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Author Topic: Req: Quick charger for mobile/tablet  (Read 2117 times)
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Satyanarayana
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« on: April 18, 2012, 12:11:23 12:11 »

I need information on how to quick charge(with in 10 to 15 min time) a mobile or tablet PC. Can some one suggest suitable device for this application

Regards

Satya
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zab
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« Reply #1 on: April 18, 2012, 01:54:31 13:54 »

 What I know these devices only need a stable supply only. The charging system is a built in option of these devices. These charges only on a predefined rate perhaps.
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Old_but_Alive
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« Reply #2 on: April 18, 2012, 02:56:45 14:56 »

you cant do it, the phone or tablet control their charging rate, NOT the psu.

I have a HP TouchPad, and it controls whether it takes a fast 2Amp charge, or a slow trickle, same for iPad's

The Charging current taken by the Touchpad (within the capability of the PSU to supply it) is controlled by the state of the D+ and D- lines of the USB port. This is both voltage and impedance sensitive. It has D+ and D- shorted, and resistors 240K to +5V and 300K to Gnd.

When a charger connects to the Touchpad, it then measures the voltage on the D lines, and if its out of spec it just trickle charges

The iPad is similar, but uses different conditions

« Last Edit: April 18, 2012, 05:20:42 17:20 by Old_but_Alive » Logged
blauwhaar
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« Reply #3 on: April 30, 2012, 07:54:48 19:54 »

A nice and simple solution i have found is with one cheap IC LM317
and some cheap resistors.

In the datasheet of the LM317 is an example how to use this device as current
limiter. On one side you put the input power, a resister for current limiting, and a output
for the [ + ] of your device to be charged. The [-] is direct connected to your device.

http://www.ti.com/general/docs/lit/getliterature.tsp?genericPartNumber=lm317&fileType=pdf

See figure 8 of this datasheet.
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Old_but_Alive
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« Reply #4 on: May 01, 2012, 08:32:06 08:32 »

@blauwhaar

that idea will just blow up a tablet or mobile phone.

A tablet or phone with USB input power requires a fixed 5volts ( 5.3V for a touchpad).
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monkey
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« Reply #5 on: May 01, 2012, 01:09:58 13:09 »

Most LI Poly batteries have a built in protection circuit to prevent over current and over discharge. The usual current limit is between 1 and 2 C, where C is the capacity in Amp Hours. e.g. a 5 AH battery can charge at max 5 to 10 amps. This means usual minimum time is 1 hour. For electric model planes and helicopters they use batteries that have no protection board, and so can charge and discharge in as low as 15 minutes. But this large current causes more heat build up and maybe only 50 full charge and discharge cycles. Of course in 15 minutes you could just not fully charge it I suppose!
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Old_but_Alive
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« Reply #6 on: May 01, 2012, 04:26:27 16:26 »

@monkey,

we are not talking about LiPo's here, we are talking about mobile phones and Tablets.
It may be that if the battery is taken out, then it may be charged separately.
I have assumed that we are talking about consumer devices, that may have a non-removable battery, and will undoubtedly have a micro usb socket to charge the device.

LiPo's are extremely volatile things, so risk starting a fire if incorrectly charged etc.

The original question was "I need information on how to quick charge(with in 10 to 15 min time) a mobile or tablet PC"

it could be dangerous stuff !!
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solutions
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« Reply #7 on: May 01, 2012, 08:16:04 20:16 »

I agree with Old_but_Alive. The question was a blue sky question, from a person naive in the art but with "an idea" that *simply* needed a cookbook solution, and cannot be done.

There are a bunch of smart guys here, but don't you think it's a bit naive to think that Apple engineers wouldn't donate their left testicles for the ability to charge an iPad in 3 minutes? Don't you think they tried to give you the best compromise of battery life (primarily destroyed by the heat of charging) and charge time?

If anyone does have a 10-15 minute charge time method, don't share it here until after you've sold it to Apple for $5,000,000.00.

If you need fast availability of a computing unit, change the battery pack in a notebook or find a tablet that can have its pack changed out.  Add a parasite pack on the back of the tablet if you must use a tablet with an internal battery.
« Last Edit: May 01, 2012, 08:19:41 20:19 by solutions » Logged
monkey
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« Reply #8 on: May 03, 2012, 12:18:35 00:18 »

Sorry I forgot to get to the conclusion of my suggestion. If you fitted a battery four times the capacity of the standard one and charged it at 1 or 2 C, then in 15 minutes you have the power of the original battery yet only need 15 minutes charge time. AFIK most netbooks use Li Poly, some older mobiles use Lithium Iron. Lithium Iron is about 75% of the power of Li Poly for the same size. I agree making the battery external would probably be needed unless you modified the case!
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