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[Tommy Peel]

Even though we don't need cars with 400HP, I bet at 70MPH I am using about 16hp, that headroom sure makes the excursion in the envelope both shorter and more enjoyable.

A simple analogy I am sure I will get flamed for.

Probably a little more than 16hp(maybe 30? on a flat road), but the analogy makes sense.    I was pretty surprised at the power difference going from a 115hp Nissan Sentra to a 130+hp Focus... I'm sure the Focus's manual transmission helps too though; I almost never have to downshift the Focus on hills at highway speeds whereas the Nissan would frequently have to.

Sorry for the hijack.... 

</off topic car talk>

[Lyle Williams]

From a regulatory compliance point of view, don't we run into a fault loop impedance limit before we get into voltage sag problems?

Ie, if you have reached the length where sag is a problem your cable run probably stopped being legal some time before that...

[Stephen Swaffer]

Using Mike's install, 400 feet (200 ft X 2 round trip) has a resisitance of .792 ohms.  Ohms law gives 151 amps on a short circuit-which should trip a breaker petty quick-but sag is still an issue.

[Lyle Williams]

Using Mike's install, 400 feet (200 ft X 2 round trip) has a resisitance of .792 ohms.  Ohms law gives 151 amps on a short circuit-which should trip a breaker petty quick-but sag is still an issue.

You need to allow for the impedance of the circuit in the walls between the breaker and the outlet, and the finite ability of the feed from the street to deliver current.  Call that another half an ohm.  Supply voltage might not be 120v, it could be lower.  Given a 20A breaker, this might take a few seconds to trip.

[Jeff Carter]

The cheapskate in me asks, if all the devices have universal power supplies that are rated 100-250V, is 105V a problem?

As long as the power supply can handle the extra current to get the same amount of power, you're fine--but I have worked with some (~2 kW) DC supplies that derate the available power below a certain AC line voltage.

[Guy Holt]

I know I had problems with the Crown XTI 1000 at 100v (long run from lousy genny) - ran hot and was clipping prematurely.  Sounded REALLY bad when it did...
But they did not shut down.

Do you remember what generator that was? How long the run was? What gauge of wire it was? And, finally how much the total load on the generator was?

Guy Holt, Gaffer
ScreenLight & Grip
www.screenlightandgrip.com

[frank kayser]

Do you remember what generator that was? How long the run was? What gauge of wire it was? And, finally how much the total load on the generator was?

Guy Holt, Gaffer
ScreenLight & Grip
www.screenlightandgrip.com

Hi Guy,
I Vaguely recollect.  Couple years ago.  A Celtic festival, late June in DC along the Potomac - miserably Hot (95+) and very humid. Rain late in the day(s)
Genny was a noisy construction POS.
Our stage used it, it was near the beer tent, and near some vendor tents.  I can only assume they tapped some power.
Figure the genny was about 75 ' from the stage (as the crow flies), and another 75' or so of it back to FOH. A single 10"EON II (250w) was set up outside FOH.
Cabling was 12ga SOOW.  I think we were running off some type of home-made distro.  No clue as to whether we had two circuits or not.
Voltage was showing a pretty steady 101 at the distro (stage side), regardless of what was running.  I had a Furman 1214 that was kicking FOH voltage up to 120 for the desk and outboard gear (minimal)
Stage was acoustic, with two Crown XTI, each channel - oops nope.
One crown XTI 1000 with four 8-ohm speakers per channel (2ohms/channel)
Thermal light popping on and off.
The other Crown got snatched for another stage (on a Whisperwatt, dang it!) 
Now that I think of it, I think we were also running one of those large direct drive pedestal fans.


Missing is the gen size, and total load.  Probably not of much help.
frank

[Guy Holt]

I Vaguely recollect....

What you do remember confirms my suspicion that your problem was not only a lousy generator but also voltage “flat topping” caused by the harmonic currents drawn by the XTi 1000 encountering the high impedance of the long 12 gauge run and the high impedance of the construction generator. Always bear in mind that voltage drop tables and calculators are for the 60Hz primary only and do not take into account the effect of harmonic frequencies. So that I don’t hijack this thread, I will go into more details on the “Non Power Factor Corrected Pro Audio Gear" thread (http://forums.prosoundweb.com/index.php/topic,151686.0.html)

Guy Holt, Gaffer
ScreenLight & Grip
www.screenlightandgrip.com

[frank kayser]

What you do remember confirms my suspicion that your problem was not only a lousy generator but also voltage “flat topping” caused by the harmonic currents drawn by the XTi 1000 encountering the high impedance of the long 12 gauge run and the high impedance of the construction generator. Always bear in mind that voltage drop tables and calculators are for the 60Hz primary only and do not take into account the effect of harmonic frequencies. So that I don’t hijack this thread, I will go into more details on the “Non Power Factor Corrected Pro Audio Gear" thread (http://forums.prosoundweb.com/index.php/topic,151686.0.html)

Guy Holt, Gaffer
ScreenLight & Grip
www.screenlightandgrip.com

Merci!

[Mike Sokol]

As long as the power supply can handle the extra current to get the same amount of power, you're fine--but I have worked with some (~2 kW) DC supplies that derate the available power below a certain AC line voltage.

This installation get's even wonkier... I took a closer look at the main panel feeding my two dedicated outlets, and they turn out to be 15 amp breakers, not 20 amp as specified. Also, looking at the install drawings I see that most of the amplifiers are wired for 2 ohm speaker loads. See a pic of the bottom of the rack below. Yikes...

However, my report to church management did some good because they've offered to run a new power line over to the gear room if I want it. Right now we're just getting the basics running so they can do a worship service this weekend, but next week I'll get to do a room tuning at full volume. I'm betting it will be pretty easy to trip those two 15 amp breakers.

[ProSoundWeb Community]