[RE-wrenches] Remote battery disconnects

[William Bryce]

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> 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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