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Celestron AUX Power Draw Limits

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#1 ButterFly

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Posted 29 December 2022 - 10:46 PM

I'm looking for some guidance as to what is a reasonable power draw from an AUX port, when it's powering a peripheral device.  Some documented safety limits the traces could handle would be nice, but anecdotal stories of what was "too much" are also acceptable.  My mount is an AVX.

 

SkyFi 3

 

I have a SkyFi 3 unit, which I love.  I observe under rather cold conditions, and the battery just has not stood up.  I almost always power the unit from another battery, or line, while it's in use.  The condition of the battery due to age, cold, and charging during the cold I couldn't prevent, meant that it wouldn't hold a charge for a full night anyway.

 

Recently, I tore out the power input USB port like a gorilla!  Soldering that back on properly was not going to happen.  Nor was unsoldering the 18650 battery because of my fear of explosions near my face.  So, I just wiggled the battery loose and broke its connections.  I replaced the battery with a 5V->3.7V buck board, and it's working fine.  I set it to 3.65V and the "battery" reads at 55% capacity.  I maintained an ordinary big USB port style power lead, just to keep it in line with what I've already been using.  I felt this was better than an ordinary battery holder, and just soldering the power leads onto the board, using the inline circuitry to charge the battery.  Again, I have gotten used to having no battery in the unit.  I haven't measured the power draw, but I surmise it's around a few watts, at most.  Again, no battery charging going on, but rather, only powering the WiFi and serial port connections.

 

Is a few watts too much for the AVX board to handle?

 

AUX to PC cable

 

I have been using CPWI more with a mount side stick PC computer, then remoting into it with a tablet or phone.  I dislike that CPWI blasts the handcontroller to highest lumens hand controller brightness.  It's just annoying, and there is no way to turn down the brightness.  And it just wastes power!

 

So, I would like to bypass the handcontroller entirely.  My plan is to use Ken Hutchinson's AUX to PC box, replacing the DB9 connector with a Prolific PL2303 USB cable.  It's the same chip used by the handcontroller, which is powered by the AUX line.  Again, no measurement, but it can't be more than a few watts, and it works with the handcontroller.

 

Any limitations I'm not considering with Ken's box that could draw more power?

 

Computer itself

 

The highest draw would be if I were to power the computer itself off the AUX port.  The stick PC uses a line to 5V 3A converter, with a micro USB port adapter.  I have successfully used 12V to 5V buck converters that can deliver 15W to power the thing just fine.  But 15W is a lot more than anything else.

 

Would 15W be way too much for the AVX's AUX traces to handle?

 

Dew Heater

 

This is now in crazyland!  My max draw is around 30W.  It's usually under 5W during ordinary usage.  I use a controller, so I could shut it off at the switch during slews if needed.



#2 mlord

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Posted 29 December 2022 - 11:00 PM

I would expect more than 1-amp (12W) total AUX draw to be bordering on dangerous ground.  But only Celestron's engineers would know, and their "tech support" fools are unlikely to know.

 

If you want to bypass the hand-controller, there are a variety of HomeBrew devices in these threads that do exactly that.   The HomeBrew Gen3 hardware works with AVX mounts.   https://www.cloudyni...btgpsmusbrelay/

 

Cheers


Edited by mlord, 29 December 2022 - 11:07 PM.


#3 ButterFly

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Posted 29 December 2022 - 11:42 PM

I would expect more than 1-amp (12W) total AUX draw to be bordering on dangerous ground.  But only Celestron's engineers would know, and their "tech support" fools are unlikely to know.

 

If you want to bypass the hand-controller, there are a variety of HomeBrew devices in these threads that do exactly that.   The HomeBrew Gen3 hardware works with AVX mounts.   https://www.cloudyni...btgpsmusbrelay/

 

Cheers

I don't need all that to just connect to a computer.  The computer has all the wifi and other things anyway.

 

Do you happen to know how much it draws while in use?



#4 enigma-2

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Posted 30 December 2022 - 05:09 AM

Advanced VX mount draws between 600-800 ma. Power supply is rated at 3.5 amp.

https://www.cloudyni...-celestron-avx/

#5 mlord

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Posted 30 December 2022 - 08:28 AM

I don't need all that to just connect to a computer.  The computer has all the wifi and other things anyway.

 

Do you happen to know how much it draws while in use?

Not sure which "it" you are asking about.  A HomeBrew mount-USB connection draws perhaps 100mA at 5V, and will be quite a bit less than that from the 12V AUX bus supply (voltage conversion efficiency is above 85% on the HomeBrew, unlike the 0% on Celestron's own products).

 

Other benefits of a HomeBrew Gen3 are that it works where Celestron's own products do NOT work.  Eg. SkySafari over WiFi on a NexstarGPS mount.  Or the Gen3 AUX Relay enables StarSense AutoAlign to work on "unsupported" mounts.


Edited by mlord, 30 December 2022 - 08:32 AM.


#6 ButterFly

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Posted 30 December 2022 - 09:13 AM

The "it" was referring to the HomeBrew Gen3 PCB: WiFi+BT+GPS+MUSB+Relay ! you linked to. How much power does the HomeBrew Gen3 PCB: WiFi+BT+GPS+MUSB+Relay ! draw from the mount?

I do like that your HomeBrew Gen3 mount-USB doesn't draw from the mount, but that thread sort of trailed off a few weeks ago.

#7 mlord

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Posted 30 December 2022 - 09:27 AM

The HomeBrew devices get their power from the mount.  The amount of power used, depends upon which features are in use at any time.  Eg. the devices turn off WiFi when a different connection method is in use.

 

So just now, I set up an ammeter between the 12V AUX and a basic HomeBrew Gen3 with WiFi+BT.  Using the WiFi connection gives a total draw of 62mA from the 12V AUX.  Switching to Bluetooth, this drops to about 55mA.

 

Converting that to watts:  12 x .062 = 0.74watts for WiFi, and 12 x .055 = 0.66watts when using only Bluetooth.

I did not measure Mount-USB consumption, but it should be about the same as using Bluetooth.

 

For comparison, my Nexstar+ (USB) hand-controller draws 68mA at idle (0.82watts).

 

Note that I measured 11.96V on the AUX, so actual power usage was slightly less than calculated above.

 

-ml


Edited by mlord, 30 December 2022 - 09:52 AM.


#8 mlord

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Posted 30 December 2022 - 09:34 AM

I do like that your HomeBrew Gen3 mount-USB doesn't draw from the mount, but that thread sort of trailed off a few weeks ago.

The Gen3 does draw from the mount.  But one can easily modify that (remove the diode and buck, or add a switch) to have it be powered solely from the host's USB port for the Mount-USB scenario.  I haven't tried/tested that, but it should work.

 

Cheers
 


Edited by mlord, 30 December 2022 - 09:35 AM.

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#9 ButterFly

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Posted 30 December 2022 - 09:43 AM

The Gen3 does draw from the mount.  But one can easily modify that (remove the diode and buck, or add a switch) to have it be powered solely from the host's USB port for the Mount-USB scenario.  I haven't tried/tested that, but it should work.

 

Cheers
 

Had me very confused there for a moment!

 

The 12V power lead isn't doing anything in your latest depicted embodiment. You are still powering the Arduino from USB with the latest embodiment, right?



#10 mlord

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Posted 30 December 2022 - 09:48 AM

That version is the original Mount-USB design, not the HomeBrew Gen3 version.  :)

 

The difference is, that design works with only some mounts, whereas the Gen3 works with all Celestron mounts since about 2001, even the really old ones.


Edited by mlord, 30 December 2022 - 09:49 AM.

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