Can power supplies/adapters be used to clean up dirty generator power?

[AmericaN8]

Just be careful using a regular grounded o'scope when probing AC Mains power. Beyond the safety considerations, you need to understand what the "ground" is for the o'scope power cord versus the ground for the o'scope probe lead. If they are not the same "ground", you can let the smoke out of your 'scope probe...

Update -- a good example is when you might try to repair one of the old "hot chassis" TV sets from back in the stone age. Very important to understand when to use isolation transformers in that kind of work.

noted, thank you!

 

[berkeman]

nah, i mean i would anticipate some interference, but this is for emergencies and boondocking. I just want to be sure my electronics won't be damaged and i really don't want the a/c or fridge to be damaged. those are very expensive.

Just think about what the AC Mains interface circuits look like for each of those appliances. If the input stage is an AC Mains rectifier followed by a switching power supply stage, it will take a lot of noise/harmonics to mess that up. If it is a motor or other device that is connected directly to the AC Mains waveform, there could be issues and you'd need to evaluate each of those cases individually and closely, IMO.

 

[AmericaN8]

a good example is when you might try to repair one of the old "hot chassis" TV sets from back in the stone age. Very important to understand when to use isolation transformers in that kind of work.

I'm not too familiar with tv repair. I have an old tube tv and that's always worked when i wanted it to. not much for it to do these days though. and I've repaired flat panel tvs, well, one anyway. So you use an isolation transformer when measuring something? I'm curious lol. I'm an electrician on a factory trawler so I am curious but i probably will never work on one of those tvs

 

[berkeman]

So you use an isolation transformer when measuring something?

An isolation transformer is used to isolate Hot/Neutral of the output from the same circuits at the input. The example of the "hot chassis" TV set is meant to show how you could not connect your 'scope ground clip lead to the chassis without blowing up the 'scope lead.

Another example would be where you are working with the AC Mains circuit and will be touching various parts of it (like when I work on my power supply designs), and may be grounded through other connections (like touching something on my workbench). You want the AC Mains powering that circuit to be floating with respect to Earth Ground so you don't complete the circuit. AC Neutral is usually Earth grounded at the distribution panels, at least in the US.

 

[AmericaN8]

 

[DaveE]

View attachment 314070

Not a problem. If something breaks downstream it's because it just wasn't designed well to live in the real world.

 

[AmericaN8]

Not a problem. If something breaks downstream it's because it just wasn't designed well to live in the real world.

I can live with that methodology. Test it and replace what breaks with something better.

 

[artis]

An isolation transformer is used to isolate Hot/Neutral of the output from the same circuits at the input. The example of the "hot chassis" TV set is meant to show how you could not connect your 'scope ground clip lead to the chassis without blowing up the 'scope lead.

Another example would be where you are working with the AC Mains circuit and will be touching various parts of it (like when I work on my power supply designs), and may be grounded through other connections (like touching something on my workbench). You want the AC Mains powering that circuit to be floating with respect to Earth Ground so you don't complete the circuit. AC Neutral is usually Earth grounded at the distribution panels, at least in the US.

Also in eastern Europe and probably elsewhere too I can confirm. I recently worked on a CNC laser cutter in a factory to set it up. the hangar has a 4 wire cable incoming and tied to the distribution box.
Neutral is tied to Earth at that box and the whole metal frame to which the box is attached is basically AC 3 phase neutral/ground.
You wouldn't want to touch any of the 3 phases while also touching any of the steel construction of the hangar.

I suppose the reason they have tied the neutral to the whole hangar metalwork is to not allow any voltage to build up within it from all the cabling running along the walls of it and also the high powered machines within it. The ground can get rather dry there and the lightweight metalwork has shallow foundation so a good "ground" is necessary.

I guess one additional factor of why an isolation xformer can come in handy is because you can size it in power and then you get both galvanic isolation from the grid + current limiting. Say your xformer is small, in case your test equipment fails a small xformer for example would limit how much current can be drawn before the fuse blows etc. Sort of like analogous to how folks used incandescent bulbs as current limiters in series when powering up something for the first time.

