Powering your truss dob

[CoombellKid]

Ok, I'm about to start my next project and I'm looking for ideas on running
power or the best way to run power through your truss Dob.

Not being electrically minded, I know this. I want a dew heater for my
secondary and a fan to cool the primary. I also want the computer unit of
the Argo Navis to be mounted on the secondary cage. I have a few ideas
on how to achieve this. But would be interested in how others have gone
about it. I plan to use two truss poles to run power up to and through a
duel wire spider to power the dew heater. I would like to hide the Argo Navis
leads and was thinking the only likely candidate is inside one of the truss
poles, but maybe a velcro flap on the light shroud could be used to do this.
But the main concern is powering the dew heater and fan and the room a
battery likely needed to power them will take up on board. So I would
like to have an outside power source. One that can be plugged into the
base board. The tricky bit is designing some sort of swivel connector that
can be incorporated into the pivot bolt between the base board and rocker.
I have a couple of ideas involving a track and brush arrangment. But has
anyone done this before and perhaps can share an idea or two.

I would also like to add, what sort of source or power pack would be needed,
It would need to last at least a weekends worth of observing. Could you
also power the Argo Navis from the same source?

regards,CS

[asterisk]

Hi Rob

John (Astronut) powers his dew heaters and fan from 2 12v sla 7.2 amp battery that he places on the base of his Lightbridge so that the whole unit moves together and stays balanced. You might PM him to find out how long he gets out of his setup, and how he has wired it.

He doesn't use Argo Navis so can't help there.

Cheers

[CoombellKid]

Hi asterisk,

Thank you for your reply. I'm more wanting to remove the power source
from having it mounted on the dob base. So I'm looking at way in which
to pass current between the to moving parts of the baseboard and rocker
box. A rotating connector if you will, that you can run current through.

The idea I have is send one side up the pivot bolt, But I'm not sure if this
will efect the encoder attached to the top. And the other side via a circular
track on the base board with spring loaded rollerbearing or brush mounted
on the under side of the rocker box that tracks as the rocker box rotates in azimuth.

regards,CS

[JethroB76]

Don't know whether you've seen this stuff but a company by the name of Mercotac do all sorts of rotating connectors...they may have something of use for your project

http://www.mercotac.com/

[tnott]

Hi,

I've just finished adding the stellarcat's powered groundboard kit to run power from a battery pack through the center point to run Servocat/Argo. Works a treat but might not suit your budget - it's also a bit complicated to copy. If you only want to run a fan, secondary dew heater and Argo Navis then an onboard 7 ah gell-cell should be heaps.

My fan and secondary heater run off 2 smaller gell-cells in the mirror box, the power for the secondary heater running up the poles. I have a plug to charge them in the box. There's been some debate about this but if Portaball have been doing it for years without a problem, then it's good enough for me. I also have another plug to power these externally in case the internal battery goes flat.

BTW - if you connect one polarity to the spider then you only have to tape one thin, insulated wire onto the spider to run the other polarity across to power the secondary heater.

Have fun.:)

[gary]

Hi Rob,

This is extremely common on truss pole Dobs these days and is referred to
as a "powered ground board" and you can purchase off the shelf solutions.

Their web site appears to be temporarily offline at the moment but have a look
at http://www.stellarcat.com

Peter Read at SDM Telescopes may also be able to assist locally.
See http://www.sdmtelescopes.com.au/

Physically, you end up with one plug on the ground board part of the scope
that stays fixed with respect to the world and into which you plug a cable
to your external battery. Indeed, spring loaded contacts are used at the
Az pivot point.

To get power to the top end, two of the truss pole split blocks have spring loaded
contacts so when you insert the truss poles into the blocks, power goes up them to the top end.
People often run fine wires under the spider to a heater on the secondary.
Again, Peter Read does this on the SDM scopes and can suggest further
subtle refinements.

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
sales@wildcard-innovations.com.au
http://www.wildcard-innovations.com.au

[CoombellKid]

Thanks Jethro

I'll check them out.



regards,CS

[CoombellKid]

Gary,

Thanks for your reply. I will contact Peter and see what he suggests. I'm
hoping maybe I can power the Argo Navis from the same source. I guess
I will need some sort of distribution box up top. Can I run one side of
the power through the pivot bolt you supply or will this interfere with the
encoder on top?

regards,CS

[CoombellKid]

btw, at this stage I want to power a primary mirror fan and up top an Argo
Navis and a Astrosystems DG-2 dew guard on the secondary.

regards,CS

[tnott]

If you get the powered ground board kit you can power as much as you want from it as it also comes with a power distribution rail with 4 RCA outlets. Eg. fan, dew heater, DSC, Servocat. Positive runs up the center bushing around the pivot bolt(both supplied), negative runs just outside the center via spring loaded brushes and a brush plate. One of the feet can hold the plug that you connect the lead into.

The system I got does assume a 3/4" thickness rocker floor and ground ring but I managed to adapt it to my unusual setup successfully.

[Orion]

A powered ground board is the way to go Rob.

[CoombellKid]

Anyone got an idea how much a ground board kit costs?

regards,CS

[JethroB76]

Are you talking from Stellarcat or from elsewhere?

Because from Garys link SC have their pricing here: http://www.stellarcat.com/Pages/pricing.html

[CoombellKid]

Thanks Jethro,

When I tried and as Gary mentioned it was offline. I haven't been back
since.

regards,CS

[CoombellKid]

Ok, I brought the powered ground board kit from Stellar Cat, My next Q
is what sort of portable power source would be best... one of those jump
starter thingys? I'm looking for something I can take away and be able
to use over several nights, So I need a deep cycle battery with a ciggerette
plug style outlet on it. To give you an idea whats on board....

Argo Navis
DG 2 (secondary heater)
Dew heater for Telrad
2" dew heater strap
Thousand Oaks Dew controler
...and a bar fridge in the rocker box... lol j/k cant fit it in there.

regards,CS

[tnott]

I just use a cheap portable 17 AH battery pack that I got from K-mart. Comes with 2 cigarette lighter outlets. I can run Argo/Servocat on it for several nights without needing a recharge. Can be charged via mains electricity or via car cigarette outlet. When it wears out I can just grab another one easily.

Deep cycle marine batteries are another step up - but more expensive and a bit of overkill for what you are using I think. Most people I know using these are running a laptop for imaging as well.

[AstroJunk]

Are you coming up to astrofest this year?

I'll be happy to give you an in depth tour of SDM006 - It is set up do all of the things you are asking about, and it's much easier to show than explain!!