Measuring solar current going into inverter.

[Bitbin]

Hi guys. I was wondering when measuring current from the solar panel into the inverter with a clamp meter. Are you supposed to measure the positive or the negative. I always measure the positive but it shows a higher current than the negative. I got an Axpert vm IV twin 4kw. The inverter screen also shows me a lower current from what i get when measuring the positive line with a clamp meter.

And how does one update the firmware of axpert inverters? Thanks in advance.

 

[sunshine_eggo]

Hi guys. I was wondering when measuring current from the solar panel into the inverter with a clamp meter. Are you supposed to measure the positive or the negative. I always measure the positive but it shows a higher current than the negative. I got an Axpert vm IV twin 4kw. The inverter screen also shows me a lower current from what i get when measuring the positive line with a clamp meter.

And how does one update the firmware of axpert inverters? Thanks in advance.

A clamp DC ammeter should show the same value on (-) or (+) wires. Do you zero out the meter before each reading?

 

[Bitbin]

A clamp DC ammeter should show the same value on (-) or (+) wires. Do you zero out the meter before each reading?

Thats what i also thought. Yea i did zero. Dont know why the difference. I measure while on high load. For example the positive showed 13 amps from pv while negative and inverter screen showed around 11 amps.

 

[timselectric]

Not normal
Or even actually possible.

 

[timselectric]

Unless you have some leakage of current. Finding an alternate path.

 

[Bitbin]

Unless you have some leakage of current. Finding an alternate path.

How do i check? I got a uni t 203+ clamp meter which has worked well for years. Dont know if there is something wrong with it or not.

 

[sunshine_eggo]

How do i check? I got a uni t 203+ clamp meter which has worked well for years. Dont know if there is something wrong with it or not.

Personally, I regard clamp DC ammeters as reference devices, i.e., they're good for sanity checks, but not necessarily a tool to confirm accuracy. When they line up, I'm happy. When they're 10% off, I'm content. 2A on 11-13A would give me a little concern.

 

[Bitbin]

Personally, I regard clamp DC ammeters as reference devices, i.e., they're good for sanity checks, but not necessarily a tool to confirm accuracy. When they line up, I'm happy. When they're 10% off, I'm content. 2A on 11-13A would give me a little concern.

Ooh so they are not that accurate? Thought they would be off maybe 1-2%. Would a digital multimeter be more accurate? Problem is they usually have a max of 10 amps and some models 20 amps

 

[Bitbin]

The thing is i dont trust the numbers my inverter shows me. And where i live i cant find any good dc current stuff for solar like a shunt.

 

[timselectric]

How do i check? I got a uni t 203+ clamp meter which has worked well for years. Dont know if there is something wrong with it or not.

I doubt it is the meter. If it's reporting consistently.
The lower reading on negative indicates leakage on the negative. 2a of the negative current is finding a different path back to the panels. Which could indicate panel leakage to ground.

 

[Bitbin]

I doubt it is the meter. If it's reporting consistently.
The lower reading on negative indicates leakage on the negative. 2a of the negative current is finding a different path back to the panels. Which could indicate panel leakage to ground.

My panels arent grounded and they are connected directly to a 63 amp cheap chinese dc breaker and then into the inverter. The inverter itself is AIO Voltronic inverter.

Any idea where the current can possibly leak?

 

[sunshine_eggo]

Ooh so they are not that accurate? Thought they would be off maybe 1-2%. Would a digital multimeter be more accurate? Problem is they usually have a max of 10 amps and some models 20 amps

Accuracy ratings can be misleading. There is a % basis and a significant digit basis. I have to look it up each time. When you're measuring a value closer to the maximum allowed, the % basis is pretty accurate. Lower readings will have a larger error due to the significant digit factor. Lastly, very small readings can be wildly inaccurate.

Listen to Tim. He knows his stuff.

 

[Checkthisout]

Turn the meter the opposite way and see if it changes on the same cable.

In other words make the polarity on the clamp wrong and see if both measurements are the same on the same cable.

 

[timselectric]

My panels arent grounded and they are connected directly to a 63 amp cheap chinese dc breaker and then into the inverter. The inverter itself is AIO Voltronic inverter.

Any idea where the current can possibly leak?

How and where are your panels mounted?

 

[OzSolar]

Lots of great comments already All I can add is that anytime I'm getting impossible readings I'm quick to question both my meter(s) and my testing methodology. I'll like to step back and study the situation, scratch out some drawings and then test if I'm getting the readings that I expect vs. those drawings. I always have at least two meters I trust on hand. It's also a good idea to put fresh batteries in a meter, even if it's not indicating "low battery".

 

[Hedges]

Check meter's battery.

Put the clamp around both PV+ and PV-
See if it reads zero.
Zero the meter and try again.
Flip over, reading other polarity.
This should rule out leakage.

Try meter not around anything, but near inverter, for possible interference. EMI/EMC.
It could get confused by switching, current or voltage noise. Current noise should be same in both wires, voltage may not be.

Observe if it changes over time - this could explain the differences you saw.
Take repeated readings.
Sun changes, and MPPT algorithm can do sweeps.

Do you have more than one PV string, which could get mixed up?

 

[CoolWill]

I have noticed some DC ammeters give different readings depending on which pole and which direction they face. If you change which wire you measure and flip the meter over 180 degrees, it should give you the same reading as it does on the other wire.

 

[Bitbin]

How and where are your panels mounted?

On top of roof on metal mount. 9 x 555w panels. 4th floor

 

[Pierre]

If you have access to a good bench power supply with digital readout you can always verify your clamp meter. I use a Fluke clamp meter as a reference for my other Chinese meters that I sell.

 

[timselectric]

On top of roof on metal mount. 9 x 555w panels. 4th floor

Turn off the PV disconnect. And check voltage from positive and negative to ground. (On the PV side of disconnect)
A voltage reading on the positive, will indicate leakage on the negative. And vice-versa.

 

[Bitbin]

Turn off the PV disconnect. And check voltage from positive and negative to ground. (On the PV side of disconnect)
A voltage reading on the positive, will indicate leakage on the negative. And vice-versa.

I tested measuring it by flipping the clamp meter and it gave me the opposite reading. Meaning the positive is now lower than the negative when both are measured on the oppisite side of the clamp meter. So i think its the clamp meter thats not 100%. It started showing the same current as the inverter screen when flipping the clamp meter

 

[Zwy]

Not normal
Or even actually possible.

Exactly.

 

[timselectric]

I tested measuring it by flipping the clamp meter and it gave me the opposite reading. Meaning the positive is now lower than the negative when both are measured on the oppisite side of the clamp meter. So i think its the clamp meter thats not 100%. It started showing the same current as thr inverter screen when flipping the clamp meter

Maybe it's because it's DC. And the meter is powered by DC (Battery).

Just guessing.
I've never noticed this before.

 

[Hedges]

And yet it read zero when not around a wire?
So not a zero-offset problem, rather different gain positive vs. negative.

Did you try a fresh battery?
If voltage low, might get into non-linear op-amp performance with output near rails.

https://meters.uni-trend.com/product/ut200plus-series/

 

[CoolWill]

And yet it read zero when not around a wire?
So not a zero-offset problem, rather different gain positive vs. negative.

Did you try a fresh battery?
If voltage low, might get into non-linear op-amp performance with output near rails.

https://meters.uni-trend.com/product/ut200plus-series/

Both my Klein and Ideal clamp meters do the same thing. There is a bias in the reading depending on which pole it is clamped on or which direction you turn the meter. The Klein meter is over an amp different one way to the other. The Ideal is a few tenths. My expensive Fluke clamp meter doesn't have this problem.