outback mx60 question

System

i m having a problem with my mx60 installed a couple days ago, if anyone wants to offer advice... i have 500 watt pv ,48v battery. i shortcircuit tested at the mx 60 service entrance and had 110v at 4.9a from panels, just over 500w. however once connected the mx60 in bulk charge mode is showing 221 watts input on its display at best( this is from a 50%discharge so i would expect full amps. VOC is same on tester and display. The output Volt and Amps match the input. A friend told me it has to do with amperage drop once load goes to batteries, but i still was expecting to get more accurate readings of input amps. i will call outback, but was wondering if this is normal, or should i be getting a more accurate reading. So to recap i am getting 1/4 - 1/2 of amperage showing on my mx60 display vs the testing equipment which seemed to confirm the panel ratings.

niel

Re: outback mx60 question

could you specify what pvs you have and in what configuration for everybody as i have a problem with a short circuit showing 110v? a short circuit current reading will have nearly 0 volts so i might suggest while you measure the sc current that a voltmeter be place across the leads at the same time to show you that you don't get 110v when the current is that high.

System2

Re: outback mx60 question

pv is 4 photowatt 1250 (125w) panels, in series. sorry, test was short circuit amps, then volts were measured. I meant that 110 volts was found at service entrance as well as at panels. individually panels read at 28.8 voc(rated 32). also on mx60 when sweep begins, 115 v at 0 amp is shown.

System2

Re: outback mx60 question

Just a couple of quick thoughts.
1) The 110 volts from what you say is during open circuit conditions, which means no load. This means that under load, the voltage might be expected to be around 65 or 70 volts, more or less.
2) You indicate the short circuit current to be 4.9 amps. Likewise, under normal loads, not under short circuit conditions the amperage will be less, perhaps around 4 to 4.3 .
These are good guesses only and won't be exact, but probably close.
Worst case: 65 X 4= 260 watts. And that would be under full, strong sun. So things may not be all that bad, just not what you were expecting.
I'm also assuming this is during "Bulk" mode of the MX-60, as once it enters absorb mode, the amperage is reduced to maintain battery absorb voltage.
Now perhaps others with exact knowledge of these panels can narrow it down.
Peace
Wayne

System2

Re: outback mx60 question

thanks for reply, it helped to get a better idea of what to expect.

mikeo

Re: outback mx60 question

My experience is that on average, you will only generate about 75-85% of the nameplage ratings on PV solar panels in real world conditions and depending on the climate and panel orientation where you live, it might even be less.
Mike

System2

Re: outback mx60 question

i had a look at panels, and specs are,
P. max 125 w
voltage peak power 25.7V
current peak power 4.8Amps
short circuit current 5Amps
VOC 32.

4 in series(500w) tests at VOC 124( close to 128) and Short circuit current 5.5Amps.

so does this indicate panels are working correctly?

Highest wattage is 264 so far on mx 60. which seems to fall far short of 75%. but looks like what wayne predicted.

I figure i m losing about 10-15% on the cable run from pv to mx60 based on 5.5 short circuit current at panels and 4.9amp short circuit at MX 60.

265 watts looks like all im going to get until i get some bigger wire, if anyone thinks a problem is indicated, let me know, thanks cam

System2

Re: outback mx60 question

You can get a good idea of the loss in your cable between the panels and the MX, by doing the following while the system is under full sun and the MX is in Bulk mode. Carefully measure and record the voltage at the cables as they leave the panels. Then, right away before conditions change, go to the MX-60 and measure and record the voltage at the PV input terminals. Now take the difference between the two voltages and multiply that by the PV Amps being delivered to the MX-60, as shown under PV amps on the left side of the MX display. That will give you an indication of the wattage being lost in the cable at the time of measurements.
Others on here can let you know what % of voltage loss is acceptable. I don't remember for sure. Seems to me it might be around 3 or 4 %, but I really don't remember. Of course less is always better, but there comes a trade off between loss and the high price of copper. Note that cable losses will be less in actual operation, than during short circuit conditions, because the amperage will be less in non short circuit conditions.
Good luck
Wayne

blwncrewchief

Re: outback mx60 question

camredwood wrote: »

i had a look at panels, and specs are,
P. max 125 w
voltage peak power 25.7V
current peak power 4.8Amps
short circuit current 5Amps
VOC 32.

