Help me understand the wording of this problem (electrical circuits homework)?

Sounds right to me.

My husband is an electrical engineer and your formula sounds right to him.

Thanks you two.

I understand ohm’s law (V=IR) just fine. I guess I’m just unfamiliar with the term “drawing” current.

The reason the problem says drawing current instead of resistance is because the equavalent circuit of a motor is a little complex and he didn’t want to get into it at this time. He used the maximum current draw because that was all you need to know to figure out what size power supply you need. This is sometimes called worst case analysis.

He probably is trying to figure out what is the maximum current required by the circuit, motor and all (max current draw from the power supply) so that he can figure how big of a power supply he needs.

Power supplies “source” current and loads “draw” current.

I don’t know why, but I had a lot of trouble with my Electrical Engineering class when it came to answering questions like this. Moreso than other engineering course, figuring out what the question was asking was tough for me.

@Rock2 is absolutely right.

I’m not sure if the that sentence means that the motor can’t draw anymore than 1.5 amps because of the current capacity of the power source (battery) itself is limited, if there is another reason due to the rating of the motor or if there are other circuit considerations here. I’ll try to answer this regardless.

Think of amps as volume and voltage as pressure. Think of a water line for example: your water pressure may be very high but if the piping diameter is too small or if the volume capacity of the source is too small then regardless of the high pressure the water supply may not be ample enough to perform all of the tasks you want it to. You need both of the correct pressure and the volume capacity to perform the proper work.

Don’t forget that a motor is an inductive load and not a resistive load. Inductive loads will produce a massive current (amp) surge when initially energized, then after the start-up period the amperage will level off to its normal current. This current will vary depending upon the horsepower (one hp is equal to 746 watts in a motor). Ohm’s Law formulas for determining the current draw of a load will not be accurate for inductive loads as they would be for resistive loads. A great example of this is a typical three phase step up/down transformer. The ohms you would measure on the transformer windings via a multimeter can be as low as 1 ohm, and you can have 480 volts feeding the coils.

@Paradox25
Your explanation is a perfect example of why the teacher didn’t go into details. It adds unnecessary complication. The teacher was teaching to the level of the students. That’s a good thing. He did not just want to show how smart he was.

To solve any problem first through out all of the irrelavant information.
Simplify.

By the way, amps are flow not volume.