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Hates Spam Suspended asked

Victron MPPT 100/30 and Smart Battery Sense reading 0.2-3V higher than battery

Hi there,

I have searched this fforum looking for answers or other users who have had a similar issue and have found some reports but no answers.


I have a 100/30 MPPT with a Smart Battery Sense connected to my AGM battery bank and I've noticed the MPPT na smart battery sense seem to be reading 0.2-0.3V higher than my battery bank according to two different multimeters.


I specifically noticed this last night when the Victron unit specified my battery voltage with a small load applied was sitting at 12.61V, yet when checking with my multimeter my battery bank was sitting on 12.32V.


I purchased the Smart Battery Sense due to noticing an error in the voltage between batteries and the MPPT, the Smart Battery Sense helped get it closer, but it was never exact.


After living off the grid ina caravan for a bit over a year with this setup, I am noticing my batteries don't seem to be holding charge as good as they first did and I suspect this is due to me having accidentally run them to low as a result of the variance from the Smart Battery Sense and the MPPT.


The lowest I had taken my batteries down to was 12.24v (according to the Victron app) which would mean the actual Battery Voltage would have been close to 11.9V or 12V - Much lower that I have ever planned to discharge the batteries.


According to both MPPT and Smart Battery Sense both units are running up to date/latest firmware.


As a half assed workaround, would changing the MPPT's charging parameters to be 0.25V higher allow the batteries to reach full charge (I assume it will) but don't want to cook the batteries at the same time?


Any advice as to what the cause and fix could be.


I am running 6 gauge wire about 800mm from MPPT to batteries so voltage drop should be fairly minimal and the Smart Battery Sense should be providing an accurate reading anyway.


Thanks,

Glenn.

voltagebattery system voltage
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8 Answers
Alexandra avatar image
Alexandra answered ·

@Hates Spam

Using voltage for SOC is not very accurate.

I cant comment on the smart sense readings. I don't use them.

Did you smart network the mppt and the sense together? And do you have a battery protect. That can help with prevention of over discharge or discharging past what you really want to.

What meter are you using? It is not unusual for them to be a few percent different. Leading to 0.2 to 0.3v difference in readings

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I am using a cheap meter, but I have double checked with a second cheap Multimeter and they both read very close to each other 0.02v difference, but they're both reading much lower than what the Victron app is claiming.
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Nothing like a using a Chinese meter to tell you the weather.
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Considering 2 multimeters are showing near identical figures and then seem to read quite accurately when measuring my DEFA battery charger in normal 14.4V mode and 14.7V mode - This suggests to me the multimeters aren't out by 0.2-0 3V like you seem to imply.


Since the multimeters provide what look like accurate reading on other electrical items, I'm at a loss as to why you assume they're 100% the problem here and that it couldn't possibly be the precious Victron unit...


I would agree with you if I was using ONE multimeter, but since I am using 2 completely different units (different brand) and BOTH are within 0.02V of each other, that suggests the Victron could be the culprit.


What are the chances of both multimeters being completely out by 0.2-0.3V each?


I apologise that I don't have the best Fluke Multimeter available and that I currently don't have a job to buy one, as a result, I'd appreciate it if you dropped the attitude.


Do you have advice on how to test the multimeters for accuracy?

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Hates Spam avatar image
Hates Spam answered ·

Hi Alexandra,

I'm aware voltage isn't the best way to confirm state of charge, however its the only option I have at the moment.


Yes, I have networked the smart battery sense to the MPPT - I'd be pretty useless if I hadn't done that.


No, I don't have battery protect.


I've just looked at the voltage and the app is stating my battery voltage is 13.05V, yet the terminals from the MPPT were reading 12.90V and the batteries were 12.88V.


It seems it might not be an issue with the Smart Battery Sense and instead an issue with my 100/30 mppt...


I'm currently reading the manual now to see if there's a way to reset the solar charge controller and/or troubleshoot.

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Hates Spam avatar image
Hates Spam answered ·
  1. If the voltage at the terminals on the MPPT are incorrect vs the apps voltage, this would suggest an issue with the MPPT, Correct?
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The app may be reporting the smart sense voltage not them mppt voltage if they are networked. So all the variables need to be eliminated.

At the same time if you check out your battery specs you will find that they allow a 0.2 to 0.3 voltage varaiance and this is due to margin of error/accuracy of meters etc.

Look up uncertainty in DMM or fluke's article.

Most agms are around 13.5 to 13.8v for charge. Some allow higher for cycle use. So not an exact science so to speak.


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The MPPT and battery sense show the exact same voltage, there is zero difference when connecting or disconnecting the Smart Battery Sense and re-pairing it with the MPPT.


