Classic 200 real amp output higher than MNGP amp output

[SolarMusher]

Hi,
Is there a way to tweak the MNGP in order to have a better amp output accuracy?
Today my BMK was showing 1.5/2 amp positive more than the MNGP. In doubt, I have re-checked the amp going into my two strings of batteries with an ampmeter and the BMK was right.
I've also checked VPV and my Classic is well calibrated.
In fact, the Classic output is more than the MNGP shows 
Any idea?
Erik

[boB]

Hi,
Is there a way to tweak the MNGP in order to have a better amp output accuracy?
Today my BMK was showing 1.5/2 amp positive more than the MNGP. In doubt, I have re-checked the amp going into my two strings of batteries with an ampmeter and the BMK was right.
I've also checked VPV and my Classic is well calibrated.
In fact, the Classic output is more than the MNGP shows 
Any idea?
Erik

Erik,
Are you sure you don't have anything besides the batteries connected to that Classic ?  Maybe an
inverter or something ?   Also, when you measure the Classic amps output, are you measuring with
a clamp probe on the negative or the positive leg of the Classic ??  The Negative leg will show less
current than the positive unless the PV negative is going straight to the Classic (i.e NOT connected
to the battery minus bus bar and one negative wire to that bus).

I am familiar with the BMK and it reads fairly accurately, except maybe at very low levels unless that
has been fixed recently.

The Classic current sense is closer than most other charge controllers for accuracy and we should be
adjusting it very close at the factory.  Of course, you might have one that is off, but first, let's look
at these questions.

boB

[SolarMusher]

Hi boB,
I have checked amp output this way:
Inverter was ON and I didn't chek current on the classic legs. VPV is fine tuned and VBatt is fairly accurate (Classic/BMK/Voltmeter)
I've read the amp output to batt on the MNGP ex: 20A
I've read the amp in and out to the battery on the BMK, in this case +22A.
I took the clamp meter and checked each battery positive leg to the battery bank (x2) directly after my parallel buss bar and it read +11A on each positive parallel leg to battery bank.
I would like to insert a picture but didn't find how  .
A+,
Erik

[Halfcrazy]

Eric
If the inverter was on than that number may be off further than it looks. Sometime try the same thing with the inverter Off.

Ryan

PS see if this picture helps explain loading a picture

[SolarMusher]

Hi Ryan,
I'm going to try with the inverter off.
Thanks,
Erik

[boB]

Depending on the current clamp probe, they can be off some in one direction
compared with the opposite direction.

For instance, try measuring current on a wire with the clamp probe hooked
on in one direction then turn it around and see how close it reads to the first
direction.  Swap directions a couple times. They are usually off a wee bit from
one direction to another.

boB

[SolarMusher]

Hi boB,
I have a logo (alert) on my clamp meter which tell me if I'm in the right sense. Hard to make mistake.
I can't stop the inverter at this time, I have fishermen in the cabins that I rent, not sure they would appreciate my tests...
I will post you back when I could.
A+
Erik

[boB]

I have a logo (alert) on my clamp meter which tell me if I'm in the right sense. Hard to make mistake.

OK, I guess I don't know that that means ??   I can only assume it means the same thing as a plus or
minus sign (+ - polarity)

What I was talking about was that the amps shown, be it negative or positive, when you turn the probe
around, should be exactly the same in either direction.   For instance, in one direction if it says
+ 2.5 amps, if you turn it around the other way, it should say -2.5 amps   but it is very rare for
a clamp on probe to be exactly the same both ways due to magnetic remanence and hystersis.


As for the inverter, how much AC load is there on it when you are measuring the DC current ??
What is your battery voltage again ??  The lower it is, the higher the current can be off for a
given power.  An Outback FX 24V inverter will draw approximately 1.2 amps sitting there
making 120V on its output.  With any kind of load, it will be higher than that.

Also, what happens if you hook that amp clamp current probe up to the Classic Positive battery
output wire ?? (NOT negative)  Is it close to what the MNGP reads or quite different ?

BTW,   I would  expect a current clamp-on probe to be inaccurate by at least 1 amp or so
either direction typically.  I have seen them very close though at times.   

boB