Long usb leads

[wjwren]

I have a 4m usb c lead to charge the phone but it takes forever on the samsung turbo charge . likewise the nest camera drops out when using a similar lead. Why is this. They were off ebay. Have i bought cheap crap or do usb leads just not work after a metre?

[G600]

I've used longer (although not 4 meters long) Anker cables without any problems

[colin79666]

The longer the cable the better quality it need to be to work. Cheap cables are often thinner and therefore over a distance they lose more power due to resistance. Even a good quality cable may struggle to provide high speed charging over more than 2-3m. USB was never designed to deliver much power, it is really a data cable but has been adapted over the generations to support higher currents.

[imck]

Have had problems with standard USB 2.0 Cables running cheap Doc Scanners when they are too long.
If just charging and no Mains Socket near the Phone, can you use a Mains Extension?

An Active USB Cable may be the answer. Have never used one myself.

[tribbles]

Basically what colin said.

The resistance increases with length, and this reduces the voltage that reaches the other end. I have used PortaPow cables in the past, which have thicker power wires (this reduces the resistance).

An active USB cable will boost the data lines by using the power in the cable - and won't boost the power.

Proper solution is to get the mains closer...

[Captain Raymond Holt]

A-level flashback

Isn’t there an inverse square law or something?

Double the length, half the power, or something?

disclaimer- I was st at physics

[s p a c e m a n]

I bulk bought a load of itech branded leads last year because they looked more durable than the normal stuff. The 4m ones seem to charge as fast as the short ones and they give the same countdown time when I swap between them.

[tribbles]

Captain Raymond Holt said:

A-level flashback

Isn’t there an inverse square law or something?

Double the length, half the power, or something?

disclaimer- I was st at physics

Explanation:

The equipment being powered has an effective resistance (load resistance), and the cables also have a resistance.

The voltage that the equipment sees is the result of a potential divider, so if the cable resistance equals the load resistance, then the voltage is halved.

If the cable resistance is zero, then the voltage is the voltage coming out of the power supply (there are no losses).

The voltage is actually equal to the power supply voltage multiplied by the load resistance, divided by the sum of the two resistances.

The resistance along the cable is linear with length, so this means the voltage is sort-of proportional to the length (and not the length squared).

Disclaimer: I used to design power supplies

[deckster]

3m is all you can expect out of USB. Sometimes depending on the cable and what's plugged into each end, you might be lucky and get a bit more. But 3m is really the point at which it significantly degrades.

You can get longer ones which use a fibre-optic cable and an adaptor built into the connectors, but those are £££.

[Heartworm]

deckster said:

3m is all you can expect out of USB. Sometimes depending on the cable and what's plugged into each end, you might be lucky and get a bit more. But 3m is really the point at which it significantly degrades.

You can get longer ones which use a fibre-optic cable and an adaptor built into the connectors, but those are £££.

Working distance of USB is 5m it not? But that's for using as an interface not for power.

[deckster]

Heartworm said:

deckster said:

3m is all you can expect out of USB. Sometimes depending on the cable and what's plugged into each end, you might be lucky and get a bit more. But 3m is really the point at which it significantly degrades.

You can get longer ones which use a fibre-optic cable and an adaptor built into the connectors, but those are £££.

Working distance of USB is 5m it not? But that's for using as an interface not for power.

Depends but yes - typically 5m for USB2 and 3m for USB3.

[anonymous-user]

I think the distinction made above between use for "power" and "signal" is correct. I use a very long USB (at least 4m) between PC and a DAC/Amp. Seems to work OK but I suspect there is some degradation over that distance. A CD played on the CD transport under the amp sounds a bit better than the same CD played in the computer.

If you want to send USB or HDMI a long distance I know you can buy quite cheap adaptors on e.g. Amazon which will enable use of Ethernet cable instead of running a long USB or HDMI. https://www.amazon.co.uk/HDE-over-Extension-Cable-...

I believe that with computer Ethernet cable the labelling of wires "cat 5" or "cat 6" etc describes the amount of signal degradation along a particular length of wire. Problems can be suppressed by twisting wires around each other when they are used for signal. I have never seen a twisted USB lead. Another method of protection can be screening with metal braid or foil to create a Faraday cage. The conductive metal screen reduces the ability of external noise to affect the signal by minimising capacitively coupled noise from other electrical sources.

The "twisting" thing can be seen if you pull apart an old GPO telephone cable. The larger cables contain "twisted pairs" of individual insulated wires. When you use a twisted pair any source of electrical noise is equally close to each of the two wires. Both wires pick up roughly equal noise voltages with the same polarity and since the current running in one wire is equal but opposite of the other wire, the two magnetic fields cancel each other out.