Adding 2nd battery monitor ti an existing Beneteau monitor

[Handsoff]

Hello knowledgable folks,

My son and I are ardent novice sailors but totally unfamiliar with boat wiring and electronics.

We have a relatively new Beneteau with an existing battery monitor. We want to add a Victron bmv-712 monitor but still maintain the Beneteau monitor. This is for bluetooth connectivity and perhaps adding additional batteries in the future. (In fact, we are not completely sure what the exiting monitor is monitoring).

Our research seems to indicate that by wiring the two shunts in series (not parallel) this should not be a problem. There may be a slight voltage drop but not significant.

I am enclosing a picture of what we believe to be the existing monitor shunt which is located in the upper left hand corner of the picture.

So the question is: if we locate the Victron shunt in proximity to the existing shunt, can we safely wire the two together and is wiring in series correct? We would prefer not to destroy or blow up anything.

Thanks in advance for your help
Marshall

[sailormed]

I would look into using the same shunt for both devices. By putting them in series you are increasing the total resistance and should reconfigure both devices with the new total shunt value, but they are both only connected to half that value, Looks like an unnecessary complication.

[smac999]

Yes put them in series.

[smac999]

Originally Posted by sailormed

I would look into using the same shunt for both devices. By putting them in series you are increasing the total resistance and should reconfigure both devices with the new total shunt value, but they are both only connected to half that value, Looks like an unnecessary complication.

The victron shunt is totally different.

Each monitor is seeing its own resistance. There is no need to do anything.

[Orion Jim]

My buddy with a First 36.7 just added a Victron 712. He left the original monitor as is and wired the new Victron, and its shunt, separately.

[Handsoff]

Thanks Orion Jim but did you buddy wire the Victron 712 shunt in series to the original shunt leaving both monitors working?

[stormalong]

Yes, they must be in series to function properly. Parallel would cause low readings on each monitor. The voltage drop across a shunt it quite small so, while there will be some inaccuracy it won't be significant.

[Dsanduril]

Series is the only way both will work, unless you can share the shunts. The BMV uses a 50mV shunt and the circuit board converts the signal right on the shunt. If your existing monitor uses a 50mV shunt (that is most common, but there are 100mV shunts also somewhat typical) and is the same current rating then you could replace the existing with the Victron, connect the old monitor to the two screws that hold the Victron circuit board, and then connect the "phone cable" to the BMV. If the old shunt has a different current rating then you would have to re-configure the old monitor, that may not be desirable/easy.

For a 50mV shunt the voltage drop across each shunt is 0.05V at full rated current. Typical boats would use somewhere from a 100A to a 500A shunt. For your typical/normal draws in the range of 10A the voltage drop from the shunt will be on the order of 0.005V or less, too low for most instruments to measure accurately. Only when you approach full current (using the windlass, for example) will you see the voltage drop creep up into the observable range, and at that point you probably have lots of bigger losses in play anyway.

[Richv]

Originally Posted by Handsoff

Hello knowledgable folks,

My son and I are ardent novice sailors but totally unfamiliar with boat wiring and electronics.

We have a relatively new Beneteau with an existing battery monitor. We want to add a Victron bmv-712 monitor but still maintain the Beneteau monitor. This is for bluetooth connectivity and perhaps adding additional batteries in the future. (In fact, we are not completely sure what the exiting monitor is monitoring).

Our research seems to indicate that by wiring the two shunts in series (not parallel) this should not be a problem. There may be a slight voltage drop but not significant.

I am enclosing a picture of what we believe to be the existing monitor shunt which is located in the upper left hand corner of the picture.

So the question is: if we locate the Victron shunt in proximity to the existing shunt, can we safely wire the two together and is wiring in series correct? We would prefer not to destroy or blow up anything.

Thanks in advance for your help
Marshall

I'm not familiar with those exact devices, but you really only need one shunt. Just connect the current sense leads of each monitor to the shunts, and the voltage sense leads to the same power points. I've done this with several different kinds of voltage/current monitors.


Just for safety, I would suggest putting 1/8A inline fuses (picofuse) in the sense leads. Just solder them in place and slip heat shrink tubing over the fuses. This is an example: https://www.digikey.com/product-deta...31TR-ND/700693

[Richv]

Originally Posted by smac999

The victron shunt is totally different.

Each monitor is seeing its own resistance. There is no need to do anything.

"From the Victron manual:
The BMV is supplied with a 500A / 50mV shunt. For most applications,
this should be suitable; however the BMV can be configured to work with
a wide range of different shunts. Shunts of up to 9999A, and/or 75mV can
be used."

If your existing unit uses a 50mV or 75mV shunt, all you need to do is program the Victron for the shunt parameters. If your system uses a 100mV shunt (rare), just tell the Victron it's a 50mV shunt and that the full-scale current is 1/2 the actual current. E.G., if you have a 1000A/100mV shunt, tell the Victron it's a 500A/50mV shunt.

[Dsanduril]

The Victron shunt (at least IME) uses a locally mounted circuit board to translate the mV signal:



If the existing shunt has the same screw spacing then you could move the board over, otherwise as noted above, you should be able to use the Victron shunt in place of the the existing - it depends on how the other battery monitor is configured and whether you want to go to the trouble of reconfiguring.

[Orion Jim]

Originally Posted by Handsoff

Thanks Orion Jim but did you buddy wire the Victron 712 shunt in series to the original shunt leaving both monitors working?

Yes. Both work independently.

[Handsoff]

Thanks everyone for all your help. After reviewing all the advice and talking with Victron dealer in San Diego, we will be installing the Victron shunt in series with the existing shunt. Again, thank you all.

[chef2sail]

Not sure I would keep both operating. If there was an issue you wouldn’t know which device was causing the problem as easily. I would leave the old monitor shunt in place but disconnect and only use the Victron one. That way you have an installed spare you know that works

BTW we have the same Victron and like it a lot.

[mitiempo]

Using 2 shunts is not a problem. I would use both, but the 712 is the best of the two.