Portable Generator Output Problem

Thread Starter

JustMe234

Joined Feb 25, 2017
68
Hello,
I just got this portable generator Pramac PX3250. And i turn it on and leave it for couple minutes on and then measure on output with a cheap multimeter 260V. This generator is configure to produce 230V on output.
I connect an air compressor on it and then the output was 240V. The compressor runs fine.
Is this safe to run on my house? I want to use it as a backup power on blackout.
pramac-px3250.jpg
 

Hymie

Joined Mar 30, 2018
991
That is quite bad regulation between no-load and loaded. You could reduce this regulation by having a minimal load permanently connected (limiting the output to say a maximum of 250Vac).

The normal mains utility supply can vary by up to +10%, so a nominal 230Vac mains supply could be as high as 253Vac, an extra 7V is unlikely to cause any problems.
 

Thread Starter

JustMe234

Joined Feb 25, 2017
68
I am afraid that 260V will kill my supplies.

That's a good idea, I will make some tests with some bulbs and see what's the output. Thanks for that.
 

MisterBill2

Joined Jan 23, 2018
9,233
I am afraid that 260V will kill my supplies.

That's a good idea, I will make some tests with some bulbs and see what's the output. Thanks for that.
Probably such a poorly regulated output will indeed kill switchmode power supplies, since it is probably NOT close to a good sine wave output. So the generator would be OK for incandescent lights and AC motors in refrigerators and older furnaces, and probably well pumps. But don't use it for computers or televisions or other electronics.. They need better regulation and cleaner power.
 

Thread Starter

JustMe234

Joined Feb 25, 2017
68
I test it with an 250W incandescent Flood light. And measure the output it drop by 1V but still to high 260V.
Then i connect an hair dryer 1500W and then the voltage drops to 233V.
 

Hymie

Joined Mar 30, 2018
991
Based on the 1500W load figures, the generator output effectively has a 4 ohm impedance in series with its output, causing the observed volt drop.

Although you are right to be concerned at such a no-load output voltage at 260Vac; many international product safety standards require products to be tested at a worst case input voltage variation of +10% based on the rated voltage of the equipment.
So an electrical item with a voltage rating of 240Vac would be subject to test at 264Vac (and 216Vac). Therefore it is unlikely that applying 260Vac will cause damage.

That said, tungsten filament lamps will be noticeably brighter and have a significantly shorter life compared with operation at their nominal voltage.
One final thought is to measure the generator output voltage with a calibrated meter to confirm the results obtained with your cheap meter.
 

MisterBill2

Joined Jan 23, 2018
9,233
I saw a similar generator take out an expensive power supply and the reason was a stuck throttle. The thing controlled the voltage by adjusting the speed. So you may be able to adjust the mechanical part of the speed controller and reduce the voltage. It may be that the linkage is sticky from old gas changing into a gummy mess that keeps the speed regulator from functioning correctly. So investigating that part seems like a good idea . That does not at all seem like it will be a good generator for other than lighting and running power tools. But you could use it to power a battery charger and then use the charged batteries to run things either directly or from an inverter.
 

Tonyr1084

Joined Sep 24, 2015
6,243
Just an opinion here - but during a power failure what is it you need to keep running? For me that would be the furnace in the winter time and the fridge and freezer in the summer time. Lights at any time of the year but only as needed. You don't need to illuminate the whole house during a temporary outage.

For longer outages such as occur after a storm, again, maintaining heat and/or refrigeration would be my two "Number One" concerns. Lighting would be a second concern. Computers, TV's and other luxury items - I can do without for a while.

Aside from getting a professionally installed "Whole Home" generator I would only want to plug those items in that I want running. And I would not recommend attempting to back feed the power to the house. The reason is that you can be generating 240 VAC and without knowing it you could be back feeding that to the pole transformer. That pole transformer doesn't care which side is getting power. If you're pushing 240 into it then on the other side it could be pushing out 25KV. Some line technician who believes there's no power on the line could find themselves in a world of danger and hurt. Or someone down stream from your home may think power is out and grab something they shouldn't. But then again, you should never grab a line whether you know (or think you know) it's energized or not.
 

Thread Starter

JustMe234

Joined Feb 25, 2017
68
I saw a similar generator take out an expensive power supply and the reason was a stuck throttle. The thing controlled the voltage by adjusting the speed. So you may be able to adjust the mechanical part of the speed controller and reduce the voltage. It may be that the linkage is sticky from old gas changing into a gummy mess that keeps the speed regulator from functioning correctly. So investigating that part seems like a good idea . That does not at all seem like it will be a good generator for other than lighting and running power tools. But you could use it to power a battery charger and then use the charged batteries to run things either directly or from an inverter.
Adjusting the speed in generator will require an frequency meter to measure what freq is at certain speed which i don't have.
I will use it mostly for lightning the house, power an heater pump(90W), fridge, TV and some low consume appliances charger etc.
 

