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BMV702 Config


andrew9484

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Hi @Don and others. With the BMV Charged Voltage set to 58.2V, Tail Current to 0.5% and Detection Time to 10 minutes, I closely observed what happened on MQTT today, which is a simple task as my main computer screen and the MQTT/CCTV computer screen is next to each other . I had to switch to grid with Axpert setting 16 at SNU (charging from solar and grid) as I was just not getting enough from the panels to power the house and charge the batteries. Voltage climbed steadily with charge current around the maximum setting of 40A on the Axpert as did SOC%. At about 98.4% charge current started decreasing and at 99.6% SOC it was about 8A. Voltage was fluctuating a bit but was above 58.2V all the time. Then for some unclear reason the output from the panels dropped to zero and the battery voltage dropped to the Axpert float setting of 54V. I switched back to solar and am still getting around 865W from the panels with the house using about 650W and just over 100W going to the batteries with a current of 1A to 2A. Yesterday I tried the same setup and the battery SOC kept on rising and eventually reached 100% although voltage also dropped to 54V when I turned on a kettle. I was running off solar only at the time and the load started drawing current from the batteries so charge current turned negative.

With regards to a  separate MPPT controller or a mains battery charger, my concern is that the MPPT controller will not know when the T105s need an equalisation charge which, according to Trojan, is only recommended when SG differs by more than 0.03. To measure that kind of accuracy one would need one of the $4000 electronic SG meters which is not even a consideration. So equalising once or twice a year, would probably be enough and for that one would need a mains charger in my view.

As if all this is not enough, I noticed today that my ICC-Pi has not been recording Solar KWH Used since 12 Feb 2017. It does however record Solar KWH Produced. I plugged the RPi USB cable into the other Axpert of my cluster but it made no difference. Perhaps this is the cause for my upside down Battery Charge and Discharge readings. I guess only @Manie will be able to tell me where the data comes from, Axpert or BMV. Maybe a reload of the ICC image on the RPi is called for. This is all becoming a bit tedious and I appreciate the input of all the many earlier posts from all who helped. Hopefully a happy end that does not include dumping the T105s and replacing them with more suitable batteries, is in sight. That would just be a bit too rich for my liking.

 

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Not to belabour the issue but only for interest's sake, here is the link to the video I posted before but this leads to Victron's own website with printed copy of the narrative.

https://www.victronenergy.com/blog/2017/04/13/instructional-video-how-to-optimise-the-bmv-700-series-sync-parameters/

I doubt that the Charge Voltage one sets the BMV to makes any material difference provided it is not lower than what is recommended in the manual. @Don has had success in charging his batteries with a float voltage minus 0.3V setting as per the manual and I had success for the past two days with the recommended setting in the video, which I will test for a while as two days of testing is hardly significant proof . As @Chris Hobson pointed out before, it is all about current and that is ultimately controlled by the internal resistance of the battery which increases as the SOC increases thereby reducing the charge current provided the charging voltage is not set at something totally out of bounds, if I still remember my physics education.

Right now my batteries are in float state with a voltage of 54.11V and yet a current of about 1.3A still goes into the batteries as my Axperts are now in grid state until 3h00 when I switch to batteries until 16h00. With winter on our doorstep the sun is already at a much lower angle and fewer daylight hours.

As to my question about Solar KWH Used in ICC-Pi, I enquired from @Manie and he replied that it had been taken out of the program so obviously only zeros will be displayed.

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22 hours ago, PaulF007 said:

Cool would be interesting if you run your batts "normal" , in other word use them at night so that the soc drops to whatever you prefer and then charge them to full on solar only in the day time. It might take a day or so to to get a full "normal" cycle. I love these types of data! 

