On Wed, Jul 29, 2020, 14:46 Lee Hart via EV <ev@lists.evdl.org> wrote:

> John Lussmyer via EV wrote:
> >> I have a 5kw on order for testing.  Maximum VDC of 450 will, I think,
> >> require some adjustment in the way I've been doing things.
> > Except that the 450VDC Max is only for the PV Input which has a MPPT
> controller.
> > I've read several places that a MPPT setup does not like being fed by
> batteries.
> I think it depends on how they work. I have two MPPT trackers that still
> work if they're fed with batteries; and one that doesn't.
> With a battery input, the big one that works maximizes its output, as if
> it's in full sun. Its input is current-limited to 8a; so that's what it
> draws, regardless of the battery voltage.
> The little one is the same, except its input current tracks its input
> voltage. There is no input protection (except a fuse); so if the input
> voltage is too high, the input current gets too high and it blows a fuse.
> The one that doesn't work is in a 24v microsine inverter. With a battery
> input, it ramps up to full power over a period of a few seconds; then
> shuts down for a few seconds; and repeats. It doesn't appear to be
> damaged; but it's also not particularly useful.

It sounds like the 24v Microsine does not like running flat out. Did you
ever measure its power output when fed from a battery vs from a solar
module large enough to max out the output? If so, was it trying to output
more power than the nameplate rating?

My hypothesis is that it has a PTC resettable fuse or circuit breaker that
is tripping and resetting based on input or output current. Some
microinverters like the Enphase M215, rated at 215 watts AC, actually allow
themselves to go up to 225 watts AC output if there is enough power
available on their inputs (~237 or more watts DC, at 95% efficiency).

Maybe your 24v Microsine assumes available input power (VxI) at any point
on the I-V curve will never exceed the nameplate output rating, and the
only way it actually limits output is via the self-resetting fuse/breaker.

A battery I-V curve is different from a solar module, as the battery
voltage holds relatively steady across a large current range. An ideal
battery with zero internal resistance would have a constant output voltage
regardless of current. An unsophiscated MPPT would just try to draw
additional current as it found ever higher maximum power, until something
else limited it. A solar module behaves different, dropping to 0 volts when
at maximum current (Isc, short circuit).

Has anyone tried putting batteries on the DC side of a modern Enphase or
APS YC500 or YC600 microinverter? Some companies have prototyped solutions
that appear to do just that by placing a battery between a solar module and
a microinverter (e.g. Yotta Energy, https://yottaenergy.com ).

-------------- next part --------------
An HTML attachment was scrubbed...
UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
ARCHIVE: http://www.evdl.org/archive/index.html
INFO: http://lists.evdl.org/listinfo.cgi/ev-evdl.org
Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)

Reply via email to