View Full Version : tesing voltage of USB port

31-01-2006, 04:59 PM
I have had 2 USB cables that connect a radio controller for model airplanes (to enable simulation) to a desktop computer "expire" - The USA supplier sugests that the voltage of the USB port may be to high

Is any one aware of a way to test the voltage of a USB port?


31-01-2006, 05:12 PM
The outer connections on the A connector should be regulated at 5 volts and will be able to supply 150 mA current.

The computer USB port would "expire" if the voltage was too high, not the cables....

Do you know exactly what happened to the cables? The excuse does not sound credible, the USB controller would not normally permit excessive voltage or current.

Billy T
31-01-2006, 07:40 PM
I agree with GF.

However, are they just plain cables with an USB connector at each end, or do they have a plug at one end and an interface unit for the radio controller at the other?

If you are not sure, can you post details so we can look the product up on the web?


Billy 8-{)

01-02-2006, 08:20 PM
cable comes with program Aerofly pro

Cable connects to USB port and has dongle that appears to give the program it registration, with an interface to the radio controller.

Loaded up good first time - after reboot would not regonise the cable, supplier sent new cable - same problem again - supplier suggest USB voltage as problem.

search Aerofly website and chat rooms without success.

Billy T
01-02-2006, 09:41 PM
It would be very unusual if the normal variations that could perhaps occur on a USB port were able to damage any attached device.

Even at +20% it is only 6 volts. Similarly, the USB voltage is derived from your power supply, and although I don't know if USB protocols add a further voltage regulator between the PSU and the port supply, it is pretty certain that they are derived from a regulated source.

Metering the USB voltage would not be difficult though, all you need is a suitable meter and Google will tell you what pins to check.

Your problem could also be software related and the computer may be losing sight of the device after one load cycle. I have a test instrument that has alzheimers and can't remember where it has been even in its own software environment. It works well on the parallel port of one computer but wanders off on another, and won't even wake up on my laptop unless it is running on mains.

If you think that port volts are the problem, load the software onto another computer and try it.

Did you sent the first cable back for testing?


Billy 8-{)


Billy 8-{)

Graham L
02-02-2006, 12:02 PM
About all I can think of is that the device might be built for 3.3 volts. I'm not sure whether that's supposed to be "legal" in USB. Even if it is, it's so easy to protect against 5V on 3.3 that the manufacturer should have done it.

I have seen references to 3.3V in USB devices, but I think it often refers to conversion for 3.3V logic. Most PC motherboard logic is 3.3V now, and I'm suspecting that the parallel port on one of my laptops is 3.3V -- the "highs" I measured this morning were just a bit over 3V. I can correct for that in my device by dropping the 5V supply to the chip which receives the signals. But I know that laptop gives 5V at the USB port ... I sometimes use it as a power supply. :D

Could it be the power manager shutting down inactive USB ports? That can cause nasty problems. I don't think a licence dongle would be very active.