 

[artis]

I'm late to this thread but I did not see anyone mention this, wouldn't the power be cleaner from a rotary generator than a cheap inverter anyway? Because a generator is a rotary electromechanical machine and in theory it cannot output anything else but a sine wave meanwhile a inverter is a switched device and switches create a mostly square waveform that then if poorly filtered can introduce nasty harmonics into the grid meanwhile a generator can only change frequency and voltage.
Not sure which would qualify being less clean.

 

[DaveE]

wouldn't the power be cleaner from a rotary generator than a cheap inverter anyway?

Yes, absolutely. But they are big and expensive. Not a great choice in most applications compared to a really good inverter. We supplied big ion lasers for state of the art semiconductor equipment and they would integrate it with a 60KW motor-generator to avoid any problems with power quality affecting the performance of the laser. They were the only customer that did this as far as I know. But in a semi fab you can (must?) spend lots of money for quality and reliability.

 

[artis]

We supplied big ion lasers for state of the art semiconductor equipment and they would integrate it with a 60KW motor-generator

Do you recall what type of motor and type of generator it was? Not just type but what kind of power they fed into the motor and what came out of the generator?
I'm just curious.

 

[berkeman]

I guess one additional factor of why an isolation xformer can come in handy is because you can size it in power and then you get both galvanic isolation from the grid + current limiting. Say your xformer is small, in case your test equipment fails a small xformer for example would limit how much current can be drawn before the fuse blows etc.

One serious downside to this is that when the isolation transformer first overheats and the insulation starts to melt and the windings start to short out and things heat up even more, the smoky smell can be pretty hard to locate in your lab, and the Fire Department may respond to your building. Please do not ask me how I know this...

Spoiler

Well, technically, we only had to evacuate the building once and call the Fire Department. In the previous incident many years ago I was able to figure out that the smoke was coming from an isolation transformer and unplug it before things got worse.

 

[anorlunda]

Please do not ask me how I know this...

That phrase is turning up in your posts with increasing frequency. I propose that you write a book with that title.

 

[DaveE]

Do you recall what type of motor and type of generator it was? Not just type but what kind of power they fed into the motor and what came out of the generator?
I'm just curious.

No, except that the input was 3Φ depending on the power available at the installation. The output was 3Φ, 277/480V.

 

[berkeman]

Do you recall what type of motor and type of generator it was? Not just type but what kind of power they fed into the motor and what came out of the generator?
I'm just curious.

We had a 3-phase 208 to 480 motor-generator in our electrical room at a previous campus, because of all of the powerline testing we did. It was about a cubic meter in size, and surprisingly quiet (until it got close to its PM interval). I don't recall the power transfer capability...

 

[artis]

We had a 3-phase 208 to 480 motor-generator in our electrical room at a previous campus, because of all of the powerline testing we did. It was about a cubic meter in size, and surprisingly quiet (until it got close to its PM interval). I don't recall the power transfer capability...

Please do not ask me how I know this...

Can I instead now ask you how you don't know this?

 

[DaveE]

We had a 3-phase 208 to 480 motor-generator in our electrical room at a previous campus, because of all of the powerline testing we did. It was about a cubic meter in size, and surprisingly quiet (until it got close to its PM interval). I don't recall the power transfer capability...

We had a 120/208V, 60Hz to 120/208V, 50Hz motor generator in our electrical room for product development. About 40KVA, which was unfortunate because we really needed 50-60KVA for worst case. There's rumors that some EEs would overload it for a while to get their data (of course I wouldn't know ANYTHING about that). Most companies don't need a big 50Hz source, but for us it was important since we designed linear DC power supplies up to about 50KW. 50Hz vs. 60Hz is a big difference for a 50KW rectifier.

