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PA off electric Generator, Inverter Required?

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  • #16
    You don't need external regulators, the generator has this built in via the field winding compensation current. In fact, external regulators and dynamic loads can cause additional problems.

    The "line conditioners" aren't much if any help either, but they are a convenient power strip.

    The genny frame should be bonded to the "neutral" on your genny already, a driven ground rod connected to the genny frame is for safety. It can also reduce noise (hum, buzz and RFI) with some equipment.


    WHew!
    Thanks.
    That helps a lot.
    Now I can't believe I used to run the whole show with a 6000 Watt
    Honda Generator, with no problems....well one problem.
    We ran out of gas during a set.

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    • #17
      And I have repaired a lot of customer equipment improperly powered by generators too.
      -------------------------------------------------------------------------------------------------------------------------------------------------------------------
      Former product development engineer: Genz Benz, a KMC Music/FMIC/JAM Industries Company, continuing factory level product support and service for Genz Benz

      Currently product development engineer: Mesa Boogie

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      • #18
        When using the larger "towable" gen sets with a user adjustable voltage knob, be sure so set the voltage from about 118 to 121 VAC before connecting a load. When these units are used on construction sites, many times the voltage knob is cranked up (too far). Cranking the voltage too high can result in a severe over voltage situation if the load drops off suddenly. Having the dummy load helps voltage stability issues.
        Engineering Axiom 21: Whomever has the key should be qualified.

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        • #19
          There are some advantages for a DJ to run a PA system off of a DC battery bank: no genset needed, therefore no noxious fumes, flamable fuels, loud engines, long power cable runs, or genset failures. Also no worries about bad power burning up gear if you use good sinewave inverters or straight DC powered gear (with DC-DC converters). If you do remote gigs on a regular basis, then it may be worthwhile to invest in such a rig.

          I have built my own remote PA system using a car amplifier with PA speakers, and DC/battery power for my rig. My system isn't big enough to do a large outdoor venue, but it's good enough for me as a solo artist who wants to jam in the middle of nowhere with good sound and volume as long as I want. I have a range of deep cycle batteries that I can use to make up a 12V bank of various capacities. Sine wave inverters large enough to run high power audio amps are expensive, so that's one reason why I use a car amp instead. Also, going from DC-AC-DC-AC for batteries to inverter to power amp rails to power amp output seems is rather power inefficient. A car amp goes from DC-AC to do only a single conversion instead of three. You do have to run some pretty heavy batteries for long running off of inverters. The music style and number of subwoofers will have a huge affect on the power demand, so that is something to think about before attempting a battery rig. For my music I can run very good volumes with relatively low current draws. My standby draw is under 1amp, while my program level is 6-30amps. That's running a pair of PR10 with a PR15 as a 2.1 setup, with a 4 channel car amp having 2 channels bridged mono for the PR15.

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          • #20
            In the power range these systems are looking at, an inverter is not a practical solution unless they want to rent deep cycle batteries and at 6kW, you are looking at 48 volt input inverters due to DC bus current.
            -------------------------------------------------------------------------------------------------------------------------------------------------------------------
            Former product development engineer: Genz Benz, a KMC Music/FMIC/JAM Industries Company, continuing factory level product support and service for Genz Benz

            Currently product development engineer: Mesa Boogie

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            • #21
              In the power range these systems are looking at, an inverter is not a practical solution unless they want to rent deep cycle batteries and at 6kW, you are looking at 48 volt input inverters due to DC bus current.
              -------------------------------------------------------------------------------------------------------------------------------------------------------------------
              Former product development engineer: Genz Benz, a KMC Music/FMIC/JAM Industries Company, continuing factory level product support and service for Genz Benz

              Currently product development engineer: Mesa Boogie

              Comment


              • #22
                In the power range these systems are looking at, an inverter is not a practical solution unless they want to rent deep cycle batteries and at 6kW, you are looking at 48 volt input inverters due to DC bus current.


                What....don't wanna run 250kcmil cable????
                "If you don't know where you are going, you might wind up someplace else" - Yogi Berra, 1925-2015

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                • #23
                  That is only if you assume that they actually need 6KW of audio power. There's a good chance they are using at least 6dB just to overcome the sound of loud generators, if not more. One of the great things about remote locations is that you generally don't have to overcome ambient noise unless you generate it with GenSets. A scaled back system using a respectable car audio amp might work, might not, depending on the circumstances. I can tell you that the sound of GenSets blaring full blast isn't music to my ears.

                  There is no need to rent deep cycle batteries when you can buy them for under $80 a pop at Sam's Club, which has the Energizer GC2 for $71.28 and the GC8 for $77.82, at least in my area. Some audio equipment may be able to run fine on the cheaper 1500-3000W MSW inverters, but that's a bit tricky to test, as you probably know. I wouldn't run audio amplifiers or other high current draw devices that will be sensitive to the shape of the power wave. That's why I use a car amplifier to avoid that situation. I know this configuration will work for many remote gigs for DJs, but not for a big venue rave or anything with that scale. Running a 48V inverter could also be worthwhile if the gigs are a regular thing, but the Xantrex and Outback 48V inverters aren't cheap either.