Hi @PaulF007, here is my SOC graphs charging my batteries on solar only for the day. We had rain until about 07h00 this morning. As you can see from the graphs, my solar production started about an hour later than normal. I had a few clouds as well during the day. It took a bit longer for the batteries to charge on solar and therefore the increased SOC before the jump to 100%. My SOC went to 100% at 15h46. I think on a cloudless day under "normal" circumstances, I could get them to 100% by 13h00. At least my batteries had a day off for a change.:)

 

soc101.thumb.JPG.098220ba937f301ddafcc27f14645990.JPG 

soc102.thumb.JPG.752c8d27584eedad86ca21fbffe8b529.JPG

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13 minutes ago, Don said:

My SOC went to 100% at 15h46. I think on a cloudless day under "normal" circumstances, I could get them to 100% by 13h00. At least my batteries had a day off for a change

Cool!

@Don

If you dont mind can you post a screenshot of you AH consumed vs SOC ? 

As well as your Batt volts vs You batt amps?

 

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7 minutes ago, Don said:

Here are the graphs.

The might of habit , found myself attempting to "zoom" into the graph he he :D.

There is one or two things that sort off worries me. Your ah consumed does not go to zero but the jump was a lot less that what it was when it was charged on the grid. The second , and I only mention this as I only learned of this a week ago ,  when last did you checked that the BMV measures 0 when there is no load on it? This might also have an impact in if the BMV measures correctly. ( LOL this one really got to me so now I am hammering it , I even took out the fluke this afternoon to check the BMV amp reading and now they are as close as dammit)

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1 hour ago, PaulF007 said:

Your ah consumed does not go to zero but the jump was a lot less that what it was when it was charged on the grid.

It has never gone to zero. It comes down to 10-15 Ah and when the BMV jumps to 100% SOC, the Ah resets to zero. 

1 hour ago, PaulF007 said:

 when last did you checked that the BMV measures 0 when there is no load on it?

When I installed it in October / November last year. 

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1 hour ago, PaulF007 said:

Your ah consumed does not go to zero but the jump was a lot less that what it was when it was charged on the grid.

Yes, charging on grid you have constant amps at the right voltage non stop. My batteries probably charge within an hour and a half when on grid. On solar, every time a cloud moves in front of the sun, the stopwatch stops. It therefore takes a lot longer on solar. I also noticed a few voltage overshoots on solar. With the solar constantly moving up and down, the MPPT had a tough time regulating the voltage. Cloud moves in, it dives down, cloud moves past, it shoots up like a rocket and when it pulls back, it is too late, the voltage overshoots.

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During my normal usage/load during the day, it is impossible to have voltage overshoots, as I am never close to bulk charging voltage. I would gradually bring my SOC up from say 85 to 95% during the day to the time the sun sets. Once the sun sets and I go to grid, the batteries are nearly fully charged. I would briefly go to bulk charge at a very stable voltage, then absorb, over to float and an hour to an hour and a half later sitting at 100%. No voltage overshoots. That suits me at this stage to do the final charging from grid..

I prefer to keep my batteries at say 90-95% SOC during the day. When the tumble drier or dishwasher stops for half an hour to 45 minutes, it is not a problem, the batteries would during that time take up the load and ensure my panels keep going without pulling back. Then from about 15h00, I start cutting down on my load and push everything the panels produce into the batteries. 

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Hi @Don, @The Terrible Triplett, @PaulF007, @Chris Hobson, @plonksterand others who have been kind enough to give me advice. Don your advice was particularly valuable and my settings on the Axperts and BMV are pretty much what you suggested with some variations, the reasons for which I will explain.
Current settings are:
BMV: Charged Voltage: 58.1V, Tail Current: 0.5%, Detection Time: 20 minutes.
Axperts: Setting 02: 20A per Axpert (Maximum Amps), Setting 11: 20A per Axpert (Maximum Grid Amps) Setting:16 CSO (Solar before Grid), Setting 26 (Bulk Charge Voltage) 58.4V, Setting 27(Floating Voltage): 54V.
On Don's advice I contacted Victron and also Trojan by email and am posting the e-mails below in the hope that it will be useful to others as well. The e-mails need to be read from the bottom upwards of course.

Victron:


Hello,

Answers in the text.


Best regards 

Met vriendelijke groet

Johannes Boonstra
Mobile: +31 651328860

-----Original Message-----
From: Edward Brittain 
Sent: woensdag 26 april 2017 14:38
To: Johannes Boonstra 
Subject: Re: BMV700

Dear Mr Boonstra,

Thank you very much for your informative and prompt reply.

