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Author Topic: What do you want in a genny?  (Read 8941 times)

Nick Enright

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Re: What do you want in a genny?
« Reply #10 on: October 02, 2014, 11:47:34 am »


The post I mentioned in my OP made the point that welders need consistent performance - ie output.  The interesting thing is that a function block diagram of the ranger has a rectifier creating a DC bus with an output controlled by a microprocessor firing thyristors-in other words it is a large SMPS with a specialized precisely controlled output-but it doesn't seem to mind the voltage/freq variations caused by rpm fluctuations.


I guess that my original post missed in it's intended statements...

1) I'm sure that the Electrical Engineers that design Lincoln generator-welders could very easily design a pure sine-wave, 60Hz, 120v, ouput on these welders.

2) In my discussion with applications engineers (who I'm sure have a pretty good background in electronics/electricity) they did not recommend using the output of these machines to power audio equipment. AT ALL, welding or not welding.

3) They mentioned that there was no way to tell what the SMPS of some of my equipment would think of the stepped wave power.


There are generators from 7kW (where inverter type go away) up to 640kW. The point is that there are generators already filling this need. There is no need to design a new product...

http://www.whisperwattgenerator.com/

(just one of a few different brands)

These generators are reliable, efficient, quiet, and easy to use.... I'm also a film set electrician, and get to play with single instruments that consume more power than entire stages. (one low budget film overloaded a 1600A gennie, or around 110kVA) they are worth the rental, and if you can keep it rented they can make some cash.




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Nick Enright
Owner / Engineer
Lyve Productions
Detroit, MI

Guy Holt

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Re: What do you want in a genny?
« Reply #11 on: October 02, 2014, 12:46:35 pm »

Perhaps I am being too technical-it just doesn't seem to make sense that a power supply happy with 90-240 vac would be overly sensitive to a gennys output voltage (provided it is not pushing the low end) and waveform?

It would be great to understand this apparent inconsistency. I have been in situations of very overloaded line power where SPMS power supplies were shutting down, but my "big iron" supply was still marching on.  Obviously there's so much more to this than meets the eye...

More from my white paper on the use of portable generators in motion picture production (available at http://www.screenlightandgrip.com/html/emailnewsletter_generators.html.) To understand what affect a highly distorted voltage waveform with peak voltage drop would have upon SMPSs it is worth reviewing how the diode/capacitor front end of SMPSs operate.



Step 1: Rectifier Bridge converts line frequency AC power to rectified sine wave.
Step 2: rectified sine wave is flattened to DC by conditioning Capacitor.

The diode/capacitor section converts AC power to DC by first feeding the AC input through a bridge rectifier, which inverts the negative half of the AC sine wave and makes it positive. The rectified current then passes into a conditioning capacitor/s that removes the 60 Hz rise and fall and flattens out the voltage - making it DC.



Yellow Trace: Rectifier Bridge converts AC power to rectified sine wave. Blue Trace: Stored Capacitor Voltage. Red Trace: Current drawn by capacitors once input voltage is greater than voltage stored in the capacitor (Blue trace.)

As shown in the illustration above, the diode-capacitor circuit only draws current during the peaks of the supply voltage waveform as it charges the conditioning capacitor to the peak of the line voltage. Since the conditioning capacitor can only charge when input voltage is greater than its stored voltage, the capacitor charges for a very brief period of the overall cycle time. Since, during this very brief charging period, the capacitor must be fully charged, large pulses of current are drawn for short durations. Consequently, all diode-capacitor circuits draw current in high amplitude short pulses that roughly coincide with the peak of the voltage waveform.



A pseudo square wave after being rectified by a full bridge rectifier

Based upon how diode-capacitor circuits operate, what effect would a "flat topped" voltage waveform exhibiting peak voltage drop (like the one pictured above) have upon loads, like lap tops, camera power supplies and battery chargers, that also utilize SMPSs? If we compare one half cycle of a rectified sine wave to one half cycle of the distorted pseudo square wave generated by non-linear loads, we see that one consequence is that the period during which the capacitors of their SMPSs must recharge is appreciably shortened. Given a shorter interval to charge, the capacitor/s will draw current in even higher amplitude shorter bursts. The diode-capacitor circuit therefore works harder, drawing more current during an even briefer charging period, reducing its power factor and increasing its apparent power or load. As a consequence protective circuit breakers may trip or fuses blow.



