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Re: Power GM8 Gemini 1
Hi Guy, Good question.? Here are some ideas: The Gemini1 is rated input from 12 to 18 volts.? All good engineers allow for some leeway, or "guardband"? on their specs, but I would not apply a DC input that I knew was spec at 18.5V output... that is also likely to be putting out more to fulfill it's guardband!, maybe 19V or more. So don't get any power supply rated over 18V...and if you get one rated 18V, you should measure it to be sure. I do use 5 amp rated output power units (12 volts output, boosted later to 17 volts).? So those are 60 watts DC rated units.? I have had one go bad, out of maybe a dozen or more I've purchased.? ?The mount and Gemini together, if well balanced, should only need at most 2 amps under a fast Slew to Target, or Park to CWD.? The extra current rating is just to be sure the unit you buy is not "under engineered." While tracking at Sidereal rate, my balanced mounts using Gemini1 and doing autoguiding use about 0.15 to 0.3 amp.?? Inside the Gemini1 is an LTC1576 chip circuit that reduces the 12-18 volts down to 5.1 volts to run the internal logic chips.? The various capacitors and diode components are not rated as high as the LTC chip, so it's another reason to avoid going over 18 volts input.?? The Gemini motors are DC so their torque is directly related to the DC voltage, and upping that to 17V will help increase the motor torque nearly 50% over 12V input.?? However your lags messages might not go away even with increased torque, if the root cause is a severe load imbalance, snagging camera or dew heater cable, or pinched worm gear.? You have to carefully look for the cause, and I think the easiest way is to have a current meter in your power supply... so see the next part of this message for how I do that.?? Also, the GM8 has a small ring gear, like ~3 inches diameter,? with 180 teeth.? The G11 has 360 teeth and a ring gear that's twice the diameter...so the G11 gets twice the torque just by its mechanical design.? Therefore the GM8 will be more sensitive to pinched worm gear, and mount imbalance, than a G11 would.?? ------- If you are interested: I make up a voltage booster, polarity protected power?supply for Gemini1 and Gemini2 units.? It has a separate 12V DC input of any polarity.. tip plus or tip minus.? That's intended for field use if you want to use a battery and attach clips.? It boosts that 12 V input up and puts out a 17V (adjustable if you wish) output of always the right polarity for the Gemini. The Gemini1 unit has the 4 pin DIN plug power cable, and the Gemini2 unit has the 5.5/2.1 mm male plug cable, tip positive. The unit also provides both DC voltage out display, and DC current out display.? See attached pictures.?? The Volts and Amps displays are the key "dashboard" for the Gemini and the mount diagnostics. The current display can help you diagnose why your Gemini is saying "lags".?? The Gemini is designed to protect your motors and itself from damage.? The lags messages or worse "stalled" messages are telling you something is wrong.?? So if the worm gets jammed by one of these causes: ?a particle of dirt in the ring gear teeth ?a high spot or defect on the ring gear or cylindrical needle bearing ?a misadjusted worm to ring gear gap ?a significant imbalance in your scope load (most likely) ?a camera/autoguider cable snag? Then the current will go substantially up...you need a current meter to see that.?? While sidereal tracking for instance with scope East or West of the meridian, you can see the current drive difference, and know there is a balance issue. An example: Recently, my well-balanced system started to misbehave.? It had become unbalanced: it turned out the scope's dovetail had gradually slid back in the tight saddle dovetail holder. (The C-14HD scope and 80mm guide scope, heavy FL reducer, and deep sky cameras and finder attachments weigh like 70 lbs, on a G11 mount). It's this kind of subtle unexpected mechanical changes that can happen, and you won't know until the "lags" messages help you know.?? Have fun, and contact me if interested in a pre-made power system for either Gemini.?? All the best, Michael On Wed, May 13, 2020, 5:18 AM George Pappayliou via <w3gp=[email protected]> wrote:
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Tim Kimbler
Steve Elmore
Michael Herman
Chip Louie