Salvaged/gifted setup

[SteveinFLA]

I’m trying to help a friend get started with some stuff she was gifted. The guy she got it from supposedly has some “documentation” he sent her that I haven’t seen. According to her, he had these 2 panels (pictures of the labels included in attachment) hooked up to a “$10 box he got from Amazon” right to the inverter (salvaged from some police surveillance van) and it “worked fine”. She did not get the “$10 box” along with the setup, so I think we’re looking for a charge controller. I just wanted to get one that would work with these 2 panels, which seem like they are not matched.
Sorry the pictures are sideways.
What’s the important info to know about sizing the charge controller? The ones I have seen on Amazon are kind of vague about max input etc.

 

[Rednecktek]

You're right, those panels aren't very well matched. If you put them together you should still see somewhere in the 500w range total though. With the voltages you'll need to get an MPPT controller.

First question is what's her nominal system voltage? If it's 12v you'll need either a 60a unit or 2x 30a units. Going for 2x 30a MPPT's will let you maximize the output of the panels but adds a little more complication.

If it's a 24v system you can do a single 40a just fine and take the hit, or a pair of 20a MPPT controllers.

If you decide to go single controller make sure the unit has a Max PV Input of at least 100v so you can go series or parallel.

Someone should be along shortly to double check the math and tell you what you should be able to get out of those panels in series or parallel. As far off as the voltages and amperages are, I'd highly recommend dual MPPT's.

 

[MichaelK]

Here is a strategy that might work for you. Both the amperages and the voltages of these panels are too widely divergent for them to be used either in parallel or serially with one single controller. As RNT describes, buying two controllers will work, but a second option is to buy a second panel that brings the voltages to within 5% of each other.

The difference between the two panels is 54.7V - 34.1V = 20.6. So, if you wire a second 20V panel in series with your 335W panel you will match voltages closely. The problem with panels in series though is that amperages need to match closely. If they do not, the net amperage will be only that of the panel in the string with the lowest amperage.

But, here is an example of a 200W panel that fits these parameters fairly well. If you wired this 200W Renogy panel in series with your 335W panel you would get 34.1V + 22.6V = 56.7V. That is only 3.6% difference, well within the 5% limit. The amperage of this new panel is 8.85A, which is only 0.95A different.

So, if you made the series string of the 335W panel with the 200W panel, and then put that in parallel with your 305W panel, you'd get about 8.85A + 5.58A = 14.43A flowing into the controller at ~ 55.7V (not exact).

An MPPT controller would convert the high raw solar voltage down to battery charging voltage. For a 12V battery, that would be 64A, or 32A into a 24V battery. Expect that to be 54A or 27A respectively in the real-world. So for 12V, you would need at least a 60-80A controller, such as Epever's Tracer 6415AN or 8415AN, or the cheaper Tracer 4210AN if you went with a 24V system.

So now, what you would need to decide is whether you want to go with the one controller-two controller strategy or with the one controller, variable amperage strategy. Do the math and see what the most cost-effective strategy works best for you? If you shop around and look for additional panels in the 20V range, you might find a better fit than my quicky search.

 

[SteveinFLA]

You're right, those panels aren't very well matched. If you put them together you should still see somewhere in the 500w range total though. With the voltages you'll need to get an MPPT controller.

First question is what's her nominal system voltage? If it's 12v you'll need either a 60a unit or 2x 30a units. Going for 2x 30a MPPT's will let you maximize the output of the panels but adds a little more complication.

If it's a 24v system you can do a single 40a just fine and take the hit, or a pair of 20a MPPT controllers.

If you decide to go single controller make sure the unit has a Max PV Input of at least 100v so you can go series or parallel.

Someone should be along shortly to double check the math and tell you what you should be able to get out of those panels in series or parallel. As far off as the voltages and amperages are, I'd highly recommend dual MPPT's.

Her system is setup for 12V. Thanks for your helpful response.

 

[Rednecktek]

For a 12v system that large, go with dual 30a or 40a MPPT's, one for each panel.

 

[SteveinFLA]

Here is a strategy that might work for you. Both the amperages and the voltages of these panels are too widely divergent for them to be used either in parallel or serially with one single controller. As RNT describes, buying two controllers will work, but a second option is to buy a second panel that brings the voltages to within 5% of each other.

The difference between the two panels is 54.7V - 34.1V = 20.6. So, if you wire a second 20V panel in series with your 335W panel you will match voltages closely. The problem with panels in series though is that amperages need to match closely. If they do not, the net amperage will be only that of the panel in the string with the lowest amperage.

But, here is an example of a 200W panel that fits these parameters fairly well. If you wired this 200W Renogy panel in series with your 335W panel you would get 34.1V + 22.6V = 56.7V. That is only 3.6% difference, well within the 5% limit. The amperage of this new panel is 8.85A, which is only 0.95A different.

So, if you made the series string of the 335W panel with the 200W panel, and then put that in parallel with your 305W panel, you'd get about 8.85A + 5.58A = 14.43A flowing into the controller at ~ 55.7V (not exact).

An MPPT controller would convert the high raw solar voltage down to battery charging voltage. For a 12V battery, that would be 64A, or 32A into a 24V battery. Expect that to be 54A or 27A respectively in the real-world. So for 12V, you would need at least a 60-80A controller, such as Epever's Tracer 6415AN or 8415AN, or the cheaper Tracer 4210AN if you went with a 24V system.

So now, what you would need to decide is whether you want to go with the one controller-two controller strategy or with the one controller, variable amperage strategy. Do the math and see what the most cost-effective strategy works best for you? If you shop around and look for additional panels in the 20V range, you might find a better fit than my quicky search.
View attachment 139998

I don’t think she has much money to spend. Her aim so far has seemed to be making the stuff she has work with the least possible additional expenditure. I appreciate your helpful design input logic.

 

[Rednecktek]

Putting those panels together will severely nerf the output of both panels, to the point where leaving one unplugged may be a benefit. About the cheapest way to utilize those panels effectively would be something like this guy which seems to be about the cheapest MPPT that will turn high voltage panel DC into battery DC.

Pro Tip: If it has USB ports on it, it's a FAKE MPPT CONTROLLER!!!!!

 

[SteveinFLA]

A problem we ran into when we tried our first “$10 box” was the input voltage was only 25V. None of the controllers I’ve looked at had any specs listed as to max input voltage. Any idea where I can find that info before ordering?
Also, any other pro tips to avoid by fake mppt’s?

 

[MichaelK]

Also, any other pro tips to avoid by fake mppt’s?

Shipping weight! Real MPPT controllers have big torroid rings of copper wire, and lots of other electronic components that add pounds to the weight of the controller. So, if the shipping weight is measured in pounds, it's real. If oz. It's fake. A second clue is the max voltage. Real MPPTs start at 100V and go up. Fakes might be 25-50V.