I have a friend who asked an electrical question I can not answer, so was hoping you all could.
My friend has an electronic device that calls for a 9v 600mA DC adapter. They can only find a 9v 800mA DC adapter locally. Will it damage the device to use the 800mA adapter instead of the 600mA adapter?
How is this situation different than our transformers (a KW for example) being able to generate 10 amps and 140 watts while our trains only draw 3 amps/42 watts?
Thank you,
Chris
Your intuition is correct. It is very much the same situation. The larger adapter should work fine.
Bob,
Thank you.
So what I get out of this is that it is really over-voltage that kills electronics and that voltage is similar to pressure in plumbing. If the pressure is to low you get nothing. But too much pressure and the fixtures leak, crack, etc. Amps is just a quantity/resevoir/pool of power which would flow through the plumbing - much like a cistern with 800 gallons waiting to be tapped into.
You have hit upon an analogy that is very often used in teaching about electricity: Voltage (properly called electromotive force or EMF) is like pressure; current is like the flow of water. (The “water” is electric charge.)
This is a good way to visualize what’s going on. But it can be carried too far, since there are a few serious problems with the analogy:
One is that water can simply spill out of an open pipe; but charge cannot ordinarily spill out of an open wire. You’ve got to have another pipe (conductor) to carry it back to the pump (battery) that creates the pressure (voltage).
Another is that the relationship between pressure and flow rate in a pipe is very nonlinear, with the pressure going up disproportionately fast as you increase the flow rate. Electrical conductors tend to be linear, with the voltage proportional to the current. This is called Ohm’s law, that the ratio of the voltage to the current is constant. We call that ratio “resistance” and measure it in ohms.
Yet another possible misunderstanding arises from the fact that we are generally interested in using the stuff, like water, that comes through pipes, whereas we don’t often have an actual use for electrons. Instead, we want to use their motion to do something, like heat a filament or make a magnetic field in a motor and don’t care whether the electrons already in the filament or in the motor or the ones in the power supply do the moving. So we let the water flow in a plumbing circuit, waiting for the hot water to arrive at the sink; but the light comes on almost instantly when we switch it on at the door.
Thanks Bob.
I’ve never been interested in clocking the speed of water in our pipes… I’m just glad it comes out of the pipe. I’ve never seen an electron, so I’m going to have to take your word that we don’t have a use for a pocket full of them.