Victron battery monitor weirdness.

[GILow]

So my faithful old Votronic battery monitor died last week. Better part of ten years faithful service. RIP Votronic monitor.

Anyway, as luck would have it, I had the Victron BMV-712 Smart battery monitor ready to install in the new boat. So I pinched it.

But it’s acting a bit weird.

This boat has 675 AH @ 12 volts of Trojan T105s. (6 batteries) They are all happy as Larry after about five years of service. They have a nice life, being connected to 760 Watts of solar via a pair of Victron 100/30 MPPT controllers and a Victron smart battery monitor. The chargers are programmed exactly as Trojan specify for float, absorption and temperature compensation etc. And for the last five years the Votronic battery monitor has registered 100% about half an hour before the solar controllers start absorption. All great.

But the Victron BMS has the biggest case of charge optimism I’ve ever seen. Wake up in the morning with the battery bank at 80% or so… check. About right.

Sun comes up, next time I check the monitor and it’s telling me the batteries are at 100%. In less than an hour.

No way. Not even close, and the solar controllers sure don’t think so, the last few days we’ve barely made it to absorption by late afternoon.

So I’ve had a look at the trend screen and it shows a practically impossible rate of charge. (See picture attached.)

I must have some setting wrong, but which one?

[wholybee]

There are three parameters that need to be set correctly in the BMV. I forget the exact names but they are:
Charged Voltage
Charged time
Tail Current

Charged voltage is your Absorption Voltage, or about one tenth of a volt less.
Charged time is how long that voltage must be maintained before resetting to 100% Somewhere in the neighborhood of 10 minutes is normal.
Tail Current is the charge current at which the bmv will reset to 100%.Typically 2-5% of capacity. Older batteries would require a higher tail current as they age.

An issue that some people experience is that when solar production drops off and charge current drops, the BMV interprets that as the battery not accepting any more charge because it is full, and resets to 100% early. It takes careful adjustment of those parameters to prevent that, or set the charged voltage higher than your absorption voltage (effectively preventing the meter from every resetting) and sync it yourself every couple days.

I would start be checking the tail current. Perhaps it needs to be lowered. And/or the charged voltage raised. IIRC Trojan has some aggressive charge voltages and the defaults in the BMV might be too low.

FWIW, if your old meter read 100% half an hour before your solar controller hit absorption, it was reading wrong also. Your batteries aren't fully charged until they are in absorption for 4-5 hours in most cases. Never before absorption even starts. (perhaps you meant float?)

[more]

Originally Posted by GILow

So my faithful old Votronic battery monitor died last week. Better part of ten years faithful service. RIP Votronic monitor.

Anyway, as luck would have it, I had the Victron BMV-712 Smart battery monitor ready to install in the new boat. So I pinched it.

But it’s acting a bit weird.

This boat has 675 AH @ 12 volts of Trojan T105s. (6 batteries) They are all happy as Larry after about five years of service. They have a nice life, being connected to 760 Watts of solar via a pair of Victron 100/30 MPPT controllers and a Victron smart battery monitor. The chargers are programmed exactly as Trojan specify for float, absorption and temperature compensation etc. And for the last five years the Votronic battery monitor has registered 100% about half an hour before the solar controllers start absorption. All great.

But the Victron BMS has the biggest case of charge optimism I’ve ever seen. Wake up in the morning with the battery bank at 80% or so… check. About right.

Sun comes up, next time I check the monitor and it’s telling me the batteries are at 100%. In less than an hour.

No way. Not even close, and the solar controllers sure don’t think so, the last few days we’ve barely made it to absorption by late afternoon.

So I’ve had a look at the trend screen and it shows a practically impossible rate of charge. (See picture attached.)

I must have some setting wrong, but which one?

Peukert exponent in setings set it at
1.25 for lead-acid batteries.
read manual
https://www.victronenergy.com/upload...unt-pdf-en.pdf

[GILow]

Originally Posted by more

Peukert exponent in setings set it at
1.25 for lead-acid batteries.
read manual
https://www.victronenergy.com/upload...unt-pdf-en.pdf

Yeah, thanks for that. Of course I’ve RTFM.

[GILow]

Originally Posted by wholybee

There are three parameters that need to be set correctly in the BMV. I forget the exact names but they are:
Charged Voltage
Charged time
Tail Current

Charged voltage is your Absorption Voltage, or about one tenth of a volt less.
Charged time is how long that voltage must be maintained before resetting to 100% Somewhere in the neighborhood of 10 minutes is normal.
Tail Current is the charge current at which the bmv will reset to 100%.Typically 2-5% of capacity. Older batteries would require a higher tail current as they age.

An issue that some people experience is that when solar production drops off and charge current drops, the BMV interprets that as the battery not accepting any more charge because it is full, and resets to 100% early. It takes careful adjustment of those parameters to prevent that, or set the charged voltage higher than your absorption voltage (effectively preventing the meter from every resetting) and sync it yourself every couple days.

I would start be checking the tail current. Perhaps it needs to be lowered. And/or the charged voltage raised. IIRC Trojan has some aggressive charge voltages and the defaults in the BMV might be too low.

FWIW, if your old meter read 100% half an hour before your solar controller hit absorption, it was reading wrong also. Your batteries aren't fully charged until they are in absorption for 4-5 hours in most cases. Never before absorption even starts. (perhaps you meant float?)

