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#1 rick-SeMI

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Posted 21 November 2012 - 10:07 AM

I like Dobsonian Telescopes :)

But, what this about is that I bought 5 muffin (computer) fans from an amateur radio swap & shop several years ago for a buck and had a few left over from one of my radio projects.

I used one of the 3 1/2 inch 12 VDC fans for this project.

I cut a thin piece of plywood and drilled holes near the edge of the the board for three small bungee cords.
The hooks fit over the locking screws.
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Here is a shot of the two wire with female coaxial plugs at either end.
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This is the coaxial jack mounted to the back of the plywood.
I drilled a small hole next to it to run the pair of power leads from the fan and used clear sealer.
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This is the label of the White's Metal detector NiCad battery pack I modified.
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After opening the cover of the NiCad pack.
Had to use a razor knife because they had glued it on.
Removed the no longer useable (corroded/white) NiCads and replaced with 2500 mAh NiMH Batteries.
I added the mini SPDT switch.
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Then I tried looking for a battery charger, as I had to solder one end of the batteries in the case.
The only one(s) I could find were for separate batteries that could be inserted individually.
Therefore, I built my own.
I'm not going to take a picture of the inside. It's NOT pretty - But, It does work :)
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The site where I obtained the circuit for the charger.
http://www.extremeci...ry-charger.html

and here

http://circuits-proj...battery-char...

I chose R2 for 300mA charge current.

Tried it out several nights ago and it worked well with no noticable vibrations while looking thru the eyepiece.

#2 rick-SeMI

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Posted 21 November 2012 - 10:20 AM

BTW, the Q1 transistor (BD-135) is similar to the TIP-120 which I got from R.S.
***Make sure you use a heat-sink on it***
Most of the other parts I had in my junk box, including the black plastic box :)

#3 jerwin

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Posted 23 November 2012 - 11:51 PM

Very nice Rick, I put a similar fan assembly onto my xt10i a few weeks back. I the ran power over a coiled phone cable for the bungee effect on the cable.

here is mine

http://www.cloudynig...5502411/Main...

Jim

#4 rick-SeMI

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Posted 24 November 2012 - 07:32 AM

I the ran power over a coiled phone cable for the bungee effect on the cable.

here is mine

http://www.cloudynig...5502411/Main...

Jim


Your's is a much neater setup than mine, Jim.
I may have to replace my power cable with a coiled cable like yours, Thanks.

#5 rguasto

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Posted 24 November 2012 - 01:46 PM

Here's my fan on my 1961 dynascope. I used a USB 80mm fan with a 60mm reducer that was almost the same size as the vent on the rear baffle. It increased the velocity a little. The power supply is a USB battery "charger" that is velcro'd to the underside of the cradle. It will run for at least 8 hours. The reducer mounts to the baffle with silicon "pull through" fasteners. there is no vibration at all since it is not screwed or bolted to the baffle.
The close baffle helps to abolish tube currents. Made a big difference.

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#6 rguasto

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Posted 24 November 2012 - 01:47 PM

.

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#7 rguasto

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Posted 24 November 2012 - 01:49 PM

one more

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#8 jerwin

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Posted 24 November 2012 - 05:13 PM

what kind of spider veins do you have in that? do you like it?

#9 kfiscus

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Posted 24 November 2012 - 05:18 PM

Does the flower pot help balance it?

Seriously, that's a cool looking rig. What are the extras visible in your last photo?

#10 rguasto

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Posted 24 November 2012 - 06:31 PM

Dynascopes had dual ring spiders, no diffraction spikes.

#11 rguasto

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Posted 24 November 2012 - 06:42 PM

We're getting off topic, but...
Extras? A shelf for my eyepiece case and a stand for my netbook (which is removeable - I haven't used in quite some time)

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#12 rguasto

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Posted 24 November 2012 - 06:45 PM

The shelf folds

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