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Old 15-10-2010, 11:00 AM
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gary is offline
Join Date: Apr 2005
Location: Mt. Kuring-Gai
Posts: 5,476
Argo Navis External DC Power

Originally Posted by Alchemy View Post
Taken some more time to read through the manual, just working on the section on encoder timing, I have a predilection to always wanting to use gadgets to their highest resolution, couple of issues come to mind , that of the batteries..... Now being in an observatory with a 12 v deep cycle battery at hand the extra cable seems a handy accessory, I cant see me going mobile as such. So how many of you have gone down the path of permanent power?
The information that came with the unit had quite some warnings about misuse of this aspect, my use would see it permanently connected ..... (Although not on all the time), so I cant see a big issue with disconnection, which has one terminal to be removed first. The documentation suggests it is connected to the battery terminals, would it be a problem if a cigarette lighter end was attached as I have my battery in a box with a bunch of those mounted on the outside, again I'm wondering if the order of disconnecting would be a problem as both would be at same time should it be removed. ( that question might be one gary might best advise perhaps).

Thanks Clive
Hi Clive,

Thanks for the post.

Argo Navis can accept an external power source anywhere between 8V and 16V DC.
As you are aware, Argo Navis can also be powered from a set of four alkaline
AA cells internal to the unit. Argo Navis always selects the power source that
has the highest voltage at any given instant.

Installations where Argo Navis is powered from a 12V battery, such as a sealed
lead acid battery (SLA), are ubiquitous. For example, a popular combination on
Dobsonian mounts is an Argo Navis and a ServoCAT slew and track servo
controller. Most users of this combination power both the Argo Navis and
ServoCAT from an external DC source. Likewise, many Argo Navis owners
who own fixed observatories also power their units from an external DC source.

There is no problem in powering the unit from a 12V battery that then feeds
a power distribution panel with cigarette lighter outlets. You can simply insert
or remove the plug at will.

Always run a dedicated power and ground pair to the unit from the power
distribution panel to the unit. The positive lead in pair should be fused with its own
dedicated 315mA inline fuse.

The warnings that come with the unit with regards 12V power distribution
provide good generic advice for powering equipment on telescopes.
In the world of mains power in homes and offices, the installations are performed
by licensed electricians and there are dedicated fixed ground returns behind the walls.

However, on telescopes using 12V power distribution, users are often masters
of their own fate and may not necessarily be conscious of the potential implications
of a wiring topology they implement. In particular, one needs to be mindful of
the implications of a wiring topology where multiple pieces of equipment are sharing
the same ground return. If the ground return cable should become open circuit,
the return currents may make their way back to the power source via some
unsuspected path, for example through the interface cable of a CCD camera
and then back through a laptop. If the shared equipment has a high power demand,
such as fans and dew heaters, the return currents that pass back through the
camera interface and laptop may also be very large. This may result in damage
to the connected equipment. As stated, this advice is entirely independent of
Argo Navis.

Telescope owners should also be mindful that 12V power sources such as lead
acid batteries can deliver very high currents in very short amounts of time.
If a short should occur in the cabling and no fuse is provided, the cabling may actually
dissipate enough energy that it can melt or start a fire. Always use current limiting
protection such as fuses.

Best Regards

Gary Kopff
Managing Director
Wildcard Innovations Pty. Ltd.
20 Kilmory Place, Mount Kuring-Gai
NSW. 2080. Australia
Phone +61-2-9457-9049
Fax +61-2-9457-9593
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