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Posted by Bernie Dwyer on 06/08/07 01:21
I wrote:
>
> Hi - are there any sparkies (electricians) here?
>
<snippety>
I'll reply in one msg rather than replying to each sub-thread.
First, thanks for your responses.
Some more info:
I used this genset 2 months ago with less total load, but similarly
spread across the phases, and it performed quite well. It's a 3-phase
diesel Hitachi, see:
http://www.coates.com.au/products/prod.aspx?G=17&P=265&S=44
Ignore the photo - it's the model 400110, 20KVa, 28amps per phase
Previous load was the same on phase 1 (unit lighting, makeup, electric
jug, etc), one 4K HMI and one 650W redhead on phase 2, and 2 redheads, 2
cameras, field monitor and smoke machine on phase 3.
It was over 90 meters away from the location, and being a silenced set,
noise was not a problem. We ran 3-phase cable 70 metres from the genset
to unit, split the phases there, and ran 1 phase to unit appliances,
then 2 remaining phases 20 metres to the set and lights, cameras, etc.
I knew that voltage drop could be a problem at that distance, but
received conflicting advice about it. I didn't actually check it with a
multi-meter, but it didn't seem to be a problem - the 4K HMI didn't get
upset, and everything else was fine.
This time there'll be the same uses by unit appliances on phase 1, but
increased loads on phases 2 and 3.
All my calculations were rounded up to the next integer for a safety
margin, e.g. 650 watts/240 volts comes to ~2.7 amps, so that got rounded
up to 3 amps for the purposes of calculating total load.
So, the total load on phases 2 and 3 will be a little less than 29 and
30 amps respectively, but this load will be constant once the DoP and
gaffer decide how much light we'll need. It might be less if we decide
we don't need a blonde or redhead, but it will never be more than 29/30
amps. I've calculated the loads based on 1x 4K HMI, 1x 2K Blonde, and 1x
650W redhead on phase 2, and 3x 2K Blonde and 1x 650W redhead on phase
3. I know that the actual wattages on phases 2 and 3 are equal, but the
rounding up is what brings it out to 29 and 30 amps respectively.
I could distribute the load more evenly if I run one or two filming
lights off phase 1 rather than phases 2 and 3, but as the electric jug
will be turning on and off at unpredictable times, it could cause the
lights to flicker or dip slightly. I suppose I could experiment and see
what happens.
One item I didn't consider - thanks for pointing it out - 20KVa/240/3
only gives me ~27 amps per phase and I've already got a higher load than
that on 2 phases. I don't know if individual phases can sustain a higher
load as long as total loading doesn't exceed 20KVa/83.33 amps, but I
wouldn't want to take the chance. I think that answers my original
question - I'm going to need a bigger genny! Probably the model 400145
or 400111 on the website above. Only trouble there, is that I have to
pay extra to get one of them transported here - the local hire shop
doesn't have one on hand. They do have a 60amp set, but that costs quite
a bit more.
Thanks again.
--
Bernie Dwyer
There are no 'z' in my address
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