My battery bank is 450AH and solar panels are a total of 2300W. The charge current 
to the batteries is usually not more than about 20A on a sunny day after consumption
 by my house has been subtracted.
[JBO] Thats a good rate !

 So I would probably need to set the tail current quite a lot lower. 
[JBO] tail current is the current that will flow through the battery eventough
 its full, thats not depending on the charge rate 

Also is it acceptable to increase the detection time to 30 minutes or even more
 to ensure the batteries are fully charged or will that cause the BMV to function
 incorrectly.
[JBO] yes, that’s ok to do.


Thanks again for your kind assistance.

Best Regards,

Edward Brittain.


On 04/25/2017 11:38 PM, Johannes Boonstra wrote:
Dear sir,

When using the BMV for systems which have a constant charge source (AC 
grid for example) the synchronisation can be done when the BMV detects 
the "float "stage Then the float voltage is used , with a few % tail 
current

At solar this is not possible as there can be a could at every moment 
which "looks"like a float situation, The charge voltage drops and also the charge current.
So then choose the absorbtion voltage to sync on

In general , 0,3 below absorbtion is Vc , the tail current is 4% and the time about 7 min.

If there are more questions, please let me know.


Best regards
Met vriendelijke groet

Johannes Boonstra
Mobile: +31 651328860


-----Original Message-----
From: Edward Brittain 
Sent: dinsdag 25 april 2017 12:53
To: Victronenergy sales
Subject: BMV700

Dear Sir/Madam,

I have a solar electricity system with a Victron BMV700 connected to a Raspberry Pi which runs a control program for my inverter with an internal MPPT charge controller. In the BMV700 user guide it is recommended that the Charged Voltage of the BMV should be set to the float voltage of the batteries minus 0.3V. In the video available on your website, it is recommended that the same setting should be set to the absorption voltage of the batteries minus 0.3V in the case of solar installations.

Could you please be so kind as to confirm at which setting I should set my BMV700 for my solar installation for optimal results in charging the batteries. Your recommendations for the Tail Current and Detection Time settings will also be greatly appreciated.

Thanking you in anticipation.

Sincerely,

Edward Brittain
 

 

Trojan:

Response:

Your battery bank is rated at 450-Ah. The initial charge rate for proper charging should in the range of 10-13% of 450-AH (45-60A), up to a maximum rate of 20% (90A). What is your equalization capable voltage? You can use a lower voltage, but it will take longer to equalize batteries. That CTek charger will not equalize these heavy duty deep cycle batteries.

Question:

Dear Sir/Madam, I have 16 T105s connected in 2 strings of 8 batteries. The 2 strings are connected in parallel. My Inverter MPPT charger has a maximum voltage rating of 58.4V which is below the T105 bulk charge rate of 59.28V. I also does not have equalization capability of 64.80V. The only solution I can think of is an external charger with equalization capability and the best I could find locally is a Ctek MXT14 charger which can do 31.6V for equalization. Could I use this to equalize the batteries in blocks of 4 as the Ctek voltage is 24V. Will it also have a very detrimental effect on the batteries if the solar MPPT charger only charge them to 58.4V daily. I mostly do not discharge below 80% SOC. Your kind advice and any suggestions and recommendations will be greatly appreciated.

James (Melvin) Cobb

Technical Support Engineer   

Trojan Battery Company

Tel: (678) 518-7318

[email protected]

www.trojanbattery.com

 

We have had a severe thunderstorm on Tuesday that caused Eskom blackouts for two days during the day. Mike Thorne told me that a client of his in the village with a 2 x Axpert cluster, similar to mine, had one of the Axperts burst into flames due to a lightning strike.Fortunately for me I had no damage but it gave me a great opportunity to test the settings. The batteries were at around 86% SOC when solar ceased and grid took over charging at 40A. The graph on MQTT showed the voltage rising to 58.4V where it stayed for about 30 minutes while the amps slowly went down to about 2A at which point the voltage dropped to 54V, just as one would like it to  work.

