Jump to content

Inverter battery volt reading vs actual battery volts


Ernie Green
 Share

Recommended Posts

Good day,

I need advice regarding the battery volts reading my Mecer 5 KV inverter shows and the actual battery bank reading i measure with my multi meter.

There is almost a 8 volt difference.

This will surely harm my battery banks.

I did reset the mecer settings to default, no difference.

 

IMG-20200823-WA0020.jpeg

Link to comment
Share on other sites

2 hours ago, Ernie Green said:

There is almost a 8 volt difference.

This will surely harm my battery banks.

Which reading is correct, the inverter or the multi-meter? Do you have another meter to confirm the correct reading as it might be possible the multimeter is faulty?

Link to comment
Share on other sites

Gerrie,

 

I used 2 different multi meters. 

I disconnected each bank and remeasured them one by one and the results stay the same, average of just over 7 volt difference between what inverter reading is and the banks. i connected each one at a time to the inverter and the problem still persist.

I restarted the inverter  and still same results.

Link to comment
Share on other sites

19 minutes ago, Ernie Green said:

I used 2 different multi meters. 

I disconnected each bank and remeasured them one by one and the results stay the same, average of just over 7 volt difference between what inverter reading is and the banks. i connected each one at a time to the inverter and the problem still persist.

If you also measured with no load and with no charging from solar panels and the difference in readings was still there it’s possible their is a problem with your inverter, but I see on the photo you posted your inverter were under about 50% load and you draw 8A from batteries while solar panels also supplied power. it might be possible that the voltage on the keypad is just the charging voltage to the batteries at that point in time.

And the batteries that is under load could measure lower until you remove the load then the voltage could bounce back up to a higher level. Someone else might be able to comment if I’m missing something here.

Link to comment
Share on other sites

Good morning Gerrie,

 

Thanks for your feedback. I suspect that my inverter has a problem.

After i took the photo, i changed the output source to utilities, allowing the system to charge the batteries to full, according to the inverter reading.

Battery Capacity was at 100%.

Take note that it was fully charged from the solar and was drawing feed from the batteries for about 30 minutes when i took the photo.

I then proceeded to disconnect all banks from the inverter.

The readings varied between 45.3 to 45.7 volts, per bank.

This indicates to me that the inverter is not reading the true volts of the batteries.

I will call my supplier / installer today to help investigate.

I would appreciate any further advice.

Link to comment
Share on other sites

2 hours ago, Ernie Green said:

The readings varied between 45.3 to 45.7 volts, per bank.

Ernie, hope that there are no damage to the batteries as that voltage seems very low at 100% charge, hopefully your supplier can sort things out. 

Link to comment
Share on other sites

Gerrie is right, that's not a good way to compare voltage readings, because of the voltage drops from cables. It's best to measure the battery voltage when there is no load on (or charge into) the battery. Measure directly at the inverter terminals to eliminate voltage drops across the battery cables. Bypass mode with the PV isolated should be close enough (there should only be about 1 A drawn for self consumption).

What has happened could be

(a) the sense resistors have changed value from when the battery voltage readings were calibrated at the factory, or

(b) the calibration value in EEPROM has somehow changed or become corrupted. Resetting to default settings does not reset the calibration values.

If it's option (a), it could be that

(a1) the resistors have changed in such a way that they are completely stable, so you can just recalibrate, or

(a2) the resistors have changed in such a way that they are drifting, either with temperature or time or mechanical stress or moisture or a combination of these, so that recalibrating at this stage is pointless. It could be that the conformal coating became damaged somehow, and moisture is affecting the resistance. In these cases, the resistors have to be replaced, sealed under a conformal coating, and then the readings have to be recalibrated. There are 8 resistors involved, R29-R36, all 1.0 MΩ. They appear to be M2012 size (0805 imperial), and are located under the large high frequency transformer in the model I have here. One megohm is a fairly high value, easily affected by moisture. Moisture will tend to lower the resistance, and these resistors are in the upper part of the voltage divider, so reducing their value will tend to exagerate the voltage (the inverter will read higher than a multimeter).

Unfortunately, (a2) is the more likely case, followed by (b), and (a1) is unlikely.

I give a recalibrating procedure in this post. I note that Weber's clever "nudge" commands will take a long time (some 140 commands) to change the reading by 7.0 V, so you might want to try my "hard way", which at least lets you change the reading by 0.45 V at a time (so 15 commands should get you close). If the resistors are replaced, then it's most likely that you won't need a massive calibration, so Weber's nudges should be fine.

I note that a single nudge is only 0.05 V, and the voltage is displayed down to tenths of a volt. But you should take note of whether the value flips between two values; if so, consider this as half way between those two values. For example, if the reading alternates between 45.6 and 45.7, consider the reading as 45.65. Do the same with your multimeter, if necessary.

[ Edit: Just as Gerrie noted, ] I also note that 44.1 V is a very low reading for any battery, and it's good if you don't leave the battery in this state too long. Certainly don't use it to power loads until this is all sorted, if at all possible. So time is "of the essence".

Edited by Coulomb
Sigh. Must have quoted instead of edited.
Link to comment
Share on other sites

2 hours ago, Ernie Green said:

Battery Capacity was at 100%.

I note that this is probably "battery capacity as judged by the inverter", and since it's so far out of calibration, that means that the battery is far from 100% full.

Link to comment
Share on other sites

Coulomb and Gerrie,

Thanks for all the effort and feedback .

I had the installer to help and found that one battery is a problem but the biggest error of it all is my multi meter, now called my ex multi meter.

lesson learned, get a second tester to verify the readings.

 

Link to comment
Share on other sites

19 minutes ago, Ernie Green said:

I had the installer to help and found that one battery is a problem

Hi Ernie,

It’s great your installer identified the problem, now it makes sense why that battery voltage were so low, that one damaged battery dragging the whole bank down, and yes multimeters can sometimes cause big headaches,  I have learnt to always have a second meter when there is any doubt. 

Thanks for sharing the finding it’s always nice finding answers. 

Link to comment
Share on other sites

11 hours ago, Ernie Green said:

lesson learned, get a second tester to verify the readings.

? But you said you verified with a second multimeter.

Lesson should be: always have a reliable meter.

I have a second hand Fluke 87 III. Apart from chewing through the 9 V batteries, it's been really good. Before that, I had 7 multimeters (about 3 of those were cheap junk ones I used for a while as voltmeters and ammeters in an earlier solar project). I also managed to calibrate its DC voltage reading against a certified 5 digit voltmeter from a colleague, so I know it's accurate as well.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...