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G11 stepper chatter

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#1 gnowellsct

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Posted 14 February 2010 - 12:02 AM

Unusual symptoms last night: the G11 was tracking but the Dec was "chattering" and moving irregularly during slewing. It was 10 F out and I was running a lot of heaters (basically three C14 heaters in various applications--on the refractor, in the eyepiece box, and around the computer).

My engineering friend Pete helped me simulate the conditions a few hours ago. We determined that when the voltage gets down to about 11V that the stepper start to behave irregularly, and they get even more irregular at 9 v.

I could have solved my problem in the field by disconnecting one of my heaters, or using a lower amp heater in one of the applications.

This of course was the SAIA stepper system. Although it is well known that servos often like to have their voltage upped, the fact is that low voltage due to cold weather is probably a "compounding additional factor" for systems that already want more power than humble steppers.

regards
Greg N

#2 Luigi

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Posted 14 February 2010 - 08:21 AM

What's your power source and the size of the wires your using to power your setup? If you're using a led acid 12V battery and it's dropping down to 11V, you're drawing to much current or discharging it too far. If it's a regulated 12.8V supply, you're overloading it. If the source isn't going this low but the voltage at the mount is when everything is turned on, you need larger wires and perhaps better connectors. The wires and connectors carrying the most current (from the PS to where the heaters and other loads split off) need to be the biggest.

#3 gnowellsct

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Posted 14 February 2010 - 08:36 PM

The power source was an 85 amp hour marine battery. I think the load was in the neighborhood of 8 amps (there's a ten amp fuse would have blown otherwise). Just gator clamps feeding into a three hole cigarette plug from the 'shack (with an in-line micro blade fuse I put in).

I think the temperature may have had an impact on the battery. But I've never tried to run three c-14 length cords all at once before. Probably should have disconnected one.

thanks
Greg N

#4 Luigi

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Posted 15 February 2010 - 10:25 AM

Certainly sounds like the source is up to snuff which suggests you need heavier gauge wires. The ciggie lighter plug connections aren't the best either. There are a few threads and one current one on better connectors for 12V power.






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