Conext ComBox reporting incorrect power values

twistedtree

Dave Angelini said:

See what Schneider says... DC in and DC out + loss are equal in all of the systems I have seen. Maybe yours is somehow making the loss look like a gain. You hurt my head! You did get a reference number for your issue. Without it you are just spinning wheels.

Yes, I got a case number, and sent them the XW6848 report as a follow up.  It will be interesting to see what they say.

Dave Angelini

Good!  Remember also, you are offgrid and that loss overnight gets rolled into the next days DC in to charge. Are you looking at the graphs over several days? You should see about a KWH of loss or more from just the inverter and small loads at night.

adding on, COMBOX logs midnite as the next day BTW.

Either way good luck!

twistedtree

I heard back from Schneider.  The XW+ meters DC and incoming AC, but not outgoing (load side) AC.  Instead, it calculates it, and not very well it would seem.  My guess is that instead of subtracting out internal losses, they mistakenly added them in.

But as I write this, I'm realizing their explanation doesn't make sense.  If the load power were calculated, then you would expect the load values it to be self-consistent.  I would expect 240V I*V to equal the reported load power, but it doesn't.  And I would expect the L1 & L2 I*V power to match the load power, but it doesn't, and doesn't match the 240V I*V power either.  And if load power is calculated from the DC power draw, how can the inverter possibly know what the balance is between L1 & L2?  Yet it reports different and varying L1 and L2 currents.

Sorry, the explanation doesn't make sense.  There is more going on here that hasn't been explained.  We will see what they say next.

Dave Angelini

I will pass this thread on to Engineering in Burnaby. They were out for weeks on the holidays. If you can, email me a copy of the response.
My e-mail is in my signature below.  Friday!!!!

BB.

I don't think it is your issue, but the data is labeled "Apparent Power" for L1 and L2 AC (I think). We normally call this apparent power VA (or volts*amps).

Apparent Power is one of those AC terms that is a bit confusing and can even be made even more confusing with lots math...:
https://en.wikipedia.org/wiki/AC_power#Active,_reactive,_and_apparent_power

Apparent power is the product of the rms values of voltage and current. Apparent power is taken into account when designing and operating power systems, because although the current associated with reactive power does no work at the load, it still must be supplied by the power source. Conductors, transformers and generators must be sized to carry the total current, not just the current that does useful work. Failure to provide for the supply of sufficient reactive power in electrical grids can lead to lowered voltage levels and under certain operating conditions to the complete collapse of the network or blackout. Another consequence is that adding the apparent power for two loads will not accurately give the total power unless they have the same phase difference between current and voltage (the same power factor).

Apparent power (VA) is either equal to or greater than real power (Watts). Typically:

• Power (Watts) = Apparent Power (Volt*Amps) * Power Factor

Where Power Factor is usually around 0.5 to near 1.0
 
Electric heaters (resistive) and filament lamps have PF~1.0

Electric motors (inducation type) are typically ~0.60 to 0.80 PF (higher PF when operated near full load).

Many LED and Florescent twisty type bulbs have PF closer to ~0.50

The DC power input to an inverter is typically closer to "real power" (Watts) + inverter losses.

-Bill

Dave Angelini

You never know Bill! You might be right! There are so many settings now on these inverters. The Zero exports and all the other modes that are being used. 

I really can't help as my firmware is in Beta mode and nothing is close to his, whatever his is at this time. I would just say for offgrid all of the options (most all...) should be disabled. I would think the support folks would have taken a look. They may still. Below is a pix of just one page of dozens that have user config settings. I circled what you are thinking.

Are you sending us any rain?

twistedtree

BB. said:

I don't think it is your issue, but the data is labeled "Apparent Power" for L1 and L2 AC (I think). We normally call this apparent power VA (or volts*amps).

