Issues in Running Power
to a Remote Observatory
Subject: Running Power to Remote Observatory --part 1 of 16 
From: John Hopper <JohnLX200 aol.com>
Date: Oct 2001
Anthony Kroes writes:
<< I plan on running two 15 amp or 20 amp circuits to the observatory (one for scope and computers, the other for lights
and misc. Distance from the main breaker panel back at the house is probably between 350'-500' (haven't measured exactly
yet - depends on whether I run the wiring through the old barn, or around it). >>
Is the barn by the house, or a significant part of the distance to the observatory?
I'd consider running a heavier service to a secondary breaker box in the barn if you might want additional power in the barn
for other reasons at a future date. Then your lower-amperage run from there to the observatory will be shorter. Part of the
cost of getting service to the barn might be offset by potentially smaller wire required the rest of the way, depending upon
exact distances and loads.
I'd definitely run 220 volt service all the way to the observatory, rather than just 110 volt. Specifically, run 3-conductor
(plus ground) wire rather than 2-conductor. This gives you your two separate 110v circuits (without going to a higher wire
gauge to carry double the amperage on one 110v circuit, but you weren't considering doing that) and avoids the waste of using
(2) 2-conductor UF cables instead which would add an unnecessary second ground wire and second neutral wire. For instance,
you can get away more cheaply with one 10/3 UF cable rather than two 10/2 UF cables, both of which are probably much better
than a single 6/2 or 4/2 cable to carry the same load, both for cost and design reasons.
I'd also definitely buy a 500 foot spool if a run is over 250 feet, and a 1000 foot spool if over 500 feet, to avoid needing
a junction box partway, unless there's a convenient spot like your barn for it. If you're not using nearly all of the cable,
dream up some use for it while your trench is open, or ask your electrical supply house about cutting the length you need,
plus some, all in one piece. Or better yet, work a deal to take the whole spool and later bring back the remainder still tightly
up for a partial refund.
-----------------------------------------
One hint if you're pulling the cable through pipe: don't connect the pipe sections together until you've pulled the cable
all the way through with a little space between pipe sections, to be able to get at it. Leave a bit of slack in the cable as
you go, too. Once it's all in place, start connecting the pipes together at the opposite end from where you can still add more
pipe over the end of the wire, also paying heed to what will happen if you have sharp bends in the route along the way where
you can't move the pipe around the bend.
-----------------------------------------
Subject: Running Power to Remote Observatory --part 2
From: Gene Horr <genehorrtexas.net>
Before doing this I would call your local utility company and get a price to run service out to your observatory. It most
locations the cost is often not much more than what the material costs alone. Just make sure the place the pole far enough
away that it doesn't block your view. You'll still need to provide a panel and run power from the pole to the observatory building.
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Subject: Running Power to Remote Observatory --part 3
From: Anthony Kroes <akroesvenomtech.com>
Gene, for the underground idea: I just upgraded my 1956 farmhouse to 200 amp service from the old 60 amp. During the same
switchover, I had the utility company run my lines from the road to the house underground. Now I don't have the wires hanging
over my yard, and the pole in the middle of my yard that used to hold the line (and a big bright farmyard light) can go away
permanently. Cost was $680 for about 150' distance (wire and trenching), but it was a set price as a service that they offer.
The sky is the limit for extending that another 400' or 500', I'll have to call, might be cheaper than I think!.
John, I will take my roller-wheel measurer this weekend and line up an exact measurement. Estimating, the barn is probably
about 200'-250' from the house, is about 50' wide (with junk, landscaping, rocks, etc.) and the observatory will be about 50'-75'
on the other side of that. Running power to the barn is a fair idea, but I use the term 'barn' loosely here. The top half is
gone, so it is not waterproof (big storm a few years ago before I bought the property). It's really a barn foundation with
the old barn floor as the remaining bit's roof. If I knew someone with at D7 Cat, I'd dig a big hole and bury the whole thing!