^^^ This suggests things should be working as normal since the Smart Battery Sense and MPPT are right next to each other. The only reason for the Smart Battery Sense was to eliminate any possibility of voltage drop over cable and because in winter the Caravan regularly experiences temperatures below 10°C averages around 8°C for most of winter in the caravan (in the Australian high country/snowy mountains).


The only issue is that two completely different brand multimeters (which seem ti be accurate on other items) are suggesting there's a variance.

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Depends on the meter accuracy. But if the meter is accurate, yes. However the difference here isn't going to cause damage.
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Hates Spam avatar image Hates Spam kevgermany ♦♦ ·


Kevgermany - I've used two different multimeters and they're both within 0.02V of each other, they don't seem to be out by 0.2-0.3V when using them on other electronic devices - This is why I'm a little stuck knowing which could be wrong, whether it's both multimeters that seem to be okay when testing other batteries, or the Victron MPPT and/or smart battery sense (however both the mppt and smart battery sense have identical voltage) so this suggests they should be working fine.


The problem is I've used the Battery voltage as a rough guide of depth of discharge (yes, inaccurate I know) - However prior to a recent air purifier being added, the batteries rarely went below 12.51V under load (according to the app) however if it is actually 0.2-0.3V lower, then I have taken them down lower than I would have liked - Especially on the night where they went down to 12.24V (according to the app) I would have cut all non essential powder draw.


I have also found a number of other people on this forum who report a near identical variance of 0.2V up to 0.7V.


Any suggestions on how to rule out whether it's the multimeters or the mppt/battery sense? Other than tracking down someone with a guaranteed in spec multimeter?

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kevgermany avatar image
kevgermany answered ·

Please post a screen shot of the mppt battery settings

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Hates Spam avatar image
Hates Spam answered ·

screenshot-20220625-083512.jpg

Here is the screenshot.


The only change I have made is currently to raise the absorption voltage to be a bit higher to compensate for what looks like a loss.


My AGM batteries are able to be charger in Absorption up to 15V, so I'm not pushing anything past it's limits.


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kevgermany avatar image
kevgermany answered ·

Let's drop the meter issue, even though it seems odd. I also have two cheap Chinese meters and they agree with each other, also when checking voltage of a known good lithium charger, and other known good voltage sources, including mppt and battery monitor.

Just re-reading your first post, MPPT and Smart battery sense report the same voltages, these differ and are higher by about 0.2 to 0.3V than the meters read. Also batteries seem to be losing capacity.

First a little more info please.

How old are the batteries and how many charge cycles?

What is the normal draw between charges (ball park)

What is the battery bank capacity?

What is normal max ambient temperature?

How big are your panels?


If you raise absorption to compensate for suspected voltage readings that are too high, float should go up as well.

Depending on use and ambient conditions, AGMs may only last a year or two. Sometimes 100 cycles or less.

Something else to bear in mind is that the smart battery sense will transmit temperature to the mppt, which will compensate by adjusting the actual voltages used away from your settings.

It would be good to see a trend graph from the mppt under charge and no charge conditions. Both battery and panel voltage under charge, battery only when not charging.

But this doesn't explain the meter/Victron voltage reading differences. Let's see what the graphs show.

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Hi Kevgermany,


Sorry, I don't really want to drop the meter issue, because that is the main issue...


Either my meter is wrong, or the Victron units are wrong and I want clarification on a way to confirm which is incorrect?


I would have thought temperature compensation would only apply while the battery is being charged, which is not the case even well after there's no sunlight - In my mind, the battery sense and mppt should settle on the correct battery voltage after the charger switches off and the temperature compensation is no longer in effect.


The batteries are about 4 years old, I honestly couldn't tell you how many charge cycles the batteries have had. They have had full time use off grid for the last 14 months and I know I rarely take them down under 12.51v (average lowest reading "under load" over the last month) they have always been healthy and cared for.

^^^ Example: 6 months ago I unplugged the system and went into town for 19 days and by day 19 the battery bank was sitting at 12.93v - it took 12 days for the batteries to get down to 13v from 13.17v after being unplugged.

• The systems avaverage "watt hours" over the last month were 636wh per day (53Ah).

• Battery bank size is 440Ah (220Ah usable) but age and temp will affect overall capacity, however it's still much higher than my daily usage.

• Current average temp inside the Caravan would be around 8°C (varies from around 5°C - 14°C when the diesel heater is on).

• Solar panels are 170w × 4 (680w total).


I will not be raising the float voltage because that is said to be 13.8v Max which it is already on.


I'm not sure what the graphs are going to show?

The batteries are healthy and they "seem to be" holding charge a little less, but I assume that's due to them being colder and not always getting 100% charge because of winter cloudy conditions.

I was afraid maybe the voltage was incorrect and thus I was draining them more than I would like and this was my reason for making the post.


I was planning on going to lithium after these batteries die but I want to make sure my MPPT and smart battery sense are showing correct voltage before I switch and destroy a new battery.


