Adding a power plug to a Tablet (LiPo Question) - Page 1
Forum section: electronics / projects

author: xack
author_rank: Newbie
timestamp: December 06, 2016, 09:24:18 pm
content: Hallo everyone,first of all I'm new to this forum and intend to stay(not only for this question)My name is Max and I'm a mechatronics student (former media designer) in germany.I followed Dave a long time on YouTube but somehow never made may way her (maybe I was not ready)Skill level (estimated): electronics maybe 3,5/10, mechanics 7/10, programming 5/10, Photoshop&Co 9/10, FFF 3D Printing 8,5/10Btw. I intend to up that e-skill so i came hereNow the situation:I have a cheap win10 tablet (Treckstor wintron 7.0) with only one Micro-USB port for charging and OTG (picture of the inside attached).Now i would like to power the tablet from the wall and still use peripherals.For that reason I first bought a special cable, which works fine for mouse/keyboard but not my canon. with a solo Micro to Mini cable it works but than I cant charge it.Now the final Question xD:I know how lipos are ment to be charged BUT what if i just put a 3,7V Source ontop of the LiPo Terminals.For my understanding so fare, if the LiPo is lower the 3,7V would drive the Tablet and maybe slowly charge the lipo.It's not a very nice way but would that do any harm to the lipo?Looking forward to become a part of this communityMax(Btw. I just started a YouTube channel called Make'n'Modify)

author: Audioguru
author_rank: Super Contributor
timestamp: December 07, 2016, 04:48:01 am
content: You have nothing to limit the charging current of the battery if its voltage is low.A LiPo battery charger circuit limits the current to avoid a fire.I do not know if the battery and/or your 3.7V source or the wiring will catch on fire without limiting the current.

author: sleemanj
author_rank: Super Contributor
timestamp: December 07, 2016, 05:04:55 am
content: I would just look for a convenient 5v point on the PCB and solder to that. Look on the other side of the pcb near to the USB socket there is probably one. Have done it myself with the odd android tablet with continually broken micro usbs

author: tatus1969
author_rank: Super Contributor
timestamp: December 07, 2016, 06:59:11 am
content: lipos will react very aggressively when mistreated. charging them without really knowing what you do, and without necessary safety mechanisms, will result in explosion or fire. don't do that

author: xack
author_rank: Newbie
timestamp: December 07, 2016, 11:19:25 pm
content: Hallo againThank you for your help. I know how bad lipos can be (building quadcopters), thats why I asked firstI still think to solve my problem I have to connect the external power where the lipo is (maybe with a TP4056).But for curiosity i added a cable to a 5V testpoint near the USB port.And... i can charge it externaly but as soon as i add any kind of OTG cable it stops charging.I had this cablehttps://www.amazon.com/System-S-Charging-SIMULTANEOUSLY-Samsung-Devices/dp/B00NQ0S468/it worked just fine for mouse and co but did not for my canon in the past....Now I had to realise that the mini USB cable is used to connect to the cam was the faulty piece -.-*But still curios, couldn't I add one of these cheap TP4056 based boards with LiPo protection, add a diode between charge board and tablet?So i could only charge it over an external source, not usb any more but should work, or am I missing something?BTW: attached a picture of the underside for those interested

author: sleemanj
author_rank: Super Contributor
timestamp: December 07, 2016, 11:38:21 pm
content: Quote from: xack on December 07, 2016, 11:19:25 pmDid you measure the 5v when you plugged in the OTG device? Maybe it's just pulling too much current and dragging the 5v down so the tablet stops trying to charge.As for using an TP4056, you need to remember that the tablet is going to be trying to pull power from those same battery connections, and therefore the TP4056 is going to be supplying both tablet and trying to charge battery, how that would work out in the 4056's constant current mode who knows. I don't think it's a great idea.

author: xack
author_rank: Newbie
timestamp: December 08, 2016, 04:44:26 pm
content: I think its becaus on OTG-Cables Senns is connected to ground, so the tablet knows...But I think the only real solution would be to use a BQ24030 (Single-Chip Charge and System Power-Path Management IC).Since the cable now works i'll keep it for laterThanks every one

author: KL27x
author_rank: Super Contributor
timestamp: December 08, 2016, 10:01:50 pm
content: The problem you won't get around, so easily, is the battery meter. Charging on the terminals directly. Charging with a proper li ion charging IC. Doesn't matter. If your battery meter is low, the tablet will shut down even while you have the external PSU connected and battery 100% fully charged. And your charge won't show up until after you plug in the regular cable or otherwise get 5v on the Vusb, and the IOS decides the battery is indeed fully charged (which takes some minutes). This is not theory-crafting pontification. BTDT (android tablet, FWIW). Still don't have a solution. Rooting and using a third party battery calibration app may or may not work. Didn't get that far.

author: ReddBeardd
author_rank: Newbie
timestamp: December 09, 2016, 04:11:16 pm
content: ok so heres what you do. You cut the two data lines going to the current USB port - and use it only for charging - find where they go on the board or somewhere else that they end up at - and use them along with 5v from somewhere else on the board and then add in a second USB port using the data from the original - and 5v from somewhere else.if the power coming from the charger is not enough to damage whatever usb device you want to use - then you may not need to use a 5v lead from somewhere else - but you wouldnt want to plug two devices into the same usb port so I would suggest disconnecting the data lines going to the charging port and making it charge only.