Calculating string amperages [RE-wrenches]

[boB Gudgel]

I said:
This diode characteristic is also why they are sometimes used as a 
voltage clamp when paralleled with a hydro or wind turbine.

I forgot to mention, and you probably concluded this anyway, but when 
one module in a string shorts, the resulting forward drop of this 
defective string is lower than what is being generated by the other 
paralleled strings.  So the defective string loads down the other 
strings to its forward voltage drop through the breakers and will 
hopefully trip the bad strings' breaker taking all the combined array 
current.

boB



boB Gudgel wrote:
> 
> 
> Hi...
> 
> You can think of PV module as a bunch of silicon diodes in series, like 
> 36 or more of them. The positive terminal is the anode and negative 
> terminal the cathode.
> 
> The Voc happens to be appoximately equal to the forward drop of these 
> series string of diodes and will start to conduct when presented with a 
> voltage at around that point.  They will conduct when the sun is shining 
> 
> on them or not. This voltage drop comes down as their temperature rises, 
> 
> just like the Voc and Mpp voltage.  This diode characteristic is also 
> why they are sometimes used as a voltage clamp when paralleled with a 
> hydro or wind turbine.
> 
> Of course they don't have to work great as a diode and will have some 
> leakage, so that's why they can act like a resistor at night.  Most 
> charge controllers have a relay or back to back MOSFETs (like the PWM 
> types CCs) to reduce this night time discharge.
> 
> I'm not sure, but I 'think' that PV modules may be better in the leakage 
> 
> department these days because of better manufacturing processes.
> 
> boB
> 
> 
> 
> 
> R. Walters wrote:
> > 
> > 
> > I'm passing Bill's  post to the list for everyone. Thanks BIll.
> > My understanding is that one of the basic functions of a charge  
> > controller is to prevent back feed of current to the modules. A  
> > normal functioning solar module becomes a resistor without sunlight  
> > on it.
> > Would one of the Manus care to respond?
> > Also, this comes back to the original start of this thread: where and  
> > what are the parallels MC connectors for, if we can't use them?
> > 
> > Ray
> 
> 
> boB Gudgel K7IQ
> MidNite/Magnum  Solar/Energy
> Washington AC



boB Gudgel K7IQ
MidNite/Magnum  Solar/Energy
Washington AC


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