Discrepancy between classic & WBJR battery amps

[offgridQLD]

I now have my WBJR installed on my battery's main negative cable. Great product and it's doing its job well and looks to be very accurate (agrees with my other battery shunt in my inverter).

I am seeing some large discrepancies between the amps the classic is showing being sent to the battery and what the WBJR is reading it's receiving.

I understand that battery loads need to be taking into consideration when reading the WBJR AMPS. I turned off all battery loads to take that out of the equation.

It's a sunny day today and the classic was showing a steady 74A going to the battery but even with all DC loads off, the WBJR was only showing just under 55A. That's almost 20A difference. So have I just discovered a HUGE resistance in my wiring from the classic to the battery (wbjr) or is the classic showing more amps than it's really producing? I believe the WBJR is accurate as it matches what my high Quality inverters logging shunt reads.

I have the biggest cable I can fit in the classics terminals 16mm2 and it's terminated to the main knife fuse holder (about 2 feet of cable) then 95mm2 cable runs about 5 feet to the WBJR then 1 foot of 95mm2 from the wbjr to the Battery neg terminal. So I wouldn't think my wiring is undersized (though in the future my wishlist for the classic is a more substantial wire terminal block - 25mm2 minimum (10mm hole not 6mm as it is now). I know I can use a bootlace pin and step down the cable size at the end but there isn't much room in there.

I have a good quality clamp meter on order, should have it next week. To try and get to the bottom of it, I'm thinking if I clamp the output wire of the classic close to the unit I should be seeing similar amp readings to what the classic is showing. Then measure again after the fuse and keep tracing it back. 20A on a 48v system is 1000w that's a lot of resistance if it is.

Anyhow it's kind of good and bad news. Good if I can find some resistance or loss as I can fix it and gain 20A of charge that was going to waste but bad if I don't find any resistance as I'm stumped then. Having metering is great as you can get to the bottom of issues you would have been blind to without it.

Is anyone seeing large discrepancy between what the classic is showing in battery charge amps and what the WBJR shunt is receiving? (obviously battery loads need to be taken out of the equation)

Kurt

[tecnodave]

Kurt,

That would be impossible, the current in a single circuit will be the same at all parts of that circuit, now you may get voltage drops but the current will not vary at any place on that circuit. I would look for some other circuit where those amps are going , either that or there is a calibration error between the shunts. I have never heard of an inverter idling with that high of current so it is somewhere else

tecno

[mtdoc]

Was there any AC load (via inverter)?

[offgridQLD]

There was no loads on the Battery the Inverter was completely shut down and there is no other loads on the battery. The only thing the battery was powering is the classic 150.

So it looks like the classic charge controller is saying its pumping out 74Amps when its really only pumping out 55Amps

I did make a post a while ago before I got the wbjr that I thought the classic was showing more amps out than was really coming out of it.

I will have the clamp meter next weekend to give me a 3rd point of reference.

Kurt

[boB]

You might see maybe an amp or two of difference if the Classic wasn't quite adjusted correctly but not
as much as you are seeing.  That is, unless the Classic is actually broken somehow.  That's possible
but have never seen this kind of problem before.

Do you have anything other than the battery negative on the battery side of
that shunt ?  Anything  at all ?

I suspect something  is drawing some current somewhere.

Series resistance should not make any difference if there are no other loads
or connections.

boB

[boB]

What is your input voltage and output voltage ?  Note the ratio of those 2 voltages and then
note the PV input current reading as well as the battery output current reading.  The ratio
of input to output current should be somewhat close to the ratio of output to input voltage.

Just a possible sanity check for you to make before you get your clamp on meter.

Maybe your Classic was someone never calibrated at all ?  I hope not, but that's a
possibility I suppose.  If that's the case, you can adjust it.  Am I having a Deja-Vu here ?

boB

[offgridQLD]

Yes one or two amps wouldn't bother me  at all as I didn't expect the classics internal shunt to be a 100% High resolution mesument. But when its showing 74A out at 55 or so volts x 74A Around 4000w but my battery (WBJR) is showing 55A x 55v 3000w that's a big discrepancy.

There is nothing at all on the 1 foot length of cable from the WBJR shunt to the negative terminal.

Yes we are having a Deja-Vu. As I suspected some time ago that my classic was showing more out than it really  was putting out as there was a discrepancy between it and my old current shunt reader. At the time I didnt want to fiddle with the classic as I wasnt 100% possessive my shunt was accurate. But now that the WBJR is giving me the same results It just might be that my classic is out.

Another thing that got my suspicious is my system 3960w of pv often outputs 4000w for sustained periods with cloud edge effect i see 4500  -5000w (then the classic linits current) But it was my understanding I should only realistically see perhaps 3300w or so  in ideal conditions?

