Standby Generator voltage drops

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Old 08-30-10, 12:25 PM
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Standby Generator voltage drops

I have a standby generator that I believe is made by GETECH. It is a self regulating generator, so no voltage regulator aside from the engine. When the power goes out, I can turn the generator on and at first it is putting out 115v at the outlets. Then after a couple of seconds, it drops to 110v, then a few seconds later it drops to 108v. The RPM of the motor does not change. Sometimes the voltage will briefly kick up to 110v, but generally it sits at 108 indefinitely until you turn it off and back on.

Any ideas? Someone suggested the capacitors, but I checked them both with a DVM and they both charge to infinity after a while.
 
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Old 08-30-10, 01:20 PM
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Are you running test under load? What kind of meter are you using?
 
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Old 08-30-10, 01:25 PM
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Yes, this is after several seconds of running, so I am assuming it is after all my appliances and such have started running off the generator power.

I am using a simple plug in meter, like the ones they use for RV's. Its an analog meter that shows the voltage when plugged into an outlet.

I have a DVM, but am somewhat afraid to touch the terminals on the generator when running to test it unloaded. I KNOW it WAS functioning because a technician came out and set the idle to whatever it was supposed to be at and verified that both legs were putting out the proper voltage at a spec'ed percent of each other. I don't recall ever having it checked under load. I do know the RPM does not change when the voltage does.

I originally decided to check the voltage because I thought my ceiling fans were running slow, but more alarming, I could 'hear' the generator motor through the fan motor...sort of like a hum at the same frequency that the generator was running at. That may or may not be a problem, but its why I checked it.

I decided to turn it off based on that and the low voltage to keep from damaging anything.
 
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Old 08-30-10, 01:54 PM
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Try the test again running only a big resistive load like a space heater set on hi or a big halogen work light.
 
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Old 08-30-10, 01:59 PM
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What will this test tell me?
 
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Old 08-30-10, 02:02 PM
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It will tell you if the voltage drop is stable under a stable load (which is normal). If the voltage is erratic under a stable load then you definitely have a problem with the generator.
 
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Old 08-30-10, 02:08 PM
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OK...so if it IS stable with a stable load....then having it drop to 108v under full load is OK?

When I fired up this generator, the power had already been off for 3 hours. So, it is likely that two refrigerator/freezer combos and one deep freeze were all trying to cool at the same time. Still, I thought the generator would compensate for that and keep voltage at 115 or so. In fact, I don't see how it can't unless the RPM changed...and that did not happen and there is no voltage regulator.

I will test as instructed though and report back when I get it done.
 
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Old 08-31-10, 09:56 AM
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When I test the unit unloaded, I want to test both 'phases' right?

So that means on my DVM, I set it to AC voltage, and check voltage across red/white and black/white...and those should be about 115 or so a piece +/- right?
 
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Old 08-31-10, 06:13 PM
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Most of the small portable generators will depend on the engine speed to regulate the voltage so if you are getting 120 volts if set up right it will be on 60 HZ if not it will read lower like 115 volts it will be about 55 HZ or so.

What you really need is HZ meter to verify the engine speed is correct range and most portable generators are dailed on 3600 RPM for two pole verison { the no load speed will be little higher like 3650 to 3750 RPM range }

You can not just depending on the engine sound for the speed you will need a HZ meter or engine tachometer which it will work with mageto ingtions { you may want to check with the small engine shop if they have that }

otherwise a simple 120 volt clock motor { not the digtial kind } you can able tell if too slow it will show X numbers of minutes and seconds behind.

That why a simple thumb of rules with all generators always set the HZ { or RPM } first then deal with voltage if they have adjustable voltage regulator[s].


Merci.
Marc
 
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Old 09-01-10, 08:26 AM
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This is not a 'portable' generator, but the same principles apply, I believe.

How do you possibly set the proper Hz loaded if your load varies?

My RPM does not change, but the voltage does under load. How is this possible? Regardless of whether its set right or not, it should remain constant with the RPM right?
 