My issue is not knowing if the readings are correct.


Thanks,

Glenn.

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Either my meter is wrong, or the Victron units are wrong and I want clarification on a way to confirm which is incorrect?

The 2 victron units are reading the same? And your 2 meters agree with each other?

You are probably going to have to buy a decent AC/DC clampmeter to break this tie. They are pretty handy and not overly expensive.

Further argument is akin to pi55ing into the wind, and wondering why you have wet feet.

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I was simply seeking advice on methods which can be implemented to confirm or rule out one or the other as being faulty - Not a difficult question and was directed more at Victron staff vs those who think they have all the answers.

However, it seems that's more technically advanced than what you're capable of!


Considering most digital multimerers are meant to be quite accurate, how am I to know for a fact that any "not overly expensive" AC/DC clampmeter that I pruchased is going to be more accurate, Huh?


I'm guessing seeking further guidance on this forum will be the equivalent of pissing time up the wall, because all I'll be met with is geniuses who assume people dont read manuals or install/use a product correctly and who also provide half assed suggestions like "buy one of these" even though it could be just as inaccurate...


Thanks for the riveting advice and it sets in stone the advice I've received thus far on here, which has been quite unhelpful other than (use a highly expensive Fluke) which I already knew would be the best option.

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Either get the meters tested, or live with it. Sorry to be blunt.
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Hates Spam avatar image Hates Spam kevgermany ♦♦ ·

Not sure why you couldn't just say that from the start, instead of asking for irrelevant information...


Maybe stick to the question in future and don't waste people's time by asking for irrelevant information.


Tis a shame I can't downvote your comments yet Kev, because I would for you, Alexandra and the other clown who gave his unnecessary 2 cents worth!


Thanks for confirming you haven't got the slightest idea yourself how to confirm accuracy of wither the Victron units or the multimeter are wrong - You're not as helpful as you think you are - P.s. I'm not sorry for being blunt, sometimes people on their high horses need to be reminded they're not all they think they are....

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@Hates Spam "Sorry, I don't really want to drop the meter issue, because that is the main issue..."


You're right, "It IS the issue"

If you want to be sure go spend $500 on a Fluke Multimeter and measure the voltage. Your crappy Chinese meter compared to another crappy Chinese (likely same specs and components) is worthless in this instance.

I have worked many many years as a metrologist and can tell you with certainty........Your meter is crap. However, Even a broken clock is right twice a day.


And guess what? The new $500 Fluke meter? after about a year out of the box, you need to send it in to be calibrated again, and every year after. This is not a guessing game. a trusty meter is a calibrated and well maintained meter. So YES, drop the meter issue unless you want to do it right.



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So you and everyone else who has commented are saying there is "no way" to test the accuracy of a DMM unless you compare it directly to a FLUKE? Surely there is something that can be purchased to confirm accuracy and/or a way to test accuracy??


The two DMM's I use are vastly different. One is 100% cheap crap nasty unit, while the other is a half respectable unit (still cheap) being a DT9205A which has the following specs (in image below) and is less than 1 year old, so it should be within manufacturers specs - But you are suggesting this multimeter is automatically going to be crap and couldn't possibly be accurate because it's chinese.


Guess I'll never know since I won't be spending $500 any day soon because I don't have a job, nor do I have $500 to spend on a single test.


It seems every answer to any question on here should automatically be: "Are you using a Fluke? If not, you're wasting your time even testing".


*How are you all so certain the Victron units are guaranteed to be accurate? What's their accuracy rating and what happens when they aren't calibrated every year, how can we all be soo certain they're still accurate?

^^^ Simple question, which I'm sure none of you will attemt to answer...


20220628-124539.jpg



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This is for the last month.

screenshot-20220625-192400-office.jpg

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You said batteries don't seem to be holding charge as well. But there's no real change in min or max battery voltage. What has happened is that yield has dropped, either due to a change in how you use the system, or less sun. Given the batteries show no change, I'd expect it to be usage. What makes you think the batteries are deteriorating?
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Hates Spam avatar image Hates Spam kevgermany ♦♦ ·

Kev,

The yield hasn't really changed, because on days where it is low I will use my generator and DEFA 10A smart charger to top them up, hence why the voltage is still high when the yields are lowering - You can not gauge my usage off that chart, so it's laughable you even attemt to know what's going on, based off my yield!


The reason I believed it wasn't holding charge as well, is because with the same loads applied the battery bank voltage was dropping significantly more than usual (it would not hold) and this was noticeable after the battery bank discharged to 12.24V (according to the app) thus it was suggesting they weren't holding as strong as previously and I thought I may have damaged them after seeing the VOLTAGE VARIANCE - However Kev, this was/is not my issue and as I said, it's most likely due to the colder temperature of the whole system.