I like the 220 idea as it can serve multiple purposes. I guess I will have to compare the cost of the right gauge 3-conductor
wire and trenching with having the utility company put it in.
Doc, I can probably get away with only a single 10 or 15 amp circuit, but it would definitely be nice not to have to worry
if I have enough juice left every time I want to add a new toy (which has been known to happen on occasion!). My current setup
uses about 8-10 amps on portable DC power (scope, laptop, Kendrick, etc.), so running from an 10 amp AC circuit would be no
problem. The second circuit was for future additions (I only want to run this once!) like a heated control room, etc. I guess
I can worry about that when the time comes....
Another option I have been playing around with is using solar. I have a solar panel already from another astronomer friend,
and could purchase 1 or 2 more ($100 each), plus a couple batteries ($65 each) to match my existing battery setup. A few bucks
for a control box and I would have less invested than any of the other options we have talked about. The field the observatory
is in faces south with a completely unobstructed view 270 degrees around NE to S to NW, so seeing the sun for charging purposes
would not be a problem. The main thing stopping me now is how do you keep the batteries from freezing in the winter if I leave
them in the observatory? Also I know the power level will be much less in the winter and would have to make sure the capacity
I use will take that into account.
I guess I could put the batteries in some sort of cart and keep them charging at the house on AC until observing time. No
panels to buy then! I could just roll the cart out to the observatory and plug in to a port on the outside wall, I wouldn't
even need to unload them or bring them inside the observatory.
Any thoughts on this? I thought it would be kind of ironic doing all my viewing and imaging at night while powering everything
from juice gathered during the day when I can't.
----------------------------------------------------------------
Subject: Running Power to Remote Observatory --part 4
From Doc G
This is not realistic. You need to figure the real steady load current. For an observatory, even with music, :-), 10 amps
total would be a lot. Then you can get by with a No. 8 wire. Even then it will be costly for the outdoor quality wire you will
need. You need to make a very realistic estimate of your power needs and limit them to reasonable levels.
Every three wire sizes gives twice the resistance. Do not forget to calculate for both directions.
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Subject: Running Power to Remote Observatory --part 5
From: Jerry Stephenson <stephejlsongs.sce.com>
Anthony, the amp capacity of the wire you use is independent of the length of the run because it is based on ambient cooling
which is constant along the length of the run. The code says you can run up to 30 amps on 14 gauge. However, the voltage drop
will be your concern so you'll have to run bigger wire to get a reliable voltage. Indeed it probably a good idea to run two
separate circuits as you suggest because turning on lights or other loads may affect voltage slightly on such a long run. 8
AWG copper wire has a resistance of .72 ohms/1000 ft. At full load this would result in a voltage drop of about 7.2 volts over
500 ft. This is reasonable since you will seldom be using such high current. In fact, if you want to assume instruments will
be using 1-2 amps, then 12 AWG would be fine. And who cares if the lights are a little dim. (115 volts vs. 120, you probably
have 125-130 volts anyhow). Make sure the motor for your roll off roof doesn't have a minimum voltage spec. Then the auxiliaries
could get by on 12 AWG also.
Depending on your budget and propensity to over design, you can make your choice. I would probably use 10 AWG unless I could
get a good deal on 8 AWG.
Indeed, aluminum wire has much different resistance and amp capacity. The rule of thumb is that aluminum has to be one size
bigger than copper. If you use aluminum, make sure you coat every connection with the required antioxidation goo.
After I had it all up and running, I would hook up a volt meter and turn on and off the biggest loads in the observatory while
observing the effect. You will figure out if you need to put the scope and camera on separate circuits or other such issue.
PS: Recognize that any load will pull more current as the voltage goes down but this isn't a problem unless the circuit is
loaded to maximum.
