开云体育

Hey everybody,

I’m a new-to-me G11 Gemini 1 owner. I have an 18V laptop power supply that’d I’d like to use to power my mount. It’s actual measured output voltage is about 18.2V though. My guess is this is close enough, but does anyone know the actual max voltage we can use? I’d hate to fry this thing if 18.0 is a brick wall.

Thanks!
Bryan

On Mon, May 13, 2024 at 04:03 PM, Bryan Duke wrote:

Hey everybody,

I’m a new-to-me G11 Gemini 1 owner. I have an 18V laptop power supply that’d I’d like to use to power my mount. It’s actual measured output voltage is about 18.2V though. My guess is this is close enough, but does anyone know the actual max voltage we can use? I’d hate to fry this thing if 18.0 is a brick wall.

Thanks!
Bryan

Hi Bryan, welcome! 18.2v is just above the maximum range, so will probably work ok, but I would prefer something closer to 16v. Any problems with the supply, a spike in the AC, or possibly some overload condition can push it even further above 18v, which could risk overheating or even frying some of the components. As important, what is the maximum current that this supply is capable of delivering and how well regulated is it?

Regards,

? ?-Paul

Thanks Paul. It's an NEC AU80001 power supply with a rated output of 18V & 4.44A. Since it's an NEC part, I'm guessing that 4.44A is fairly accurate. There are a few people who have talked about using them with success with their G11 mounts on CN, but I haven't tried it myself yet. To be fair, I don't know how well regulated it is.

?

The Gemini manual states "The Gemini System requires 12–18 Volts DC, 3 Amps to operate." Putting on my engineer hat, those voltages are just 2 significant digits each...so, I guess that's what gives me a little bit of pause. Is that 18.000V max, 18.4V max, etc.?

Thanks,
Bryan

On Mon, May 13, 2024 at 04:30 PM, Bryan Duke wrote:

The Gemini manual states "The Gemini System requires 12–18 Volts DC, 3 Amps to operate." Putting on my engineer hat, those voltages are just 2 significant digits each...so, I guess that's what gives me a little bit of pause. Is that 18.000V max, 18.4V max, etc.?

I'd err on the conservative side and use a lower voltage power supply. It's not much of a benefit to have 18v over 16v, but having some Gemini component overheat or even burn out, or just shorten its lifespan due to overvoltage, seems like a pretty significant potential downside.

Bryan

more than likely that voltage measured is “un-loaded” meaning it doesn’t have a load drawing current…..which usually drops (or loads) the Voltage somewhat?

18.2V is ok, components inside rated on this rail are 25v capacitors and H bridge and voltage converters. ? ?All can take can take this 18.2V

That said, Laptop PSUs are usually “well regulated” and are quite stable Vout. ? ?Indeed I have one I use on a G2. NEC should be a good one well made?

cheers
--
Brendan

Thanks for the info, gents. It's great to hear the components are rated at 25V - that's exactly what I was hoping to hear.

I'll wire up a new connector and give it a try soon.

-Bryan

The smoke check was good. It works fine in the shop, so it’s time to mount this thing on my pier. “First” light soon!

Thanks for all the help, everyone.
-Bryan

That 25V is minimum rated component the capacitors along the input rail for “H” bridge drive.?

The others using this input rail are rated at 55V for the H bridge and I think 36V for the buck converter. ? So you’re good?

Losmandy obviously have to set a limit of Vin as not all owner supplies are equal and a poorly regulated my peak higher than Vavg. ?

In reality you don’t need a greatly regulated power for the Gemini as it makes its power internally from buck converter. ?But I’d never use a junk PSU to run it. ?

So I understand why they chose 18VDC

Cheers Bryan, looks good, love the right angle 4 pin DIN!

--
Brendan

On Mon, May 13, 2024 at 06:45 PM, Bryan Duke wrote:

Thanks for the info, gents. It's great to hear the components are rated at 25V - that's exactly what I was hoping to hear.

I'll wire up a new connector and give it a try soon.

-Bryan

Bryan,

The conservative electronic parts standard is to use components rated for double the designed voltage. The 18vdc upper limit is already pushing well beyond conventional electrical wisdom for long life and.reliabilty.?

The rush to use the maximum input voltage was really a bandaid for mounts that are not mechanically perfect, not perfectly adjusted or balanced or use the original Gemini 1 servo motos which were lower torque to begin with and in many cases now 20 years later have worn brushes and need to be replaced.?

