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]

BOO!

[LScamper]

red31 wrote,

"I thought is charged and discharged at the freq of the AC, like 60 times a second."

Exactly correct!

"I thought its purpose is to reduce torque of a starting spinning thingy & reduce pf by shifting the voltage/current waves."

Not quite. The purpose of the starting capacitor is to create a phase shift in the starting winding. This phase shift creates a rotating magnetic field in the motor. A rotating magnetic field is needed to get the motor armature turning. After it starts turning the starter winding is no longer needed and is disconnected automatically. The start capacitor has nothing to do with power factor.

[MEXICOWANDERER]

• Capacitor
• If It's not needed it is not needed
• If it is needed with an underpowered prime mover you'll know it right away
• Close the switch and the engine lugs and dies
• With capacitor enabled engine powers inrush but labors when button is released. Cap should stay in circuit
• Start versus run in this case is a matter of common sense
• Run caps are designed to stay in circuit
• Starting caps are not
• They are inexpensive
• But go through the rigamarole of getting a start cap but discover you really need as run cap as well. Most folks would blanch
• Using a cap should definitely not be standard practice like using a booster on a roof air
• I saved this until now: I have a 55uf run cap for use with the Hyperwatt
• Unless it is throttled back it definitely blows a 15 amp breaker if an additional load is placed like a combination of huge refrigerator and several fans
• Put the cap in circuit and the breaker does not blow
• But even a drawn-on 15-amp home circuit will not distort like a cheap generator sine wave distorts
• When my finances catches up to the month maybe November, I'll test hop this with a Harbor Freight 2-stroke generator. That will reveal a definition finding.
• If startup with a weak sister public power circuit causes a line voltage burp, doing so with a marginal generator may (?) be over-the-top
• Finally the BORG does indeed blow hotel breakers even using one charger
• I am forced to ramp potential charge rate to 0 then ramp up once the 680uf caps charge

[BFL13]

The specs for my PowerMax 100 amp PF-corrected converter include:

" •Max inrush current, single cycle: 40 amps"

Some years back I tried to get some use out of that info wrt why the issue thermistor kept frying (since resolved--they now come with a different thermistor), but Salvo (wherever he went) said this was useless info being for a single cycle on the sine wave or whatever it was--I was lost by then. 🙂

Anyway, I do run the 100 amper with my Honda EU3000is, and it is not so clear what happens at different times, if it is in-rush or running VA.

You have two things: A. the motor can conk out, or B. The motor can keep running but the circuit breaker can pop (so you have to shut off the motor and restart it to reset the CB)

On very cold mornings, I can start the Honda in Eco and plug in the 100 amper and the motor will conk out. OK so I learned to start it and let it warm up longer. I also leave it with Eco-off until after the 100 amper is running ok.

You can also pop the breaker with too much of a load. Sometimes the breaker will hold for a few minutes and then pop. Or it can pop right away. There seems to be a relationship between the CB popping or not, and whether the motor is in Eco or not. Can't understand that, but I think it is true. (I have only had this gen for 14 years and still have not figured out what's what with it.)

Anyway, the thing to do on cold mornings is to start it with Eco off, let it warm up a bit, and then plug in the 100 amper (it has PF correction), wait till it is all going Ok, then plug in the non- PF corrected 55 amper, and see that the Trimetric is showing 155 amps. Wait a bt to be sure, and now turn the Honda to Eco. Stays Ok from there on.

I have no clue about what is in-rush and what is just running VA required, and what is motor and what is CB or what combo of those is in play. But that is what I have learned to do "in the field--the hard way" 🙂

[red31]

LScamper wrote:
"So when the pushbutton switch is pressed the capacitor will charge up"

I thought that a capacitor across an AC source would just act as a load with current leading the voltage by 90 degrees and no power dissipated. Did not know that it would charge up and hold that charge until discharged into a parallel load. Learn something new every day!

I thought is charged and discharged at the freq of the AC, like 60 times a second., I thought its purpose is to reduce torque of a starting spinning thingy & reduce pf by shifting the voltage/current waves.

[MrWizard]

MExi
clarify, talking about a 'run' cap ? not a Start Cap ?

why ? its not on the circuit after you release the button ?

what did i miss ?

[MEXICOWANDERER]

It corrects a BADLY warped pf. If it didn't there would be no capacitor start motors. WHERE IS THE INDUCTOR WE NEED AN INDUCTOR! Try the generator stator.

This is EXACTLY why I chose a military surplus KATO generator head. Per Kw the stator has about half again the number of windings. Bottom line conclusion: A huge reserve, cooler coils and higher efficiency. It comes with a huge price tag increase because the rotor needs to generate surplus flux to saturate the stator when called upon.

It's very easy to get lost in accepted practices like theory of RCL and come to the conclusion that "Well, that's a wrap". Small generators use a bare minimum of copper in the stator. One needs to actually connect an oscilloscope and analyze what is happening to waveform under duress.

"Golly gee I never figured lag in waveform could cause an inoperative condition, 'cause it isn't explained in books - I mean the theory of application".

Fifty amperes of inrush coupled to an entire fragile generation of waveform means NO WORKEE. Great. That's the problem. Even a fool can find a "problem". It's the resolution of a "problem" that is a challenge.

Throw Dogma a Bone(a) and keep searching 🙂

[LScamper]

"So when the pushbutton switch is pressed the capacitor will charge up"

I thought that a capacitor across an AC source would just act as a load with current leading the voltage by 90 degrees and no power dissipated. Did not know that it would charge up and hold that charge until discharged into a parallel load. Learn something new every day!

[MrWizard]

i bet it was fine for one start
setting the a/c to cycle the compressor, likley put a big strain on the little battery and it was NOT being recharged fast enough,
repeated compressor starts , resulted in non-operation, and bad 12 amphr battery, and lots of service complaints

[Kayteg1]

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.

[theoldwizard1]

MEXICOWANDERER wrote:

A pushbutton contact switch called momentary only connects while being pressed.

Wire the pushbutton switch as a very short umbilical to the Megawatt on off switch.

So when the pushbutton switch is pressed the capacitor will charge up

Exactly how starting capacitors work on a motor, except it is automatic.

[MEXICOWANDERER]

....and you thought that inbred-looking banjo player sitting on the bridge could duel versus a guitar...

IN A CRUNCH...

Small generator. Too small. When the switch is flipped to start the Megawatt, the generator dies...

The Megawatt needs it's own switch no matter what.

Use the capacitor as noted in the given link.

A pushbutton contact switch called momentary only connects while being pressed.

Wire the pushbutton switch as a very short umbilical to the Megawatt on off switch.

So when the pushbutton switch is pressed the capacitor will charge up

Got it?

Start the generator
Push the capacitor button down and keep it down...until...
You flip the Megawatt switch

The generator should "grunt" when you push the capacitor button
And grunt again, when the Megawatt switch is thrown.

No more generator stalling out.

But if you release the pushbutton and the generator stalls, yank the pushbutton out of the circuit and leave the capacitor connected permanently.

Beatzuh heck out of buying another generator.

***The cap hookup goes on the generator side of the on/off switch

[2oldman]

dueling thermistors

[LScamper]

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