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Eq Platform for $29.5

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#76 Edward E

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Posted 08 June 2010 - 04:17 PM

Picture 5 of 11:

...the other side. Note that this side has 2 screws, not one like the other.

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#77 Edward E

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Posted 08 June 2010 - 04:18 PM

Picture 6 of 11:

"exploded" view.

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#78 Edward E

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Posted 08 June 2010 - 04:20 PM

Picture 7 of 11:

Side, exploded view.

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#79 Edward E

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Posted 08 June 2010 - 04:27 PM

Picture 8 of 11:

The PC Board removed from the shell and flipped over. The ICs circled in red are TL494 pulse width modulation ICs and the IC circled in blue is a LM324 Quad Op Amp IC.

The PWM IC at the top, center of the picture is the "slave" which is controlled by the "master" PWM IC located at the bottom left of the picture. The "master" IC's timing resistor is what we want to change out.

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#80 Edward E

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Posted 08 June 2010 - 04:37 PM

Picture 9 of 11:

Close up of lower, left IC. The yellow device (left of white/red wires) is the timing capaitor. The circled, blue, 120k ohm resistor (timing resistor) to the right of the yellow capacitor is what we want to remove and replace with another resistor or potentiometer.

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#81 Edward E

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Posted 08 June 2010 - 04:54 PM

Picture 10 of 11:

This picture is of the 100k ohm pot with a 68k ohm resistor soldered to it. This combination gives me finer control of the resistance needed for sidereal or lunar tracking than just using a larger pot. The white/black wires coming from the top of the pic will be attached to the white/red wire soldered onto the inverter board.

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#82 Edward E

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Posted 08 June 2010 - 05:09 PM

Picture 11 of 11:

Assembled case. The case is a 9 volt battery holder with an on/off switch and connection wires used to power a 9 volt device. I am using this case so that when the inverter is in use, I can took an oscilloscope to the red/black wires to adjust the frequency or a multimeter (with the inverter powered off) to read the final resistance once the proper tracking rate (sidereal/lunar) is found. The splayed white/black wires will be attached to the +/- connectors inside the case when the unit is fully assembled.

I hope these pictures and descriptions will be of help to anyone wishing to modify one of these "cheap" inverts to use with their mounts.

A big thank you to Ed, DavidG and others for their suggestions and help with this project.

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#83 Ed Jones

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Posted 08 June 2010 - 06:31 PM

Thanks for posting it Edward! It doesn't look difficult to do.

#84 ZeroID

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Posted 08 June 2010 - 10:30 PM

Many thanks to both Ed for the platform details( plus bonus for the side shot ) and Edward for the neat pix and explanation of the inverter control. Looks all feasible to me, better fire up the workshop.!!

#85 Edward E

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Posted 09 June 2010 - 12:58 PM

Very nice eq platform Ed! I really enjoyed reading how you built it; very clever tool use.

#86 Edward E

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Posted 18 June 2010 - 11:11 AM

UPDATE: The inverter mod works very well. I have done some fine tuning but have surpassed the resolution of the 1M Ohm pot and encountered a blind spot on this pot in the range that I need to set it at. I am making a small PCB equipped with two, mini, high resolution, multi turn pots attached to a medium size switch for Sidereal & Lunar tracking (to go into the small black hand case). Added flexible wire with a strain relief device on the inverter to prevent wire tangle (wire currently used is stiff and becomes a tangled mess) and the risk of pulling the wires out of the inverter's PCB. I will post pics when the new setup is complete.

#87 Edward E

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Posted 17 July 2010 - 04:57 PM

UPDATE: The inverter mod works very well. I have done some fine tuning but have surpassed the resolution of the 1M Ohm pot and encountered a blind spot on this pot in the range that I need to set it at. I am making a small PCB equipped with two, mini, high resolution, multi turn pots attached to a medium size switch for Sidereal & Lunar tracking (to go into the small black hand case). Added flexible wire with a strain relief device on the inverter to prevent wire tangle (wire currently used is stiff and becomes a tangled mess) and the risk of pulling the wires out of the inverter's PCB. I will post pics when the new setup is complete.



Here is the revised hand controller (HC) for my modified inverter. The large, open hole is where the old 1M Ohm pot use to be. You can see the two adjustment screws for the new precision mini pots through the two small holes to the right. The switch to change from sidereal to lunar tracking is at the bottom of the photo.

