Solar panel switcher (voltage based)

Thread Starter

Lying Sweetly

Joined Jan 2, 2018
5
So, as some anonymous person said "All I want is really very simple..."
I have a solar controller that can handle up to 150VDC input and pass up to 92 Amps to my batteries.
I have more solar panels than those currently installed, and I would like to use them on cloudy days (when the series voltage drops below some level - lets say 120V).
What I am looking for is a very simple (hah!) controller that will turn on a relay when the voltage drops (thus putting an extra group of solar panels online) and turn it off when it rises to somewhere close to 150V.
Since the solar panels are some distance away from any low voltage power source, it would be very nice if the circuit could be powered by the current/voltage being fed down the cables to the batteries, to save me running extra wire to the solar panels.
See, simple. Help!
 

Thread Starter

Lying Sweetly

Joined Jan 2, 2018
5
Apparently, there is a time limit for editing ones posts. Not sure why if no one has replied at that point. Anyway, my edited post is below.

So, as some anonymous person said "All I want is really very simple..."

I have a solar controller that can handle up to 150VDC input and pass up to 92 Amps to my batteries.
I have more solar panels than those currently installed, and I would like to use them on cloudy days (when the series voltage drops below some level - lets say 120V), and there are lots of cloudy days.

What I am looking for is a very simple (hah!) controller that will turn on a relay when the voltage drops (thus putting an extra solar panel online in series) and turn it off when it rises to somewhere close to 150V. Of course, putting more panels online, one at a time, would be preferable, as long as the circuit remains simple.

Since the solar panels are some distance away from any low voltage power source, it would be very nice if the circuit could be powered by the current/voltage being fed down the cables to the batteries, to save me running extra wire to the solar panels.

Please give me a simple circuit, in parts count and design, for my simple mind. It is over 40 years since I did any circuit design.

See, simple. Help!
 

wayneh

Joined Sep 9, 2010
16,398
One thing you’ll need to define is The hysteresis. If the voltage drops and the extra panels get engaged, now the voltage will rise, but you don’t want them to cut out again. So you might want 20-30V if hysteresis.

The function you need is called a window comparator. Search on that and see if you agree. It’s pretty easy to implement, although the higher power of your application will require attention to specifications and safety concerns.
 

Thread Starter

Lying Sweetly

Joined Jan 2, 2018
5
One thing you’ll need to define is The hysteresis. If the voltage drops and the extra panels get engaged, now the voltage will rise, but you don’t want them to cut out again. So you might want 20-30V if hysteresis.

The function you need is called a window comparator. Search on that and see if you agree. It’s pretty easy to implement, although the higher power of your application will require attention to specifications and safety concerns.
Yes. That's heading in the right direction. Indeed, the question is the hysteresis point. [scratches head...] Difficult to know without doing some empirical testing. I could set up the circuit so that everything functions at much lower voltage than than the 150V limit of my solar controller, thus protecting it, and when everything works correctly, move the switch points up to maintain the desired 150V max. But that's where my old noggin frazzles out. Any advice/specifics to get me moving in that direction?
 

N11778

Joined Dec 4, 2015
174
Draw a Very Simple block diagram of what you have now for us. panels, panel voltages, watts/panel
controller, bats, inverter, load.
 

N11778

Joined Dec 4, 2015
174
looks like you could just hook the extra solar panels in parallel with the existing ones.
the controller should be able to handle it.
 

sghioto

Joined Dec 31, 2017
1,045
Well the diagram shows three 24 volt , 270w panels in parallel or is that meant to be in series? If parallel is correct they would have to be added in groups of three as shown in order to maintain the same current level.
Steve G
 

Thread Starter

Lying Sweetly

Joined Jan 2, 2018
5
looks like you could just hook the extra solar panels in parallel with the existing ones.
the controller should be able to handle it.
Sorry, I guess I could have made it clearer. The existing panels are in series (3 x 40V open voltage = 120V) and thus the problem is that adding another in series exceeds the 150V rating of the controller. The open voltage is important because the controller will eat all the current it can at whatever voltage is present. So, the panels run flat out at the highest voltage possible. If I add more panels in parallel they would have to have nearly identical voltage or their output would would either prevail or be suppressed (depending on the new parallel group's open voltage compared with the existing group). Thus I need a solution that brings additional panels online in series when the collective voltage drops low enough to accommodate 1 or more new panels. I have lots of spare panels available but their specs are not the same as the existing ones. That's the problem. Probably something else I forgot to explain, so fire away with questions.
 

dendad

Joined Feb 20, 2016
3,564
I would vote for more in parallel too. You may have to diode isolate each bank.
If you go for any series setup, you will almost certainly pop your inverter due to over volts without a buck/boost pre regulator. And I think you will find parallel will extend your power pretty well. That would be pretty easy to test to see how much difference parallel connections makes.
 

N11778

Joined Dec 4, 2015
174
3 more series and then in parallel with the existing ones.
Keeping in mind there like the old Xmas lights, if a small shadow hits one in series they all quit.
 
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