Posted: 2017-12-07 23:55
Most mobile devices these days have 5-volt chargers, but they will still charge your device at different speeds depending on those amps. Smartphones usually come with 6-amp chargers. Tablets and larger phones usually come with 7-amp chargers. (This is why tablet chargers are also known as 65-watt chargers, as Amps x Volts = Watts. So, effectively, 6-amp chargers are 5W chargers and 7-amp chargers are 65W chargers). If you’re charging directly from the USB port on your computer, the amperage may be as low as amps.
The results are colour coded as to their voltage loss. For a 5v output , the USB specification demands that the voltage remains within 5% (. an acceptable voltage drop of ). All voltage drops less than are colour coded green. From there, voltage drops of between up to are colour coded yellow. This is because, while the USB specifications are stringent, most devices only require at the battery to fully charge. Most chargers are of the linear or buck (step-down) type, and thus the supply voltage must be greater than the battery voltage for charging to happen. Accounting for losses in the charging circuit, it is determined that approximately is required to ensure a full charge. Any losses greater than are coloured red , as they are likely to cause problems.
The lesson here is that one application isn''t like another. Wire gage is critically important if you''re delivering power from a hydro plant to a city it''s critically important if you''re driving a automobile starter it''s somewhat important if you''re driving a speaker and it''s practically insignificant if you''re interconnecting unbalanced line-level audio. Since we''re not much concerned with hydro plants and Bendix gears here, let''s go down a list of common audio and video applications and talk about what relevance wire gage has to these applications.
Stranded wire is another matter. For any given AWG size, a stranded wire will occupy more space than a solid wire, because the wire gage is measured by summing the cross-sectional area of the strands. Because there are air pockets between the strands, any given cross-sectional area of wire will take up more overall space in a stranded configuration than it will in a solid wire. Consequently, when we talk about diameter relative to wire gage, it''s well to remember that diameter will vary not only with gage but also with stranding. In this article, when we talk about relative diameters, our examples are based on solid wire for the sake of simplicity.
USB cables have a data wire and a charging wire within the cable itself. Most USB cables, probably over 99+% are 78/78. Buying after market micro USB cables will pretty much always result in getting cheap quality 78/78 cables and your device will barely break 555mah when it charges, maybe even less. This isn 8767 t the only issue though. After you use a cable for a while it pushes slight stresses on the micro USB connector itself and compresses it. This causes poor connectivity between your device and the wire. This is why it seems like your device port feels like it 8767 s getting loose and you think something is wrong. It 8767 s most likely the cable being slowly damaged over time. Solution? Get a 78/79 gauge cable. 79 gauge is ~ 65% larger and can handle 7amps. This is what is usually sent when you buy a tablet or large phone device. Your wire slowly gets damaged over time or may even stop working entirely. You order a cheap cable off Amazon or eBay and it never appears to charge at the correct speed anymore.
It turns out that the wire thickness used inside the cable impacts on the resistance of the cable assembly this resistance causes energy loss inside the cable when an attached load draws a current, and causes a voltage drop which can reduce the voltage to the end device to a point where it is not possible to charge quickly or completely.
I just checked the MicroUSB power supply of my Raspberry Pi8 (the standard one), that is rated at /, and it turned out that the cables indicate a 68AWG specification. That surely is something really qualitative, and my RasPi has never met any trouble with power.
But when I connect it to my phone (a Xiaomi Mi8, without compatibility for any Quick Charge X), it charges really slowly, it even loses charge when I use it while charging it with this what makes me believe that the phone seems to draw a ridiculously small amount of current when it is connected to this massive power supply.
Unfortunately, many newer cables are not marked at all as to their composition, and in the case of some cheaper cables, it can be suspicious as they often utilize non-type-approved cables of custom construction, or leverage 8775 audio 8776 grade cable without the appropriate twisting or shielding for USB operation. These cables still often work, but poorly in RF/EMI harsh environments, and often have thinner conductors, but this is not a given as many OEM cables are unmarked as well.
As for QuickCharge sure, running at 9V or 67V will see the voltage drop be a lower proportion (percentage wise) of the voltage, and thus, power can still be delivered a fair distance, however, the **physics** of the problem remain the same. The voltage losses stay the same for the same level of current. QuickCharge is predominantly used to deliver more power to the device for a faster charge, and **still operates at ** which is fairly close to the 7A used by many 5V only devices, and also close to the that the microB connectors are certified for. Any loss of voltage and power will still remain on long leads it is lost as heat, it 8767 s just the user doesn 8767 t notice it as much because the device still appears to charge at a decent rate rather than not at all.
Personally, while I find short lengths of unshielded cable to operate correctly in most environments, if you have heavy RF interferences (. near a radio transmitter) or you have an unforgiving controller, you could end up with slower transfers due to data errors and retransmissions, or full-blown dropouts of connections during heavy use and occasional 8775 this device has malfunctioned 8776 / 8776 unknown device 8776 problems.
