Question about solar and my LiFePo4 batteries

[steveh27]

In my Class B Xplorer 230XL I have two 100AH LiFePo4 batteries giving me 200 AHs. While I bought them in June 2019 I have not used them until this spring due to getting multiple myeloma, a blood cancer, which ate my hip requiring a partial hip transplant and a stem cell transplant and chemo. In remission now, but it will return.

I have used my RV since mid April without the solar. WHen plugged in my PD4635 worked well and when driving the alternator would charge until my Trimetric battery meter showed 14.4 volts and then charging would shut down. All good. This past week I've tried using my portable 120 watt solar suitcase. I've had this since 2012 and it has worked OK with my previous 105AH lead acid battery. It is rated at 6.67 amps and 21.6 OCV. I did replace the cheap controller with a Solar 30 which seems good. I have used it a lot when I boondocked in FLA during Feb and Mar. I know it is rare to get the max amps but sometimes I did get 6 amps, usually over 5 amps. I've tried it twice recently and only once got 4 amps. I tested it and got 21.33 volts OCV but only 4.2 amps. This was at noon on May 20 with a clear sky but maybe a bit of slight haze.

Yesterday I tried it again for 10 hours. It was a clear sky with some infrequent slight haze. I took readings every hour from the controller and the Trimetric. When starting the Trimetric showed 71% SOC and I got the highest amp input of 4.2 amps which was never reached again. The next 2 hours it was 3.7 amps and then for the next 2 hours was 3-3.6 amps. After that it was under 3 amps. The total collected for the 10 hours was 28 amps, a 2.8 AH average - not good. When I quit the Trimetric showed 86% SOC. The controller and Trimetric usually showed the same AH inputs. The voltage at the controller ranged from 14.6 to 14.2 V. The Trimetric ranged from 13.4 to 13.5 V.

Any ideas as to why I was not able to get closer to the rated 6.67 amps?

[steveh27]

It is the controller connection. The last time I had it out I wiggled the wires going in and the amps jumped way up to normal then back down.

[StirCrazy]

the only way your going to get better is by moving to a MPPT. your figting tow things here a 12V pannel and a PWM controler. if you take your panel and devide it by 17V that will give you your potential max output with a PWM controler on a 12V pannel as they are in efficent in the conversion. you can improve that a bit with a MPPT controler, but realy from a 120V suitcase pannel there are so many other factors that will play in. shading, wire size and lenght, conection to the battery and so on..

[wa8yxm]

I had a bit of problem with those connections on my controller too. Finally got 'em right.

[steveh27]

I think the problem is in the hookups to the Solar 30 controller. I may not have the wires in correctly. I found one wire not in properly. It is weird how to use those screws.

[BFL13]

Good news. Thanks for the follow-up report.

[steveh27]

I washed the panels and tested the LSC amps again, and got 6.3 amps, so the panels are good. I just bought another 60 watt panel and it's lsc is 3.3 amps. I am going to rig these up to use together with the one controller. It will be portable and collapsible.

[steveh27]

wa8yxm wrote:
120 watts divided by 12 volts is 10 amps
you hit six (60%) and that's after factoring in losses in the wire and the controller.

I was always told figure half.. (50%) is good.

It is rated at 6.67 amps. The VOC tested at 20 volts plus, it is rated at 21.6 volts.

[wa8yxm]

120 watts divided by 12 volts is 10 amps
you hit six (60%) and that's after factoring in losses in the wire and the controller.

I was always told figure half.. (50%) is good.

[Almot]

If you mean junction box of the panel - that black thing attached at the back - I would guess that if voltages are OK, the panels are fine too. The problem is likely in the connections outside of that junction box. But... I remember Mex bitching about corrosion in the panel boxes in his climate.

[steveh27]

Almot wrote:
Maybe one of the panels is dying - 120W solar suitcase consists of 2*60W in parallel. Or there is a poor connection somewhere. Measure the current inline for either panel, directly on the panel lead, and then again on the output lead of the entire 120W array - before the controller. Easier to measure with clamp-on DC meter but with some care possible to do with a regular meter.

I am thinking of taking apart the junction boxes, then checking each panel separately. But the voltage did check out as rated.

[Almot]

Maybe one of the panels is dying - 120W solar suitcase consists of 2*60W in parallel. Or there is a poor connection somewhere. Measure the current inline for either panel, directly on the panel lead, and then again on the output lead of the entire 120W array - before the controller. Easier to measure with clamp-on DC meter but with some care possible to do with a regular meter.

[BFL13]

If panel Isc is above 1.8 by a bunch, that display amps would be a problem. You could check panel direct and put your meter in line with one of the leads set to reading amps and check those amps vs Isc at the time. (As long as you don't expect 10 amps to blow the meter!)

If the lead-acid batt is a flooded type, it would be safe to let the voltage climb, but even an AGM starting at 12.4 should be ok long enough to take the amps readings.

[steveh27]

I just hooked up my panels to a lead acid battery which had 12.4 volts. I am only getting 1.8 amps at 1 pm on a pretty bright day.

I checked the Solar 30 controller setting and the PV off is set for 14.8 volts.

[steveh27]

BFL,

That is quite an education, thanks.