Axpert Ac Charge "leaking"

[PaulF007]

7 minutes ago, Mark said:

with cumulus to upload the data

Same here , I upload to www.wunderground.com as it is easier to "see" there. Tried the web server Cumulus "hosts" but it was just too much tinkering for my liking.

[Mark]

Same here , I upload to www.wunderground.com as it is easier to "see" there. Tried the web server Cumulus "hosts" but it was just too much tinkering for my liking.

I upload to my own domain which makes it easier... nice web page view and history. Would love to get it to upload to emon so may contact the developer as some stage. [emoji2]

Sent from my SM-G800F using Tapatalk

[Guest]

BMV Setup - my 2 cents:
1) Follow the tutorials as posted above.
2) Make sure the batts are completely full, proper way to check is a)) controller is in float or even better b)) measure the gravity per cell.
3) Now manually sync BMV as 100%. - Do this every 1-3 months as you see fit / as per your system.
4) At the same time, make sure NOTHING is connected to the batteries, only the BMV, to ensure NO current goes in or out.
5) Then ZERO the BMV ensuring it knows nothing is coming in or out of the batts.

Point 4/5 I picked up yonks ago when my inverter was switched off and controllers where off, yet BMV still showed 1amp going into the batts.

In some cases one would need to disconnect the inverter / controllers completely ensure nothing can go in or out of the batteries.

[___]

8 hours ago, PaulF007 said:

I assumed that the BMV will "know" when there is energy flowing through the shunt but I was wrong! I have to tell it when there is no energy and then it can work from there.So can we rely on most of these monitoring devices?

Some theory for you to help with the understanding. The BMV's shunt is a basically a resistor with a very low value, calibrated so that it creates a 50mV drop when there is 500A flowing through the shunt. To appreciate just how small that is, consider that a 1 Ampere flow creates a voltage drop so low that you can't even measure it with a good oscilloscope!

The shunt also has to measure current going in both ways. Usually you do this by placing one end of the shunt at a known voltage, usually half of supply, which for the BMV wil be 3.3/2 = 1.65V. That means you will get a voltage between 1.15V and 2.15V back from the shunt which correspond linearly to a range of -500A to 500A. If it sits at exactly 1.65V, the current should be zero.

As you might imagine, even a slight difference in reference voltage will cause a big misreading, which is why these devices must be calibrated. They normally ship from the factory already calibrated, but you can recalibrate them.

In other words, one must have some consideration as to just how good this piece of equipment is!

I recalibrated mine once, but the result was exactly the same as before I did that :-)

[Guest]

6 minutes ago, plonkster said:

In other words, one must have some consideration as to just how good this piece of equipment is!

Ditto.

In chatting with people to calculate the SOC using data from devices, it became quite clear to me that the BMV's, as you say, are quite a fancy piece of equipment doing a whole lot of interesting stuff that once you start to look at duplicating, gets very interesting very fast.

Now add the amount of configuration Victron allow you to do on your BMV for your particular setup, makes them even more powerful in trying to calculate what a chemical reaction has "in store" for you. (Pun intended.)

And then you add temp and age of batteries to that chemical process ... Respect for BMV's.

 

[Pieta]

Hi ,

First off all thanks for all the amazing topics that are available!  For a newbie like me on Solar this certainly helps a lot!!!

Wonder if someone can help? It might have been discussed before but I could not find anything on the problem as set out below...

Have written a program in VB6 (Please don't laugh!!!) to interface with 2 x Axpert 5KVA Inverters but has found a problem as the PV input currents does not add up...When measuring current from the Solar panels to the inputs of the Axpert Inverters with an amp probe the current seems to be less than the current indicated as PV Input current on the Inverter display and different software available. The PV input voltages however are more or less the same when measured with a multi-meter.