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#88 Edward E

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Posted 17 July 2010 - 05:01 PM

Here is the HC with the front cover removed so that the electronic components are visible.

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#89 Gene7

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Posted 23 September 2010 - 03:37 PM

Good evening folks: Here is a small and inexpensive inverter that has proven to be temperature stable. Here are instructions for for making the frequency adjustable.

Attn:

I received the Wagan 2107 inverter and did some tests. Since it does not produce a true sine wave some error in measuring output amps was expected. This did occur in one of the tests where the output watts exceeded the input, not possible. The specifications for the unit are:

80 watts, 60 Hz +/- 5 Hz, 12V in, 110 V +/- 5 out, weight 150 grams. From JR Music. About $20. USD. Also has a USB power connection.



Equipment used was two digital volt/ammeters, a digital amp probe, a synchronous clock, and a 6 watt synchronous motor. For the 35 deg. F. test the inverter was allowed to stabilize and operate in the frig. Here are the results:

6 watt, 110 volt motor.
Room temp. 9.96 watts in, 10.8 watts out (not possible), 120V. out.

2.5 watt, 115 volt motor, (clock).
Room temp. 4.21 watts in, 3.12 watts out. 57.5 Hz. speed, 120V out.
35 deg. test 57.6 Hz. speed

Idle watts used.
1.75 watts, or .15 amps.

Although about 4% below the design speed of 60 cycle, the inverter is very temperature stable. The next step will be to see if I can get a pot attached for minor speed adjustment. My concern is not the 4% lower speed, but the desirability of being able to do an electronic speed adjustment instead of the very difficult task of doing a mechanical matching adjustment.

So, there you have it. Any more questions anyone? I will update you on my attempts to add an adjustment pot. Thanks. Gene Smith


I successfully identified the timing resistor and capacitor in the Wagan inverter. It uses a AZ7500BP-E1 16 DIP I.C. The circuit is listed on-line. Pin 5 is the timing Capacitor, and Pin 6 is the timing resistor just to the right of it. Both are blue metalized film low temperature drift components. See the attached pictures below. The yellow wire is attached to the top of the timing resistor and pin 5 of the I.C. The green wire is attached to the ground, as is the other end of the resistor. Note that the P.C. board conducting strips for these components do a 45 degree jog to the left next to the I.C.

http://www.PhotoShar...seup0232102.jpg

http://www.PhotoShar...seup0264784.jpg

As received the inverter produces a frequency of 57.5 Hz. I connected a 1.5 meg. resistor in parallel across the 135.K timing resistor. This increased the frequency to 61.5 Hz. I suggest that a parallel resistance of 1 meg. in series with a 5 meg. pot would give a reasonable frequency adjustment of a few cycles above and below 60 Hz. Another unit may have a different range and thus require different resistors.

Do the necessary preparation before trying to attach these wires. See detailed section below.



DETAILED SUGGESTIONS

I removed the black front cover of the inverter by applying slight pressure. Seems to have been solvent bonded to the light colored body, but not very well. A couple small screws removed the USB connector from the front cover. One screw allowed the body to come apart and the rear power supply connection removed from the body. Although the circuit board is crowded, it is the conventional through soldered component type and not surface mount, thank goodness.

I saw an A27500BP-E1 integrated circuit, which is a DIP- 16 pin I.C. A first real clue was 4 blue resistors and a small blue capacitor. Blue components are metal film and temperature stable, an indication that they may be timing components. Google told me the I.C. is a pulse width modulation control, and gave me a circuit diagram. Sure enough, pin 5 is the timing capacitor and pin 6 is the timing resistor, both blue components. The capacitor is .1 uF and the resistor is 135 K ohms.

Go about attaching the lead wires in a methodical manor. I used a large self supporting magnifying glass. #28 stranded wire is suggested, as well as a point tip heat controlled iron, a can of flux, and small wire solder. I am unsteady so I used some holding aids to position the wires. Secure the P.C. board so it does not skate around. A block of wood can help steady the iron. After the pictures I placed a small gob of clear epoxy over the solder joints to prevent breaking during wire flexing. #28 wire is hard to find even on-line. One source is for strain gage wiring.

