Do Canceling Meter Legs Work? (Was Re: ratcheting cyclometers) [RE-wrenches]

mlafferty at universalenergies.com mlafferty at universalenergies.com
Tue Jan 20 08:19:58 PST 2004


Robert N asked: <In his Friday post>

>  Well, I hope Doug is not missing anything, and it certainly wasn't 
immediately obvious to me - But on close inspection, I'm uncertain. I 
did some research on the Internet to learn more about how watthour 
meters work. I have yet to find any complete internal circuit diagrams, 
or thorough texts about meters, but the information I've found so far 
suggests that, in effect, the meter multiplies the sensed current by 
the sensed voltage difference between the two line terminals. Some 240v 
meters can be adjusted for use on 120v systems by changing the wire 
routing and installing a jumper to neutral, as has currently been 
discussed. In the case Doug describes, we seem to be doing a 240v 
installation where the direction of one leg is reversed to allow in and 
out currents to cancel one another under some circumstances. My problem 
is that the voltage differential the meter will sense across the two 
line terminals will actually be zero. We are not talking about 2 
different 120v legs of a 240v, 1-phase system, that are 180 degrees out 
of phase and thus would have 240v difference between them. We are 
talking about 2 different parallel branches from the same 120v inverter 
output, which have 0v difference between them. I'm afraid this means 
the proposed setup won't work.

Robert:

First of all, I apologize for not reading all the way to the bottom of
your post (Didn't see the part below Doug P's original post).  It looked
to me like you were just saying "Thanks Doug".... Beyond that, I must
say that you did indeed do your homework and raise valid points.  Your
"multiply volts by amps" description isn't the whole picture, though.
(Part of why I said earlier "to a reasonable degree of accuracy"...)
Methinks that Chris W, Kent S, or Bill B would be able to descibe it all
far better than I.  Would love for one or all of them to chime in here!

The "right" way to do this is undetermined, so far.  Both technically
and "administratively".  It is one of the ongoing and looming
challenges.  WE need to figure out a suitable solution before "they" do
it for us!   Keep thinking about it!  Physically and technically, we can
do it accurately with multiple meters of various configurations and
"addition-subtraction" but that is too expensive and too complex.  It
also ends up looking "messy".  I gotta believe that the Inverter Manus
can incorporate something that would be "acceptable" for all sides.

Essentially, you are looking to meter "Inverter Output"... Correct?  If
so, install a "ratcheting" (detented) 120 VAC Meter between the Inverter
& Load Center and call it a day.  (Let's keep the Burons happy and
assume that there will NEVER be a Genset connected!  This potential is
one of the BIG ones in the "political policy" arena!  I'll leave it at
that.)

I have held for a long time that it will require 3 meters as you
described.  Doug's post caused me to think that the single meter
approach might work for a single inverter.  After reading through your
post, I am caused to re-think that logic.  I will probably set up a test
"for my own knowledge" at some point over the next couple of months.  If
someone or two or three of us get to it before I do and care to share
the results here, please do.  Ultimately this type of thing will affect
each of us.  It already does here in CA as witnessed by the "monitoring"
requirement.  It's a deep and twisted issue.  Trust me.

I do have a question for you, Robert... What were you planning to do
when you sold the systems in the first place?  Three meters?  Four
meters?  No meters?

Not pointing any fingers... Just raising some food for thought.  From a
"business philosophy" perspective, "selling in the blind" isn't a good
practice.  One of three possible outcomes comes to mind, each with their
own ramifications.

1) Best case - You end up guessing correctly and make your normal profit
while "learning something" for the future.

2) You guess "high" to cover your butt and end up charging the customer
too much.  This drives up the "systems cost" on the Buron end and they
have more fuel for their fire that "PV is too expensive", ultimately
causing them to discontinue support and leaving us no leg to stand on in
fighting them.

3) You guess too "low".  This causes a couple of bad things to happen.
First, part of the issue is that, because this will end up being a
"learn as you go" process, extra time spent finding out often leads to
frustration and disgust (bad feelings in your gut about the "whole
thing").  At the same time you are developing this bad feeling, you know
you are losing money with every minute spent on it, leading to two
options depending on your ethics... "Throw anything in and walk away
from it" or "Follow through and eat it".  Both situations generally lead
to ongoing "Customer Service" issues.  Both scenarios lead to lost money
and time on your part.  They also skew the Customer's perspective about
"Wrench knowledge" in general and the overall cost of the system being
lower than it should be.  Believe me, Customers talk to other potential
Customers.  One of the first things they talk about is price.  A lot of
humans like to "brag" about "what a good deal they got" so it is common
for them to say they "got more and paid less".  When the potential
Customer calls you up, they are under the impression that "you should
give them what you gave the other guy".

It goes on in a vicious circle but it all too often ends up in what I
believe is the Worst Case Scenario:

Otherwise good and decent Wrenches are financially and to some extent
emotionally hurt.  Some of them will "lose the faith" and give up.  We
need experienced, responsible, bright, and positive people.  We can't
afford to lose them.    

If you guessed, I sure hope you guessed right!

Three cents,

Matt Lafferty
Universal Energies Institute
mlafferty at universalenergies.com
(916) 422-9772
(916) 628-7694 Cell
(916) 914-2247 Fax
www.universalenergies.com

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