Victron BMV 712 - Does it have a memory?

[jetzi]

I recently installed a Victron BMV 712 with my 110 Ah sealed lead acid domestic battery. I put the shunt in the battery negative, and I put the main positive on the positive terminal on my domestic. I got the optional temperature sensor but I am saving that for use with my lithiums, so the secondary input I set to be the starter battery voltage (because why not).

 

The app is really nice, but I noticed that the graphs it draws under "Trends" only go back so far as you last connected to the BMV via bluetooth. If I close/minimise the app, that closes the connection. I found that a bit of a shame, because I wanted to be able to compare my usage over the whole day. Never mind, I thought, I'll have to have the app permanently running on a separate device to log these data points.

 

Today it was a really bright sunny day and I harvested 500Wh, plus I ran the engine for a good 6 hours, so I thought today would be the day that I calibrate the SoC to 100%. I did this, and forgot about it for around 8 hours, until now, when I wanted to see how much power I'd used. Opened up the app now, and it says

 

SoC: 100%

Voltage: 12.45V

Current: 0.8A

Power: 9W

Consumed Ah: 0Ah

Time remaining: Infinite

Starter battery: 12.73V

Relay state: Open

 

So this implies that I've used no power since setting the SoC to 100% - definitely not the case, I've been using power since the sun went down and the engine went off.

 

I decided to leave the app open for awhile and use some power, to see if the Consumed number increases - to see if it works at all. After putting a ~8A load on for 30 mins or so (4Ah?) I'm still seeing 0Ah consumed. I am pretty sure I have seen this number higher than 0. If I go to History, I see Cumulative Ah drawn of -101Ah.

 

What am I doing wrong here?

[WotEver]

19 minutes ago, ivan&alice said:

I recently installed a Victron BMV 712 with my 110 Ah sealed lead acid domestic battery. I put the shunt in the battery negative...

Is the shunt now the ONLY connection to the domestic negative?  Absolutely no other connections to the negative post?

[Dr Bob]

3 minutes ago, WotEver said:

Is the shunt now the ONLY connection to the domestic negative?  Absolutely no other connections to the negative post?

I can see why you are asking that Tony, but if the meter is showing 0.8A draw then the Ahrs should be showing a number bigger (I really mean less)  than 0. Also the Cummulative Ahr is -101 Ahrs so it is counting amps out.

Yes there may be other draws not counted if the shunt is wired wrong but the Ahr should be reading - something.

Ivan, you havent done something silly like jamming in the two buttons that you use to sync back to 100%?

I cant see why the 0Ahr is zero. I will ponder the question over a glass of malt I am about to pour.......and no there is no decent history...which is why i connected mine to a rasp Pi.

[PeterF]

Or the Victron Colour Control GX or Victron Venus GX for those of us who have never home baked a raspberry PI.

[nicknorman]

Looks the shunt is wired wrong way round so it thinks the discharge is a charge. I don’t have a BMV but I would normally expect a discharge of 0.8A to be shown as -0.8A. And that would explain why the SoC isn’t dropping and infinite time remaining.

 

i expect if you now run the engine, it will start to show AH consumed and SoC decreasing.

Edited April 21, 2020 by nicknorman

[Jen-in-Wellies]

21 minutes ago, nicknorman said:

Looks the shunt is wired wrong way round so it thinks the discharge is a charge. I don’t have a BMV but I would normally expect a discharge of 0.8A to be shown as -0.8A. And that would explain why the SoC isn’t dropping and infinite time remaining.

 

i expect if you now run the engine, it will start to show AH consumed and SoC decreasing.

It is worse than that. If the shunt is connected the wrong way round it will make the engine run backwards too. The only solution is to swap the gear control cable on to the other side of the morse control lever so ahead becomes ahead again and astern astern. Going for an eight hour cruise will kill your batteries irretrievably.  ?

Jen

Edited April 21, 2020 by Jen-in-Wellies

[Alan de Enfield]

1 minute ago, Jen-in-Wellies said:

It is worse than that. If the shunt is connected the wrong way round it will make the engine run backwards too. The only solution is to swap the gear control cable on to the other side of the morse control lever so ahead becomes ahead again and astern astern. Going for an eight hour cruise will kill your batteries irretrievably.  ?

Jen

Would it not just be simpler to turn the prop around and put it on 'backwards' ?