 

[AmericaN8]

Just a little update for the heck of it, using a handheld o-scope the wave form is still pretty dirty. Looks more like a sawtooth than it does a sine wave.

 

[CW2]

Interesting thread here. I think Steven's question is valid and some of the replies were not great and some were just uncalled for. I have nearly the same question as Steven which is why I am here.

A standard electric generator will produce 10 to 15% of Total Harmonic Distortion. Mine is closer to the 15% range. I was primarily using it to power the furnace, refrigerator, and some lights. The manufacturer of the generator does not recommend using any electronics with this generator. The IEEE std 519-2014 states the THD needs to be less than 5% for electronics so clearly I am not in that range. (In comparison, an Inverter generator has a rating of 3% or less so they are safe for electronics).

As I understand it, Stevens question was if a laptop power supply would filter the THD so it could be used with a standard generator. I have the same question. It seems like it will but maybe a high end large screen TV maybe not so much. I have my modem, router and NAS connected to a APC BE650G1 650 VA UPS. If I connect the TV to this UPS will it allow their use with 15% THD coming into the UPS?

 

[rbelli1]

Well, technically, we only had to evacuate the building once and call the Fire Department.

It's funny how you can find a companies best and worst employees by how many times they had to call the fire department.

BoB

 

[Tom.G]

I have my modem, router and NAS connected to a APC BE650G1 650 VA UPS. If I connect the TV to this UPS will it allow their use with 15% THD coming into the UPS?

In normal operation, these small back up systems do a little filtering and just feed the incoming AC to the output sockets. When the incoming power disappears, they switch to the battery-powered inverter. So in normal operation the won't help much, if any. There are (larger) models that operate continuously so the output is always relatively clean, and no switch-over transient. (more $$$ though)

You would be better off buying a Constant-Voltage sine wave transformer, the low power ones are available from 30W thru 7,500W, but they are not cheap.

I actually had to do this for a computer installation back around 1976. It was a business (a service bureau) that had an Open House introducing their new services.

It also happened to be the first warm Spring day. The power line voltage sagged when everyones air conditioner came on. Oops! Between the voltage sag and a marginal computer power supply, the "New" computer wouldn't even boot-up. Two days later the whole system was on a Constant-Voltage (CV) transformer.

Everyone was (mostly) happy.

Here is a datasheet link to one of the major US suppliers of Constant-Voltage (CV) transformers:
https://www.appleton.emerson.com/do...usoidal-transformers-solahd-en-us-7438572.pdf

You MAY be able to find an industrial grade Line Conditioner or Line Filter that would be adequate for a lower cost. Hopefully someone else here has better information/sources for those.

Cheers,
Tom

p.s. Historically, one of the main reasons device manufacturers don't recommend electronics usage with a generator is that some generators are/were prone to voltage spikes on their output lines. Then the consumer complains about a short lifetime and wants a warranty replacement of the electronic device.

 

[artis]

A standard electric generator will produce 10 to 15% of Total Harmonic Distortion.

I think one would also need to specify the generator type as those values then might vary. Are you talking about a diesel driven synchronous generator?
And even for a single type generator I think the output distortion is partly related to the pole count , size , and winding pattern of the generator.
Someone more knowledgeable in generators could correct me , but I would think large power generators produce less of said distortion.
@anorlunda ?

 

[anorlunda]

Someone more knowledgeable in generators could correct me , but I would think large power generators produce less of said distortion.
@anorlunda ?

Sorry, but portable generators are not my field. The grid delivers low harmonics in most cases, and traditionally most generators on the grid are synchronous. But solar and wind bring other types of generators and they manage low harmonic content. Also, with the grid there are many other sources other than the generators for THD creation and THD filtering.

But the main reason grid power is very clean is that power quality standards including THD are mandated by the regulations. Sources of harmonics must be tracked down and either eliminated or filtered. In other words, the solution for big problems is to spend big money.