4 in series(500w) tests at VOC 124( close to 128) and Short circuit current 5.5Amps.

so does this indicate panels are working correctly?

Highest wattage is 264 so far on mx 60. which seems to fall far short of 75%. but looks like what wayne predicted.

I figure i m losing about 10-15% on the cable run from pv to mx60 based on 5.5 short circuit current at panels and 4.9amp short circuit at MX 60.

265 watts looks like all im going to get until i get some bigger wire, if anyone thinks a problem is indicated, let me know, thanks cam

What are you seeing on the input and output volt/amps on your mx when it is in bulk? You should be seeing something roughly like: Input 100 volts 5 amps and Output 50 volts and 10 amps. Something definitely is wrong like the mx is locking the panel voltage to the battery voltage and not tracking properly or something is set wrong. Your voc and isc to the panel specs look ok and to loose that much power in the wiring you would have to have a 30%-50% drop. Also by those specs those are 18v nominal panels and 4 in series is too high a voc unless you live in a very hot climate. 124voc x 125% = 155v and a damaged controller. Anymore info you can provide?

System2

Re: outback mx60 question

I do live in a hot climate, 110 in summer and 22 coldest night at 2500'. Temp for last 3 days has been 75F peak. got thumbs up from Outback on 4 panels before i started wiring. hasnt frozen since wired up so well below 150voc.
The input Watts and output watts are about the same, as example on Bulk INPUT i would see 75v input at 2 amps, and Output to battery would be 50v at 3amps. Both sides very close to equaling the shown wattage.

Next sunny day i will check the voltage loss and post back. I am running 20 feet on 12 gauge wire PV to MX60 and 10' on 6 gauge wire MX60 to battery. Tommorrow i will try some 8 gauge and see what difference it makes, I figured some extra 12g i had lying about would do for 5 amps max at 100v but i m starting to think i need to beef up significantly just to rule it out. VOC and ISC drop seemed small on the 12g. MX 60 is new from dealer. Also i could hook up another 500watt string of identical panels which may indicate something.
As for settings, i have normal charge settings, max 60amp input setting, Doesnt seem to sweep except on restart because output amps never hits 5. I ll reread the manual, but i didn t see any settings there that could limit input current.

Any other info or tests i might need? I had the ISC and VOC tested by a nabcep electrical contracter so i believe the test results are correct,
thanks for the help, cam

crewzer

Re: outback mx60 question

Cam,

Your array’s STC specs for four modules wired in series are 25.7 Vmp x 4 = 102.8 Vmp x 4.8 A Imp. In real world conditions, you should see ~85 V x 4.8 A (~400 W) around local solar noon on a sunny, clear, and cool day with the controller operating in MPPT (Bulk) mode. Array voltage will be a bit higher in the winter, and somewhat lower in the summer.

Your array’s STC Voc spec is 32 V x 4 = 128 V. While that’s well below the MX60 absolute input voltage limit of 150 V, it’s not all that far below the operational limit of ~141 V. In fact, with but a 10% cushion above the array’s STC spec of 128 Voc, exposing the array to morning temperature below 32 F might cause the MX60 to briefly suspend operation.

Thin wire will reduce array voltage at the controller, but not array current. 12 AWG wire is not uncommon for small PV arrays, especially when the array voltage is high and the array current is low.

Low array current is usually the result of haze, air pollution, or high humidity; poorly aligned modules (wrong tilt angle and/or azimuth angle); module shading (tree branches, overhead electrical wires, etc.); or dirty modules (bird souvenirs, leaves, dirt and grime, etc.).

