Using 5V connection cable for power

jimme100

Hello,

I read the manual for the ASIAIR and it says you recommend using a 12V power supply and the included adapter to the included 5V micro USB cable.

I have these cables, but thought I could just use the 5V USB to micro USB directly to my power supply's USB port. The manual says if you do this then the USB port has to supply 2.5A @ 5V.

My power supply manual shows the USB power port as supplying USB 3.1A (max) @ 5V. I assume i can just use the 5V USB cable from my power supply's USB ports to the ASIAIR without using the 12v cable and adapter

I would like to use just the USB port on my power supply as I assume that it will use less power from my battery than using a 12V power supply with a 5V converter. I'm thinking that even though the ASIAIR uses the same amount of power no matter what method is used, maybe 5V direct from the 5V cable would use less power from my battery than converting 12V to 5V... Is this the case?

Also, is there anyplace you can suggest to buy a 5V USB cable that would be a little longer than the one that is included and would work with the ASIAIR? I'm assuming the 5V cable is 3ft. is there a 6ft cable that you can use and send me a link for?

Tech@ZWO

hello

Please use the original accessories

Considering the risk of low voltage,the cable is shorter and Thicker than the common one

jimme100

Jiang,

Except for telling me to use the original cable, you didn't answer any of my questions...

I'll try to keep this simple...

Assuming i use your 5v cable, and my power supply is USB 3.1A (max) @ 5V, can i power the ASIAIR with just the 5V cable without any issues?

if the above works, will it draw less power from my power supply than using a 12V power supply, your adapter, and the 5v cable.

Regards,

Skyhunter1

w7ay

>> Assuming i use your 5v cable, and my power supply is USB 3.1A (max) @ 5V, can i power the ASIAIR with just the 5V cable without any issues?

It depends on the length of the USB cable and the wire gauge.

The typical USB cable that uses 24 gauge wires for power contributes about 25 milliohms per foot. A four foot cable would account for 200 milliohms (4 feet for power and 4 feet for ground return). With 3.1A peak current, the voltage drop would be 0.62 volts. If you start with 5.1V, the supply voltage that the Raspberry Pi sees can drop below 4.5 volts. This will not work consistently. It will work under low processor/IO loads, and if you don't over stress the USB ports on the Raspberry PI, but will not work if the Pi ever peaks above 3A (or perhaps even 2A).

Some high quality USB "charging cables" use 18 gauge for 5V and ground return wires, and those will have a resistance of about 6.5 milliohms per foot. A four foot cable would then give about 0.15V drop at the peak (8 feet total path for 4 foot cable). This is probably tolerable. However, most of the "charging cables" are short. If you can find one that is long enough, and it is certified to be 18 gauge, it might work. Do not use extension cables, since each pair of connector also contributes to ohmic losses.

The moral of the story is to keep the side of the 5V cable short, and make the 12V side as long as you need, since the typical buck converter from 12V to 5V can work down to 9V or less.

I didn't check what buck converter chip in in the ZWO adapter; if efficiency of the ZWO converter is of concern to you, typical 12V-5V buck converters have better than 75% efficiency, and can even be better than 90%. For that matter, you might want to check the efficiency of the buck converter that is in your power tank -- it might be even worse than the ZWO power adapter. Also, check to make sure that the output voltage stays above 5V when it is loaded.

For what its worth, I have taken the converter board from the ZWO adapter and mounted it inside the same box as the Raspberry Pi, with less than 3 inches of 20 gauge cable that is soldered directly to the Raspberry Pi (thereby also bypassing the ohmic loss of a micro-USB power connector). I supply my custom Raspberry PI with 12V.

Chen

jimme100

W7AY wrote:

>> Assuming i use your 5v cable, and my power supply is USB 3.1A (max) @ 5V, can i power the ASIAIR with just the 5V cable without any issues?

It depends on the length of the USB cable and the wire gauge.

