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Slighlty Different Voltages

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Posted by Danno on August 6, 2004, 5:53 pm

   I know I saw a post similar to this recently, but I can't dredge it up...
I currently have an ICP 75W panel, it apparently pushes at 15V. I would like to
wire a Sharp panel in parallel with it, but the Sharp panels push at 17.2V.
Will it be OK to hook these up like this? I use a standard (non MPPT) charge
controller, but would eventually like to get into an MPPT. Would the differing
voltages affect the efficiency?

Solar-powered Linux: Slackware9.1   2.4.26   IBM ThinkPad560
1993 BRC Banzai w/60T Real Chainring & Shimano Deore XT

Posted by Vaughn Simon on August 6, 2004, 7:56 pm

like to

     I have dissimilar panels wired together and find it to be a non-issue.
A simple test is to connect them both together with an ammeter in the
circuit.  If you can remove the wire from either panel and see the charge
current decrease (and I think you will) , you are home free.

 >Would the differing voltages affect the efficiency?

     Doubtless, it would be better if they were the same, but you are
probably better off with the two dissimilar panels wired together than with
either one of the two by itself.


Posted by Alf on August 6, 2004, 9:47 pm
   It is considered almost universally unacceptable to wire panels with this
large a difference in voltage together to use with an MPPT controller. You
will get little to no benefit from the controller and at considerable cost.
   A standard charge controller like a C-40 or ProStar model will work perfectly
with this arrangement.
Penobscot Solar Design

Penobscot Solar Design

Posted by DJ on August 7, 2004, 1:56 am
Measure it to be sure! You're talking "closed circuit voltages" with
both these panels I assume?

Define "ok". Will it fry anything, no. Will you get the sum of the
rated amperages going into your battery bank? Likely not.

 But free electricity is a good thing no matter how you get it.


Posted by Danno on August 7, 2004, 6:07 am
  Thanks for the responses. My concern was that, in my zest to increase my
charging capacity, I would ruin my current (limited) ability. I am running
my current system through a "standard" charge controller (ICP CC20), with a
float of 14.4V. It is capable of handling the increased amperage of the new
panel. I guess I'll have to put the MPPT idea on the back shelf for a while...
  Am I correct in assuming that the maximum voltage of the Sharp
will not be reached; that it will be held at 15V by the first panel. Or does
the charge controller limit both to 14.4V? I would like to take a look at the
output curve of the panel to see just how much power I'd actually be making.

Solar-powered Linux: Slackware9.1   2.4.26   IBM ThinkPad560
1993 BRC Banzai w/60T Real Chainring & Shimano Deore XT

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