# How to Combine Power Adapter?



## Rexkh (Mar 15, 2015)

Hi Everyone

I'm curious about how electricity work so I decide to ask here. If I combine 2 power adapter, would voltage or amperage increase. Ex. Both adapter's output is 5V 1A. If I combine them, would it be 10V 1A or 5V 2A?


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## twa2w (Mar 5, 2016)

;-) how do you intend to combine them? Series or parallel


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## Rexkh (Mar 15, 2015)

Connect Positive to Positive and Negative to Negative.


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## like_to_retire (Oct 9, 2016)

Rexkh said:


> If I combine 2 power adapter, would voltage or amperage increase. Ex. Both adapter's output is 5V 1A. If I combine them, would it be 10V 1A or 5V 2A?


When you connect them together, you are feeding the output of one adapter into the output of the other. Obviously, this a bad thing. It can be overcome by using steering diodes, but then you lose the voltage dropped across the diodes (~0.7V). 

In addition, if the voltages are mismatched (which they would most likely be in a cheap wall adapter) then one adapter would supply more current than the other to a load that is demanding higher current than it may be able to supply.

Short answer - not a good idea. Adapter are cheap, so best to get one that suits the job.


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## Just a Guy (Mar 27, 2012)

Think of DC electricity as flowing water. Current is the rate of flow (amps) and volume of water is the potential energy measured in voltage (when the water runs out, the electricity is done and the battery is dead). The rate of flow is controlled by the width of a pipe (the wider the pipe, the more water flows). 

If you connect the pipes in a line (in series), the volume of water increases giving you more voltage (when you put two batteries in a line he voltage increases allowing your flashlight to work) but the pipe is still the same width, so the flow is the same (current). 

If you line up the two tanks next to each other (in parallel), you now have the same amount of water (volts) flowing out of two pipes (amps) so the current is flowing twice as fast. 

Of course, there's many areas where things can go wrong if you don't know what you are doing (like accidentally pumping too much water through pipes that aren't designed to handle the volume) which can cause problems. Also, if you pump too much water into something not designed to hold it, or handle the pressure, it will also break. Another common mistake is people who try to connect two tanks together with no actual release. Imagine two large tanks, connected together with a thin walled pipe...the pipe may burst.

When you're dealing with low volts and current, especially DC, you probably won't kill yourself, but you can still do a lot of damage. If you're dealing with transformers however (plugs that go into the walls and convert 120v AC into low voltage DC) you can easily kill yourself if you make a mistake and accidentally start touching the AC side because you don't know what you are doing.


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## carverman (Nov 8, 2010)

Rexkh said:


> Hi Everyone
> 
> I'm curious about how electricity work so I decide to ask here. If I combine 2 power adapter, would voltage or amperage increase. Ex. Both adapter's output is 5V 1A. If I combine them, would it be 10V 1A or 5V 2A?


If both AC to DC adapters are rated at 5V 1 amp, then if hooked up in parallel, the voltage would be about the same under load, but the current supplied by each diode bridge (due to the heating effects on the diode conductance under rated load (1 amp)
would be different, and that would result in a current imbalance. (1.1amp on one adapter and more than likely 0.9 amps onthe other bridge. 

The diode bridge configuration is normally either 2 diodes or a 4 diodes per adapter.
These are considered FULL WAVE diode bridges. 

If the adapter is unregulated 5 volts, each bridge will supply a certain amount of current, because the bridge diodes are never matched, and neither is the tranformer secondary windings that supply the bridge rectifiers.

You could try a wirewound 1 ohm resistor to isolate each leg (positive and negative) of the output of each bridge, that may work, but generally as others are saying, it's not a good idea unless both sets of bridge diodes are heatsinked on the same heatsink for thermal rise, and that's not possible in those cheap adapters.


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## STech (Jun 7, 2016)

It would be better (and safer) if you just tell us what you're trying to accomplish.


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## Just a Guy (Mar 27, 2012)

Carverman, 

While I totally agree with your response, judging by the original question, your answer was completely useless to the original poster. He needed it to be in simple English. 

One thing I learned while I was teaching, you need to know your audience.


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## OhGreatGuru (May 24, 2009)

But Carverman's response has the merit of indicating it is much more complicated than it sounds. Given the phrasing of the question, I think like_to_retire had the best advice for the "audience" - not a good idea.


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## carverman (Nov 8, 2010)

Just a Guy said:


> Carverman,
> 
> While I totally agree with your response, judging by the original question, your answer was completely useless to the original poster. He needed it to be in simple English.
> 
> *One thing I learned while I was teaching, you need to know your audience.*


 Point taken. Sorry about the long winded technical opinion, JAG

I used to be an electronic engineer at Nortel in a previous life.
You can parallel devices together in a some cases, but you have to be careful how you do it.

As an example; I have built some heavy current 50amp 24volt regulated power supplies in my day for industrial applications where 6 series pass power regulator transistors each sharing the full load at 8 amps each were parallelled together, but for each transistor, mounted on the same power heatsink, there was a small value wirewound resistor in it's emitter, which allowed some difference in voltage drop and current, and they all shared the full load without thermally fighting with each other. 

The short of the OP's question..it MAY work, but probably not a good idea.


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## carverman (Nov 8, 2010)

OhGreatGuru said:


> But Carverman's response has the merit of indicating it is much more complicated than it sounds. Given the phrasing of the question, I think like_to_retire had the best advice for the "audience" - not a good idea.


Correct.


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