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Can I connect the DewBuster™ controller to my telescope's DC OUT connector?
NO! Many telescopes have a DC power output which is intended for low current accessories. These CAN NOT HANDLE THE HIGH CURRENTS THAT YOUR HEATERS will draw and may damage
your telescope. The DewBuster™ controller's power cord should always be
connected as close to the battery as possible and not share an extension with
any other accessories.
Can I run the DewBuster™ controller on 120 VAC house current?
Yes by using a power supply with a GFI (Ground Fault Interrupter) to prevent
electrical shock. The DewBuster™ controller runs on 12 to 13.8 Volts DC which
can be supplied by a 13.8 VDC power supply. The larger the power supply the more
Amps of current it can supply. Add together the Amps of each of your heaters
(see table below) plus the Amps of any other equipment you may
run off the power supply and select a power supply rated for about double the
total Amps.
BuyReliant carries a good selection of
Pyramid power supplies at
excellent prices. Their
5-Amp PS-9 ($22) and
10-Amp PS-15 ($40)
are excellent choices featuring both a cigarette
socket and 1/4" ring terminal connections. Since these power supplies are intended for indoor use,
you will need to fabricate a cover that
does not block the ventilation but prevents moisture from dripping into the
power supply at night when dew forms on your equipment. Be sure to use a GFI so
that if moisture does get into the power supply it will shut off power. Home
Depot and many department stores carry GFI's and most newer homes already have
the outside receptacles connected to a GFI (often the GFI in the
bathroom).
Amps at
Heater Size
100% Power
------------------------ ---------
0.965" to 2"
0.2
3" to 4" or Hand Control 0.8
Telrad
1.0
5" to 8"
1.6
9/10"
2.0
11"
2.4
12" 2.8
14/16"
5.0
I normally use 120AC. Can I use an inverter on
my 12V battery to give me 120VAC in the field so I can just plug in normally?
Each voltage conversion wastes energy and inverters that convert 12V battery
to 120VAC are less than 50% efficient. So your 12V battery may last 2 to 4 times
longer if you run directly from the battery.
How much power does the DewBuster™ controller use?
The DewBuster™ controller's internal circuitry draws less than 0.1 Amps.
Just like a light fixture, it is the wattage of what you plug in that determines
how much energy will be used. To calculate how much power will be used, add the amps of each
of your heaters (see table above). If you have heaters built with the
instructions on this web site, then the table above will give a rough
estimate of the power draw. If you want a more precise number, then multiply
0.036 times the number of
resistors used in the heater to get the current
draw in Amps.
Does the DewBuster™ controller really save much battery power?
Yes, here why: You set up your scope and turn on the
DewBuster™ controller to maybe 5 degrees. The DewBuster™ controller senses that the telescope tube is warmer than the air (sun
just set) so it
sends no power to the corrector plate heater, conserving battery power and helping the
scope cool down. As night
sets in and the sky starts slowly sucking the heat out of your scope, the
DewBuster™ controller starts gradually applying power to maintain
the temperature. Since the air temperature is continually dropping, not much
heat is required until the middle of the night but the battery will have more
energy left to handle the larger power demand.
Can I still start my car when the low battery light comes on?
The DewBuster™ controller's low battery circuitry is intended to prevent
battery damage, not to reserve enough energy to start you car. Whether any given
battery voltage will still start a car depends on the battery's capacity and condition,
how much current the starter motor draws, and how easily the
engine starts. It is also important to realize that
car batteries are not designed for deep cycle use and will soon fail if repeatedly
deep discharged. It is best to use a dedicated deep-cycle battery to power your
telescope.
How much time will my heaters operate after the Low Battery light comes
on?
When the yellow "Low Battery" light reaches full brightness, the DewBuster™ controller's smart end-of-life circuit
is reducing heater power levels to
prevent damaging the battery by running it completely dead. Depending on your battery size (AH)
and the current drain of your heaters, you may get minutes or hours. Watch the
"Low Battery" light to see how fast it brightens and this will indicate how fast
your battery is running down. You can also prolong battery time by disconnecting
nonessential heaters.
