Kaneka GSA? [RE-wrenches]
Bill Brooks
bill at brooksolar.com
Wed Aug 23 21:53:13 PDT 2006
Aaron,
The trick that most people don't remember is that the parallelled string is
a source of current in addition to the fuse. The total current on the module
cannot be more than the fuse rating, regardless of what Kaneka claims the
busbars are rated for. Since UL does not rate busbars within the module,
that rating is meaningless.
Therefore, the therefore is there for the purpose of reducing the fuse
rating to the total current available to the module. So a 5-amp max series
fuse module that has a 1.5A max current from a parallelled string needs a
3.5-amp fuse to keep the whole available current to 5-amps.
Bill.
-----Original Message-----
From: Aaron Wellendorf [mailto:aaron at dcpower-systems.com]
Sent: Wednesday, August 23, 2006 4:47 PM
To: RE-wrenches at topica.com
Subject: RE: Kaneka GSA? [RE-wrenches]
Bill,
The Kaneka Isc is 1.19A. That doesn't change your calcs because 1.19A x 1.25
= 1.49A. Thus 5A - 1.49A still equals a 3.5A fuse. However...
I'm not understanding why you need to subtract the [1.49A] from the 5A. You
said "Therefore you must subtract the 1.25 amps from the 5 amp rating so the
max fuse rating is 3.75 amps." What is the "therefore" there for?
These calculations are not in the Kaneka literature, but they came up in my
question and answer sessions with the Kaneka reps. I had figured a 4A fuse
was okay, since Kaneka said the internal buss bars were rated for 7A. Kaneka
told me 4A fuse was acceptable.
Please explain. Thanks.
Aaron Wellendorf
DC Power Systems
----------------
So Matt,
What would the appropriate fuse rating be for two series strings in
parallel?
Assuming the Isc is 1 amp, then Imax = 1 amp x 1.25 = 1.25 amp [690.8(A)].
Therefore you must subtract the 1.25 amps from the 5 amp rating so the max
fuse rating is 3.75 amps
Two strings in parallel have a max current of 2.5 amps (1.25 x 2), and the
minimum series fuse rating is 2.5 amps x 1.25 = 3.1 amps [690.8(B)]. So the
correct number is 3.5 amps.
The only fuse allowable for this arrangement of two strings in parallel is a
3.5 amp fuse. I'd be interested to see if they have this in their
literature.
Bill.
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