electric chargers

Guide to Using the Correct Charger or Power Adapter (and What Happens If You Don’t)

Reminder of formulae for electrics:

• R = V/I (I originates from French 'intensité de courant')
• V = I*R
• P = V*I (Watts = Volts x Amps)
• I = P/V
• V = sqrt(P*R)
• I = sqrt(P/R)

Too many Amps is OK, too many Volts is Not OK

It’s OK if your power supply is rated for MORE current (Amps) than the device needs. The device will only draw the current it actually needs. But it’s not good to use a supply rated for less current. Imagine you want to tow a trailer. Normally, you would hitch the trailer up behind your car. Imagine, instead, you hitch the trailer to a tractor. What happens? Not much. The tractor pulls the trailer effortlessly and most of its power is never used. Now imagine you hitch the trailer to your bicycle. What happens? You may not move at all, or you may be able to move, but you are going to overheat and get exhausted. So, with insufficient Amps, your device may not work at all, or it it does, it will be hard on the power supply, which may overheat and/or fail.
To reiterate: excess AMPS are OK, excess VOLTS are NOT. If you have a device that needs 20 volts, and you feed it 100, your device will probably not survive. Even though a half a volt difference is small, it may be enough to overheat your laptop over time. If it’s the other way around (laptop 20v, charger 19.5v), you should have no problem. Your laptop will simply be under voltage but not much.

Polarity

To read the –C+ symbols look at the way the “C” is facing. –C+ means polarity is positive, but if the C is backwards it’s negative.
Adapter wires can be solid black for negative and black with white stripe for positive. You can cut and switch them to reverse polarity.

Most devices are centre positive (denoted by the dot within the C being connected to the +)