I'm building up a small system, and was doing some preliminary testing and getting some strange results. Important stats:
- 16S1P lithium iron phosphate with BMS. Charge level is about 50%. This pack is known to be functional and is in good balance (<0.05 V maximum voltage difference). 200 Ah capacity.
- SmartSolar MPPT 150 / 85 MC4 VE, rated for 48V packs (says so on the label affixed to the unit). Sorry I don't have a serial number at the moment but can get one if needed.
- I have a set of identical solar panels, all 100W nominal 12 volt panels, Voc measures about 21-23 volts on all panels in full noon sun. All appear to be functioning.
- I understand that the charge controller needs at least 5V higher solar voltage than the battery voltage.
I was doing some preliminary testing with just a few solar panels before ramping up any capacity, mostly just to make sure the MPPT was working, and I saw some strange results. I'm sure I'm just missing something obvious.
I wired 3 panels in series and measured a voltage in full sun of around 66 V. Plugged that into the MPPT and it worked perfectly. After only a few seconds it started putting 245 W into the battery pack, and I confirmed charge current with my clamp meter as well as the battery pack's BMS. So far so good, and not bad considering I'm not that far above the battery pack voltage.
The MPPT controller is rated for up to 150 V open circuit, so I think I should be good to add a 4th panel in series. Which should bring the panel voltage up into the 88-90 V range. Well within the 150 V rating. I added a 4th panel, and the MPPT reported the expected voltage (confirmed with a voltmeter just to be safe). But after adding a 4th panel, I get a charge of 1-5 W, even after waiting around 10 minutes in full sun. Clearly the charge controller isn't happy, but I'm nowhere near the capacity in either voltage or current (unless I misread something or looked at the wrong spec sheet, totally possible!).
I initially assumed a possible bad panel or connector, but I have a bunch of the same model panel, and tried swapping out a few along with checking all connections. All good, plus the MPPT is showing expected panel voltage. I used the built-in LiFePo4 settings in the MPPT configuration (settable via the DIP switch on the unit), which seem to work fine with the 3 panels.
Like I said, I'm sure it's something dumb, but what am I missing? Thanks!
