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<p>What everyone else is saying appears to all be good info. My
summary (which could be off):</p>
<p>1) You don't want to signal the relay based on AC voltage.
Period.<br>
2) the BB inverter will signal the GT inverter through frequency
shift, once the batteries reach absorption voltage.</p>
<p>3) The relay is for redundancy, in case the frequency shift <i>thingy</i>
doesn't turn off the GT inverter.</p>
<p>4) The relay should be signaled off of an aux relay, either on
the BB inverter, a DC Charge controller, or an independent DC
voltage controller, set for HVD (High Voltage disconnect) sensing
battery voltage. <br>
</p>
<pre class="moz-signature" cols="72">Ray Walters
Remote Solar
303 505-8760</pre>
<div class="moz-cite-prefix">On 11/3/19 11:58 AM, Mark Frye wrote:<br>
</div>
<blockquote type="cite"
cite="mid:831a4c8d-8bb8-ec8c-e9af-e403093133cb@berkeleysolar.com">
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<p>OK, the posts are coming in on the "no" side, but with
uncertainty about how any given BB inverter might work.</p>
<p><br>
</p>
<p>I still think that the BB charger is in charge (no pun) of
sending power to the battery and if it the battery is at it's
set point then the duty cycle on the transistors in the
rectifier go down - zero. At that point the impedance of the AC
line would appear to go up. In response the GT inverters would
increase there output voltage in an attempt to over come the
higher impedance.</p>
<p><br>
</p>
<p>The voltage monitoring switch that I spec'd has a response
delay setting. If I am running in offgrid mode, the main worry
is voltage sag due to load. So generally, the inverter would be
running at or below AC voltage set point. There may be spikes
above voltage set point when a load is disconnected, but I could
filter that out with the delay on the sensor.</p>
<p><br>
</p>
<p>Still, this is why I am asking.</p>
<p><br>
</p>
<p>Anyone on the list have more confidence in their understand of
BB inverters in off-grid mode with AC coupled GT inverters?<br>
</p>
<p><br>
</p>
<p>Mark<br>
</p>
<p><br>
</p>
<div class="moz-cite-prefix">On 11/3/2019 10:44 AM, Kienan
Maxfield wrote:<br>
</div>
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<div style="font-family: Calibri, Helvetica, sans-serif;
font-size: 12pt; color: rgb(0, 0, 0);"> Mark,</div>
<div style="font-family: Calibri, Helvetica, sans-serif;
font-size: 12pt; color: rgb(0, 0, 0);"> <br>
</div>
<div style="font-family: Calibri, Helvetica, sans-serif;
font-size: 12pt; color: rgb(0, 0, 0);"> I think that you're
not understanding what Brian is saying. In any case, your
proposal will not work with most equipment. There may be some
equipment that would work that way, but not anything I'm aware
of. Let me tell you what will happen in a normal system,
assuming that the manufacturer hasn't built in an AC coupling
control mechanism (like frequency shifting)</div>
<div style="font-family: Calibri, Helvetica, sans-serif;
font-size: 12pt; color: rgb(0, 0, 0);"> <span style="color:
rgb(0, 0, 0); font-family: Calibri, Helvetica, sans-serif;
font-size: 12pt; background: var(--white);"><br>
</span></div>
<div style="font-family: Calibri, Helvetica, sans-serif;
font-size: 12pt; color: rgb(0, 0, 0);"> <span style="color:
rgb(0, 0, 0); font-family: Calibri, Helvetica, sans-serif;
font-size: 12pt; background: var(--white);">The BB inverter
will maintain a stable AC voltage by allowing the GT
inverters to back feed into the batteries. If the batteries
start overcharging, the BB inverter will not raise the AC
voltage in response. What will happen instead is that there
will be no measurable difference in the AC voltage, but the
DC voltage will continue to rise until it hits the multimode
BB inverter's high battery cut out voltage, and the BB
inverter will shut off, and your entire AC line will drop to
0 volts. This will turn off the GT inverter, and as the
battery voltage falls back into an acceptable range, the BB
inverter may or may not automatically turn back on. If it
does automatically turn back on, then the GT inverter will
wait for 5 minutes and then they'll start back-feeding until
the battery voltage goes above the overvoltage setpoint, and
the whole system shuts off again. So this is what is
normally happening if you hear about an AC coupling system
that shuts off once every 6 minutes or so during the day...
