[SOLVED] Nexus 7 charger/cable issues

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el56

el56

Senior Member
Sep 26, 2008
204
58
Toronto
Samsung Galaxy Note II
Nexus 7 (2013)
janedoesmith said:
Increasing the length of the cable increases the charging circuit impedance and decreases the charging rate.
[...]
Cables longer than 6 feet is not suggested regardless of lower AWG as the connectors itself (especially at the MicroUSB end) will be the bulk of the impedance for that cable.
Click to expand...
Click to collapse

I notice that the Monoprice 28/24AWG cables come in various lengths -- 1.5, 3, 6, 10 and 15 feet.

If the bulk of the impedence is from the connectors, what about using a single longer cable instead of an extension? Would a single 10ft or 15ft cable also not be recommended?

Conversely, would the 1.5ft cable charge significantly faster than the 6ft one?
 
E

Entropy512

Senior Recognized Developer
Aug 31, 2007
14,088
25,086
Owego, NY
el56 said:
I notice that the Monoprice 28/24AWG cables come in various lengths -- 1.5, 3, 6, 10 and 15 feet.

If the bulk of the impedence is from the connectors, what about using a single longer cable instead of an extension? Would a single 10ft or 15ft cable also not be recommended?

Conversely, would the 1.5ft cable charge significantly faster than the 6ft one?
Click to expand...
Click to collapse

It depends. I am seeing (but need to look further) that it seems like the N7's charge rate depends heavily on input voltage - it is far more sensitive to "brownouts" than any other device I've used. I still need to do some more investigation though.

My Tab 10.1's charger results in CurrentWidget reporting 1400 mA into the battery
The stock charger results in around 1100 mA getting reported
My Scosche charger (modified to charge Samsung Tabs and normal phones) results in 750-800 mA into the battery

Note that CurrentWidget requires a kernel modification to work properly - http://review.cyanogenmod.com/#/c/20891/

These are all with the same cable in use.

To some degree, this can vary due to changes in system power usage, since the battery current is input current minus system current - however there seems to be a clear charger-to-charger pattern.

The odd thing is - unloaded, the Tab 10.1's charger has lower voltage than the stock charger. I have not checked to see how the voltage behaves under load - I would need to do some splicing and soldering to be able to check this.

Thinking back - I think the modded Scosche charger also charged my 10.1 more slowly than its stock charger. I need to check this weekend.
 
el56

el56

Senior Member
Sep 26, 2008
204
58
Toronto
Samsung Galaxy Note II
Nexus 7 (2013)
Based on the comments above and in other threads, the HP Touchpad charger should work well with the Nexus 7.
I personally like its suitability for travel, with folding blades and a design that doesn't block other outlets. And we can be reasonably certain they won't contain any iPad cruft. :)
These chargers are still widely available on eBay for $8 or less, including shipping anywhere in the world. North American shipping addresses can get it even less expensively, my winning bid in one auction was $2.50 (including shipping).
But I imagine that stock will eventually run out. If the Touchpad isn't in production anymore, likely neither is its charger :p
$(KGrHqR,!qoE-Z(JsHVzBPoNPE4e4g~~60_12.JPG
 
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tom_yellowblue

Senior Member
Feb 7, 2012
65
14
short/y said:
Has anyone tried the Monoprice wall or car chargers?

Wall: http://www.monoprice.com/products/p...=10851&cs_id=1085102&p_id=8856&seq=1&format=2

Car: http://www.monoprice.com/products/p...=10826&cs_id=1082603&p_id=8858&seq=1&format=2
Click to expand...
Click to collapse

I have both of those chargers. They both work with my Nexus 7 as long as I use my modified charging cables. Short the data pins on the micro USB side, leave the data pins on the charger side floating. See my description here:
http://xdaforums.com/showpost.php?p=29835066&postcount=105
http://xdaforums.com/showpost.php?p=29877229&postcount=110
 
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short/y

short/y

Senior Member
Mar 9, 2006
658
67
Silly-con Valley
tom_yellowblue said:
I have both of those chargers. They both work with my Nexus 7 as long as I use my modified charging cables. Short the data pins on the micro USB side, leave the data pins on the charger side floating. See my description here:
http://xdaforums.com/showpost.php?p=29835066&postcount=105
http://xdaforums.com/showpost.php?p=29877229&postcount=110
Click to expand...
Click to collapse
OK, cool, thanks. If I've read the threads correctly, it'll charge without modifying the cables but the N7 won't indicate it's charging.


