Sunday, December 29, 2013
Power Problems
Electrical
power ain’t always a problem, muchachos, but it can be. Today’s amateur
astronomer is ever more likely to be running a computerized go-to telescope, sometimes
controlling that with a laptop computer, and often observing with power hungry
CCDs or video cameras, so “juice” in the field—or at home—is an important
subject.
Actually, that
was not the original topic for this Sunday morning’s blog. This one was
supposed to have been “A Guide to Department Store Telescopes,” an article designed
to help you help the owners of semi-putrid Christmas scopes. But you know what?
Down here at least, the good old Department Store Christmas Scope is an
endangered species.
Five-six
years ago, the Christmas scope still inhabited the big retailers’ shelves from
October to January, but since then it has practically disappeared. Its decline
actually began some years before that with the closing of the big-box “jewelry”
stores like Service Merchandise, who sold everything under the sun, including
cheap telescopes, before they were put in the ground by WallyWorld, Target, and
Costco.
The final
nail in the Christmas Scope’s coffin was Walmart banishing the poor things. For years, Tascos and Bushnells and Meades
would appear in WallyWorld’s optical department at the start of the season.
Then, one year their yearly migration didn't happen, and I haven’t seen ‘em since.
Their disappearance coincided with the start of the Depression—sorry, “Great Recession”—so that might have had something to do with it. Also, the optical
department of Walmart where they were sold is run by an independent contractor,
and maybe that contractor has changed or changed policies.
Anyhoo, the
only Department Store Scopes I’ve seen lately have been pitiful semi-toy
refractors like the one here, which are mainly found in drugstores like CVS and
Rite-Aid and sporting goods outlets like Academy. Maybe somewhere Christmas 4-inch
reflectors and 60mm refractors live on and are still luring kids and adults,
but they don’t seem out in numbers big enough to warrant a blog post. If you know
somebody who did get a puny Christmas
telescope, see thisun from a cupla years back for
some tips on how to tune it up.
 |
| Pore little CVS scope... |
So, on to
our subject for this first Sunday morning after Christmas, electricity and amateur
astronomers. That used to be short and sweet:
a pair of D cells for your red flashlight and maybe—MAYBE—a 9-volt
transistor radio battery for them new-fangled digital setting circles. Goto
scopes and laptops changed that. Most amateurs are using one or the other
on the observing field now, if not both, and need plenty of electricity.
So how do you power a telescope mount or a laptop? With
AC (mains) current out of the wall or with a battery of some kind. But before
we investigate the “hows,” we’d better talk about the “whats,” the basics of
electricity.
Basic
electrical/electronics theory can be confusing to the point of scary for
the neophyte. It is full of strange and puzzling words describing various
quantities and effects: volts, ohms,
amps, watts, henrys, farads, and more. Luckily, us amateur astronomers only
have to be concerned with two of these critters most of the time, volts and
amps (amperes).
You can get
a complete grounding (yuk-yuk) in electricity online or in what I consider and always
have considered the best reference for learning electronics, The (ARRL) Radio Amateur’s Handbook (a.k.a. The ARRL Handbook for Radio Communications).
I won’t naysay it if you want to pick up that time-honored tome and read the
whole story of volts, amps, ohms and their cousins. However, for those who
ain’t interested in that, I can boil it down for y’all this morning. If you
want to understand volts and amps easily, a good analogy is water flowing through a pipe.
Voltage, volts, the electromotive force (E.M.F.),
is equivalent to water pressure in
them pipes. Too high a water pressure can damage your dishwasher, and too high
a voltage can damage your telescope mount. Some telescope mounts take care of too
high (or low) a “pressure” by voltage
regulation, having components in the power section of the mount that
decrease (or increase) the incoming voltage under changing input voltage and
load conditions. Within limits, the mount won’t be affected by the “wrong”
voltage. Others depend on the power supply to furnish a voltage of the proper level.
 |
| A"TIP" voltage regulator IC... |
The other
biggie is amps, amperes, “current.”
If voltage is equivalent to water pressure in pipes, current is like the amount
of water flowing through those pipes. Amps is similar to “gallons per minute.”
A lot of newbies have a basic misunderstanding of current. They worry that
using a power supply rated for 14-amps of current output, for example, will damage a telescope that only needs
7-amps. Not so. The scope (or any other device) will only use the amount of
current it needs. Even a flashlight battery can supply a lot of amps (for a little while). Again, the scope will only use the amount it needs.
Closely
related to amps is a specification associated with batteries, “amp hours.” Theoretically,
a 6-amp hour rated battery can supply 1-amp of current for 6-hours (or 3-amps
for 2-hours, etc.). It is like the volume of a tank feeding water pipes. One
important thing about amp hours? Always choose a battery rated higher than you think you will require.
