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Forum Index : Solar : Solar Component Hackery.

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Davo99
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Joined: 03/06/2019
Location: Australia
Posts: 1578
Posted: 11:50pm 28 Aug 2019
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Confused again......  

  Quote  The source impedance at the panels might be around 156v/3.84amps = 40.6 ohms.
Load impedance at the element 94.9v/6.32amps = 15.0 ohms.

So we tweak our duty cycle to match the 40 ohm source to the 15 ohm load to see a power peak which we should see when each panel is loaded to the magic 26.0 volts.


Simplified, is it correct to say I need to keep the voltage to 26V per panel, basicly regardless of how many panels there are in the string?

If so, then given the controller I am using has a 90V Limit ( and I can clearly see the 100V Capacitor on the board) then I am Limited to 3 of these panels as using 6 would mean I'd have to have the panels at 156v (6x26) which would be way over the voltage rating of the board?

Is there a simple way to drive a Higher voltage Mosfet off this board so I could run 6 Panels at 156 V without over volting the PWM board and blowing it?
This would be useful to be able to do for a number of things including smaller, cheaper Controllers and the endless board rated at 5-20V. I think it's simple but I just can't get my head around it.

I didn't have to wait long for the crappy overcast day you said to wait for and try again, it's here today so I'll go out and see what I get with the 3 panels directly Connected and then if I can get a better result with the PWM.

Thanks again for the help, I'm learning, albeit probably too slowly.
 
Warpspeed
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Joined: 09/08/2007
Location: Australia
Posts: 4406
Posted: 12:48am 29 Aug 2019
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  Davo99 said  
Simplified, is it correct to say I need to keep the voltage to 26V per panel, basically regardless of how many panels there are in the string?

Yes exactly, and regardless how much sun there is as well.
  Quote  
Is there a simple way to drive a Higher voltage Mosfet off this board so I could run 6 Panels at 156 V without over volting the PWM board and blowing it?

Very unlikely, as the switching power supplies that drive the internal functions of the controller will also very likely be limited to 90v

This can all be approached from the opposite direction. Use two strings of three panels that you have, and your existing 90v controller, but find a heating element (or elements) with a much lower resistance than 15 ohms.
  Quote  
I didn't have to wait long for the crappy overcast day you said to wait for and try again, it's here today so I'll go out and see what I get with the 3 panels directly Connected and then if I can get a better result with the PWM.

Thanks again for the help, I'm learning, albeit probably too slowly.
Cheers,  Tony.
 
Warpspeed
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Joined: 09/08/2007
Location: Australia
Posts: 4406
Posted: 12:59am 29 Aug 2019
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With full evil cloud cover, you should find that max full controller duty cycle, will pull the panel voltage right down below the 26v power peak.

Winding back the controller duty cycle will reduce the loading on the panels allowing the panel voltage to rise back up to the optimum 26v, where the measured power should reach a maximum.

It won't be a very sharp power peak, a couple of volts either way will very likely only reduce power by a very few percent. Its more a broad flat hump than a peak.
Cheers,  Tony.
 
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