Battery monitor shunt

[Wilbor]

I have a 500amp shunt for my BEP battery monitor on the negative circuit on the house batteries, it also has a Wizbang junior for the Midnight Classic 200 solar controller attached to it, all works well. I am considering fitting a Victron BMV700, are there any known issues with fitting two shunts to the negative wire? i.e. one after the other

[grizzzman]

If the BMV700 uses the same shunt, you could just piggyback the wiring to the same shunt.

[jon_d]

Rob,

A shunt is calibrated to has a certain voltage drop for a certain current. That's why you need to consider the current and voltage specification.

soooo.


If the controllers use the same value shunts; ie 500Amp- 50mV

If the controllers use different values, just join them in series.


there is a twist though; if the ration of the shunt is the same, it's possible to use the same shunt.
(ie 500A/50mV and 200A/20mV)

[bagmaker]

could one of them be put on the positive side?

[BruceS]

Victron shunt has a 'dedicated' connection that is needed to 'feed' the gauge. I'd use both shunts.
Terry?

[Wilbor]

Thanks for that. I am happy to use the two shunts in series victron BMV700's are a good price at the moment, there must be a new model coming out soon. Why do most if not all manufacturers recommend a shunt go on the negative line?

[BruceS]

Rob the Victron shunt HAS to be in the neg wire because it has a wire that goes from the pos wire that plugs into the shunt. Obviously it uses that to detect the voltage? If the shunt was in the pos wire & the 'detector was also in the pos, it would show Nil volts. (differential)
It's just the way it has been made.
My Victron 702 I'm using on my 48V has the 1st sensor wire in the 1st spot at 24v & the 2nd in the last spot to also read 24v & combined voltage as well.
If you have 24v you could do 12V & 12V & it'd show if ever one battery runs low or drops a cell.

[Wilbor]

Thanks Bruce, I have a 12v system so no worries there. I looked at the 702 and the only difference I could work out was it showed voltage for two batteries, are there two shunts as well?

[T1 Terry]

The 702 is a pain in the rectum if used to read split voltage on a 12v battery or house battery and start battery but seems to work ok on 24v and 48v systems. The second battery voltage detected by the 702 is voltage only, all the other readings are to do with the primary battery, if you really do need to know how the other battery is fairing, buy a second Victron 700 BMV.
The only down side of multiple shunts in line is the lower limits of the smallest shunt. An example is the Plasmatronics shunt, limited to 200 amps where the Victron can handle 500 amps. Not only will the readings be incorrect through the 200 amp shunt if the draw is more than 200 amps, it will also introduce a voltage drop and heat issues if pushed beyond its design parameters.
Fortunately the Plasmatronics shunt can be fitted in the positive cable or the negative cable, if we are fitting a Victron 700BMV where there is already a Plasmatronics shunt in the negative cable we wire the solar through the Plasmatronics shunt and then on to the load side of the Victron shunt, that way the Dingo/PL20 will show all the solar in while the Victron will only show what went into the battery and not the current used directly by any appliances running. The Victron is a stand along battery monitor, it doesn't care what happened else where, it is only looking at the battery data and nothing else. This means Watts/amps either going in or coming out of the battery is after the other charging sources have supplied any loads, a real catch for those new to the use of stand alone battery monitors.

T1 Terry