Jim
Yes I think volume is the $$$ driver. Another idea is get a Cummins/Onan
12kW RV house power generator. RV market unit might be more aggressively
priced and would have higher temp ratings then a residential unit. 240V
50A.
Best Regards
DS
On Wed, Jan 22, 2020 at 2:27 PM jimlux <jimlux@xxxxxxxxxxxxx> wrote:
> On 1/22/20 10:51 AM, David Sharpe wrote:
> > Jim
> >
> > Do you presently have 120/208 “house power? If you want 3 phase usually
> > horrible expensive from utility. Another out there house power option is
> > 240 high leg delta (you get 120/240 from one Xfmr, 3 phase from all 3,
> and
> > no ungrounded system risks since 120/240 xfmr establishes N-G connection.
>
> Nope.. no 3phase house power. And, being portable is why I was kind of
> heading the generator route.
>
>
>
> >
> > At really large powers I’m like you I’d love a really large MG set from
> 25
> > -2500HP and up. Flywheel action provides 2.5-5X momentary overload
> > capacity and who needs a stinking variac, when I can very simply control
> > output voltage by field control of generator at O.5-1% of output load.
> >
> > The only advantage of a solid state voltage control like I’m working on
> > (IGBT across Full Bridge, PWM control) is SS can be EPO electronically in
> > simulated 2ms with fault detection. A large MG set even with vacuum
> bottle
> > CB technology will be an order of magnitude slower, AT BEST.
> >
> > If your looking for a generator I’d insist on a brushed rotor so you can
> > manually adjust Vo. Most generators have on board regulators that will
> > shut down unit if you exceed compliance ranges of generator.
> Irregardless,
> > you have to stay within the PQ stability limits of your unit or you will
> > cause thermal damage to stator or rotor depending on under over
> excitation,
> > and reactive power tolerance and unit input output limits.
>
>
> Is that something that is typical on these smallish generators? These
> days, I think they're all brushless.
>
>
> For instance, a Generac 25kVA trailer mounted says:
> Marathon Electric®
> o Brushless
> o 4 pole
> o Class H insulation
> Voltage regulation +/- 1% with Marathon SE350 Voltage Regulator
>
> Looking at an MQ whisperwatt (which would be WAY more than I want to
> spend, but is a common rental unit in the LA area), they say Brushless
> excitation with AVR.
>
> https://www.multiquip.com/multiquip/DCA25SSIU4F.htm
>
>
> I did find an example that calls out "Direct" for the excitation
> (whatever that means), and another that says "brushless 12-lead"
>
> I notice, too, that you pay a substantial premium for 3 phase in
> generators, which sort of surprised me - the engine is the same, and I
> would have thought the alternator cost was about the same for a given
> power rating - after all, it's driven by copper and iron costs and
> manufacturing, and that's pretty similar. Must be a "volume" thing -
> they sell lots of 20-25kVA single phase 240V generators for residential
> and office backup duty, so those are $4-5k and the 3phase units are $8-9k.
>
>
>
>
>
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--
Dave Sharpe, TCBOR/HEAS
Chesterfield, VA USA
Sharpe's Axiom of Murphy's Law
"Physics trumps opinion!"
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