Sent from my Nexus 7 using Tapatalk 2
 
T

tom_yellowblue

Senior Member
Feb 7, 2012
65
14
short/y said:
OK, cool, thanks. If I've read the threads correctly, it'll charge without modifying the cables but the N7 won't indicate it's charging.
Click to expand...
Click to collapse

I hooked the Monoprice wall charger up to a Kill A Watt meter and what I saw was that with the OEM cable it only used 2-3 watts (it fluctuated a bit). The Nexus 7 reported that it was discharging, but 0 watts were used when the cable was unplugged so it seems like it was actually being charged. Using a charging-only cable the charger used 5-6 watts.

So I'd say that it will charge with the normal cable, but only at about half the rate. The battery was 90% full, I'll have to check it another time when the battery is lower.
 
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gogol

gogol

Senior Member
May 20, 2005
3,735
216
tom_yellowblue said:
I have both of those chargers. They both work with my Nexus 7 as long as I use my modified charging cables. Short the data pins on the micro USB side, leave the data pins on the charger side floating. See my description here:
http://xdaforums.com/showpost.php?p=29835066&postcount=105
http://xdaforums.com/showpost.php?p=29877229&postcount=110
Click to expand...
Click to collapse

Nice, but probably if you have time and another spare cable ... you could make instruction with photos ... :)

Thanks.
 
short/y

short/y

Senior Member
Mar 9, 2006
658
67
Silly-con Valley
el56 said:
Based on the comments above and in other threads, the HP Touchpad charger should work well with the Nexus 7.
I personally like its suitability for travel, with folding blades and a design that doesn't block other outlets. And we can be reasonably certain they won't contain any iPad cruft. :)
These chargers are still widely available on eBay for $8 or less, including shipping anywhere in the world. North American shipping addresses can get it even less expensively, my winning bid in one auction was $2.50 (including shipping).
But I imagine that stock will eventually run out. If the Touchpad isn't in production anymore, likely neither is its charger :p
Click to expand...
Click to collapse
Anyone have experience with these on the N7? There are still quite a few on eBay.


Sent from my Galaxy Nexus using Tapatalk 2
 
K

kd5dmg

Member
Dec 15, 2011
38
4
I have one arriving this week. Got it from amazon.

Will post results as soon as it arrives.

Sent from my Nexus 7 using xda premium
 
E

Entropy512

Senior Recognized Developer
Aug 31, 2007
14,088
25,086
Owego, NY
short/y said:
Has anyone tried the Monoprice wall or car chargers?

Wall: http://www.monoprice.com/products/p...=10851&cs_id=1085102&p_id=8856&seq=1&format=2

Car: http://www.monoprice.com/products/p...=10826&cs_id=1082603&p_id=8858&seq=1&format=2
Click to expand...
Click to collapse

I would be careful with Monoprice chargers. While I have always been VERY happy with their cables, a few months ago I ordered a few 1A car chargers from them.

The "1A" chargers they sell are, at best, good for 300-400 mA. Peak switch current is limited to 500-600 mA, and the average will be lower than that. This can be confirmed by looking at the internals and reading the datasheet for the switching power supply chipset used.

However at $5, I may order two and rip one apart to look inside. :)
 
e.mote

e.mote

Senior Member
Feb 16, 2011
2,160
887
For tinkerers, a good tool to have is a low-(DC)-current clamp meter. It will tell you the charge current w/o the hassle of putting together a rig to measure it inline. These are intended for auto electrical testing, but the hi-res (1mA) ones can be used for electronics as well.

Here's one that had a video review. Claimed resolution is 1mA, but accuracy is +/- 7mA in this test. More than adequate for determining charge rate.

This particular model is $127, which is cheap as meters go. But if that's out of your price range, you can find clamp meters with DC current capability for $30-40'ish on eBay. These are mainly intended for AC (high current) testing, so resolution is low at 0.1A.

513G84nYpAL._SL500_AA300_.jpg

 
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E

Entropy512

Senior Recognized Developer
Aug 31, 2007
14,088
25,086
Owego, NY
e.mote said:
For tinkerers, a good tool to have is a low-(DC)-current clamp meter. It will tell you the charge current w/o the hassle of putting together a rig to measure it inline. These are intended for auto electrical testing, but the hi-res (1mA) ones can be used for electronics as well.