And yes, I have seen a system where the homeowner was told
that this was normal, and it's just how the system was
supposed to work..</span></div>
<div style="font-family: Calibri, Helvetica, sans-serif;
font-size: 12pt; color: rgb(0, 0, 0);"> <span style="color:
rgb(0, 0, 0); font-family: Calibri, Helvetica, sans-serif;
font-size: 12pt; background: var(--white);"><br>
</span></div>
<div style="font-family: Calibri, Helvetica, sans-serif;
font-size: 12pt; color: rgb(0, 0, 0);"> <span style="color:
rgb(0, 0, 0); font-family: Calibri, Helvetica, sans-serif;
font-size: 12pt; background: var(--white);">So if the
inverter has an AC Coupling control mechanism, and that AC
coupling mode is turned on, then it will change the
characteristics of the AC line in order to notify the GT
inverter to turn off, or to decrease its output. The only
way that I've ever heard about any manufacturers
implementing this is through frequency shifting. Now it
would be perfectly possible to do it through voltage
shifting (or voltage raising) and I've talked to some
engineers who said that on a technological level, it
wouldn't be any harder for a manufacturer to do voltage
shifting than frequency shifting, but no manufacturer has
actually pursued that. So basically, your only options are </span></div>
<div>
<ol>
<li style="color: rgb(0, 0, 0); font-family: Calibri,
Helvetica, sans-serif; font-size: 12pt;"> use a BB
inverter that has frequency shifting control for AC
coupling</li>
<li style="color: rgb(0, 0, 0); font-family: Calibri,
Helvetica, sans-serif; font-size: 12pt;"> run a wire from
the battery room to the GT inverters that you can use for
controlling them based on the battery voltage</li>
<li style="color: rgb(0, 0, 0); font-family: Calibri,
Helvetica, sans-serif; font-size: 12pt;"> experiment with
something custom and just expect a high probability of
eventual failure (but let us know how it goes)</li>
<ol style="color: rgb(0, 0, 0); font-family: Calibri,
Helvetica, sans-serif; font-size: 12pt; list-style:
lower-alpha;">
<li>You might be able to find a device that would read the
battery voltage, and then transmit that information
wirelessly, then have another device at the GT inverters
that decodes that information and then drives a relay
accordingly. (I have no idea how to do this, for me,
this is in the hypothetical realm.) Or maybe it could
transmit the info via PLC?</li>
</ol>
<li><font face="Calibri, Helvetica, sans-serif"
color="#000000"><span style="caret-color: rgb(0, 0, 0);">or
the fourth option is to set the BB inverter's high
battery cut out voltage to just above the absorb
voltage and just plan on the power going out multiple
times per sunny day. I wouldn't go for this one unless
it's your own home and you're feeling very
adventuresome.</span></font></li>
</ol>
<div><font face="Calibri, Helvetica, sans-serif"
color="#000000"><span style="caret-color: rgb(0, 0, 0);">Essentially
the bottom line is that monitoring the AC line will
never work unless the BB inverter has a built-in</span></font><span
style="caret-color: rgb(0, 0, 0); background:
var(--white);"> AC coupling control mechanism, then you'll
be monitoring for the frequency rather than the voltage.</span></div>
</div>
<div style="font-family: Calibri, Helvetica, sans-serif;
font-size: 12pt; color: rgb(0, 0, 0);"> <br>
</div>
<div style="font-family: Calibri, Helvetica, sans-serif;
font-size: 12pt; color: rgb(0, 0, 0);"> Sorry for not having
anything more helpful to say.</div>
<div style="font-family: Calibri, Helvetica, sans-serif;
font-size: 12pt; color: rgb(0, 0, 0);"> Kienan</div>
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<div id="divRplyFwdMsg" dir="ltr"><font style="font-size:11pt"
face="Calibri, sans-serif" color="#000000"><b>From:</b>
RE-wrenches <a class="moz-txt-link-rfc2396E"
href="mailto:re-wrenches-bounces@lists.re-wrenches.org"