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Old 09-01-10, 12:44 PM
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When you say the rpm does not change, how are you measuring this? By ear? You really need to verify that it is putting out 60hz AC. My guess that it is slightly slow. Slow Rpms = Lower voltage. Do you know how to adjust the governor of the genset? If you do, adjust the no load voltage to about 124 volts. When you load up the genset you should see some drop in voltage which is normal. Ideally this will put you in the 115 - 120 volt range which is where you want to be.
 
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Old 09-01-10, 12:56 PM
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Originally Posted by agdodge4x4 View Post
This is not a 'portable' generator, but the same principles apply, I believe.

How do you possibly set the proper Hz loaded if your load varies?
There is a thing called a governor on the genset. Its job is to control the throttle setting in respone to load changes so that the proper Rpm is maintained. Most governers are not perfect however and they will vary the RPM slightly (2-5%) from no load to full load.
 
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Old 09-01-10, 01:40 PM
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What I mean is how can the voltage change while the RPM remains constant. This generator has no voltage regulator. It is self regulated with RPM only.
 
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Old 09-01-10, 02:11 PM
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What is the size of the generator and the size of the loads (in amps) on it? It sounds like you have normal voltage drop when putting loads on the generator. If the voltage is getting down to 108 V, there could be too much load on the generator.
 
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Old 09-01-10, 03:03 PM
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Originally Posted by agdodge4x4 View Post
What I mean is how can the voltage change while the RPM remains constant. This generator has no voltage regulator. It is self regulated with RPM only.
The SHORT answer for your generator is that it cant. So that usually means that low voltage is a result of low Rpms. IF you spin that puppy at 3600rpm I bet you a doughnut that you will get 120v at 60 Hz. If the "technician" set the no load volts at 115 (which is 5v low btw) it is not suprising to me that it is dropping to 108v under a load. Ideally the genset shout be set to produce 120V under half load. That way it spins a little fast with no load and a little slow under 100% load, but is still within tolerance.

I hope this helps, because I dont know how else to explain it.
 
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Old 09-02-10, 12:20 AM
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There is one Item it kinda really click on my mind here this item it do have HZ feature { you will have to find it but pretty easy to find the HZ setting }

so here it is Kill-A-Watts

That will help you set in the HZ what you are looking for and when you put a load on it you can actally see the HZ will change if the govoner is not set up right and it will help you with troubleshooting.




Merci.
Marc
 
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Old 09-02-10, 09:18 AM
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OK, this all helps tremendously. The FIRST thing I want to do before testing anything is make sure the generator is running at 3600 NO LOAD. Then I will go from there. I could use the Kill a watt, but it has to plug in to a socket. To make that work, I would have to kill main power to the house, then turn off every breaker except the one that feeds the plugs in the generator room. That should be a no load test them provided nothing is plugged into that circtuit.
 
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Old 09-04-10, 05:04 PM
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OK, my no load rpm is about 3600, maybe a hair more. I have no way of checking except a VibraTach. The no load voltage output on both legs is 120v +/- .1-.2 volts or so.

It also appears that the original device to check voltage is not correct. It says my utility voltage is about 115, when my DVM says its 120v. So, though I havent tested anything under load, if the error is linear, then the load voltage is actually about 110v.

I will check later but does that sound about right for a load of lights, two fridges/freezer combos and a deep freeze?

Also, the reason I was worried is because I can 'hear' my generator through my motors in my house...the same frequency hum that the generator is running at is easily heard in the living room fan.

Is this normal???
 
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Old 09-04-10, 09:07 PM
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For a two-pole generator to output 60 Hz. the rotational speed must be EXACTLY 3600 rpm. That is why the suggestion has been made to use a frequency meter rather than a tachometer. I can't go along with using the "Kill-a Watt" meter for that purpose because mine reads 59.9 Hz. and I KNOW that the utility maintains the frequency much closer than that.

Many of the higher end digital multimeters are also capable of reading frequency but in all cases the meter reading is no better than the calibration. This may be true with your present multimeter, it may not be closely calibrated to a known standard.

