Megawatt Inrush And Small Generators

[MEXICOWANDERER]

In the interests of accuracy I have copied John Marles, comments verbatim and they appear below

"Inrush is 50A/115VAC 50A/230VAC for a few milliseconds on the S-400 and S-350. Its controlled by duel thermistors. For the small generators some large start caps would solve the problem as long as those don't trip the generator while charging"
Thank you,
John

My comment...

Choose RUN capacitors, switch power to them first then enable the power supply. It's a great aid to ease startup current burden.

RUN capacitors are not expensive

http://www.surpluscenter.com/Electrical/Capacitors/Motor-Run-Capacitors/50-MFD-370-Volt-AC-Run-Capac...

[MEXICOWANDERER]

"Forcing the field" is not uncommon on large generator sets. My 12.5 "built" Kw Kubota really grunts but it can force 17 Kw for several seconds. The turbo whistles and the exhaust trails a faint black plume. Takes a good quality voltage regulator to supply extra amps. And a fast response low (cornering frequency) safety reg shutdown. It all costs money.

Most companies roar and fume over the last cent needed to make a product. Japanese board meetings are an entirely different creature than USA board meetings.

Wonder when they are going to get around manufacturing an ECU managed direct fuel injected overhead camshaft generator? Bet the EPA will be the one to force their hand.

[theoldwizard1]

Kayteg1 wrote:
I think it was Yamaha generator few years ago who offer boost from starting battery for dealing with AC.
They concept vanish from the market, so I assume it was not working too well.

The Yamaha EF3000iSEB is still being sold. No one else in the industry seems to have gone this way.

[MEXICOWANDERER]

My theory is "If it works before your very eyes it may not be magic at all"

[ctilsie242]

Kayteg1 wrote:
I think it was Yamaha generator few years ago who offer boost from starting battery for dealing with AC.
They concept vanish from the market, so I assume it was not working too well.

Yamaha still sells the 3000 iSEB model, which uses its starting battery to allow for 500 more watts for eight seconds.

I personally would not bother with the Yamaha model... for half the price, I can get a dual fuel Champion that can put out 3400 watts.

If one wants an exotic (though expensive) solution for running an A/C off a small generator, one could buy a good PSW inverter, and have the A/C pull off that. Inverters can take more load for a brief period of time than smaller generators.

[LScamper]

Press button charge cap..... If you say it enough times it must be true!

[Tom_M1]

Not clear at all. Where is this cap installed?

[MEXICOWANDERER]

Yep. Not to be connected across an unswitched device.

Press button (clear so far?) Charge cap. Power supply has no power.

Then throw power switch to power supply

Power supply starts up

Listen and react to how the small generator reacts

Release capacitor charging momentary action button.

If the generator starts lugging harder with the capacitor out of circuit, then it would be best to leave it in.

Let me clarify something. Normally the power supply starts with the load attached. Yes the load can be disconnected via the low side. This means incorporating a decent sized relay into the circuit with 12-volt control. Augmenting the high side with a cap is cheaper, simpler, more reliable, just as "labor intensive" for management, and can when controlled correctly help to correct THD of the output waveform when it is under load.

Keep whistling the tune

Tiny generator. Crude stator.

This correction is not needed on generators that have a surplus amount of wattage available.

This correction is not needed with circuits that are not borderline loaded to capacity.

It is a specific remedy for a specific issue. E=MC2 theory works great unless the generator stalls or a breaker trips. Keep in mind the power supply goes to work the instant the power switch is thrown. Inrush + Load.

Yes the little pot can be turned back to eliminate load current. It is # 10 hassle to reset it.

[Tom_M1]

About the only way I can think of where a run capacitor would help, is putting it across the power switch. When the switch is open the cap would act as a current limiting device allowing the filter caps to charge up slowly. Closing the power switch would short out the run cap applying full power to the supply.

[LScamper]

mvas post is 100 percent correct!

road-runner
"I'm wondering this myself. In an induction motor, isn't the run capacitor used to energize a second stator winding? Using it across the 120 volt input to a power supply would only serve to increase the load on the generator, IMO."

Another 100 percent correct!

[mvas]

MrWizard wrote:
I think i know what he is saying
The cap goes across the megawatt input,
It will be charged when you hold the pushbutton switch closed
It will be charged at the RMS voltage level
It is NOT going to go from zero to 178 back to zero
The stored RMS 120v will add Momentary starting current to input/, induction circuit of the mega watt, allowing a small generator to energize the circuit and charge batteries
It's not the 700w charging that stops an 800w generator, it's the inrush current very similar to starting an induction motor like a compressor

Since a run cap is designed to be left in the circuit, using it as a momentary start cap will not hurt it, and if needed , it could be hard wired to the mega watt and left in the circuit,
The input of the megawatt becomes an LC load circuit, not just An L load

I am sorry, but what you are saying about the capacitor is simply not true.
The voltage across the capacitor is and must change 120 times per second!

First Half Cycle ...
The voltage across the capacitor ramps to +170 Volts peak.
Then it ramps down to 0 Volts.

Second Half Cycle...
The voltage across the capacitor ramps to -170 Volts peak.
Then it ramps down to 0 Volts.

These two half cycles will repeat 60 times per second while the button is pressed.
The Voltage is AC = Alternating Current, NOT DC.

The capacitor charges and discharges 120 times per second.
Nothing that you say, can stop this from happening.
Nothing.

[MrWizard]

I think i know what he is saying
The cap goes across the megawatt input,
It will be charged when you hold the pushbutton switch closed
It will be charged at the RMS voltage level
It is not going to go from zero to 178 back to zero
The stored RMS 120v will add Momentary starting current to input/, induction circuit of the mega watt, allowing a small generator to energize the circuit and charge batteries
It's not the 700w charging that stops an 800w generator, it's the inrush current very similar to starting an induction motor like a compressor

Since a run cap is designed to be left in the circuit, using it as a momentary start cap will not hurt it, and if needed , it could be hard wired to the mega watt and left in the circuit,
The input of the megawatt becomes an LC load circuit, not just An L load

[Tom_M1]

I'm a retired electronic tech and can't quite grasp what Mex is trying to say. He tends to talk in riddles which sometimes adds to the confusion. It sounds like he is telling us to add the capacitor directly across the output of the generator. A capacitor can not store an AC voltage so there will be no boost to the starting current of the power supply.

[road-runner]

LScamper wrote:
How will a capacitor help? Are you talking about putting it across the 120V generator output?

I'm wondering this myself. In an induction motor, isn't the run capacitor used to energize a second stator winding? Using it across the 120 volt input to a power supply would only serve to increase the load on the generator, IMO.

[MEXICOWANDERER]

MEXICOWANDERER wrote:
But it sure do affect power draw. Small generators are really touchy about horsepower/watt curves meaning horsepower implies speed. Hah! If a Harbor Freight 700 watt generator had a three pound flywheel* this wouldn't even be an issue 🙂


*In addition to the rotor.
I fitted a 108 lbs flywheel to my Kubota for exactly that reason. When I visited Transamericad delaval in Oakland, their 8-cylinder 17,000 hp engines spun a 6-1/2 ton flywheel. I was around 19-years of age accompanying my father. The engineer spoke words of inertial mass kinetics vs engine speed slump and recovery time. Old radar-ears here, sucked it up.

Wide-eyed I watched another massive engine reverse rotation. The engine spun down to 0 RPM pneumatic servos pushed (or pulled) twin camshafts, the engine continued for 3 cycles then reversed. Not the generator engine. If it has a catwalk, it is a big engine.