:wink: Did You Know ...

Andy_P · Posted: Fri Jun 27, 2008 2:08 am Post subject:

Voltage supplied on on a USB port is a defined simple standard - 5V.

Current capacity is slightly more complicated.
The USB spec. says that a receiving device must first connect in a low-power mode (drawing 100 mA maximum) and state how much current they need, before switching, with the host's permission, into high-power mode up to a maximum of 500mA.

Mains and car chargers are not intelligent hosts and are also deliberately designed to be able to supply more current than this, which will help to charge the battery quicker.

So on balance I reckon "rtj70" wins... Cool

The method by which the devices recognise when they are connected to a dumb charger rather than a PC, is not as well implemented as it could be. The car charger for my TomTom works fine , but a Garmin Nuvi would often decide to go into computer link mode when it was connected to it. Pulling the cigar lighter plug out momentarily would sort it out, but pulling the USB plug out wouldn't.

lbendlin · Posted: Fri Jun 27, 2008 2:59 am Post subject:

guys, you are all wrong. There is much more to USB charging than just the voltage.

1. Voltage : 5 V. UNIVERSAL
2. Amperage: a PC port provides 500 mA. Not enough for most devices. Good wall or lighter chargers provide 2 A, bad ones only 1 A or less
3. Data line signaling!!! As MaFt was mentioning sometimes the data lines are used to signal slow/fast charging.

In the worst case scenario (think iPAQ 310) you can ONLY use the vendor charger. All other USB chargers make it look like they charge the device but in reality they actually drain the battery. Read my review.
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Andy_P · Posted: Fri Jun 27, 2008 3:17 am Post subject:

Strawbs · Posted: Fri Jun 27, 2008 3:27 am Post subject:

Strawbs · Posted: Fri Jun 27, 2008 3:35 am Post subject:

Floriank · Occasional Visitor Joined: Jul 02, 2007 Posts: 22

Yawn......... Wink

rtj70 · Regular Visitor Joined: Jun 18, 2005 Posts: 144

When my TomTom 720 is plugged into my PC but not connected to home it shows up as a single USB mass storage device using 500mA. If I connect, because of the memory card it appears as 2 such devices each taking 500mA.

Since 500mA is all the port will provide then it is enough for a TomTom 720 to charge/run. The same power is drawn/used by my iPod Touch.

Strawbs · Posted: Fri Jun 27, 2008 12:31 pm Post subject:

rtj70 · Regular Visitor Joined: Jun 18, 2005 Posts: 144

"and when your TT 720 is plugged into the mains?"

No idea because (a) I do not have a mains charger nor need one and (b) I do not have anything to measure current draw for any of my electrical items in the house.

franb · Banned Joined: Aug 10, 2007 Posts: 244

Just my two penn'orth.

Doesn't matter what current it provides (assuming it's sufficient) as the device (any) will ONLY draw what it needs; not the max available.

lbendlin · Posted: Fri Jun 27, 2008 2:31 pm Post subject:

True, but if the max available is 500 mA, and the charging circuit could handle 1.5A this basically means it takes you at least three times as long to charge the battery as would be needed.

And before you repeat my mistake - I had a "1 A" USB car charger connected to two devices , a GO910 and a One XL (via Y-cable). The charger worked for a while, then blew up, delivering straight 12 V to both devices. Both motherboards had to be exchanged.

Trevor1234 · Posted: Fri Jun 27, 2008 4:14 pm Post subject:

Hi Strawbs
Now you can see how easy it is to start a war.
_________________
Tomtom Go 720.
Navcore 9.510
Central and Western Europe v855.2884
GPS World Traffic cameras
Home 2.7
iPhone 3G

Strawbs · Posted: Fri Jun 27, 2008 4:20 pm Post subject:

Trevor1234 · Posted: Fri Jun 27, 2008 4:34 pm Post subject:

Hi Strawbs
A Archduke Ferdinand went out for a peacefull drive in 1914. A chap stepped out as he drove past and shot him. That’s how WW1 started. If Archduke Ferdinand had stayed at home the war would never have began. So, it was his fault.
And yours.
_________________
Tomtom Go 720.
Navcore 9.510
Central and Western Europe v855.2884
GPS World Traffic cameras
Home 2.7
iPhone 3G

Pocketgps · Posted: Fri Jun 27, 2008 5:08 pm Post subject:

Using a pc to charge your device via the usb lead will actually make the battery last a lot longer (30-40% in my experience). The lower charge current that the pc provides is better than fast charging the battery.

I have bought over 70 batteries for my rc cars, planes, helicopters over the last 20 years or more from NiCD, NiMH to the lastest LiPo.

Slow charging is always best if most boring.

The LiPo's I treat with much respect costing £60-80 a time.

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