Left: half cycle of rectified sine wave. Right: half cycle of rectified pseudo square wave. Blue Line: Minimum Capacitor Voltage. Red Lines denote interval during which current will be drawn by capacitors once input voltage is greater than voltage stored in the capacitor.[/img]

Another adverse effect is that more harmonic currents are generated as less of the power waveform is used by the circuit. In fact, a viscous cycle can get started. The more harmonic currents that are generated, the more distorted the power supplied by the generator becomes. The more distorted the power waveform becomes the more harmonic currents are generated. In this fashion, something akin to a feedback loop can get started until the effect of the harmonics is enhanced to the point where equipment stops working all together.



Blue Line: Minimum Capacitor Voltage. Red Lines denote interval during which current will be drawn
by capacitors once input voltage is greater than voltage stored in the capacitor.

To see why this might happen we have only to compare the pseudo square wave created by 1200 watts of non-PFC SMPS load to that created by 2500 watts of non-PFC SMPS load above. Based upon our discussion of how diode-capacitor circuits operate, we can see in the oscilloscope shot on the right that the peak value of the psuedo square wave created by the 2500W load (after it has be rectified) may not reach a sufficient level to charge the capacitor/s of a power supply. Whether the ballast of a light, or the AC power supply of a lap top, the equipment may be starved of power even though its power indicator lights up, and a true RMS voltmeter would indicate about 120 volts on the line. Common symptoms of power starvation are computers locking up, breakers tripping, and HMIs not striking or holding their strike.



Same as Above Left: Conventional AVR Power w/ Pkg. of non-PFC Elec. Ballasts & Kino Flo Wall-o-Lite. Center: Scope time base adjusted to
bring elongated waveform back on screen. Right: Inverter Power w/ Pkg. of non-PFC Elec. Ballasts & Kino Flo Wall-o-Lite.

The third frame on the right, is the same package of lights but with power factor corrected electronic HMI ballasts on the EU6500is (an inverter generator.) As you can see, the difference between the resulting waveforms is startling. Even though we are running the same overall load in terms of watts, the fact that the ballasts are power factor corrected, that the power generated by the inverter generator has very little inherent harmonic distortion (less than 2.5%), and that the system impedance is very low, results in virtually no voltage waveform distortion of the power running through the distribution system. For this reason, sensitive electronic equipment running on the same power will continue to operate reliably and effectively without damage even though the overall load on the generator has increased.

Guy Holt, Gaffer
ScreenLight & Grip
www.screenlightandgrip.com
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Stephen Swaffer

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Re: What do you want in a genny?
« Reply #12 on: October 02, 2014, 02:08:24 pm »




I'm sure that the Electrical Engineers that design Lincoln generator-welders could very easily design a pure sine-wave, 60Hz, 120v, ouput on these welders.

I made almost exactly the same statement in an earlier post.  But engineering and even "electrical engineering" is a very broad subject-I would not expect them to know or even care what a specific device might need.

"There are generators from 7kW (where inverter type go away) up to 640kW. The point is that there are generators already filling this need. There is no need to design a new product..."

With apologies to Ray and no intention to "hit" him, he mentioned using a genny in a pinch that was not "ground connected".  I am not clear if he meant not bonded to rest of gennys or not ground neutral bonded.  G-N bonding is a SAFETY issue and IMO if gennys are not designed and built to make it easy to correctly configure the G-N bond there is lots of room for improvement.  The Whisperwatts (at least some?) have locking switches to select phase/voltage.  Why cannot smaller gennys have a similar system for GN bonding?  As long as users have to use work arounds to properly and safely use a genny-inverter or not-the available designs are not adequate.  While safety  is the end users responsibility-convenient or not, I think it best to make safety convenient whenever possible.

"These generators are reliable, efficient, quiet, and easy to use.... I'm also a film set electrician, and get to play with single instruments that consume more power than entire stages. (one low budget film overloaded a 1600A gennie, or around 110kVA) they are worth the rental, and if you can keep it rented they can make some cash."