Apparent Power is one of those AC terms that is a bit confusing and can even be made even more confusing with lots math...:
https://en.wikipedia.org/wiki/AC_power#Active,_reactive,_and_apparent_power

Apparent power is the product of the rms values of voltage and current. Apparent power is taken into account when designing and operating power systems, because although the current associated with reactive power does no work at the load, it still must be supplied by the power source. Conductors, transformers and generators must be sized to carry the total current, not just the current that does useful work. Failure to provide for the supply of sufficient reactive power in electrical grids can lead to lowered voltage levels and under certain operating conditions to the complete collapse of the network or blackout. Another consequence is that adding the apparent power for two loads will not accurately give the total power unless they have the same phase difference between current and voltage (the same power factor).

Apparent power (VA) is either equal to or greater than real power (Watts). Typically:

• Power (Watts) = Apparent Power (Volt*Amps) * Power Factor

Where Power Factor is usually around 0.5 to near 1.0
 
Electric heaters (resistive) and filament lamps have PF~1.0

Electric motors (inducation type) are typically ~0.60 to 0.80 PF (higher PF when operated near full load).

Many LED and Florescent twisty type bulbs have PF closer to ~0.50

The DC power input to an inverter is typically closer to "real power" (Watts) + inverter losses.

-Bill

For better or worse, I actually understand power factor.  It's been a long time so I'm rusty, but I was pretty good at it back in the day.  It's just the relationship between the voltage waveform and the current waveform.  For capacitive loads, the current will lead the voltage, and for inductive loads it will lag.  Resistive loads have current and voltage in sync, so a pf of 1 as you said.  I don't entirely remember the vector math, but I think the power factor is the tangent of the angle between current and voltage.  Watts are real power, and is the sine of the angle times the current, and imaginary power is the cosine.  Or maybe I have that backwards.  What matters is that W is always less than or equal to VA.  It can never be more.  VA is the product of current and voltage regardless of the phase relationship.

Anyway, if Dave had a headache from the earlier discussion, he has probably passed out by now.....

Bottom line here is that the XW is reporting VA=W  which means pf=1.  Now I have no idea if that's what it actually is.  All the other numbers appear to be made up, so there is no reason to expect the PF isn't made up too.

twistedtree

Dave Angelini said:

You never know Bill! You might be right! There are so many settings now on these inverters. The Zero exports and all the other modes that are being used. 

I really can't help as my firmware is in Beta mode and nothing is close to his, whatever his is at this time. I would just say for offgrid all of the options (most all...) should be disabled. I would think the support folks would have taken a look. They may still. Below is a pix of just one page of dozens that have user config settings. I circled what you are thinking.

Are you sending us any rain?

I've seen that setting before, and I think the old SW trace units has a similar hidden feature.  It's odd because the PF is not something a power source determines.  It's how the the voltage and current respond to a load.  I suspect changing it somehow improves how the inverter responds to non-resistive loads.  But that's just a guess.

mike95490

I too, have that PF setting, and have left it alone, at 1.

BB.

Power factor is the cosine of the angle, not the tangent.

Bill

twistedtree

BB. said:

Power factor is the cosine of the angle, not the tangent.

Bill

Thanks.  See, I WAS rusty.

Dave Angelini

The angle of the dangle was how we were taught to cheat the memory!
I sent your response Peter.
It is a very old design  (XW & XW+) designed to do all the grid stuff also, and if that was left out, it would be more accurate at very low power levels that we use offgrid. The loss is always there when doing what we do. I am not saying that it can't be changed in the algorithm but it should be looked at for the XW Pro I would think. I have heard all kinds of good things are in the works that I am not liberty to pontificate on.

As old as the XW is, I  think as the XW system, there is nothing better. Bullet proof reliability!

The rain did arrive Bill about 5 am so I got to throw the valve in the dark to save it! THX!

BB.

Interestingly, a GT inverter feeding back to the grid can adjust the power factor back into the grid.

I think Germany was looking (or implemented) something like a GT inverter must feed 0.80 pf lagging (?). This better matched the average loads (lots of motors) of the grid.

