[RE-wrenches] Remote battery disconnects
Jason Szumlanski
jason at floridasolardesigngroup.com
Fri Feb 3 05:26:38 PST 2023
Just a quick comment about flipping breakers randomly. This also applies to
AC-coupled systems. There should be zero risk of flipping breakers in
random order. These devices are there to prevent overcurrent and disconnect
circuits safely under load. If there is a specific order in which breakers
must be turned on for the system to function properly, I consider that poor
system design. And the issue is pervasive in the industry. If there is a
safety hazard with flipping breakers in random order, these components
should never pass testing IMO.
On Thu, Feb 2, 2023 at 6:53 PM Kienan Maxfield via RE-wrenches <
re-wrenches at lists.re-wrenches.org> wrote:
> Hello all,
>
> I have been an off-grid specialist for 12 years now, and I have never seen
> or heard of a charge controller blowing itself up when it was disconnected
> from the battery while it was in steady state. What I mean is that if it's
> in bulk mode, or absorb mode, or float mode, and the battery disconnect is
> suddenly opened, nothing has ever happened. And this actually has happened
> a lot of times in my career. Most of my clients have a DIY attitude, so if
> they think something is wrong, they'll start flipping breakers off randomly
> until they have shut everything down in order to "reset" the system, and
> then they turn it all back on, and if the problem persists, they feel like
> they've tried something, so then they call. I've had helpers who just can't
> remember which breaker to shut off first. Since I've never seen or heard of
> an actual case where this happened, I don't worry about it to much.
>
> I have seen something similar blow up an Outback FM80 once. The charge
> controller was 7 years old at the time. I was watching the whole time. The
> system was shut down when we arrived, then the PV breaker was turned on,
> then the battery breaker was turned on momentarily, then the battery
> breaker was shut back off. The charge controller went into the startup
> procedure, and it went to sweep the IV curve, and as it did, it was pumping
> all that power into it's capacitors and it had nowhere to go. I watched the
> voltage on the screen skyrocket and then it suddenly burned out with a
> small pop. The charge controller was stuck in the startup, and it wasn't
> able to stop producing current. If the battery breaker had been left on
> while it stabilized, then it was shut off, it would have been fine. So if
> you turn on the system, don't suddenly trip the disconnect until it has
> been on for a minute.
>
> Also, inverters have capacitors that are much, much, much larger than the
> capacitors in the charge controller, so when a main battery disconnect is
> thrown and the charge controller is connected to an inverter
>
> Now, I completely avoid cheap charge controllers (Amazon charge
> controllers, etc.). I don't touch them with a 10 foot pole. I have seen so
> many DIYers reject my advice, install a cheap one, and have it burn up
> within a couple of years or less. I wouldn't be surprised if suddenly
> disconnecting the battery would be a likely cause of failure in these cases.
>
> Also, with any quality brand, if this somehow did happen, they'll still
> honor it under their warranty, and this will be a rare occurrence.
>
> William said that SolArk can't handle having the breaker thrown while it's
> charging the battery, so there are definitely exceptions. I've never used
> SolArk, but with everything else I've heard about them, I'm really not too
> surprised. I'm not faulting SolArk, and I'm not a SolArk hater, I just know
> that their hands are somewhat bound by the real manufacturer who is in
> China. SolArk only has limited control of their product. But as boB from
> MidNite pointed out, it all equipment can and should be designed with this
> in mind. Fuses will blow, breakers will get tripped, and any quality
> manufacturer is going to take that into consideration. They can take the
> low road and simply plan on replacing some under warranty, or the can
> engineer the product to withstand it.
>
> One last note about codes, there are some codes that I hate and try to
> avoid, but I also personally know 2 or 3 of the people on the code panels.
> There are some people on the code panels who are not kind to our industry,
> but there are a couple of people on those panels who really are our
> advocates. If someone is on the code panel, they are actually limited in
> how they can suggest new changes to the codes, they can only promote public
> inputs that are submitted by people like us, so even if it feels like a
> waist of time, it really is important that we all submit our ideas and
> thoughts through the official pathways so that our advocates who really
> want to promote our best interests have something they can leverage for us.
> To those here who do help with the codes and help to advocate for us, THANK
> YOU SO MUCH!!!
>
> Thanks,
> Kienan
>
>
> *Green-Go Solar Distribution LLC Maxfield Solar LLC (installation and
> consulting company) *
> *maxfieldsolar at hotmail.com*
> *(801) 631-5584(Cell)*
> ------------------------------
> *From:* RE-wrenches <re-wrenches-bounces at lists.re-wrenches.org> on behalf
> of bob--- via RE-wrenches <re-wrenches at lists.re-wrenches.org>
> *Sent:* Wednesday, February 1, 2023 8:06 PM
> *To:* RE-wrenches <re-wrenches at lists.re-wrenches.org>
> *Cc:* bob at midnitesolar.com <bob at midnitesolar.com>
> *Subject:* Re: [RE-wrenches] Remote battery disconnects
>
>
> SPDs or (MOVs) on the PV input side of a charge controller are not wired
> to snub excessive PV voltage.
>
> They are wired from PV+ to GND and the other from PV- to GND and only the
> two in series, at double the
> MOV clamp voltage would have any effect on clamping the PV+/PV- voltage.
> SPDs are wired to keep the charge controller's insulation system to below
> the Hi-Pot voltage the unit is
> tested with. i.e. They are wired for common-mode and not differential.
> That voltage is much higher
> than maximum controller or inverter input voltage.
>
> What *IS* in place that might help limit PV voltage is the PV array
> itself. Any PV voltage that would try go
> go above the array's Voc would be clamped across the array. This would
> be during the day or at night and
> of course that Voc is determined mainly by PV cell temperature. Solar
> panels are just a bunch of diodes
> in series so will be forward-biased when Voc is exceeded by an inverter or
> charge controller.
> PV modules make great space heaters and can even melt snow, ya know. 😁
>
> As for charge controllers blowing up when charging hard and then
> disconnecting, I am very anal in
> designing in safe guards to keep this from happening on the MidNite
> Classic at least. That was done
> several years ago now.
>
> But even then, electronics, especially power electronics, break once in a
> while and it is sometimes very
> hard to know why it happened.
>
> With our new HV MPPT controllers, their E-Panels also include
> remote-trip PV breakers, triggered by the controller's
> hardware in order to reduce battery side over-voltage in case something
> goes wrong.
>
> So, I understand that we have a remote battery disconnect device basically
> done but have held off due to
> not knowing how important it would actually be. 300 amps from an external
> switch closure or open.
> Our older BD module basically went away with the bird house and bird next
> shut down system.
>
> There are NEC requirements that are not enforced and some installers
> don't worry about including,
> but from this discussion, it sounds like this battery disconnect better be
> finished sooner than later.
>
> Now we know. Thanks !
>
> 🌜boB🌛 MidNite Solar
>
>
>
>
> On 2/1/2023 2:49 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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