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Wrenches,<br>
More on the monitoring of GTWB systems, using a TriMetric, from
Ralph Heisey, the developer of the TriMetric. Please include Ralph
(<a class="moz-txt-link-abbreviated" href="mailto:bogart@bogartengineering.com">bogart@bogartengineering.com</a>) in any further discussion.<br>
Allan<br>
<br>
<div class="moz-forward-container">Hi Allan
<div>For grid tie systems that are only quite occasionally
discharged, I have suggested that people set the TriMetric <br>
voltage setpoint to just below the FLOAT voltage setting, and
set the amps setpoint to a LOW value that is a little above the
float current. Then it will stay at 100% during float, and
when occasionally the batteries are used the "% full" display
will be useful. But after an occasional partial discharge, the
voltage will go to absorb (presumably) but the meter won't reset
to "100" until the amps decline, and the system goes back to
float.</div>
<div><br>
</div>
<div>I don't have this kind of system myself-- so I would be
interested in knowing if this seems like a good solution-- or if
not, why it is not.</div>
<div><br>
</div>
<div>Ralph<br>
<div><br>
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<div> -------- Original Message --------
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valign="BASELINE">Date: </th>
<td>Fri, 10 Aug 2012 13:54:20 -0700 (PDT)</td>
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<th align="RIGHT" nowrap="nowrap"
valign="BASELINE">From: </th>
<td><a moz-do-not-send="true"
href="mailto:toddcory@finestplanet.com"
target="_blank">toddcory@finestplanet.com</a></td>
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<th align="RIGHT" nowrap="nowrap"
valign="BASELINE">To: </th>
<td>RE-wrenches <a moz-do-not-send="true"
href="mailto:re-wrenches@lists.re-wrenches.org"
target="_blank"><re-wrenches@lists.re-wrenches.org></a></td>
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<font face="arial" size="4">
<p style="margin:0;padding:0"><span
style="font-size:14pt">actually this is not the
problem i have with amp hour meters on grid tie
with battery systems. </span></p>
<p style="margin:0;padding:0"><br>
a floated battery does <span
style="text-decoration:underline">not</span>
need an occasional bulk charge. it is being float
charged which compensates for any internal self
discharge. the only thing needed is an occasional
eq to stir the electrolyte.</p>
<p style="margin:0;padding:0"> </p>
<p style="margin:0;padding:0"><span
style="font-size:14pt">here is how the meter
inaccuracy problem happens:</span></p>
<p style="margin:0;padding:0"><span
style="font-size:14pt">amp hour meters treat
charge and discharge differently. normally this
is a good thing, because batteries are not 100%
efficient. on a grid tie system, the batteries
are floated nearly the whole time... but there
are still small charge and discharge currents
going in and out of the battery. with an amp
hour meter set at 99% efficiency, it will still
take 101 amp hours of charging to off set 100
amp hour of discharging. <span
style="text-decoration:underline">this is what
leads to the inaccuracy</span> (where the
meter progressively shows an increasing
discharge to the battery). if there was the
ability to set an amp hour meters efficiency at
100% the inaccuracy would not accumulate... but
when the grid is down, the meter will falsely
show faster recharge because the batteries are
probably around 90% efficient... so that is not
a great solution either.</span></p>
<p style="margin:0;padding:0"> </p>
<p style="margin:0;padding:0"><span
style="font-size:14pt">this is why my idea to
leave the amp hour meter set to automatically
determine battery efficiency, and use a time
delay relay to short out the shunt when the grid
is up. when the grid is down the shunt would be
back in the circuit and the meter would perform
accurately. the time delay feature on the relay
would allow for a couple of hours of recharging
after the grid is restored before the shunt was
taken out of the circuit again.</span></p>
<p style="margin:0;padding:0"> </p>
<p style="margin:0;padding:0"><span
style="font-size:14pt">it seems strange to have
to come up with hackey solutions like this for
more and more common battery back-up grid tie
systems.</span></p>
<p style="margin:0;padding:0"> </p>
<p style="margin:0;padding:0"><span
style="font-size:14pt">todd</span></p>
<p style="margin:0;padding:0"> </p>
<p style="margin:0;padding:0"> </p>
<p style="margin:0;padding:0"> </p>
<p style="margin:0;padding:0"> </p>
<p style="margin:0;padding:0"> </p>
<p style="margin:0;padding:0">On Friday, August 10,
2012 7:51am, "Mick Abraham" <a
moz-do-not-send="true"
href="mailto:mick@abrahamsolar.com"
target="_blank"><mick@abrahamsolar.com></a>
said:<br>
<br>
</p>
<div>
<p style="margin:0;padding:0">Happy Friday, all~<br>
<br>
Allan & Todd were discussing the issue where
a "reset type" amp hour battery monitor (such as
TriMetric) never gets to "reset to full" when
operating on a GTWBB "grid tie with battery
backup" system...because the battery stays in
float and the monitor never sees a bulk charge
voltage. <br>
<br>
The problem here seems to reside more with the
chicken than with the egg. A battery in "float"
for long intervals will actually still undergo
some self discharge, so it needs an occasional
"rebulk" charge to restore full state of charge.
<br>
<br>
<strong>Inverter manufacturers please take note
that a simple addition to your code base could
cause a GTWBB inverter to rev up the battery
charge voltage back through the
bulk/absorption phase on a calendar basis such
as once per month. </strong>Victron Energy
already does this with their inverter/chargers
but Victron is not certified for US terrestrial
and it's not set up for grid tie.<br>
<br>
If the inverter system would do an occasional
"rebulk", that would also cause the battery
capacity monitor to reset. Until that function
becomes automatic within the inverter(s), the
next best suggestion is for the client to
manually simulate a power company blackout once
per month by cycling the input AC breaker off,
then on. This kicks up a bulk cycle, ensures
good SOC on the battery, stirs up the
electrolyte if the batteries are floodies, and
resets the battery capacity monitor all with a
single intervention. <br>
<br>
The same manual intervention might also serve as
a good time for the owner to check water levels
on a flooded pack, near the end of the charge
cycle. <br>
Jolliness,<br>
<br>
Mick Abraham<br>
</p>
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