Victron BMV-712 questions

[uncle_bob]

Originally Posted by nryn

Thought I’d tack a post on the same topic on to this thread rather than start a new one. It’s primarily battery related, not solar related, though perhaps the solar equipment comes into play. Need some help sorting some questionable BMV-712 readings out.

My setup:

• 2019 Globetrotter 27 Factory Solar (so, 2 AGM Group 24 batteries)
• 2 additional 80W roof-mounted solar panels (for a total of 4)
• Victron BMV-712 Battery monitor
• Victron MPPT 100/50 Solar Charge Controller

On this 3-month trip we’ve primarily been on hookups so I haven’t been monitoring the battery much. But I’m rounding a corner on the trip after which the family will have flown home and I’ll be doing more dry camping, so I’m trying to develop a battery use routine, starting here in Seward, Alaska at our dry oceanfront site.

Basically, I don’t understand the BMV-712. I suspect some setting is off but I’d like to confirm. Despite consecutive full days of ample solar charge, the BMV-712 is reading a near-50% SOC. I’m not worried about it because the SeeLevel (which I trust more at this point) reports a near-full battery. But maybe you all can help me sort out what’s going on.

First, here’s what I see on the SeeLevel at 9AM after a couple hours of meager solar input. Totally fine and on the right track:



Here’s what the BMV-712 displays:



Here are the BMV-712 Settings:


Now for the solar. Here’s what the controller is showing at 9:30AM:


Here’s the last few days of solar performance:


And here are the MPPT’s Settings:


A few other notes:

• The SmartSolar and the BMV share data via the Victron Networking feature
• I reset the SmartSolar a few days ago because I was getting zero solar input (was diagnosing zero solar input and didn’t realize the tech who replaced the fridge about 6 weeks ago enabled the solar killswitch—problem since fixed). The BMV has never been reset.
• I have generator so none of this is critical. Still, it would be nice to trust the monitor.

Any thoughts? My current plan is to wait until I have an electrical hookups (or run the generator this evening) and can guarantee a full charge, then reset the BMV and see what happens. But perhaps someone more knowledgeable than me (i.e. anyone more intelligent than the average Alaskan moose) can help me figure out what’s what.

Thanks.

Hi

At the very least "AGM Spiral Cell" is not at all what you want for your battery settings. You do *not* want to take it up to 16.5V as part of the charge process. Lord only knows what. battery *does* want that, the stock AGM's most certainly do not.

I'd get that sorted out first.

After that check to see that the shunt is wired correctly and not in backwards. Also make sure that the only thing on the one side of the shunt is that battery and that absolutely nothing else is hooked there or to the battery negative.

Bob

[nryn]

The other presets are more arcane—2 for gel and some for Li-ion.

Not sure what the settings would be for factory solar AGMs on the stock converter (Lifeline Group 24s) but I’ll look into it.

[uncle_bob]

Originally Posted by nryn

The other presets are more arcane—2 for gel and some for Li-ion.

Not sure what the settings would be for factory solar AGMs on the stock converter (Lifeline Group 24s) but I’ll look into it.

Hi

The defaults are all for Victron's proprietary batteries or something equally odd. You need to key in the proper settings as "custom". The drill is the same for the 712, the Multi's and the MPPT's.

You decide to equalize or not, pick a bulk voltage, and pick a float voltage. There are billions of threads here debating the "what to do" on each type and brand of. battery.

Bob

[billrector]

Hi again....I’m the original OP of this thread and I’m back with further confusion on the readout of the 712. Since I wrote last, I have installed 400W of solar and 2 new Fullriver 6V batteries with 224 Ah (total). I have also installed the temperature monitor and my Victron Solar is on the same network as the battery monitor.

We are camping in cold conditions and the furnace has been running. We are boondocking and relying on solar for our energy. We have ample sunshine!