My source https://cdn2.hubspot.net/hubfs/446633/White_Papers/WP273.pdf
claims that his testing shows that inverter type portable generators delivered the lowest THD. For alternator type portable generators, he blames the automatic voltage regulators, AVR, for harmonic creation.

 

[CW2]

Interesting thread here. I think Steven's question is valid and some of the replies were not great and some were just uncalled for. I have nearly the same question as Steven which is why I am here. I believe the question really relates to

In normal operation, these small back up systems do a little filtering and just feed the incoming AC to the output sockets. When the incoming power disappears, they switch to the battery-powered inverter. So in normal operation the won't help much, if any. There are (larger) models that operate continuously so the output is always relatively clean, and no switch-over transient. (more $$$ though)

You would be better off buying a Constant-Voltage sine wave transformer, the low power ones are available from 30W thru 7,500W, but they are not cheap.

I actually had to do this for a computer installation back around 1976. It was a business (a service bureau) that had an Open House introducing their new services.

It also happened to be the first warm Spring day. The power line voltage sagged when everyones air conditioner came on. Oops! Between the voltage sag and a marginal computer power supply, the "New" computer wouldn't even boot-up. Two days later the whole system was on a Constant-Voltage (CV) transformer.

Everyone was (mostly) happy.

Here is a datasheet link to one of the major US suppliers of Constant-Voltage (CV) transformers:
https://www.appleton.emerson.com/do...usoidal-transformers-solahd-en-us-7438572.pdf

You MAY be able to find an industrial grade Line Conditioner or Line Filter that would be adequate for a lower cost. Hopefully someone else here has better information/sources for those.

Cheers,
Tom

p.s. Historically, one of the main reasons device manufacturers don't recommend electronics usage with a generator is that some generators are/were prone to voltage spikes on their output lines. Then the consumer complains about a short lifetime and wants a warranty replacement of the electronic device.

Thank you for the great reply. I had looked at Online double conversion UPS's but I would need 2 and that would cost more than if I just went out and purchased a new inverter generator to supply just my electronics, leaving my old generator to supply the house. I have never tried using my electronic devices with the old generator because of the warning from the generator manufacturer. Am I being overly cautious? Could the THD damage my devices, or as Steven had asked when starting this thread, will the power supply for a laptop computer filter out the THD noise. The TV is probably a different story since there is no power conversion coming in. Thanks

 

[CW2]

Sorry, but portable generators are not my field. The grid delivers low harmonics in most cases, and traditionally most generators on the grid are synchronous. But solar and wind bring other types of generators and they manage low harmonic content. Also, with the grid there are many other sources other than the generators for THD creation and THD filtering.

But the main reason grid power is very clean is that power quality standards including THD are mandated by the regulations. Sources of harmonics must be tracked down and either eliminated or filtered. In other words, the solution for big problems is to spend big money.

My source https://cdn2.hubspot.net/hubfs/446633/White_Papers/WP273.pdf
claims that his testing shows that inverter type portable generators delivered the lowest THD. For alternator type portable generators, he blames the automatic voltage regulators, AVR, for harmonic creation.

Yes, an inverter generator would take care of the problem as they are usually in the 3% THD range. Also, most permanent home generators have circuitry to keep the THD to around 5%. The problem comes in with standard portable generator that can produce 10 to 30% THD depending upon the supplier and the quality of the unit. As I understand it, the industry has established no more than 5% THD for electronics. So the problem then is those generators that produce 15 to 20% THD.

 

[mcblatz]

What if I am plugged into a battery backup/surge protector? Will this clean up the frequency.

 

[berkeman]

Welcome to PF.

What if I am plugged into a battery backup/surge protector? Will this clean up the frequency.

A UPS unit will contain an inverter to convert the DC battery power to AC Mains power. The harmonic distortion (THD) rating will depend on the specs of the inverter. It's not a matter of cleaning up the 50/60 Hz frequency, it's a matter of how "clean" the AC Mains sine wave is (since it's being generated with switching magnetic circuits).

https://en.wikipedia.org/wiki/Power_inverter