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Subject: Running Power to Remote Observatory --part 6
From: Shay Walters
Another thing to keep in mind is that you want to size your breaker so that it _WILL_ trip if there is a short at the most
distant point in the line. You don't want to have a 20-amp breaker feeding a line that has enough resistance that it will draw
only 15 amps with a short at the far end. This is a very real scenario, so you do need to figure your wire resistance and size
the breaker smaller than the current a short will draw. In electrician's handbooks, there are tables that will give you this
information for various sizes of wire.
Wires running in walls, and even underground, are fairly well insulated and will build up quite a bit of heat from heavy current
flow. This is the type of situation that leads to electrically-caused fires.
-----------------------------------------------
Subject: Running Power to Remote Observatory --part 7
From: Mike Dodd <mdoddmindspring.com>
> The code says you can run up to 30 amps on 14 gauge.
Really? I always thought 14 gauge wire was suitable only for 15 amp circuits, 12 gauge for 20 amp circuits, and 8 gauge for
30 amp circuits.
Better still, here's a link to a site that will calculate the appropriate wire size for a specified length and current draw,
based on the National Electric Code:
<http://www.cossin.com/page4.html>
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Subject: Running Power to Remote Observatory --part 8
From: Anthony Kroes <akroesvenomtech.com>
WOW! It WAS more than I wanted to know! Good info and a neat page, but according to the official N.E. Code, If I am running
a 15 amp circuit 350' I need to use #4 wire. Ouch! That's a big bite.
According to their interactive calculator, they 'recommend' that I only go 140' with a 15 amp circuit using 8 gauge wire.
Those batteries are looking better and better by the minute, sled or not!
If I am drawing 8-10 amps on my 12v DC setup, then that would be about a 1 amp draw on a 120 AC circuit. Thus using a 10 amp
circuit to power the observatory would work just fine. As you mention though, that does not include the efficiency of the power
supply/transformer, and perhaps the AC power bricks for my DC accessories may not be the same wattage as the direct DC versions
and may use more or less juice, but it should be comparable.
My main problem with this issue is figuring the resistance/voltage drop over a certain distance. Someone quoted .72 ohms/1000ft
of a 10 gauge wire, but where does that info come from? How about 8 gauge, or 12 gauge? What is the formula for computing the
'drop' once you know the resistance? How much 'drop' is 'OK' to still run computer equipment? How much spare current should
I plan for? I know how to compute my existing needs, but should I plan for having 50% extra right away, or only 25%?
-----------------------------------------------
Subject: Running Power to Remote Observatory --part 9
From: Doc G
Mike Dodd wrote:
> > The code says you can run up to 30 amps on 14 gauge.
>
> Really? I always thought 14 gauge wire was suitable only for 15 amp circuits, 12
gauge for 20 amp circuits, and 8 gauge for 30 amp circuits.
You are correct for typical house wiring. Code may vary from city to city but 30 amps on 14 gauge is out of the question.
The drop you get is dependent on the length of the run. In a house, it is rarely more than 30 to 50 feet. For 300 to 500 feet
you are talking about another situation.
It would be best to have the power company do this job since it is not a minor one. It is not unusual to pay $10 a foot for
underground power runs for full 100 amp (120-0-120) service.
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Subject: Running Power to Remote Observatory --part 10
From: Mike Zook
You should use the amperage you want at the observatory to figure this. If you need only a couple hundred watts, allow an
additional safety factor, divide by 120, and you get the amps needed. You will probably find that #10 or 8 wire is sufficient.
You can buy #8 URD (direct bury underground) wire fairly cheaply and if you are prepared to install it yourself the installation
won't cost much. Make sure you bury it deep enough to meet code.
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Subject: Running Power to Remote Observatory --part 11
From: Doc G
<stephejlsongs.sce.com>
wrote:
> Doc G wrote:
> "Every three wire sizes gives twice the resistance. Do not forget to
> calculate for both directions.
>
> Doc, I think you don't need to calculate for both directions. Think of it
> as a circuit, you are at the midpoint. You need to calculate for both
> directions to get back to the source but you see only half the voltage drop
> at the midpoint of the circuit (the observatory).
