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Author Topic: Generator question  (Read 30279 times)

TJ (Tom) Cornish

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Re: Generator question
« Reply #40 on: September 17, 2015, 07:58:27 AM »

I'm glad to see a lively discussion here.  There's been some really good information, and some less-good information posted.  This is a complicated issue and is worth the time to talk about it.

RE - Honda parallel kit - there is a paralleling kit, but that wasn't how Debbie was using her pair of EU3000s - she was plugging some things into one, and other things into the other.  There are pros and cons to both methods.  In both cases, the chassis grounds of the generators should be connected.

Without the parallel kit, each generator makes an independent 20A 120V unbonded circuit.  With the parallel kit, you get a 50A 120V receptacle, generally designed for an RV.  The hot, neutral, and ground are paralleled, but it is still unbonded.

Bonding the ground to neutral is part of standard electrical service practice, because without it, a fault to ground won't trip the breaker or GFCI. 

The Honda generators ship without this bond and without GFCI receptacles because the thinking is that in a single-circuit generator, there really isn't another fault path for the current to go anyway.  I.e you can hold the hot wire and stand barefoot in a puddle all you want, but since there's no connection between the earth ground and the current-carrying wires, there's no circuit, whereas if you do have a ground -> neutral bond, now you are depending on the GFCI device to function, and sometimes they fail.

This becomes more complicated when you have multiple fault paths.  Say you have a pinched extension cord that happens to short your neutral wire to the stage which creates a ground -> neutral bond, and you also have a guitar amp with a hot chassis fault - now you're in trouble.

A system with multiple circuits - such as a pair of unrelated generators or multiple circuits from a larger generator can create multiple fault paths as well.

Multiple ground -> neutral bonds are problematic, because effectively you turn the ground wire into a current carrying conductor.  This is fine for the initial bond at the service because the bond needs to be somewhere to close the fault current circuit and you have tied this point to earth with a nice big ground rod driven into the ground, but if you have more than one bond, current can potentially flow on the chassis of the generators relative to earth - in other words you can get shocked touching a generator.

We have been talking about 3 basic setups: Paralleled Hondas, Unparalleled Hondas, and the EU6500/EU7000.  Brief pros and cons:

- Paralleled Honda EU3000is: Provides a 30A 120V receptacle with a pair of EU2000is or a 50A 120V receptacle with a pair of EU3000s.  If you need these larger single circuits, this is your only choice with small generators.  If you don't need these high-current circuits and don't have an external distro to manage it, the parallel kit is arguably not better than just dividing the load between your two generators.  For safest operation, you need to do a ground -> neutral bond external to the generator (best done inside your 30A or 50A distro, IMO), and you need to use external GFCI protection.  A ground rod is a good idea if you're using the G-N bond in your distro, or a critical idea if you're using multiple bonds at the generators.  The parallel kit provides an additional point of vulnerability in that you are using single wire connectors.  If the neutral wire fails or becomes disconnected, you could be in trouble.

- Non-paralleled Honda EU3000is: Each generator provides a 20A 120V circuit with a little generator headroom for peak loads.  If you're just running devices that fit on 20A circuits, this is arguably simpler and better than trying to use the parallel kit and and external distro.  Safest operation requires the generator frames to be bonded with a #10 wire, and each generator to have a ground -> neutral bond (can be accomplished by making a male plug with a jumper between ground and neutral and plugging one of these into each generator).  These generators should be as close together as possible, and a ground rod should be used to ensure that the generator frames stays at the same electrical potential as the earth.  External GFCIs are required.

- Honda EU6500is: Generator provides 2 20A 120V circuits on the panel, or with an external distro can provide 30A 120V/240V.  The significant advantages are a much larger power platform that can handle higher peak loads, and a unified electrical system.  This is much less of a band-aid compared to using multiple generators - with or without the parallel kit.  A ground -> neutral bond is required (can be done using a male L5-30 plug with the G->N jumper), but now this bond is happening only at the current source. External GFCIs are required. 

By the way, if you're using a metal stage, you need to bond your stage to your electrical system ground too.
« Last Edit: September 17, 2015, 09:34:33 AM by TJ (Tom) Cornish »
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Art Hays

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Re: Generator question
« Reply #41 on: September 17, 2015, 12:08:07 PM »

From the generator schematics I can't see how paralleling two EU2000's is any different from using one EU6500 other than convenience, e.g. capacity issues and how you draw the loads. 

Thanks, Tom.  A very clear summary of all the issues!

