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davidpheteplace avatar image
davidpheteplace asked

400 Watt Panels only Charging 260W on MPPT 100/30

I was just testing a second suitcase I put together last week. I turned on the inverter and a small space heater on low to provide a load. I ran this test at 12:15 pm in full sun at 7500 ft altitude with no haze. I thought I would produce more watts, but something must be limiting it since I only got 260W running both 200W suitcases. I did note that the battery temperature was at 21 degrees F (using SmartSense), so maybe that is limiting the wattage the solar charger letting through. I let it run for a while and my SOC was 88%.

charge current limit
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Warwick Bruce Chapman avatar image Warwick Bruce Chapman commented ·

Are you sure that there was sufficient load to utilize everything the panel had to offer?

Drain your bank to 50% or put a kettle on the boil or something like that to ensure that the system is using every possible joule the panel can give it.

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Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

400Wp is the maximum you can get at perfect conditions.
You 284W are 71% of that and without knowing your installation of the panels I think that is pretty good.
You will never have 100%.

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Justin Cook avatar image
Justin Cook answered ·

@davidpheteplace, I'd suggest checking your panels again (particularly your connections, perhaps) because your panel voltage is super low at 16.29v (in fact, if it were just waking up, the MPPT wouldn't even start charging your battery with that voltage from the panels).

What's the VOC rating of your panels? I'd expect to see closer to ~19-20v from a parallel array in the conditions that you're describing; something seems amiss.

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davidpheteplace avatar image
davidpheteplace answered ·

@Justin Cook, The open voltage of one Renogy 200W solar suitcase is 21.2V. There are two connected in series/parallel. There is 25 feet of 6 gauge welding wire connecting the two suitcases to the MPPT 100/30 solar controller. The parallel connection in the cable are made with Ancor 309203 butt connectors (and I used a proper Greenlee crimper for all crimps). Can you see any issues with these components or connections. Should I run the diagnostics for each separate suitcase to compare the results (which may test if the series/parallel joiner cable is at fault)?

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Justin Cook avatar image Justin Cook ♦♦ commented ·

@davidpheteplace, when you say 25', do you mean that the suitcases are literally 25' away from the controller? If so, this might be part of the problem: 25' one-way = 50' round-trip, and your voltage drop over 6AWG wire at that distance is nearly 3% (calculating based on the ~20A @ ~16v from your screenshot).

I'm definitely surprised to see such a low voltage from the suitcases... the two panels in each suitcase must be parallel connected, not series'd. Have you tried -as another user suggested- connecting the two suitcases in series to get your voltage up? This would also help your voltage drop over that distance, as you'd be golden with 6AWG at 50' if you bumped the voltage up to ~32v and the amperage down to ~10A.

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JohnC avatar image
JohnC answered ·

Hi David.

I looked up those panels on the Renogy website, and the specs show just 183W rather than 200W. That would disappoint me straight off.

Your wires are overkill if anything, and provided no jointing issues, should be fine.

You could also try wiring the panels in series to see if that helps (higher V, lower A). Might help lengthen your solar day at dawn & dusk anyway.

Your mppt seems to be tracking the Vmpp ok, but it's lower than the spec sheet. Might be the low temp, but I've no experience there.


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davidpheteplace avatar image davidpheteplace commented ·

@JohnC. Hi john. I am curious where you are seeing 183W on Renogy for this suitcase? These are Eclipse 100W panels. For the suitcase, I only see 200W in the spec sheets on the web site.

I think I may have figured out part of the problem. When I started this test, the battery SOC was near 99%, so the battery voltage was over 12.6V. The solar charger reads the initial voltage to determine the absorption time. At 12.6V+, it reduces the absorption time by 1/6 to one hour. Maybe that is what is limiting the solar through-put to 284W at 16.29V??

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JohnC avatar image JohnC ♦ davidpheteplace commented ·

The W isn't stated directly, but if you multiply out the 'optimum' V and A they spec you get 183W. That's how it works, and normally makers simply show Vmp and Imp for those. Maybe they're fudging somehow, or a print error? But something's not right..

Your solar output won't be throttled by Vbat until Abs level is reached. In Bulk state the charger is giving it's all, unless you have a 'Battery Safe' mode checked, and it's limiting the rate of V rise. If you have that, try a simpler algorithm to test it.

Go by Justin's wire suggestions, he worked it out, while I just guessed..


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