Perhaps a more trouble free method would be to cut the resistor lead at the top of the resistor and remove both halves. Replace with a like value blue metalized film resistor. Let both lead ends extend perhaps a 1/4 inch to give room for lead attachment. Insulate and secure ends with epoxy when bent down. Gene Smith

#90 jlpowell77

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Posted 23 January 2013 - 12:25 AM

Hey there - I recognize that this is an ancient thread. However, I am just beginning to build my own equatorial platform and I am enthralled by the simplicity of this design.

However...I am not that quick...and I can't quick figure out how the south end fits on the platform. I see the three bearings....however...where in the process do you cut the south end? how does it fit to the platform? Any chance you have any pictures?

Thanks!

JP

#91 Ed Jones

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Posted 23 January 2013 - 10:15 AM

JP,
Look at post 2419781. It is a drawing of the side view. The south bearing is mounted parallel to the north bearing with its center of curvature on the virtual polar axis. One small error in this drawing is that most folks make the south bearing edge perpendicular. Two of the bearing run on this edge and the bearing in the middle keeps the platform from sliding back. The south bearing I make with the sanding disk on the table saw the same way as the north bearing except the sanding disk is not tilted.

When I wrote this post I wasn't making the south bearing edge perpendicular as seen in this picture. However I have since switched to making it perpendicular because there is no real advantage and in fact making it perpendicular eliminated the goofy little block with compound angles. They mount directly on the south bearing block whick is just angled to your lattitude for the middle bearing and 90-lat for the other two bearings. I've also started putting laminate on the bearings which takes more abuse and is better than metal against metal.

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#92 tag1260

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Posted 26 March 2013 - 05:56 PM

Ed

For the motor that you are using, how do you figure the diameter of the drive roller? I'm at 40 degrees (Actually also in Ohio right on I-70 but the other side of the state.). So far the only thing I can figure is that I need to cover 7.31" an hour of my North bearing. (NB being 27.94" radius.) I just don't know where to go from there and I don't even know if that 7.31" is relevant .

Thanks
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#93 Ed Jones

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Posted 26 March 2013 - 08:19 PM

Tag,
The ratio of the North bearing diameter to the drive roller is 1436 min./minutes per rev. So for a 4 rph motor the ratio is 95.7 to 1 and with a 1/2 inch drive shaft the North bearing radius is 23.93 inches.

#94 tag1260

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Posted 26 March 2013 - 09:35 PM

Thanks ed. Unfortunately you've confused me on all my other figures with that North bearing radius. Oh well, back to the drawing board.
Thanks again
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#95 tag1260

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Posted 27 March 2013 - 07:05 AM

Just looked over my figures again. I guess I should have mentioned my figures are for a VNS style platform. I'm guessing that yours are for the angled North Bearing. Back to trying to figure out a simple and inexpensive drive setup.
Thanks

#96 Ed Jones

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Posted 27 March 2013 - 09:13 AM

For the correct drive shaft diameter and motor speed they are both calculated the same.

#97 tag1260

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Posted 27 March 2013 - 09:26 AM

So your saying that the 1/2" diameter will work wit either radius? I'm showing a 23.95" radius for the slant bearing and 27.96" for the vertical.

Thanks and sorry for being so much trouble.
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#98 Ed Jones

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Posted 27 March 2013 - 09:49 AM

The VNS sector is actually a section of an ellipse not a radius when laid flat. As far as the motor speed and shaft diameter both are calculated using the radial distance from the virtual polar axis. Converting that to the elliptical curve of a VNS sector I've never done because a curved sector is so much easier to make. The curved sector has a more constant speed as well.

#99 tag1260

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Posted 27 March 2013 - 10:11 AM

Ed,
I have cut no wood yet so I can change designs. I also have a pretty well equipped wood shop at my disposal.
Will my South bearing be the same radius or will that have to be changed also? Does the angled North bearing mount in the same place as my vertical?
So many questions, I know but without actual plans in front of me, I'm lost at figuring this out.

Again, I appreciate the help.
Thanks
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#100 Ed Jones

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Posted 27 March 2013 - 10:54 AM

Tag,
First you will need a plan drawn on paper or AutoCad. I have a write-up on my web page Both north and south bearings are concentric with the virtual axis so unless you live on the equator they will have a different radius.






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