Experience at the drop zone. [RE-wrenches]

[asap at podnine.com]

Dear Wrenches,
Below is an interesting story about a friend's experience in helping set up
remote electric power for a skydiving club.  He asked me to post it and I
felt it would be appropriate in this forum.

Thanks,
Peter Duchon
CEO
1AU, Inc.
www.1aupv.com
Systems Integrator
ASAP POWER!
www.asappower.com

**********
About three years ago, a small skydiving operation that I used to work at
(as an instructor) moved to a new location. There was no power there, so
they bought a generator. This got old quickly since they had a few loads
(a computer, a cash register, a small phone system, an aircraft radio) that
needed reliable power. So me, being the nice guy that I am, set up a small
UPS system for them. It consisted of a Prosine 1000, a Todd 12 volt
charger, a bank of four T-105's, fusing and cabling, and a Generac manual
transfer switch, so six loads could be powered off either inverter or
generator. I explained that the critical loads should be kept on the
inverter, and other loads (lighting, the PA, the TV's) should remain on the
generator. Total backed up load was about 350 watts; total load including
lighting was about 1000. I convinced him to switch from incandescents to
CF's so he could have a few inverter-backed-up lights when the generator
was off. I also talked him into 250 watts worth of solar (Unisolar 64's)
so that when no one was there the phone system would remain working (about
20 watts.)

I was away from the drop zone for about six months. When I got back I was
amazed at how the place had grown and how many myths had grown up around
the power system. "It won't charge unless you switch all the loads to
generator." "You can't start the generator during the day because of the
solar." Total load was now around 1500 watts, which included a small
refrigerator, fans, more TV's and a new trailer. The inverter now was
handling it _all_ and doing quite an amazing job for a 1000 watt
inverter. It would periodically blow its output breaker, which is why I
got called back. It would also periodically glitch the computer due to all
the switching they were doing. I explained that they didn't have to be
switching loads all the time, but by this time the myths were pretty well
established.

I sat down and showed the owner how to do a load analysis, and went around
myself and changed all the bulbs to CF bulbs. The number he came up with
was a peak load of around 1800 watts, average around 1000. I told him that
he had to include all his future projected loads; he said that he had done
that. I doubled his estimate and told him he needed to spend the money and
do it right. "Doing it right" meant building a vented battery box and
setting up a system that included:

SW4024
Battery monitor
660A-H battery bank
DC disconnect
C40 charge controller

Balancing transformer for the cheapo Home Depot 5500 watt 240VAC generators
he was using "Start generator" light controlled by a relay on the SW that
came on at
about 22 volts. (Generators were all recoil start.)

I considered going to 48 volts but they had an aircraft-start requirement
that required a massive 24 volt battery bank (600A momentary load) so it
seemed to make sense to go with 24V and have that DC output available for
charging the starter battery bank.

He paid for it and I installed it. He was suprised that he wasn't actually
_getting_ 5500 watts out of the $249 Home Depot specials; best I ever saw
was about 3000. But that was enough to both run the place and charge the
batteries at a decent rate.

A short time later we moved the system to a new location. It got an array
of 32 T105's, which was good - the old 12-battery bank was being
overstressed by the loads, and the new array ran much cooler with less
electrolyte loss. It also got a 150kW propane generator with a Honda
engine, hopefully the last in a long line of cheap generators whose
carcasses now littered the parking lot. This was massive overkill (and
really inefficient) but it let him run the big trailer air conditioners in
the summer; it also let the SW inverter automatically start the generator.
A few weeks ago I visited again, due to more breakers popping. This time
it was the DC breaker that was going. Load was now exceeding 6000 watts,
and included a soda machine, VCR's, ventilation fans, refrigerators, a 1500
watt coffee pot, and an occasional electric heater. Each new load was
explained by "well, it doesn't take _that_ much power, does it?" or "it's
the military guys; they plug that stuff in sometimes." The generator
essentially started in the morning and shut off at night. I told him he
had to reduce loads; the coffee pot in particular had to go. He agreed and
has a plan to get thermos bottles or something.

It's pretty clear to me now that I have to switch over to a 48 volt system,
go to an SW5548 and plan on getting a second one once he realizes he can
plug all that stuff back in. I was tempted to get a second SW4024, but the
additional 4-0 cabling, load disconnect and monitoring hardware erases any
cost savings between the 4024 and the 5548.

When I first envisioned the system I thought that solar would carry a
considerable part of the load. In many ways it's an ideal application for
solar; skydiving is sun-synchronous, since people jump generally only when
the sun is out. However, the owner is all about maximum watts for minimum
money, and has an ROI horizon of just a few years. So the sad 250 watt
array is still doing its part, but doesn't contribute much on a percentage
basis, and probably won't get much bigger.

Lessons learned:
1. Load estimates can be absurdly optimistic. People understand that
watts=cost so they tend to lowball. I think that people, especially at
small businesses, then tend to use the power available until they run into
a hard limit (like the DC breaker.) I find myself wishing I had put 5 amp
breakers on all the outlet runs.
2. It can be a mistake to rely on someone to operate a system in a certain
way. People will develop ideas on how a system should operate that can be
hard to change. "I've been here for six months! I know what works and
what doesn't." Having the SW handle the transfer switching and generator
start has improved reliability of the system by at least a factor of 10.
2a. If the system does need to be operated in a certain way, write it down
using small words and in large type and post it next to the controls.
3. You can't rely on people (system users) to do something extra if it
doesn't solve an immediate problem. It would have been very easy to switch
over from incandescents to CF's at any time, but since the system was
working without doing that, there was no impetus to do so.
I'm not allowed to post here; I asked a friend of mine to post this as a
lessons-learned sort of thing. It was definitely a learning experience for
me.

-- Bill von Novak

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