Voltage drop Question

[jal395]

I have a 12V 5A power supply with a three foot cord to the DC 5.5mm plug. I need about 10 more feet and was wondering what gauge wire I would need and what percentage voltage drop is acceptable to still allow the device to function properly. The device is a small touch screen computer of about 10 inches diagonally running windows 7. Ultimately the objective is to run the thinner DC wire through the wall. I wanted to avoid having the power supply in view by hiding it in the ceiling. Any ideas would be welcome.

 

[lametec]

Just because it's a 12V power supply doesn't necessarily mean the unit needs 12V to operate. It might do just fine at 10V. Also, just because it's a 5A power supply doesn't mean the unit draws 5A.

So to get a proper answer to your question, you need to know, at the very least, the current draw.

If not, the best we can do is use 12V and 5A as the base of the calculations. You didn't say what gauge the current wire is either, so we can't calculate a theoretical voltage drop as is, even.

Let's guess that the current wire is 16 awg. At 12V and 5A, you'll see a 0.1V drop. Now extend this wire another 10', and you'll get a 0.5V drop.

Assuming the 3' wire is permanently attached to the PSU, if you add 10' of 14 awg wire, you'll see a 0.35V drop all together.

This is assuming 16 awg wire for the first 3'.

 

[Stuart in MN]

What lametec posted sounds right, given the assumptions. Check the specs of the computer, the voltage requirements for electronic devices like that are often fairly loose so if the supply voltage is 11 or 11.5 volts it may still work fine.

You can find any number of voltage drop calculators online where you can plug in various values for current, voltage, wire size and length, etc. to determine what will work best for you, here's one: http://www.calculator.net/voltage-drop-calculator.html

 

[nehog]

12 Volts DC, 5 amps, 18 AWG will give a voltage drop of 0.32 volts for 10 ft. You should do just fine with that. Complex electronics have voltage regulators to drop the input voltage some, and this compensates for a slightly lower voltage in most cases.

 

[BillK]

Jal,
You need to find the specs on the device itself, not the power supply. I bet that it does not even draw 1 amp. That being the case you should not have a problem extending the wire another 10 feet.