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Why do some devices not work properly when a USB hub is involved?

pipnina
By pipnina
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Go to solution Solved by Kisai,
2 hours ago, pipnina said:

I've been using astronomy gear for a while now, and for ages I've been annoyed by my astro cam glitching out and needing a reboot as it would refuse to take pictures randomly. And last night it refused to take any images... Until I unplugged it from the USB hub and plugged it into my laptop directly. Then it worked perfectly with no complaints.

 

There's three things in play here:

1. Bandwidth

2. Power

3. Noise

 

When you plug the device directly into the PC, it's plugged into the "root hub" and has 100% of the available bandwidth and power that port has.

 

When it's plugged into a hub, powered or not, it's sharing the bandwidth, and the hub doesn't give 35 watts of power to a USB 2.0 device. A powered hub tends to only give 250mw per port of power unless it's designed for "USB fast charging" (which some laptops with 9th gen Intel CPU's have.)

 

Noise comes from other devices just being too "loud", for example a bluetooth dongle or a WiFi dongle, or a camera are too noisy when plugged into a hub that they will bump off other devices.

 

 

2 hours ago, pipnina said:

But the mini camera for guiding has no issues being plugged in via the hub, nor does the filter wheel, or focuser.

 

This isn't some cheapo USB hub either. It's a £250 Pegasus power box advance V2 designed for astro kit. I could understand if cheapo hubs had issues (I have used off the shelf normal hubs which handled matters much worse than the Pegasus to be fair), but this is intended for use with astro equipment and I was very happy being able to get my laptop to scope cabling done through only two cables (one to USB hub and one to mount, since the hub and mount both want to be treated as rs232 devices or something weird like that so they didn't work daisy chained)

 

That Pegasus box though takes 12v power, distributes it via 4 live ports and 2 PWM dew heater ports, and also acts as a USB3 hub and given the price shouldn't it be able to direct USB data properly like the USB controller in the laptop manages multiple ports? What am I missing here?

 

Honestly if it's having problem's it's the underlying USB controller. As much as hubs say they do X and Y, what they really mean is X or Y, and not at the same time.

 

USB is such a master clusterf--k when it comes to compatibility between devices that it's amazing it ever works at all.

 

 

Posted

I've been using astronomy gear for a while now, and for ages I've been annoyed by my astro cam glitching out and needing a reboot as it would refuse to take pictures randomly. And last night it refused to take any images... Until I unplugged it from the USB hub and plugged it into my laptop directly. Then it worked perfectly with no complaints.

 

But the mini camera for guiding has no issues being plugged in via the hub, nor does the filter wheel, or focuser.

 

This isn't some cheapo USB hub either. It's a £250 Pegasus power box advance V2 designed for astro kit. I could understand if cheapo hubs had issues (I have used off the shelf normal hubs which handled matters much worse than the Pegasus to be fair), but this is intended for use with astro equipment and I was very happy being able to get my laptop to scope cabling done through only two cables (one to USB hub and one to mount, since the hub and mount both want to be treated as rs232 devices or something weird like that so they didn't work daisy chained)

 

That Pegasus box though takes 12v power, distributes it via 4 live ports and 2 PWM dew heater ports, and also acts as a USB3 hub and given the price shouldn't it be able to direct USB data properly like the USB controller in the laptop manages multiple ports? What am I missing here?

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Posted

Signal degradation, usb controller overload with too many devices...

 

Basically ones things split at the usb port any odd behavior can be expected and some equipment will simply load the controller more than others. When split this can cause issues.

 

So the only real way is to have it plugged in directly or expiriment with what order of devices works

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  • Solution
2 hours ago, pipnina said:

I've been using astronomy gear for a while now, and for ages I've been annoyed by my astro cam glitching out and needing a reboot as it would refuse to take pictures randomly. And last night it refused to take any images... Until I unplugged it from the USB hub and plugged it into my laptop directly. Then it worked perfectly with no complaints.

 

There's three things in play here:

1. Bandwidth

2. Power

3. Noise

 

When you plug the device directly into the PC, it's plugged into the "root hub" and has 100% of the available bandwidth and power that port has.

 

When it's plugged into a hub, powered or not, it's sharing the bandwidth, and the hub doesn't give 35 watts of power to a USB 2.0 device. A powered hub tends to only give 250mw per port of power unless it's designed for "USB fast charging" (which some laptops with 9th gen Intel CPU's have.)

 

Noise comes from other devices just being too "loud", for example a bluetooth dongle or a WiFi dongle, or a camera are too noisy when plugged into a hub that they will bump off other devices.

 

 

2 hours ago, pipnina said:

But the mini camera for guiding has no issues being plugged in via the hub, nor does the filter wheel, or focuser.

 

This isn't some cheapo USB hub either. It's a £250 Pegasus power box advance V2 designed for astro kit. I could understand if cheapo hubs had issues (I have used off the shelf normal hubs which handled matters much worse than the Pegasus to be fair), but this is intended for use with astro equipment and I was very happy being able to get my laptop to scope cabling done through only two cables (one to USB hub and one to mount, since the hub and mount both want to be treated as rs232 devices or something weird like that so they didn't work daisy chained)

 

That Pegasus box though takes 12v power, distributes it via 4 live ports and 2 PWM dew heater ports, and also acts as a USB3 hub and given the price shouldn't it be able to direct USB data properly like the USB controller in the laptop manages multiple ports? What am I missing here?

 

Honestly if it's having problem's it's the underlying USB controller. As much as hubs say they do X and Y, what they really mean is X or Y, and not at the same time.

 

USB is such a master clusterf--k when it comes to compatibility between devices that it's amazing it ever works at all.

 

 

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