I did find some more info on my question above.  If the loads aren't well behaved with regard to power factor then the harmonic currents can kind of circulate between paralleled generators lowering the total output available ('cross currents').

I also found that OSHA requires generators to have a ground-neutral bond on job sites (so there's info on the web about how to modify generators to do this).  But when connecting a generator in a standby application using a transfer switch, say at a home, you don't want to have two bonds since the panel is already bonded.  This may be another reason Honda ships without the ground-neutral bond.
« Last Edit: September 17, 2015, 12:13:34 PM by Art Hays »
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TJ (Tom) Cornish

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Re: Generator question
« Reply #42 on: September 17, 2015, 12:31:48 PM »

Thanks, Tom.  A very clear summary of all the issues!

I did find some more info on my question above.  If the loads aren't well behaved with regard to power factor then the harmonic currents can kind of circulate between paralleled generators lowering the total output available ('cross currents').
This is an additional advantage of the EU6500 series if you can run some of your gear at 240v, since this sidesteps the harmonics issue.  Most power amps and powered speakers can be run at 240v. My solution is to use a distro that uses an L14-30 inlet from the generator and provides a 20A 240V L6-20 receptacle and a couple Edison circuits.  I then use a Poor Man's distro like this one http://triktags.com/power.htm to distribute the 240V power via Powercons to amps/powered speakers, which is an acceptable use of the Powercon connector, as long as it's breakered at no more than 20A (this is the importance of the first distro).  The 120V receptacles from the first distro supply stage power and all other 120V needs.

I also found that OSHA requires generators to have a ground-neutral bond on job sites (so there's info on the web about how to modify generators to do this).  But when connecting a generator in a standby application using a transfer switch, say at a home, you don't want to have two bonds since the panel is already bonded.  This may be another reason Honda ships without the ground-neutral bond.
OSHA is another ingredient in the soup, and occasionally conflicts with the NEC.  The Hondas ship unbonded for the reason I mentioned earlier about the presumed safety of an isolated system, as well as for the home backup power application you mention.  I wish they put a selectable G->N bond on the generator, but I suppose that's just another thing to confuse the average user.
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g'bye, Dick Rees

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Re: Generator question
« Reply #43 on: September 17, 2015, 12:32:50 PM »

Thanks, Tom.  A very clear summary of all the issues!

I did find some more info on my question above.  If the loads aren't well behaved with regard to power factor then the harmonic currents can kind of circulate between paralleled generators lowering the total output available ('cross currents').

I also found that OSHA requires generators to have a ground-neutral bond on job sites (so there's info on the web about how to modify generators to do this).  But when connecting a generator in a standby application using a transfer switch, say at a home, you don't want to have two bonds since the panel is already bonded.  This may be another reason Honda ships without the ground-neutral bond.


All of ths has been covered in depth in the POWER FORUM.  It's worth the search and the read and you won't have to go through it piece by piece again.

Everybody go over there and look it up.
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Stephen Kirby

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Re: Generator question
« Reply #44 on: September 17, 2015, 01:35:33 PM »

Please don't take this personally-I am sure there are plenty of audio and business principles you could school me on-but this statement shows a basic misunderstanding of grounding and bonding issues and how electrical power works.
Thus the reason I brought up the questions.  I'm trying to translate electronics and EMI stuff into power distribution.  My understanding is that the ability to dissipate energy is more or less the definition of ground.  Where something is isolated from the ability dissipate the energy, there will be a potential between it and something that does.  One reason a ground connection is often called a "drain".  At electronics frequencies, the potential between one drain and another is a major headache.

e.g.

  These generators should be as close together as possible, and a ground rod should be used to ensure that the generator frames stays at the same electrical potential as the earth.

Without that tie to earth, something that is either tied loosely to earth or has a greater ability to dissipate energy like a big metal stage sitting on dirt (not a serious connection but a better drain nonetheless) can develop a potential between it and something with no such reference or drain.  Thus the comment (maybe using the wrong terminology for electrical power) that the generator is floating relative to the stage.  And the concern that there could be a potential between anything connected to the generator's ground or neutral and the stage.

