USB C mysteries

I have a USB C lap top charger. IE it is used to charge lap tops via a USB C connection.

Actually I have two of these. I use the spare one to charge my cell phone & my bluetooth headset (it’s faster than the wallwart chargers).

I also have a Snug power bank that I can use to charge cell phones (USB C or micro-USB), tablets, kindles, headset etc.

Now I bought my wife a very handy portable fan that can easily be placed where ever she is sitting and which also has a built in light. So this is very handy for her when she is knitting. It has a USB C port for charging.

Last night it ran out of battery. No problem… I’ll just use the lap top charger.

Only thing is it didn’t charge. No lights came on to indicate charging, and after an hour the batteries had no charge in them.

Puzzled I used the power bank. Straight away the charge light comes on. After 10 minutes or so the power bank is still on and the SOC display is going down. Eventually the fan was completely charged and the power bank then turned off.

So when is USB C not USB C?

Your mistake is to assume a laptop charger is just a laptop charger. They have a bunch of extra circuitries that does communication over the usb-c cable with the laptop. The laptop can dictate how much power it wants to draw etc on demand and the charger will change voltage etc to accomodate this. Now cellphones also supports this to a degree for quickcharge etc.

Anyways, there are things like USB PD (power delivery) protocols and QC (quick charge) protocols etc. It is possible the laptop charger is limited to only work when the communication for the laptop is opened up.

The fan’s problem is, it is possibly something very basic, doesn’t do communication, and so the charger turns off for safety reasons. Eg. to not blow up the fan in case it can’t handle the power the charger will put.

Technically, the charger is suppose to fall back to usb-a levels of power delivery, but I guess that specific charger does not.

Anyways, lots of reading you CAN do on the subject, but that is the summary.

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Yes. Silly me. The power brick supports but is not limited to Quickcharge 3.0. And obviously (now you’ve pointed it out) there has to negotiation between the charger and the object to be charged as to which charging protocol to use.

My phone has some sort of circuitry in it to manage charging and to allow various fast charge protocols. The fan, as far as I can see, has two no-name brand cells, slightly bigger than a flash light cell.

The power brick and the laptop charger obviously have different default modes. The power brick charges the fan, but not in any quick mode.

Thank you for your reply.

When I saw one of these for the first time (with the cable that was thicker than the USB C plug) I reckoned to myself I’ll avoid this lot for as long as I can.
Can’t say I’ve changed my mind either since then…

USB C standards or rather specs is a real minefield, almost like HDMI specs.

If you buy a USB C cable or charger, you have to read very carefully what you are buying and exactly what it supports.

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Correct me if I’m wrong but USB C doesn’t appear to taking over??

Indeed. If nothing is talking back, it should just remain at 5V max 2A or something like that. Like a dumb charger. At least, that is what I thought it does.

My wife forgot her USB-C style laptop charger at home one day. We were about 80km away when we realised this. We had to make a quick decision: Drive back to get it, try to buy one from a shop, or make do with what we have. Since it was Friday afternoon, Worcestor was the closest town (in the wrong direction) likely to have it, and trying a few phone calls were unsuccessful, I took the power bank from my bag and plugged it into the laptop, fully expecting it to not work. I was surprised to see the laptop accept the power and actually charge! Not very fast, not such that you can run it for hours on end, but enough that we could go with option 3: Make do.

The laptop is an Asus Zen-book. Pretty impressive little things.

Some of these cheap devices only connect the power pins. With USB-C you have to pull down one of the CC lines before you get 5V. My guess here is that the laptop charger actually implements the spec correctly, but the fan does not.

Some cheap chargers actually are just USB-A devices (some with a USB-C socket), so they just output 5V always, some support QC2, which can also output other voltages but with a much more primitive protocol.

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