process takes, and I provided an answer.

    It happens that I used exactly that derivation during the design assesment of a safety critical electromagnet. When, later on, we got hold of the current vs time plots from real hardware, they closely overlaid my theoretical output, which had been used for design purposes in the interim.

    Alas, the mathematics did come straight off the top of my head - a misspent youth?

    I know that my posts aren't aimed at the average poster who just wants to fix his car - however, I hope there are one or two who are interested in going just that little bit further.

    I'm not quite sure why you're being so ratty about it.
     
  11. television

    television Always remembered RIP

    Messages:
    164,074
    Likes Received:
    277
    Joined:
    Mar 14, 2005
    Location:
    Daventry
    Your Mercedes:
    2002 SL500, 216 CL500, all fully loaded
    I am a little ratty because of some of the comment passed,,when they are not understood,,I was accused more than once of talking in Chinese.

    To work in transformer design you need a BSC and more ,it is one of the most complicated subject in electronics.

    In my working life I use a transformer tester to find a short turn in a coil,,this cannot be measured in any other way,,as 1 short circuit turn on any coil will render it useless. Even on a duo valve with very few turns, if the varnish has come off and 1 turn is shorting, that coil is no good, and the same applies to a simple ignition coil where 15k turns are used.

    I do not mind a discussion at all,,I just object to any rudeness and incorrect theories put up. One could take this one step further and talk about the driver circuits and the way that semiconductors can be used way outside of their normal known characteristics
     
  12. Number_Cruncher

    Number_Cruncher Senior Member

    Messages:
    1,806
    Likes Received:
    1
    Joined:
    Oct 10, 2007
    Your Mercedes:
    1995 W124 E300D TE
    >>I just object to any rudeness

    I hope that you will not find any rudeness from me in this thread, however, I would ask you to check your posts for rudeness too.

    If I have posted anything that's wrong, please point it out.

    As a general rule, I avoid going into too much detail about qualifications - what matters is the truth of what has been posted.

    >>this cannot be measured in any other way

    At work, we use a Wayne Kerr [yes really!] LCR meter to check the chokes and inductors we wind.
     
    Last edited: Aug 16, 2009
  13. television

    television Always remembered RIP

    Messages:
    164,074
    Likes Received:
    277
    Joined:
    Mar 14, 2005
    Location:
    Daventry
    Your Mercedes:
    2002 SL500, 216 CL500, all fully loaded
    No you have not been rude,,sorry if I have been towards you. It has been messy due to all of the quotes.

    Errors in the post I have pointed out. I will try and scope up my own car on this part,,without knowing what is supplying the duo valve,,much becomes pointless as we have reactance on an AC circuit. choppers now are old hat,,I was the one that assumed the power supply is interrupted DC owing to the size of the semiconductors that drive the valves
     
  14. Alex Crow

    Alex Crow Senior Member

    Messages:
    10,677
    Likes Received:
    29
    Joined:
    Jul 9, 2009
    Location:
    Super Suffolk
    Your Mercedes:
    W169, W124, w202, W203, KTM 250 EXC, VW T25 camper and a Polo in a pear tree
    i think it is fairly obviously interrupted dc, even to a layman such as myself. however the frequency of the control is extremely low, albeit it with an occasionally very low duty cycle.

    Malcolm, when i am accused of talking chinese i take it as the highest compliment. it is an expression used to simply state that one does not understand the detail. similar in use to 'it's all greek to me'. i actually intended you to be pleased that you had demostrated your superior understanding of electronics.

    nor did i intend to give the impression that i was being in any way derogitory about the chinese, or the greeks i just mentioned. ('ooooh, he's having a go at the meek now!!' - life of brian)

    you are quite right to say i have confused impedance for resistance - although the law v=ir can be applied to both, impedance is in ac circuits regarding inductance as you have rightly corrected me. furthermore i have neglected to realise that the effect of emf in inductance relates to it's voltage, not current. i live and learn.

    on a good day you, as others on this thread have, demonstrate a high degree of intelligence. sadly you also seem to be easily offended - this was never my intention - so once again, i in no way intended to offend yourself, chinese or greek people, oh...and err...the meek.
     
  15. television

    television Always remembered RIP

    Messages:
    164,074
    Likes Received:
    277
    Joined:
    Mar 14, 2005
    Location:
    Daventry
    Your Mercedes:
    2002 SL500, 216 CL500, all fully loaded
    Alexander,,will you allow me to say sorry for the way that I have reacted to the post here. Yes it is a weakness within me that I can let something in my private life affect the way in that I post on here, I managed better than at some other times on here, so that is something :D I just took it all the wrong way.

    I should not have been so picky on expressions used,just in the current/ voltage bits,,you cannot have one without the other, even Lenz uses the word current in his descriptions of the laws of induction. It is in many cases more important to monitor the current of a device under test than the voltage, though a voltage reading is easier to obtain.
     