I woke this morning to battery voltage at 12.1 volts when furnace is not running. 43 degrees outside. 52Ah consumed since last charge and monitor showing 85% SOC. Okay....again, this is confusing. The last thing I want to do is damage these batteries!

The battery specs show 60% capacity at 40 degrees. That means I should have a capacity of 134 Ah (224 x 0.6) at full charge at that temperature. If I have consumed 52 Ah then shouldn’t I be at 61% (1-(52/134)) SOC and not 85%? I know the BMV is more sophisticated than that but.....

The next few days are going to be super cold and I’d like to be able to take these batteries to their limits but I’m struggling to determine what that is!

[Tronadora]

Not an expert, but maybe what I've observed on my BMV-712 will help. I have 220Ah Lifeline 6V batteries. When I'm at 50% SOC it should read 110Ah consumed but it kept telling me I had about 58% after consuming 110Ah. I finally experimented with the Peukert Exponent setting and ended up reducing it down to 1.12 to get things to sync up. When you play with that setting it adjusts the readout in near real time.



When I'm down to 50% SOC my batteries read about 11.9 or 12.0 volts. As low as I want to go. And that is "at rest", meaning no loads to drag down the voltage and no charging to lift the voltage.

[uncle_bob]

Originally Posted by billrector

Hi again....I’m the original OP of this thread and I’m back with further confusion on the readout of the 712. Since I wrote last, I have installed 400W of solar and 2 new Fullriver 6V batteries with 224 Ah (total). I have also installed the temperature monitor and my Victron Solar is on the same network as the battery monitor.

We are camping in cold conditions and the furnace has been running. We are boondocking and relying on solar for our energy. We have ample sunshine!

I woke this morning to battery voltage at 12.1 volts when furnace is not running. 43 degrees outside. 52Ah consumed since last charge and monitor showing 85% SOC. Okay....again, this is confusing. The last thing I want to do is damage these batteries!

The battery specs show 60% capacity at 40 degrees. That means I should have a capacity of 134 Ah (224 x 0.6) at full charge at that temperature. If I have consumed 52 Ah then shouldn’t I be at 61% (1-(52/134)) SOC and not 85%? I know the BMV is more sophisticated than that but.....

The next few days are going to be super cold and I’d like to be able to take these batteries to their limits but I’m struggling to determine what that is!

Hi

How have you programmed you're 712? How well does it match up with the batteries you have? It will only be as accurate as your settings allow it to be. The settings relating to temperature likely are a bit off. That all assumes there isn't a wiring error ....

If you consumed your 52AH when the battery was at 70F, you will be in a different situation than if your consumption was at 42 .... You have to look at the entire discharge profile to see what's what.

On any lead acid battery, discharge (or charge) current will have a significant impact on the voltage reading. Unless you have been at zero current for an hour or so, the voltage may not be a good indicator.

Bob

[billrector]

Originally Posted by uncle_bob

Hi

How have you programmed you're 712? How well does it match up with the batteries you have? It will only be as accurate as your settings allow it to be. The settings relating to temperature likely are a bit off. That all assumes there isn't a wiring error ....

If you consumed your 52AH when the battery was at 70F, you will be in a different situation than if your consumption was at 42 .... You have to look at the entire discharge profile to see what's what.

On any lead acid battery, discharge (or charge) current will have a significant impact on the voltage reading. Unless you have been at zero current for an hour or so, the voltage may not be a good indicator.

Bob

Hi Bob,

Here are my settings. I have only changed the Ah and charging voltage settings. The rest are just defaults and honestly, I don’t even know what they mean!

[billrector]

Originally Posted by billrector

Hi Bob,

Here are my settings. I have only changed the Ah and charging voltage settings. The rest are just defaults and honestly, I don’t even know what they mean!

Attachment 353985

Here are the solar charge settings also.

[uncle_bob]

Hi

There are other settings on some of the other pages.

