Generator Frequency Fluctuations - Whats safe?

Submitted: Wednesday, Feb 06, 2013 at 18:50
ThreadID: 100413 Views:7495 Replies:4 FollowUps:4
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As mentioned on another thread I recently got a second-hand Honda eu10i and am very happy with it. While reading other threads a member mentioned a usage meter that you could get from Jaycar and it tells you voltage, frequency and watts being used. Definitely worth the 20 bucks as I have been testing how many watts are used all my appliances around the house.

The Honda tested at an absolute constant 50Hz and 239 volts. The house mains power tested at the same consistent 50Hz and 244 Volts. I was definitely impressed by the Honda in this respect. So as a comparison I then tested my 750 watt GMC 2 stroke. I wasn't expecting the same result as its not a pure sine wave inverter. It tested at a varying 215 to 220 volts and a frequency varying from 47 to 50Hz. This didn't seem too bad as I have heard other horror stories of some getting upward of 280 volts ad 60Hz. It did make me stop and think as I was about to give the GMC away to my brother, with its fluctuations, what things can you run off this generator without doing damage? What's safe to run with these fluctuations and what's not?
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Reply By: Ross M - Wednesday, Feb 06, 2013 at 19:19

Wednesday, Feb 06, 2013 at 19:19

On the GMC you can use anything which isn't voltage and frequency sensitive.
ie, Globes, conventional, battery charger, kettle (if wattage large enough), fan heater too, possibly, but it may not like 60 "HURTS".
Anything designed to run on 240 v ac which has a voltage sensitive power conversion or switching can only be use on the Honda with safety for the appliance.

Laptop supplies, these are switch mode types and only a few will run on other than full 50 HZ sine wave, most like the sine wave and possibly will not start and become stalled and may burn out or blow their internal fuse if connected to a varying voltage, off frequency wave form..

Switch mode battery chargers, usually multi stage units also like 50 hz full sine wave.

If a switch mode device does happen to start and run, on something other than clean power, it usually cannot switch properly and the poor waveform can cause the unit to run hotter than normal because it can't make proper use of the shape of the energy being fed into it.

If the GMC happens to run at 50 hertz and 240 v while under load, then nearly everything should be ok, it is just when these two are not held constant the delicate stuff may not like it. No good if it is an expensive device.

Ross M
AnswerID: 504212

Follow Up By: patsproule - Thursday, Feb 07, 2013 at 07:36

Thursday, Feb 07, 2013 at 07:36
Modern multi-voltage switchmode power supplies are actually a lot less sensitive than most people think. They are designed to handle a large range of input voltages and frequencies (Hertz by the way). The main thing they dont like is a full square wave input as it makes the laminations in the transformer buzz (SM supplies still run a small transformer). I've had a bit of experience with this running OB trucks on the odd dubious genny and on all but one occasion (dodgy welder genset) it was fine. And I'm talking about a unit with about 100 SM supplies or more.

I too can vouch for the output of the Honda EU range - we run the current OB truck off a pair off EU65i's and no matter what you do to them the output is a beautifully stable sine wave even when loaded to the limit on each. We prefer them over the mains.

FollowupID: 781028

Follow Up By: Ross M - Thursday, Feb 07, 2013 at 13:47

Thursday, Feb 07, 2013 at 13:47
Didn't you like my little hurts joke.

What is an OB truck? Some of use probably don't know what they are.

I have two old laptops and one will run on a less than suitable wave form but does run hot ie both from mod square wave inverter and low frequency generator. The other laptop SW supply just like it clean and no fuzz and won't run at all, where the other one will.

The Honda will keep on giving clean power because of the inverter output and unless the electronic control gets out of spec, the wave form and voltage will remain within specs.
FollowupID: 781040

Reply By: MEMBER - Darian, SA - Wednesday, Feb 06, 2013 at 19:56

Wednesday, Feb 06, 2013 at 19:56
I no technician, but am interested under what sort of load types you tested both ? I had the thought that maybe the Honda might produce those figures consistently across a range of appliance types and load levels, while the GMC might drop it's bundle when trying to do the same ? I've got a 1k Yamaha with much the same specs as your Honda.
AnswerID: 504214

Follow Up By: Palaeoboy - Thursday, Feb 07, 2013 at 16:21

Thursday, Feb 07, 2013 at 16:21
Hi Darian, the readings I took were with no load at all. Having read your post though I thought before reply I would test with a 500 watt load to both units to see what the results were. The Honda remained consistently at 50Hz with the Voltage dropping ever so slightly to 235 Volts. The GMC 2 stroke didnt fluctuate as much under load as it did with no load at all. It gave a steady 48Hz and 244 Volts. For an $89 generator I thought wasnt too bad however the same question arises does that 2Hz make much difference? It doesnt sound much but without understanding it could be the difference between burning out an appliance and not, thats what Im not sure about?
FollowupID: 781043

Follow Up By: MEMBER - Darian, SA - Thursday, Feb 07, 2013 at 16:38

Thursday, Feb 07, 2013 at 16:38
Hope an expert can advise on the significance of the minor variation in Hz - I'm really an electroklutz when it comes to the fine print.... I just seemed to recall the point being made somewhere that testing with load where possible, adds validity to the exercise.
FollowupID: 781044

Reply By: Marny - Wednesday, Feb 06, 2013 at 21:06

Wednesday, Feb 06, 2013 at 21:06
You will also find that most things these days are rated at 50/60hz.
AnswerID: 504222

Reply By: 08crd - Wednesday, Feb 06, 2013 at 23:52

Wednesday, Feb 06, 2013 at 23:52
Just remember with a generator, it can only put out what the prime mover can put in.
I could put a 10kva generator on the end of a 150cc motor. It will still only put out approx 2kva, actually it will probably put out less because of the extra weight of the 10kva rotor.
Power out = power in - losses
AnswerID: 504232

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