I’d suggest confirming that your array is well aligned, shade-free, and clean. Good alignment for this time of year is a tilt angle (up from horizontal) equal to local latitude, and facing south.

Note that the MX60’s input current display is a calculated value, and not a measured value. My recollection is that’s its accuracy at low values can be suspect.

As you know, The MX60 controller’s active MPPT function does not operate when the controller’s output current is < 5 A. This info is contained in the manual. Instead, the MX60 sets the array voltage at the array Voc times the % setting in the "U-Pick” menu.

The OutBack factory default "U-Pick" setting is 77%. I found early on that I could increase bulk stage “< 5A” output current by increasing the “U-Pick” % setting to something in the 85% range. You might want to go into your MX60, check the setting, and experiment with different values.

Another factor in your system (high array voltage, relatively low power) is that the controller may be operating at less than 90% efficiency. Check page 66 of the MX’s latest manual.

In summary, check your array for alignment, shading, and dirt/debris, and try fiddling with the “U-Pick” % setting to optimize the array’s voltage vs. current intersection and increase output current.

HTH,
Jim / crewzer

System2

Re: outback mx60 question

thanks, i will be having another round of reading the manual. Play some more with VOC U pick.

Regarding panel orientation/shading/grime, it is near perfect angle, washed panels, and no trees until 6pm, clear days. ISC was 5.5 with tester, vs 5 on spec sheet.

I ll wire in 10g wire, which should be ample, and look at voltage drop.

Regarding the calculated values and possibility of unreliable readings or low efficiency at low amperage i will hook up the other 4 panels tommorrow to see if this helps, by having 2 strings on 2 breakers i can compare strings and see of there is a discrepancy.

I ll ring Outback in a couple days, if i can t make something happen, see what they suggest.

Thanks so much for the assistance everyone, i m learning a lot.

crewzer

Re: outback mx60 question

Cam,

The 5.5 A Isc reading is encouraging, as is the report about your clean array’s good alignment and lack of shading.

Adding a second string of modules should result in different behavior and performance from the controller. It will spend much more of its time in MPPT (bulk) mode operating at >5 A output current, which will allow it to operate in its semi-active MPPT mode. Operating efficiency should improve as well.

It’s worth noting that PV array’s rarely deliver their STC rated power. Among other parameters, STC specs are based on PV module cell temperature of 25 C (77 F), which translates into an ambient temperature of ~ -10 C, or ~ 14 F. Since PV module voltage drops as cell temperature increases, modules operating in “normal” ambient temperatures deliver significantly lower voltage. A typical voltage coefficient of temperature is in the range between -0.4% / C and -0.5% / C.

Using the Evergreen 180 W module as a typical and convenient example, here are its STC specs:

Power: 180W
Voc: 32.6 V
Vmp: 25.9 V
Isc: 7.78 A
Imp: 6.95 A

And, here are its “Normal Operating Cell Temperature” (NOCT) Conditions (800 w/m^2, 20 C ambient) specs:

Power: 129 W (-28.3 %)
Voc: 29.8 V (-8.6 %)
Vmp: 23.3 V (-10 %)
Isc: 6.20 (-20.3 %)
Imp: 5.53 (-20.4 %)

The voltage reduction is primarily due to the higher ambient temperature. The current reduction (~ -20%) is primarily due to the reduced insolation (also -20%). So, as your ambient temperatures increase this spring and summer, expect for array voltage to suffer accordingly. This is normal behavior, and it’s not an indication of a problem with your charge controller, regardless of manufacturer or model.

Good luck with your experiments and tweaking, and I hope you’ll post additional observations and results. Additional entertaining reading and technical resources are available over at OutBack’s forum. See: www.outbackpower.com/forum

HTH,
Jim / crewzer

System2

Re: outback mx60 question

Found problem , panels tested perrfectly for VOC and ISC. however there are some small burn marks where the cells are soldered together. Lesson, if you are buying used panels, you need to test under load as well. Sellers will probably refund. thanks for all the help.