It seems to me, judging from Trojan's advice that if I should set the Axperts' float voltage to 58.4V for a time and charge at 40A to 60A total from grid and solar, that may just do the trick to equalise with the Axperts instead of using a separate charger. I don't believe it will be necessary more than perhaps once or twice a year. I have not measured the SG of all the individual cells yet but random cells measured showed the same SG and close to 1.27 when the BMV shows 100% SOC. If I try doing my proposed equalisation method, I would have a better idea of how it would work in charging the cells to the specified 1.277.

Any advice will be much appreciated.

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4 hours ago, ebrsa said:

equalise with the Axperts instead of using a separate charger.

It can be done, it just takes a long time. If you hold a battery at absorb voltage (especially with a proper balancer), assuming they are all in fairly good shape, the cells eventually all get back into shape.

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@plonkster All the batteries are about 6 months old and I have HA02 balancers installed between all of them. Would you perhaps care to put a figure on "a long time" just so I have some idea what to expect. My reason for equalisation is to prevent stratification of the electrolyte and desulfation of the plates. So just the normal reasons and of course to try and prolong battery life as a result.

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A long time... that's going to depend, basically you keep going until the tail current is low and the SGs are up. Depends on the batteries, with my agms, starting from 80% SoC, 8 hours of absorb does it. Tail current drops below 0.5% midpoint comes right, obviously I can't measure the SG.. :-)

Sent from my GT-I9195 using Tapatalk

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Okay, here's a story picture. Since it was cloudy again today in Cape Town, I took the time to properly pull the batteries up to 100%. This is they story of the last 2%. What isn't included in here is the >3% deviation we had earlier in the day. I can fix that with a balancer.

In the pictures you can see how the tail current comes down. This is a 200Ah AGM bank, we end up at a tail current of 0.8% or so, and eventually the deviation disappears completely. Each image is timestamped too.

Selection_046.png

Selection_047.png

Selection_050.png

Selection_051.png

Selection_052.png

Selection_055.png

Selection_056.png

Selection_058.png

Selection_059.png

Selection_060.png

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  • 2 weeks later...
14 hours ago, SolarNoob said:

Im having a problem where my float voltage (as I understand it) isnt high enough. Float is set to 54V on my infini 3kw but it only keeps the voltage at 52.3V?

Has anyone seen this before? The inverter and the BMV are reporting the same voltage but shouldnt it be floating at 54V?

I think the problem might be with the When float charging current is less than... setting, just above the system time setting. In your case, what would essentially happen, is that when the float current becomes less than 10A, for longer than 1 minute, the charger will switch off and stay off until the battery voltage dropped to 50V, only then will the charger start charging the batteries again.

In your case the max charge current is set to 22.5A and thus the charging process will start off at a maximum current of 22.5A (depending on the SOC of the battery bank) for the bulk charge cycle until the battery voltage reaches 58V (bulk charging voltage as per your setting). The charger will then go into absorption mode until the charging current reaches 5A (as per the manual). The charger will then go into float mode and keep the battery bank at 54V (float voltage as per your setting). Since the battery bank's voltage is around 58V at that point in time and the float voltage is set to 54V the float current will effectively be 0A and will be 0A for some time until the battery voltage dropped to a value below 54V. Currently your setting When float charging current is less than... is configured to switch off the charger when the float current is below 10A for 1 minute - it would most definitely be below 10A for probably much longer than 1 minute, so effectively the charger will be switched off only 1 minute after it went into float charging mode and only again switched on when the battery voltage dropped to below 50V. If no current is drawn from the battery bank, the battery bank voltage will gradually drop over an extended period until 50V is reached. (My battery bank takes about 4-5 weeks to drop from 52.8V to 50.8V) That is probably why your battery bank voltage seems to stay at 52.3V - it drops very very slowly.

Initially I monitored the charging process on my infini and noticed that the charging current measured by the inverter is out with about 0,3A - the inverter will continuously display a charging current of 0,4A while the BMV and multimeter will not measure any current flowing into the battery bank and therefor I've changed the setting When float charging current is less than... on my set-up to switch off the charger if the float charging current was less than 0,4A for more than 60 minutes and to switch the charger on again, when the battery voltage drops to 50.8V.