Whether or not the readings you are getting between no-load and loaded (ideally you would measure no-load and full-load) are acceptable is dependent upon many factors, including the rated capacity and ultimate (short term) capacity of the generator along with the design of the generator and its control system. No mechanical governor can hold an absolute speed so having the engine run a few rpms "high" at no load and a few rpms "low" at full load is common. Whether or not these high and low parameters are compatible with your load is something that is impossible to state without knowing a whole lot more about your particular installation.

The phenomena of "hearing" the generator through various electric motors is not uncommon, especially with "smaller" generators. (I used to work for an electric utility so any generator that would be used for auxiliary power at a residence is a small generator to me.) The smaller the engine/generator combo and the wider the speed changes allowed by the governor the more pronounced the effect will be.
 
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Old 09-04-10, 09:15 PM
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So, if I am at 110v fully loaded, is that still 'safe' and not in danger of damaging equipment? I need to be able to run things like fridges and such for extended periods of time without messing them up.
 
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Old 09-04-10, 09:29 PM
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I would consider 110 volts to be a bit low but yes, that should not be a problem as electrical appliances are made to work within a range of voltage plus or minus of about ten percent of 120 volts. That would mean a low of 108 volts to a high of 132 volts are within the acceptable range. The closer you can hold to 120 volts the better for the appliances as either extreme will tend to shorten the life of the appliance.
 
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Old 09-04-10, 11:21 PM
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The only item I did not see you mention what size itself.

What you will do is load up the generator in normal fashon like you useally do for power outage and check the voltage and amps keep in your mind most of the generators will have two windings on two pole units so one set for 120 volts and second set for 120 volts.{ some have 4 winding but more common on lower speed units }

Now for example here a 5 KW genny each winding only can handle 2500 watt each side of winding before you overload them unless you have a FULL POWER switch option which it will do is parallel the windings to get full capitcy but no 240 volt load on this setting.

So I will suggest that you get a clamp on ampmeter to read the current drawage on both legs to make sure you are not out of the balnce or overload one set.

with 5 KW you should have max of 20.8 per leg { 2500 watt each }{ will read line to netrual not line to line load }

For other size it the same way unless you have full power option as I mention above.

That should clear up this part a bit to get the best performace on your generator.

And be aware with motor start up like fridge and furnace motor they will tempory take a bit of power to start up but once they running it is not too bad at all.
 
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Old 09-05-10, 10:45 AM
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I have no clue what this generator puts out. I cannot tell if its a 4 pole or a 2 pole generator. It is apparantly a Getec KS.

Its a 2 pole and it is either a 18.5kva, 22, 25 or 31kva. The tag is disintegrated.
 
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Old 09-05-10, 11:00 AM
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Wow! a 18.5 kva should have no problems powering three refrigerators and some lights. IF you are dropping 10V when only loading your genny about 10% to 25% of rated load, you have a problem somewhere.


I reccomend like some of the others have that you should get a good meter with the capability to measure HZ and ideally a clamp meter to measure the current it is putting out. Without good solid info it is difficult for anyone to be of much help to you.
 
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Old 09-05-10, 11:28 AM
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Hang on....wait a second...back up the train.

I tested this unit again, with an actual DVM. With the unit running and fully loaded and it read 119-120 volts the whole time. I then plugged in my 'other' meter to the same circuit and it read 108V....it looks like the darn meter I used originally is faulty. It reads 108 on gen power, and 110 on utility.

My DVM reads 119-120 on both.

sheesh....

I have two panels, one for 'heavy loads' like on demand water heaters, AC, etc, and one for 'lighter' loads. The generator is only hooked up to the lighter load panel with an ATS. Do you guys think it is possible to run a 5ton AC unit with this generator? I don't think so, but I wanted to ask. It might be bigger than 18.5kva, but for now, lets assume its not.
 
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Old 09-05-10, 11:42 AM
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With 18 KW unit if that the case yeah the 5 tonne A/C unit will start up without issue with generator at all.

I have 20 KW slow speed diesel generator and I used with 4 tonne A/C unit and it did start up without any issue at all due my A/C unit is three phase unit but single phase you should have not much issue starting up like that big due the generator is pretty big.

IIRC the 5 tonne will draw about 35 amp running { check the outdoor unit nameplate to make sure due there are few diffrent ratings on it }

Merci.
Marc
 
 

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