[Jen-in-Wellies]

Just now, Alan de Enfield said:

Would it not just be simpler to turn the prop around and put it on 'backwards' ?

Of course! This is why a second opinion is always best when making a decision and why CWDF is such a useful resource of technical advice for boaters. A much simpler fix than mine. Still doesn't solve the batteries being discharged by the engine running though.

Jen

[nicknorman]

No, I think that putting the prop on the other way round would make no difference. It would be both facing the other way and rotating the other way (from it’s point of view), net effect nothing changed.

[WotEver]

3 minutes ago, nicknorman said:

No, I think that putting the prop on the other way round would make no difference. It would be both facing the other way and rotating the other way (from it’s point of view), net effect nothing changed.

The extra wobble from the inverse taper might help though...

[nicknorman]

3 minutes ago, WotEver said:

The extra wobble from the inverse taper might help though...

Not if you wrax it up REALLY TIGHT with a BIG HAMMER!

[Alan de Enfield]

20 minutes ago, nicknorman said:

No, I think that putting the prop on the other way round would make no difference. It would be both facing the other way and rotating the other way (from it’s point of view), net effect nothing changed.

Surely it would be 'pushing' rather than 'pulling'.

That must make a difference.

[Dr Bob]

1 hour ago, Jen-in-Wellies said:

It is worse than that. If the shunt is connected the wrong way round it will make the engine run backwards too. The only solution is to swap the gear control cable on to the other side of the morse control lever so ahead becomes ahead again and astern astern. Going for an eight hour cruise will kill your batteries irretrievably.  ?

Jen

No, you're making the assumption Ivan has the BMV wired to the alternator which is not true, so it cant go the wrong way round. Reversing the shunt will mean the electrons are going the wrong way and with only solar attached that means they will head in that direction and the panels will emit light rather than absorb them. This could cause problems at night if the boat next door does not like artificial light. Boat security at night should be improved though.

1 hour ago, nicknorman said:

Looks the shunt is wired wrong way round so it thinks the discharge is a charge. I don’t have a BMV but I would normally expect a discharge of 0.8A to be shown as -0.8A. And that would explain why the SoC isn’t dropping and infinite time remaining.

 

i expect if you now run the engine, it will start to show AH consumed and SoC decreasing.

Clever!

It is pretty difficult to connect the BMV 712 shunt the wrong way round. The destruction book is quite explicit in what to do and is not confusing in any way. Ivan must be more of a muppet than me if he got it the wrong way round. Come on Ivan. Own up!

[jetzi]

I will check shortly and report back. I am not sure which will be worse - the embarassment of having connected it the wrong way around or the mystery of not knowing why it isn't working!

[jetzi]

Shunt was the wrong way around ?

Glossing over that point quickly...

 

@Dr Bob does your raspberry pi do anything other than run the Victron app? What happens if it crashed or restarted? I'd like to be able to store the data over years if possible. Is the data written to permanent storage at any point?

[Richard10002]

48 minutes ago, ivan&alice said:

Shunt was the wrong way around ?

Glossing over that point quickly...

Not at all...

 

Good job you asked the question, and good job there are enough people here for one to come up with the most unlikely, (or likely), answer.

 

Unless you didn't RTFM, it's obviously not as explicit as Bob suggests  

[jetzi]

1 minute ago, Richard10002 said:

Not at all...

 

Good job you asked the question, and good job there are enough people here for one to come up with the most unlikely, (or likely), answer.

 

Unless you didn't RTFM, it's obviously not as explicit as Bob suggests  

Well the one end of the shunt is marked "Battery" and the other is marked "Charger".

 

Considering that in my system, the shunt connects between the domestic battery -ve (the actual battery) and the starter "battery" -ve (actually the load/charger) I was half right!

 

It's very easy and very explicit in TFM, which I didn't R hard enough I guess. I've just out-muppetted Bob. I really don't have a valid excuse. Thank heavens in this particular case current flows both ways through a shunt and no damage was done, apart from that to my battery stats and my pride. It's good to have a warning like this every now and again before I really break something expensive.

 

For example, my MPPT.

 

I understand that one must always connect the battery first, and the PV afterwards; when disconnecting, disconnect the PV first and the battery afterwards. In other words, the MPPT should never have the PV connected without a battery. (However I read that Victron have made the SmartSolar MPPT a little more muppetproof than most with regard to this connection order).