Think of the lines two wires as a circuit. The line out resistance plus the load resistance plus the line back resistance
divided into the voltage applied gives the current.
Make either the line out or the line back resistance large and you get no current.
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Subject: Running Power to Remote Observatory --part 12
From: John Hopper <JohnLX200aol.com>
<AuroraCEAearthlink.net>
writes:
< Spend the money and have the power installed by the electric company, it will be worth the nominal investment in
the long run.>
Be wary of establishing a separate electric service from your house, though. My electric company hit me for about $30/month
for the separate service before using a single watt-hour, plus a higher commercial rate for my pumping station boosting the
town water pressure to make it up my hill. Unfortunately it was impractical to run heavy enough wire to run a 2HP pump 1200
feet from my house, off my house service, so there was no choice.
But a low-demand situation like an observatory can easily be handled by having your electrician run a 220 circuit out there
350 feet from your main box. If you're willing to limit your loads, downrate your breakers accordingly, and avoid using long,
thin extension cords from the observatory, you can keep the wire size reasonable.
I seriously doubt that you'll wind up with each of your two circuits any worse off after an uninterrupted 350 foot run of
10/3 UF than you would by powering a small ShopVac from a house outlet rated 15 amps, possibly at the end of a long line of
connections at other $0.49 outlets along the way, and a 100-foot 16/2 extension cord plugged into it from there rated 10 amps.
10 gauge copper wire 700 feet long (350x2, Doc G was of course right to use both directions!!) has a resistance of about 0.77
ohms. Therefore, if you short the end of it, the current at 120 volts input is over 150 amps. So much for the theory that such
a skinny wire will prevent circuit breakers from seeing a short.
Now let's put a 1440 watt hair dryer at the 120v service entrance. It draws 12 amps at 120v, and is therefore a resistor with
a value of 10 ohms. Now plug it in at the observatory, the total resistance is 10.77 ohms, the total power drawn by heating
both the wires and the hair dryer is 1337 watts. The voltage across the hair dryer is 111.42v (to ground, it's 115.71v at hot
and 4.29v at neutral); its power is 1241.5 watts; and the actual current is 11.14 amps to this 12-amp-nominal power hog. The
remaining 95 watts is spread across heating the 700 feet of wire. So less than 1 watt goes into a 7 foot length of wire, corresponding
to a 42 inch section of buried cable. If you're running a second hair dryer on the second circuit simultaneously, your entire
cable is seeing a worst-case situation of 1 watt of heat dissipated per 21 inches of 10/3 UF cable buried underground in Wisconsin.
Not enough to even melt the permafrost most of the time ;-)
Follow code, certainly. Physically installing it even better than code requires makes sense to me. But don't feel obligated
to put 2-gauge wire in so that you can use 20 amp breakers with negligible voltage drop, if your typical load per circuit is
1-2 amps and the largest load is typically 3-4 amps, getting you within about 2 volts of your service entrance...better than
at your more heavily loaded outlets in the house.
Computers, battery chargers, and telescopes just don't draw much power, nor are they terribly sensitive to exact input voltage.
And as shown above, even if they nominally draw 10 amps, you'd still be fine with 10 amp circuit breakers.
To give a practical feel for the voltage drop, a 350 foot run of 10 gauge has the same resistance as 140 feet of 14 gauge,
the most common size for 120v house wiring, and a moderately heavy duty size for 50 or 100 foot extension cords. By contrast,
350 feet of 8 gauge is equivalent to 140 feet of 12 gauge, the heaviest size normally used for 120v house wiring, and also
the heaviest size normally used in long extension cords for home construction from a generator, etc.
Bear in mind that calculators "recommending" extreme conservatism beyond already conservative code, are allowing
for many stupid things that do not apply to your straight underground shot at night in Wisconsin, like a bunch of intermediate
junctions, regular Romex interior cable (with paper wrapping inside it!) inside wooden stud walls instead of UF direct burial
cable underground or in conduit, allowance for not adding to brownout situations when everyone is running their air conditioner
in Houston, etc.
