Active 3.0 USB cable question

[Andrew INT]

Hi,

After much a do with putting up with British weather, I have decided to civilise astronomy by moving my laptop indoors.

I'm looking to purchase a 15m active 3.0 USB  cable in order to run four devices through a USB hub (imaging camera, guide camera, filter wheel and ASCOM cable). 

My question is this: I've read (through an Amazon customer review) that each extension chipset in the cable counts as one device...and that a USB port is limited to five devices. Is anyone able to confirm this please? Does anybody use a 15m extension cable with one or more chipsets along it? I don't want to spend £60 or so on a cable that can't run four devices.

Thanks for any advice folks!

[Clarkey]

I have a 10m USB 3 active cable with 2 intermediate chipsets linked to a 12v powered 7 port USB hub. I've not had any problems. I also have another 12v hub with 4 USB ports and 3 charging ports that run USB dew heaters. Works well. Don't forget the hub is only one device.

Edited May 9, 2021 by Clarkey

[Andrew INT]

Thanks Clarkey, that's good to hear! I know that a raspberry pi would probably be a better solution, but I'm really not very IT literate. Extension cables I can deal with!

Cheers

[Clarkey]

That's my excuse too! Just some advice if you go down this route. Firstly I have covered all the chipsets to keep moisture out. The cable readily gets covered in ice and dew. Also I have added a small (30cm) extension on each end - again taped on - to reduce the risk of damage to the plugs on the active unit. As the cables are expensive I would rather risk damaging the plug on a cheap extra extension when I trip over it in the dark....

Edited May 9, 2021 by Clarkey

[symmetal]

1 hour ago, Andrew INT said:

My question is this: I've read (through an Amazon customer review) that each extension chipset in the cable counts as one device...and that a USB port is limited to five devices. Is anyone able to confirm this please? Does anybody use a 15m extension cable with one or more chipsets along it? I don't want to spend £60 or so on a cable that can't run four devices.

The Amazon review is confusing USB devices and USB tiers.

There is a maximum of 7 tiers allowable on a USB port on your computer. The computer USB port is 1 tier, and each USB hub connected in a chain also counts as a tier. Also all the devices plugged into the last hub in the chain also count as 1 tier. So you basically can have up to 5 hubs in a USB chain off 1 computer usb outport.

Each computer USB port can connect to  a maximum of 127 USB devices, connected to the output ports on all the USB hubs in the chain.

Your active USB extension cable is effectively a 1 output hub so counts as a tier. You can then connect a usb hub, another tier, to the extension cable at your mount to plug your devices into. If it's a 10 output hub you can connect 10 devices. If you have more devices than hub output ports you can chain up to 4 hubs from your extension cable.

It's best to use an external powered hub at your mount as the computer may struggle to power the extension cable, hub and all your devices if you use just a bus powered hub.

Using an active USB extension cable you won't be able to reach maximum USB 3 transfer speeds as the extension cable electronics will limit the maximum allowable speed in order to allow it to work over the longer distance. Unless you're planetary imaging with a large image size and a high frame rate, you won't really notice much  difference. 🙂

Alan

Edited May 9, 2021 by symmetal

[Andrew INT]

Thanks Alan for clarifying that! I was also going to buy an additional power supply for the cable. My current usb hub isn't powered- do you think that would still be okay?

[Budgie1]

I'm using a 15m USB 3 cable between my laptop & mount. I went for THIS ONE off Amazon and have it connected directly to the laptop at the male end and to a powered USB3 hub at the other. It's expensive but it's well built and the cable is quite heavy duty.

In my case I have an ASI120MM Mini guide camera plugged into the ASI294MC Pro, this is connected to the powered USB hub, along with the EQDIR cable for the mount and two USB powered dew straps. I don't have any extra power supply for the 15m cable and it works fine. I did swap back to my old active USB2 cable a few weeks ago and could instantly see the difference in the delay downloading the images from the imaging camera.

Just make sure the powered USB hub at the mount is USB3 as well, otherwise you won't see the extra speeds.

2 minutes ago, Andrew INT said:

 I was also going to buy an additional power supply for the cable. My current usb hub isn't powered- do you think that would still be okay?

Over 15m you will need some power for the cable, be it external (plugged into one of the chip sets) or from a powered USB hub at the mount. On the cable I got, the chip sets are at the mount end of the cable & in the middle. I already had the powered USB hub on the mount so I didn't need any additional power connection.

[symmetal]

2 hours ago, Andrew INT said:

Thanks Alan for clarifying that! I was also going to buy an additional power supply for the cable. My current usb hub isn't powered- do you think that would still be okay?

I would certainly recommend using a powered hub. The power supply for the extension cable may supply some extra current for the USB bus, but it depends on its design. Although your existing setup seems to run fine using the unpowered hub, using a powered hub would certainly help to alleviate any power issues which might occur in the future. Faults due to the 5V USB bus limiting the current momentarily when a filter wheel activates for example, can be difficult to track down.

If your active USB extension cable has an electronic module half way down as well as at the end this would count as 2 tiers as both modules are 1 port hubs. So you could still daisy chain 3 more hubs on the cable output if you so wished. 🙂

Alan

Edited May 9, 2021 by symmetal

[Andrew INT]

Thanks for the info Budgie1, that's really helpful...and reassuring! I had looked at that exact cable, and another one for about £40. I'll order the one you have. Did yours come with a PSU?

I'll also order a powered usb hub (thanks for the advice Alan). I have a £100 budget so should just about do it

[M40]

22 hours ago, Clarkey said:

I have covered all the chipsets to keep moisture out

I have used a plastic chocbox to enclose the mid point chipset, if you goto screwfix and search chocbox you will get the idea. HTH

[Budgie1]

2 hours ago, Andrew INT said:

Did yours come with a PSU?

Yes, it comes with one PSU which plugs into the side of one of the chip sets, although I've never needed to use it.