Another example, and maybe something different than my understanding was happening here, some years ago I had a machine (SMT placement machine) that would periodically lose it's mind and crash randomly.  Drove us nuts for a couple months until one day I happened to touch the machine and an output conveyor at the same time and felt a tingle.  I grabbed a meter and measured 40 odd VAC between the two chassis.  The big machine was hardwired into a 3 phase service but the conveyor was just plugged into Edison outlets.  Tracing that back I found that some production worker had inserted an outlet strip so they could plug a fan or something else into it that had the ground pin cut off.  That let the chassis of the conveyor float up to the point where when vibration caused the two frames to touch, the blip into the ground was enough to cause the embedded computer to crash.  I've since made sure to specify plenty of extra Edison outlets on any line in installed and banned plastic outlet strips that workers and supervisors seem to sneak into plants.  And which I've had no end of audio problems with in my music world due to poor ground connections.

There are a lot of folks like me and Debbie running small systems in various situations like the one she describes in the OP who may be overwhelmed by the discussions in the power sub-forum.  Or coming from different disciplines that look at things differently from different experiences.  If I've got this all wet, I'm sure we could all benefit from a basic understanding.
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TJ (Tom) Cornish

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Re: Generator question
« Reply #45 on: September 17, 2015, 02:19:08 PM »

Stephen, some good thoughts.  I think we tend to forget that electricity is analog, not digital, and as such we end up with a lot of continuums.  In between "broken" and "Working" we have lots of "sort of working" or "sometimes working" situations; and in the safety dimension we have "really dangerous", "somewhat dangerous", "possibly dangerous depending on the circumstances", ...

The case of bonding generators fits this exactly.  In a simple case, the unbonded, non-GFCI single-circuit generator is simpler, less likely to fail, and safer in a single fault situation than a bonded generator. However, that same practice in a more complicated environment quickly becomes less-safe than a bonded setup.

I haven't seen a way to distill down power distribution down to something trivial - it is a knowledge investment just like other audio skills.
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Stephen Swaffer

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Re: Generator question
« Reply #46 on: September 17, 2015, 11:50:45 PM »


I haven't seen a way to distill down power distribution down to something trivial - it is a knowledge investment just like other audio skills.

However, your earlier post did a good job of distilling down to a simple "connect the dots" procedure when using the Honda generators-as least as far as safety is concerned.

There are plenty of other nuances to learn-such as was mentioned a 20 amp generator circuit may not have the same reserve power for surges as a 20 amp POCO supplied circuit, etc.  Those things you can take time to learn and grow with-but on the safety side if you have to "connect the dots" for a while do it-just don't skip any-even they don't really seem important.

Thus the reason I brought up the questions.  I'm trying to translate electronics and EMI stuff into power distribution.  My understanding is that the ability to dissipate energy is more or less the definition of ground.  Where something is isolated from the ability dissipate the energy, there will be a potential between it and something that does.  One reason a ground connection is often called a "drain".  At electronics frequencies, the potential between one drain and another is a major headache.

e.g.

Without that tie to earth, something that is either tied loosely to earth or has a greater ability to dissipate energy like a big metal stage sitting on dirt (not a serious connection but a better drain nonetheless) can develop a potential between it and something with no such reference or drain.  Thus the comment (maybe using the wrong terminology for electrical power) that the generator is floating relative to the stage.  And the concern that there could be a potential between anything connected to the generator's ground or neutral and the stage.

In power distribution, the "ground" connection or wire is not supposed to have current flowing on it-code prohibits "objectionable" current.  (I realize that is theoritical and there will likely always be minor stray currents.) The "ground"-as in the earth is used for safety-and to dissipate energy from lightning or other major faults.  The ground wires as in equipment grounding conductors in a system are there to provide a path for fault current to trip breakers or blow fuses.

You are correct in saying the generator is floating-it is not referenced to the stage. I guess in my mind, ground is more a point of reference-which is useless unless we intentionally make a connection to that point of reference. To compare with electronics, a similar situation would be if I asked "what is the voltage at point A?"  Meaningless unless I give you a reference point.  Similarly, 2 different PC boards with disconnected commons create issues when trying to determine potential  difference-obviously the situation is "out of control".  By grounding and thus referencing to ground we make fault conditions and corrective actions more predictable.
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Steve Swaffer

Stephen Kirby

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Re: Generator question
« Reply #47 on: September 19, 2015, 12:15:59 AM »

Thanks Steve.

So the neutral is effectively the "drain" and reference and "ground" is a fault path for anything that goes haywire.?  Therefore I expect that you want to have neutrals commoned at the same point they're tied to a ground point.  So that any return current drains back to the same potential and any fault detection is double referenced to the same point.  Which is how I understand house wiring.
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Guy Holt

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Re: Generator question
« Reply #48 on: September 20, 2015, 10:50:56 AM »

 
When im in a club, i can run my rig,lighting backline and foh all on 1 20 amp circuit. I did an outdoor show which used a generator to provide power…. As soon as the first note dropped the meter on the regulator dropped as low as it could go. … My questions to the forum are; could the generator have been undersized?

