Battery monitor

[johnnys]

Hi all, I bought a Dufour 365 at Southampton BS due in March (not ideal for East Coast 1.9m draft). Getting together some kit to put on it I purchased a Nasa battery monitor at the London show. It has a 100amp shunt, hopefully no problem for current draw, but looking at the boat spec it has a 115 amp alternator. The domestic batteries are 200amp/hr and engine 75amp/hr, the intention is to only monitor domestics. I am not well up with the black art of charging, does the team think there is any chance of putting over 100 amps through the shunt and if so what happens??
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[VicS]

Very unlikely you'll exceed 100 amps. If you do it will only be for a short time. Why not get intouch with Nasa for advice directly from them.

 

[snowleopard]

No way will an alternator push over 100A into a 200AH battery unless it were totally utterly flat.

You could draw over 100A if you had a big anchor windlass but then you'd run the engine to take some of the load.

So your shunt should be perfectly adequate.

 

[savageseadog]

Only slight issue is that the shunt could heat up a bit and lose accuracy with the positive temperature coefficient of resistivity. Other related issue the shunt will be more prone to oxidise. Practically speaking probably OK though.

 

[Artemis_C2121]

Hi John

As has been said should be ok with a little space to breath around it cant see your going to pump out 100 A for more that a brief moment if ever.
I was also impressed with the 365 Graham mentioned he would be getting one at fambridge soon may twist his arm to borrow it for a test sail

Nev

 

[Clyde_Wanderer]

If you email alan@nasamarine.com, he will advice you.
They were very helpfull when I emailed them with a BM1 question.

 

[johnnys]

Thanks for all the advice, I will certainly contact Nasa but it sounds as though it won't be too much of a problem.

 

[hubert]

The active part of the shunt is MANGANIN which has a Zero temperature characteristic so will not loose acuracy if it gets warm.

 

[Jonny_H]

The BEP Marine monitors come with a much bigger shunt (500 amps?). When I spoke to Merlin about it they told me it was in built like that in case you ever needed to start the engine off the domestic batteries (due to engine battery failure) which could pull well over 100 amps and therefore blow a smaller shunt.

However, under normal use I agree 100 amps should be fine.

Jonny