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Adapting Surplus Power Supplies For The Arduino

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Ed
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I have some old power supplies for cell phones, etc that I would like to adapt for use with Arduino projects. My research has shown that the preferred power supply is a 9V 1A but the Arduino will handle up to 20V. I have some LG TA-P02WR AC Adaptor Power Cellphone Charger Output 5V DC 1A that would be ideal but I can't find an adapter for the end plugs. Does anyone know what type of plug they have on them?

image

I also have some 12V 3A chargers for Comcast cable boxes and they have 2.1mm center positive plugs and work with the Arduino. My concern is the 3A. Is that too much amperage for an Arduino?

Ed


   
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Ron
 Ron
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@ed Amperage is pulled not pushed so not a problem. Your picture is too dark, use the flash. Not sure what you mean by an adaptor. Arduino's have standard pins but many will use the little power supplies that fit on the breadboard. They plug into the power rails and accept both USB and 2.1mm often from a 9V battery.

Here is what one looks like.

Screen Shot 2022 05 13 at 17.12.34

 

"Don't tell people how to do things. Tell them what to do and let them surprise you with their results.” - G.S. Patton, Gen. USA
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Ed
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@zander Thanks for the reply Ron. I agree with you that the Arduino won't pull any more current than it needs so 3A is OK. I was hoping to find out the name of the connector type already on the LG power supply so I could try and find an adapter between it and a 2.1mm plug on the Arduino. I took the connector apart on the LG and it just has two wires in it, red and black. I'm going to order some 2.1mm center positive connectors to hook it up. 

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Ron
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@ed I can't see the connector, the picture is too dark, but I would do what you suggest and just wire it up to some 2.1mm connectors.

"Don't tell people how to do things. Tell them what to do and let them surprise you with their results.” - G.S. Patton, Gen. USA
"Never wrestle with a pig....the pig loves it and you end up covered in mud..." anon


   
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DaveE
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hi @ed,

re:

but the Arduino will handle up to 20V

This statement is 'maybe partly true' .. but it sounds optimistic and there is certainly a magic smoke dragon hiding close by it that you will regret waking up!

Some Arduinos and many other small circuit boards, such as the ESP 8266/32s, currently on offer often have an onboard linear voltage regulator, such as an AM1117 to drop the incoming power voltage to that required for the processor - typically 3.3V or 5V. Other ''roughly similar' regulators are also used, each with its own characteristics.

The maximum 'safe' input voltage is determined by a number of different factors .. exceeding any one of these factors risks waking up the dragon!

The 'absolute' maximum input voltage of the regulator is one such factor. The AM1117 appears to have been heavily copied or cloned, and there is no guarantee that all the variants have the same characteristics. One data sheet I found:

http://www.advanced-monolithic.com/pdf/ds1117.pdf          includes :

image

So, clearly any board using this device should never exceed 15V, and further reading of the data sheet specifies its chacteristics to a maximum of 12V, so I would treat the 12V to 15V range as a 'safety margin' for spikes, etc., with 12V being the 'normal' maximum.

A second way of waking the dragon is to overheat the regulator. It is only a small device, and being a linear regulator, can only drop the voltage by acting like a 'magic' resistor. Hence the amount of heat is directly proportional to the current flow.

e.g. if the input voltage is 12V, the processor voltage is 5V, then every 1 milliAmp of current demand by the processor and its associated circuitry, results in 7 milliWatts dissipation in the processor.

Unfortunately, predicting the current demand of something like an Arduino board is impossible without knowing exactly what circuit it is to be connected into and even what software it will be running .. and even then it is tricky.

Thus a 12V power supply drving an Arduino running 'Blinky' with a single small (low current) LED might be fine, but the same Arduino in a robotics application, driving a number of peripherals might fry its voltage regulator.

In principle, the voltage regulators can protect themselves from overheating, by shutting down. My 'limited' experience is that this is only partly successful ... I have had to replace some that were cooked ...

--------

Moral of the story. Aim to give your regulators a cool life .. the incoming power voltage needs to exceed output voltage by the the 'dropout voltage' ... dropout voltage is typically 1.3V for AMS1117 .. but not much more

So maybe ... output voltage 5V  ... aim for 6.5-7V input

                  output voltage 3.3V ... aim for 5V input

 

AND Of course, ensure you are supplying power to the input of the regulator ... Arduinos, etc. include pins which connect to the OUTPUT of the regulator ... sometimes the pin labelling is confusing and not all boards provide a regulator.

Good luck with your project. Dave


   
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Ron
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@davee @ed Another approach I have used is to connect a buck converter in front of the board. I live in an RV thus have plentiful 12VDC power and use the buck to drop it to 5ish. 

"Don't tell people how to do things. Tell them what to do and let them surprise you with their results.” - G.S. Patton, Gen. USA
"Never wrestle with a pig....the pig loves it and you end up covered in mud..." anon


   
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DaveE
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Hi @zander and @ed,

  Ron, thanks, you are of course, correct.

Another approach I have used is to connect a buck converter in front of the board.

Sorry, perhaps I should have been more explicit, but I meant to imply that 'pre-voltage regulator' may be required to convert from an available supply voltage (say 12v) to a suitable voltage, like 6.5V or 5V.

And of course, a buck regulator can often be the most suitable and convenient unit for this 'pre-voltage regulator' role.

Best wishes all. Dave

 


   
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Ed
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@zander and @daves Thanks for the replies. I'm going to use 9V batteries with a 2.1mm plug for general testing and a regulated power supply of 5V for permanent setups. I've been doing a lot of prototyping and my setup has gotten too big for the desk I keep my laptop on so to test out a new piece of code I have to move the Arduino between my laptop and another work area where I have the prototype set up. The other work area is not fully finished just yet (I have not put the regulated power supply completely together yet - I plan to actually have two: one for Arduinos only and one for other things like servos) but am still wanting to work using batteries or old power supplies for other electronics that I have lying around and can adapt. I have a bunch of those little miniature digital voltmeters and I put them everywhere to see how the system voltage is holding up. The most stable of all power supplies so far is my laptop.

Ed


   
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Ron
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@ed I imagine few of us are as well set up as Bill.

"Don't tell people how to do things. Tell them what to do and let them surprise you with their results.” - G.S. Patton, Gen. USA
"Never wrestle with a pig....the pig loves it and you end up covered in mud..." anon


   
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