Many good recommendations offered, but no real explanation for what the OP experienced. Clearly the generator was not undersized (at least not in the sense that OP means) for surely a trailer-mounted generator is capable of delivering a single 20A circuit.  And while 14AWG cable is slightly undersized for the OP’s load, 25’ is not long enough of a run to cause the kind of voltage drop he experienced.  The cause of the severe voltage drop as soon as the load kicked in was clearly something else.  Without knowing all the details of his load, I am going to guess the harmonics drawn by some or all of his load was the cause simply because what worked fine on grid power, did not on generated power.

I don’t know about the JBL PRX powered speakers, or the QSC HPR 181 subwoofers, because manufacturers generally don’t specify, but it is very likely that the 12 LED Par64s are not power factor corrected and so draw harmonic currents.  In a recent survey of LED lights that I conducted, all of the LED Pars (like the Chauvet Slim Par Pro below) were not power factor corrected (pfc.) With power factors as low as .45, LED Pars can draw twice the current than a tungsten light of the same wattage and draw considerable harmonic currents. The harmonic currents non-pfc LED lights draw can cause severe voltage waveform distortion in the power supplied by generators while having no effect on the power provided by the grid (To see which LED lights are power factor corrected or not, use this link - http://www.screenlightandgrip.com/html/emailnewsletter_generators.html#anchorHigh Output AC LEDs - to see some of the results of my tests.)


The Chauvet Slim Par Pro RGBA has a pf of .61 and Total Harmonic Distortion of 81%

As is evident in the power quality meter reading of the Chauvet Slim Par Pro above, the high peaked pulsed current (lower waveform on the left) drawn by its’ smoothing capacitors is a distorted waveform that does not resemble the sinusoid of AC voltage or the current drawn by an incandescent light. As such, the current drawn includes a number of harmonic currents in addition to the 60hz fundamental (see Fast Fourier Transformation above right).  The accumulative effect of twelve of these lights can cause not only line loss but also cause voltage “flat topping.” If the voltage waveform distortion is severe, it can also cause voltage regulator sensing problems and inaccurate instrument readings, which would explain the problems experienced by the OP.

Let’s look at the line loss component of this problem first. As you can see in the Fast Fourier Transformation of the Chauvet Slim Par Pro above, non-pfc LEDs draw a distorted current waveform that is rich in harmonics. The higher harmonic frequencies create what is known as "skin effect" in cable. Skin effect is a phenomenon where the higher frequencies cause the electrons to flow toward the outer sides of a conductor. Since the flow of the electrons is no longer evenly distributed across the cross sectional diameter of the conductor, more electrons are flowing through less copper and the resistance of the conductor increases. This increase in resistance reduces the ability of the conductor to carry current, resulting in greater voltage drop over shorter distances. In this case, the situation was aggravated by the fact that the cable was undersized for the load to begin with.


The area of the cross sectional diameter of a conductor used by DC current (left), Low Frequency AC Current (center), High Frequency AC Currents (right).

But, skin effect alone would not account for the problems the OP experienced. The other contributing factor was probably voltage “flat topping” caused by the high impedance of the industrial generator used.  What causes flat-topped voltage? According to Ohm’s Law current reacts with impedance to cause voltage drop. For example, when encountering the high impedance of an industrial generator, a 3rd harmonic current will produce a voltage drop at a 3rd harmonic voltage. Likewise a 5th harmonic current will produce a voltage drop at a 5th harmonic voltage, etc. Each harmonic current drawn by the non-power factor corrected LED flows through the system impedance, resulting in a voltage drop at that harmonic frequency. In other words, where a distorted current waveform is made up of the fundamental plus one or more harmonic currents, each of these currents flowing into an impedance will according to Ohm’s Law, result in a voltage drop resulting in voltage harmonics appearing at the load bus and distortion of the voltage waveform like that exhibited in the right oscilloscope shot below.


Left: Pkg. of 2-1200 HMI Par w/ non-pfc ballasts & Kino Wall-o-Lite powered by grid power. Right: Same Lighting Pkg. powered by industrial Generator (Honda EX5500) Note different effect that the same non-linear load harmonics have on grid power and power from an industrial generator.