  16. bigshineybike

    bigshineybike Member

    Messages:
    12
    Likes Received:
    0
    Joined:
    May 3, 2008
    Location:
    Surrey UK
    Your Mercedes:
    E300D estate 1996 multivalve, VW 1.6se auto, Triumph T509, Montesa Cota 348
    duo valve closer to resolution

    Hey all , sorry that it all seemed to get a bit personal up there.
    I have just come in from the garage to look up some more threads on duo valves.

    Most of the above i have only glanced at for clues, fine detail , I keep it for the science forums.
    However you have all made a contribution to me finding fault with my 1996 E300d W124.

    I had checked everything but with an old moving pointer low budget multimeter.

    This morning with the control unit taken out of the dash board i took accurate digital readings from the multi plug.

    I was able to see proper readings to show
    the roof sensor pin 11 to 3 was giving 7.8 ohm
    matrix sensor left and right pins 5 & 7 to 11 gave 10.4 and 10.8 ohms
    and pins 6 &8 to 10, the duo valve left and right, read 15.2 ohms and 3.8 ohms.

    so given that the control unit gets upset when it sees a wrong reading that is why I have two hi-heat hairdriers built into the dash board!
    (and increasingly frizzy hair!)

    I now have the duovalve in bits and got the coils out from their housings.
    the side that was reading 15 ohms is all rotten, signs of overheating, varnish gone from the copper wire. Quite obviously its had it.

    Off on holidays tommorow so I guess ill be looking for some corks for the hoses!

    When I get back is it practical to rewind the coils myself?

    Its worth noting that there are some rubber o rings that make a water tight seal at either end of the coil, there were signs mine have leaked so anyone wanting to have a look be warned.

    I found this pictoral including how to wind coils
    http://www.v12uberalles.com/Rear_AC_System.htm
     
    Last edited: Aug 16, 2009
  17. television

    television Always remembered RIP

    Messages:
    164,074
    Likes Received:
    277
    Joined:
    Mar 14, 2005
    Location:
    Daventry
    Your Mercedes:
    2002 SL500, 216 CL500, all fully loaded
    Rewinding coils can be hard,,getting the turns neat does require a lathe or a slow speed drill clamped down, and the new wire reel held down with a felt tensioning pad to keep the wire taught.


    Speaking truthfully it is hard to keep the turns neat and stacked,if a turn crosses another it will create a weak spot.

    You have to count the turn that you take off, measure the gauge.

    Doing a search "Coil rewinding "does bring up loads of firms,and one here

    http://www.eslelectromech.co.uk/content/transformers_coils

    I did the locking solenoids on a XJS never again by hand

    The resistance values are vague, between 10 and 18 ohm,,so the same wire and count the turns is the only real way.

    If you can replace the O rings and gaskets then get them wound.


    Sorry for making a pigs ear on the postings here, I should know better.:Oops:
     
  18. Number_Cruncher

    Number_Cruncher Senior Member

    Messages:
    1,806
    Likes Received:
    1
    Joined:
    Oct 10, 2007
    Your Mercedes:
    1995 W124 E300D TE
    >>if a turn crosses another it will create a weak spot.

    It's impossible to avoid completely. Most text books which describe wire packing and possible densities during winding tend to get it wrong. The neat section views of coils forming neat patterns are utterly mythical.

    For controlled winding using home based apparatus, I would use a hand drill (one of those with a large bevel gear that has a handle on it - allows good control and reduces the counting task by a factor of 5 or so!) to turn the bobbin, passing the wire through something soft to keep some tension - like TV's felt pad suggestion. Another pair of hands will be needed to "feed" the wire across the bobbin to get the lay of the wire as good as you can.
     
  19. Alex Crow

    Alex Crow Senior Member

    Messages:
    10,677
    Likes Received:
    29
    Joined:
    Jul 9, 2009
    Location:
    Super Suffolk
    Your Mercedes:
    W169, W124, w202, W203, KTM 250 EXC, VW T25 camper and a Polo in a pear tree
    hellp mr b.s.bike, your faulty coil will be the 3.8 ohms one, a very common problem.

    if you look back i have posted about this early on, before the showing off, misunderstandings, mistakes, recriminations, throwing of handbags, apologies and making friends again. all the joys of the forum.

    wonder how many more will crop up now??
     
  20. television

    television Always remembered RIP

    Messages:
    164,074
    Likes Received:
    277
    Joined:
    Mar 14, 2005
    Location:
    Daventry
    Your Mercedes:
    2002 SL500, 216 CL500, all fully loaded
    On the ones that I have done the way you keeps the wire taught play a big roll, using your hands tend to put very small kinks in the wire,,yes very small but they add up and the after result is that you cannot get all of the turns back on to the spool.

    My comment was about the wires crossing others I did not explain well, when the first layer is on, the second set of turns will fare better if they sit in between the windings of the previous ones, as soon as you jump one, a turn is lost.

    I do not know if a hand drill would have the energy to keep the wire tight enough
     

Share This Page