USB hub, reducing the voltage.

[Freff]

Hi electronic gurus.

I need to reduce the voltage to my powered usb hub. At present it is used indoors and therefore I can use the mains adapter which converts it to 5v.

I want to be able to use the hub in the field with just the 12v power pack. Is there a cable with resister or something I can make up to do the job. A diagram with details would be very useful, I'm not electronic savvy. Many thanks.

[astromerlin]

Hi, A resistor wont do it. What you need is a dc to dc converter, something like this.

http://www.ebay.co.uk/itm/DC-DC-Converter-Regulator-12V-Stepdown-to-5V-3A-15W-Car-Power-Supply-Module-/271011531461?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item3f198bcac5

[Macavity]

Building or BUYING a 12v to 5v converter is entirely possible. But not always 100% straightforward! I suspect you need to have some notion of the hub's current requirements. Check the hub itself or the mains adapter? How many ports does the hub have have? The USB standard specifies 500mA max loading on each port - but some only supply some (reasonable) fraction of this. Attempting something similar myself shortly.

Added: Something like the above would save some effort building / researching - Ta, Astromerlin!

[pete_l]

If you put a dropper resistor in the power line to the hub, the voltage seen by the hub and any peripherals being fed from it will vary, depending on the amount of current they all draw.

This is not a good situation. You should consider using a stabilised power supply to feed the hub.

The simplest would be a 7805 regulator chip (suitably spec'd, they come in different current ratings), but a small switch-mode power supply will be more efficient (generate less heat). The one astromerlin refers to should do the trick

[Zakalwe]

Maplins do a 12 DC to DC converter. Any caravanning supplier should also be able to source one too.

[Freff]

My dilemma is my non powered hub appears to fail when using my netbook. My netbook connects my grab-n-go set up by a 5mtr repeater usb cable terminating with a 4-way unpowered hub. That supplies a 350D, QHY5 camera, EQmod adapter and serial-usb converter.

All's well if I use my Vaio laptop, but not if I use the Netbook. I don't understand why this is, I thought the usb socket supplied 5v on all conputers.

I like the idea astromerlin suggests, I really don't want to making up anything I can buy that cheaply.

[Gina]

Insufficient current capacity to power all the devices, I would guess. HTH

[Zakalwe]

Insufficient power, as Gina says. Or you might be exceeding the number of hubs on a single USB bus (5 IIRC). The Active USB lead will count as at least one hub (some are two or more), the hub at the end is another one. The Netbook probably has a hub on the motherboard.

[Gilez]

I'm not sure what rating you need or the current you intend to draw of your hub, but maybe a modified cigarette lighter USB adapter might do the job.

You can definitely get them rated at 2a, but might be able to get a higher rated one from somewhere.

[jackrussell0232]

Tony,

By far the simplest and safest way is to use one of these http://www.amazon.co...64683101&sr=1-1. Its a 12v (native) usb hub.

They do 4 port or 7 port versions and reviews seem pretty favourable. I've been using one for a while now, as it was the last thing I had needing 5Vdc. Now I've got everything running off 12V.

Hope this helps,

Jack

[Jessun]

By far the simplest and safest way is to use one of these http://www.amazon.co...64683101&sr=1-1. Its a 12v (native) usb hub.

Just +1 for that hub. Never a glitch.

/Jesper

[Freff]

Thanks

Tony,

By far the simplest and safest way is to use one of these http://www.amazon.co...64683101&sr=1-1. Its a 12v (native) usb hub.

They do 4 port or 7 port versions and reviews seem pretty favourable. I've been using one for a while now, as it was the last thing I had needing 5Vdc. Now I've got everything running off 12V.

Hope this helps,

Jack

Thanks Jack I just found the same http://www.amazon.co.uk/StarTech-com-Mountable-Port-Rugged-Industrial/dp/B001H7AFO6/ref=sr_1_1?ie=UTF8&qid=1364684448&sr=8-1 after looking on CN. I think that will do nicely.

[pete_l]

My dilemma is my non powered hub appears to fail when using my netbook. My netbook connects my grab-n-go set up by a 5mtr repeater usb cable terminating with a 4-way unpowered hub. That supplies a 350D, QHY5 camera, EQmod adapter and serial-usb converter.

I had a similar problem, except I was simply trying to run a webcam off a 5 metre USB extension cable. The camera worked fine when plugged directly into my lappy, and looked like it was working when plugged into the long cable (i.e. the green light came on). However it failed as soon as I tried to open the device to take video from it.

It turned out that the resistance of the wires inside the cable that carried the +5V / 0V supply was so high that when the webcam was active (as opposed to just sitting there, looking pretty) and supposed to be sending video, the extra current it drew dropped the voltage at the webcam down to 3.6 Volts - not enough to run its electronics. The moral of the story being that long cables have significant voltage drops - whether due to the thinness of the conductors or poorly crimped connections.

After that I made sure that all my USB cables and hubs were self-powered at the remote end and didn't rely on the power coming from the PC / laptop,

[Macavity]

Just as a matter of personal education: Each time you connect a USB device to a Laptop, Hub etc.,

it is assigned a unique, *constant* port number, maybe? Seems true of ASCOM, EQMod, Focussers?

Sometimes this is manifest in the "Device Manager", but sometimes not? I should know, but...