This pattern does not appear in the voltage waveform of the grid power above because of its’ much lower impedance.  Which means that none-linear loads which work fine on utility power, will react entirely different when powered by a generator set. In practice, when you plug non-linear loads like non-pfc  amplifiers, power wedges, and LED lights into a wall outlet you need not be concerned about current harmonics producing voltage distortion. The impedance of the power source is so low, the distortion of the original applied power waveform so small (less than 3%), and the power plant generating capacity so large by comparison to the load, that harmonic currents will not effect the voltage at the load bus.

However, it is an all-together different situation when plugging these same loads into a small portable generator that is not specifically designed to remediate the effects of harmonics. Given the comparatively large sub-transient impedance of industrial generators, and the high THD value of their inherent power waveform (see no load waveforms below), you have a situation where even a small amount of harmonics being fed back into the power stream will result in a large amount of harmonic distortion in its’ voltage.


Left: Original Grid Waveform w/no load & low THD (>3%)
Right: Original waveform of an industrial generator (Honda EX5500)  w/ no-load & high THD (@17%)

The rudimentary AVR systems used in portable industrial generators are especially ill equipped to deal with the voltage distortion caused by the harmonics drawn by LED lights because the harmonic currents they draw create flux in the armature coils of the generator’s stator that reacts additively with the generator’s exciter flux in the field poles of the generator’s rotor to increase saturation and produce a higher terminal voltage than called for a given load.  Consequently, the AVR system responds erroneously to control voltage by reducing excitation.  Because an AVR system is a closed-loop control system, as the voltage is incorrectly lowered, based on the distorted information, it is then even more incorrect.  The end result is that the regulator goes to its minimum excitation capability and the voltage output drops severely.

The impedance of a generator is not an easily known quantity. Depending on its’ size and design, the impedance of a generator will be 5 to 100 times that of a utility transformer and it will change as the load changes. But where the OP was using an industrial generator, the internal reactance would have been sufficient to cause appreciable voltage distortion and consequently a severe voltage drop on the generator output.

We can now also understand why a Honda inverter generator would have served the OP better.  As demonstrated above harmonic currents react with impedance to cause voltage waveform distortion.  The magnitude of the voltage waveform distortion is a function of the source impedance. Which means that the generator with the lowest internal reactance to an instantaneous current change at a given load will typically have the lowest value of total harmonic distortion under nonlinear load conditions. This is one of the great benefits to using inverter generators over industrial generators: inverter generators have much lower internal reactance and so they are less prone to voltage waveform distortion caused by the harmonic currents drawn by switching power supplies.


Left: A 1200W non-linear Load powered by Grid Power. Center: A 1200W non-linear Load powered by an industrial generator. Right: A 1200W non-linear Load powered by Inverter Power.

As can be seen in the oscilloscope shots above, inverter generators are less prone to voltage waveform distortion because, as mentioned previously, the inverters completely process the raw power generated by its alternator (converting it to DC before converting it back to AC) – making the AC power it generates completely independent of the engine. In fact, its’ microprocessor controller can vary the engine speed without affecting the voltage or frequency of the power the inverter module puts out. Now that the internal reactance of the engine is separated from the power output, harmonic currents encounter very little impedance; and, as is evident in the oscilloscope shot above right, there is considerably less voltage distortion at the load bus of inverter generators than there are conventional generators. The net benefit is that non-linear loads, like the switching power supplies of non-pfc equipment, do not adversely affect the power of inverter generators as they do the power of industrial generators. Which means that non-linear loads will operate more reliably on inverter generators.

For a more detailed explanation of what causes voltage waveform distortion and how to mitigate it, see my white paper on the use of portable generators in motion picture production that is available at http://www.screenlightandgrip.com/html/emailnewsletter_generators.html.

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

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Re: Generator question
« Reply #49 on: September 20, 2015, 03:58:19 PM »

Guys response could be the answer-another possibility is a bad (corroded) connection/loose wire internal to the genny or anywhere prior to the Furman with a high resistance.  This would mimic a genny with a high internal impedance. It would also allow the voltage to be just fine under no load-but drive it lower and lower with an increase in load.

We are all familiar with the car battery that lights the dome light but everything dies when you hit the starter-could be a dead battery (inadequate genny) or it could be an oxidized battery terminal.

Just something else to look for and troubleshoot that might be fixable in the hour or 2 immediately before a gig when there is not enough time to find another genny.
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Steve Swaffer

ProSoundWeb Community

Re: Generator question
« Reply #49 on: September 20, 2015, 03:58:19 PM »


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