Victron & Schaudt Battery Monitor Settings (1 Viewer)

OldAgeTravellers

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I fitted three of the Sonnenschein 12-65-Y as recommended by @Lenny HB, in October, which seem to be holding up well on our first long outing but I am getting a massive discrepancy developing between the Schaudt DT203 panel and my Victron Battery Monitor BMV-702 with Bluetooth. I set the Schaudt EBL 101 to GEL and the Votronic MPPT solar reg is set to GEL. We have 300watt of solar. Apart from three short journeys of 3km 26km & 49km we have been off grid in the Algarve since 4th Jan.
The Schaudt panel has gradually been getting lower and lower even though we are getting a reasonable amount of sun (between 5 & 10 amps), it is now showing 50% which is 50% usable ie 75%, the BMV has been returning to 100% most days. Now I may not have set the parameters of the BMV properly my settings are:
Battery Capacity = 234Ah, Charged Voltage = 14.4 volt, Tail Current = 4%,
Charged Detection Time = 3 minute, Peukert exponent = 1.05, Charge efficiency factor = 99%
Current Threashold = 0.10A, Time-to-Go Averaging Period = 3minute
Any suggestions, I believe these gell's need to sit at 14.4V for a few hours before reaching 100% perhaps this is the reason, maybe the Schaudt is taking that into account as it does measure all amps in and out. Or maybe we have to go on leccy overnight to reset it!
Also I believe Lenny said these Gells could be taken down to 30% safely but reading on the Victron site they say below 50% will significantly reduce their life well the Victron ones anyway.
I am a bit worried to use the Satellite,TV,Stereo setup in the evenings as that uses the most (about 6Amps) and the panel is getting lower and lower by the end of the charging day. Although we are not at critical level yet. but would like to get another week or so off grid but do not know which to believe. What is the actual critical minimum voltage these Gells can go down to without shortening their life? Anybody got a chart of charge % for voltage. I can only find a lead acid one.
Thanks all suggestions gratefully received.
Steve
 

Basildog

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Watch and weep ;)

Not so sure everything he says is as relevant these days but I have always found Trojan batteries the best.
 

Minxy

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I put a chart on this thread which may be of interest:

https://www.motorhomefun.co.uk/foru...power-mechanically.189780/page-8#post-3163915

Chart below:

upload_2019-1-13_22-7-20-png.276969


Also this thread might help ... or confuse!

https://www.motorhomefun.co.uk/foru...ead-acid-batteries.190087/page-5#post-3168885
 

Lenny HB

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Hi Steve, I'll have a look at the setting on my BMV tomorrow as I have the same battery set up.
How do off load voltage reading compare with the the state of charge indicated as this might give you an idea of which display is true state of charge. Hymer don't fit the LCD panels now so I can't compare I seem to remember that the DT panel the battery capacity should be set 80% of total.

Yes the Gels do need to be on an absorption phase for a few hours to fully charge as when they get to 14.3v they are only 80% charged. Votronic absorption phase is 4 hours.

Any high discharge will shorten the number of cycles a battery can stand, with taking them do to 20% a regular basis you will still get a long life. An occasional discharge tob20% will not have any measurable effect on there life.
 
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Minxy

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@Lenny HB ... "thanking" ... I'm trying to think of the word you meant to say! Spanking perhaps? :D

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Minxy

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That mind of your girl - I'm game but only if you are weaing suspenders;)

Edited now.
Oooo-eeerrrr ... now you are on about 'taking them down' ... I tell you what, you can have my suspenders if you promise to wear them!
















upload_2019-1-20_23-41-35.jpeg
 

Deneb

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https://marinehowto.com/programming-a-battery-monitor/

Although I have SLA batteries, I found reducing the tail current setting to 2% increased the accuracy of my BMW. Nevertheless, if allowing it to autosync I do find that its accuracy decreases incrementally each day.

I tend to check the charge indication on my Votronic MPPT controller, and manually synchronise the BMV only when the MPPT controller is indicating that the batteries are fully charged.

But as the author of the link above summarises, despite his lengthy article:

"simply turn off or program out auto-sync…

For the die hard electrically minded individuals out there it is possible to program auto-sync to still work, but this is a recipe you’ll need to figure out for your own system and your system only. There are far too many variables to give a cookie-cutter recipe for auto-sync especially when we start mixing in solar or wind etc.."
 