The 14.7V "charged voltage" probably should be 14.2V. A lot depends on how your charger(s) are set up ( = do they get to 14.7V ? ) . It also depends a bit on the spec's on your batteries. ( = do they want to see 14.7V ?, there is a temperature spec on the charge voltage ... )

I would set the tail current down to about 1% or so. That would be 2.2A and still a lot of current. On a battery that likely takes many hours to charge, a "charge detection time" of a 10 to 20 minutes probably makes more sense.

The big question is the temperature setting over under the "misc" menu. Also if you are charging up around 14.7V, does the charger temperature compensate and how is it set?

(I'm guessing a bit here. Fullriver makes a lot of batteries. I'm assuming you have AGM's / DC224-6's ....)

Bob

[uncle_bob]

Originally Posted by billrector

Here are the solar charge settings also.
Attachment 353986

Hi

Ok, a 6V battery has three cells in it. Your 12V stack has six cells. Assuming we are talking about AGM's the spec sheet calls for 2 mv / F temperature compensation. That would be 12 mv / F.( under temperature compensation)

If you run up to an equalization voltage of 16.x V, that is not likely to be "in spec" for all of the electronics on the trailer. They might take it or they might not. Anything over 15V is a risk.

Still need to look at the temperature screen for the 712.

=======

This all assumes the shunt is wired correctly. Is the shunt the *only* thing in the negative battery lead? ( = no other wires to the negative post). I know this has been asked before, things do get changed over a year's time .....

Bob

[billrector]

Originally Posted by uncle_bob

Hi

There are other settings on some of the other pages.

The 14.7V "charged voltage" probably should be 14.2V. A lot depends on how your charger(s) are set up ( = do they get to 14.7V ? ) . It also depends a bit on the spec's on your batteries. ( = do they want to see 14.7V ?, there is a temperature spec on the charge voltage ... )

I would set the tail current down to about 1% or so. That would be 2.2A and still a lot of current. On a battery that likely takes many hours to charge, a "charge detection time" of a 10 to 20 minutes probably makes more sense.

The big question is the temperature setting over under the "misc" menu. Also if you are charging up around 14.7V, does the charger temperature compensate and how is it set?

(I'm guessing a bit here. Fullriver makes a lot of batteries. I'm assuming you have AGM's / DC224-6's ....)

Bob

Bob,

I got the 14.7 bulk and absorption values came from the Fullriver battery spec (yes, I have the one you referenced). I’m using a Victron MPPT controller.

I will adjust the tail current as you suggested.

The spec on the batter is -4mV/C/cell which I believe is -13.3mV/F for the entire battery bank. I have entered this in the MPPT controller settings.

Here is what is under misc. on the battery settings. You are correct, this shows zero. Should this also be -13.3?

[billrector]

Originally Posted by uncle_bob

Hi

Ok, a 6V battery has three cells in it. Your 12V stack has six cells. Assuming we are talking about AGM's the spec sheet calls for 2 mv / F temperature compensation. That would be 12 mv / F.( under temperature compensation)

If you run up to an equalization voltage of 16.x V, that is not likely to be "in spec" for all of the electronics on the trailer. They might take it or they might not. Anything over 15V is a risk.

Still need to look at the temperature screen for the 712.

=======

This all assumes the shunt is wired correctly. Is the shunt the *only* thing in the negative battery lead? ( = no other wires to the negative post). I know this has been asked before, things do get changed over a year's time .....

Bob

To answer your last question, nothing is connected to the negative terminal of the battery bank.

[billrector]

I went to the Victron site and they suggest that the “charge voltage” be set at 0.3 volts less than the float voltage. For by battery that would be 13.6-0.3 or 13.3 volts! That is substantially below the 14.7 previously in my settings. I used that value because the battery spec has a charge voltage of 14.7 (bulk and absorption) in the spec.

So does that sound right?

[uncle_bob]

Originally Posted by billrector

Bob,

I got the 14.7 bulk and absorption values came from the Fullriver battery spec (yes, I have the one you referenced). I’m using a Victron MPPT controller.

