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mercu1 avatar image
mercu1 asked

Battery Monitor Intermittent Overload Current

As you may know, Victron does not provide direct support to anyone except authorized dealers and distributors and the Victron distributor known as ARW Maritime has directed me to this forum. I am seeking an answer from Victron Engineering.

I am an electrical engineer and an ABYC certified marine electrician. I am seeking some support regarding an installation of a Victron BMV-712 battery monitor.

This is a marine application. I am using the standard 500A/50mv shunt supplied with the BMV-712. The battery bank that is being monitored has a bow thruster connected to the battery. The bow thruster is an intermittent load and draws well over 500 amps. Because the load is intermittent I am not worried about damaging the shunt. It will be a lot of trouble for me to disconnect the thruster negative cable from the battery and reconnect it to the load side of the shunt so I don’t want to do that if it will not help anything. What do I mean by “if it will not help anything”. The BMV-712 measures amp-hours. I suspect that when current in the shunt exceeds 500A the monitor will not accurately measure amp-hours. I suspect it will not measure amp-hours at all. If this is the case then I will not bother to connect the thruster negative cable to the load side of the shunt and I will leave it as is which is connected directly to battery negative. I understand that another system design approach would be to use a shunt with higher current rating. I have some reasons for not wanting to do that. I would rather except some inaccuracy that may come with intermittent overload of the shunt.

Victron is a fantastic engineering company and I am sure the Victron Engineering team can provide very accurate assessment of my question and a very complete answer. I am asking Victron engineering to respond to this question of where does it make sense to connect the negative cable from the thruster in this application.

BMV Battery Monitor
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1 Answer
Mike Dorsett avatar image
Mike Dorsett answered ·

The bow thruster is an intermittent load and draws well over 500 amps.

Ok, so if the bow thruster is not connected, then the shunt / ADC won't overload

One way to safely measure the overload capacity would be to set up a small pot across a battery so as you get ~120mV across the pot. The sense leads that go to the shunt can then be connected to the pot. You then can adjust the pot to set the current read on the BVM, and see where it overloads (saturates). Typically I would expect a 63mV input to saturate between 80 and 120mV. I would be surprised to see an answer from the design team.

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