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<p><font size="4">Thanks for doing this. Chris</font><br>
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<div class="moz-cite-prefix">On 2/1/2023 4:49 PM, Brian Mehalic via
RE-wrenches wrote:<br>
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<div dir="ltr">Most firefighters are not electrical engineers; nor
are most insurance agents. However both of those groups are
stakeholders with influence over codes and standards. Some may
say too much influence, but the fact of the matter is that code
making is a group/consensus process, and very often none of the
groups get exactly what they want (in fact sometimes a group
accepts exactly what it doesn't want to leverage that for
something they do; yes it often smacks of politics). I would
appeal to y'all to submit a proposal for the 2026 NEC® - they
are due by September of this year. Better yet would be to
circulate language that this, or some other, group can work on,
agree on, write a solid technical justification for, and sign
their names to and submit - the more stakeholders that support a
proposal the more weight it has.
<div><br>
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<div>It seems that the PV Industry Forum, or another similar
body, may again begin work to develop PV and storage industry
stakeholder-consensus PIs to submit; in the past this was a
very successful endeavor. I'll post on this list if and when
that happens so that anyone that is interested can get
involved, but don't let that possibility keep you from
submitting any PIs on your own.<br>
<div><br>
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<div>Maybe in the meantime, a control system that shuts off
the PV, and then the batteries, would be worth designing.<br
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<div>Brian Mehalic<br>
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<div dir="ltr" class="gmail_attr">On Wed, Feb 1, 2023 at 2:10 PM
James Jefferson Jarvis via RE-wrenches <<a
href="mailto:re-wrenches@lists.re-wrenches.org"
target="_blank" moz-do-not-send="true"
class="moz-txt-link-freetext">re-wrenches@lists.re-wrenches.org</a>>
wrote:<br>
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0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><br>
<br>
On 2/1/2023 2:58 PM, Starlight via RE-wrenches wrote:<br>
> Have you (or any) installed surge suppression on the PV
input side to <br>
> clamp the open circuit voltage surge?<br>
<br>
That's not where the issue is and isn't really a solution. As
I <br>
explained in my previous e-mail, the issue is the open circuit
on the <br>
output leaves no where for the energy in the MPPT controllers
inductor <br>
to go and the only option is for the voltage to rise until it
finds <br>
somewhere to go.<br>
<br>
Surge suppressors, such as sold by Midnite Solar, are nothing
more than <br>
Metal Oxide Varistors. Or in the case of Delta, they are
pieces of wire <br>
in sand. They require large rise in voltage before they
conduct.<br>
<br>
MOVs are sometimes found on the battery side of inverters and
charge <br>
controllers, but their clamp time and voltage before clamping
requires <br>
additional circuitry that works faster to protect fragile
semiconductors.<br>
<br>
<br>
If you are proposing using a surge supressor to regulate the
voltage of <br>
an island between a charge controller and an inverter when the
battery <br>
is disconnected, that's also a no go. Once the MOV clamps, it
stays <br>
clamped until voltage goes essentially to zero or until it
blows up. <br>
It's not a regulator.<br>
<br>
-<br>
<br>
To further stir the pot, it is definitely possible to design
electronics <br>
that can deal with load dumps and survive most anything.
Aerospace <br>
electronics come pretty close. But all that costs money and
takes space <br>
to do. Are we comfortable with requiring $16,000 charge
controllers so <br>
they can handle load dumps reliably from a poorly thought out
NEC <br>
requirement? I think the fossil fuel industry would be very
happy with <br>
the cost of renewable energy electronics being an order of
magnitude <br>
more expensive.<br>
<br>
<br>
<br>
<br>
> <br>
> Larry Crutcher<br>
> Starlight Solar Power Systems<br>
> <br>
> <br>
> <br>
> On Feb 1, 2023, at 1:23 PM, William Bryce via RE-wrenches
<br>
> <<a href="mailto:re-wrenches@lists.re-wrenches.org"
target="_blank" moz-do-not-send="true"
class="moz-txt-link-freetext">re-wrenches@lists.re-wrenches.org</a>
<br>
> <mailto:<a
href="mailto:re-wrenches@lists.re-wrenches.org"
target="_blank" moz-do-not-send="true"
class="moz-txt-link-freetext">re-wrenches@lists.re-wrenches.org</a>>>
wrote:<br>
> <br>
> I can also backup what Jim has said, and have seen the
same gear <br>
> destroyed by removing the battery abruptly when the
controller is under <br>
> heavy load. They can die, and sometimes die
spectacularly.<br>
> <br>
> Have seen SolArk inverters integrated MPPT controllers
blow up when <br>
> lithium battery BMS disconnects. Not a field fixable
issue.<br>
> <br>
> Just flip off the breaker when the solar is working hard
and and the <br>
> SolArk will give up the smoke.<br>
