I’m hoping you can help me with this, or at lest point me in the right direction. I have a motorhome that I’m going to add solar panels to. I have 12 100ah gel cell batteries. These are alpha cell 195 gxl batteries, I got them for free, so that is why I am using them. I know that you want to put a Slower charge on gel cell batteries, so the question is do I want to go with a 40 amp charge controller and 600-900 watts of solar, but will I not be able to utilize all of that charging/wattage coming from the solar panels? The controller I have been planning on is the Tracer 4215BN, but I’m just starting to wonder if that is more than I will need.

Check to see if that charge controller has a setting for Gel batteries.

PAGE 15 HEREhttps://www.epsolarpv.com/upload/cert/file/2003/Tracer-BN-SMS-EL-V1.2.pdf

1st of all, do you know the difference tween gell and AGM ?1st thing to do is make sure you are dealing w/ gell and not AGM

You will need a larger MPPT controller for 600-900 watts, around 60-90 amps.

Okay, so the Controller works with Gel Cells. I was wondering if having 600-900 watts of solar would excessive if the charging could never utilize that much power, but thinking of it now, that should help as the sun is rising or setting and each panel is barely coming into operation right? if I have 1 100 watt panel in low light, I would be getting a few watts out of it, but if I have 9 panels with low light, I may get closer to 100 watts out of them altogether. Is my logic correct here?

What solar panels, and what charge controller do I need?

pianotuna
Nomad III
Apr 14, 2020
Check to see if that charge controller has a setting for Gel batteries.
lawrosa
Explorer
Apr 14, 2020
PAGE 15 HERE

https://www.epsolarpv.com/upload/cert/file/2003/Tracer-BN-SMS-EL-V1.2.pdf
RJsfishin
Explorer
Apr 14, 2020
1st of all, do you know the difference tween gell and AGM ?
1st thing to do is make sure you are dealing w/ gell and not AGM
ppine
Explorer II
Apr 14, 2020
You will need a larger MPPT controller for 600-900 watts, around 60-90 amps.
Kd7vea
Explorer
Apr 14, 2020
Okay, so the Controller works with Gel Cells. I was wondering if having 600-900 watts of solar would excessive if the charging could never utilize that much power, but thinking of it now, that should help as the sun is rising or setting and each panel is barely coming into operation right? if I have 1 100 watt panel in low light, I would be getting a few watts out of it, but if I have 9 panels with low light, I may get closer to 100 watts out of them altogether. Is my logic correct here?
CA_Traveler
Explorer III
Apr 14, 2020
For flat panel estimates I use 67% of the panel watts. Most of a clear summer day will be under 40A. At noonish on a clear summer day the controller will limit you to 40A. Maximum battery charging amps (assuming no house loads) is 40/number of batteries.
pianotuna
Nomad III
Apr 14, 2020
No one ever worried about having too much solar.
ppine
Explorer II
Apr 14, 2020
pianotuna wrote:
No one ever worried about having too much solar.

You can if your controller can not handle the amperage.
Kd7vea
Explorer
Apr 14, 2020
pianotuna Trust me, I'm not worried about having too much solar, I'm worried about having plenty of solar, but the batteries not being able to take all of the charge that the panels are capable of producing. My thought is why produce 10kw of solar energy if the charge controller can only use 1kw to charge the batteries. I would love to run a lithium battery bank, but I got 12 good Gel cells for free, so I figured I would try them out, but I know that the Gell Batteries have to take a slower charge. Also, we purchased our motorhome for $3000, and have sunk another $4000 into getting it put back together inside, so I dont want to waste money where it wouldnt benifit us. As normal, everything we have done to get this thing ready to use has cost 2 times what we initially planned. Welcome to the joys of owning an RV!
red31
Explorer
Apr 14, 2020
ya need to check your gel's specs, I see max of 30A/100ah in one brand's spec. 3 or 4A /100ah is not much.