MisterBill2

Joined Jan 23, 2018
9,233
Adjusting the speed in generator will require an frequency meter to measure what freq is at certain speed which i don't have.
I will use it mostly for lightning the house, power an heater pump(90W), fridge, TV and some low consume appliances charger etc.
Lighting and heating systems should survive, and probably the refrigerator, if it does not have that "smart" set of features. I do not recommend connecting any electronics that matter to an inexpensive generator like yours. There is a reason why the good units cost three times as much. And most of those appliances with motors can live quite well with a slightly lower frequency. I am not aware of ANY desktop computers having been safely powered by a low priced generator.
 

Thread Starter

JustMe234

Joined Feb 25, 2017
68
Lighting and heating systems should survive, and probably the refrigerator, if it does not have that "smart" set of features. I do not recommend connecting any electronics that matter to an inexpensive generator like yours. There is a reason why the good units cost three times as much. And most of those appliances with motors can live quite well with a slightly lower frequency. I am not aware of ANY desktop computers having been safely powered by a low priced generator.
That's a good advice. Now this drive me to buy an electric stabilizer if i want to use "Smart things". These looks can hold this job.

On the other hand i will try to borrow some professionals meters to verify the results.
 

MisterBill2

Joined Jan 23, 2018
9,233
That's a good advice. Now this drive me to buy an electric stabilizer if i want to use "Smart things". These looks can hold this job.

On the other hand i will try to borrow some professionals meters to verify the results.
Don't use one of those ferro-resonant constant voltage transformers BECAUSE they must have an exact frequency to function correctly. So verify from the manufacturer that whatever stablizer you want is NOT FREQUENCY SENSITIVE. That matters a lot.
 

Thread Starter

JustMe234

Joined Feb 25, 2017
68
I remove the cover of the generator and the only filter i see was this 18uF Capacitor. Maybe the AVR is on the motor side?

Cap.jpgSchuko.jpgStatorView.jpg
 

MisterBill2

Joined Jan 23, 2018
9,233
Why do you think that? Switch mode power supplies work by first converting the AC to DC. A wall wart not so much, but a real SMPS will work just fine.
Quiet a few power supplies also use a capacitive voltage divider. The higher harmonic content will certainly result in a higher voltage output. This opinion is the result of having watched just exactly such destruction, produced by a similar generator with a similar behavior. Fortunately I was not really involved, except that I was watching them set up the generator and connections. Not my generator and not my power supply, and while it was my extension cord, they did the connecting. Hopefully not everybody has to have the same experience. If we don't learn from what others do we are doomed to make similar mistakes.
 

Hymie

Joined Mar 30, 2018
991
I would strongly agree with Tonyr108 that you should consider having the system connected by a suitably qualified electrician.

To avoid the possibility of back feeding the mains supply, the connection of the generator output should be made via a DPDT contactor which connects the house electrics to the normal mains supply or the generator (with no possibility of the utility mains supply being connected to the generator output). This contactor will need to be rated at 100A.

If the generator has an electric start, you configure the installation such that on loss of mains power the generator automatically starts up and switches over to the house supply – and once normal mains power is resumed, the system switches back to the mains supply and cuts the generator.
 

Reloadron

Joined Jan 15, 2015
6,058
All of my reads on these are they are designed for 230 or 240 volt operation. Honda engine and alternator body made in Italy. They seem very popular in the UK. I have no idea why you would read such a high output voltage but I would absolutely measure output voltage under at least a 50% load using a known accurate AC voltmeter, preferably a true RMS type meter. While I was at it I would also measure the output frequency which at 3,000 RPM should be 50 Hz. You need to measure at least with a meter you know to be accurate. Then I would move along from there. If in fact the output is that high I would be contacting the vendor for more data.

Ron
 

MisterBill2

Joined Jan 23, 2018
9,233
I would strongly agree with Tonyr108 that you should consider having the system connected by a suitably qualified electrician.

To avoid the possibility of back feeding the mains supply, the connection of the generator output should be made via a DPDT contactor which connects the house electrics to the normal mains supply or the generator (with no possibility of the utility mains supply being connected to the generator output). This contactor will need to be rated at 100A.

If the generator has an electric start, you configure the installation such that on loss of mains power the generator automatically starts up and switches over to the house supply – and once normal mains power is resumed, the system switches back to the mains supply and cuts the generator.
Why presume that everybody here is incompetent to do things? Those who are beginners are fairly obvious, while it is just as clear, at least to me, that quite a few have a rather high level of competence, insight, and skills, as well as the knowledge of exactly how to do things. In addition, the majority of those doing the work for profit are primarily pointed towards getting done as fast as possible, getting the money, and being on their way. I have repaired many such projects over the years.
 
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