I wondered about those defaults. Victron seemed adamant about them so I left well alone, but yes, now that you mention it, Trojan does like to charge hard.

Regarding the old meter, yes, technically 100% BEFORE absorption is not fully charged, but it was a one of those situations where I knew it well enough to know where I stood. It didn’t have an ability to handle Mr Peukert so I just did that in my head.

[SailingHarmonie]

Originally Posted by GILow

So my faithful old Votronic battery monitor died last week. Better part of ten years faithful service. RIP Votronic monitor.

Anyway, as luck would have it, I had the Victron BMV-712 Smart battery monitor ready to install in the new boat. So I pinched it.

But it’s acting a bit weird.

This boat has 675 AH @ 12 volts of Trojan T105s. (6 batteries) They are all happy as Larry after about five years of service. They have a nice life, being connected to 760 Watts of solar via a pair of Victron 100/30 MPPT controllers and a Victron smart battery monitor. The chargers are programmed exactly as Trojan specify for float, absorption and temperature compensation etc. And for the last five years the Votronic battery monitor has registered 100% about half an hour before the solar controllers start absorption. All great.

But the Victron BMS has the biggest case of charge optimism I’ve ever seen. Wake up in the morning with the battery bank at 80% or so… check. About right.

Sun comes up, next time I check the monitor and it’s telling me the batteries are at 100%. In less than an hour.

No way. Not even close, and the solar controllers sure don’t think so, the last few days we’ve barely made it to absorption by late afternoon.

So I’ve had a look at the trend screen and it shows a practically impossible rate of charge. (See picture attached.)

I must have some setting wrong, but which one?

It would be most helpful sorting this out if you could post the graph and include current flow. It certain looks like the monitor is resetting to 100% as part of the synch process. Now the next step is to figure out if the issue is you batteries/charging set up, or the monitor settings.

[GILow]

Originally Posted by SailingHarmonie

It would be most helpful sorting this out if you could post the graph and include current flow. It certain looks like the monitor is resetting to 100% as part of the synch process. Now the next step is to figure out if the issue is you batteries/charging set up, or the monitor settings.

Yeah, current is no good because, as I implied the controllers are not even in absorption when this happens, and being solar the charge current is all over the place. Meaningless at that time of morning really. Also, this charge system has been perfect for years, sure the controller MAY have chosen to die in sympathy with the old battery monitor, but it’s unlikely.

This feels like the Victron recommended voltage threshold is just too low as wholybee is suggesting. I’m going to make those changes and see how it behaves tomorrow,

[smac999]

The default charged voltage setting (13.2v) does not work with solar. It should be set to ~0.5v below absorb for lead batt. So around 14.2v. Otherwise as soon as the battery hits 13.2v (on the way up). It triggers a reset because the solar amps is so small in the morning. Or if a cloud goes by. (Charging drops Under tail current setting so it think s battery is full). Where as a battery charger would be a solid ~100a on the whole charge up. Abd not be under tail current till near full.

The 4% tail current default is probably ok for flooded batts. So is the 1.25 perkurt.

[GILow]

Originally Posted by smac999

The default charged voltage setting (13.2v) does not work with solar. It should be set to ~0.5v below absorb for lead batt. So around 14.2v. Otherwise as soon as the battery hits 13.2v (on the way up). It triggers a reset because the solar amps is so small in the morning. Or if a cloud goes by. (Charging drops Under tail current setting so it think s battery is full). Where as a battery charger would be a solid ~100a on the whole charge up. Abd not be under tail current till near full.

The 4% tail current default is probably ok for flooded batts. So is the 1.25 perkurt.

Thank you, you’ve made me feel good because an hour ago I slapped myself and told myself to just go with my gut feel and use 14.2.

And you’ve articulated something that was bothering me about the Victron algorithm, which was that it seemed more appropriate to mains chargers than solar.

[GILow]

So far, so good…

Voltage and current over the same time period for clarity. Solar input is being hampered by the current swinging the bow into the sun and throwing a shadow over both panel banks.

[GILow]

Yep, 14.2 for Charged Voltage and kept the 4% tail current. Looks about right now. Thanks to all for the useful contributions.

[s/v Jedi]

Originally Posted by GILow

Yep, 14.2 for Charged Voltage and kept the 4% tail current. Looks about right now. Thanks to all for the useful contributions.

What is the absorption voltage in the mppt configuration?

[rslifkin]

With my AGMs, I have the Victron "full charge" settings set for 13.3v and 0.5% tail current for at least 10 minutes. It never syncs to 100% prematurely, only after completing absorb, dropping to float and then being in float for a bit. Basically, 0.5% won't happen for any sustained period at or above 13.3 volts unless the batteries are pretty much full.

[GILow]

Originally Posted by s/v Jedi

What is the absorption voltage in the mppt configuration?

A picture is worth a thousand words. Well, a couple of dozen in this case.

[GILow]

Originally Posted by rslifkin

With my AGMs, I have the Victron "full charge" settings set for 13.3v and 0.5% tail current for at least 10 minutes. It never syncs to 100% prematurely, only after completing absorb, dropping to float and then being in float for a bit. Basically, 0.5% won't happen for any sustained period at or above 13.3 volts unless the batteries are pretty much full.

I’ve not had much to do with AGMs yet but it is my understanding that they are less “resistive” to charge than FLA?

Also, are you charging with solar or some other source? As smac999 notes, solar fluctuations can really muddy the picture.