Unfortunately, not everyone has the option to use the very best, every time-part of my curiosity is that I am specing home standby generators for a customer as we speak.  The home stand by are "brushless alternator, computer friendly" the larger mobile generators by the same manufacturer are "brushed, superior waveform."  IMO quite the subjective description. The only units they give a THD value are for inverter units-which makes it impossible to compare the power quality of their "portable" "inverter" "mobile" and "home standby " units.  No this is not an offshore bargain basement manufacturer.

I guess I am left relying on "Uncle Dick's" wisdom-I am sure I could do worse. 
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Steve Swaffer

Ray Aberle

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Re: What do you want in a genny?
« Reply #13 on: October 02, 2014, 05:06:26 pm »

I had two generators, both Honda EU models, powering a stage-- one powering mains/foh/monitors, and the second one was handling stage power. Having not thought about this in the past, should I have a grounding connection between two generators in this case?

-Ray
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Guy Holt

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Re: What do you want in a genny?
« Reply #14 on: October 02, 2014, 05:19:30 pm »

The only units they give a THD value are for inverter units-which makes it impossible to compare the power quality of their "portable" "inverter" "mobile" and "home standby " units.  No this is not an offshore bargain basement manufacturer.

This might help (from Honda Archives):


Guy Holt, Gaffer
ScreenLight & Grip
www.screenlightandgrip.com
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jasonfinnigan

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Re: What do you want in a genny?
« Reply #15 on: October 02, 2014, 05:20:54 pm »

I had two generators, both Honda EU models, powering a stage-- one powering mains/foh/monitors, and the second one was handling stage power. Having not thought about this in the past, should I have a grounding connection between two generators in this case?

-Ray

Yes, If there is a difference in the two generators ground potential then you'd have ground loops from the on stage gear. or more importantly hot hazard from the mics or other grounded metal objects on stage where a person could be the ground path between the two grounds that aren't the same voltage. (ex a Mic getting it's ground from the FOH Generator, and a guitar player with his amp/pedal board ground on the stage generator).
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Guy Holt

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Re: What do you want in a genny?
« Reply #16 on: October 02, 2014, 05:43:39 pm »

Having not thought about this in the past, should I have a grounding connection between two generators in this case?

From my IA Grounding/Bonding Workshop:


Guy Holt, Gaffer
ScreenLight & Grip
www.screenlightandgrip.com
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Guy Holt

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Re: What do you want in a genny?
« Reply #17 on: October 02, 2014, 05:57:01 pm »

There are generators from 7kW (where inverter type go away) up to 640kW.

  Inverters are good-but limited in size.  Then there is always the g-n bond issue.

The new Honda EU7000is can be paralleled for 100A output with the N-G bonded in the paralleling box. They can also be modified to run off a 14 gallon fuel caddy so that they run 20 hours without refueling.

The point is that there are generators already filling this need. There is no need to design a new product...

http://www.whisperwattgenerator.com/

These generators are reliable, efficient, quiet, and easy to use....

And, prone to voltage waveform distortion when supplying non-linear loads.

Guy Holt, Gaffer
ScreenLight & Grip
www.screenlightandgrip.com

« Last Edit: October 02, 2014, 06:09:29 pm by Guy Holt »
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jasonfinnigan

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Re: What do you want in a genny?
« Reply #18 on: October 02, 2014, 06:07:10 pm »

The new Honda EU7000is can be paralleled for 100A output with the N-G bonded in the paralleling box.

And, prone to voltage waveform distortion when supplying non-linear loads.


Yeah but it only has a 6hour run time at load. Thats why the Stand-by type generators are typically used for festival power.
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Guy Holt

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Re: What do you want in a genny?
« Reply #19 on: October 02, 2014, 06:11:05 pm »

Yeah but it only has a 6hour run time at load. Thats why the Stand-by type generators are typically used for festival power.

They can also be modified to run off a 14 gallon fuel caddy so that they run 20 hours without refueling.

Guy Holt, Gaffer
ScreenLignt & Grip
www.screenlightandgrip.com
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ProSoundWeb Community

Re: What do you want in a genny?
« Reply #19 on: October 02, 2014, 06:11:05 pm »


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