Can the low battery circuit be disabled when using a dedicated battery?
No. When a 12-Volt battery drops below 10
Volts, battery damage occurs and it will not recharge to its full amp-hour
capacity. This feature is always active on the DewBuster™
controller to prevent battery damage.
What size battery should I get?
First determine the maximum battery current by adding together the amps of
each heater (see table below) plus double the current used by any additional
devices. Now multiply this total current by the number of hours you wish to
operate from before recharging the battery. This will give you the minimum
battery size that will run your equipment for the desired amount of time
(battery discharged 50%). If you will operate in extremely cold weather get a battery
twice as big since
battery capacity is reduced as temperature drops. Be sure to recharge your
battery after each use, do not wait until it is discharged completely.
Amps at
Heater Size
100% Power
------------------------ ---------
0.965" to 2"
0.2
3" to 4" or Hand Control 0.8
Telrad
1.0
5" to 8"
1.6
9/10"
2.0
11"
2.4
12" 2.8
14/16"
5.0
EXAMPLE:
Telescope Amps x2
2.0 Amp
8" heater
1.6 Amp
Eyepiece heater 0.2 Amp
---------
Total 3.8 Amps
Run time
x 5 Hours
---------
Minimum Battery Amp-Hours 19 AH
At a department store you find a Jump-Start portable power system with a 17AH battery. This battery would last about 4.5 hours (17AH / 3.8Amps= 4.5 Hours) which is close enough for your needs.
When battery shopping, what numbers are important?
Only buy a deep-cycle battery. The only spec that we are
interested in is the battery capacity, usually stated in Amp-Hours (AH). The AH
can be divided by the number of Amps being used to find out how long it takes to
completely discharge the battery. Some batteries will specify Reserve Capacity
(RC) which is the number of minutes the battery can supply 25 Amps before it
completely discharges. RC can be multiplied by 0.4 to calculate AH, but do not
assume the battery is a deep-cycle unless it says so. Standard car batteries are not suitable for "deep-cycle"
use and will not last long.
Can I use one of those "Jump-Start" portable
power units?
These work well if they are of sufficient capacity. As
with regular deep-cycle batteries, for long life, avoid running them completely
dead during each observing session and recharge between uses. Most will specify
their battery's Amp-Hour rating somewhere in the specifications. Most contain a
17 to 21 AH battery which works well with small to medium sized telescopes.
Units with AGM batteries are the best.
Can I use a cigarette plug splitter?
Splitters cause voltage losses and may cause the DewBuster™ controller's Low
Battery light to come on prematurely (if removing the splitter and plugging
directly into the socket makes the light go out then the splitter is the
problem). If you must use a splitter, get a heavy duty one as standard splitters are intended
for low current applications like cell phones. Radio Shack carries several splitters
rated for 10 amps or more. Chose a splitter that
is rated for at least twice the Amps your heaters use at 100%
power (see chart above) even if this is greater than your power supply can
produce. Before resorting to a splitter, check whether your power source has
alternative connections. Many have terminals that allow connecting wires so you
can cut the cigarette plug off of a heavy duty splitter and connect the wires
directly to the terminals of the power supply. This eliminates having two
cigarette connectors in series.
What method does the DewBuster™ controller use to vary heater power levels?
The DewBuster™ controller uses Pulse Width Modulation (PWM) meaning the
heater receives full battery voltage but it is cycled on and off. The ratio of
on time to off time is what determines how much heat is generated. If it is on 40%
of the time then this would be 40% power
level which generates 40% of the heat that would be produced if it were on all
the time.
Will the DewBuster™ controller cause electrical noise that will interfere with my CCD
imaging?
I have had no reports of any problems, and many users have reported that
their DewBuster™ controller eliminated the CCD interference that their previous
controller was causing.
I have had one report of some interference from a video camera and the problem was eliminated by using separate power supplies for the DewBuster™ controller and video camera.
If you experience problems I will work with you to solve them. If you are not satisfied, you may return your DewBuster™ controller in like-new condition within 30 days for a refund (shipping can not be refunded).