Hi, guys!
I bought a 1500UPG on ebay (5.0 CPU and 2.6 LCD firmware). It has a problem in that it ceases production for no apparent reason. Simply reduces output to 0-50 watts, allowing DC input voltage to rise to about 60 VDC. . Status LED steady green, no warning or error messages. A complete reset of the inverter begins production again, at full output, lasting anywhere from 5 minutes to all day. My solar array is ten Sanyo 48 volt panels in parallel, 3 years old, from my off-grid system. Work great, have seen them produce 2200 watts days ago. To begin a troubleshooting process, I connected the input of the inverter across my 48 volt battery bank instead of directly to the array. This makes the inverter work at 100% output, all day (or until clouds cover the array), never fails. The only anomaly I can find is that the DC input voltage displayed on the LCD is 1-8 volts higher than that measured with two independent DVMs, one made by LG, the S. Korean manufacturer. Could this indicate the inverter is not sensing the correct DC input voltage? The displayed input voltage fluctuates +/- several volts when connected to the solar array, only fluctuates +/- 2 volts when connected to the battery. Noise on the input line? Is there a calibration pot for the LCD? The problem is not a heat issue, not a grounding issue. Any ideas? Thanks!

I'd check the wiring , you have the combiner, the breakers and then into the power board. if one is lose, the CPU would see the voltage dip and back off on the loading ... I'd take a screwdriver to every single screw. Could also be a worn DC breaker.

Also, check the the ribbon cable from the power board to the CPU card is seated

Hi, Solar Guppy! Thanks for the quick reply. I checked the power and ribbon cable connections. Both fine. My 1500 is connected to either the solar array or the battery bank (48v 200 Ah) via Anderson Power 120A (blue) connectors. I think the faulty connection theory can be ruled out, as the inverter performs flawlessly when connected directly to the battery bank (the battery bank is being charged thru a Xantrex C40 charge controller at this point). Exact same DC input path from the Anderson Power input connector thru the combiner board, thru the breakers to the input of the Power Board. The input voltage reading bothers me. Today, after checking the DC input connections, before the inverter went back online (300 sec delay period), I saw the LCD input voltage reading +12 volts higher than the DVM reading (67 VDC versus 55 VDC). If the CPU sees this disparity under high-illumination of the solar array, when the true DC input voltage can go as high as the manufacturer's Voc of 69 VDC (or even higher, theoretically), the CPU might "think" it is seeing 81 VDC input, which is pretty close to the high end sunsweep range of 85 volts. What happens when the DC input voltage is high, but still below the "absolute max" input voltage of 125 VDC? Does the inverter reduce output? Display an error message? Go offline? Is there a way to confirm that the jumpers on the CPU board are correct? By the way, I'm an EE. Thanks, Barry thudman149

Did you tighten down all the wire connections, there are more than a dozen inside the Suntie? Yes the reading being off will cause the unit not to track or perform correctly. To me it sounds like a negative wire is lose, at the DC breaker or connections to the power board. Don't be dismissive, torque all the connections/connectors, its not uncommon for Aluminum connectors to have this issue over time.

If it reading wrong that's the issue. U2A on the power board is the buffer ( LM358 ).. R8 ( 309k )/R30 (12.6K ) is the divider network from the PV input the output of the opamp goes to pin 12 of the CPU connector.

You can verify that the Vsense on the CPU card itself, also check that JP2 is installed ( CPU card ), this connects the Digital and Analog grounds on the CPU card, if that was removed, would cause some odd issues

Running off battery's could work as to the Suntie it looks like the VI curve is a cliff, one side unlimited power, the other none ... very different than working off PV where it is a much wider range and the need for accurate PV voltage to function, so problem could always be resent to perform differently.

Hi, Mr. Solar Guppy! Once again, thanks for the quick reply. I really did tighten all the connections, I even remanufactured the cable that feeds DC to the 1500. Seems to me than if there were a bad connection or flaky breaker in the DC input path, there would be a power output reduction when operating on battery as well as when drawing current out of solar panels directly. The 1500 works perfectly on battery, even down to 47.5 VDC before beginning to reduce output below 1500 watts. Since the components on the CPU card are easier to get to than R8/R30, I looked at the CPU card first. JP2 is jumpered together with soldered wire, which is then fed thru a disc ceramic (looks like a 0.22 uF, but numbers are hard to read) and then grounded to the aluminum box with one of the screws which hold the CPU board bracket to the aluminum box. JP4 is open. JP3 is open. JP1 may be a problem; it is open, but the pin farthest away from the DB9 connector is connected via an insulated wire to Pins 1 and 2 of a LP2951 voltage regulator. This regulator is on top of U4. Pins 1 and 2 of the regulator are the output and sense. Pin 3 (shutdown) and pin 5 (not-error) are cut off and not used. But Pin 4 is the GROUND, and it is not connected, even though it looks like it IS connected (somebody hit it with solder). If this device is truly intended to be used as a regulator, it won't work with the ground disconnected. The other pins of the LP2951 seem normal. If you can tell me which pin of the PIC to check for Vsense, I can verify continuity on the CPU board from the J2 connector. Thanks, Barry, thudman149

You may have found your problem, the rework added a linear regulator to be a dedicated power for the PIC micro, wire to J1 is correct but the part need ground for sure! the Output needs to be 5 volts rock solid, if it varying, that would explain what your seeing as the ADC of the PIC is off the regulator voltage.

So with care, get pin 4 grounded ( piggy backed to the chips pin #4 underneath as I recall ) and that should take of of your issue

Hi, Mr. Solar Guppy! I connected the ground on the regulator and reinstalled the CPU board. Status LED steady green, but power output 45 watts. The LCD display now has new items displayed as well as previous items: Pmax, DC Power, AC Power, and "Variable Power Mode Enabled". Never seen these before. The DC input voltage displayed on the LCD is now within 2 volts of the independent DVM and is stable (about 58-60 VDC). The mppt voltage is stuck at around 48 VDC and does not change. Any ideas? Thanks, Barry, thudman149

Sounds Like you enabled the test mode by installing/ moving the Jumper at JP3?, looks like if pins #1 & #2 have the jumper across it that's how it is enabled, 3 to 4 is the default I seem to recal. Its been 7 years since I looked at this stuff and don't have a CPU card to look at but the screen you describe enabled a manual mode ... adjusting the pot changes either the mppt or power limit but I can't remember which

Hi, Mr. Solar Guppy--I did not change any jumpers. JP3 seems to me to be "open". As I look at JP3 from the component side of the board, it seems that IF the jumper is installed on one pair of pins, called "Man Sweep", it does "something" and IF the jumper is installed on the other pair of pins, called "New 929" it does "something else". The jumper is (and always has been since I have owned the inverter), installed across the pair of pins closest to the board. I guess this constitutes an "open", but maybe I am wrong. I really appreciate your digging back into your memory banks to help with this. Thanks, Barry, thudman149

Make Sure "Man Sweep" is not connected ( I don't know which direction this means on the jumper ), also check the linear regulator is putting out 5 volts. On the Man Sweep pins, pin one is gnd and pin 2 should be ~4 volts , this goes to U6 pin #5. To enable this feature, it would be at gnd ....

JP3 should be just ground as pins #1 & #3 are both ground leaving #2 & #4 open, if it was connecting #2 and #4 that might cause what you are seeing, just pull the jumper as its not needed for normal operation