Two USB chargers using Y-cable to increase current

Forums › Gadgets, robotics, home automation, electronics (including wearables) › Two USB chargers using Y-cable to increase current

BillyFieldman

24 posts

Geek

Topic # 179311 3-Sep-2015 15:32

I have 2 USB phone chargers - the LG charger is rated 5.0V, 0.7A and the Samsung charger is rated 5.0V, 1.0A. And I have a portable powerbank which takes hours to charge using any of those chargers.

Is it safe for me to get one of these Y-cables so I can connect it to both USB chargers for a combined 1.7A so that I can charge the powerbank faster? http://www.amazon.com/Black-Female-Extra-Extension-Mobile/dp/B00L32D088/ref=pd_sim_147_4?ie=UTF8&refRID=05Z674PCDMHS
0NPSH0X3&dpSrc=sims&dpST=_AC_UL160_SR160%2C160_

floydbloke

1374 posts

Uber Geek
+1 received by user: 471

Reply # 1379306 3-Sep-2015 17:33

Bite the bullet. Find a seller who'll ship to NZ and buy a 40W or higher Anker multiport desktop charger. No looking back, you won't regret the investment.

Aredwood

1560 posts

Uber Geek
+1 received by user: 463

Subscriber

Reply # 1379348 3-Sep-2015 18:58

Unlikely to work. Might even blow up one of the power supplies. Just buy a decent one as above.

sbiddle

24994 posts

Uber Geek
+1 received by user: 4880

Moderator

Trusted

Biddle Corp

Subscriber

Reply # 1379355 3-Sep-2015 19:07

There is no guarantee the powerbank will charge any faster - you don't know (or haven't said) that current it will actually draw.

The best solution assuming it will charge at more than 1A is to simply buy a proper charger.

timmmay

12599 posts

Uber Geek
+1 received by user: 2028

Trusted

Subscriber

Reply # 1379359 3-Sep-2015 19:18

One person supports this post

I'd actually like to see what happens... but I wouldn't like you to try it at my house or with my phone, because what might happen is explosion or fire. Probably not, but if you do please record with video.

AWS Certified Solution Architect Professional, Sysop Administrator Associate, and Developer Associate
TOGAF certified enterprise architect
Professional photographer

roobarb

483 posts

Ultimate Geek
+1 received by user: 286

Trusted

Reply # 1379387 3-Sep-2015 20:30

A raspberry pi PSU is typically rated 5.0V 2.0A.

I don't recommend wiring two PSU in parallel, I expect they will sink each other unless you also have diodes in series, then you are into wiring up a rectifier.

hellonearthisman

1815 posts

Uber Geek
+1 received by user: 51

Trusted

Reply # 1379467 4-Sep-2015 03:27

Why not get an old computer power supply and connect some USB plugs to the 5v lines.
There are a lot of tutorials on how to do that, would give you ample power to drive most things.

http://www.instructables.com/id/The-Ultimate-ATX-Power-Supply-Mod-With-USB-Chargin/?ALLSTEPS

http://electronics.stackexchange.com/questions/73242/can-an-atx-psu-power-a-usb-port-directly

http://hackaday.com/2014/05/27/overkill-phone-charger-because-well-why-not/

sbiddle

24994 posts

Uber Geek
+1 received by user: 4880

Moderator

Trusted

Biddle Corp

Subscriber

Reply # 1379501 4-Sep-2015 08:16

hellonearthisman: Why not get an old computer power supply and connect some USB plugs to the 5v lines.
There are a lot of tutorials on how to do that, would give you ample power to drive most things.

http://www.instructables.com/id/The-Ultimate-ATX-Power-Supply-Mod-With-USB-Chargin/?ALLSTEPS

http://electronics.stackexchange.com/questions/73242/can-an-atx-psu-power-a-usb-port-directly

http://hackaday.com/2014/05/27/overkill-phone-charger-because-well-why-not/

That's fine if you want a 5VDC supply, but remember that USB devices don't just need 5DVC - they need a charger capable of smart charging.

As discussed in various other threads on here about chargers most modern devices won't charge at full speed unless they have a smart charger of one form of another. Some new devices support the QC2.0 standard and will only fast charge if the charger supports the QC2.0 standard. Likewise many other products won't fast charge newer Android and Apple devices unless they're a smart charger such as an Anker.

There are lots and lots of 5V USB chargers and battery packs around that are simply useless and will only charge devices at 500mA because they lack and smarts.

Niel

3267 posts

Uber Geek
+1 received by user: 77

Trusted

Reply # 1380770 6-Sep-2015 20:57

Switch mode supplies have a diode in series with the output. You can combine them, but you need to use 2 identical ones as the different designs can have slightly different output voltages. And ideally you should draw only twice the minimum of the 2 so that you will not run one over its rating.

The issue however is that switch mode power adapters have y-capacitors across the mains to DC isolation barrier (except when the power adapter is earthed, but an earth pin does not necessarily mean it is earthed). This is needed for safety and for EMC. Connecting 2 power adapters together with neither of them earthed (by design), means you will likely either compromise or stress the safety isolation. So don't do it.

If it is either Apple or smart power adapters, then you will screw up the signalling that identifies the power adapters to devices. Don't do it.

If it uses a standard USB Charging Standard power adapter (i.e. data lines shorted together), then you will not screw up any signalling. But read above, don't do it unless you know and understand the implications.

You can never have enough Volvos!

Niel

3267 posts

Uber Geek
+1 received by user: 77

Trusted

Reply # 1380772 6-Sep-2015 21:00

Smart chargers are over rated, it just needs to follow the standard. Either USB Charging Standard, or Apple. But there is nothing smart about either. The smarts is in some power adapters that detect if the device is an Apple device or not. And it is my impression it starts off in Apple mode and just switches to USB mode if the current draw is very low.

You can never have enough Volvos!

richms

19660 posts

Uber Geek
+1 received by user: 3489

Trusted

Subscriber

Reply # 1380788 6-Sep-2015 21:21

You need to determine if the charger is hitting its current limit and sagging or not. a USB charger doctor is the cheapest and easiest way to do that. If the voltage is dropping to 3.7ish on a moderatly charged powerbank, then more current would be faster. If its holding at 5 then the charger is not the limiting factor.

Im yet to find a powerbank that gives a crap what is happening with the data pins. They just have a lipo charger chip in it with the current limit set to 1 amp in all I have had. Put it on a 2A charger and its still only going to go at an amp. If you find a charger which really does only allow for 500 mA to be drawn, then it would charge slow. But it seems no matter what they are labeled, you can get 1.5A or so out of any of the USB wallwarts before they sag, but a couple I have tried will just switch off and sulk rather than being current limited.

Richard rich.ms