[RE-wrenches] Remote battery disconnects
Kienan Maxfield
maxfieldsolar at hotmail.com
Thu Feb 2 15:53:10 PST 2023
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<mailto: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>
> <mailto: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>
> <mailto: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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