If the Wattage of the Solar panels are calculated by multiplying PV Input currents measured with an amp probe and with the PV input voltage measured with a multi-meter then there seems to be an error. It seems that the PV Input Current shown on the inverter is actually not the PV Input current but the MPPT output current. We think that the PV input current readings that we get from the inverter display and when polling is measured only after the MPPT's has already made its conversion. That is why the PV input current that is displayed is higher as when measured with an amp probe on the Solar input side. All the information are not available when polling with QPGS and a ratio has to be used to get to the correct Solar PV input current. We think this can lead to incorrect Solar panel input wattage display. We have used the ratio of the Battery voltage divided by the PV Input voltage and then multiplied by the "PV Input current"  (MPPT current) as given when polling to give the real PV Input current. PV input volts x PV input current = MPPT output volts ( Same as battery voltage ) x MPPT output current (Battery and Load current when in inverting mode - This is similar to the ratio of transformer input to output voltages and currents) When we use this ratio the PV Input current before the MPPT's are more or less the same as when measured with the amp probe. There might be a slight difference due to losses.

Hope someone can maybe lead us in the right direction if we misunderstand the concept.

Kind regards

Pieta

 

 

[Chris Hobson]

2 hours ago, Pieta said:

Have written a program in VB6 (Please don't laugh!!!) to interface with 2 x Axpert 5KVA Inverters but has found a problem as the PV input currents does not add up...When measuring current from the Solar panels to the inputs of the Axpert Inverters with an amp probe the current seems to be less than the current indicated as PV Input current on the Inverter display and different software available. The PV input voltages however are more or less the same when measured with a multi-meter.

If the Wattage of the Solar panels are calculated by multiplying PV Input currents measured with an amp probe and with the PV input voltage measured with a multi-meter then there seems to be an error. It seems that the PV Input Current shown on the inverter is actually not the PV Input current but the MPPT output current. We think that the PV input current readings that we get from the inverter display and when polling is measured only after the MPPT's has already made its conversion. That is why the PV input current that is displayed is higher as when measured with an amp probe on the Solar input side. All the information are not available when polling with QPGS and a ratio has to be used to get to the correct Solar PV input current. We think this can lead to incorrect Solar panel input wattage display. We have used the ratio of the Battery voltage divided by the PV Input voltage and then multiplied by the "PV Input current"  (MPPT current) as given when polling to give the real PV Input current. PV input volts x PV input current = MPPT output volts ( Same as battery voltage ) x MPPT output current (Battery and Load current when in inverting mode - This is similar to the ratio of transformer input to output voltages and currents) When we use this ratio the PV Input current before the MPPT's are more or less the same as when measured with the amp probe. There might be a slight difference due to losses.

Hope someone can maybe lead us in the right direction if we misunderstand the concept.

Kind regards

Pieta

 

 

Hi Pieta

You are correct the PV current reading is taken after modification by the MPPT. So if you are trying to work out PV Watts you multiply PV current by Battery Voltage rather than PV Voltage. On the fly calculations are usually within 50W of the PV Watt readings that the Axpert provides.

To calculate true PV current I divide PV Watts by PV Voltage. This value is then reported to my Emoncms dashboard. Day after day I have confirmation that solar panels are a constant current device. When there is enough sunlight the Amps are usually within 1A of my strings' rated maximum. 

[PaulF007]

Hi @Pieta

I quicly checked and the "QPIGS" command gives you PV amps and PV Volts and if you run the "Q1" command you will receive PV Watts. I also did a quick check and if you take the 

Q1 - PV watts / QPIGS - PV Volts = The same as QPIGS - PV amps (or very close) 

So maybe try and run the Q1 command and see if the inverter responds.

[Chris Hobson]

1 hour ago, PaulF007 said:

Hi @Pieta

I quicly checked and the "QPIGS" command gives you PV amps and PV Volts and if you run the "Q1" command you will receive PV Watts. I also did a quick check and if you take the 

Q1 - PV watts / QPIGS - PV Volts = The same as QPIGS - PV amps (or very close) 

So maybe try and run the Q1 command and see if the inverter responds.

