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I have a kid's electric toy car with a 12 V battery and 2 DC motors (Model: RS380/6 V & 12 V with 15000 RPM) connected to battery in parallel and to wheels using gearboxes. For some reason, the 6 V motor burned out. I replaced it with another 6 VDC motor, but it met the same fate within an hour (the other 12 V motor also heats up, but it keeps working with some minor delays.)

  • Is it possible to use a 12 V motor with different RPM ?(12 V/15000 RPM & 12 V/18000 RPM.) Will this put stress on the battery and make it drain faster?
  • Would it be better if I replace both motors with 6 V motors (15000 RPM?) The motors are connected in parallel, so I think the current will be divided in half across each motor.

My main concern is that the motors do not burn out.

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    \$\begingroup\$ you're connecting a 6 V motor to a 12 V power supply ... why are you surprised that it burns out? ... the two 6 V motors will meet the same fate, unless the power supply cannot maintain its output voltage \$\endgroup\$
    – jsotola
    Feb 21, 2023 at 5:46
  • \$\begingroup\$ This is how I got this r.c car(manufacturer fault) \$\endgroup\$
    – Zain
    Feb 21, 2023 at 6:02

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Is this possible to use 12v motor with a different rpm(12v/15000 rpm & 12v/18000rpm),

Possible, yes. But they'll act differently. Is that OK?

will this put stress on battery and make it drain faster.

Compared to what? If compared to two identical 12 V motors: no it shouldn't.

Will this be better, If I replace both motors with 6v motors(15000 rpm), as motor are connected in series so I think voltage will be divided in half across each motor?

Two 12 V motors in parallel is better than two 6 V motors in series. If one 6V motor in series stalls, the other 6 V motor will see 12 V and burn up.

EDIT after your edit

...6 V motors ... connected in parallel,

Powering a 6 V motor with 12 V will burn it.

I think the current will be divided in half across each motor.

Yes, roughly: each motor sees a similar current, depending on the difference in their speeds. But it's way too much current, divided into two motors = still too much current in each motor.

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  • \$\begingroup\$ As both motors are connected to opposite wheel so from act differently you mean 1 wheel will turn faster than the other, will this change when both motors are under load i.e., kid sat on car? \$\endgroup\$
    – Zain
    Feb 21, 2023 at 5:09
  • \$\begingroup\$ I have made edit to my question after realising that motors are in parallel not in series. \$\endgroup\$
    – Zain
    Feb 21, 2023 at 5:25
  • \$\begingroup\$ I edited my answer accordingly. \$\endgroup\$ Feb 21, 2023 at 13:24
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According to Ohm's law there's 12 V and two resistances (active or reactive it doesn't matter I think). In one branch there's one value of current. I think the 6 V motor died because of overcurrent (it can be another reason such as mechanical wear of brushes if it is a brush motor) and there's overcurrent on the other. In that logic two 12 V motors would act better. But you should consider that these motors will act differently.

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  • \$\begingroup\$ From act differently you mean 1 wheel will turn faster than the other, will this change when both motors are under a load i.e., kid sat on car? \$\endgroup\$
    – Zain
    Feb 21, 2023 at 5:27
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    \$\begingroup\$ Ohm's law applies to resistors, not motors \$\endgroup\$
    – user28910
    Feb 21, 2023 at 12:00
  • \$\begingroup\$ @user28910 I am shocked by how many people, including degreed Electrical Engineers, do not understand this fundamental concept: "Ohm's law applies to resistors" and only to resistive circuits. Thank you! \$\endgroup\$ Feb 21, 2023 at 13:26
  • \$\begingroup\$ All motors has a equivalent circuit, but, it is a little complicated to use in that case. But, if you didnt know, rotor/stator of various motors has a resistance. And THIS is important because there's voltage drop too. \$\endgroup\$ Feb 27, 2023 at 5:29

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