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OldAgeTravellers

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Not sure what direction we are going here you two! Perhaps best taken behind the bike sheds.
Thanks Basildog, but that clip,was only about guarantees but I will do a search.
Thanks Lenny the figures from your meter would be interesting.
Minxy the chart is also interesting especially this morning. We woke to battery voltage of 11.8V indicated by both meters and a cheap ciggy socket one, which by your chart is dead. But the DT said 43% which should be usable power (or is it?) and the Victron said 84% so a bit over half of usable. But the misses had jumped out of bed and put the heater on (which should have sensed low voltage, but didn't). The voltage quickly jumped back to 12.2 when I turned the heaters off and the sun was shining. So hopefully have not Knack***d the £500 worth of new batteries.
Which is another point it is not easy to get an off load voltage reading when living in a Motorhome with the sun shining without switching off the panel and pulling the solar fuses for a couple of hours and risking the flying saucepans from "Er-indoors".
Steve
p.s. Thanks Deneb, came in while I was typing. I will have a read.
 

Basildog

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Not sure what direction we are going here you two! Perhaps best taken behind the bike sheds.
Thanks Basildog, but that clip,was only about guarantees but I will do a search.
Thanks Lenny the figures from your meter would be interesting.
Minxy the chart is also interesting especially this morning. We woke to battery voltage of 11.8V indicated by both meters and a cheap ciggy socket one, which by your chart is dead. But the DT said 43% which should be usable power (or is it?) and the Victron said 84% so a bit over half of usable. But the misses had jumped out of bed and put the heater on (which should have sensed low voltage, but didn't). The voltage quickly jumped back to 12.2 when I turned the heaters off and the sun was shining. So hopefully have not Knack***d the £500 worth of new batteries.
Which is another point it is not easy to get an off load voltage reading when living in a Motorhome with the sun shining without switching off the panel and pulling the solar fuses for a couple of hours and risking the flying saucepans from "Er-indoors".
Steve
p.s. Thanks Deneb, came in while I was typing. I will have a read.
Personally I would get it on ehu or a generator for a serious charge up so you know you are starting from full .
The solar god lithium eating sun worshipers will tell you differently but no matter where you are (Europe) in the winter us mortals will get flat batteries.
I did look into it seriously years ago but to properly harvest solar your panels actually need to be appropriately 10 degrees from vertical !
For those of us without the magical panels and miracle batteries the solar output drops to something like 10 percent of panel rating and if in the U.K. the average daily winter sunshine is 1 hour .
 

Lenny HB

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Before Kinky Minxy wakes up lets get back on course.

Not a good start, my BMV decided it needed an update before it would talk to me, the update failed and has completely screwed it. Anyway if I don't get it sorted I've asked my mate for his setting (I set his up the same as mine).

I think your BMV settings need tweaking they don't sound quite right and it sounds like your DT panel is reading low and probably needs resetting.

They way you have been using the van I think you are probably expecting too much from the solar. This time of year in the Algarve I would expect your solar to be working around 30-40% of max.
On a day with bright clear sky around midday I would expect 7 amps max but only for a few hours around midday before 11 am and after 2:30 pm probably down to 3 amps and falling either side of those times.
On the brightest clearest days say 30 a/h in a day if you are lucky but the slightest haze or cloud passing the output will drop considerably. Other days you will probably only get about 20 a/h or less.
I know my usage if using the TV and a bit of heating would be 30 to 35 a/h a day.

At this time of year on a lot of days the batteries won't get fully charged as sunlight will be going before they have completed the absorption phase, however because you can discharge Gels further there is no disadvantage over flooded cells.
 
