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Electric generators power different from grid powe

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jdemaris

09-17-2005 19:42:21




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Ran into a problem recently with several electric generators. I was trying to use a shop-sized battery charger by plugging into a gas powered portable generator, and found out it would barely put out a 1/4 of what it was supposed to. I had it on a 40 amp charge rate and it barely put out 8 amps. I then tried a smaller 15 amp charger, and found out it didn't work near its capacity either. So, I then tried some different generators. All the same problem - and they all work fine otherwise running power tools and such. I tried a small Coleman 1000 watt generator, a larger Coleman 1850 unit, a Homelite 4400 unit, a Generac 5500, and finally my PTO powered Generac 17,000 watt unit. The 17,000 watt unit worked fine, the others did not. I then tried a Fairbanks-Morse Continental powered 19,000 watt generator and it too worked fine. I did some research and found out the following. Power from the electric company that is rated at 120 volts actually peaks at 170 volts on each Hertz cycle. Most battery chargers are designed to clip off a small section of the peak current in each Hertz cycle between the 160-170 volt range. Now, many if not most smaller or cheaper generators only put out a peak voltage of 150 - 160 volts, which goes unnoticed when using power tools, TVs, etc. But, it does not work with battery chargers. Does anybody know of a good way to check peak voltage in a generator without spending big dollars on a Fluke peak-voltage meter or carrying around an oscilloscope? I've been given a "rule-of-thumb" designation of generators that states: if it costs under $2000 it probably does not put out proper voltage, and if it's over $2000 it does. I was also told that most "jobsite generators" don't have the correct power, and most "standby" generators made for household backup systems will. I've also read that the new inverter style generators that Honda and Yamaha are now selling make power that is the same as grid current since they use DC generator heads instead of AC and run the power through a full sine-wave inverter.

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tech4

09-19-2005 16:16:22




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 Re: Electric generators power different from grid in reply to jdemaris, 09-17-2005 19:42:21  
You might want to read this site that addresses that problem. There are diodes that break down at certain voltages called zener diodes that are used as regulators and your charger probably uses SCR's that have a gate that controls the point that the rectifiers work. These are quite common in constant current power supplies and many other applications. It is the same as the dimmer switches used in lighting systems. True the peak voltage has some effect but it is the fact that the voltage is dirty out of the cheaper generators and it is not allowing the SCR's to be triggered correctly. This could be corrected electronically in the charger by cleaning up that trigger voltage but it would require additional components. Again I say try some additional loading on the generator although that may seem wrong and see if it works. There is no real mystery with common diodes and AC generators. The alternator in every automobile there is has an AC alternator that produces AC and rectified by the internal diodes and the voltage controlled by varing the field current. AC out of an alternator is neither clean or steady in frequency as the diodes could care less. Your battery in a car charges at all speeds and all kinds of battery conditions in the millions of automobiles. It is the electronics in your charger that is at fault and again I say that should be the manufactures responsibilty. Battery chargers are not rocket science or big mysteries.

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MarkB_MI

09-18-2005 20:30:37




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 Re: Electric generators power different from grid in reply to jdemaris, 09-17-2005 19:42:21  
A couple of thoughts. First, no inexpensive generator is going to have a true sinusoidal output. But it ought to be close enough.

I think what somebody was trying to tell you about "..clipping off a small section of the peak current.." is this: You can only charge your battery when the rectifier in the charger is forward biased. Think of the rectifier as a check valve on an air compressor. The valve only opens when the compressor piston nears the top of its stroke. As pressure (or voltage) rises in the tank (battery), the period of time that the valve is open (rectifier is forward-biased) becomes shorter and shorter. So what may be happening is that the generator can't produce enough voltage to forward-bias the rectifier.

Another possibility would be that when the rectifier is forward-biased, the generator can't source enough current to be useful. An oscilloscope would show that the generator output is "clipped" as soon as you turn on your charger, but is fine otherwise.

