Unable to start up replacement battery monitor

[Wanderer Vagabond]

I hope there are some experts on battery monitors out there because this problem has me flummoxed.

 

The story is that the casing of my old Victron BMV 600 Battery Monitor split, probably as a result of pressing the buttons on it a bit too hard, it was an old unit and the buttons were a bit temperamental. Looking for a replacement I bought a Victron BMV 702 which to me just looked like and updated version (it's not a Smart system or anything like that). The shunt from the old monitor is still installed and since the wiring and RJ12 cable looked identical I simply removed the old unit and plugged the new unit into the RJ12 cable. Now the old unit still works but is a bit fragile and when connected the data comes up on the screen and if left connected whilst the engine is running it will automatically synchronize which to me suggest that the wiring is OK. When I disconnect the RJ12 cable from the back of the old unit and plug it into the back of the new unit, nothing happens. There is no display, pressing buttons has no effect and it just wont seem to fire up. Has anyone any suggestion as to why? or have I got a duff unit?

[MtB]

2 minutes ago, Wanderer Vagabond said:

I hope there are some experts on battery monitors out there because this problem has me flummoxed.

 

The story is that the casing of my old Victron BMV 600 Battery Monitor split, probably as a result of pressing the buttons on it a bit too hard, it was an old unit and the buttons were a bit temperamental. Looking for a replacement I bought a Victron BMV 702 which to me just looked like and updated version (it's not a Smart system or anything like that). The shunt from the old monitor is still installed and since the wiring and RJ12 cable looked identical I simply removed the old unit and plugged the new unit into the RJ12 cable. Now the old unit still works but is a bit fragile and when connected the data comes up on the screen and if left connected whilst the engine is running it will automatically synchronize which to me suggest that the wiring is OK. When I disconnect the RJ12 cable from the back of the old unit and plug it into the back of the new unit, nothing happens. There is no display, pressing buttons has no effect and it just wont seem to fire up. Has anyone any suggestion as to why? or have I got a duff unit?

 

 

Sounds to me as though despite looking the same, the old and new shunts and/or cables are not. 

 

I'd fit the shunt and cable that came with the new 702 if I were you, if only to rule it out. Then if it still doesn't work, contact Victron.

 

 

[Rob-M]

I agree with MTB, I expect the new model has different connections but uses the same connector type.

However, a quick Google turned up this blog, https://www.victronenergy.com/blog/2014/01/12/bmv-702-insights/, which states the 600S and 702 are interchangeable and the shunt didn't need replacing.

[Wanderer Vagabond]

14 minutes ago, Rob-M said:

I agree with MTB, I expect the new model has different connections but uses the same connector type.

However, a quick Google turned up this blog, https://www.victronenergy.com/blog/2014/01/12/bmv-702-insights/, which states the 600S and 702 are interchangeable and the shunt didn't need replacing.

Thanks for the link, what he describes is pretty much what I was expecting, there seems no obvious difference between the shunts (except that two battery banks can be monitored, rather than just the one on my old unit) and the RJ12 cable is generic. I'm calling in at Calcutt Chandlery tomorrow for fuel and will seek some advice there if possible. If they can't help I think I'll be cruising back to Midland Chandlers at Braunston (where the unit was bought). 

[MtB]

11 hours ago, Wanderer Vagabond said:

Thanks for the link, what he describes is pretty much what I was expecting, there seems no obvious difference between the shunts (except that two battery banks can be monitored, rather than just the one on my old unit) and the RJ12 cable is generic. I'm calling in at Calcutt Chandlery tomorrow for fuel and will seek some advice there if possible. If they can't help I think I'll be cruising back to Midland Chandlers at Braunston (where the unit was bought). 

 

 

Another approach is to find another boat with a working 702 (plenty about I suspect) , then ask them if they might kindly allow you to unplug the cable from the back of theirs and plug their known-to-be-working cable into the back of yours, and see if yours wakes up. 

 

 

Edited September 12, 2022 by MtB

[Jen-in-Wellies]

12 hours ago, MtB said:

Sounds to me as though despite looking the same, the old and new shunts and/or cables are not. 