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Lenny HB

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Not sure what direction we are going here you two! Perhaps best taken behind the bike sheds.
Thanks Basildog, but that clip,was only about guarantees but I will do a search.
Thanks Lenny the figures from your meter would be interesting.
Minxy the chart is also interesting especially this morning. We woke to battery voltage of 11.8V indicated by both meters and a cheap ciggy socket one, which by your chart is dead. But the DT said 43% which should be usable power (or is it?) and the Victron said 84% so a bit over half of usable. But the misses had jumped out of bed and put the heater on (which should have sensed low voltage, but didn't). The voltage quickly jumped back to 12.2 when I turned the heaters off and the sun was shining. So hopefully have not Knack***d the £500 worth of new batteries.
Which is another point it is not easy to get an off load voltage reading when living in a Motorhome with the sun shining without switching off the panel and pulling the solar fuses for a couple of hours and risking the flying saucepans from "Er-indoors".
Steve
p.s. Thanks Deneb, came in while I was typing. I will have a read.
Send Judy back to bed and pull the solar fuses, turn every thing off for an hour then check the battery voltage, that will be as close as you can get to an off load voltage reading, the system will still be taking nearly ½ amp with the control panel on so you could add 0.1 v to your readings to make you feel good.
A flat battery on load is around 10 v the EBL trips out at 10.5 v.
 
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OldAgeTravellers

OldAgeTravellers

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Personally I would get it on ehu or a generator for a serious charge up so you know you are starting from full .
The solar god lithium eating sun worshipers will tell you differently but no matter where you are (Europe) in the winter us mortals will get flat batteries.
I did look into it seriously years ago but to properly harvest solar your panels actually need to be appropriately 10 degrees from vertical !
For those of us without the magical panels and miracle batteries the solar output drops to something like 10 percent of panel rating and if in the U.K. the average daily winter sunshine is 1 hour .
Thanks Basildog, we are actually in the Algarve at the moment and as I said yesterday we got about 8 hours of sun producing between 5 & 10 amps into the batteries with clean flatpanels, so perhaps 60Ah which should have been easily enough for what we used last night.
I think I have a few hours digesting what @Deneb linked to which was exactly what I was looking for, I obviously didn't do the right search. All I need now is a similar one on the Schaudt DT203 so I can make sense of the two different readings.
Yes I do need to get on to hook up for a night so I can reset the 203.
I actually have an app on my phone for solar tilt which says 57.3 deg at this latitude so 32.7 off vertical. Thanks for the input.
Steve
 

Lenny HB

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Just downloaded the manual for you. To get into the settings the Hymer pin should be 8251.
 

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Lenny HB

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My Setting on the BMV:

Battery Capacity = 234Ah
Charged Voltage = 13.2v
Tail Current = 4%,
Charged Detection Time = 3 minute
Peukert exponent = 1.25
Charge efficiency factor = 99%
Current Threashold = 0.10A
Time-to-Go Averaging Period = 3 min

Your BMV will never read correctly with your charged voltage setting of 14.4v as it determines the fully charged state when the battery votage is above the charged voltage and less than the 4% tail current. With either your Votronic regulator or your EBL the charged voltage can never get above 14.4v, you need to change that to 13.2 v.

Changing the charge efficency to 95% will give readings erring on the safe side as no battery is 100/99% efficent.

Your Peukert exponent is too low this will give higher % charge readings, I couldn't find the info for the Sonnenschein but Gels generally are 1.1 to 1.25 (I think Exide is 1.1 but not sure) I left mine at the default of 1.25 as my batteries were a year old and the Peukert exponent rises with age.

Once you have changed the setting it will need synchronising, it should do it automatically once the batteries are fully charged or you can do it manually.

My one is still screwed will have to see if I can update it manually.
 
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OldAgeTravellers

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My Setting on the BMV:

Battery Capacity = 234Ah
Charged Voltage = 13.2v
Tail Current = 4%,
Charged Detection Time = 3 minute
Peukert exponent = 1.25
Charge efficiency factor = 99%
Current Threashold = 0.10A
Time-to-Go Averaging Period = 3 min

Your BMV will never read correctly with your charged voltage setting of 14.4v as it determines the fully charged state when the battery votage is above the charged voltage and less than the 4% tail current. With either your Votronic regulator or your EBL the charged voltage can never get above 14.4v, you need to change that to 13.2 v.

Changing the charge efficency to 95% will give readings erring on the safe side as no battery is 100/99% efficent.

Your Peukert exponent is too low this will give higher % charge readings, I couldn't find the info for the Sonnenschein but Gels generally are 1.1 to 1.25 (I think Exide is 1.1 but not sure) I left mine at the default of 1.25 as my batteries were a year old and the Peukert exponent rises with age.

Once you have changed the setting it will need synchronising, it should do it automatically once the batteries are fully charged or you can do it manually.

