USB spec tolerances allow voltages as low as 4.45V. I've personally measured several devices between 4.85 and 4.9 that successfully charged anything I plugged in.Keep in mind that a 4.88 volt battery pack is not even theoreticaly able to supply the 5 + volts needed to charge a phone. Besides that, a USB charging arrangement does indeed need to communicate with the phone before any power transfer can happen. The entire USB concept is based on a whole lot of communication going on.
The Mac products in our family seem to be very picky and demand a Mac charger.USB spec tolerances allow voltages as low as 4.45V. I've personally measured several devices between 4.85 and 4.9 that successfully charged anything I plugged in.
As for communication, I know many power hungry devices rely on communication to determine whether they can draw higher currents or not, and they'll default to a lower current draw if they don't get a response.
I haven't seen anything myself that wouldn't charge on dumb devices with no communication. I'm not saying such devices don't exist, but I think they're unusual.
The whole realm of demanding proprietary accessories is rather evil, at best. I know that there are arguments offered that convince our legislators, but that is because the lobbyist with the most money wins. I have HP laptop computers that will not accept other than an HP power supply, which costs $120, as opposed to $25 for a good brand one from Amazon. The other brands are cheaper.One of the reasons I hate those products. Our iPhones will allow any charger, but only work with Apple certified cables. So ridiculous. Oh, well.
That depends on what device you're trying to charge. This stack exchange discussion seems to have a lot of good information on the subject:Lots of misinformation in this thread. What you need is two voltage dividers setting the voltages on the D+ and D- pins. I am too lazy to look up what they need to be (for various charging rates). If you have a charger that works, you could measure these voltages and duplicate them.
Thank you.That depends on what device you're trying to charge. This stack exchange discussion seems to have a lot of good information on the subject:
To make an Android phone charge, connect the Data +/- wires together ( green / white), this will put the phone in Charge mode,and feed it with 5V...Thanks for all reply.
clarify some thing as:
1. the battery source I used are Ni-Cd from a cordless drill 9.6 V now (was 4.88V) + 7805, output 4.93 V;
2. The I phone charger measured output 5.11V stable, and the one Android charger output 3.5-4.4 vary (don't know why?), which is the best charger for me;
3. The i phone can be charged by : both chargers and laptop; the Android can be charged by both chargers, laptop, and battery bank （bought on EBAY）;
4. only the battery bank can be charged by my battery source.
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