How to Limit an AC Adapter that Gives 5v 1.5A, to Give 0.5A?

Thread Starter

Zohar

Joined Nov 19, 2015
70
Hi

My phone comes with an AC Adapter that Outputs 5v 1.5A.
It is not QuickCharge technology or anything like this, but simply 5v, with the above mentioned 1.5A current.

I would not like to charge my phone with 1.5A, and instead, limit it to 0.5A.

Is there a small circuit, or even better, a single component, that can do the job?

Something that I can upt right after the AC Adapter, and before the Smartphone,
that will keep the current at 0.5A (or less, according to how much the phone is trying to pull).


Thank you very much
 

ericgibbs

Joined Jan 29, 2010
12,509
hi Z,
Your fone will only draw the current it needs from the 1.5A supply, so if the fone requires only 0.5A, thats all it will draw from the possible 1.5A
OK.
E
 

Thread Starter

Zohar

Joined Nov 19, 2015
70
Hi

I know..

But my phone doesn't draw 0.5A, it draws 1.5A.
I am not happy with it, and would like to make the charging process slower, and hence cooler.

(the battery gets really hot, and I am not happy with it..
But Sony is probably more than happy, because it means shorter battery life, which means faster replacement)
 

ericgibbs

Joined Jan 29, 2010
12,509
hi,
OK.
The problem in adding current limiting circuit is that the limiter will have a voltage drop across, so the battery may never fully charge.
One simple way I would try is by adding series power resistor in one line of the psu to fone connecting wire, say a 4.7R 5Watt.

Run some tests to find the best resistor value for your fone.
E
 

Thread Starter

Zohar

Joined Nov 19, 2015
70
Hi Eric

Thank you.

So a circuit will be problematic due to a voltage drop problem,
but a Resistor will not cause a meaningful voltage drop?

BTW is that 4.7Ω or 4.7KΩ?
 

Alec_t

Joined Sep 17, 2013
12,004
Any active circuit or resistor will cause a voltage drop from the initial 5V. The phone may not like that.
The only other way I can think of for reducing the average charge current, using the existing 5V adapter, would be to use PWM; but again, the phone would probably sulk.
If you had, say, a 9V supply then you would have some headroom for a current-limiter and could still have 5V at the output. Whether or not that would work would depend on whether the phone makes sneaky checks to make sure it is getting power from its OEM adapter.
 

Thread Starter

Zohar

Joined Nov 19, 2015
70
I see.

Maybe there's some AC Adapter that has a configurable Current Limit setting bult-in?

but I am talking about a Plug shape AC Adapter,
not about big Desk power supplies, or Brick power supplies.

Anyone knows something like this?

Usually in Plug shape power supplies I see an option to choose the Voltage,
maybe there's one with an option to choose the Max. Current too?
 

MrChips

Joined Oct 2, 2009
23,245
You cannot control both current I and voltage V at the same time.
They are interrelated by Ohm's Law.

I = V / R

If a load takes 1.5A @ 5V
then the load represents a resistance of

R = V / I = 5V /1.5A = 3.33Ω

You can try a series of 1Ω 1W resistors and find out what works best to your liking.
 

crutschow

Joined Mar 14, 2008
27,004
Perhaps a very slow PWM would work, such as 15s on and 30s off, which would give an average current of 0.5A, and will reduce the battery heating.
That could be done with a 555 timer and a MOSFET (example circuit below).
The MOSFET needs to be a logic-level type (Vgs(thrs) max ≤ 2V).

upload_2019-7-25_7-53-41.png
 

Thread Starter

Zohar

Joined Nov 19, 2015
70
Thank you, tho I am not sure my phone will like the switch from flat voltage to PWM..
Simply limiting is much less of an intervention - that the phone should not be affected by, in any way..
(other than getting its battery less hot)


BTW, really nice diagram :)
What program/website did you use to create it?

I am using Microcontrollers a lot in the last years,
so instead of using a 555+surrounding components, my way to implement PWM would be a microcontroller, + a Transistor, for the high current.
 

crutschow

Joined Mar 14, 2008
27,004
Simply limiting is much less of an intervention - that the phone should not be affected by, in any way..
The problem, as mentioned by others, is that any current limit will lower the voltage to the phone, and the phone may not like that.
The slow PWM I proposed would allow the phone to charge normally for some period, and then turn off for a longer period to allow the battery to cool down.
You can experiment with the on and off times to see what works best.
BTW, really nice diagram :)
What program/website did you use to create it?
It's the free LTspice simulator program from Analog Devices.
my way to implement PWM would be a microcontroller, + a Transistor, for the high current.
That should work fine also.
 
Last edited:
"my phone" needs more info. Apple puts it in a wierd class by itself.

The charging cable can limit the charging capability depending on a resistive divider. I don;t know all of the details. Finding them is difficult too.

Some info is here: https://obddiag.net/usb-power.html

This is no means all of the info.

I have a charger that wasn't labeled. I checked with a USB gizmo that monitors voltage and current) that one port is 1.5A and the other 0.5. Only 1 will charge my phone at 0.5A. Both ports will charge my GPS. Some adapters won;t charge my phone at all at 0.5A. Ancient Motorola phone.
 
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