I built a multi-voltage output battery pack for my Losmandy mounts and have tested using both the automotive 12v (13.5vdc) standard output voltage and the maximum Gemini 2 voltage of 18vdc using the same 55 pound payload and could see no difference in normal operation or guiding while imaging.?
?
You can make your own adventure here and go with the out of spec 18.2v free power supply or just go with the standard 12v for maximum reliability. BTW there are excellent $15 12V @ 5A regulated switching power supplies on Amazon. It seems silly to use an out of spec power supply just because you have one when for $15 you can buy the right part for your $3,000 mount.?

--

Chip Louie Chief Daydreamer Imagination Hardware?

? ?Astrospheric Weather for Imagers - Click on my sig!

Thank you both. Great points and info. Chip, it's great to hear you're seeing the same results at both ends of the voltage range. That's a completely valid point about cheap & easy to get power supplies that are under 18V. Shoot, that 90deg DIN connector cost more than the power supplies you mentioned.

My mount has the early high torque motors and was recently cleaned & re-lubed.

I had it under the stars for my first time tonight. I have some kinks to work out with NINA & slews, but otherwise everything seems to be working well.

Thanks for the help!
Bryan

On Thu, May 16, 2024 at 02:16 AM, Bryan Duke wrote:

Thank you both. Great points and info. Chip, it's great to hear you're seeing the same results at both ends of the voltage range. That's a completely valid point about cheap & easy to get power supplies that are under 18V. Shoot, that 90deg DIN connector cost more than the power supplies you mentioned.

My mount has the early high torque motors and was recently cleaned & re-lubed.

I had it under the stars for my first time tonight. I have some kinks to work out with NINA & slews, but otherwise everything seems to be working well.

Thanks for the help!
Bryan

I never tested or timed it but AFAIK Gemini slew speed is set by the Gemini under the "speed" settings and the encoders which look at motor speed and counts for position just let the Gemini know to send more or less juice to the motors to regulate speed. I think for some folks the additional voltage helped overcome mechanical stiction/friction and startup loads issues due to poor adjustment or balance.??

There have been a few different Losmandy servo motors available. The "high torque" motors are marked as such with a "HT" marking and/or have additional machined cooling fins on the servo motor body. The Maxon servo motors had full length body cooling fins and the original Gemini 1 standard torque servos have smooth bodies and no fins at all.? ? ?

--

Chip Louie Chief Daydreamer Imagination Hardware?

? ?Astrospheric Weather for Imagers - Click on my sig!

I asked Tanya about it and she said mine are the early high torque motors before the cooling fins were added. The previous owner used a 13.8V/5A Pyramid power supply and said it worked well, but I wanted something less bulky that would mount more easily & cleanly on my pier.

I did some initial tests (PE measurements, autoguiding tests, etc) with the 18+V NEC power supply, but I ordered an NEC ADP57 to try. It's a 15V/4A power supply, so I'm guessing it'll be plenty and also keep me very safely in the middle of the spec voltage range. I don't expect to see any difference in performance, but I'll do another round of PE & autoguiding measurements to check that a little.

Based on what others have said, I don't expect the slightly-over-18V power supply to cause any issues. However, like you said, it's easy to be under 18V. If the ADP57 works well, I'll stick with that and not think about it any more.

Thanks!
-Bryan

Just a follow up in case anyone else in the future is looking for a power supply. I've had about 4 nights with the NEC ADP57 and it's working great. I bought a "Genuine New NEC Versa AC Adapter ADP57 15V, 4A" off eBay for $10 and soldered on an Amphenol T 3300 005 90deg DIN connector from Mouser ($20).

I did some load testing before I used it. Like the previous NEC power supply I used, the output voltage was above the spec value at zero load. At 4A however, the voltage was 15.0V. I haven't load tested the previous 18V NEC power supply, but my guess is it's below 18V once it's powering even a parked mount. YMMV.

Next project: design my own spring-loaded worm assembly for my 2007 G11. (Maybe.)

Much appreciated Mr. Duke!
I'm retiring my Kendrick power supply and will need that 4 pin Amphenol to craft a cable. 90 degree = perfect application!
For the record: I see nor hear any difference between applying 12 or 18vdc to my GM8 with the Gemini 1. The current draw goes up .2 amp. I'm sticking with 12v for simplicity.??
1,000 Thanks for providing the part number!!?