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I am very new to the word of electrical circuits.

As I finally decide to learn about electricity and componants, I bought this kit to start in a fun way:

enter image description here

The motor according to the seller is a DC 1.5-3V and 24000 rpm. So a single AA 1.5V battery should be enough for this motor.

I connected 4 motors in parallel to have more torque in the system but I cannot figure out what battery voltage should be the best for this circuit. As the motor is 3V rated, the 4 motors are connected in parallel it should only need a 3V power source to run (i.e. 2 AA 1.5v batteries.)

The 4 motors are connected in parallel with the power source and there is no other component in the circuit.

When I use 2 AA 1.5V batteries the motors run for a very short period and slow and stop, and when I use x4 AA 1.5 batteries the motors run but the wire starts heating a lot.

What is happening here? How do I work out the right voltage for this circuit

I have been searching the answer on this forum for 3 days but I'm still not sure.

Here is the picture of my setup: As you see on the picture, the wires were so hot that the case with 4 AA batteries melt and the yellow connector moved away...

enter image description here

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  • \$\begingroup\$ You've put your batteries in series by the sound of it. \$\endgroup\$ – Andy aka Dec 9 '20 at 13:29
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    \$\begingroup\$ Pics of your actual setups would probably help a lot in diagnosing the issues. Ideally specs for the motors, and diagrams as well but I guess if you are a beginner we can start simple. \$\endgroup\$ – Wesley Lee Dec 9 '20 at 13:47
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If those motors are 24000rpm you'll need to gear them WAY down to do anything useful.

Run them with nothing at all on the shaft and 2xAA batteries should last a good while. Check this now.

You haven't said, but I'm guessing you have put wheels or propellors on them ungeared, so they are practically stalled and draining your batteries fast. (Easy to hear the difference in speed)

Use those gears to gear them down about 5:1 for those propellors or 25:1 to run those wheels across the floor as a starting point.

To be more scientific about it you'd need a multimeter that can measure several amps of current, and measure the current both completely unloaded and with load .. you'll easily see the difference. A bit more information here...

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  • \$\begingroup\$ The motors are 24000rpm... ''according to the seller''. I use some gear but it's only to drive the wheel as you can see in the picture. I'm not sure there is any reduction ratio involve here... I don't know really. I need to found out how to gear them down at 25:1 to run the main wheels. Thank you for your help \$\endgroup\$ – Told mils Dec 9 '20 at 22:45
  • \$\begingroup\$ If they were 2400rpm they'd produce 10x as much torque and you'd be having much less problem. You can actually buy geared motors, but I think I can see enough bits in that picture to put together suitable gearing. Without counting teeth, that looks like 3:1 reduction in the picture. \$\endgroup\$ – Brian Drummond Dec 9 '20 at 23:27
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when I use 2 AA 1.5V batteries the motors run for a very short period and slow and stop

You're correct that wiring 3V motors in parallel (all reds together, all blacks together) are still 3V motors. But now there are more of them, which means you need more of something else from the batteries: current.

Voltage, current, and resistance are the pillars of all electricity and electronics. Learn these by studying Ohm's Law.

and when I use x4 AA 1.5 batt. the motors run but the wire start heating a lot.

If you wired these batteries in series (red battery A to black battery B) then this adds the voltage of the batteries. 3V+3V = 6V, which is too much for these 3V motors. At twice the rated input voltage, they will try to run too fast and consume too much current, leading to burned-out motors and/or overheated wires.

If you wired these batteries in parallel (red battery A to red battery B), then the volts are the same (3V) but now you've doubled the supply current. That is ideal for 3V motors in parallel. What you've discovered is that the little wires connecting everything have resistance, and trying to push too much current through them causes them to heat up. To handle more current, thicker wires (or more of them) are needed.

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  • \$\begingroup\$ Thank you for this comment. I understand from your comment that only 2AA batteries wired in series will give me the 3V I need for this circuit... I did not think that doubling the supply current will increase the temperature. Can you confirm (looking at the pics of my setup) that I will solve the heat issue by using thicker wires ? \$\endgroup\$ – Told mils Dec 9 '20 at 17:33
  • \$\begingroup\$ Well every conductor, including wires, switches, even battery terminal contacts have some resistance. The bigger and better-connected these are, the more current they can carry without heating up. An automobile starter motor uses up to 1000 Amperes of current when cranking the engine, so those battery terminals are hefty and bolted-on to reduce resistance. You could try adding a second set of identical wires to the motors; that should reduce their temperature-rise quite a bit. If instead the push-on connectors or battery terminals are getting hot, those would have to be addressed similarly. \$\endgroup\$ – rdtsc Dec 9 '20 at 17:51
  • \$\begingroup\$ You could also power two of the motors by one battery, and two by a second battery - two separate circuits, but both working at the same time. \$\endgroup\$ – rdtsc Dec 9 '20 at 17:52
  • \$\begingroup\$ As you can see on my setup the 4 motors are connected to the same wheel axle. when you say ''...two separate circuits, but both working at the same time..'' I assume the two separate circuits will have one same on/off switch to be able to start and stop at the same time. But if one power source run out, its related motors will stop working and will become some kind of heavy load or even counter force for the two others motors... am I right here...? \$\endgroup\$ – Told mils Dec 9 '20 at 23:10

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