My one is still screwed will have to see if I can update it manually.
Thanks for this Lenny and the download above. We moved a few miles on to a site for a couple of nights with electric so I can sort this out. The Schaudt charger has been putting 30A in so it will be able to float for a few hours tomorrow so the Hymer panel should reset. And I can sync the BM as well.
I found the video I used to set the system up originally and only in the text it says he is using Lithium Batteries which I didn't spot which is why I had the odd figures. I will report back how things are going when we get back in the wild. But a month without hookup and not a great deal of driving is not bad in winter. But then we had a couple of cloudy days and that did for us.
Thanks everybody for all the help.
Steve

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Lenny HB

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With the EBL charging at 30 amps I take you have the auxillary LS1218 charger.
The BMV should sync automatically once the batteries are fully charged.
 

Lenny HB

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https://marinehowto.com/programming-a-battery-monitor/

Although I have SLA batteries, I found reducing the tail current setting to 2% increased the accuracy of my BMW. Nevertheless, if allowing it to autosync I do find that its accuracy decreases incrementally each day.

I tend to check the charge indication on my Votronic MPPT controller, and manually synchronise the BMV only when the MPPT controller is indicating that the batteries are fully charged.

But as the author of the link above summarises, despite his lengthy article:

"simply turn off or program out auto-sync…

For the die hard electrically minded individuals out there it is possible to program auto-sync to still work, but this is a recipe you’ll need to figure out for your own system and your system only. There are far too many variables to give a cookie-cutter recipe for auto-sync especially when we start mixing in solar or wind etc.."
That's interesting. We were away for a few days at the begining of the month obviously not a lot of solar. I noticed one evening the BMV was giving conflicting readings, the charge % was giving a far higher reading than the off load voltage suggested. It did appear to sort itself out after a good day sunshine, still a bit out.

Makes sense about the sync as I would have thought it only needs to sync when installed or re-programed. I think I will be playing with my settings.
 
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OldAgeTravellers

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With the EBL charging at 30 amps I take you have the auxillary LS1218 charger.
The BMV should sync automatically once the batteries are fully charged.
Hi Lenny, no I have the standard charger but I was also getting 10 amps from Solar at the time as well, It charged up and soaked ok overnight so I could manually sync the BMV.
I had a good read of the article linked to by @Deneb, a lot of very good info, as a result I have reduced the battery capacity to 230Ah until I can do a reasonable test when I get home. Unfortunately his main advice of stopping automatic sync on the BMV I can't find a way to change that. I wish the makers would publish more info on the batteries that was easy to find.
I also watched a few of Charles Sterling's video's yesterday, he totally discounts Gells as absolutely useless but the distruction test of different battery types and quality was interesting. He gave up on the Lithium when he couldn't destroy it in six months of total abuse. Perhaps Ernie might treat me to some one day. Unfortunately he didn't include Gells in the test as he dislikes them so much.
Thanks for all the feedback everybody. It would still be nice to find out why the Schaudt differs so much from the BMV. But now they will both be synced we will see what the next three weeks off grid will bring.
Steve

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Deneb

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That's interesting. We were away for a few days at the begining of the month obviously not a lot of solar. I noticed one evening the BMV was giving conflicting readings, the charge % was giving a far higher reading than the off load voltage suggested. It did appear to sort itself out after a good day sunshine, still a bit out.

Makes sense about the sync as I would have thought it only needs to sync when installed or re-programed. I think I will be playing with my settings.

Just read your previous post with your settings Lenny. By setting your charge voltage at 13.2V you are creating a situation where a solar charge on a cloudy day with only a few amps going in and the MPP keeping the voltage low, can cause the BMV to register a full charge when the batteries could be in any state of charge in reality.

@OldAgeTravellers the way to disable autosync on the BMV is to program sync settings which the battery will never see. Increase the charge voltage setting to higher than the maximum input voltage from both your mains charger and solar controller, and the BMV will never auto sync.

That's what I have done, and I manually sync the BMV only when I am sure from either the indication on the solar controller or from the voltage and amp readings on the BMV when on mains charge (i.e. on float voltage and amps input lower than 2% capacity) that the batteries are full. I also set the battery capacity lower than the rating of my batteries, which causes my BMV to under-report SOC slightly, but I'd rather that than it being over-optimistic. My batteries are 2x 90Ah and I have the BMV set to 160Ah.