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Subject: Running Power to Remote Observatory --part 13
From: Gordon Lupien <glupiennetsville.net>
I was considering setting a couple marine batteries in mine when I get it done. Running a reasonable gauge wire down to the
place with a regulated 13.8v power supply in the house and the batteries on the other end in the observatory. This would work
fine with just about any REASONABLE gauge wire, as long as you regulated the current with the power supply so that you don't
send more than the rated capacity of your selected wire. The resistance in the wire would *NOT* be a problem or concern either,
because as the batteries reached full charge, the current would drop down to nothing, and the voltage would end up coming up
to 13.8v at the observatory end when the batteries were charged. You would have to do some calculations to see what you could
get away with depending on how fast you wanted to charge the batteries, etc. Adjustable 12v power supplies can be found at
just about any surplus store for a couple $.
At any rate, you can then use home current, or solar, etc. to charge. In addition, you don't need to have it checked by anyone
because it is 12v. You can use an inverter in the observatory if you really needed AC. Just about everything runs on 12v, or
less anyways after the transformer/power supply. The observatory would run quiet, and be available even if the power went out
(and you wouldn't ruin any of those nice shots by loosing power either).
In addition, you could just pull a battery out (which would always be fully charged and ready) and go to a dark site/star
party if you designed it right. The batteries would last a long time, because they would always be maintained at their top
charge of 13.8V (for lead-acid). You take the life out of a lead-acid battery by leaving it discharged for any length of time.
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Subject: Running Power to Remote Observatory --part 14
From: Roy Gillard <roygillardmsn.com>
I agree with Doc, Ray, and John. I would have the cable installed by the power company as they will assure that the voltage/current
at the OBS would be sufficient. They can run the power at elevated voltages with smaller currents for long distances with negligible
loss. When the line reaches the OBS a line transformer is installed by the power company to convert the voltage down increasing
the current capacity. (i.e. 1200v @
1.5A= 120v @ 15A.)
If you decide to run 8 gauge wire yourself, you could put a APC battery backup at the OBS which will maintain a constant
115vc to
the electronics and filter out any equipment noise spikes generated on the long wire. The APC battery backup could be used
if you decide to go with a generator. Be aware though that the generator voltage can change output significantly with varying
loads. I know that some generators lose regulation when the gas tank is near empty and begin to surge. This could destroy
all your valuable equipment unless protected. Also, if you need to work on your scope or other equipment in the winter, then
you
would want enough power to give some heat to work in comfort. Roy
--------------------
Subject: Running Power to Remote Observatory --part 15
From: Rick Richardson <rick.richardsonusermail.com>
I used a generator after hurricane Fran hit our area. They can be noisy nearby. The latest ones are very reliable and the
current and voltages are stable. A 5000 watt generator is note going to induce enough vibration for your scope to notice if
it is 20 or 30 feet away. I would suggest building a nice little house for it with vented intake and exhaust. Makes it easier
to store the fuel and maintain the generator.
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Subject: Running Power to Remote Observatory --part 16 of 16
From: Doug Groesbeck <douggrohome.com>
Anthony, both strung and buried wire will bring their own unique requirements. Strung lines would need to have the proper
sheathing to withstand the weathering effects they'd be subjected to. Buried wire would need to be adequately trenched and
marked to keep it below the frostline and avoid accidental cutting whilst digging - conduit might also be required to meet
minimum code requirements.
Strung wire might be the easier route, if you can arrange the poles at regular intervals to avoid excess droop in the wire
(bad thing) and to keep it high enough to avoid being snagged by a truck. A proper sub-feed box from the main panel, housing
a main breaker for the feed, routed to a proper weatherhead is also the preferred route. A small breaker panel in the outbuilding
would also be advised. I imagine that a 20 amp service would be more than adequate for your needs - I've seen plenty of newer
houses that have three bedrooms running off a single 20 amp circuit.
