Can you increase speed without increasing current in a electric motor?

In a reasonably efficient motor the voltage relates to the speed, the current to the torque and the electrical power V*I is then related to mechanical power speed*torque. This allows voltage to increase speed with only a minor increase in current so long as the load remains constant.

The efficiency does have an effect though. Better quality or larger motors tend to have efficiencies around 90%. That means about 10% is wasted, and it may be that this causes an increase in current with increased speed, and that the speed is not exactly proportional to voltage, and load increases give moderate speed reductions. With a small 12V motor it is not uncommon for these to be only 50% efficient, and these effects are magnified.

The current is not directly related to the DC resistance, except when it is stalled. This motor draws 1.2A when stalled if it has a DC resistance of 10 ohms, and less (until almost zero if it is efficient) when at operating speed with no load. Any current drawn at a settled speed is related to efficiency, i.e. overcoming losses, and load, power delivered to the output shaft.

With an efficient motor and no load we expect the no load current to be small, so at 48V it would run nearly 4 times faster despite the 30 ohm resistor. The maximum stall current is 1.2A still, and the speed would be poorly regulated with changes in load due to the series resistor. As load increases the current increases and the voltage across the motor reduces, so the speed reduces (quite dramatically probably in this example).

Motors are rated for the maximum voltage (to limit the RPM) and maximum current (to prevent the windings getting too hot).

I suspect that the resistance you mention is calculated from the current drawn with 12V at operating speed, and some load, which amounts to internal losses if there is no external load.

All the above can be confusing if the motor is inefficient (its own load is as big or even bigger than the external load). Some loads are highly non-linear, or at least increase with speed. A fan is an example. The power for the fan is related to the cube of the speed, so small speed changes make a big difference to the load.

The answer is that a speed increase by increased voltage gives a moderate increase in current depending on the motor efficiency, and if the load is involved, the load characteristics. The new speed needs to be within the speed rating of the motor and the load (even if only because efficiency can change for the worse if too fast, but also because the life of bearings, brushes, commutator etc can be reduced or the motor just fly to pieces.) The current under load at the new speed and load also needs to be within the current rating of the motor. Adding the 30 ohm resistor will not work as you expected, though a very inefficient motor may be more like your expectation than a very efficient one..

Basic DC motors work like this, The motor rotation generates a "back EMF" so the current is the voltage difference divided by the motor resistance. The current varies as the torque. So the stalled torque (zero EMF) varies as the input voltage divided by the motor resistance. But given no load, the motor will spin up to the point where the EMF matches the input voltage and current falls towards zero.

The back EMF is the product of the speed and the field strength, so if you reduce the magnetic field, the motor will have to turn faster to generate the same EMF. Normally this would require more current but if you reduced the load as well, it could run faster without increasing the current.

undemanding DC automobiles paintings like this, The motor rotation generates a "lower back EMF" so the present is the voltage distinction divided by the motor resistance. the present varies because of the fact the torque. So the stalled torque (0 EMF) varies because of the fact the enter voltage divided by the motor resistance. yet given no load, the motor will spin as much as the element the place the EMF suits the enter voltage and modern-day falls in direction of 0. The lower back EMF is the made of the cost and the sphere power, so in case you chop back the magnetic container, the motor will could desire to instruct swifter to generate the comparable EMF. in many cases this could require extra modern-day yet once you decreased the burden besides, it could desire to run swifter without increasing the present.

Yes, it works the same as 12V set up. 36V electricity power turns into wasting HEAT. The motor runs the same way without any improvement,same speed as it runs on 12V.