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?

First idea is that there was a small load on the batteries, taking some of the solar amps. Loads come first and the batteries get what is left over if any. Compare the amps on the Trimetric (battery amps) with the amps showing on the controller (solar amps)Another thing to check is take the Isc of the panel out past the controller (put meter across the pos and neg wires from the panel) and compare with what the controller displays as amps. They should be the same except for a tiny loss on the wiring from panel to controller.If there is a bad connection or whatever making high R, that could reduce the amps getting to the controller and its output.I have a Solar 30 and it does a good job. Sometimes the set-screws for the wires to it get loose which you could check on yours.

BFL,Thanks for your reply. I have a 0.2 amp load on the batteries probably from the propane alarm. My 10 hour chart was showing the amps on the Trimetric (battery amps) with the amps showing on the controller (solar amps). I said they were the same, but some were off by 0.2 amps. I did the lsc test and it showed 4.2 amps as I reported. This was at noon on May 20 with a clear sky but maybe a bit of slight haze. So I think the panels are OK. But averaging 2.8 AHs over 10 hours was not good. I may try the panels on my older lead acid battery when it gets discharged. I'm using it as a trolling motor battery.I know about those screws on the Solar 30. I wonder what would happen if I briefly tried it without the controller?Steve

With no controller, voltage to the battery will go up and up, which means the BMS should cut off charging at its high limit. Possibly risky for LFPs, don't know much about that. Ihe higher voltage won't change the amps if the amps are at Isc If the Isc at the panel was 4 amps, then that's what you can get with that sky. You might have less light than it "looks" and just have to wait for better sunlight conditions.If the pigtails are in a connection box on the back of the panel, their connections can be checked. Some panels have their pigtails coming out you can't get at where they come from. The panel could also be dirty or shaded, but you will know that.

That's kind of what I thought regarding the sky. There were no clouds but some sort of high thin haze.

You can only get full rated output for an hour on either side of true noon, and only under perfectly clear sky and then only if the panels are perfectly aimed at the sun. Anything else will cut output slightly. Also, lithium iron phosphate batteries typically require the charge controller to output 14.4 to 14.6 volts peak to charge fully. This calls for reprogramming from the lead acid program that is the usual default.

Question about solar and my LiFePo4 batteries | Good Sam Community

27 Replies

Lwiddis
Explorer II
Jun 06, 2021
With panel prices these days, fill the roof!
Dusty_R
Explorer
Jun 06, 2021
Michigan ranks 47th of the 48 continental states in available sunshine.
naturist
Nomad
Jun 06, 2021
You can only get full rated output for an hour on either side of true noon, and only under perfectly clear sky and then only if the panels are perfectly aimed at the sun. Anything else will cut output slightly. Also, lithium iron phosphate batteries typically require the charge controller to output 14.4 to 14.6 volts peak to charge fully. This calls for reprogramming from the lead acid program that is the usual default.
steveh27
Explorer
Jun 06, 2021
That's kind of what I thought regarding the sky. There were no clouds but some sort of high thin haze.
BFL13
Explorer II
Jun 06, 2021
With no controller, voltage to the battery will go up and up, which means the BMS should cut off charging at its high limit. Possibly risky for LFPs, don't know much about that. Ihe higher voltage won't change the amps if the amps are at Isc

If the Isc at the panel was 4 amps, then that's what you can get with that sky. You might have less light than it "looks" and just have to wait for better sunlight conditions.

If the pigtails are in a connection box on the back of the panel, their connections can be checked. Some panels have their pigtails coming out you can't get at where they come from. The panel could also be dirty or shaded, but you will know that.
steveh27
Explorer
Jun 06, 2021
BFL,

Thanks for your reply. I have a 0.2 amp load on the batteries probably from the propane alarm. My 10 hour chart was showing the amps on the Trimetric (battery amps) with the amps showing on the controller (solar amps). I said they were the same, but some were off by 0.2 amps. I did the lsc test and it showed 4.2 amps as I reported. This was at noon on May 20 with a clear sky but maybe a bit of slight haze. So I think the panels are OK. But averaging 2.8 AHs over 10 hours was not good. I may try the panels on my older lead acid battery when it gets discharged. I'm using it as a trolling motor battery.

I know about those screws on the Solar 30. I wonder what would happen if I briefly tried it without the controller?

Steve
BFL13
Explorer II
Jun 06, 2021
First idea is that there was a small load on the batteries, taking some of the solar amps. Loads come first and the batteries get what is left over if any. Compare the amps on the Trimetric (battery amps) with the amps showing on the controller (solar amps)

Another thing to check is take the Isc of the panel out past the controller (put meter across the pos and neg wires from the panel) and compare with what the controller displays as amps. They should be the same except for a tiny loss on the wiring from panel to controller.

If there is a bad connection or whatever making high R, that could reduce the amps getting to the controller and its output.

I have a Solar 30 and it does a good job. Sometimes the set-screws for the wires to it get loose which you could check on yours.

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Question about solar and my LiFePo4 batteries

27 Replies

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