| RETURN TO FAQ |
| HOME PAGE |
 |
How often should I recharge my battery?
Be sure to recharge your battery after each use, regardless of how much
power was used from it. This is because a partially charged battery will develop
sulfation and if stored this way it will not fully recharge. You should also
consider investing in a "smart charger" which will charge your battery and then
switch to "float" where it will maintain the battery at 13.6V (AGM or gel) or
13.8V (liquid acid) during storage so that the battery will not sef-discharge.
Conventional chargers and trickle chargers do not float so they should not be
left on the battery indefinitely or they will damage it from overcharging.
What size battery should I get?
Add together the amps for each of your heaters (see table below) and divide
by two (heaters run at half power). Add the Amps used by your telescope or any
other accessories. Multiply by the hours you wish to operate. This will give you
the minimum battery size but it is best to select a battery at least twice this
size because it is not good to run a battery down completely every time.
Extremely cold weather will also reduce battery capacity so factor that in as
well. For example, an 8" SCT (1.6A Corrector Plate + 0.2A Eyepiece + 0.2A
Finderscope) has heaters that use 2 Amps at full power or 1 Amp at normal half
power. It will also operate the telescope mount which will consume about 1 Amp
so the total power used will be 2 Amps and to operate for 5 hours would take
about 10 AH. Since it is best to only run the battery down about half way, a
19AH battery would be a good choice.
Heater Size
Amps at Full 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
When battery shopping, what
numbers are important?
Only buy a deep-cycle battery because they have thicker plates that can
tolerate deep discharge and recharge. Standard car batteries are not suitable
for "deep-cycle" use because they have thin plates that will deteriorate when
deeply discharged. 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.
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, but read
the side of the box to be sure of the battery size.
Do you recommend a Power Tank?
These are basically a battery and they contain the same AGM batteries as the
Jump-Start units which can be found at department and automotive stores for 1/3
the price. So unless you need the extra features you are just paying extra for
the same size battery. As with the Jump-Start units, read the battery specs and
get a unit with at least a 17 AH battery.
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.
What power connector is better, Cigarette Plug or Ring
Terminals?
The cigarette plug on the DewBuster™ Controller is a high quality plug and
usually works fine with 8" and smaller telescopes, however larger telescopes
benefit from ring terminals because most cigarette sockets will get hot when
even a few amps of current flow through them. Cigarette plugs also tend to push
themselves out of the socket due to vibrations and tugging upon the cord.
Ring
Terminal connections, on the other hand, provide tight low resistance
connections that do not loosen up and will handle a great deal of electrical
current. The
quick-disconnect Molex plug allows an easy
means to disconnect the power cord without having to unscrew the ring terminals,
and it offers much lower resistance connections than a cigarette plug. I
highly recommend ring terminals with any size scope, but with SCT's above 8" it
becomes more of a necessity with every extra inch.
Can I run the DewBuster™ Controller on 120 VAC house
current?
Yes by using a
13.8 VDC Power Supply. When selecting a power
supply, add together the Amps of each of your heaters (see table below) plus any
other equipment you may run off the power supply and select a power supply rated
for about double the total Amps.
Pyramid makes some good power supplies and the
5-Amp PS-9 and 10-Amp PS-15
are excellent choices featuring both a cigarette socket and
1/4"
ring terminal connections. Since these power supplies are intended
for indoor use, protect them from moisture but insure they have adequate
ventilation so that they will not burn up. Be sure to use a
GFI (Ground Fault Interrupter) to prevent
electrical shock. Home Depot and many department stores carry GFI's and most
homes already have their outside receptacles protected by a GFI (often the
bathroom GFI).
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.
Can I power my telescope from one of the DewBuster™
Controller's 12V Power Output jacks?
Maybe. Non-computerized telescopes or computerized telescopes 6" or smaller
will probably work. However on large computerized telescopes you may have
problems because as the large heater turns on and off the voltage at the
DewBuster™ Controller will dip and this may cause erratic behavior of the
computer. The heavy
duty power cord option helps reduce these voltage fluctuations, but
very large telescopes may still experience problems. There is no harm in trying
and some computers are more tolerant of voltage dips than others, so if the
computer misbehaves then connect it as close to the battery or power supply as
possible so that the power to the telescope will not have to travel through the
same wires as the DewBuster™ Controller.
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, because during the early part of the night when the air temperature is
dropping the DewBuster™ Controller will send very little power to the heaters
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's temperature sensor detects this and starts gradually applying power
but only what is needed to keep the telescope warmer than the air. Late at night
when radiant cooling and dew are at their worst, the battery will have more
energy left to handle the larger power demand and the DewBuster™ Controller will
still be minimizing the power to the heaters to prevent dew while not wasting
power.
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 illuminates, the DewBuster™ Controller
is reducing heater power to prevent running the battery completely dead and
damaging it. Depending on your battery size (AH) and the current drain of your
heaters (Amps), you may get minutes or hours. When the "Low Battery" light
begins to flicker you should consider disconnecting nonessential heaters. When
the light remains on constantly you do not have much time left. The DewBuster™
Controller will not damage your battery even if it is left on for an extended
period of time with the yellow light on, however other devices should be
disconnected or they may drain your battery completely and damage it.
Can the low battery circuit be disabled when
using a dedicated battery?
No. When a 12-Volt battery is drained below 10-Volts it will be permanently
damaged, so this feature is always active on the DewBuster™ Controller.
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.
Can you build a version of the DewBuster™ Controller that operates on 24VDC
like my Takahashi?
Unfortunately this can not be done because the heater strips will burn up.
Let's say you have a heater strip with 10 Ohms resistance, Ohms law tells us the
current flow will be 1.2 Amps at 12 Volts or 2.4 Amps at 24 Volts. The amount of
heat (Watts) produced by this heater is equal to Amps x Volts. So at 12 Volts
this heater produces 14.4 Watts of heat, however at 24 Volts the heat increases
to 57.6 Watts. This is 4 times the amount of heat which will make the nichrome
heating wire inside glow red hot and burn up the heater strip.
Will the DewBuster™ Controller cause electrical noise that will interfere
with my CCD imaging?
The DewBuster™ Controller is properly designed and thus minimizes EMF
interference. I have had no reports of EFM problems and many users have reported
that their DewBuster™ Controller eliminated the CCD interference that their
previous controller was causing. I have seen a few cases of using inadequate
power supplies and when the DewBuster™ Controller switches heaters on and off
the voltage would dip and the camera images were affected. This is easy
to pinpoint, simply turn the DewBuster off and if the problem disappears then
try powering the camera from a separate power source than the
DewBuster™ Controller. If you experience problems I will work with you to solve
them. If you are not satisfied, you may return your DewBuster™ Controller within
30 days for a refund (shipping can not be refunded).