The typical USB cable that uses 24 gauge wires for power contributes about 25 milliohms per foot. A four foot cable would account for 200 milliohms (4 feet for power and 4 feet for ground return). With 3.1A peak current, the voltage drop would be 0.62 volts. If you start with 5.1V, the supply voltage that the Raspberry Pi sees can drop below 4.5 volts. This will not work consistently. It will work under low processor/IO loads, and if you don't over stress the USB ports on the Raspberry PI, but will not work if the Pi ever peaks above 3A (or perhaps even 2A).

Some high quality USB "charging cables" use 18 gauge for 5V and ground return wires, and those will have a resistance of about 6.5 milliohms per foot. A four foot cable would then give about 0.15V drop at the peak (8 feet total path for 4 foot cable). This is probably tolerable. However, most of the "charging cables" are short. If you can find one that is long enough, and it is certified to be 18 gauge, it might work. Do not use extension cables, since each pair of connector also contributes to ohmic losses.

The moral of the story is to keep the side of the 5V cable short, and make the 12V side as long as you need, since the typical buck converter from 12V to 5V can work down to 9V or less.

I didn't check what buck converter chip in in the ZWO adapter; if efficiency of the ZWO converter is of concern to you, typical 12V-5V buck converters have better than 75% efficiency, and can even be better than 90%. For that matter, you might want to check the efficiency of the buck converter that is in your power tank -- it might be even worse than the ZWO power adapter. Also, check to make sure that the output voltage stays above 5V when it is loaded.

For what its worth, I have taken the converter board from the ZWO adapter and mounted it inside the same box as the Raspberry Pi, with less than 3 inches of 20 gauge cable that is soldered directly to the Raspberry Pi (thereby also bypassing the ohmic loss of a micro-USB power connector). I supply my custom Raspberry PI with 12V.

Chen

Thnaks Chen. Im not an electrical engineer, but i see what youre saying so ill use the 12v to converter to 5v cable setup to make sure the power is sufficient. can you tell me if the draw on my power supply will be 12 volts and that is converted to 5v for the AIR, or if the draw will be just 5v. I have a very good supply, but 2 x 12 volt adapters (i power my mount with the power supply as well) will be borderline sufficient for a night of imaging. if the total draw of the ASIair 12v - to adapter - to 5v setup will just draw 5v then i'm fine. hope i'm explaining this well. I want 1 x 12 volt power draw. (mount) and 1 x 5v power draw (asiAIR). A 17v power draw (12 + 5V) will be better than a 24v one (2 x 12) in terms of how long the supply will provide power in total hours.

I appreciate your help

Regards,

Skyhunter1

w7ay

>> can you tell me if the draw on my power supply will be 12 volts and that is converted to 5v for the AIR, or if the draw will be just 5v.

You will be connecting the ZWO 12V-5V adapter to the 12V outlet of your power tank. The 5V (USB Type A) output from the ZWO adapter goes to the power connector (micro-USB) of the Raspberry Pi.

The current draw from your 12V power tank will be the current draw of the Raspberry Pi multiplied by 5, divided by 12, and divided by the efficiency of the buck converter.

E.g., if the buck converter has an efficiency of 80%, then the current draw from your power tank's 12V outlet would be I*5/(12*0.8) Amps, when the current draw of the Raspberry Pi is I Amps. Multiply that by the number of hours, and that will give the Ampre-hour (A-hr) at 12V.

I just measured the ASIAIR current draw from the 12V connector of the ZWO 12V-5V adapter, when connected to a power supply that sources 13.7V.

When booting, the current spiked up over 0.4A. Actual peaks are probably quite a bit over that, since I am reading from an averaging meter.

When connected through 5 GHz WiFi, with ASI071MC-Pro (cooler not connected), but nothing active, the "12V" draw is about 0.33A . While downloading an image, the current again spiked up to a little over 0.4A.

The cooler of the camera that you are using is likely to pull more current that the current draw from the ASIAIR. I did not check focusing or guiding, but expect current draw to be a bit higher too when those are active.

Don't worry about not being an EE. I am an EE, but well past my sell-by date, at over 70 years old :-).

Chen