NASA BM1 wiring help please

Discussion in 'Tech/Mech General' started by icantremember, Jan 23, 2014.

  1. icantremember

    icantremember Funster

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    I have a NASA BM1 compact fitted and two leisure batteries .... I have just realised that this has been fitted with the negative of one battery attached to one end of the shunt and the neg of the other battery along with all the feeds attached to the other end of the shunt.

    As far as I know both the battery negs should be on one end of the shunt and all the feeds on the other end.

    Please can someone confirm if I am correct or is it correctly wired.
     
  2. gozomike

    gozomike Funster Life Member Life Member

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    Hi. Yes the two batt negs need to be wired together on one side of the shunt and the feeds go to the other. As it is it will just measure the current on one battery also it will put a small resistance in series with the one battery which will make the usage uneven.
     
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  3. icantremember

    icantremember Funster

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    Thanks Mike, I was sure that is how it should be done..... mine was fitted by a professional 'cos I couldn't be bothered .... so now I have to rewire it:Angry:

    Just goes to show if you want a job done properly ......
     
  4. Geo

    Geo Trader - Funster

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    Destruction's
    HERE:thumb:
     
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  5. haganap

    haganap Funster Life Member

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    I hate to disagree, and could be wrong (Im at work not in Morroco) But I think you will find Mikes version incorrect.

    I seem to remember ringing them about this. You only connect one neg to the shunt, you adjust the Battery Bank capacity upon the NASA as per Geo's instruction leaflet ie on the NASA itself. The NASA measures the whole battery bank this way and not individual batteries.

    Now before I get slated, please ring and check, im not sure, it's just I remember asking ht esame question and being suprised by the answer, the guy who fitted it for you may well of been correct.:thumb:

    HERE YOU GO WITHIN THE INSTRUCTIONS

    Q&A Half way down on page 7

    and a bit from my blog
    That carried out the next thing I concentrated on doing was to install a Nasa BM1 this is a comprehensive very special bit of battery monitoring commonly found on boats. It would be used to establish how many amps were going in coming out, what my inverter would pull solar panels would put in etc etc. The installation for this is really quite simple although I did have a little trouble understanding what a shunt does and how it should be wired. A quick call to the manufacturers helped me understand that one bit goes on the neg post and everything you want measured goes on the other post hence measuring the output. So with that carried out and wired in, I was ready and able to carry on with the main job in hand.
     
    Last edited: Jan 23, 2014
  6. treetops1

    treetops1 Funster

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    Excuse my ignorance what is a shunt ? lol
     
  7. Geo

    Geo Trader - Funster

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    In electronics, a shunt is a device which allows electric current to pass around another point in the circuit by creating a low resistance path. The term is also widely used in photovoltaics to describe an unwanted short circuit between the front and back surface contacts of a solar cell, usually caused by wafer damage. The origin of the term is in the verb 'to shunt' meaning to turn away or follow a different path.
     

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  8. gozomike

    gozomike Funster Life Member Life Member

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    In effect a low value resistance which is in the circuit so as the unit can measure the slight volts drop across it and then give this as a current reading.

    I am trying to keep this simple.:Smile:
     
  9. callumwa

    callumwa Read Only Funster

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    An ammeter shunt allows the measurement of current values too large to be directly measured by a particular ammeter. In this case the shunt, a manganin resistor of accurately known resistance, is placed in series with the load so that all of the current to be measured will flow through it.
     
  10. icantremember

    icantremember Funster

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    I'm sorry Paul but I can't see where your suggestion differs from Mike's and Geo's, however, as you suggest I have emailed NASA Marine and their reply seems to confirm my thoughts and those of Mike & Geo ....

    Hi Brian,

    If both leisure batteries are treated as a single bank then they should both be wired through the shunt, the one on the non load end of shunt is not being measured.

    Regards,

    -- NASA MARINE Boulton Road Stevenage Herts SG1 4QG www.nasamarine.com
     
  11. Techno

    Techno Funster Life Member

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  12. haganap

    haganap Funster Life Member

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    Yes,. Iv'e just read Mike's post again and I can't see it?

    I think when I read it, the suggestion was that negatives from both batteries go to the shunt?

    I have one negative to the shunt, as the batteries are wired in line, IE as in one battery bank. Readin Mike;s post, it made me think that each negative from each battery, went to the shunt?

    but then again I did, say i could be wrong :Wink:

    Anyhow, what I do know is that mine is wired exactly Like Techno's and I know if his is right, then mine is too :thumb: ( I copied his)
     
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