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Power - Operating off a gas generator???

Discussion in 'Amps and Cabs [BG]' started by mikejs, Jul 11, 2011.

  1. mikejs


    May 22, 2008
    OK here is one for our bass - electrical engineers experts.

    We have a gig coming up where the only power supply will be a gas generator. We have done it in the past and run three power amps all instrument amps from the generator.

    But... I just got a new Markbass amp and I am a bit more concerned about plugging it in. There is a extra plug on the Furman conditioner that we are using for the power amps... but still not feeling 100% comfortable.

    Are my fears warranted or not???

    Thanks in advance!

  2. craig.p


    Sep 28, 2008
    New Hampshire
    Make sure the generator outputs a proper sine wave. Most generators that do this will have something in their descriptions such as, "Safe for electronic devices." Still wouldn't hurt to chase down the spec and/or product description.

    If at all possible, run your own private extension cord back to the generator, and place a quality noise suppressor between the extension female plug and your amp's main plug. I prefer Tripp-Lite Isobars but there are lots of similarly good ones out there. There was a recent thread on "what do you use for noise suppression" (or some such) if you feel like chasing it down. Definitely don't use some $19.99 pos from the local hardware store.

    I would not plug into the same "buss" your power amps use, because then you'd be hostage to the line voltage fluctuations on your power amps' buss due to wire gauge and line length. By "buss" I mean everything from the sockets the power amps plug into all the way back to the generator outlet itself. Of course these fluctuations will be caused by the power amps themselves. There's no reason to expose your amp to this. This is why I suggest a separate run from the generator to your amp and only to your amp.

    Hope this helps.
  3. I've played dozens of gigs on generators. I used a tripplite LCR 2400 which correct for line voltage sag or overvoltage and also filters out noise and such. It also weighs a ton! However even when I didnt use such precautions the worst that happened was some older amps were very noisy.
    One caveat, on some generators there is actually a switch for 50hz/60hz. Make sure it is on 60hz! Especially if its a tube amp! I toasted a borrowed amp this way once and ended up paying for the power transformer.
  4. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Make sure the generator has a stable output voltage (because you're in a top secret location I can't tell you whether it should be 120V or 230V, but I'll assume you know) and enough capacity for everything you're running on it. Ground it properly.

    AC power directly from a nearby generator is about as clean as you'll ever get.

    You don't need a power "conditioner." Especially for the power amps.
  5. meatwad


    Apr 9, 2008
    Smallville, USA
    I played a show once on a generator, and all went well until it ran out of gas. We never knew if it was a power surge or what, but our guitarist's amp never worked again after that.
  6. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    I bet THAT slowed him down a bit! :bag:
  7. BBEgo


    Apr 14, 2010
    Corona, CA
    The only thing I've ever experienced from using a generator is that the line voltage was like 130v. That kinda freaked me out. But the amps sounded great, and there were no weird ground loops. I'd almost prefer it to some of the crappy wiring I've had to use in the bars, and that includes the House of Blues in Anaheim. Almost shocked my face off!
  8. cheezewiz

    cheezewiz Supporting Member

    Mar 27, 2002
    I have played quite a few gigs on generators and never had any problems.
  9. TRichardsbass

    TRichardsbass Commercial User

    Jun 3, 2009
    Between Muscle Shoals and Nashville
    Bassgearu, Music Industry Consulting and Sales
    As all the others said, the problem with most generators is "dirty power". Voltage spikes, dips, load issues and noise. I'm with Calaveresgrande, make sure there is a good filter/converter in front of your power chord. Then all is well.
  10. f.c.geil


    May 12, 2011
    If you use a pure sine wave type generator and a power conditioner, then you'll get better power than that found in many venues. If you don't, you'll eventually kill your gear. Most of our equipment is fairly sensitive electronically, so you really don't want to feed it dirty power.
  11. Here's one goofy thing: Cheaper "contractor type" generators typically put out a pretty good sine wave--they are making the AC signal the "old fashioned" way with an alternator. That's good, but the bad: the voltage is set with an automatic voltage regulator (AVR) and frequency depends on the RPM of the engine. As long as the AVR does its thing, and the engine is running sorta close, you'll be fine. If the line frequency is 55 Hz instead of 60, or 63 Hz, it won't matter--all amps rectify the AC signal into DC. If the voltage is way out of range (say below 105 or above 135) though you can have problems.

    More expensive "invertor type" generators will have more precisely controlled voltage and frequency, but the sine wave is electronically derived and could be noisier.

