[RE-wrenches] Remote battery disconnects
Christopher Warfel
cwarfel at entech-engineering.com
Sat Feb 4 12:57:50 PST 2023
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 at 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 at lists.re-wrenches.org
> > <mailto:re-wrenches at 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 at lists.re-wrenches.org
> > <mailto:re-wrenches at 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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--
Christopher Warfel
ENTECH Engineering, Inc.
PO Box 871, Block Island, RI 02807
401-466-8978
<http://entech-engineering.com>
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