Do I Really Need 2 amps

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ikw777
ikw777
QLD
2995 posts
QLD, 2995 posts
16 Apr 2013 2:38pm
Wanting a car-charger for my Samsung Galaxy Tab 10.1 tablet pc. It nominally requires 5 volts at 2 amps. The chargers available here in Christchurch supply the 5 volts but fewer amps (850ma). Will this be enough to charge the device with? Slower?

I note the Tab will charge from a laptop USB port if the Tab is turned off. That's only .5 amps isn't it?
FormulaNova
FormulaNova
WA
15105 posts
WA, 15105 posts
16 Apr 2013 1:48pm
As d1 has said, usb3 can supply 900ma. If you just plug the tablet into a dumb charger, it will only charge at 100ma.
I found that a dumb 1amp charger plugged into a usb3 hub can charge at the full 900ma.
FormulaNova
FormulaNova
WA
15105 posts
WA, 15105 posts
16 Apr 2013 1:50pm
I had one of the telstra tablets and you could keep it topped up with a 1 amp supply, but if you let it run down, it wouldnt charge up as it really needed a 2 amp supply.
FormulaNova
FormulaNova
WA
15105 posts
WA, 15105 posts
16 Apr 2013 1:54pm
Yet another reply..
If you use that jaycar adapter, it may work, but some devices need to talk with the charger before it can charge at the higher rate.
My discovery was that a cheap usb3 hub from Woolworths did the talking and allowed faster charging. 100ma is next to useless.
ikw777
ikw777
QLD
2995 posts
QLD, 2995 posts
16 Apr 2013 3:54pm
Message received. I'll get one with the right amperage.

it turns out there's a Jaycar here in Christchurch so I might be able to get the model d1 linked to.

Cheers!
d1
d1
WA
304 posts
d1 d1
WA, 304 posts
16 Apr 2013 2:29pm
FormulaNova said...
Yet another reply..
If you use that jaycar adapter, it may work, but some devices need to talk with the charger before it can charge at the higher rate.
My discovery was that a cheap usb3 hub from Woolworths did the talking and allowed faster charging. 100ma is next to useless.


A device attached to a PC-based USB host may only draw 100 mA upon initial connection and should only proceed to draw the full 500 or 900 mA if it manages to successfully negotiate this with the host. The current provided is not actually limited by the USB host, so the responsibility for adherence to the power negotiation protocol lies with the device manufacturer. A well-behaved device should limit itself to 100 mA if it doesn't manage to negotiate higher current draw.

However, the USB standard also specifies a dedicated USB charger. A (modern) device recognizes that it's attached to a charger, because, unlike a standard USB host, the middle two lines of the USB connector (D+ and D-) are shorted together. When the device detects that it's connected to a charger, it can commence drawing the full amount of available current right away, without the need for power negotiation.

It's a familiar topic, because not too long ago I ran a small business that designed and manufactured certain USB devices and hosts

FormulaNova
FormulaNova
WA
15105 posts
WA, 15105 posts
16 Apr 2013 4:32pm
d1 said...

However, the USB standard also specifies a dedicated USB charger. A (modern) device recognizes that it's attached to a charger, because, unlike a standard USB host, the middle two lines of the USB connector (D+ and D-) are shorted together. When the device detects that it's connected to a charger, it can commence drawing the full amount of available current right away, without the need for power negotiation.

It's a familiar topic, because not too long ago I ran a small business that designed and manufactured certain USB devices and hosts




I might give that a go, and short out the d+ and -, and see how it works. These chargers are $1 each, so nothing to lose. I was disappointed when I first used them as they are supposed to be 1amp, but nothing would charge from them at more than 100ma.

When I tried the USB3 Hub I was impressed, and it even seemed to charge other USB devices faster than their original chargers.


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