If the gear
you have connected to your battery consumes 2-amps of power continuously and
you normally observe for four hours, you will need a battery with more than 8-amp hours capacity. Various factors
prevent an 8-amp hour battery from really
supplying 2-amps for four hours (or 1-amp for 8-hours). One of the ubiquitous
17-amp hour batteries would be a better bet.
You are
probably already aware there are two types of electricity, AC and DC. But do
you really know what that means? The difference between the two is key to
understanding electricity and electronics. A battery has a negative electrode
(excess of electrons) and a positive electrode (lack of electrons) and that never
changes. DC current flows in one direction only. The AC that comes out of the
wall is different. Its polarity and thus the direction of current flow is constantly switching back and forth, 60 times a second in the U.S. of A.
If you view a DC current on an oscilloscope (a device that shows a graphic
representation of current and signals on a screen), DC is a flatline. AC
appears as a sine wave.
And that is
it, y’all, all the electrical theory you need. Well, almost all. One thing that
confuses some amateur astronomers in the lowly fuse. Yes, you want a fuse in
your power cord or in your telescope. But not because it will save your
equipment from being destroyed by a short (a path to ground being formed
somewhere in the circuit, resulting in a high amount of current flowing and
doing much bad juju). A fuse MIGHT in some cases prevent some damage to the
equipment is serves. But a fuse’s true purpose is to protect the power supply side of the circuit and prevent fires.
Period. No fuse can blow quickly enough
to always prevent damage to solid-state components.
You can operate
your telescope with DC (batteries) or AC that has been converted to the DC your scope, like most electronic devices, needs.
Which is better? As is often the case in amateur astronomy, “that depends.” For
some applications, a battery is clearly superior. If you are running a video
camera as I often do, you will find the “pure” DC of a battery generally
produces cleaner, less noisy images than the minimalist “wall-wart” AC supplies
that often come with vidcams. Since video is susceptible to poorly filtered current
(DC that hasn’t been perfectly converted from AC), I generally run my
video camera off a 12-volt battery.
In the past,
I ran everything—go-to mount, telescope, PC, CCD camera, everything—from batteries.
I was afraid of damaging the equipment with poor AC when I was at a site that
had mains power. As I became more comfortable with go-to scopes and computers,
and also became lazier, I began running everything except the video cameras
with AC whenever I could. I’ve never had a problem doing that anywhere, but I
do use good power supplies and run the AC through a surge suppressor.
But, let’s
say you want or need to operate off batteries. I have to do that at our club
site. What kind of batteries? Even if your go-to telescope can run off internal
AA, C, or D 1.5-volt cells, forget ‘em. Those little batteries are sufficient
for digital setting circles, sure, but for driving mount motors? Not unless you
like lining the pockets of the dadgum Energizer Bunny by constantly replacing
batteries. How about rechargeable AAs, Cs, and Ds? That sounds like a good
solution, but they can rarely supply the voltage and current a scope needs.
Almost all
go-to telescopes can be operated with 12-volt batteries, and that is the way you
want to go. But, again, there are choices. Lawn tractor battery? Gel cell? Deep
cycle marine battery? Car battery? I generally discourage the use of lawn
tractor and car batteries. They are not bad in the field, but the fact that you
have to connect your gear (or a female cigarette lighter receptacle) to their
posts, often in the dark, can be a recipe for disaster.
Reversing
the polarity of the power cable going to your mount, accidentally connecting
“plus” to “minus” or vice versa, can spell doom for your scope’s electronics. You
can buy a battery box and permanently wire a female cigarette lighter
receptacle to it, but that’s a lot of
trouble if’n you are lazy like Unk, and you’ll have to shell out more $$$ for a
battery charger. I think there are better solutions.
I make an
exception to my dislike for vehicle batteries when it comes to deep cycle
marine (“trolling motor”) batteries. They have a couple of advantages. They are
available in high amp-hour ratings:
75-ah, 100-ah, and more. That may be necessary if you are running a lot
of power hungry gear or must operate for several days without charging. They
are also tolerant of being fully discharged, which will eventually kill a
normal lead-acid battery—that’s the “deep cycle” part of their equation.
Downside? They are HEAVY. How do you make a lead acid battery a deep cycle? By making its lead plates thicker. As
with other vehicle batteries, you will have to provide a charger and be careful
about polarity.
 |
| Anderson Power Poles... |
Then there
are the modern batteries, more sophisticated ones like gel cells, lithium
batteries, and innovatively constructed lead acid batteries. The good with
'em is they can often provide the same amount of juice as a conventional lead-acid
battery in a smaller, lighter package. One company, iOptron, even makes a
battery in the shape of a GEM counterweight. Unfortunately, more sophisticated
batteries are also usually more expensive, especially once you add a charger,
than my number one choice, the ubiquitous jumpstart power pack.
