Thanks for doing this. Chris
On 2/1/2023 4:49 PM, Brian Mehalic via RE-wrenches wrote:
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.
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.
Maybe in the meantime, a control system that shuts off the PV, and
then the batteries, would be worth designing.
Brian Mehalic
On Wed, Feb 1, 2023 at 2:10 PM James Jefferson Jarvis via RE-wrenches
<re-wrenches@lists.re-wrenches.org> wrote:
On 2/1/2023 2:58 PM, Starlight via RE-wrenches wrote:
> Have you (or any) installed surge suppression on the PV input
side to
> clamp the open circuit voltage surge?
That's not where the issue is and isn't really a solution. As I
explained in my previous e-mail, the issue is the open circuit on the
output leaves no where for the energy in the MPPT controllers
inductor
to go and the only option is for the voltage to rise until it finds
somewhere to go.
Surge suppressors, such as sold by Midnite Solar, are nothing more
than
Metal Oxide Varistors. Or in the case of Delta, they are pieces of
wire
in sand. They require large rise in voltage before they conduct.
MOVs are sometimes found on the battery side of inverters and charge
controllers, but their clamp time and voltage before clamping
requires
additional circuitry that works faster to protect fragile
semiconductors.
If you are proposing using a surge supressor to regulate the
voltage of
an island between a charge controller and an inverter when the
battery
is disconnected, that's also a no go. Once the MOV clamps, it stays
clamped until voltage goes essentially to zero or until it blows up.
It's not a regulator.
-
To further stir the pot, it is definitely possible to design
electronics
that can deal with load dumps and survive most anything. Aerospace
electronics come pretty close. But all that costs money and takes
space
to do. Are we comfortable with requiring $16,000 charge
controllers so
they can handle load dumps reliably from a poorly thought out NEC
requirement? I think the fossil fuel industry would be very happy
with
the cost of renewable energy electronics being an order of magnitude
more expensive.
>
> Larry Crutcher
> Starlight Solar Power Systems
>
>
>
> On Feb 1, 2023, at 1:23 PM, William Bryce via RE-wrenches
> <re-wrenches@lists.re-wrenches.org
> <mailto:re-wrenches@lists.re-wrenches.org>> wrote:
>
> I can also backup what Jim has said, and have seen the same gear
> destroyed by removing the battery abruptly when the controller
is under
> heavy load. They can die, and sometimes die spectacularly.
>
> Have seen SolArk inverters integrated MPPT controllers blow up when
> lithium battery BMS disconnects. Not a field fixable issue.
>
> Just flip off the breaker when the solar is working hard and and
the
> SolArk will give up the smoke.
>
> Like I originally said, it’s the non talked about issue that is
a big
> issue depending on what gear your using.
>
> On Wed, Feb 1, 2023 at 2:49 PM James Jefferson Jarvis via
RE-wrenches
> <re-wrenches@lists.re-wrenches.org
> <mailto:re-wrenches@lists.re-wrenches.org>> wrote:
>
>
>
> On 2/1/2023 12:25 PM, Alex MeVay via RE-wrenches wrote:
> > Although our controllers are probably smaller than what
you would be
> > considering in this discussion, surviving a load dump
(suddenly
> > disconnected battery) is an engineering requirement for
us, and
> likely
> > would be for other responsible MFG's on this list
(boB?). The charge
> > controller can either handle full input voltage on the
output, or
> > there is a comparator that will shut the controller down
instantly
> > when the output voltage gets too high.
>
> So that's part of the picture.
>
> The other part of the picture is the rest of the system. The
discussion
> and what NEC is mandating is that the battery be
disconnected. As
> far as
> I can tell, there isn't an explicit requirement in all cases
that
> all of
> the power inputs into the system are all going to go away at
exactly
> the
> same time .... or ever. This leaves things like charge
controllers
> getting input power potentially from PV or wind or grid or
generator or
> something else. And nothing in the NEC, as far as I can tell, is
> mandating that all of the DC loads be disconnected. So the
loads are
> online. Now the regulation circuit (switching power supply
in the case
> of a MPPT controller) is regulating variable loads and
nothing is
> providing substantial resistance to change. Normally the
battery is
> acting like a very very very big capacitor. But without the
battery,
> there isn't enough damping in the control loops and voltage
stability
> will suffer. This is where you get 250 volts on your
normally 48 volt
> battery bus. Or 3 volts. Or -80 volts. Or all of those in a
fraction of
> second. This sort of thing is hard on electronics and will cause
> failures.
>
>
> Alex's comment about Genasun's controllers handling full
input voltage
> on the output is probably unique to their niche product.
Looking at
> their biggest controller, it appears to support VOC of 34
volts. At 34
> volts, he can use 50V or 100V rated components on his
output. For a
> 150V
> input controller, you probably can. But you wouldn't because it
> would be
> too expensive. But on a 600V or 1000V controller, there's
just no way
> that you do that because 1000V rated components are big and
expensive
> and their spacing requirements are huge compared 100V level
sort of
> stuff. So the way bigger MPPT controllers deal with load
dump is with
> transient voltage supression or other diodes to handle the
voltage
> spike
> caused by the inductor when the load goes away. When operated in
> parameters, these parts don't wear out. But it can be
interesting to
> size them adequately to account for inductance elsewhere in
the system
> adding to voltage and energy that has to be absorbed.
>
>
> There is a very simple experiment that anybody can perform
to see how
> equipment handles a load dump: Simply wait for a sunny day
and turn off
> the battery breaker. If no magic smoke was released, turn
back on
> battery breaker. If still no magic smoke was released, then
great, your
> system survived a load dump.
>
> If you are at all uncomfortable doing this and/or your
system gets
> destroyed in the process, think back to my earlier security
comments
> about having a self destruct switch on the outside of your
building
> allowing anyone walking by to do this experiment for you.
>
> I have personally destroyed Outback, Midnite, and Morningstar
> controllers inadvertently or intentionally doing load dumps
by shutting
> off their output breaker. Typically the TVS diodes short out and
> secondary over current protection (circuit breaker) trips
before things
> catch on fire. Usuaully the UL94V0 rating on the circuit
board and the
> box the circuit board is in prevents fire from spreading
when things do
> get wild.
>
> But I've also seen all of those brands survive a load dump.
>
> I have multiple customer who have fielded lithium battery
systems to
> cold locations and have had battery BMS disconnect the
battery from the
> rest of the system. Ten's of thousands of dollars of
equipment has been
> destroyed in these islanding events.
>
>
> Some thoughts, for what they are worth.
>
> -James Jarvis
> APRS World, LLC
>
>
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