Here's one that had a video review. Claimed resolution is 1mA, but accuracy is +/- 7mA in this test. More than adequate for determining charge rate.

This particular model is $127, which is cheap as meters go. But if that's out of your price range, you can find clamp meters with DC current capability for $30-40'ish on eBay. These are mainly intended for AC (high current) testing, so resolution is low at 0.1A.

Click to expand...
Click to collapse
Oh, that's nice - Although you would still have to separate + and - of whatever your charging cable is, so it can't directly measure most USB cables.
 
R

robrob777

Senior Member
Mar 31, 2010
722
115
in my case it was stuck at 0% left it plugged in for 5 min and it was turning off immediately.

So what i did is to leave it off and charging for 2 mins, after that I turned on and still on 0% but after 1 min it charged to 1% .

Hopefully it is a kernel issue (touchpad Android had the problem)
 
C

Chinpokomon

Senior Member
Feb 9, 2009
213
15
el56 said:
... the HP Touchpad charger should work well with the Nexus 7.
Click to expand...
Click to collapse

I thought the same thing last week. I tried the TouchPad charger, seeing that it should be able to supply the current needed, and after several hours, it hadn't hardly charged at all. I had even less success when I tried to charge my Galaxy Nexus from the TouchPad charger; it didn't even seem to recognize it as being plugged in.

Sent from my Nexus 7 using xda app-developers app
 
A

AZImmortal

Senior Member
Dec 22, 2010
504
74
I wanted to mostly confirm janedoesmith's findings (I don't have the means to confirm everything). I charged my Nexus 7 overnight using a Samsung 1A charger and Samsung micro USB cable, and after checking Battery Monitor Widget's log, I can confirm that it fully charged my Nexus 7 at the same rate as the stock charger and cable (55% to 100% in two hours), so it does indeed seem that using a 2A charger is unnecessary and that you only need a high quality 1A charger with a low impedance cable. This is a bit disappointing because it means that the Nexus 7 only charges as fast as a smartphone. If it charged as fast as other tablets, then total charging time would likely be only about two hours to go from zero to 100%.

janedoesmith: Have you by chance been able to test the current drawn from a computer's USB port?
 
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    janedoesmith
    I have been closely watching these threads and found some mixed results.
    http://xdaforums.com/showthread.php?t=1791717
    http://xdaforums.com/showthread.php?t=1780211
    http://xdaforums.com/showthread.php?t=1793059
    http://xdaforums.com/showthread.php?t=1781680
    http://xdaforums.com/showthread.php?t=1784322
    http://xdaforums.com/showthread.php?t=1785976

    So, I conducted some experiments and the results are below. For those of you that don't care for the data, you can scroll down to the CONCLUSION.

    Some of the information presented here are derived directly from the above threads and from the Internet. All values are approximate and measured using a digital multimeter. Some of you may already know but for the sake of other readers, I will be using the following terminology and acronyms.

    AWG = American Wire Gauge. The thickness or the diameter of an electrical conductor(s) within a single wire. Most flexible wires contain multi-stranded conductors instead of a single solid conductor. The important thing is, as the AWG number DECREASES, the thickness of the conductor INCREASE. Thicker wires can carry more current
    OEM = Original Equipment Manufacturer
    Connector Pigtail = A connector with its individual wires exposed and part of the wire's insulation removed as a means to perform electrical measurements.
    (XX / YY) = "XX" represents the AWG of the data wires (D+ / D-). "YY" represents the AWG of the power / ground wires (+5v / GRN). Some USB cables will be imprinted with its rating on the cable itself such as "28AWG/1P 26AWG/2C". I will be referring to this cable as (28/26) meaning the data cables are 28AWG and the power / ground wires are 26AWG
    USB data wires = The White wire (D-) and the Green wire (D+) contained within the USB cable.