> <br>
> Like I originally said, it’s the non talked about issue
that is a big <br>
> issue depending on what gear your using.<br>
> <br>
> On Wed, Feb 1, 2023 at 2:49 PM James Jefferson Jarvis via
RE-wrenches <br>
> <<a href="mailto:re-wrenches@lists.re-wrenches.org"
target="_blank" moz-do-not-send="true"
class="moz-txt-link-freetext">re-wrenches@lists.re-wrenches.org</a>
<br>
> <mailto:<a
href="mailto:re-wrenches@lists.re-wrenches.org"
target="_blank" moz-do-not-send="true"
class="moz-txt-link-freetext">re-wrenches@lists.re-wrenches.org</a>>>
wrote:<br>
> <br>
> <br>
> <br>
> On 2/1/2023 12:25 PM, Alex MeVay via RE-wrenches
wrote:<br>
> > Although our controllers are probably smaller
than what you would be<br>
> > considering in this discussion, surviving a
load dump (suddenly<br>
> > disconnected battery) is an engineering
requirement for us, and<br>
> likely<br>
> > would be for other responsible MFG's on this
list (boB?). The charge<br>
> > controller can either handle full input voltage
on the output, or<br>
> > there is a comparator that will shut the
controller down instantly<br>
> > when the output voltage gets too high.<br>
> <br>
> So that's part of the picture.<br>
> <br>
> The other part of the picture is the rest of the
system. The discussion<br>
> and what NEC is mandating is that the battery be
disconnected. As<br>
> far as<br>
> I can tell, there isn't an explicit requirement in
all cases that<br>
> all of<br>
> the power inputs into the system are all going to go
away at exactly<br>
> the<br>
> same time .... or ever. This leaves things like
charge controllers<br>
> getting input power potentially from PV or wind or
grid or generator or<br>
> something else. And nothing in the NEC, as far as I
can tell, is<br>
> mandating that all of the DC loads be disconnected.
So the loads are<br>
> online. Now the regulation circuit (switching power
supply in the case<br>
> of a MPPT controller) is regulating variable loads
and nothing is<br>
> providing substantial resistance to change. Normally
the battery is<br>
> acting like a very very very big capacitor. But
without the battery,<br>
> there isn't enough damping in the control loops and
voltage stability<br>
> will suffer. This is where you get 250 volts on your
normally 48 volt<br>
> battery bus. Or 3 volts. Or -80 volts. Or all of
those in a fraction of<br>
> second. This sort of thing is hard on electronics and
will cause<br>
> failures.<br>
> <br>
> <br>
> Alex's comment about Genasun's controllers handling
full input voltage<br>
> on the output is probably unique to their niche
product. Looking at<br>
> their biggest controller, it appears to support VOC
of 34 volts. At 34<br>
> volts, he can use 50V or 100V rated components on his
output. For a<br>
> 150V<br>
> input controller, you probably can. But you wouldn't
because it<br>
> would be<br>
> too expensive. But on a 600V or 1000V controller,
there's just no way<br>
> that you do that because 1000V rated components are
big and expensive<br>
> and their spacing requirements are huge compared 100V
level sort of<br>
> stuff. So the way bigger MPPT controllers deal with
load dump is with<br>
> transient voltage supression or other diodes to
handle the voltage<br>
> spike<br>
> caused by the inductor when the load goes away. When
operated in<br>
> parameters, these parts don't wear out. But it can be
interesting to<br>
> size them adequately to account for inductance
elsewhere in the system<br>
> adding to voltage and energy that has to be absorbed.<br>
> <br>
> <br>
> There is a very simple experiment that anybody can
perform to see how<br>
> equipment handles a load dump: Simply wait for a
sunny day and turn off<br>
> the battery breaker. If no magic smoke was released,
turn back on<br>
> battery breaker. If still no magic smoke was
released, then great, your<br>
> system survived a load dump.<br>
> <br>
> If you are at all uncomfortable doing this and/or
your system gets<br>
> destroyed in the process, think back to my earlier
security comments<br>
> about having a self destruct switch on the outside of
your building<br>
> allowing anyone walking by to do this experiment for
you.<br>
> <br>
> I have personally destroyed Outback, Midnite, and
Morningstar<br>
> controllers inadvertently or intentionally doing load
dumps by shutting<br>
> off their output breaker. Typically the TVS diodes
short out and<br>
> secondary over current protection (circuit breaker)
trips before things<br>
> catch on fire. Usuaully the UL94V0 rating on the
circuit board and the<br>
> box the circuit board is in prevents fire from
spreading when things do<br>
> get wild.<br>
> <br>
> But I've also seen all of those brands survive a load
dump.<br>
> <br>
> I have multiple customer who have fielded lithium
battery systems to<br>
> cold locations and have had battery BMS disconnect
the battery from the<br>
> rest of the system. Ten's of thousands of dollars of
equipment has been<br>
> destroyed in these islanding events.<br>
> <br>
> <br>
> Some thoughts, for what they are worth.<br>
> <br>
> -James Jarvis<br>
> APRS World, LLC<br>
> <br>
> <br>
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