If you’ve
been to a star party or just out to your local club’s observing field, you’ve
seen “jumpstart” battery packs, 12-volt batteries in plastic enclosures
equipped with built-in chargers, 12-volt cigarette lighter receptacles, and
more. That “more” starts with a pair of attached cables to, yeah, let you
jump-start your vehicle in an emergency. That’s just the beginning; I’ve seen
everything from lights, to air compressors, to AM-FM radios built into jumpstarters.
These
battery packs have been a big hit with amateurs for a couple of reasons. The
most important being that they are self-contained and portable. Yes, they can be
fairly heavy, since they are built around lead-acid batteries, but they have
built-in handles that make them much easier to deal with than a car battery. They are also relatively inexpensive, around
50 – 75-dollars including a charger.
They are not
perfect, of course. The highest capacity readily available jump starters are
rated for about 25-ah, with 17-ah being more common. Luckily, a 17-ah job is
enough to run most scope mounts for an entire night, even when you also power a
dew heater system from the battery. The only other problem is that jumpstarters
are at least as likely as other lead acid batteries to fail from abuse. It’s
easy to keep one going, though. The jumpstarter I use for Big Bertha, my
NexStar 11 GPS, is over 10 years old. The secret? Charge for 12-hours after
each use. If you don’t use the battery over the course of a month, charge it for
12-hours anyway. The same goes for all other lead-acid batteries including deep cycle marine batteries.
Where do you
get a good jumpstarter? When the scope companies saw how popular they were with
amateur astronomers, they began slapping their names on these battery packs.
The units sold by astronomy merchants, often as “power tanks,” are no better
than other jumpstart batteries and are sometimes worse. They are most assuredly
more expensive than the brands I use. I’ve gotten good ones from Walmart, Pep
Boys, and Harbor Freight. Main thing to look for? Don’t buy one with less than
17-amp hours of capacity.
 |
| A small inverter sufficient for a laptop... |
Other than
that? Keep your connections and connectors well maintained. Some amateur
astronomers replace cigarette lighter style plugs and receptacles with the
Anderson Power Pole connectors used by radio amateurs, but I’ve kept on
trucking with “ciggie” plugs and haven’t had major problems. Do keep a supply
of the fuses cigarette lighter plugs have in their tips on hand. I’ve been
known to blow them occasionally and been left dead in the water at a dark site.
Operating
off batteries at a remote site seems simple. Till you realize you’ve got a
piece of gear—like a laptop or video monitor—that needs AC, not DC. Most of us
don’t want to haul around even a small generator, and if we did, our fellow
observers wouldn’t look kindly on the noise and exhaust. What you need is an inverter, a widget that turns DC into
AC. When I first began using a laptop in the field, I quickly discovered its internal battery wouldn't last even half the evening. But I was afraid of inverters,
thinking their AC would be “rough” and might hurt the PC. Instead, I invested
in an expensive and underpowered 12-volt DC supply for my computer.
The joke was
on Unk. Modern inverters, even inexpensive ones, produce good AC. What kind do
you need? The prime consideration is that the inverter is able to supply enough
power for your device(s). Make sure its rating (usually given in watts) is high
enough. There are two general classes: small inverters that plug into a
cigarette lighter receptacle, and higher capacity jobs that attach to the posts
of a battery via clamps. When you are thinking inverters, be aware considerable
energy is expended in making AC out of DC and that you should always use a
higher capacity battery to power the inverter than you think you will need. As for
where to get an inverter, try an automotive discounter or Unk’s beloved Harbor
Freight.
Several
years ago when the Herschel Project first got into the deep waters of the
Herschel 2500 and I began spending a lot of hours observing at the Chiefland
Astronomy Village, I decided to make the switch to AC when I was down there.
There was plenty of reliable AC power available on the field, and I was tired
of having batteries give out before the end of an observing run. Before I could
move everything to AC, though, I had to round up a couple of AC power supplies.
 |
| Unk's big honkin' Astron... |
I was wary
of the freaking wall-warts, but had to admit the one Celestron supplied with my
NexStar 11 worked fine. So does the one they recently sold me for my VX mount.
I haven’t put either one on an oscilloscope to see how good the DC they produce
looks, but both have been reliable and glitch free in the field. Still, if you
are overly protective of your telescope, as some of us are, you might want to consider something better. A big step
up from wall-warts is a regulated supply, which will maintain its output
voltage at a steady level under varying input and load conditions. These power
supplies are larger and usually capable of supplying more current (amps) than
the wall warts. They are also usually better filtered; they produce cleaner DC.
