Re: Update to odd tracking/RA behavior


Roland Christen
 

I don't think the power supply is your problem. I still say it's something mechanical. You say that it's in the RA axis, correct? Then i would do a simple tracking test to determine if the RA axis is tracking smoothly for long periods of time. Tracking, not guiding. Here's how I would do this:

1) offset your azimuth axis by a couple of degrees so that the RA will drift.
2) aim the scope at the celestial equator
3) turn on your PE correction
4) take a 1/2 hour exposure or even up to 1 hour exposure.

The above is a classic tried and true method to characterize your RA axis tracking (something that is forgotten in today's computerized world).

You will get a series star trails. These trails will tell you everything you need to know about how well the RA axis is tracking, and whether during that time you are getting any sudden jumps in RA. The beauty of this test is that it eliminates everything but the raw tracking ability of the mount in RA.

I have experienced a sudden movement of some 20 arc seconds during a guiding test on my observatory mount. Fortunately three of us were looking at the screen when it happened. The guider box received a cosmic ray hit that was off center and very bright. This fooled the guider software into thinking that the guide star had moved and proceeded to send a large correction signal to the mount. This sort of thing can happen at any time during guiding and there is really no solution.

Assuming that it is not a cosmic ray hit, you might want to check the tightness of the spur gears in the reduction gearbox. If the center gear is adjusted too tightly against the two mating gears, you can have the possibility of erratic tracking. Please check to see if the geartrain has a small amount of clearance so that it moves smoothly. You should not try to eliminate all backlash to the point where the gears are binding.

Rolando



-----Original Message-----
From: 'Mike Shade' mshade@q.com [ap-gto]
To: ap-gto
Sent: Fri, Oct 27, 2017 12:17 pm
Subject: RE: [ap-gto] Update to odd tracking/RA behavior

The power supply that I was using was an old Radio Shack unit, 13.8V 10A unit...I replaced it with the Pyramid. All I am running on it is the 1600GTO slewing at 600X.



If the pyramid is a unreliable unit, what power supplies are people using. Again, this only powers the mount. I bought this through AP a few years ago, seldom used. It powered my 1200GTO occasionally.



Thanks...



Mike J. Shade: mshade@q.com

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From: ap-gto@... [mailto:ap-gto@...]
Sent: Friday, October 27, 2017 10:03 AM
To: ap-gto@...
Subject: Re: [ap-gto] Update to odd tracking/RA behavior





Mike,



Assuming you replaced the original PS with a new “PYRAMID PS-9KX” (13.8 vdc @ 5 amp steady current, & 7 amp max), its 4-page document says:

(5) THIS UNIT HAS ELECTRONIC OVERLOAD PROTECTION WITH INSTANT AUTOMATIC RESET FUNCTION.
IF OUTPUT IS OVERLOADED - THE OUTPUT POWER WILL AUTOMATICALLY SHUT OFF
RELEASE POWER CORD OF YOUR EQUIPMENT FROM THE OUTPUT TERMINALS AND CHECK THE ACTUAL
POWER RATING OF YOUR EQUIPMENT. THIS UNIT WILL “AUTOMATICALLY RESET INSTANTLY”

(6) OVER TEMPERATURE PROTECTION CIRCUITRY IS USED IN PS-9KX TO PREVENT OVER HEAT DAMAGE.
UNIT WILL BE SHUT DOWN ... AFTER 15 MINUTES ( MIN) AT 100% RATED LOAD
AND AFTER 25 MINUTES ( MIN ) AT 80% OF RATED LOAD



Have you checked how much current is being drawn from the 5 amp supply? If you are using only 80% of rated amps, this 4 amp power drain can cause a momentary power loss at the 25 minute mark at this level – even sooner, at the end of 15 minutes, if it supplies its “full rated” 5 amps for 15 minutes.



It will recover automatically, as soon as it cools off, so you will never know if there was a power glitch, except for those trailing star images.

I had it fool me once when the AP-900 seemed to be running just fine. Then it lost power during “one of its MANY slews”, after more than an hour of (apparently) normal operation. As I was looking for the cause of the system power loss, it came back to life all on its own, and slewed the OTA into the pier before I got to it. So, I assume my scope system (mount and STL) were running at even less than the rated 80% trip level, and it then glitched much later, at 4 times their warning period. So, even operating at less than 80% power drain is not reliable – just takes longer to fail.



Seems it likes to run at much less than advertised amps – probably just 3.5 amps continuously, where it won’t crow-bar, some time during the night – then come back like nothing had happened. I wonder if the design would have been safer to just shut itself down, in the case of powering motors. That’s why I stopped using my PYRAMID supplies – can’t trust them to not screw things up, dangerously.



I wonder if this” power dip and auto recovery” ... is what you are experiencing. Check your amps,

and get a larger rated PYRAMID, perhaps the 10 amp would be safer. Even every production unit of the same supply, can differ, so your presently “better performance” may have a longer trip time, with a faster auto recovery, than the previous PS.



Joe





[Non-text portions of this message have been removed]



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Posted by: "Mike Shade" <mshade@q.com>
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