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1 hour ago, superdiy said:

When float charging current is less than

That's probably a feature akin to "Storage mode" in other inverter/chargers. The idea is that if the batteries are obviously full, you go to a lower non-gassing voltage just to maintain them. Float voltage is actually a gassing voltage, which is why prolonged float-charging should usually be avoided.

For my 200Ah batteries the current drops to 1.3A when they are fully charged and balanced, so  the magic numbers for me would probably be 2 ampere and at least 60 minutes.

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15 hours ago, SolarNoob said:

Thanks for the detailed reply @superdiy, you are correct. I adjusted that parameter and the batteries went into float correctly this afternoon. How long should the batteries be in float?

Maybe @plonkster can advise on the desired float time...

As per my explanation, I've monitored the current into the batteries during float and configured it to switch off the charger if the current dropped below 0,4A and stayed below that for more than 60 minutes.

15 hours ago, SolarNoob said:

How are my other voltages in my settings? I'm currently trying to tweak my setup a bit and would like to ensure the config is correct.

You can adjust the max charging current to 25A, 22.5A is exactly 10% of the Ah rating, but you can easily go up to 13% - 14% of the Ah rating, which would be approximately 30A.

My float voltage is set to 52.8V (according to the older T105RE datasheet), because my batteries were manufactured before the newer datasheet became available, but I don't think the float voltage will make much of a difference - you can keep yours on 54V.

The other settings look fine.

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40 minutes ago, superdiy said:

 can advise on the desired float time...

If you cycle them every day, storage mode does not make much sense. Usually you would go to storage mode only after 24 hours of float charging, but in daily cycling that will never happen. So I'd set that minute box to a thousand minutes or however high it will go. I'm gleaning my info here.

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On 5/11/2017 at 9:21 AM, plonkster said:

If you cycle them every day, storage mode does not make much sense. Usually you would go to storage mode only after 24 hours of float charging, but in daily cycling that will never happen. So I'd set that minute box to a thousand minutes or however high it will go. I'm gleaning my info here.

That is quite an interesting read. I think I might need to monitor my bank's voltage a bit and maybe tweak my When float charging current is less than settings to compensate.

After completion of the absorption period, a battery charger in general switches to the float charge mode. In case of a 3-stage charger the float voltage should be sufficiently high to compensate for self discharge of the battery, but should at the same time be as low as possible in order to limit corrosion of the positive plates and gassing. In practice the balance isn’t perfect: flooded batteries will gas substantially more than when left open circuited and will need regular topping up.

We have therefore introduced a fourth stage: the Storage mode. The Storage mode kicks in whenever the battery has not been subjected to discharge during 24 hours. In the Storage mode float voltage is reduced to 2,2 V/cell (13,2 V for a 12 V battery), which is close to the open circuit voltage of a fully charged battery. Corrosion and gassing are reduced to absolute minimum, but self-discharge is not compensated. To compensate for self discharge, and to stir up the electrolyte, the voltage is raised back to absorption level once every week.

Note: although sealed (VLRA AGM or gel) batteries can be float charged at 13,5 V to 13,8 V during long periods of time (no topping up needed!), some studies have shown that the Storage mode will increase service life of sealed batteries (see for ex. ‘Batterie Technik’ by Heinz Wenzl, Expert Verlag, 1999). Adding a forth charge stage, the Storage mode, also provides the option to increase the voltage during the third, ‘float’ stage to 2,33 V/cell (14 V for a 12 V battery). This is the charge voltage generally used for starter batteries in vehicles, and is ideal to ‘supercharge’ an already charged battery. 

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  • 2 weeks later...

So these batteries are now giving notice... posting it on this thread as this is where I posted most of the other info. Charge current is down to under 1% of Ah capacity, we're way past 100%, and the imbalance is not going away...

Selection_070.png.663f432b3abbbdcba4bfe7ba292e6436.png

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