[bosulli]

I will stick this question in cutting as it regards an in the field plasma cutter set up. I am looking at plasma cutters, and notice some say you need clean power or low harmonic disturbance. Some inverter machines do not have this warning. What happens when you do run an inverter based machine on an 'older' generator, and is there an accessory that will regulate or clean up the power to connect to a 2007 Miller Bobcat?

Thanks,

[thatoneguy]

As far as I know "clean power" just means non-fluctuating... But im probably wrong. So if you're going to run a plasma on a Engine Driven Welder I would just make sure nobody else is using the generator at the same time as you. Bobcat uses the same generator for welding and the plugs. As opposed to a trailblazer that has separate output for the welding and the plugs as to not disturb either. So if you are going to run your plasma cutter with your bobcat I would recommend not running anything else at the same time. Again, im totally spit ballin'.

[bosulli]

Thanks Thatoneguy. The Miller tech says they run their machines off their generators, but he wold not certify it 'clean power'.

I see your Everlast collection. Today I ordered the Everlast 51P plasma and 185DV tig. They gave me a bundle deal. Think I'm ok, but will continue to research.

[bosulli]

found many articles that put my clean power worries aside. Here is the most indepth one. A reply from this post -

http://www.dslreports.com/forum/r271172 ... er-Cleanup

To begin with, most people, including many equipment manufacturer's, many electricians, and just about all the average Joe's in the world, haven't got a damn clue about power quality. And many who do, have no idea what the effects on power systems, equipment like generators, UPS, 'sensitive electronics equipment', etc., cause. In fact, if the average person were to take an oscilloscope and look at what they think is a 'pure sine wave' coming from their source, they would be absolutely horrified; and probably wouldn't be sure if they've made a mistake in hooking it up. The terms 'dirty power' and 'clean power', generally mean absolutely nothing in the power industry, and are used mainly by people who don't know anything about power quality issues; and snake oil salesmen trying to sell their overpriced products to these very people. So, let's get some fact's straight.

First, most electronics equipment that people think of with bogus terms like 'sensitive electronics equipment' aren't sensitive at all. In fact, for the most part; this equipment cares the least about the quality of its power input. Bear in mind, that most of this equipment first converts its power source to DC, before using any of it. It will be the equipment itself, including its filters and voltage regulators that determines the quality of its DC power - not the source. Yes, there could be some ripple transmitted to the DC power; but that is primarily a function of how crappy its power supply is. Most of the buzz about the need to 'clean up your power' actually comes from manufacturer's selling equipment that supposedly does just that. And more often than not, it's pure BS.

Computers, PCs, and anything with a switch mode power supply (SMPS), draws its power in two large bursts of current during each cycle of a sine wave. It basically doesn't give a crap what the source looks like as long as there is power to draw. And oppositely, SMPSs do more to damage the quality of the input power from their source, than anything else. If you want clean power, don't put SMPSs on circuits with other equipment. This equipment is designed to function as long as its input source is within the CBEMA (ITIC) curve. Basically, its designed to function without rebooting with a very crappy source. This means that some 90% of equipment people think are 'sensitive electronics', in fact are not; and also damage the quality of the source horrendously by loading it up with harmonics.

Now, lets talk about UPS. The majority of UPS - especially ones that cost under $20,000 - simply present a large non-linear power supply to their source. Just like the SMPSs, they wreak havoc on the power quality of their source. Someone mentioned 'double-conversion' UPS. Nice; but clueless. (Sorry.) The output of a double-conversion UPS is almost always much, much poorer than the source sine wave entering. They use PWM or some other method to convert the DC back into AC, resulting in one of the most choppy 'sine waves' one could ever see. Yeah - they ensure the voltage doesn't drop when their input does; and they filter transients. However, that's about all they do. Aside from that, the power quality of their output is horrible. Again, anything under $20,000 and the output is going to look more like a square wave than anything. (Add capacitance of the circuit, and its much poorer than that.) The majority of low cost (under $20k) UPS, chop their output into three squarish looking chunks each half cycle. You have to pay big bucks to get a 12 or 18 pulse UPS, with adequate input and output filtering. But its not a problem, because the SMPS equipment that is connected to UPS systems 99% of the time, doesn't care one bit.

Now lets talk generators. Even cheap, low quality ones. Mostly the power quality problems from cheap generators fall into two issues - varying input voltage and frequency; and harmonics. Not big deal, because most of the equipment you load onto a generator, doesn't care about any of this. Certainly, none of the equipment with SMPSs cares at all. Take a look at their nameplate. Typically 90 to 240V, 50 or 60 Hz. They will work at a frequency of probably 30 to 100. As long as your generator doesn't drop below 90V for more than a second, they will operate just fine as well. SMPS's generating harmonics into the source may actually cause more issues for your generator (overheating), than the other way around.

Now for the big surprise. What types of loads have the most concern from harmonics, voltage and frequency? Motor loads. Harmonics causes the windings of cheap motors (and generator windings) to overheat. Motors that deal well with harmonics are made to be run on variable frequency drives. They cost more money, because they have larger windings, and often special treatment to their bearings. Obviously, dropping voltages can cause motors not to start. Minor frequency issues won't upset them; but should the frequency of your source drift severely, your motors will have problems. Trying to use a UPS to help this, will only make it worse - mega harmonics.