The above implies that using the battery isolator could cause damage to the MPPT, right? Because if I shut off the battery, the MPPT is going to be connected to the PV but not the battery? This came up because I wanted to use the isolator before switching the shunt polarity. However I decided I'd better disconnect the solar first. I then wondered if perhaps the panels might not like being disconnected under load, all connected in series as they are that's 160V abruptly pulled from the bare wire terminal - sparky sparky!

 

In the end I shaded the panels, flipped the isolator, switched the BMV shunt and reversed the process in less than a minute, and the MPPT seemed completely fine.

 

But what should I do here for the future? I feel like a circuit breaker on the PV positive wire would be a wise idea, placed directly next to the isolator with a plaque in Muppettese instructing said muppet to flip the circuit breaker before flipping the isolator. Would this do any mischief to the panels themselves - perhaps they should they have a dump load attached?

Am I overthinking this whole thing out of embarassment for the shunt error?

[Dr Bob]

1 hour ago, ivan&alice said:

 I've just out-muppetted Bob.

That deserves a greenie.

2 hours ago, ivan&alice said:

 

 

@Dr Bob does your raspberry pi do anything other than run the Victron app? What happens if it crashed or restarted? I'd like to be able to store the data over years if possible. Is the data written to permanent storage at any point?

The data can be stored on an sd card on the Pi but I just use the victron site to record all the data, ie the Pi sends the data every minute to the victron site but it must store quite a bit on board as it all there even if the router goes down for an hour or so. The victron site holds the data for 6 months but it is easy to download it all in an excel spreadsheet every 3 months or so. If the pi crashes you only loose the data until it is rebooted. Mine has not crashed in the 12 months since installing it - contected to the victron site 24/7

[jetzi]

6 minutes ago, Dr Bob said:

The data can be stored on an sd card on the Pi but I just use the victron site to record all the data, ie the Pi sends the data every minute to the victron site but it must store quite a bit on board as it all there even if the router goes down for an hour or so. The victron site holds the data for 6 months but it is easy to download it all in an excel spreadsheet every 3 months or so. If the pi crashes you only loose the data until it is rebooted. Mine has not crashed in the 12 months since installing it - contected to the victron site 24/7

Thanks for the explanation! Makes sense.

[Richard10002]

4 hours ago, ivan&alice said:

Well the one end of the shunt is marked "Battery" and the other is marked "Charger".

Aha!  I had forgotten as it is a few months since I fitted mine in December.

 

4 hours ago, ivan&alice said:

In the end I shaded the panels, flipped the isolator, switched the BMV shunt and reversed the process in less than a minute, and the MPPT seemed completely fine.

 

But what should I do here for the future? I feel like a circuit breaker on the PV positive wire would be a wise idea,

I have a circuit breaker between Panels and controller. It just makes it easy to do a whole variety of things without worrying, or without covering the panels, or without waiting for dark.

 

It's a DC breaker with a 48V limit, so I have my 2 panels in parallel. I think you can get higher voltage breakers.

[WotEver]

5 hours ago, ivan&alice said:

The above implies that using the battery isolator could cause damage to the MPPT, right?

Nope. Because the BSS specifically permits Solar (and other chargers) to bypass the isolator and connect direct to the battery via a fuse. Otherwise how can you switch off your isolator when leaving your boat yet expect your battery to be maintained?

[David Mack]

20 hours ago, ivan&alice said:

 

But what should I do here for the future? I feel like a circuit breaker on the PV positive wire would be a wise idea, placed directly next to the isolator with a plaque in Muppettese instructing said muppet to flip the circuit breaker before flipping the isolator. Would this do any mischief to the panels themselves - perhaps they should they have a dump load attached?

That's what I have (although I don't have a plaque in Muppettese).

I used this breaker.

https://www.bimblesolar.com/extras/dc-circuit-brakers/25a-din-breaker-tomzn

The Bimble website includes this diagram 

[Dr Bob]

31 minutes ago, David Mack said:

That's what I have (although I don't have a plaque in Muppettese).

 

 

My denstist cleans mine off every 6 months.

[Keith M]

It is poor practice to have no protection or isolation between the panels and the regulator 

 

[nicknorman]

47 minutes ago, Keith M said:

It is poor practice to have no protection or isolation between the panels and the regulator 

 

Why?

 

Well, unless the panel oc voltage is high enough to be a danger, then an isolator is a good idea. What are you trying to protect against with your suggested “protection”?

Edited April 22, 2020 by nicknorman