The linear
regulated supply is the old-reliable of the game. Great big transformer,
rectifiers, and capacitors to create smooth DC, and a voltage regulator section
to keep that voltage at a set level. The only bad thing you can say about ‘em
is that they are heavy. The Astron AS35-M 35-amp power supply I use in my radio
shack weighs dang near 30 fraking pounds.
The more
modern switching power supplies tend to be both lighter and cheaper. A
switching “mode” power supply is harder to understand than a
traditional linear supply. If you are interested, Wikipedia
has a nice, understandable article on them. But for today, it’s sufficient for
us to know they are lighter and cheaper because they don’t need the big
transformer of a linear unit. There’s always a gotcha in the world of
electronics, though, and the electronic magic a switcher uses to create DC
produces far more “RFI,” interference, than a linear supply. That can be a
consideration when using one to power communications gear, but usually won’t be
a problem with go-to telescopes.
 |
| A Jetstream switcher... |
Of course,
you’ll need to get the AC to your AC power supply, and you’ll usually need an
extension cord to do that. How good a cord depends on circumstances. If you are
using an unregulated supply and have to run a long cord to the nearest
receptacle, you want a high quality extension. Otherwise, the voltage drop
incurred in a long run can prevent the wall-wart from outputting enough voltage
and might make the scope computer hiccup (a laptop PC will be OK, since it’s
actually running off its internal battery even when plugged into the wall). The AC
outlets are nearby at my observing sites, not much more than 100-feet away
worst case, so “Walmart’s best” (and cheapest) is fine for me. I tie-wrap a
power-strip/surge suppressor to a tripod leg and plug both my power supplies
into that.
“Supplies?” In
addition to the wall-warts furnished by the manufacturer of my scopes, I have a
small regulated power supply, a switcher, I use to power my DewBuster heaters.
I could probably get by with another wall-wart for that, but I had a switching supply lying around, the one that came with my old SAC7B CCD camera, so I used it.
If you run
off AC, you should, of course, be mindful of safety concerns. Keep your power
supply out of the wet grass and use a three-prong extension cord so it is
grounded. Naturally, don’t allow your power supply to get wet when you are
rained out at the Possum Holler Star Party (most wall warts are sealed and
won’t mind the rain).
That’s about
all there is to the juice game for amateur astronomers, muchachos. Just be
careful. Even a little inverter powered off a small battery can put a mighty
big hurtin’ on you if you go poking around where you don’t belong. So don’t poke around if’n you don’t know
what in pea-turkey you are doing. If you have electrical problems and know you
are out of your depth, enlist the aid of a buddy (maybe a local ham) who knows
the ropes. I want you to be around for another year of observing in 2014.
Next Time:
Happy New Year at Chaos Manor South…
Comments:
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Enjoyed the amateur radio tie in. In fact, I've been surprised that what I've learned in the 18 months since I've been licensed has helped out in my astronomy hobby.
Two years ago, I didn't know an amp or a volt from a Messier or a Herschel. Now, I can explain how dew heaters work and I can even do the calculations to appropriately design my own.
In fact, now that I know how motors work and have a rudimentary understanding of what goes on circuit boards, the electronics of my mounts are far less a black box than they used to be.
--Michael
Two years ago, I didn't know an amp or a volt from a Messier or a Herschel. Now, I can explain how dew heaters work and I can even do the calculations to appropriately design my own.
In fact, now that I know how motors work and have a rudimentary understanding of what goes on circuit boards, the electronics of my mounts are far less a black box than they used to be.
--Michael
# posted by 
: 11:00 AM
: 11:00 AM
Rod,
Nice summary. I didn't see a mention of car adapters. Cigarette lighter adapter power cords are available for computers and cameras. If you have to operate gear in the field away from AC, as much as possible, you want to avoid using an inverter. When asked, I encourage people to get the car adapters. Helps the 12 volt battery last longer. Especially if doing long runs, such as time lapse.
cheers,
Blake
Nice summary. I didn't see a mention of car adapters. Cigarette lighter adapter power cords are available for computers and cameras. If you have to operate gear in the field away from AC, as much as possible, you want to avoid using an inverter. When asked, I encourage people to get the car adapters. Helps the 12 volt battery last longer. Especially if doing long runs, such as time lapse.
cheers,
Blake
Alas, my experience with an cigarette adapter for the computer wasn't a happy one. I've been very happy with an inverter. The computer is the only thing running off it and it works well. :-)
Expensive, and when I would plug in a USB device, a CCD cam, that used the USB bus for power, the dadgum powersupply would trip offline. Oh, I was as mad as a wet hen. ;-)
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