solar panel voltage reduction

[Shadow Catcher]

What can I say I messed up I have a 180W solar panel that puts out more than 34V when in full sun. Unfortunately the Sunsei controller will not handle more than 24V. The controller is already wired into the new trailer so replacing it with a more capable unit is problematic. I have been looking for a way of reducing voltage efficiently and seem to be exceeding my level of incompetence in knowing what the possibilities are.

[eamarquardt]

I think any "simple" solution (like a resistor) will degrade your system's performance when the light isn't sufficient to drive your panels to their maximum output. In additon a simple resistor will drop more voltage when your current demand is high and less when demand is low and I doubt that it would safely reduce the voltage when your panels output (voltage) is high and the load out of your controller (amps) low because a resistor relies on current flow to drop the voltage. IE: If you put 1 amp through one ohm you'll drop 1 volt. If you put 6 amps through the same one ohm resistor you'll drop 6 volts. So, depending on the current your controller requires at any given time the voltage drop of a resistor will vary and not keep your voltage below 24 volts.

So, an electronic regulator is needed to do the job safely and efficiently.

Here is a regulator kit (look at the 24 volt version) that could reduce the output of your panels to 24 volt to provide the input to your current controller. The specs for the 24 volt controller suy that it will accept your panels voltage output. I'd contact the sellers to ensure that it will meet your needs given that you want to put it in front of your Sunsei controller.

http://www.cirkits.com/scc3/scc3specs.html

Not sure how much a new controller that will handle your panels voltage would cost but it might be the "best" solution.

Hope this helps.

Cheers,

Gus

[bdosborn]

There's an easy way to deal with the voltage difference, get an MPPT controller. The bad news is that they are expensive (~$200). The good news is they're more efficient and you can get more power out of the panel. I have a morningstar Sunsaver 15 MPPT. The MPPT is a DC-DC converter that allows the panel to run at its most efficient voltage range while converting the output to a voltage that's compatible with a 12V battery.

You can get a meter to attach to the Sunsaver that lets you keep track of the amp-hours you've harvested as well as voltage and current and stuff.

So take heart, you'll have to spend some money but you'll have a better system in the end.

http://www.morningstarcorp.com/en/sunsavermppt
MPPT Linky at Solar Forum
Bruce

[Shadow Catcher]

I spent a bunch of hours last night working on this problem, and quite simply all I need to do is drop the voltage in half to be able to use the controller I have and that is installed.
A simple DC-DC controller of some sort would seem to be the solution, it does not have to regulate anything as the existing controller does that. Another solar controller is ultimately the the last solution and means replacing the existing. Using the Cirkit is a possibility if it can be set up to not regulate to charge a battery.

[Shadow Catcher]

Would a Pulse Width Modulator possibly work? I know they are motor controllers but the principle seems to be essentially the same as DC DC controllers.

[eamarquardt]

A PWM turns the power full on and full off at a speed determined by the control pot. So if you put a PWM in front of your controller it will provide pretty much the voltage output of your panels to your controller but just for a fraction of a moment and then turn it off, and do this over and over. With some big capacitors you might be able to smooth out the pulses and reduce the voltage but you'd have to be constantly adjusting the PWM to get the voltage output out of the capacitors you want. I don't think it's a practical solution but it's an interesting thought.

I tend to think a new controller (as Bruce suggested) is probably the best compromise (no compromise is perfect and the cost is an issue and I'm sure you don't want your current controller to go to waste) to get what you want.

Hope this helps.

Cheers,

Gus

[Rock]

Can't you hack the panel into 2 parallel circuits that will put out twice the amperage at half the voltage? The individual cells put out 0.5V I think, so they're wired together in such a way to put out 34V at whatever amperage. It would likely involve opening the panel and studying the wiring for a bit, but if you can get it open without ruining it it's totally doable.

Eric

[Shadow Catcher]

I felt it might be an idea to post progress and hopefully outcome. I dropped the idea of a PMW (thank you ermarquardt for an explanation I could almost understand) and concentrated on finding a DC DC controller, and found a SynQor PQ60260HTB10 Module that will take up to 75V DC and drop it to 24V DC with 92% efficiency, for $15 on ebay. Since the solar panel is set up on the garage feeding a grid tie inverter i will be able to test it out with out risk to the converter.

[eamarquardt]

Thank you ermarquardt for an explanation I could almost understand.

It's amazing what you can find on EBay! Neat that you found exactly what you needed. Don't feel bad about not understanding my explanation, sometimes I don't understand them either!

Cheers,

Gus