USB Charging

[Deckhanddave]

Hi

I've noticed a few posts in various areas on the web regarding Ployer tablets and charging. I decided to look into the charge rate of USB chargers and found quite a lot of variance. Some of the people who have had problems with slow charging etc.. might find the following article of use.

How USB charging works, or how to avoid blowing up your smartphone | ExtremeTech

Dave

 

[ttttkk]

Hi, I just bought my first tablet, and which is momo 12. I tried to charge it with usb but with no success.

 

[Deckhanddave]

Hi ttttkk

I can tell you that my Momo7 has a 2000mah charger with it. That's quite a high rate and it still takes some time to recharge. If you try using the USB on a computer to charge it, then it may not charge at all or if so, very very slowly. This is due to the output of a computers Usb port. Also, if you use a mobile phone usb charger, then the output may not be high enough to charge it within a reasonable time. For example my Momo charger is 2000mah. If it takes 4 hours to charge using that charger then it will take about 16 hours to charge using a phone charger rated at 500mah, if my math is correct. Anyway, that gives you an idea of what you can expect. You haven't said exactly how you tried to charge it other than by Usb so it's difficult to offer any other advice.

 

[J515OP]

That is a good article and is correct as is your math. Standard USB computer devices run fine at 500mA (keyboards, mice, usb stick, older mp3 player, etc.). Modern devices such as smart phones, e-readers and tablets require around 2000mA to charge properly though. If you use a standard USB port it can take a very long time to charge or if the device is in use at the time, it may actually continue to lose charge. The best policy is to use the USB cable and wall charger that came with the device to charge that device properly.

 

[Deckhanddave]

Hi J515OP

Thanks for the confirmation. When I started looking into tablets I was surprised at the myths and uncertainty surrounding Usb charging. With that in mind I tried to dispel some of it and reduce the ignorance surrounding it. Another worry for many is overcharging, ie... using a more powerful charger than necessary. It shouldn't be possible. The item being charged is responsible for drawing the amount it needs and not the charger pushing it. So, a 500mah charger supplied with a phone will be very very slow at charging a tablet needing 2000mah but a tablet charger at 2000mah will charge a phone at the rate set by it's manufacturer and will not blow it, unless there is a fault with the item being charged.

One other thing that bugs me somewhat is the way manufacturers are showing their ratings for Usb chargers. I've found several saying they are rated at 5 watts/10watts some saying they are rated at 1000mah or shown as 1amp but then you find they are rated at half that when they are twin ports. I've been looking for a twin with 2000mah each port. Sounds easy, it isn't. Another I found had four outputs. Again rated at 10 watts but when I delved further they were 500mah each. If you have any input you'd like to share on this, J515OP then please add it to this post. It may help others that read it and that's what I'm trying to do.

 

[J515OP]

Yes, you are correct again. For now the standard carried through USB is 5V. The formula for is Watts = Volts x Amps.

So given a 5V standard you get the following common outputs.

Standard USB 5V @ .5A = 2.5W of charging power.
Standard USB 5V @ 1A = 5W of charging power.

High power USB 5V @ ~2A = 10W of charging power (specialty bricks included with newer Android and iOS tablets are ~2A).

Microsoft Surface RT 12V @ 2A = 24W of charging power (unusual among current devices).

Most of the time the only information you get without reading the fine print (if you can find it) is "works with iPad" which means the output is 5V @ ~2A. Also not commonly mentioned is that if there is more than one USB port the total output will be split among the ports. So a two port USB wall charger indicating that it will charge at 1A will only charge a single device at that rate. If a second device is plugged in then the charge rate becomes 0.5A for each device doubling the charging time.

As always it is caveat emptor (let the buyer be ware). This only confirms that you need to carefully research the charger you are buying and if in doubt use the factory included solution (cable and brick) for your device.

JP

 

[Deckhanddave]

Nicely put. I'm now hoping that anyone who is trying to get info on Usb charging has enough info from this to know what they need. When I first started looking into it I knew very little. Now, I believe, I'm pretty clued up and have most of the answers I needed.

One last thing I would mention is, on several occasions I've read about cross cables and product specific cabling in relation to charging. I believe, from what I've read, is that people sometimes use product/manufacturer specific cables and chargers with other brand products. The simple way to avoid this problem is to find a generic Usb charger with a suitable generic cable or that supplied with your product. If it is a 'generic' Usb cable or charger then it should conform to Usb standards which says it should be compatible for use with any Usb product. I believe this information correct but wouldn't be surprised if there is an anomaly out there somewhere. Any further input J5150P? Lastly, is there any info or item regards Usb charging that I've missed and might be raised here for future reference? If not, I'll stop posting on this unless someone posts a comment or question.

Dave

 

[leeshor]

One thing you mentioned was the possibility of using a charger that's to strong. Again, you are correct in that the devices will adjust and draw what they need. I have a charger that outputs 15v DC when plugged into my tablet but 5v DC when I use it for my phone. The ma rating is adjusted accordingly.

 

[J515OP]

Dave, I hesitate about recommending generic USB cables for one reason: Barnes & Noble Nook devices use a special micro USB tip with extra pins for even faster charging. Using a generic cable will not provide these pins and therefor will restrict the charging rate compared to the factory Nook cable. If Nook devices do this then surely there must be others out there that are doing it also. Just make sure you research your particular device and if charging seems slow, take a good close look at the specs and cables involved.

JP

 

[Deckhanddave]

I knew there would be some anomalies out there and you have one You are spot on right and I believe that is the case, because mini/micro Usb for charging's sake doesn't have to totally conform to Usb standards. However, using a generic in your case, whilst it may slow down charging, won't do it any harm and I think that is the point to remember. In theory, I say theory because I can't be 100% sure it's fact, you should be able to switch around with Usb chargers and not do any harm at all. That was what appeared to worry most people on the postings I read in regards to Usb charging and what I wanted to try and help clarify.

 

[J515OP]

I can verify that it only results in slower charging, no harm done People can rest assured that they will not damage their devices as long as they are using standard/generic USB cables and ports.

 

[Deckhanddave]

Thanks again for that J5150P. I guess that finishes this thread off unless, as said before, someone posts on it. Now I've got a couple more fish to fry. Skype problems. Sandisk's Memory Zone not working. Video's not playing since moved to SD card. hey ho, why I 'love' technology! I'll check what's already posted and create a new post if i can't find any. TTFN