    Testing Jig:
    1. 12 inch USB A male to USB A female extension cable (28/28) cut in half to produce 1-USB A Male pigtail and 1-USB A Female pigtail.
    2. 12 inch MicroUSB B male to MicroUSB B female extension cable (28/26) cut in half to produce 1-MicroUSB B Male pigtail and 1-MicroUSB B Female pigtail. http://www.ebay.com/itm/Micro-USB-B..._USB_Cables_Hubs_Adapters&hash=item3f1497b3e1
    3. 18 inch test leads (18 AWG). http://www.harborfreight.com/18-inch-low-voltage-multi-colored-test-leads-66717.html

    I used 3 different MicroUSB cables and 1 USB A extension cable:
    OEM = 3 feet, unknown AWG (not imprinted on the cable), impedance of power/ground wires = 0.2 ohms, length of MicroUSB male end = 6 mm, resistance / continuity check reveals nothing special. It is a standard MicroUSB cable.
    Monoprice = 6 feet, (28/24), impedance of power/ground wires = 0.2 ohms, length of MicroUSB male end = 5.5 mm, resistance/continuity check reveals nothing special. I purchased 2 of this cable. The MicroUSB male end on the other cable measured 6 mm. http://www.monoprice.com/products/p...=10303&cs_id=1030307&p_id=5458&seq=1&format=2
    Amazon = 6 feet, unknown AWG (not imprinted on the cable), impedance of power/ground wires = 0.5 ohms, length of MicroUSB male end = 5.5 mm on both, resistance/continuity check reveals nothing special. http://www.amazon.com/Case-Star-Bla...id=1344416273&sr=8-70&keywords=microusb+cable
    Generic extension cable = USB A male to USB A female, 6 feet, (28/24), impedance of power/ground wires = 0.2 ohms.

    I used 4 different chargers:
    OEM = Rated at 2 A, resistance between data pins = 0.5 ohms (shorted).
    iPhone 4 OEM charger = rated at 1 A, resistance between data pins = 53100 ohms.
    Belkin = 2 port, each port rated at 500 mA, resistance between data pins = 58000 ohms. http://www.amazon.com/Belkin-Mini-Surge-Protector-Charger/dp/B0015DYMVO
    AT&T Car charger = An iPhone charger with an auxiliary USB charging port, unknown rating, resistance between data pins = not connected (infinity).

    Amperage readings measured at the cable using connector pigtails with test leads and with a completely drained Nexus 7 (Surprising Results!!!):
    OEM charger + OEM cable = Charges at 821mA AND displays AC charging.
    OEM charger + OEM cable with the data wires disconnected (open)= Charges at 821mA BUT displays Discharging.
    OEM charger + OEM cable + Generic extension cable = Charges at 631 mA AND displays AC charging.
    OEM charger + OEM cable with the data wires disconnected (open) + Generic extension cable = Charges at 631 mA BUT displays Discharging.
    OEM charger + Monoprice cable = charges at 823 mA BUT displays Discharging.
    OEM charger + Monoprice cable with data wires shorted = charges at 823 mA AND displays AC charging.
    OEM charger + Monoprice cable + Generic extension cable = charges at 635 mA BUT displays Discharging.
    OEM charger + Monoprice cable with data wires shorted + Generic extension cable = charges at 635 mA AND displays AC charging.
    OEM charger + Amazon cable = charges at 451 mA BUT displays Discharging.
    OEM charger + Amazon cable with data wires shorted = charges at 451 mA AND displays AC charging.
    OEM charger + Amazon cable + Generic extension cable= charges at 258 mA BUT displays Discharging.
    OEM charger + Amazon cable with data wires shorted + Generic extension cable= charges at 258 mA AND displays AC charging.

    iPhone 4 OEM charger + all above cable combination = charges at a maximum rate of 635 mA BUT displays Discharging. Increasing the length of the cable decreased the charging rate.
    iPhone 4 OEM charger + all above cable combination + data wires shorted = charges at a maximum rate of 635 mA AND displays AC charging. Increasing the length of the cable decreased the charging rate.

    Belkin charger + all above cable combination = charges at 259 mA BUT displays discharging. Increasing the length of the cable did not change charging rate.
    Belkin charger + all above cable combination + data wires shorted = charges at 259 mA AND displays AC charging. Increasing the length of the cable did not change charging rate.

    AT&T car charger + all above cable combination = maximum charging rate of 830 mA BUT displays discharging. Increasing the length of the cable decreased the charging rate.
    AT&T car charger + all above cable combination + data wires shorted = maximum charging rate of 830 mA AND displays AC charging. Increasing the length of the cable decreased the charging rate.

    NOTE: With the Nexus 7 powered off, all combinations of above chargers and cables, regardless of whether the data wires were shorted or not displayed the charging indicator.