If off grid for 2 or 3 days with no mains charge and insufficient solar input to fully charge the batteries though, it is surprising how much the BMV can drift - only detectable when you know that the batteries are back up to fully charged and the BMV is still reporting 90% SOC or less, but that is the point at which you can manually resync.

With a lot of time and a lot of fiddling, you could probably get the accuracy down, but with the way that battery capacity naturally curves over the life of a battery anyway, it is never going to be fully accurate at all times and you could spend half your life getting to a point where you are fairly happy with autosync only for it to drift off as the battery capacity naturally changes during its aging process, hence why I prefer to program out auto sync and only sync manually.

I'm not sure if the below is already covered in the link I posted previously, but I saved it as a separate document, and probably worth repeating anyway as it summarises the situation quite nicely, including the comments on the quote from Victron. Obviously aimed at the sailing community, but the principles are similar for MHs:

Avoid Using Auto-Sync or Auto-Reset When Cruising!

Many Ah counters attempt to re-set to 100% at the same point in time your batteries reach full. In theory this is great. In practice, in the real world, this is very often an utter failure. In regards to auto-sync many Ah counter owners who cruise and PSOC cycle the banks will be far better served to simply program this out or turn this feature off until you return to the dock. The problems surrounding Ah counters and auto-sync are so problematic the issue has even earned itself a nickname, "The Gotcha Factor".

To program auto-sync out/off simply plug in parameters that are not possible for the charging system to meet. In this image I have programmed the Vc or “Voltage Charged” to 14.6V. Considering this is for a GEL battery, which never charges above 14.2V, the battery monitor cannot “auto-sync" at the wrong time because Charged Voltage will never get to 14.6V. Simple stuff!

Unless you have one single charge source, and you tie to a dock after every use of your boat, or even RV, and leave it there charging for more than 24 hours, you would be wise to not use auto-sync. For boats with multiple charge sources, especially solar & wind, you can spend lots and lots of time trying to get this programming right and still fail to do so.

This quote from Matthijs Vader of Victron sums up how these monitors re-set& sync to your bank.

"Synchronization works with simple logic: if the voltage is high, and at the same time there is not a lot of current going into the battery, the battery will have to be full. So the monitor resets its SoC back to 100% and the monitor is accurate again.

Now, all monitors have parameters for this, we called them Charged Voltage and Tail current. SoC is reset to 100% when the voltage is higher than the specified Charged Voltage threshold and the amps going into the battery are below the Tail Current. The lower you set your tail current, the more accurate your battery monitor will be (on a theoretical basis). The battery monitor will reset to 100% when the battery is completely full. The problem is that batteries are seldomly completely topped up, and therefore these parameters are very seldomly met.

The simplest solution is to loosen up the Tail Current setting. For example, set it to 5% of your battery bank capacity (or even a bit higher when necessary in your specific application). This way the battery monitor will synchronize more often. The drawback is that you'll get a SoC that might be a bit optimistic, but hey, it will be much better than the SoC you see at the moment! And, it will be stable."


The key takeaway here from Matthijs is "Seldomly met". There is also an assumption that every current/charging source can always produce more than the "tail current", which is not the case with solar or wind both of which could trick these monitor into prematurely thinking the bank has met "full parameters". I do not recommend loosening up the "tail current" as you will be technically undercharging the battery and this will lead to sulfation and shorter battery life.

“But isn’t my battery full when the ampere hours on the screen are returned to zero?”

Contrary to popular misconception some Ah counting battery monitors do not reset based on Ah’s returned to the battery going to 0.0 Ah. Instead they use a number of factors such as voltage, time, current and time at both current and voltage to try and determine when the battery is actually full.

Unfortunately, with multiple charge sources and house loads, they can get confused and tricked into prematurely re-setting to 100% SOC prematurely. Some older model Ah counters do require -Ah's to be returned to 0.0 before it resets to 100% but this feature has since been removed by some Ah counter manufacturers for liability reasons as told to me by one of them.

"We don't want a customer with an out of calibration monitor over charging a battery by trying to get back to 0.0 Ah's because this could pose a potentially dangerous situation."