Hi Paul then there must be a separate value for PV Amps which is after the MPPT used by the LCD screen and Watchpower.

 

 

[Chris Hobson]

Hi Paul just check the values you are getting  versus your panels' combined I_sc rating something is not right. I am guessing but you should not see values greater than 35A.

[PaulF007]

22 hours ago, Chris Hobson said:

Hi Paul just check the values you are getting  versus your panels' combined I_sc rating something is not right. I am guessing but you should not see values greater than 35A

Hi @Chris Hobson , I think you are correct it seems like that is the MPPT amps and not the Panel amps  apologies fellow members .
But the Solar watts is still correct from the Inverter because that was what I used when I did the Axpert / Victron comparison and the values were very close to each other. I also did a quick test ( Panel Watts / Panel Volts) and it seems like the Axpert is not reporting the panel amps , which would make sense now as there would need to be a extra dc shunt to measure that  , I think .

 

[Chris Hobson]

1 hour ago, PaulF007 said:

Hi @Chris Hobson , I think you are correct it seems like that is the MPPT amps and not the Panel amps  apologies fellow members .
But the Solar watts is still correct from the Inverter because that was what I used when I did the Axpert / Victron comparison and the values were very close to each other. I also did a quick test ( Panel Watts / Panel Volts) and it seems like the Axpert is not reporting the panel amps , which would make sense now as there would need to be a extra dc shunt to measure that  , I think .

I cheat and use the same ( Panel Watts / Panel Volts) calculation and record the value in Emoncms. It is of little consequence but shows that given enough sunlight panels behave like constant current devices. Increases in panel watts is due to variation in voltage not really variation in current.

Addition: Occasionally I  get a value considerably larger than my panels combined I_sc but I think this just due to recorded Voltage values lagging when there is a surge in PV Watts.

[PaulF007]

46 minutes ago, Chris Hobson said:

but I think this just due to recorded Voltage values lagging when there is a surge in PV Watts.

That and the fact that it is a second calculation from a first calculation. I noticed that in the beginning when I used emon's virtual feed to do some calculations. 

[___]

33 minutes ago, PaulF007 said:

second calculation from a first calculation

Over a decade ago, and somewhat off-topic, but I remember that branch of applied maths: Estimating the maximum error that can arise through successive small errors (usually because microprocessors make floating point mistakes). And then there were ways of refactoring such math to avoid the errors. I remember one easy one: When subtracting, try and get the two terms to be more or less of the same order. That avoids floating point underflow and massively improves accuracy :-)

[PaulF007]

1 minute ago, plonkster said:

When subtracting, try and get the two terms to be more or less of the same order. That avoids floating point underflow and massively improves accuracy :-)

He he , sorry had a chuckle just now , I would have never though - try , more or less , floating point would be coupled with improving accuracy . But yes you are correct.

[Chris Hobson]

32 minutes ago, plonkster said:

make floating point mistakes

What I am seeing is not floating point mistakes. 44A where the I_sc is 32.96A

[___]

2 hours ago, Chris Hobson said:

What I am seeing is not floating point mistakes

Yeah I know, I didn't mean to say that they are. I meant to say they are one example of the kind of error that creeps in when you do successive calculations.

I see the same kind of thing on the CCGX. Whenever devices send data the various processes get notifications and quite a few of them keep track of these values so they don't have to query it every time. This inherently creates a kind of race condition where some processes might have processed the notification and others have not. Then they have this central processes (com.victronenergy.system) that collates the information, and many processes again work on those values. So you have a nice long pipeline with lots of opportunity for an amp here or there... and that is why the numbers on the screen almost never add up perfectly :-)

[Pieta]

Thanks for the Info! Agree with you there are definitely a difference from the indication to the real values! Will have some time the weekend to play around again. At least we are on the right track...

Thanks a million!