Need help choosing a charge controler

bobbyturbopants · Oct 2, 2019

I was giving an old solar array of 12 Siemens 55 watt panels. I have two AGM auto batteries and only using for led lights in a cabin, maybe a tv later, have a 1500 watt DC to ac inverter might use. So what controller would work and how do I run the panels to em

svetz · Oct 2, 2019

How many in series and parallel? If you're not sure read What does it mean to have solar panels in parallel and series?

bobbyturbopants · Oct 2, 2019

svetz said:
How many in series and parallel? If you're not sure read What does it mean to have solar panels in parallel and series?

Ok so I think I get it , so a controller that says 100volts means if my panels are 20 volts I can run like 4 in series to get like 80 something volts and hook up 3 sets of 4 since there's 12. I have 8 gauge wire so should be good?

bobbyturbopants · Oct 2, 2019

bobbyturbopants said:
Ok so I think I get it , so a controller that says 100volts means if my panels are 20 volts I can run like 4 in series to get like 80 something volts and hook up 3 sets of 4 since there's 12. I have 8 gauge wire so should be good?

gnubie · Oct 2, 2019

The spec to take notice of when it comes to controller voltage vs panel/array voltage is the open circuit voltage. Open circuit = 21.7, so 86.8 volts. The controller should be rated to handle at least 100v. If you live in a place that gets really cold (below 0c) on a bright sunny cold day the panels can actually output more voltage so the controller should be able to handle at least 110v.

A good controller will use components on the solar input that can handle more than the controllers specs, that's a safety margin. Cheap controllers likely use lower grade and lower spec'd components or even fakes so it's even more important to pay attention to maximum voltage ratings for them.

svetz · Oct 3, 2019

How to figure out temperature correction is covered in the FAQ post: Figuring out how many panels in series and parallel based on your MPPT

bulrush · Oct 3, 2019

See Will's "12v solar charge controller buyer's guide" for starters:

You'll need to understand the basics first.

My advice below is based on results in Michigan, or roughly 43 degrees latitude.

When a panel says it's rated at "100watts" that means it will output 100 watts in lab conditions. This will not likely happen in real life. In real life, on a perfectly sunny day, with the panels are the perfect angle, you will get about 80% or so of the rated output in volts and amps (volts * amps = watts). Across the whole summer season you might get 50-70% of the output or less, averaged on a daily basis, which accounts for cloudy or rainy or overcast days. But your panel output varies a lot based on your latitude, your geographical location and how much sun you get. Panels located closer to the equator get more solar energy that reaches the earth (and the panels) because there is less atmosphere for the energy to travel through. Further from the equator the solar energy has to travel through more atmosphere and less energy reaches your panels.
Solar panels should be angled towards the sun so the rays hit the panel at 90 degrees for a good part of the day. To do this, take your latitude, and that will be the angle of the PV panel with the ground. So panels that are at the equator will work best if they lay flat on the ground. Panels at the north or south pole will be nearly vertical, though I think they are pretty much useless at the poles anyway.
When a charge controller says the input is rated for 36vdc, it means the max it can take as input is 36vdc. Design your system so your panels do not go over that.
With other electronic components rated at say, 12v, that's the max voltage they can handle, they can also handle anything under that. So if you need a 50v diode, and can only find a 100v diode, the 100v diode will work fine as it is oversized. Most diodes also "eat up" some voltage, 3-4 volts, which is also called a "voltage drop". But this also depends on the diode type.

I learn more about electronics from Bigclive on Youtube as he takes apart all kinds of stuff, determines if it's a shoddy circuit, or if it might kill you, or if it's a pretty good circuit for the price. https://www.youtube.com/user/bigclivedotcom

And his dry British humor is fun, but he's very knowledgeable.

b.james · Oct 5, 2019

Diodes drop 0.6 of a volt generally and special types ,shottky ,zenner etc even less . If you want 3 volts to run an arduino sensing module throw about 3 diodes in series and feed 5 volts in . You will get around 3 volts out.

Need help choosing a charge controler

bobbyturbopants

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svetz

Works in theory! Practice? That's something else

bobbyturbopants

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bobbyturbopants

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gnubie

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svetz

Works in theory! Practice? That's something else

bulrush

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