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Old 02-06-2016, 03:43 PM   #29
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I just found a couple of references which say that panels should be no more than 10% different in Vmp. With an MPPT controller, max efficiency will be affected, as it will sense a voltage between the two panel voltages. Some controllers work better than others with the variation of Vmp.
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Old 02-06-2016, 03:48 PM   #30
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I just found a couple of references which say that panels should be no more than 10% different in Vmp. With an MPPT controller, max efficiency will be affected, as it will sense a voltage between the two panel voltages. Some controllers work better than others with the variation of Vmp.
Kind'a what I said….no? I still don't go for the 10% but as with anything else….YMMV!!
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Old 02-06-2016, 04:20 PM   #31
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More power! Been projecting (sp) today. Swapped the controllers out and added the 75 watt to the suit case panels. With full early afternoon sun output was around 9.5 Amps at 14 volts. Up from 6 amp with the Renogy panels only. Not quite as much as I hoped but a nice improvement at zero cost. What is next on the agenda? Not sure. As soon as I win the lottery I plan on getting a full system installed. Until that day happens I think what I have will work just fine for my limited needs. The local power company has nothing to fear from me.
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Old 02-06-2016, 05:07 PM   #32
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Kind'a what I said….no? I still don't go for the 10% but as with anything else….YMMV!!
Yes, I was just struggling with the .2V statement. I'd wager that two panels from the same manufacturer and model might vary that much, due to build variation.

I'm going to try with mine and see. I have one at 17.9 Vmp and one at 18.9 Vmp. I think I'll go ahead and install a marine cutoff switch on the rooftop one...if for no other reason than battery removal, service etc. Then, If I do see an issue when using the suitcase, while the trailer is in the forest, I can switch the rooftop off and just plug in the suitcase.
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Old 02-06-2016, 05:20 PM   #33
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Brings up another issue PWM vs MPPT. Bogart Engineering has this explanation for PWM vs MPPT.

http://bogartengineering.com/support/faq

With my projected project of 2 100w 12v panels on the roof which would be used most of the time then adding my 200 Watt (2 100w 12v panel) Zamp suitcase for times when the roof is partially shaded, I would think PWM controller would be sufficient and more cost effective. Trimetric 2030 monitor and paired with the SC 2030.

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Old 02-06-2016, 05:59 PM   #34
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Brings up another issue PWM vs MPPT. Bogart Engineering has this explanation for PWM vs MPPT.

http://bogartengineering.com/support/faq

With my projected project of 2 100w 12v panels on the roof which would be used most of the time then adding my 200 Watt (2 100w 12v panel) Zamp suitcase for times when the roof is partially shaded, I would think PWM controller would be sufficient and more cost effective. Trimetric 2030 monitor and paired with the SC 2030.

Kelvin
I've read that, and he pretty much accuses Blue Sky of lying in their 30% claims, yet I see that all the time from mine. Also his claims about ideal situations. Mhem. Reads like counter-marketing to me to explain away short comings.
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Old 02-06-2016, 07:17 PM   #35
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I don't really understand where Bogart is coming from on this. Is he then the ONLY ONE in the entire solar industry that feels this way.

Look at any quality MPPT solar charge controller on the market like:
• Blue Sky
• Morningstar
• Magnum
• Victron
• Outback
• Midnight Solar

They all are not blowing smoke, as Bogart suggests! I think he has been hanging around with Angry Bob (sorry, that's Solar Bob now!).
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Old 02-06-2016, 07:29 PM   #36
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Sounds like Bogart is just trying to push the product brands he sells. Normal marketing practice, every retailer does it.
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Old 02-06-2016, 09:37 PM   #37
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Rich (dznf0g) pretty much explained all it. Friend here has a Renogy suitcase, same one you have with a 300 watt Renogy kit on the roof. He kept finding that the roof controller was still charging but the suitcase kept reading as full. Basically the systems were mismatched.

So I helped him bypass the PWM on the back of the suitcase, and we wired it with a SAE plug into the one controller for the roof solar. Works better that way.
What kind of controller for his roof does he have?
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Old 02-06-2016, 09:55 PM   #38
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What kind of controller for his roof does he have?
Whatever that 40amp one is that comes with the Renogy kit.
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Old 02-07-2016, 08:46 AM   #39
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When I bought my small system the gentleman told me that for what I was doing the PVM would be just fine that loss would be negligible. I already knew about the difference but followed his advice. At optimum power have a 3.3V loss on my system using the PVM or just under 20% or about 63 watts in a perfect scenario. What the advice told me is that you never get that perfect anyway so it is, in actuality less of a loss. Here is a good non technical description of PWM versus MPPT and what the difference is really all about:

https://www.victronenergy.com/blog/2...r-pwm-or-mppt/

It is the same principle the electric company uses to step down electricity to homes. I do understand that with a MPPT it is advantageous to go with higher voltage- 24V panels and in doing so the wiring size requirement is less AND you get more power as it has that extra voltage to step down to AMPS per se. It just depends on how much you want to spend.
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Old 02-07-2016, 09:24 AM   #40
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Just read two more write-ups including the Bogart one above.

Question, when WOULD a PWM controller be a better choice?

It is obvious that the companies make them and sell em. The write-ups say "for smaller systems" so what is smaller? To me, when looking at the stories on the websites where they are hooking up 10 panels etc. That is big. So, is a three panel system small? Just sayin.
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Old 02-07-2016, 09:28 AM   #41
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To me a big system is what you see on houses and industrial uses. Small systems are on our trailers.
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Old 02-07-2016, 10:15 AM   #42
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To me a big system is what you see on houses and industrial uses. Small systems are on our trailers.
I would think wattage would be a better factor to determining small vs big.

Since we left Colorado we've mostly been camping in perfect conditions. You get that a lot on the South West. So I wouldn't discount it as being a rare occurrence.
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