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jdemaris

09-19-2005 09:00:41




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 Re: Electric generators power different from grid in reply to MarkB_MI, 09-18-2005 20:30:37  
The information as it relates to the charger "clipping" the 160-170 volt peak is providing in the tech. information from the manufacturor. As far as recifiers go, I don't know exactly what is being used - but I do know there are voltage sensitive rectifiers that not only server has electric "check valves", but also server as "pass' and "no pass" gateways dependent on voltage. The problem of many electric generators not being able to properly run DC battery chargers seems to be a common one. I didn't know about it when I first encountered it, but have now discussed this with several solar-electric dealers and installers. As far as small generators not producing the same sine-wave as grid current, some do and some do not. From what I've read, the new "inverter" series from Honda and Yamaha work very well.

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tech4

09-18-2005 10:28:05




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 Re: Electric generators power different from grid in reply to jdemaris, 09-17-2005 19:42:21  
My first thoughts were BS but I realized your seem to have tried several generators and had a problem with more than one. Also my thinking was along the lines of the old fashion transformer-rectifier-filter output as in the old battery chargers. Even at 12 volt and 40 amps that is only 480 watts which is still less than a 1/2 kilowatt and a 5 killowatt generator should handle that nicely. Then I decided to do some research and the type charger you are using is state of the art using electronics and power phase control and the lightly loaded generator is producing a very distorted output. I don't think it has anything to do with the peak voltage as that is somewhat of a given and I am sure the electronics has regulators that compensate for power grid voltages which may be anywhere from 110 to 125 volts sometimes. I see 2 possible solutions load the generator with a resistive load (light bulbs or coil heaters) to smooth out the generator or use a higher KW rated generator that puts out a smoother waveform. Try the resistive load first with the smaller generator and see at what point the charger begins to come to full output. I can see that there is an electronic solution that the charger manf. should incorporate in chargers that could correct that problem.

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Mark Salser

09-18-2005 09:51:53




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 Re: Electric generators power different from grid in reply to jdemaris, 09-17-2005 19:42:21  
jdemaris,

I don't know if you already know about backwoodssolar.com or not, but I would recommend that you give them a call and/or check out their website. I have installed a couple of PV systems on horse trailers using equipment I purchased from them and I have found them to be tremendously knowledgable and very willing to provide helpful advice even when they didn't sell me equipment. Also, their catalog is not only a good source for parts etc, but it is also full of good advice about how to design and size a system, and they are focused on creating useful systems at reasonable prices rather than rediculously expensive systems.

In regard to your specific problem, they sell chargers that work well with lower quality generator power, voltage boosters to overcome the problem that you are currently experiencing, and generators that produce true sine wave power identical to grid power. You should give them a call. By the way, I have absolutely no association with their company, but I have found them to be tremendously helpful.

And by the way, thank you for all of your extremely informative posts on the Crawler, Dozers, etc discussion forum.

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jdemaris

09-18-2005 10:32:00




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 Re: Electric generators power different from grid in reply to Mark Salser, 09-18-2005 09:51:53  
Thanks for the info - I've bought from them before, and yes, they are surprisingly knowledgeble. Their catalog alone provides more useful information then some books I've read on the subject. They can name some specific electric generators that work well, and some specific ones that do not. The problem lies, in my situation, when I have a chance to buy a generator at a good price but don't know what quality power it puts out. Especially if it's distant. I've spoken to a few dealers that sell generators (mostly on Ebay), and many, if not most, are clueless. One recently scolded me for even asking about peak voltage, informing me that "all his generators put out steady 120 volts AC". That seems to be sort of an oxymoron. If AC denotes alternating current that alternates polarity 60 times a second (sometimes 50 in Canada), I don't think "steady" is a proper term.

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Stickler

09-18-2005 17:18:44




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 Re: Electric generators power different from grid in reply to jdemaris, 09-18-2005 10:32:00  
Huh????? ?? So just where in Canada is grid power 50hz? I happen to operate power stations for a living, and I can say for a fact that our power is 60hz�0.02hz!



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jdemaris

09-19-2005 08:51:07




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 Re: Canadian electricity in reply to Stickler, 09-18-2005 17:18:44  
There were, at one time, many areas in Canada that used 25 or 50 cycle alternating current. Since you indicate you're in Canada, seems you ought to know that. Considering the context of this forum (being somewhat history based), my comments are not just applied to technology only being used today. Besides tractors, I collect older radios. I have many Canadian radios including a Viking that sits besides me right now. The back reads: "50 cycle 120 volt AC current only". THe owner's manual lists the radio as available from the factory for 120 volts AC in 25 cycle, 50 cycle, or 60 cycle. Viking was made by T. Eaton Co. of Canada. There is also a warning for use in Canada, stating: "any person operating this receiving set without having first having obtained a license from the Minister of Transport of Canada is liable for summary conviction . . . and said receiving set may be forfeited to His Majesty by order of the Minister." On the subject of Canadian power generation, the 75,000 kilowatt Rankine station and part of the Adam Beck station at Niagara Falls produce 25 cycle power.

