Question; running a CNC off a diesel generator

Is it the computer that has problems, or is there per chance a UPS plugged in?

i

Most *modern* PC power supplies are pretty good about both varitions in frequency and voltage. Most will run on 50 or 60hz with no problems and will tollerate 10% swings in voltage. I'll bet he's got his big Genny hooked up incorrectly, you know, gnd vs neut or is only getting 90VAC or some such...

--.- Dave

Nowadays computers use switching power supplies, not linear ones. They are designed expecting a sine wave input. Generators, in general, do not provide a pure sine wave. Honda sells a few small models that do. I suspect that the bigger generator has a poor output the switch power can't handle.

Assuming that there is a 12V battery to start the generator and there is sufficient charging current for it, then you could hook up a

12vdc to 120vac inverter to it. Get one that has pure sine wave output. You'll need to size it for the load you are using. And only use it to run the sensitive computer/CNC controls.

Wayne D.

Is the generator three phase or single? I'm assuming the cnc is three phase. I use a 50 kw three phase gen. that works fine, but high draw cnc (40 h.p.) is sometimes an issue. If the cnc needs quick power to say, get a lathe up to max rpm, the generator can't respond fast enough. Even though the generator is big enough, the cnc may drop below its min voltage setting and shut down.Getting to high rpm may have to be done in steps.

JohnF wrote in news: snipped-for-privacy@4ax.com:

Is he trying to run the 110VAC SINGLE PHASE computer straight off of the THREE PHASE generator?

innews: snipped-for-privacy@4ax.com:

Would that cause problems? One leg to ground is single ph isn't it?

I re-read his email to me and he said the monitor was jumping around when hooked to the generator. I suspect the monitor is more sensitive to frequency than the computer. Overall, I have no clue as to how he has it hooked up. I've asked him if there is a transformer in the machine but haven't gotten a reply yet. I don't know if filtering through a transformer would do any good if it's a frequency problem anyway.

It's a Denyo MQ 25 generator.

JohnF

innews: snipped-for-privacy@4ax.com:

Depends on the generator and how it is wired, Wye or Delta. Most of the generators I've seen us a Wye connection with the center grounded. That will give you three circuits with 110 volts to ground. This is usually the most usable system since most things run well on 110 volts. You can also get 208 volts between any two high legs of the Wye, and three phase off the three high legs.

unless the generator has an excessive amount of noise on the output there should be no problem running a computer directly from it. Easy way to check is to get an AM radio plugged in on it and see if you can hear the noise on the low end of the band.

John

Yes but No, not for a computer to run. you need a Hot wire, Neutral and a separate ground to dissapate any static electricity that generates in the case of the computer. Some three phase gensets have a neutral some don't. I have seen the pc boards on ice machines go beserk due mostly to a lack of a good ground but ditto for the lack of a neutral. Often times the ground wire and neutral are bonded together in your house panel but rest assured they both have to be there. Hope this helps. As was mentioned in an earlier reply a converter could be used and have all three conductors you need. Good luck Lyndell P.S. Wild guess here but you might be able to drive a good ground rod where the earth will stay moist and call the ground on the genset your neutral and call the ground rod your ground. Others here with strong electrical background may be able to confirm or disspell this idea. BTW what you are looking for preferably is a four wire three phase genset with a ground bar. Three hot wires, neutral, and ground bar. All told five connectors.

Ahh so the problem is the Jug... I wouldn't think a monitor would be that sensitive to freq either, computers don't put out video that has ANY relationship to 60HZ, but probably are more suscepitable to voltage. Again this *may* be a gnd-neut kind of issue.

Saddly I don't think yer gonna get any closer to an answer till you check out the rig yourself...

--.- Dave

Um... I'll stick my neck out here and say I think any decent GenSet puts out a *reasonable* sine wave... I doubt seriously it's that...

And FWIW most of these cheapo UPS don't put out a sine wave... and they drive computers just fine...

--.- Dave

The ground and the neutral are tied together at the generator, and the generator is tied to the earth with a ground rod or series of ground rods. The neutral is the return circuit for the system. The neutral carries current in normal operation, the ground conductor does not.

Like you said, without the ground on the equipment the whole chassis system is floating and offers no shielding against stray signals, noise and other random electrical pulses that will cause havoc with the computer.

John

OK, if the only thing he was running was the computer and monitor, it may be that the generator's governor wasn't working at such light load. Many larger gen sets have a flywheel on the generator, and a centrifugal clutch/governor. You set the engine for 1825 or 1850 RPM, and the generator governor keeps the alternator turning at 1800 RPM. One thing that sometimes helps with sensitive loads is to turn the engine RPM up so the clutch is slipping enough to not be grabby, like a bad car clutch. Another thought is to hook up a larger load for the generator to keep the clutch working smoothly.

If he's going to have to run two generators, the grounds and neutrals need to be tied together, preferably at one point, so computers can be hooked to CNC's, etc. without fireworks.

Jon

Unless the "small portable generator" in question is one of the Honda or Yamaha inverter type units, the diesel set is in all likelihood more stable. A quality diesel set will have a larger flywheel, more rotating mass and an engine with a lot more torque available which all translate into more stable power particularly for frequency stability with large load changes. The quality of the regulator on the diesel set is also a factor and most should have a better one than most small units.

A PC in particular will normally have a switching type power supply that is very tolerant of input power variations. Most of these PC supplies have input rating of 100-240VAC 45-65HZ so both voltage and frequency stability aren't very important to them. I expect if the PC won't run on the diesel generator, your friend is indeed close to electrocuting himself and you should get up there quickly.

Pete C.

Reading the thread further and finding mention of the diesel set being an MQ unit I only have urgent advice - Get up there fast before you are attending your friends funeral! The MQ units are high quality and should have no problem at all powering a computer if they are connected properly.

Pete C.

What Dave said. Also note that the MQ diesel set indicated is a high quality unit.

LOL, will advise

JohnF

Makes sense, I'll email him about a ground rod.

Thanks

JohnF

Ok. You guys are right.

I did run a UPS once that caused the PC to howl, although it ran ok. That put me off on using anything but a clean sine wave into electronics. When I bought a backup gen I got the Honda EU.

Wayne D.