I would suggest calling either a local electrical contractor or electrical supply vendor for suggestions on the type and gauge
of wire for the intended application, plus some insights on how to make it meet (or come close to) local code requirements.
Inspectors frown on (and fine for) hackneyed wiring to other structures.
Subject: "Off the Grid" Observatories --part 1 of 6
From: Gene Horr <genehorrtexas.net>
Date: Dec 2002
Rachel Dewey wrote:
> Does anyone have an experience building a small observatory with its
> own electric power (solar, batteries charged elsewhere, generator?)
What are your power requirements?
Mount alone for less than a week or mount + computer for a weekend = Battery Mount + dewheaters for a week, or mount + computer
for 4 days = Battery + Solar Anything beyond that I would consider a generator.
Battery:
You want a deep cycle ("Marine") battery. The bigger the better <g>. Figure on 1/2 the rated capacity for your
use. Even these designs are able to take deep discharges better than a "conventional" battery you'll get longer life
by not stressing them.
Solar:
Look at RV supply houses for a good system. It should have some sort of regulator to vary the voltage to allow proper charging.
Unless you spend a lot of money on a large array the supply won't be able to keep up with a computer. You'll be doing something
like: night 1 discharge 20% day 1 charge 5%, night 2 discharge 20%, day 2 charge 5%. Downside is that you won't know until
you arrive whether everything is working correctly. Consider a spare battery that you take home and charge so that if something
happened you can still do your work.
Generator:
Consider a line regulator mandatory. Most affordable units don't produce anywhere near clean enough power.
For heavy drain the cheapest solution: You can pick up a cheap gasoline model for a few hundred dollars that will run the
mount, computer, a small refrigerator or hot pad, even a small A/C unit during the day. Plus you can run power tools for your
repairs. If the noise or smell bothers you at night run it during the day to charge the battery(ies). For more money Honda
makes units that run _very_ quiet.
Gasoline fueled units are cheap and easily available. Diesels are generally much more expensive, but provide better fuel economy
and much longer life. Some people are bothered by the exhaust, though. Diesel is the safest to work around. Very high flash
point. The most convenient is propane if you can get it delivered to your site.
------------------------------------------------------------
Subject: "Off the Grid" Observatories --part 2
From: Jon Brewster <jon.brewsterhp.com>
I've never seen this come up either, but yahoogroups.com has a RoboticObservatory group that might be of help...
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Subject: "Off the Grid" Observatories --part 3 
From: Roger Hamlett <ttelmahntlworld.com>
You need to work out your power requirements, and the likely sources. The power requirement of a scope alone, is relatively
small (only perhaps 1A at 12v). However if you start instead looking at CCD imaging, and temperatures that are going to require
dew heaters, the needs shoot up (a modern powerful laptop, can be 3 or 4A, heaters add a couple of amps, camera another amp
or two. If you start really pushing the requirements up (heater on scope, separate heater on guide scope, camera, separate
guide camera, electric focus, laptop), the needs can get up to perhaps 15A at 12v. You should take battery capacity as half
the rated capacity (to allow for the cold, and battery aging). You then have to decide how long your likely sessions are, and
the 'recharge' time between. Work the consumption all out in 'watt hours', and you will know how large the battery store needs
to be. Then given the recharge time, you can estimate the input needed.
As examples:
5 hours per night at 1A = 60Whr.
8 hours per night at 15A = 1440WHr.
In the former case, using 12v a 30AHr battery, will give 15 hours of use, even at only 50% rated capacity. In the latter,
to get the same 15Hr capacity, would need a 450AHr battery system...
Now the possible sources (that I can think of), are:
1) Solar - great for 'trickle charging', hence great to keep system 'topped up'. Gets expensive for larger power demands (though
a lot less now than in the past), and needs a large area (it is about 1.3m^2, for 10A, at 12v, assuming normal sunlight, and
a panel angled permanently at a reasonable angle). A cell panel to give 10A at 12v, will be over $1000, and will also need
a regulator system.
