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Post by dnickj on Feb 23, 2009 13:22:15 GMT
Hi i am looking to install a NASA BM1 battery monitor to the domestic side of the installation on a SO40 at present all the negative feeds are connected to a common isolator and the start and domestic live feeds are taken each to their own isolator with the charging taken care of by a split charging device. The wiring diag for the new monitor shows the shunt connected to the domestic -ve and a +ve connection to the domestic bank. I assume i could install the shunt between the -ve isolator and the domestic switch panel with the live connected to the domestic +ve isolator Will this work - or does anyone know better - thanks
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Post by Trevor on Feb 23, 2009 22:34:01 GMT
Hello Dnickj,
If you find another thread on this forum called "electric current meter on an SO36i" you can see a picture of how I mounted the shunt of our boat.
This may show you a really convenient place to mount the shunt without modifying things too much.
I hope this helps.
Happy sailing,
Trevor
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Post by MalcolmP on Feb 24, 2009 20:44:34 GMT
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Post by sailingpages on Feb 25, 2009 0:01:43 GMT
Hi,
Trevor's modification is fantastic for monitoring domestic loads, but unfortunately will not let you monitor charging currents from the engine or shore-power charger.
For a battery monitor to work properly (to give approx. state of charge %, or Amp-Hours remain), it needs to sense both charging currents and load currents. To monitor the domestic battery bank, the shunt for the BM1 needs to go between the common negative isolator and the negative of the domestic battery bank only. A separate connection from the negative isolator to the start battery -ve may be needed if the domestic and start batteries are wired in parallel to the negative isolator (as was the case on my 36i).
Cheers, Geoff.
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Post by Trevor on Feb 25, 2009 9:42:25 GMT
Hi Geoff, Thanks for the correction and I agree. The shunt position I proposed will not work for a serious battery monitor. After thinking about it my advice would have given dnickj a bum steer. Happy sailing. Trevor
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Post by sailingpages on Feb 26, 2009 13:30:46 GMT
No worries Trevor, The distribution boards is a lot easier place to want to put a shunt though. I have finished putting my Lifeline AGM start battery onto a shelf I installed just behind the isolator switches. Not much room to work in there, particularly now.
I really like your solution for adding current monitoring to the 36i using the existing panel. I'm going to modify our boat with this once my warranty work is complete. I think I found the correct socket contacts to suit the MATE-N-LOK connector on the back of the digital panel, though because I haven't done the modification yet, I can't guarantee this yet. I have updated the appropriate thread above with this thought.
Cheers, Geoff.
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