Kurt

[offgridQLD]

What is your input voltage and output voltage ?  Note the ratio of those 2 voltages and then
note the PV input current reading as well as the battery output current reading.  The ratio
of input to output current should be somewhat close to the ratio of output to input voltage.

Ok I'm not on site now but  just taking a fixed referance point today 11:40AM on my mymindnite log.

11:40AM

input voltage 60.2v
input amps 64.5A

Output voltage 55.7V
output Amps 88.2A

Yikes there we go its saying its getting 3943w in and 4912W out  26% difference

Kurt

[boB]

Ok Im not on site but  just taking a referance point today 11:40AM on my mymindnite log.

11:40AM

input voltage 60.2v
input amps 64.5A

Output voltage 55.7V
output Amps 88.2A

Kurt

Yep.  That pretty much settles it.  Your Classic is current-sense challenged.

Input to output voltage is very close to each other and input to output current are far apart.

boB

[offgridQLD]

Dam it I thought my PV was just  doing really well 

Hey the good news is this explains why my battery's are so inefficient because I'm not really pumping as many kwh each day into them as the classics telling me

Got to look on the possessive aspects

Well next weekend I will have my clamp meter and between that and the WBJR shunt I should be able to dial it in .

Just have to dig up the instructions how to tweak the classics gain calibration pot from my previous post a while back.

[boB]

Dam it I thought my PV was just  doing really well 

Hey the good news is this explains why my battery's are so inefficient because I'm not really pumping as many kwh each day into them as the classics telling me

Got to look on the bright sided.

Well next weekend I will have my clamp meter and between that and the WBJR shunt I should be able to dial it in .

Just have to dig up the instructions how to tweak the classics calabration from my previous post a while back.

You have to also be careful when measuring current with a clamp on meter when looking at the negative line.
That is, if the negative line is common to both battery and PV input.  If they are shared, you will actually see the "difference" of input and output current on that line.  Of course, clamp on probes also don't usually read the same in one direction as the opposite direction because of residual magnetization of the probe.

I would just trust the WB Jr.  It's going to be more accurate than any clamp on meter as long as all of your loads and inverter are turned off.  The Classic is normally very accurate too.  I believe the Classic is the most accurate ammeter in any charge controller out there.  (normally) Unfortunately, not in your case.  But as long as a shunt hasn't fallen out or something like that, you should be able to adjust it.  If not, we'll still make it right for you.

boB

[offgridQLD]

No problem good points. The clamp meter is just as a quick guide. I needed one anyhow for other projects.

I just purchased A 2nd classic a few weeks back  for my future upgrade so I could swap it out with the old classic and see how that one is.

Like you say I will just use the WBJR with every load on the battery shut down to calibrate.

I just took a few more sample points throughout the day and they all calculate to show a output error from the classic.


Two more sample points of In vs out from classic

9:16am ,

Input 60.5v - 21.4A =1294w in

Output  50.8v - 33.2A = 1686w out.

Roughly 30% difference.



3:04pm ,

Input 75.5v - 4.9A = 369w

Output 54.1v - 9.1A = 492w out.

Roughly 33% difference.



Kurt

[offgridQLD]

Ok just to make sure the old instructions you gave me a while back  are still ok

You will need a fairly small, adjustment screwdriver.

The left side towards the front is a hole gaining access to the trimpot labelled GBATT.
(see picture)

Turn very slightly counter-clockwise (I think) and watch the current come down.

Easy now... be careful !

Make sure the offset hasn't been affected (it shouldn't) by turning mode to off
and back on again to recheck the reading.  If it reads closer, great.

boB

And use the WBJR readings (with zero load on the battery) as a reference to dial it in.

Kurt

[boB]

Yep.  That should work pretty good I wou;d think.

If it doesn't adjust enough, then your Classic may have some other issue keeping it
from measuring correctly.  There is that possibility.  Won't hurt to give it a try though.

boB

[offgridQLD]

Ok just to try and confirm some data today I took five reference points from the mymidnite logs and compared input and output data from the classic. I have a spread of  both high and low power to try and confirm a gain issue.

6:56AM, Input 66.1v at 7.9A , Output 52.1v at 13A,  522w in VS 677w out 29% discrepancy

7:33AM, Input 65.9v at 34.2A, Output 56v at 51.8A, 2253w in VS 2900w out 28% discrepancy

8:10AM, Input 61.9v at 15.2A, Output 55.4v at 21.8A, 940w in VS 1207w out 28% discrepancy

9:06AM, Input 74v at 15.8A, Output 59.9v at 25.1A, 1169w in VS 1503w out 28% discrepancy

9:24AM, Input 73v at 13.3A, Output 60v at 21A, 970w in VS 1260w out, 29% discrepancy


So its looking very consistent even with a range of output levels, I always come up with  28-29%.

Kurt