^^^ I was concerned, but that's not what I was asking about...


I will drive 2hrs into town to see if I can find someone who may be able to test my multimeter for accuracy and/or buy some resistors and other cheap items to perform some tests on myself, if I can't find anyone.


I just find it funny you wanted lots of irrelevant information that wasn't what I was asking about and then seem to get offended when I remind you what my actual question is...


So far the help I've received from members of this forum have been in the form of criticism for having only a cheaper multimeter and being unsure which voltage reading to trust - VERY disappointing to see such a snobby community with what come across as amateurs themselves who haven't got the slightest idea!

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Klim8skeptic - Thank you for your riveting suggestion.


Tis clear you haven't got any suggestions on how to "test" a multimeter for accuracy and thus your suggestion is for me to buy another style of multimeter that could easily be just as out.


Do you have suggestions on which "not overly expensive" AD/DC clampmeters are actually accurate?


Or was that your whole enlighten suggestion with a with a bit of a pissant attitude to boot?

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Do you have suggestions on which "not overly expensive" AD/DC clampmeters are actually accurate?

I use an UNI-T UT210E clampmeter. 20/100a ac/dc current measurement. Pretty good value for $54.00

I have not had it tested/calibrated. Current seems to match the BMV readings, voltage readings across my 4 devices is within 10mv at battery voltages.

Jaycar have some good value meters. Digital Multimeters | Jaycar Electronics < link.

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Thanks for the better response. How are you aware the meter is calibrated other than it reading similar to the BMV?


I have read multiple posts on this exact forum before I asked my question (whilst searching for answers) of a number of Victron owners who have multimeters or clamp meters which read the same as the BMV, yet the MPPT and battery's sense are showing different voktages and they were asking near identical questions to me and getting no answers from anyone on here (even Victron moderators/staff) hence why I mention in my original post that I've seen similar issues regarding voltage on this forum.


As a result, the "buy a clampmeter" suggestion isn't gautanteed to be any more accurate than what my current multimeter potentially is.


When I can afford a clampmeter, I will look at picking one up and I will research which ones are considered accurate before purchasing - The only issues is that won't happen any week/months soon and I don't want to damage my battery bank in the meantime whilst guessing if the Victron reading are accurate.

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dc4me avatar image
dc4me answered ·

I have found this site to have great information. Sometimes people that post their problems don't know how to set up what they have. Electrical systems have many different approaches. Hence the reason people may ask questions to better help. But to ask for help and have the attitude this OP has is not right. I wouldn't have any inclination to help if I got the response that the OP gave. If you don't think the Information is right one can go elsewhere. But the incivility is not warranted. I hope the OP finds his answer just so we don't have to see him back.

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Sorry that you feel that way...


Not sure if you realise, but I got attitude from those who commented before I gave it back - Guess you're blind to that, Aye?


Please elaborate on how the irrelevant questions that Kevgermany asked were going to assist with my question of how to confirm accuracy of the DMM or Victron units?


His question and desire to move away from my actual question at hand was not helpful, as I clearly explained in my reply to him.

^^^It seems that since I was not wanting to stray away from my original question and was direct about that in my response, this seems to have upset you...PLEASE elaborate on how those questions asked by Kev were actually relevant?

I ask because I do not in any way see the relevance and how it would help answer my question? Perhaps I missed something that you and Kev didn't?


That's FANTASTIC that you have had a good experience on this forum and found it helpful! I on the other hand and in this instance HAVEN'T and I haven't appreciated the pathetic/rude/or vague suggestions from those who commented, especially when they claim to be switched on when it comes to working with solar/victron equipment.


Go have a cry that I'm not impressed with the "so called help" I got from 3 users on this forum.


If I am going to get asked for irrelevant information when seeking answers from this forum, you don't need to cry because I won't be back to waste my time ;-).

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kevgermany avatar image
kevgermany answered ·

I'm really sorry we couldn't help, despite your offensive comments.

I'm closing this thread.

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What is the accuracy of the Victron MPPT and Smart Sense built in voltage meters?

How can you guarantee their accuracy when apparently everything other than a FLUKE will be inaccurate? Since the Victron units aren't being recalibrated each year, what makes you and others so certain the Victron isn't out of spec?


Those comments weren't offensive comment's, I can show you what offensive comments are if you want Kevin?


Did my answers to your questions help you in any way? No they didn't.

I'm still at a loss as to what you were hoping to achieve by asking for a screenshot of my battery settings, my battery bank size, pv array size and daily usage? What did you help me with after asking that information, nothing, absolutely bloody nothing.


If you have the ability to lock this thread, do one better and delete it, since it does nothing for anyone other than to let them know that they shouldn't bother trying to test or diagnose anything unless they use a FLUKE DMM.


This forum should be called "Unless you own a FLUKE, don't bother".

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