Otherwise, lots of 1.00pf GT inverters makes for a very poor pf for the utility (utilities only charge non - industrial customers for power (watts) of pf=1.0

They supply residential customers with poor power factor "for free".

Bill

westbranch

They supply residential customers with poor power factor "for free".
Thanks for that bright note so early in 2018 Bil, I always knew there was a bad side to that largess...

Dave we are just out of the DEEP freeze, got to - 29*C here, and now into a whole weeks projection of snow.
No worries about collecting  it till spring (March), well at least not in the dark.
HNY guys, another mad hatters year ahead.... the pics out of Melbourne are not pretty....

Dave Angelini

I still am not really seeing this problem like you do Peter. I loaded a screen shot. You can see day6 yesterday where we had bad solar weather. The days are 12 am to 12am and even though  DC out is more than DC in, it makes sense the power use after sundown to midnight in my system.

The system is not making unmeasured power. It makes sense. The power factor, apparent, real power losses are what they are, at these low levels on a 7KW power system in my opinion.

All except day 6 had a Soc at sundown of 99% from the canbus data inside the LG battery. Added solar screen above

Dave Angelini

westbranch said:

They supply residential customers with poor power factor "for free".
Thanks for that bright note so early in 2018 Bil, I always knew there was a bad side to that largess...

Dave we are just out of the DEEP freeze, got to - 29*C here, and now into a whole weeks projection of snow.
No worries about collecting  it till spring (March), well at least not in the dark.
HNY guys, another mad hatters year ahead.... the pics out of Melbourne are not pretty....

Eric,
Stay warm!  We capture water for the tanks whenever we can. It is fire season 1 week after it rains here. All year long!
At least we do not have santa anna's and Diablo fire winds. Nasty Business!
What is up in Melbourne?

twistedtree

Dave Angelini said:

I still am not really seeing this problem like you do Peter. I loaded a screen shot. You can see day6 yesterday where we had bad solar weather. The days are 12 am to 12am and even though  DC out is more than DC in, it makes sense the power use after sundown to midnight in my system.

The system is not making unmeasured power. It makes sense. The power factor, apparent, real power losses are what they are, at these low levels on a 7KW power system in my opinion.

All except day 6 had a Soc at sundown of 99% from the canbus data inside the LG battery.

At night when there is no solar power, click on the System Performance overview and look at the battery power vs the load power. Mine currently shows 450W coming out of the batteries, and 550W going to the loads.  That of course is impossible.

Then click on the XW under System Devices.  Note the Battery Power near the top of the report.  Then go look at all the "load" values.  None of the load volts times amps agrees with the load VA or W, which of course they should.  And none of the load W or VA values make sense relative to the  battery W.

But wait, my wife just turned on the dryer (gas) so there is now more like an 800-900W load.  Now the numbers look much better.  More than half the time the battery load is greater than the AC loads, which makes sense.  So it does appear to be worse the lower the loads.

Dave Angelini

There is delay in the system and as said error in small values that get averaged out over time.
This is not just a 7KW inverter but part of a system that can have over 100 KW of inverters and devices designed circa 2003.
What do your charts show? Why don't you do an experiment and log battery power and load power. I bet they are not that different.

westbranch

Staying warm is easy, it's going for supplies that we have some troubles with.  I wanted to clear some of the accumulated snow off the drive way and I knew that the battery , sitting in -25 weather was going to be a grunt,..... the |Honda 500cc single lunger with HI compression starts balking at  ~-18 / Zero* F...  put the charger on for couple hrs, No luck... eventually borrowed neighbours little Jumper Battery by MOTOMASTER (Can Tire) and got it going then I stalled the motor 3 times with an over draw on the weak battery, bt lifting the winch... yo get the pic... Today just sub freezing and bang, starts first try!

Melbourne is having some, in town, wild fires.... Not quite as bad as you had but the winds are roaring

South Australian homes lost in bushfire as New South Wales on high alert

Melbourne firefighters welcome a cool change after damaging blaze, but Benalla grassfire threatens homes

Published: 7 Jan 2018