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buickanddeere

09-20-2005 20:28:40




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 Re: Canadian electricity in reply to jdemaris, 09-19-2005 08:51:07  
The Rankine Station which is beside the Horse Shoe Falls was closed in the mid 1990's if memory serves. Three units at Sir Adam Beck I are 25 cycle. The rest were converted to 60. There is a 25 to 60 or 60 to 25 MG set in the Highbury Electrical swichyard in London. The 25Hz loads served are a couple of AC to DC gen sets at the steel rolling mills in Hamilton.



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Stickler

09-19-2005 17:27:38




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 Re: Canadian electricity in reply to jdemaris, 09-19-2005 08:51:07  
AND..... ..we haven't had radio licenses since before WWII



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Stickler

09-19-2005 17:25:48




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 Re: Canadian electricity in reply to jdemaris, 09-19-2005 08:51:07  
That's long before I was alive then, and I'm 46. If anyone is still generating at 25hz, then they have some mighty fancy conversion equipment, because grid power is definitely all at 60hz, the entire country.



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Stickler

09-19-2005 17:44:42




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 Re: Canadian electricity in reply to Stickler, 09-19-2005 17:25:48  
have a boo here. Towards the end, they talk about the frequency changers and the fact that grid power was converted to 60hz in the 1950's.

http://www.technology.niagarac.on.ca/people/mcsele/Rankine.html



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Coloken

09-18-2005 06:08:49




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 Re: Electric generators power different from grid in reply to jdemaris, 09-17-2005 19:42:21  
interesting discussion. We asume true sine-wave wave form, but they must not be doing it. Would a 117 volt (RMS) square wave run a charger at all? Now wait a minute..We are not clipping the 117 volts. when we put 117 volts AC, into a transformer to bring it down to 12 volt ( more like 17, and lets over look the rectifiers drop) the transformer should put it back to sine-wave. Being an old farmer, I would go over and crank up the governer to what ever it took to charge.

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buickanddeere

09-17-2005 22:03:27




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 Re: Electric generators power different from grid in reply to jdemaris, 09-17-2005 19:42:21  
If the generator puts out a true AC 60HZ sine wave at 120V rms (root mean squared) which is 169.7V peak? There should be no difference between grid power and generator power. If the generator lacks a true voltage control regulator. And/or is under sized. The output voltage, frequency and likely the current will be too high at light loads. And too low at full load or during overload. Try those poor performing generators again while measuring terminal voltages. Some loads throw harmonics back into the supply line. Electronic items with switching power supplies etc are notorious. The output from a small generator and depending on it's voltage regulation can be messed up.

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jdemaris

09-18-2005 05:42:23




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 Re: Electric generators power different from grid in reply to buickanddeere, 09-17-2005 22:03:27  
I ran into this problem while working on a solar-electric hybrid system at a remote cabin. The system uses a bank of photovoltaic panels, a generator, a bank of 10 deep-cycle 6 volt batteries, and a large inverter/charger. The inverter/charger has a built-in 80 amp battery charger for the battery bank (hooked in series-parallel and kept at 12 volts). After discovering that the 80 amp charger will only put out 1/4 of its rated output, I read the manual closely and found the disclaimer about it not working with many electric generators. After further investigation with solar-electric installers, I found this problem to be a common one. There are voltage amplifiers available that enable small generators to work better with chargers. There are also stand-alone battery chargers that use a non-conventional technology and therefore work better with a low voltage peak or a modified sine-wave. All this stuff is expensive, however. I am looking for an easy way to tell, when a generator purchase is in mind, if it will, or will not run a battery charger. I will be helping to install a few more photovoltaic hybrid systems here in the Northeast where the added generator is, more-or-less, a necessity for short or cloudy days.

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