One of the biggest problems us inverter guys have is charging from
portable generators. The problem it seems is that a 3000 watt portable
generator isn't really good for 3000 watts continuous.
Which is fine, but that's not my problem. In my case I'm trying to
draw, at maximum, less than 1kW in charging power from a 3.5 or 4kW
genset. And I get higher battery charging current by adding a
resistive load of as much as 1.5kW in parallel with the charger.
I'm "wasting"* energy to get more instantaneous power input to the
batteries; a good indication that the overall system is Somewhat
Stupid. (*Not totally wasted as the heater is in the house.)
This is why I believe I'll likely end up with a pure DC charging
system at some point, and the swank charging capabilities of my future
VFX will go idle.
Maybe.
Somehow, without actually buying every component and making the tests
myself, I need to make an estimate of comparative charging / (gas +
machine wear) ratio using the two approaches (AC/DC or DC/DC).
Although I'm definitely not made of money, I care less about the
upfront hardware cost than I do about minimizing the number of
dinosaurs I have to burn to charge my batteries.
The DC charging approach also has some appeal for easy future
adaptation to fossil fuel alternatives, such as a wood-fired Stirling.
But unless Outback wishes to sponsor a comparison between an
off-the-shelf portable generator charging batteries through a (V)FX
and a DC system (gas engine -> alternator with field control), this is
probably way more rambling than you care to read.
We recently put
some new code in our inverter and Mate controller to help diagnose
problems. What we find is that after 45 minutes or so the inverter
sometimes disconnects from the generator. This is assumed to be an
inverter problem since the generator is still running. Wellm now we
can look up on the Mate and see the reason for disconnect. What
happens is that over time, the generator heats up, the voltage drops
and so does the frequency. The inverter has a very wide range of
frequency and voltage it can work with, but it does have limits. The
inverter / chargers are also very powerful. They can pull the
generator AC output voltage down to 90 volts in order to get every
drop of power out of the generator. If the generator can't handle it,
then we disconnect. There are two or three cures for this.
1. Buy a generator rated for Prime Power. (it won't have wheels or a
handle)
Understood, though I'll probably never go there.
2. Turn the AC input current down so the inverter doesn't yank the
generator around so much.
I presume this is configurable as with Trace SW stuff?
3. Get a step down transformer if you have a 240V generator. Using a
6000 watt 240V generator at 120 volts means that you only have a 3000
watt (at best) generator. The step down transformer insures that both
120v windings on the generator are getting used. This is called
generator balancing.
My Honda has a switch - 240/120 or 120 only. I've always assumed that
using the latter setting and the 120V/25A socket on the generator
should offer a similar benefit to going 240V -> xfrmr -> 120V, yes? If
it didn't, that's one very useless switch.
Power factor has not been a significant issue, but then we have PFC,
so I guess it won't be with us.
I'm not certain whether the issue is really PF / PFC; I only know that
with two different generators and with three different uncorrected
chargers of two different brands, I can get more charging current out
of the generator by running a Big Resistive Load in parallel with the
charger.
It may simply be that this enables the generator regulation to work
better than it does when looking into a big fat rectifier/reservoir
capacitor combo and delivering all the current in honking great
spikes.
Regardless, sincere thanks for taking the time to share your thoughts.
-=s