moz-do-not-send="true"><re-wrenches-bounces@lists.re-wrenches.org></a>
on behalf of Mark Frye <a class="moz-txt-link-rfc2396E"
href="mailto:markf@berkeleysolar.com"
moz-do-not-send="true"><markf@berkeleysolar.com></a><br>
<b>Sent:</b> Sunday, November 3, 2019 11:00 AM<br>
<b>To:</b> <a class="moz-txt-link-abbreviated"
href="mailto:re-wrenches@lists.re-wrenches.org"
moz-do-not-send="true">re-wrenches@lists.re-wrenches.org</a>
<a class="moz-txt-link-rfc2396E"
href="mailto:re-wrenches@lists.re-wrenches.org"
moz-do-not-send="true"><re-wrenches@lists.re-wrenches.org></a><br>
<b>Subject:</b> Re: [RE-wrenches] Parts List For AC Couple
Disconnect</font>
<div> </div>
</div>
<div class="BodyFragment"><font size="2"><span
style="font-size:11pt;">
<div class="PlainText">OK Brian,<br>
<br>
So I think you are confirming that monitoring AC side
voltage is an <br>
acceptable way of deciding when to disconnect the GT
inverters.<br>
<br>
With my parts list, I have a delay time that would hold
the GT inverters <br>
off-line for some period of time (I would probably set
to 1 hour) before <br>
coming back on line after tipping off.<br>
<br>
<br>
Mark<br>
<br>
On 11/3/2019 9:53 AM, Brian Mehalic wrote:<br>
> With frequency-on/off, frequency power control, or
other \u201cinverter integrated\u201d control based on battery
voltage/state of charge there is also control in regards
to when the ac coupled inverters come back on. And yes,
this is definitely needed to prevent overcharge (or get
three-stage charging from the AC coupled system). Of
course if it doesn\u2019t work, yes the bus voltage will rise
and trip the BB offline.<br>
><br>
> AC bus voltage will go down as soon as the ac
couple inverters are kicked off, so if that\u2019s your
measured value unless your control system has a delay or
other component to control reconnection and charging i
think it could essentially chatter off and on and off
and...<br>
><br>
> Brian<br>
><br>
>> On Nov 3, 2019, at 9:38 AM, Mark Frye <a
class="moz-txt-link-rfc2396E"
href="mailto:markf@berkeleysolar.com"
moz-do-not-send="true"><markf@berkeleysolar.com></a>
wrote:<br>
>><br>
>> \ufeffHi William,<br>
>><br>
>> Thanks, you bring up issues that are important
to me here.<br>
>><br>
>> In particular, my situation is that the GT
inverter is inter-tied a couple sub panels upstream of
where I want to put the BB inverter. The distance is
long, so I am looking for a solution where I don't have
to run a cable between the two.<br>
>><br>
>> In general, I do wonder about using AC line
voltage rise to take the Gt inverters off line. The main
goal is to prevent excess voltage at the battery, so
monitoring battery voltage is most direct, and there are
simple solutions for that.<br>
>><br>
>> Is AC line voltage a suitable metric for
achieving the same goal?<br>
>><br>
>> Here is where I could use Wrench knowledge to
confirm my thinking, that being:<br>
>><br>
>> - With excess energy in the system, the charger
moves it into the battery, raising it's voltage until it
reaches it high charging voltage set point<br>
>><br>
>> - Once the battery reaches it's high voltage
set point, the charger stops putting energy into the
battery<br>
>><br>
>> - With no other place to put the excess energy,
the AC voltage rises<br>
>><br>
>> Am I getting this right, the reason to
disconnect AC coupled inverters when the battery if full
is not to prevent the batteries from being overcharged,
but rather to prevent the AC line from becoming
unstable?<br>
>><br>
>> I am hoping this is correct and that with $200
of industrial grade devices from Digikey I can implement
a robust control that will disconnect the GT inverters
before the AC line goes so high that the BB inverter
faults.<br>
>><br>
>> Mark<br>
>><br>
>><br>
>><br>
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