These are the parameters the many Ah counters use to determine “full”.

Charged Voltage – This is the voltage the battery monitor looks for in order to qualify for a “full charge” reset. Voltage above XX.XX volts = CHECK

Tail Current – Tail Current is the amount of charge current the charge source needs to be below in order to qualify for a “full charge” auto-sync reset. Current below X.XX amps = CHECK

Charged Detection Time – The monitor looks at Charged Voltage and Tail Current and applies a min Time Factor at those levels. If the time for voltage and amperage meet the minimum time applied factor this = Auto-Sync Reset to 100% SOC

The "Gotcha" Conundrum:

Now let’s look at this in a real world scenario. Your boat has a solar array and it’s early to mid morning. The batteries are still in bulk charge mode, and the solar is just barely able to get them to your Charged Voltage setting of 13.2V. Because of the low current supplied by the solar array, due to it being early in the day, all the PV system can muster is 13.2V, and at a current below your Tail Current. If the system proceeds like this for longer than the Charged Detection Time, regardless of where you are in the SOC range, the monitor resets to 100% SOC.

System loads on your boat, such as water makers, refrigeration etc. can also pull charging voltage and net charge current below the charged detection parameters, if your charge source is not able to muster it all. This house load can also indirectly cause the monitor to reset on voltage, tail current and charged detection time.

There are many scenarios we can paint that can cause these monitors to reset falsely & prematurely thus creating bad counting errors.

For the average cruising boater, away from the dock, simply turn off or program out auto-sync and sync the monitor manually.
 

Lenny HB

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ust read your previous post with your settings Lenny. By setting your charge voltage at 13.2V you are creating a situation where a solar charge on a cloudy day with only a few amps going in and the MPP keeping the voltage low, can cause the BMV to register a full charge when the batteries could be in any state of charge in reality.
Not really as the BMV only sees a 100% SOC when the charged voltage is exceeded and the tail current is less than the the set value, although I think it is worth altering my Tail value from 4% down to 2%.
Victron recommend a Charged voltage of 13.2 v for all 12 v batteries apart from Lo-ion.
I think I will email them when I get my unit working, hate the fact there is no option to stop updates especially when they totaly screw it.
 
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Not really as the BMV only sees a 100% SOC when the charged voltage is exceeded and the tail current is less than the the set value, although I think it is worth altering my Tail value from 4% down to 2%.
Victron recommend a Charged voltage of 13.2 v for all 12 v batteries apart from Lo-ion.
I think I will email them when I get my unit working, hate the fact there is no option to stop updates especially when they totaly screw it.
I think from reading the whole of the piece that @Deneb linked to on page 1 here, the BM manufacturers want you to let their meters sync themselves which only works properly if you regularly go on hook-up but can be deceived easily with solar or other possibly low current supplies. The authors long experience I think is interesting and the way mine drifts so rapidly when constantly on limited solar only leads me to believe him. He has noticed over the years how BM manufacturers have removed important features.
After suggestions here and reading his piece, my settings are now:

Battery Capacity = 230Ah reduced until good measurement at home.
Charged Voltage = 14.6v
Tail Current = 2%
Charged Detection Time = 5 min
Peugeot exponent= 1.25 this may need revising with more info
Charge Efficiency Factor = 95%
Current threshold =0.10A
Time-to-go averaging period = 3m

I will only sync when I know for sure the battery's are at 100%.

What would be nice is if I can get to point where there is some correlation between the Schaudt panel and the BMV.
I am not sure that Schaudt will give that much info about their process though.
Lenny, is it the meter or app that failed on update, I am not sure my meter has ever had an update. My meter firmware is v3.08 and the BT dongle v2.10 Mine is the BMV-702
Steve
 

Deneb

Free Member
Oct 20, 2015
1,598
2,335
Europe
Funster No
39,680
MH
PVC
Not really as the BMV only sees a 100% SOC when the charged voltage is exceeded and the tail current is less than the the set value, although I think it is worth altering my Tail value from 4% down to 2%.
Victron recommend a Charged voltage of 13.2 v for all 12 v batteries apart from Lo-ion.
I think I will email them when I get my unit working, hate the fact there is no option to stop updates especially when they totaly screw it.