2) Wind - depends on local conditions. Small generators are readily available from marine chandlers (they also sell solar
trickle systems). Modern alternator systems, can give good outputs from quite small generators, if the local wind is likely
to be reasonable. A unit about 1m across, will give about 100W at 19knots and perhaps 25W at about 10W. The disadvantage of
both these systems, is that in the event of a 'poor' day (windless or sunless respectively), the battery has to be large enough
to allow several days of use.
3) Generator. Here you have a choice of fuel (LPG, diesel, petrol), and a variety of sizes. Generally cheaper systems will
be more annoying (louder, and harder to start...). Really good systems, will be almost silent (Honda for instance do a specialized
range, that are designed for applications like hospitals).
There are then 'exotic' systems, such as geothermal, but these are unlikely to be practical for this application.
The 'batteries charged elsewhere' solution, is perfectly sensible for the low to middle power consumption levels. A single
60Ah battery will run most systems for a night (except the 'worst case' above), and also removes the need to leave systems
exposed outside the observatory. The generator will be the better solution, if demand is at the higher end of the range, again
making it possible to have a 'bunker' beside the observatory itself, with nothing exposed.
You also have to look at your own comfort. If temperatures are really low, heating of some form may be needed, and if (for
instance) gas is available for this, it might be worth considering a generator powered from the same fuel.
----------------------------------------------------------------
Subject: "Off the Grid" Observatories --part 4
From: Bill Brown <hhabilis2cs.com>
There is an outstanding article in, I believe, the Nov. 2002 issue of "Sky & Telescope" concerning the use of
solar power for an observatory.
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Subject: "Off the Grid" Observatories --part 5
From: David Bahr <dbahrregis.edu>
Another slightly older but still excellent article on a solar powered observatory is in the April 1997 "Sky and Telescope."
----------------------------------------------------------------
Subject: "Off the Grid" Observatories --part 6 of 6
From: Glenn Skinner <lostbowyerlwdc.com>
I have been working on a solar powered robotic observatory for the past couple years, I am getting closer to completion, but
there have been many issues to overcome. If you want to see an overview of my project go to: <www.observingstars.com/robotic_observatory_project.htm>
One of the biggest problems I've run into is that during cold weather when the batteries loose capacity, the dome motors,
dew heaters, and scope motors induce a large amount of noise into the DC line resulting in noise in the camera and affects
the wireless network card in the computer resulting in loss of signal from the dome. I am using two 100 ah gel cells to power
the observatory, and I have split the power grid into two circuits: one controls the dome motors and dew heaters, and the other
circuit to run the electronics. Even in this configuration, I get noise when the scope slews, I may move the scope to the other
circuit to see if it is better there. Currently I have only one 20watt solar panel, but I will be adding two Unisolar 64 watt
panels in the near future. They cost around $350 each and will produce even when shaded. They contain no glass, and are virtually
indestructible. I use three voltage regulators for recharging, they are designed for solar use and cost about $30 each. They
are sealed units and require no maintenance.
Subject: Proper Cable Routing Through Conduit --part 1 of 5
From: Gene Horr <genehorrtexas.net> Date:
Feb 2004
John Mahony wrote:
> My experience with electronics is pretty limited so I could use some help
> with what I hope is a simple question: I understand that you shouldn't
> route a high speed data line in the same conduit as an AC power line, but
> does that apply to the relatively slow serial/RS232 connection between the
> computer and the scope? At our public observatory, there's a 2" conduit
> under the floor for the power to the scope, but the computer cable is
> currently on the floor, under a rug to keep people from tripping over it in
> the dark. I'd like to run it through the same conduit as the power.
It is not a good idea from the safety standpoint. If you get a nick in both of the cables you could wind up with 110v through
one of the RS-232 lines. RS-232 is robust but not _that_ robust. Now, as long as both of the cables are unbroken then it would
work. But for a public facility I would personally consider another option.
