Electrics Q for Telescope project

Calibos

This is not a Telescope/Astronomy question posted in the wrong forum but an electrics question

I've a big 7ft tall telescope that I have modded like it was a boyracers car. I have attached loads of 12v devices all over it and these are powered from a 20ah AGM battery. This battery sat onboard on the base of the telescope.


scope nearly finished 2 by Ca1ibos, on Flickr

Two problems became apparent after a while. One is that with all the 12v gear on the Telescope and even more to be added and the fact that this gear is powered up for half the night when in use, well that high capacity 20ah battery is lookin' a bit weedy at this stage. I need something with a greater capacity to run all night. My 20ah battery is already slightly warping my base with its weight causing the Telescope to be much stiffer to turn because the baseboard is now making contact and dragging on the groundboard. The problem can only get worse if I could even fit a larger capacity battery onboard on the telescope base.

So I would like to get a much higher capacity (and physically larger and heavier battery) but not have it onboard the telescope but sitting on the ground near it instead. I wouldn't be the first to do this either. Because you turn the Telescope while looking around the sky, one can run into the problem of 'cord wrap'. This is solved by other astronomers with what they call a powered groundboard where the Battery cable is connected to the bottom part of the groundboard of the Telescope that doesn't move. Usually these wires are connected to two small diametre metal rings. Power is picked up from the two metal rings by two wired carbon brushes mounted to the top part of the base that turns. This way power can be transferred between the non rotating bottom part of the base and the rotating top part of the base.

However, for reasons there is no point going into, I can't do it that way......but I had a brainwave!

The bearing that the Telescope turns on is basically a lazysusan bearing not unlike whats used on those rotating dinnertable platters. Because of the heavy weight of the telescope this lazysusan needle thrust bearing is sandwiched between two thin metal sheets/discs. These metal sheets prevent all the needle rollers causing dimples in the wood surfaces of the telescope. I realised that there is an inner circle of needle roller bearings and an outer circle of needle roller bearings and that the spoked wheel of the lazysusan is made of plastic. If I cut these metal sheets/discs so that now there is an electrically isolated inner circle of metal that the inner ring of needle bearings run on and a wide outer ring that the outer circle of needle roller bearings run on, well I now have a way of getting Pos and Neg from the non rotating bottom of the scope to the rotating top part. There are always going to be most of the metal needle bearings in contact with the top and bottom metal sheets at the same time. So POS from battery is wired to electrically isolated bottom sheet inner circle, NEG from battery is wired to electrically isolated bottom sheet outer ring. Power transferred via the electrically isolated inner and outer ring of metal needle bearings to the corresponding upper metal sheets. POS and NEG wires from the appropriate upper sheets through the baseboard into the base where they are wired to my power distribution block that all the gear is connected to.

However. Does large sections of 2mm thick sheet metal prevent too high a resistance or something like that to be able to deliver a reliable 12v and upto 5 or 6 amps of current?


lazy susan by Ca1ibos, on Flickr

Thanks in advance for any advice....other than get a life you nerd:D

DublinDilbert

If I understand you correctly it sounds like it will work. The thickness of the metal conductive sheet won't make a difference. 6A isn't a massive amount of current. But i would put a small 12V alarm battery (cheap in wholesalers) on the top side of the telescope, cause as the bearing rotates you may temporarily loose connection as it moves.

I would probably avoid trying to pass power across the bearing. I would get a couple of smaller batteries to power your kit up, then bring a larger battery so you can charge the smaller ones after a few hours.

indie armada

would i be right in saying what the op is describing is a sprial cable, similar to the concept used in the steering wheel on a car to opperate the airbag.
could some sort of conducting mesh or material be sandwiched between the two plates to ensure constant continuity.

DublinDilbert

Yea I was thinking of a spiral cassette like for an air bag. There's a limited number of turns the steering wheel will turn in each direction and will always return to the centre.

If the centre is open you could pass like a phone bungy cable up it. On vaccum cleaner rewinds they use carbon brushes to conduct the power across between the rewind and appliance.

Actually if the centre point of the pivot is free why not pass a shaft up it and use slip rings / brushes to contact it.

Calibos

DublinDilbert wrote: »

Yea I was thinking of a spiral cassette like for an air bag. There's a limited number of turns the steering wheel will turn in each direction and will always return to the centre.

If the centre is open you could pass like a phone bungy cable up it. On vaccum cleaner rewinds they use carbon brushes to conduct the power across between the rewind and appliance.

Actually if the centre point of the pivot is free why not pass a shaft up it and use slip rings / brushes to contact it.

However, for reasons there is no point going into, I can't do it that way......

I've a motor system that moves the telescope controlled by a planetarium app on my iPhone. The motor hardware that turns the scope is mounted at the central pivot and thus I can't use a small slipring or run a cable through the central pivot bushing.

A spiral casseete with a limited number of turns cant work because it would be hard enough for my brain to remember that the scope had to be unwound 350 degrees anticlockwise to get to that star that was only 10 degrees clockwise away. There is also no way of telling the electronics that control the motor system something similar. This motor system has the torque to drive much larger telescopes. Mine is actually on of the smallest and lightest its designed to work with. The motor would tear the cassette thingie to shreads and then rip out the floor of the wooden telescope before it ever stopped or self destructed:D

I really appreciate you guys brainstorming this with me though.

ted1

would it much hassle to not have the scope turn 360. You could just use use a cable and rotate the scope the opposite direction