[SML] distant generators

[Dale Farmer]

Without actually cracking open the book to confirm, entertainment rated 
cables are mandated, and they are 600V rated.  They were getting about 
200VAC, so lets assume they were getting 240VAC from the generator.  40 
volt drop over 200 feet is more than I would expect for typical loads. 
the mention of melting plugs further leads me to believe they were 
trying to pull more amps than the cable is rated for because of the 
voltage drop interacting with the power supplies trying to feed the gear.


There are a number of possible solutions to the problem stated.   The 
simplest and easiest is to just run a couple of additional regular 
extension cords from the generator to the sound table, and spread the 
loads over more cords.  This increases the effective wire gauge since 
voltage drop increases the higher the amperage draw.  (Don't ask me why, 
that gets into physics, and that class was 30 years ago.) If the sound 
gear is sensitive to voltage drop, put in a mid grade UPS that has 
voltage boost capability at the end of each cord.  That will draw more 
amps as the voltage drop gets bigger, so measure how many amps each cord 
is drawing and balance the loads.

   Outdoor venues often require long cable runs.   200 feet is not that 
long of a run.

Increasing the voltage at the generator and have a transformer to bring 
it back down to nominal voltage at point of use is another.  But if done 
by someone who isn't familiar with the oddities of voltage drop and how 
the power supplies in electronic gear affects it.  There is also power 
factor issues that further complicate things.

   Another one is to increase the wire gauge of the cable you use to 
make the long run. ten AWG extension cords are available at your local 
big box home center.  If they have someone capable of using a variable 
tap transformer without a darwin award, they have someone who can go buy 
a spool of heavy cable and connectors to make a temporary use power 
cable.  Another possibly more cost effective means is to rent from the 
same people you got the generator from a heavy gauge feeder to a distro 
box placed at the point of use.  One could also create a ring main power 
line, modulo local electrical code inspector approval.

There are other strategies one can use to mitigate the noise of the 
generator.  One is renting a drummer enclosure from your local band gear 
rental shop. It is designed to tame the sound of an overly loud drummer 
on a stage, it works just fine to tame the sound of a small generator. 
Just parking a truck between the generator and the set might be enough. 
Buy a couple sheets of plywood and a bundle or two of fiberglass 
insulation.  Carpenter can whomp up an ugly but functional noise 
reduction wall around the generator in an hour or so with that. 
Alternative go to your used office furniture vendor and rent or buy a 
couple sets of office cubical dividers. They are cheapish, and absorb 
speaking voice frequencies pretty well.  If they didn't get rained on or 
damaged, the vendor might buy them back at the end of the shoot.

Dale

On 7/28/2018 4:45 PM, Jerry Durand via Stagecraft wrote:
> I just read an article in Protocol magazine about using small (<= 10kW) 
> generators on a film set.  It was mentioned that for sound they had to 
> place one generator 200 feet away and to compensate for the line drop in 
> all that wire they used a tapped transformer to drop the ~200V coming 
> out of the extension cord to 120V.
> 
> It seems, if code would allow, a better idea to put a boost (step-up) 
> transformer at the generator to raise the 240V closer to 300V and THEN 
> have a buck (step-down) transformer at the lamp end of the extension.  
> The higher voltage would result in much lower loses in the wire, fewer 
> melted plugs (a problem they reported) and get you more usable Watts at 
> the lighting end.
> 
> So, the question would be, most low voltage USA wire is marked for at 
> least 300V max use.  How far could you push the 240V up without 
> upsetting the AHJ?  Maybe 277?
> 
> Of course if you happened to have access to a spool of 600V wire, you 
> could just bump it up to 440V at the generator and use really 
> lightweight wire going to the buck transformer at the lights.
> 
> -- 
> Jerry Durand, Durand Interstellar, Inc.
> www.DurandInterstellar.com
> tel: +1 408 356-3886
> @DurandInterstel
> 
> 
> 
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