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                  • #24
                    After the power went out last year due to a hurricane, we did a block party off my small generator. I brought bare equipment and it went OK. I knew I was running too much power through it though.

                    About 1 month later, my good guitar amp crapped out on me. When the manufacturer was fixing it, they said they've never seen the power transformer die like that. Sometimes you don't see the damage you do until later. This thread has got great info I will remember.
                    http://www.TomMatz.com

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                    • #25
                      For the op's system, that's a lot of energy storage and I doubt 6dB is needed to overcome a (good) generator. Figure 6kW x 25% = 2kw/h x 6 hours and that's 12kWh. How many deep cycle batteries would you need to provide this... there's about 800Wh available in a good 12v deep cycle battery, so you are looking at 15-16 batteries to get you through the gig? Not practical IMO, at this point it's time to look at a forklift battery.
                      -------------------------------------------------------------------------------------------------------------------------------------------------------------------
                      Former product development engineer: Genz Benz, a KMC Music/FMIC/JAM Industries Company, continuing factory level product support and service for Genz Benz

                      Currently product development engineer: Mesa Boogie

                      Comment


                      • #26
                        Except that the AH draw for program music is much, much lower than the power capacity of the audio amp, particularly when you are using a car amplifier.

                        My standby draw on the car amp is about 600mA. I'm only drawing the amps when I'm pushing the air. The AH draw also depends on the content of the music. If you are mostly using the horns and not pushing the deep bass, then you can run very loud with little draw because of the efficiency of the horns. Anything that depends on subs and heavy bass will suck huge amps, but many other kinds of music take much less power to run for a long time on batteries.

                        Now if you are using regular audio power amplifiers, you could be sucking huge amps just in overhead, since they are usually designed with no consideration to AH draw on batteries. For a lot of music, you do not really need more than two or four GC batteries to run for more hours than you'd want to listen. All that needs to be part of the AH calculation though, and I use my clamp-on DC ammeter to closely monitor the draw so that I can know exactly what to expect for battery draw. I never discharge below 50% in order to preserve the cycle life of my cells. A pair of 6V Golf Cart batteries last a lot longer than a pair of 12V marine deep cycle, in my experience. I too was very skeptical about the ability to run quality music at loud volumes for a long time on batteries, but I was able to address these issues to my satisifaction by experimenting with a number of different configurations to settle on my final solution. I wasn't happy with any of the battery powered amps I found to handle my needs.

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                        • #27
                          For any typical audio power amp (not car audio) the system typically draws on average between 1/4 and 1/8 the rated power of the amps where sized reasonably. 1/8 is the typical minimum and 1/4 counts for inefficiencies throughout the conversion chain including inverter, I**R loss, power supplies.

                          So take the 1/8-power currrent draw at rated power (from the manufacturer data) and double it and this will be a good estimate of the system power draw for long term energy reqts.

                          This is a good application forthe most efficient speakers you can find, and maybe car audio amps offer a bit of efficiency benefits here too but I was referring to what the OP had listed and his SPL needs.
                          -------------------------------------------------------------------------------------------------------------------------------------------------------------------
                          Former product development engineer: Genz Benz, a KMC Music/FMIC/JAM Industries Company, continuing factory level product support and service for Genz Benz

                          Currently product development engineer: Mesa Boogie

                          Comment


                          • #28
                            Yes, agedhorse, I understand the inefficiencies of the typical audio power amp, which is why I bypassed them to use car audio, which is designed to run off Automotive 10.5-15VDC power directly.

                            I found that my 1500 MSW inverter has a larger standby draw, 1A, than my car amplifier at 600mA. So even out of the starting gate, the car amp is ahead in the efficiency game. In the end, I found that the car amp eliminated all the losses due to the extra power conversions that were removed, to keep the amps pushing air instead of heating equipment.

                            I agree that if you just keep all your existing equipment that is power inefficent and runs off generators, then switching to battery/inverter alone may be impractical. But once you bring in the ability to improve the efficiency of the demand, not just the supply, then you open up a lot more possibilities. This is why people running on solar power usually choose to run much more power efficient appliances than the typical consumer models, so that it makes the whole battery/DC/panel requirements much lower than "normal".

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                            • #29
                              The actual amp losses are pretty miuch identical, the additional current is probably reactive from a linear transformer and with some inverters this will be returned to the inverter's energy storage assuming it's a non-linear converter. It's not (all) real power.
                              -------------------------------------------------------------------------------------------------------------------------------------------------------------------
                              Former product development engineer: Genz Benz, a KMC Music/FMIC/JAM Industries Company, continuing factory level product support and service for Genz Benz

                              Currently product development engineer: Mesa Boogie

                              Comment


                              • #30
                                Let's also compare apples with apples. Car audio is firmly buried in bull**************** marketing of specifications. A "more efficient" car amp is more likely a much less powerful amp than the "equivalent" SR amp.
                                "If you don't know where you are going, you might wind up someplace else" - Yogi Berra, 1925-2015

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