I will adjust the tail current as you suggested.

The spec on the batter is -4mV/C/cell which I believe is -13.3mV/F for the entire battery bank. I have entered this in the MPPT controller settings.

Here is what is under misc. on the battery settings. You are correct, this shows zero. Should this also be -13.3?

Attachment 353995

Hi

Ok, with that setting the 712 *assumes* there is no change at all in battery capacity over temperature. The curve for any battery will never be "ideal". The spec sheet for yours shows a capacity change of 104% down to 76% as temperature goes from 100F down to 20 F. More or less 28% over 80 degrees or 0.35% per degree F. Pick another temperature range and you would get a different number.

====

The Fullriver spec sheet calls out 4 mV / C and also calls out 2 mV / F as the correct per cell voltage coefficient. Since they (obviously) are not the same thing ... which one do you use ..... hmmm .....

====

The 14.7 V charge voltage *assumes* that both the solar charger and the converter charger are temperature compensated with a sensor mounted on the battery. A typical converter / charger isn't likely to have a probe like that so it needs to be set lower.

The 14.7V number is a bit odd for an AGM. Since it's from the manufacturer, one has to assume they know their batteries. It's a good example of why you need to look at the spec sheet.

If indeed solar is the main (or only) way things are charged, I'd do a quick look at the history section to see how high the battery voltage has been getting.

====

So this gets us back to the earlier question of what's going on. We're right back to :

1) The batteries are broke (12.1 V at 40F is not a good thing on those batteries)
2) The 712 is broke

I'd grab a DVM and see what the voltage on the battery posts reads with no loads. Then compare that to what the 712 is telling you.

If you have a good DC clamp amp meter, it would tell you if the shunt is working correctly.

Bob

[billrector]

Update: got to 24 degrees last night and had the propane heat on (but set to only 50). Normally run 1-2 amps with nothing major running and 8-9 with heater running.

Woke up to batteries at 12.2 and battery monitor (after all the adjustments) indicating 74% SOC. BMV says 51Ah used since 100 % charge. So, still seems like something is off.

I forgot to bring my Fluke, but prior tests indicate BMV at least was accurate and all amp readings seem reasonable.

[uncle_bob]

Hi

Over 12 hours 2A would be 24 AH, If you ran 8A for 3 hours that would get you to around 50AH. You have a battery set to 220AH as 100%. You used 51AH and it says you are at 74% . All that seems to be pretty close. ( 26% of 220 is 57.2). What's bugging you?

Bob

[billrector]

Originally Posted by uncle_bob

Hi

Over 12 hours 2A would be 24 AH, If you ran 8A for 3 hours that would get you to around 50AH. You have a battery set to 220AH as 100%. You used 51AH and it says you are at 74% . All that seems to be pretty close. ( 26% of 220 is 57.2). What's bugging you?

Bob

Battery was at 12.2 and 74%? Which do I take seriously?

[uncle_bob]

Originally Posted by billrector

Battery was at 12.2 and 74%? Which do I take seriously?

Hi

Was there a load on the battery at the time? How long since there had been a load (or charging)? The voltage only applies if the battery is sitting there.

If indeed the battery is broke, the only way to work that out is to test the battery. The 712 seems to be doing fine.

Head over to Home Depot and spend $20 on a multimeter. It will be good enough to confirm the voltage on each of the two batteries. If one is at 6.4 and the other is at 5.8, you have a problem with that battery.

Bob

[ROBERT CROSS]

Ours was, never seemed to relate correctly to the SOC.

Went to the website and re-read the manual....da.🤔

You-reek-a...there is a low SOC relay that was set at the factory default.
We have 200ah BB's...I want to use 180a available, so I set the relay at 20%.
Appears to be much closer to actuality, testing now.

1st pic @ default
2nd @ 20%
3rd settings page.

Bob
🇺🇸