I forgot to include the reference for PV battery charging without a charge
controller. It is 'Solar Photovoltaic Applications Seminar: Design,
Installation and Operation of Small, Stand-Alone Photovoltaic Power Systems,'
July 1980, 351 pages, DOE/CS/32522-T1
"Direct electrical connection of the array to the battery system without
regulation is advisable only when the peak output current of the array is less
than 5% of the charge capacity of the batteries (amp-hour rating) in the system
(charge equals current x time)."
This document is one of the first comprehensive PV system design books and well
worth reading. I could not find it for free on the internet. Jim Fortenberry at
Jet Propulsion Laboratory gave me his copy in 1986 when the Reagan
Administration stopped the JPL solar program and Block V testing the same year
UL 1703 was published.
Joel Davidson
----- Original Message -----
From: Bob-O Schultze
To: RE-wrenches
Sent: Sunday, March 28, 2010 9:18 AM
Subject: [RE-wrenches] NABCEP Exam was: PV excellent battery charger
Folks,
While none of us obviously has access to the wording of the specific question
itself, I can assure you that there are no "tricky" or non-sensical questions
on ANY of the NABCEP exams. Our Subject Matter Experts (SMEs) who come up with
the questions AND the answers aren't a bunch of nerds in a university
somewhere, they are us; working wrenches like ourselves. All the questions and
answered are submitted to a round table discussion of the SMEs to be accepted,
modified to be made clearer, or thrown out. At the same time, they are reviewed
by a professional testing expert for clarity, readability, and correct usage of
the language. Of the four answer choices, there are almost always two which are
dead wrong, one which could be arrived at if you didn't follow all the steps of
the question or didn't exactly know the material, and the correct answer. If
you think all that is easy to do, try it sometime.
After the test is taken, the testing expert analyses the raw data and the
SMEs review any items which seem questionable. For example, if most of the test
takers INCLUDING those who did very well on the test otherwise missed a certain
question, they take a hard look at it to see if there is ambiguity or if it can
be interpreted differently from the way it was intended. It does happen that in
spite of all the work put into developing the question, it is flawed in some
way. When that happens, the question is discarded and all the test takers in
that round get credit for it.
As to putting together a study guide, that's even harder. Remember that it's
a "Guide", not a book like the NEC wherein lie all the answers to the
questions. The Entry Level test is not a snap by any means, but it is basic in
nature to our field and there are no questions on it that an installer would
have to face, IE, anything to do with the NEC. The Installer Certification test
is difficult, as it should be. Unless you know our trade inside and out PLUS
have done some study in the areas which you don't do at all or very often (we
all have those), you will have difficulty in achieving a passing score. I know
many good Wrenches who missed it at least the first time. Some of those just
say, "Screw it, I don't need this shit". Others have challenged themselves to
hit the books again and brush up on the areas they found out (from taking the
test the first time) where they were weak and nailed it on the next round.
Everyone I've ever talked to, including myself, has said that they are a better
craftsperson for having taken and passed the test.
Bob-O
On Mar 27, 2010, at 8:02 PM, Darryl Thayer wrote:
I have never seen the exam but I have been told several of the
questions are nonsense. Just like the study guide, and from what I hear
there are questions of similar nature on the installers exam. Something is
wrong with the test generation.
Darryl
--- On Sat, 3/27/10, Warren Lauzon <[email protected]> wrote:
From: Warren Lauzon <[email protected]>
Subject: Re: [RE-wrenches] PV excellent battery charger
To: "RE-wrenches" <[email protected]>
Date: Saturday, March 27, 2010, 10:55 AM
To be honest, I don't think the question makes any sense. There are
several "right" answers, but no good ones. I hope that is not the extent of the
battery questions on that exam.
..................................................................................................
Northern Arizona Wind & Sun - Electricity From The Sun Since 1979
Solar Discussion Forum: http://www.wind-sun.com/ForumVB/
..................................................................................................
----- Original Message -----
From: Drake Chamberlin
To: RE-wrenches
Sent: Saturday, March 27, 2010 9:28 AM
Subject: Re: [RE-wrenches] PV excellent battery charger
Hi Dave,
At 10:44 AM 3/26/2010, you wrote:
Is the answer here (at least the one that NABCEP intends) just
that the VMP of a "12V module" is higher than the voltage of a 12V battery?
With the higher voltage it will charge the battery with its corresponding
current based on the I-V curve. The objective reads "Explain why PV modules
make excellent battery chargers based on their I-V characteristics
This may be the answer they want. The "Objectives" deals with the
5 key points on the IV curve, Vmp, Imp, Voc, Isc and Pmp. >From a study of the
curve, the obvious "excellent" load is one that takes power from Pmp, which
direct battery charging doesn't do. When I draw the curve, the Vmp of the
module is above the resulting voltage on the curve.
What you say about the power loss not being released as heat in the
batteries, just not produced, makes sense to me. I've never seen any real
documentation about what happens to the power not gained in a non MPPT battery
charging system.
We can definitely agree that "excellent battery charger" is an
exaggeration.
Thanks,
Drake
Drake Chamberlin
Athens Electric
OH License 44810
CO License 3773
NABCEP TM Certified PV Installer
Office - 740-448-7328
Mobile - 740-856-9648
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