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  1. #81
    pieter2 is offline Registered User
    Location : the Netherlands
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    I rewired the black and white wires. This does not change anything. At the end of the new black and white wires I measured 0,3. At the beginning of the wires (on the shunt) the measurent is 0,0.
    I have positioned the new wires different from the old (to avoid possible magnetic fields). Nothing changed.
    We seem to be out of ideas, are we?

  2. #82
    VicS is offline Registered User
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    We seem to be out of ideas, are we?
    I reckon we are!

    I do not understand how this 0.3 volt difference can arise unless one of the wires is carrying a significant current or there is a bad connection or resistance somewhere

    The white wire probably caries very little current as it is, with the yellow wire, only measuring the volts across the shunt ( that by the way should only be 50mV max IIRC) The black wire only caries the current which the instrument takes. Only few mA if the back-lighting is not on.

  3. #83
    Join Date
    May 2010
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    slightly off topic I fitted a BM1 recently and athough mine works fine i do think the shunt is a bit poor by that i mean small. By the time youve got the main neg off it and the starter bat neg off it the bolt is too small for anything else. I would have gladly paid a bit more for something a bit more substantial.

  4. #84
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    Quote Originally Posted by dougg View Post
    slightly off topic I fitted a BM1 recently and athough mine works fine i do think the shunt is a bit poor by that i mean small. By the time youve got the main neg off it and the starter bat neg off it the bolt is too small for anything else.
    You should connect the shunt to the starter battery negative and make the starter battery negative the common ground i.e. there is no need to connect more than one cable (either end) to the shunt.
    ------------------------------------
    Loves sailing, hates gardening

  5. #85
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    Quote Originally Posted by VicS View Post
    I reckon we are!

    I do not understand how this 0.3 volt difference can arise unless one of the wires is carrying a significant current or there is a bad connection or resistance somewhere

    The white wire probably caries very little current as it is, with the yellow wire, only measuring the volts across the shunt ( that by the way should only be 50mV max IIRC) The black wire only caries the current which the instrument takes. Only few mA if the back-lighting is not on.
    Agreed! I've given up.
    ------------------------------------
    Loves sailing, hates gardening

  6. #86
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    May 2010
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    Quote Originally Posted by Playtime View Post
    You should connect the shunt to the starter battery negative and make the starter battery negative the common ground i.e. there is no need to connect more than one cable (either end) to the shunt.
    Nice thanks.

  7. #87
    VicS is offline Registered User
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    Quote Originally Posted by dougg View Post
    Nice thanks.
    Already posted in this thread but this diagram shows the idea


  8. #88
    pieter2 is offline Registered User
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    Default got a new one!

    I got a new BM-1 (with a fair discount from the shop owner). I used the old wire, but the new shunt. Everything works like it should (up to now). So I suppose the problem was the display unit itself.
    fyi: the new version has an orange wire that may be connected with the + of the starting battery. Also the shunt looks very different (a bit cheap actually). But at least it functions like it should.
    Thanks for all you help on this topic!

  9. #89
    VicS is offline Registered User
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    Glad you have got it sorted and thanks for letting us know.

    A faulty unit was about the only possibility left.

    Please add the orange wire to my diagram.

  10. #90
    VicMallows is offline Registered User
    Location : Emsworth, Chichester Hbr, UK
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    For the benefit of anyone else still following the thread who may have problems, I have come across yet another instance where erratic behaviour of a BM-1 has been caused by very slight resistance in the main (red) power feed at the in-line fuse holder. This again caused unexplained readings when the backlight was turned on/off.

    A similar internal fault (dry joint etc) could very well have been the problem all along.

    Vic

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