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Old 02-04-2015, 07:50 AM   #1
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Solar Charge Controller Sizing

I have a Renogy 100w suitcase portable system with a 10 amp PMW controller fastened to the back of the panel. I am thinking of moving the controller near the battery bank and using longer cable from the panels to the controller so I will have more flexibility in placement. The panels put out 6.17 amps. If I were to get a second 100w suitcase set without controller and combine the panels, what are the implications of using the 10a controller versus getting a 30 amp controller?
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Old 02-04-2015, 08:57 AM   #2
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If and when your 10A controller gets to the 10A max from the two panels it will die and you will need to buy the 30A controller. I would not think that any damage will occur to the panels unless you can not replace the controller because it is as you said, 'built in'. Be sure to use cable heavy enough to support the combined 10-12 amps combined current of the two panels for the new longer length you spoke of. Never skimp on the cable as you just loose too much of your power. I would try using the 10A controller unless it is enclosed in the rig and could cause a fire hazard if/when it dies from the over current if the two panels kill it. Note that the second panel needs to closely match the original panel's output voltage.

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Originally Posted by SkiSmuggs View Post
I have a Renogy 100w suitcase portable system with a 10 amp PMW controller fastened to the back of the panel. I am thinking of moving the controller near the battery bank and using longer cable from the panels to the controller so I will have more flexibility in placement. The panels put out 6.17 amps. If I were to get a second 100w suitcase set without controller and combine the panels, what are the implications of using the 10a controller versus getting a 30 amp controller?
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Old 02-04-2015, 09:49 AM   #3
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The 6.17a is measured or in the spec? The peak spec I would think. Which is when optimally positioned with optimal sun. Do you place them as such, have them laid flat, or other? This impacts the actual output of the panel.

As for the controller does it have any headroom in the 10a rating or capability for handling over current?

These factors impact whether you are actually exceeding, or able to exceed, the 10a rating of the controller.
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Old 02-04-2015, 10:18 AM   #4
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I was just thinking ahead as I haven't done anything other than purchase the 100W suitcase last summer, but do plan to put the or a controller in the RV close to the battery bank so I can use longer cable with minimal loss. I could just do it with the 10a for now, and if/when I get a matching set of panels, get a 30a to replace the 10a. I was just exploring whether I need to do that and it sounds as though I should. Or I could just get a 30a controller now so I only have to do the installation once.
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Old 02-04-2015, 07:40 PM   #5
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If and when your 10A controller gets to the 10A max from the two panels it will die...
oh really? where did you get that? I heard numerous times there is no such a thing that the panel capacity is too big.
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Old 02-04-2015, 09:55 PM   #6
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Ok, where did you hear it, is it printed somewhere?
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Old 02-05-2015, 12:39 PM   #7
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Ok, where did you hear it, is it printed somewhere?
i read a number of posts on this topic, and i personally talked with a solar pro...
yes, here is the one printed right here

Such a thing as too much solar power?
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Old 02-05-2015, 01:20 PM   #8
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I did read about the Morningstar MPPT controller, that stated you could input more then the max watts, but with no gain in max output.

That does not mean all controllers will handle any amount of input. And if they did, they would still limit the output to their rated amps, or burn up.

I designed a 675 watts solar system, why would I run them thru a lower amp output controller, then they are capable of producing?

Just me thinking
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Old 02-05-2015, 02:13 PM   #9
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Quote:
Originally Posted by twinboat View Post
I did read about the Morningstar MPPT controller, that stated you could input more then the max watts, but with no gain in max output.

That does not mean all controllers will handle any amount of input. And if they did, they would still limit the output to their rated amps, or burn up.

I designed a 675 watts solar system, why would I run them thru a lower amp output controller, then they are capable of producing?

Just me thinking

If the 675w system is spec'ed at max 675w and installed such that the max is not realized (for example laid flat rather than tilted on a Motorhome roof) a controller capable of handling the full 675w is not a requirement.
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Old 02-05-2015, 02:16 PM   #10
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If you have not had much real time usage with the suitcase SP. You might want to use it in a portable method for a period of time.

I've seen a few people with portable, easy to setup and pack away SP's, retain these for usage while in the shade of trees. You might consider adding a few SP's that are permanently mounted, and add a controller to feed these down to the battery. Then retain the suitcase SP for times when your in the shade.

When buying components (cables, controllers, etc.) I'm in the camp that believes in a reasonable amount of headroom in design, for the addition of more SP's if ever desired. Figure out what you need to support what you're installing, and then bump up to allow for more future capacity.

Best of luck to you on whatever way you go!
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Old 02-05-2015, 03:18 PM   #11
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Quote:
Originally Posted by twinboat View Post
I did read about the Morningstar MPPT controller, that stated you could input more then the max watts, but with no gain in max output.

That does not mean all controllers will handle any amount of input. And if they did, they would still limit the output to their rated amps, or burn up.

I designed a 675 watts solar system, why would I run them thru a lower amp output controller, then they are capable of producing?

Just me thinking
i was not against the statement of limiting output nor why people would do it knowing that wouldn't generate gain... but you never know, for I was one at a time that I used a smaller capacity controller I was having before I bought a bigger one. the post stated "it will die", apparently that is not true and can not be backed up by reality. we surely don't want to leave a misleading info on an open board which could be read by new comers for generations.

happy trails...
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Old 02-06-2015, 09:37 AM   #12
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Most of the higher end controllers protect themselves from over input. At this level of controller this might not be the case. The risk is burning up the existing controller. A phone call to the manufacturer asking what if, would be a good solution.

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