# Running 3A component from two 2As?

Discussion in 'General Electronics Discussion' started by jadical, Jun 11, 2016.

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Jun 11, 2016
So I'm a complete electronics beginner, and I'm just wondering if there's a simple way (i.e. some kind of ready-made adapter) to somehow get 3A out of my cell phone charger/battery bank, which has only two 2A USB outputs.

I also have a tiny 80mA component that I want to run from the battery, so I need to somehow take the 1A I have remaining, and step it down to 80mA, if all this makes sense

Is this remotely feasible for a beginner? and thanks

2. ### HellasTechn

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Apr 14, 2013
That is not possible because the charger you use is (most probably) rated 2A total current output capacity not 2A per usb port.
You do not need to step down anything. The 2A stated on your power source (the charger in this case) means that it can deliver up to 2 amps for a device to work or a battery to charge on the other hand your 80ma rated device only draws 80ma from above stated current. So you are just fine.

In other words and according to ohms law the devices only draw the current they need at a given voltage no matter the source's current capacity as long as it is larger that what they need.

You want your power source to be "strong" enough and in general terms the stronger the better.

davenn likes this.
3. ### HellasTechn

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Apr 14, 2013
You are welcomed.
Welcome to Electronics Point.

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Jun 11, 2016
Okay thanks, that answers one question

I'll find out for sure, and if it won't work I'll find something that will. So assuming I can get the 4A, is it possible?

I also forgot to mention that the small 80mA device uses 3V which is less than the charger's 5V. Is that a problem, and if so how could I fix it?

Thanks for you help

5. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
it might work fine. It might burn out.

it depends on what it is

6. ### HellasTechn

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Apr 14, 2013
you can easily fix this with an LM7803 voltage regulator or with a 25 Ohm 1/4 watt resistor in series with the +5 volt rail.

Last edited: Jun 11, 2016
7. ### HellasTechn

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Apr 14, 2013
If that is the case then yes you can put both USB outputs in paralel and get the 4 Amps.

Keep in mind that specially the chineese usb chargers are always over rated.

I seriously doubt that it can deliver 2 amps per usb port.

Can you tell us the brand and model of the charger ?

P.S.
Is it a wall charger or a power bank ? If it is a power bank it may be able to deliver 2 Amps per port.

davenn likes this.

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Jun 11, 2016
Okay, that sounds simple enough

It's a power bank. I'm shopping around on eBay, asking questions and trying to find a good one. Then I'll find out for sure when I get it.

So how would I go about putting them in parallel and also connecting the second device?

9. ### davennModerator

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Sep 5, 2009
if the 2 USB ports are being supplied by the same 5V PSU in the unit
Paralleling them will NOT give double the current !!

Dave

10. ### HellasTechn

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Apr 14, 2013
That is true.

jadical thinks that it may be able to supply 2 Amps per usb port which i say again i seriously doubt that it can.

Most likely it has 2 usb ports that are in parallel and fed from the same psu rails.

11. ### HellasTechn

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Apr 14, 2013
Assuming that it is an advanced charger or power bank and it can give a max of 2 Amps per usb port then and only they he can connect them in parallel and drain 4 Amps total.

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Jun 11, 2016
Hmm, that seems a bit dishonest to put two 2A ports on it if they can't both do 2A at once

13. ### HellasTechn

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Apr 14, 2013
e.g. In a way like PC usb ports can deliver up to 700ma i think and if you put them in parralel you can get double.
Only in a PC it is the USB controller that regulates that.

14. ### HellasTechn

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Apr 14, 2013
Well technically speaking they say 2A they do not specify. It is an other marketing thing !
What is there really honest?

If i was to get one that delivers 2A per port i would expect it to be marked as "2 x 2 Amp charger"

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Jun 11, 2016
I'm honest

Any suggestions for alternatives? I've never worked with naked batteries, so I'm not sure I can handle that

16. ### davennModerator

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Sep 5, 2009
again, no, it would need 2 different 5V PSU's within the unit to do that and that is very unlikely to be the case

Dave

17. ### davennModerator

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Sep 5, 2009

again, no, read my previous comment

18. ### HellasTechn

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Apr 14, 2013
I understand what you say and i agree But i am takling purely theoretically here. Yes there can be a PSU that gives 2 outputs 2Amps each. I am not even suggesting theat a cellphone charger can do that.

19. ### HellasTechn

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Apr 14, 2013
Two different sections within the unit, each dedicated to one port.
Basically we say the same thing in different words.

Yes i totally agree.

Last edited: Jun 12, 2016
20. ### HellasTechn

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Apr 14, 2013
Most powerbanks use 18650 batteries
If you ask me, i would not encourage you to experiment with theese. In general they are high power batteries and not the best kind to experiment with.

If i where you i would just try to power whatever device is that you want to run (5volt device) and see if it works ok. It may be rated 3 Amps but it may require less and what i now say is only a guess. On the other hand your power bank is rated 2 Amps but may not be able to deliver 2 Amps OR sustain that current output for long enough (that is also a guess).