Solar panel controller or not

[Burgeogull]

I got a couple questions:

1. I have 2 12volt batteries on my trailer. One line of panels is a 100 watt and 2 20 watts all connected with mc4 connectors. They go to a 10 amp controller, after the controller it's about 4 feet to the batteries with a 15 amp fuse on the power line. Is there a need for a controller? Is there a need for that fuse? Should the fuse be smaller.

2. Another 2 40 watt panels for a total of 80 watts, wires spliced and soldered and go to a 7 amp controller. No fuse going the next 5 feet to the same two batteries.

Is there anything I can or should do to tweak this a bit?




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[captnrick3]

Originally Posted by Burgeogull

I got a couple questions:

1. I have 2 12volt batteries on my trailer. One line of panels is a 100 watt and 2 20 watts all connected with mc4 connectors. They go to a 10 amp controller, after the controller it's about 4 feet to the batteries with a 15 amp fuse on the power line. Is there a need for a controller? Is there a need for that fuse? Should the fuse be smaller.

2. Another 2 40 watt panels for a total of 80 watts, wires spliced and soldered and go to a 7 amp controller. No fuse going the next 5 feet to the same two batteries.

Is there anything I can or should do to tweak this a bit?

Just my two cents worth




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You would be way ahead by replacing the batteries with two 6's rather than the two 12's. Will get far better deep cycle power. The controller is necessary since I assume your panels are producing about 18V, they will boil the batteries dry quickly. Dis similar panels are not ideal, but verify that they are all the same output voltage. If any are lower than some others, the lower voltage panels will not produce much if anything at all. If they are all the same, should work OK. The fuse at the batteries is always necessary, even a 30 amp. would be fine just to prevent a fire in case of a short. Use no less than 10 guage wire and you should be good to go.

If your batteries are new and you want to use them, they will work, just be aware that they will deplete fairly quickly and keep in mind the 6's when replacement time comes around.

[Cypressloser]

Captnrick is correct, without charge controller you will cook your batteries in no time.

[Burgeogull]

Ok thanks guys. I was figuring as much but wanted a couple of opinions.


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[glen1971]

I'd consider adding a second controller, so that your different sized panels are on different controllers.. Individually fuse each one..

[RPAspey]

Problem you have is different panels. If you had similar panels, and a controller to handle the current, then you'd need nothing else.

Since you have different panels, you should have different controllers. BUT, unless the controllers feed different batteries (isolated from each other) they will "fight" each other thus the total output may be LESS than the expected sum of both. You see, if one controller has a higher output voltage, that one will charge and the other may go idle.

Bottom line, charge the batteries separately, each battery with its own CC.

[captnrick3]

Might be more cost effective just to get panels that are all alike, also far less complicated. I had a similar issue on a 5th wheel some years back but didn't realize how to correct it at the time. I had enough equipment in my battery bay it looked like a spaceship but still only had marginal solar output. We have all learned quite a bit since those early days of solar power production.

[fr1rd831]

You can mix panels just fine if the specs are right

If you are mixing/matching panels, you want to match Vmp-panels to within 10% or better (the farther away from each other they are, the less efficient the overall power generation will be).

For adding panels in series, you want to match Imp-panel to within 10% of rated current or better.

If you can post the specs on each panel, voltages and amperage to see what your options are. If all panels are within 10% you could get a larger and better controller that will simplify things a little. If you get an mppt type controller you will get more out of your panels. I definitely agree with replacing the 12 volt batteries for 2x6 volt batteries.

[fr1rd831]

Forgot to mention, you should always fuse when combining panels