---------------------------------------------------
Subject: Proper Cable Routing Through Conduit --part 2
From: Roger Hamlett <ttelmahntlworld.com>
The problem is that the AC waveform on a power line, will induce significant signals onto the data line. This applies to
any line, and how bad the problem is will depend on the length of the line, the pattern of the respective wires, the layout
of the conductors in the wires, and the signal levels involved. RS232, is fairly resistant to such pickup, and if the length
involved is short, should not give a problem (the problem gets really bad, when people are trying to run signals to an observatory
over several hundred feet). I'd select a shielded signal cable for the RS232 wire, and ground the shield to the metal of the
conduit, at one end only. Assuming the distance is not too great, you should be fine.
This is where using shielded cable is doubly useful, since a 'nick', will short to the shield. Really, if there is space
in the conduit, it is worth considering putting a small 'self adhesive' conduit in the corner of the existing box. This provides
another layer of physical protection between the cables.
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Subject: Proper Cable Routing Through Conduit --part 3
From: Bill Beeman <bbeemanbeemangroup.com>
I would second Gene's suggestion; it is almost certainly a code violation. Another approach that may solve the problem is
to use a flat wireway to carry the data lines. The heavy-duty version of this would be something like the Hubbell Tredtrak
cable protector. A lighter duty version would be Hubbell Floortrak. Good protection for the cable in either case.
They can be had from W. W. Grainger, and probably from McMaster-Carr if you can't find a local source.
Aside from the code and safety issues, I've spent too much time sorting out intermittent issues that turned out to be induced
interference into data lines. It is worth a little effort to avoid the possibility.
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Subject: Proper Cable Routing Through Conduit --part 4
From: Shay Walters <shaywaltersyahoo.com>
Mixing high voltage (above 30 volts) and low voltage (the RS-232) in the same conduit is also against the NEC - National
Electrical Code, which you should be meeting for any public facility. They should run in separate conduits. If a new conduit
isn't practical, try wireless. www.maxstream.net has a wireless RS-232 modem that I have had very good results with over distances
around 1000 ft. They can go much further (many miles) with better antennas. These cost about $250 each and you'll need two
of them.
---------------------------------------------------
Subject: Proper Cable Routing Through Conduit --part 5 of 5
From: Walt Cooney <waltccox.net>
I have run into a problem with my system that I think is a result of power cord interference. I just posted some info on
my problem last night on the DC3 mail list. Here's the meat of that message:
I have been using a laptop to run my telescope and camera with ACP for the last couple of years. I am now trying to use a
desktop. The frustrating thing is that ACP would lose contact with the telescope when I use the desktop. It wouldn't happen
often. It might happen just once a night but when that is half way through a night's scripting run and you have already gone
to bed that really sucks.
Since it was intermittent, I thought it might be a flaky serial port. So this weekend I hooked up the LX-200 to an add-on
card serial port. It lost contact several times over the course of a couple of hours. Then I lost contact with my AP-7p parallel
port camera. Hmmm. I realized one other thing that was different about using the desktop vs. the laptop. To run the desktop
I run a lot more juice through the power cord than I do with the laptop. The desktop has to power the machine and the monitor
(15"). The power cord is just scattered on the ground with the LX-200 cable and the camera cable. In addition, the power
cord is a roll that is mostly still on the reel so the e- run round and round this reel not too terribly far from my telescope
and camera cable. Thinking about the additional electrical interference, I separated the cables by a foot or so from the power
cord and didn't have any more drop outs all night.
My situation might be more extreme than yours in that I am using telephone cord for my RS-232 cable which has no shielding
or wire twists. The telephone line is 25' long. The reel might also be generating a pretty good signal. I'm no expert and I
am not absolutely sure that this was my problem yet but it sure seems like it. Hopefully you won't have a problem. You can
always try it out and see.
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