    CONCLUSION:
    1. Nexus 7 OEM charger is nothing special, just the data pins are shorted.
    2. Nexus 7 OEM MicroUSB cable is nothing special. It is a standard MicroUSB cable.
    3. Any USB car/wall charger should charge the Nexus 7.
    4. Nexus 7 will charge regardless of whether it displays "AC Charging" or not.
    5. The charging rate is dependent on the capacity of the charger and the total charging circuit impedance (lower the impedance the better).
    6. Increasing the length of the cable increases the charging circuit impedance and decreases the charging rate.

    SOLUTION:
    1. Use a high quality, high amperage USB charger.
    2. Use a cable with an AWG of (28/24) or lower.
    3. Cables longer than 6 feet is not suggested regardless of lower AWG as the connectors itself (especially at the MicroUSB end) will be the bulk of the impedance for that cable.
    4. If you desire to have "AC Charging" be displayed on your Nexus 7, short the data wires/pins. Remember, this has no effect on the charging rate.
    5. If you plan to modify the charger, take a resistance measurement of the data pins first (unplugged), any readings other than 0 ohms or infinity (open or not connected), you will need to isolate the data pins from the charging circuit prior to shorting. If you do not, you risk damaging the charger and/or your precious Nexus 7.
    6. If you plan to modify the cable, short the data wires at the MicroUSB end and leave the data wires open or not connected at the charger end. Use heat shrink to insulate the exposed conductor of the data wires.
    7. Make sure the MicroUSB connector end is about 6.0 mm in length.
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    M
    Mechanio
    cipiripper said:
    can I plug Nexus7 in 5V 3.0A car charger? Will it burn, melt or anything like that
    Click to expand...
    Click to collapse

    Think of it this way: the light sockets in your house might be hooked to a 10A breaker, and 10A * 120V = 1200W. If you put a 40W light bulb in there it doesn't draw the whole 1200W; it draws 40W, like it was designed to. The extra power is there, but each device draws only what it needs (UNLESS something goes horribly wrong, like when something gets shorted-out internally; but that would be a problem no matter which charger you were hooked to.)

    (There are other issues with some devices or chargers like constant-current supplies, but generally those issues do not affect commercial devices.)

    The number of amps the power supply can source does have relevance to how fast the device charges (which is why the 2A charges faster than the 500mA from a computer USB port) but they are both still limited to safe levels in commercial devices.
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    P
    Popatam
    Bought lot of 10 usb cables
    Ebay item 390317506982 Seller goodbuy711

    Description says "Proper current to your USB device via Heavy-duty 22AWG power wire"
    But in reality this is cheap thin 28AWG cable.
    Beware this seller.

    Sorry, can't post urls. Wanted to attach photo of this s**t.
    View
    2
    el56
    el56
    osm0sis said:
    This is the other combo I'm definitely considering. Do you happen to know what the mA in (per the OP) is for this cord+charger combination?

    Do either of these look legit? I don't want to get an eBay "knock-off" variety by mistake..
    http://www.ebay.ca/itm/Brand-New-10...adapter-HP-TouchPad-FB341AA-ABA-/330772367905
    http://www.ebay.ca/itm/New-HP-Touch...er-Charger-Original-FB341AA-ABA-/200728721755
    Click to expand...
    Click to collapse

    Both of those appear legit. The "KMASHI" label on one of them is indeed the OEM -- the devices I purchased have both a small KMASHI hologram sticker and printed HP markings. The two-piece design is real but it's solid once assembled.The UPC label is a part number on a clear sleeve that peels off. Printing on the barrel indicates HP part number 157-10157-00, which seems to check out as legit.
    Listed input is 100-240V, 0.4A, output is 5.3V 2.0A

    One of the eBay sellers you quoted -- hkx-power -- was my source too, but I note they only ship to the US and Canada. The other source you quoted ships worldwide.

    BTW, I'm still happy with them. Good luck!
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    J
    janedoesmith
    gogol said:
    I am surprised with the charging rate of 821mA ...



    So, basically, we don't really need 2A charger?
    Click to expand...
    Click to collapse

    You do need a 2A charger. All testing was done when the N7 was completely dead. I suspect when the battery is at like 50%, the charging rate will peak to 1300-1500mA and start decreasing when the battery nears its capacity.

    I didn't make measurements at the various charge stages as this experiment was just about whether it charges with the various chargers and cable combinations.
    View

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