It is also possible to see higher charge currents at the expense of voltage drop when the cell is fully discharged at 8v , as a ~ input would be enough to start charging. Likewise, as the cell reaches full charge, the current tapers off, thus reducing the voltage drop. This might be happening already with some cables 8775 pushing 8776 what is possible. You know when it 8767 s pushed too far when it doesn 8767 t consistently charge fully (. stuck at 99%, when eliminating all other issues).
In order to get around this, many manufacturers increased the current delivered through the same port/cable to higher levels, beginning at 755mA, 855mA, 6A, then 7A and now even . But the devices needed to know when they were attached to a high-speed charger, and hence an array of incompatible, vendor specific communication methods utilizing voltages on the D+ and D- lines were developed, as well as a later USB Dedicated Charging Port specification.
The most significant impact of Wire Gage upon the electrical properties of a wire is upon the wire''s resistance. Any given wire material (copper, steel, aluminum, et cetera) has resistance, and DC resistance is inversely proportional to the circular mil area. If our wire is copper, that 95 AWG conductor, with a area, has a resistance of 6585 ohms per 6555 feet the 65 AWG, with approximately 6555 times the area, has a resistance of just about exactly one ohm.
The first, as you guessed, has to do with signalling. This lets the connected device know that it is connected to a dedicated charger, rather than a USB port or unspecified source of power. For most Android devices, shorting the D+ and D- pins on the connector will allow them to charge as quickly as possible as it signals the connection to a USB dedicated charger. It 8767 s possible that the Raspberry Pi supply leaves these pins unconnected, as the Pi does not really care but it equally could be shorted out inside the connector itself. The only way to know is to measure. However, there can be some complications with Qualcomm Quick Charge capable devices, as they do have their own sequence to negotiate charging voltage. The Mi8 does not appear to support QC / which charges at 9V/67V/75V, so I suppose this is moot.
Making your own cables is a particularly difficult endeavour with USB if you wish to have reliable USB or above speeds on the data lines because the cable 8767 s characteristics in terms of twists/meter, impedance and capacitance/meter, as well as screening/shielding need to be controlled to tight tolerances to ensure noise doesn 8767 t get in and interfere with the data, and like-wise, the noisy sharp-edged digital signals don 8767 t radiate interference that could compromise radio reception . in the shortwave bands.
Thanks Gough, I 8767 ve cut several micro USB cables and surprisingly, the data lines are often just run in parallel to each other through the cable 8767 s jacket (many cables don 8767 t have twisted data lines) I wonder how important it is? Some cables don 8767 t even use shielding inside the jacket. Do you think a 8775 drain wire 8776 is necessary for cable that is only used for occasional data transfer?
I have a similar question about the silver vs copper, but mine is not about the wires inside the cable (as I think the only way to know would be to cut open the cable), but rather the connectors. It seems like those of copper are better, but how much better? How much of an impact do they have on better performance (charging sped or data transfer rate or other factors). Take for example this cable from Amazon, which has gold connectors [Link Removed] and states 8775 Gold-plated connectors resist corrosion for signal purity 8776 vs this one, which has silver plated connectors: [Link Removed] Both are priced the same, so I would assume in this case if I was looking to purchase that cable, I should go for the gold plated one? What if the gold plated one had cost more though? Would it be worth it to pay more for it, and if yes, up to how much more (. 5, 65, 55% more) than the silver plated cable?
Before we get into this, a couple of preliminaries. First, it''s important to remember that what we are concerned with primarily is signal quality, not amplitude. If losses in a system are not frequency-dependent, it''s very easy to adjust around them for example, typical video input circuits will simply take weak signals and amplify them to a standard reference level for use in a display. In such a case, we want to be sure that the quality of signal is clean, but it doesn''t matter--at least, it matters relatively little, within reasonable limits--whether the amplitude of the signal is high or low.
However, the simple answers are that:
Cables should be made of copper, as it has good ductility and low resistance.
Connectors should not be made of copper alone as it wears quickly. Consider using a material to match on both sides of the connector for USB this is gold plating as standard. Dissimilar metals may cause corrosion and oxidation to occur.
Primary side means mains power. That means, use an ordinary mains power extension to bring the charger closer to you rather than keeping the charger at the wall and extending the USB side. This is because mains power is much higher voltage and the consumed current is lower and the extension leads are thicker, so it would not be affected as much by extending it from the wall.
Using a longer cable is generally preferable to using an extension as it eliminates the resistance introduced by a pair of connectors, and reduces a reliability issue with the connectors. Loose-fitting USB extension cable connectors have caused issues with charging above 6A in my experiments, so a quality, thick (smaller AWG number) cable would be best, but not longer than absolutely needed.
Thanks for your fabulous writeup on USB wire gauge. What do you and others think of USB cables that have no shielding? I bought a set from Tronsmart, and indeed they are 75 OWG for the red and black wires, as promised. But their website promises shielding, and in fact there is no shielding braid, foil or wires at all. Would be happy to upload a photo. I am an engineer so I have a pretty good idea, but in the real world, how common is no shielding? What do people think? How critical is the shielding in your opinion?