 

I'd fit the shunt and cable that came with the new 702 if I were you, if only to rule it out. Then if it still doesn't work, contact Victron.

This seems such an obvious thing to try, despite what the Victron blog is saying, I'm surprised at the reluctance to give it a go. The old cable, or one of the connectors could be on its way out, or have been damaged when fiddling about. There is a brand new shunt and cable sitting there!

Edited September 12, 2022 by Jen-in-Wellies

[cuthound]

The shunt is really just a very accurate low value resistor, typically dropping 50 or 75 millivolts at its full rated load, therefore unless the connections are different it shouldn't make any difference to the monitor 

 

I would check that the cables have identical connections within the connectors and that the connectors on the old cable, shunt and new monitor are undamaged.

Edited September 12, 2022 by cuthound
Missing worms

[MtB]

3 minutes ago, cuthound said:

The shunt is really just a very accurate low value resistor, typically dropping 50 or 75 millivolts at its full rated load, therefore unless the connections are different it shouldn't make any difference to the monitor 

 

 

No it isn't. Well yes it is, but there is a little PCB rammed with electronics attached to it, for comms with the display. 

 

The dedicated shunt, the cable and the display all together make up the whole thing.

[cuthound]

Just now, MtB said:

 

 

No it isn't. Well yes it is, but there is a little PCB rammed with electronics attached to it, for comms with the display. 

 

The dedicated shunt, the cable and the display all together make up the whole thing.

 

But as Victron say the 600 and 700 series shunts are comparable it is very likely the PCB a well as the same are the same for both. A quick communication with Victron would establish this one way or the other.

[Wanderer Vagabond]

Well having now resolved the issue, Vectron lied. As was suggested in the above link the shunts should be interchangeable however whilst the old monitor will work on the new shunt, the new monitor won't work on the old shunt. Looking at them both I have no idea why since, other than an additional terminal to connect to the engine battery if you want to (not used yet), they seem identical.

 

It seems odd because in the enclosed handbook it says that the monitor can be used with a variety of different shunts, just not the one from the 600 obviously.

[PeterF]

The above link was from 2014, that data may well be out of date after 8 years, perhaps the BMVs used to include a component that is no longer available and had to rework the meter with new components and it is no longer compatible. 8 years is a long time in electronics.

[Wanderer Vagabond]

7 hours ago, cuthound said:

The shunt is really just a very accurate low value resistor, typically dropping 50 or 75 millivolts at its full rated load, therefore unless the connections are different it shouldn't make any difference to the monitor 

 

I would check that the cables have identical connections within the connectors and that the connectors on the old cable, shunt and new monitor are undamaged.

Yup, everything mentioned is just fine. I am still using the old RJ12 cable (couldn't be *rsed to feed the new one on the circuitous route around the engine). Both the new and the old positive, fused, cables work with both monitors, the only thing that makes any difference is the new shunt. The old shunt still works with the old monitor and if the monitor casing hadn't fallen apart, I'd still be using it.

[cuthound]

12 hours ago, Wanderer Vagabond said:

Yup, everything mentioned is just fine. I am still using the old RJ12 cable (couldn't be *rsed to feed the new one on the circuitous route around the engine). Both the new and the old positive, fused, cables work with both monitors, the only thing that makes any difference is the new shunt. The old shunt still works with the old monitor and if the monitor casing hadn't fallen apart, I'd still be using it.

 

Could be worth taking the new monitor back and getting a replacement. If that doesn't work then bite the bullet and change shunts.

[Higgs]

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[cuthound]

1 hour ago, Higgs said:

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A meter with a built in 10amp shunt isn't suitable for either the starter or domestic batteries on a boat.

 

[Higgs]

22 minutes ago, cuthound said:

 

A meter with a built in 10amp shunt isn't suitable for either the starter or domestic batteries on a boat.

 

 

I've got a couple. They give me an indication. And I use them to connect through to USB charger units. They give me an indication of charge and roughly zero when a charge is complete. They are also used to test the charging capacity of some small panels I have. 

 

Placed at the end of the boat furthest away from the batteries, they give an idea of the voltage drop. 

 

 

Edited September 13, 2022 by Higgs