Yes, so early morning for example. Your solar is hovering around 13.8 - 14.V (or anywhere higher than 13.2V with your settings) but only managing to put in a fraction of an amp - in any case less than your tail setting value. If the controller tries to increase the voltage it loses the current so hovers around the voltage at which it can put in the maximum current available, which isn't much due to the lack of strong sunlight. The voltage is above your programmed charge voltage, current lower than your tail current. If it continues in that condition for more than your programmed detection time your BMV will synchronise to a full charge no matter what the condition of your batteries. I've seen it happen with mine several times. My van is parked outside so I can monitor the BMV through the app on my phone and have experimented with various battery SOC and weather conditions.

You can circumvent much of that by increasing the charge voltage to just below your normal absorption voltage, and making the detection time longer. That way, the BMV will sync at the end of the bulk charging phase, as long as the voltage is up where it should be, and the current has dropped below your tail current, i.e. at the end of the bulk phase just before the charger drops to float. Lengthening the detection time reduces, but doesn't totally prevent the situations where the BMV will sync prematurely because the charging voltage and current have dropped due to passing clouds, or the panels being in shadow. I had more success with these settings than Victrons' recommendation to set the charged voltage just below the float voltage.

Nevertheless, unless your BMV is connected to a system with a guaranteed consistent charge input (mains charger), no additional charging sources and no possibility of draw from consumers during the charging process, autosync can never be 100% accurate. Introduce variable solar input, the possibility of consumers being in use during charging, unreliable weather factors and autosync is never going to work with 100% reliability. At least using manual sync you know the exact conditions under which the sync occurred - not so if you got a false sync whilst you were away from the van, or otherwise occupied!

A couple of other quotes I found when I was looking into this a while back:

From Victron: "In solar systems or other applications with fluctuating charge currents, the 'charged' voltage should be set only slightly below the absorption charge voltage (for example: 14.1V in case of 14.4V absorption voltage.) This will prevent the BMV from switching prematurely to 100% state of charge."

From another forum: "I found that my solar setup often charges the batteries at greater than 14V but only at 2-4 amps because of limited sun. I raised the BMV-700 charge voltage setting because it is rare for my system voltage to be below 13.2V on a day with any sun, and I lowered the tail current setting because I regularly see less than 4% of battery capacity flowing into my bank even when the batteries are nowhere near approaching 100% SOC." and "The defaults in the BMV appear to have been selected more for marine applications where charging is more often conducted with an alternator rather than a solar system."


As I say, I improved matters on my system by setting charged voltage to 14.4V, tail current to 2% and increasing the detection time slightly to 5 minutes. With multiple charging sources and the inconsistency of solar input, I still found enough instances to convince me that I was better of disabling auto sync altogether.
 

Lenny HB

LIFE MEMBER
Oct 18, 2007
54,145
152,949
On the coast in West Sussex
Funster No
658
MH
Hymer B678 DL
Exp
Since 2008 & many years tugging
Yes, so early morning for example. Your solar is hovering around 13.8 - 14.V (or anywhere higher than 13.2V with your settings) but only managing to put in a fraction of an amp - in any case less than your tail setting value. If the controller tries to increase the voltage it loses the current so hovers around the voltage at which it can put in the maximum current available, which isn't much due to the lack of strong sunlight. The voltage is above your programmed charge voltage, current lower than your tail current. If it continues in that condition for more than your programmed detection time your BMV will synchronise to a full charge no matter what the condition of your batteries. I've seen it happen with mine several times. My van is parked outside so I can monitor the BMV through the app on my phone and have experimented with various battery SOC and weather conditions.
I see where you are coming from now, my brain obviously wasn't in gear, and I was forgetting abut the effects of early morning/evening etc.

From Victron: "In solar systems or other applications with fluctuating charge currents, the 'charged' voltage should be set only slightly below the absorption charge voltage (for example: 14.1V in case of 14.4V absorption voltage.) This will prevent the BMV from switching prematurely to 100% state of charge."
I think I original had it set to 14.1v, when I first fitted it I didn't have the bluetooth dongle and you set by doing a sync when the charge voltage was .1 to .2v below the max charge voltage. With the bluetooth monitor much easier to set it to what you want and like a fool I read the instructions when I fitted it.

We use the van for around 150 nights a year and the number of nights on hook up you can count on one hand also I rarely plug in at home.

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