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alfonso avatar image
alfonso asked

3 batteries in boat

ac-sl1200-bmv.jpg

My Currently my installation is this and I wanted to add a victron battery monitor.

2 X Volvo Penta 4.3 GXI 225 hp engines with 75 A alternator each.

1 X Victron Phoenix Smart IP43 Battery Charger, 12/50 (3)

2 X Victron Energy ARG080201000R Argodiode 80-2AC 80 A

3 X Independent batteries from 12v to 150 ah each.

I want to add a monitor for the 3 batteries so I bought a victron BMV 702 (motor batteries) and a BMV700 (Auxiliary battery).

Attached is the installation diagram that I think is correct. Can you tell me if it is correct? Thanks.

BMV Battery Monitor
ac-sl1200-bmv.jpg (479.2 KiB)
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3 Answers
JohnC avatar image
JohnC answered ·

Hi @Alfonso

The BMV on "bat aux" is correct.

The other will only monitor "bat1". To monitor both 1/2 together, take the -ve from "bat2" directly to the BATTERY terminal, not the LOAD terminal. Essentially, join the 2 bat -ves together before the shunt.

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alfonso avatar image
alfonso answered ·

hi John,

but the bmv 702 instructions for main / aux batteries state this:

install3.jpg


 
                
 
               
 
              
 
              
 
              
 
               
 
                 
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                   JohnC avatar image 
                  JohnC ♦ 
                   commented  
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                   @Alfonso 
                   
Yes, but there the BMV will give the full current treatment to #1 batt and only measure the Voltage on #2 as one of the 3 auxiliary functions.

                   
You've followed this in your own diagram, but all you'll see is the V of bat2. If that's all you want then fine. 

                  
 
                 
 
                 
 
                   
                     
                     
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               alfonso avatar image 
             
 
             
 
              
 
               alfonso 
               answered · 
                  
                  
              
 
              
 
               
 
                
 
                 
The problem with measuring bat1 and bat 2 together is that you could have measurement errors. For example, if bat1 has a voltage of 13.7v (full) and bat2 has 11.9v (discharged) the shunt would show 12.8v, apparently everything is correct but it is not. Ultimately bat1 and bat2 are only used to start the engines and should not have consumption (if the ignition is not on). Now I wonder if the bmv702 shunt is really useful or just a direct voltage monitor to each battery (bat1 and bat2) would be enough.
 
                 

 
                
 
               
 
              
 
               
               
              
 
               
 
               
 
                 
                 
                 
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                   JohnC avatar image 
                  JohnC ♦ 
                   commented  
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The V's won't 'average' as they're on the +ve side of each batt. B1 cable will give the V on bat1 and B2 the V on bat2. No matter which way you wire the shunt.

                   
But yeh, for most a V reading on starter batts would suffice. 

                   


                  
 
                 
 
                 
 
                   
                     
                     
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                    alfonso avatar image 
                   alfonso  
                      JohnC ♦   
                    commented  
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So what information do I get by connecting the - of bat2 to the shunt battery? If I understand it correctly, I get joint consumption information from bat1 and bat2 if I connect them both - to the battery of the shunt.
 
                    
I appreciate all the information. I am learning a lot from your advice.
 
                   
 
                  
 
                  
 
                    
                      
                      
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                     JohnC avatar image 
                    JohnC ♦ 
                       alfonso   
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                     You'd get the (joint) consumption info, but you may find the charge info of more use. Be interesting where the Tail current finishes up if you were charging both or just one.
                     
I haven't done this though, but might be fun.. :)

                     

                    
 
                   
 
                   
 
                     
                       
                       
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