What impact can I cause if I neglect voltage ratings?

Question

For instance, a DC motor rated 48 V and 0.6 A (29 W) being supplied with a solar panel rated 18.2 V and 2.75 A (50 W). Can it run?

Answer 1

Depends. It might, but not very well.

You have two devices, they will not work well together.

The ratings on the motor: 48V, 0.6A, are nominal. This is what the motor requires to run normally. However, the current value is a maximum normal. It will draw a lot less than 0.6A when the motor is unloaded, and a lot more than 0.6A if the motor is stalled. These values are available in the motor datasheet (if they aren’t, then you shouldn’t be buying that motor). The voltage value is more reliable: that is what the motor will run well with. Reducing this voltage will make reduce performance by an amount which depends on the controller and various other factors inherent to the motor.

A 18.2V, 2.75A solar panel does not provide 2.75A at 18.2V. It can provide at most 2.75A and at most 18.2V. Most of the time you are lucky to get 50% power out of a PV panel, and that’s with a Maximum Power Point Tracker, which balances the current and voltage out of panel to give you as much power as possible. This would tend to go into some conditioning circuitry which would then go into an energy store (battery or high capacity capacitor).

So putting these together... You have at most 18.2V going into a motor designed for 48V. This will result in a lot lower current (as V=IR), so there will be a lot less torque on the rotor than there should be. If there is no load and there is very low friction it may well run. You may need to spin the shaft to give it a bit of a kick to start it.

To answer your question: maybe, but only in ideal, unloaded conditions.

Alternatively, as your solar panel may be able to produce 50W, and the motor is only rated to 29W, you may be able to use a boost converter to go from the panel output (after the MTTP and conditioning set up) to give you 48V, which would then be able to power the motor. This set up has the advantage that the conditioning will include some energy storage, which should be able to handel power demands and supply changes to some degree.

Answer 2

"neglect voltage rating" is quite a broad statement. What do you mean exactly with that?

The meaning of the voltage rating of a component/piece of equipment if heavily context-dependent. It may mean it's the absolute maximum voltage that can be applied to the component, but it may also mean it's the voltage the component is expected to be used with. In case of voltage generators it may mean the output voltage the generators puts out, but in the case of current generators it may be the maximum voltage the generator can generate in its attempt of putting out a given current ("compliance voltage").

There are components which have more than one "voltage rating". For example, it's customary for semiconductor devices to have a specification for "absolute maximum voltage" (the voltage above which the component is not guaranteed to survive) and the "recommended operating voltage (range)" which is the voltage (range) at (over) which the component is supposed to operate according to the specifications.

In the case of the DC motor you mention, that rating means that the motor is designed to work powered at a constant voltage of 48V. In these conditions it may draw up to 0.6A, and that happens when the maximum allowed torque is applied to the shaft. You can use a lower voltage, and the motor will have lower speed, but also lower maximum power. Higher voltage might be possible for limited amount of time, but the details depend on the type of motor.

In general, for any component/piece of equipment you should always examine its datasheet and interpret the information you get from it according to the general principles of operation that govern that kind of system. That's true for any kind of rating.

For example, a DC motor can also be driven with a PWM signal instead of plain DC. A PWM signal is essentially a varuable duty-cycle square wave, hence it's like turning the motor on and off very quickly. This allows controlling the motor speed using an MCU, for example.