The generator itself may actually be the most concerned about issues being generated by its loads. Loads with leading power factor (such as can happen with loads with high capacitance, large filters or high harmonics) can wreak havoc on the generator, cause it not to run, and actually physically damage it. Harmonics being generated by the loads can add to the harmonics being produced by the generator and cause over-heating. The only solution for this is to over-size the generator (or de-rate the one you have). Leading power factor problems are generally solved by introducing isolation transformers between the generator and its loads. Isolation transformers go a long way towards cleaning up the power that a generator or motor is seeing; but to really work wonders, it needs to be a three-phase system. (3-phase delta-wye transformers filter out triplen harmonics.) Electrostatic shields between the windings will improve the transformer's filtering of transients.

In addition to motors, there certainly are some other loads that don't like AC sources with rich harmonics. Could be televisions; not really sure. Probably, after the issues I've discussed; the most concerning issue to loads, especially electronics, is transients. These are much more prevalent from your utility source, than your generator. Switching transients from the utility opening and closing circuits; as well as large industrial loads being switched in and out, are the primary culprits. Nearby lighting strikes are also to blame. The best way to protect your equipment from these utility power quality problems, is via high quality surge suppression. So, if you want to waste money in an attempt to 'clean up your power'; go ahead - plunk down as much as you can afford and buy an expensive UPS. Chances are probably 95% or better, you've just made your power quality worse. (FYI - UPS are for having 'uninterrupted' power - not quality power.) If you are concerned about power quality, the first thing to spend your money on is high-quality surge suppression. That is likely all you need. The only thing more, in addition to cleaning up transients (an uninterrupted power) that an expensive double-conversion UPS will give you is a steady output voltage - at the cost of high harmonic content. Most of your equipment doesn't care.

Seriously, what you are trying to do is akin to replacing the carburetor on a car that is running fine; because you think it may not be running fine. Don't waste your money trying to fix something that has no symptoms and is not broken. First, you'll probably make it worse. Second, you'll be out of a lot of money, that you could have used usefully for something else. If you really have money burning a hole in your pocket; hire someone with the equipment and know-how to perform a power quality study, and provide a proper interpretation. Then spend money fixing anything that is truly a problem.

[Poland308]

Long post but solid info. I spend some time in high end server rooms working around much of what you are talking about. Derateing the generator and the isolation transformers are probably the biggest things to focouse on when talking about "clean" power.

[thatoneguy]

Thanks Thatoneguy. The Miller tech says they run their machines off their generators, but he wold not certify it 'clean power'.

I see your Everlast collection. Today I ordered the Everlast 51P plasma and 185DV tig. They gave me a bundle deal. Think I'm ok, but will continue to research.

Ya my garage was broken into awhile back and I got cleaned out. After reading a bunch of reviews and trying my buddies Everlast, I bought one. Now I love them and replaced all my machines that were stolen with them. Eventually I want to become a distributor for Everlast but I don't think I could do that anytime soon...

[DLewis0289]

Rotary generated AC has a nice look on the scope (sinusoid), it's the time function that has the potential (no pun intended) to be unstable (Hertz/Frequency). UPS (cheap ones) on the other hand is an ugly waveform, almost like SCR's chopping amuck the other way, still crosses zero intact etc, but the top and bottom gone, but the time function is rock solid.

As much as I revere Tesla and despise Edison, Alternating Currents crowning achievement is transmission.

[Otto Nobedder]

While I feel I just read the bastard child of a novel and an engineering report, as someone with a BS level education in electronics, bosulli was right on every point.

The clean power myth is spread by people marketing generators or filters.

Steve S

[Otto Nobedder]

The only point I will add, is to look at the fine print in your machine's warranty, and make sure you are using (or own) a generator that is within the manufacturer's recommendations, so they can't chickenshit you in the event of a warranty issue.

Steve S

[jimcolt]

While I cannot speak for other inverter plasma manufacturers....the Hypertherm Powermax units all have a chart that suggests generator sizing, and these inverters were designed and tested on common generator output power.

Here is the chart for a Powermax45, which is rated for production cutting through 1/2" (it will pierce that thick without consumable damage) and severance cutting to 3/4". The chart first shows a typical 8 kW generator output and suggest that at full amperage output you will have full "arc stretch" capability....which means you can cut to the severance thickness (which takes a higher load voltage (stretched arc) vs cutting the production rating of 1/2"). It also shows that with a 6kW generator you can cut limited thickness at 45 amps output....likely to the production thickness of 1/2"......but if you turn the output power down to 30 amps with a 6kW genset...you can cut everything the specs (in the operators manual) suggest for 30 amp operation. Jim Colt Hypertherm

Pmx45generatorchart.png (21.33 KiB) Viewed 4041 times

I would be a bit wary of running the low cost import inverter plasma cutters on a generator output as many of them seem to be a bit shaky when it comes to voltage surges and spikes that could be associated with a small generator output power.

Recently I was in a friends shop and we needed to cut some 5/8" steel by hand.....outside of the shop. He did not have a long enough power cord to connect to the Powermax85 plasma......so I rolled out the Miller engine drive welder and plugged into the generator 230 volt outlet. The Miller was rated at 12kW (12,000 watts). On the first cut I triued running the Powermax at its full 85 amps output....and the arc would fire and immediately extinguish. Knowing that I probably had inadequate power (The Powermax85 manual says it needs a 20kW generator)....I turned the Powermax output amperage down to 65 amps....and was able to cut but the generator was really loading and the arc extinguished a couple of times while cutting. Reduced output amperage to 60 amps and was able to cut just fine. The Powermax units sense input power...and will simply shut down when it detects an issue.

Jim Colt Hypertherm

[bosulli]

A follow up note to my original post. The original goal was to set up new Everlast 51P plasma cutter for field applications using a Bobcat 225 as power source. I cut down a metal pipe fence without any issues.