    I've played several gigs on generators without major problems.
  12. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Actually, it's not. Generator power tends to be extremely clean.
  13. DWBass

    DWBass The Funkfather

    Generators scare me. Played through a few in my lifetime and they have all 'sagged' at one time or another causing power drops and sound cutouts. Me no likey especially when I'm using my own gear. If backline is supplied.....I don't care.
  14. jastacey


    Feb 8, 2009
    One of the main issues when using a gas powered generator, is having someone keeping an eye on the gas supply, when the run out of gas, they spike the power, and that's what kills amps ..... If I'm using my gear, I won't play the gig, but if it's back lined and I'm not liable ... sure I'll do it ... I might add, that those huge trailered diesel powered generators, are the only one's I'll plug my gear into, as they have some very good regulated power , If you going to use any generator and you need to remove all doubt about the power, use a good Multi-Meter and check the voltage & frequency, before you plug in, the smaller 5-10 HP gas generators, when running unloaded will read about 121 -124 volts and around 62 Hz, when you load them down, those numbers will drop slightly to 118-120 and 59-60Hz
  15. now I am not an electrical engineer. I am just a computer guy. But I was told when I blew up a borrowed amp, that a generator running at too low of a frequency will damage power input transformers on amps tha use them (tube amps). The explanation was that the transformer, like a speaker, has a lower limit on its frequency below which it "farts out" or cant resolve the frequency and dissipates it as heat.
    CAn anyone confirm or refute this?
  16. jaywa


    May 5, 2008
    Iowa City, IA
    I've heard lots of horror stories about gear blown up because of generators. We've got a generator powered, outdoor festival coming up where multiple bands are going to be using our P.A. and I'm not looking forward to that at all.

    I would just say, insert surge protection anywhere and everywhere you can in the chain, and make sure the generator has plenty of fuel to get through the whole gig.

    Oh yeah and make sure the generator is downwind of the stage (cough-cough).
  17. craig.p


    Sep 28, 2008
    New Hampshire
    Let me see if I can answer Cal's question succinctly.

    1. Transformers are expensive, so in non-military gear they're spec'd out to run at or near full capacity, i.e. just this side of core saturation. Part of the spec is the frequency of operation; to save money, this is often spec'd tight, with All Bets Are Off perilously close at either side of the frequency spec. This is usually a safe way to go as long as everyone, including the power company and the equipment operator, holds up his end WRT staying on frequency.

    2. At the saturation point, where the core material's flux capability is exhausted, a transformer's inductance drops way off, and so its effective impedance drops way off, too. This is what happens when you run a transformer at too low a frequency AND ask for the same current you'd want from it at its spec'd frequency. This causes current flow inside the transformer to increase. If you're lucky, the main fuse will blow in time. If not, the transformer windings will overheat.

    This is an oversimplification and missing significant detail but I hope it gets the main point across.
  18. I agree with craig that IF the transformer was spec'd "right at the hairy edge", then going much lower in frequency would start warming up the transformer perhaps beyond its design limits.

    However, even low budget guitar amps or bass amps aren't (IMHO) spec'd that close. Many power transformers are already rated to handle 60 or 50 Hz, such as the ones on the Triad page here Triad Magnetics Product Specs

    For those transformers that weren't directly listed that way (as 60/50 Hz), still going from 60 Hz down to say 55 Hz would not be an issue at all IMHO. (Even down to 50 Hz on the power supply will likely not create an issue under normal use.) This isn't a "resolving the frequency" issue, it's a matter of heat dissipation in the transformer. Of course it's best to have the generator supplying something sorta close to 60 Hz, but it's not cataclysmic if everything's not exactly 60.0 Hz. The world's not gonna end and amps aren't gonna start blowing up at 58 Hz.

    Under/over voltage, on the other hand...and poor grounding with ground-loop induced hums...that's the main issues I see with generators, but a generator of decent design, well-maintained in good operating condition, should be fine.
  19. Oh, I should note that inverter-class generators, like the expensive Honda gensets, derive their frequency and voltage electronically, so they should be pretty good on votlage and frequency if they are operating correctly (chances are they will be, since they have internal fault-detection circuitry).

    Contractor grade (cheaper) gensets that use an alternator depend on a governor to maintain engine speed (and hence frequency) which if it's good working condition should be pretty close, within a Hz or so (actual readings I've seen on travel trailer sites report good numbers). Same with voltage, unless somebody jacked with the AVR.

    A savvy setup guy/gal, knowing the show would be run off of a genset, would bring his/her trusty Fluke DMM along and test the power supply before plugging in.
  20. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    We had a gig recently at which the power was going to be from a generator. I put up a moderate stink over it, and the event manager found some power for us at a nearby building. I try to avoid operating on generator power at all costs.