I'm trying to fix my kid's power wheel. When you press the gas pedal, nothing happens. I took it apart and checked everything. I noticed that when I disconnect the wires from the motor and check them with a DVM, it registers roughly 12v when I press the gas pedal. The weird thing is when I connect the wires to the motor and check the voltage, I don't register anything when I press the gas pedal. I can't figure out what would cause that. Any ideas? Motor shot?
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1$\begingroup$ If you are careful, you can connect the battery directly to the motor to see if it runs. You may want to put a sacrificial fuse in the setup so you don't smoke any wires just in case the motor is shorted. This way you'll know if it's the motor or the controller. Additional troubleshooting steps may continue after this easy narrowing of suspects. $\endgroup$– ScienceGeyserMar 8, 2021 at 8:20
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Two reasonable options I can think of for why you're getting zero volts when the system is hooked up:
- The battery is shot. Try probing battery voltage - a 12 volt lead-acid battery is dead if the voltage is less than about 11.8 volts. If the battery is fully charged then it should be about 12.8 volts.
- The motor is shot. Try probing motor resistance. Typically, if the motor is bad, I would expect a wire break, in which case you'd see an infinite resistance, or the insulation is damaged, shorting the wiring and you'd get zero resistance. Since you're seeing zero volts with the pedal down I would guess the motor is shorted.
If you're probing the motor, be sure you're probing it at the motor with the motor disconnected or else you're probing the entire control circuit, too, which could give false readings. The battery state of charge estimate by measuring voltage is supposed to be with the battery "rested," but it sounds like it's not working so that shouldn't be an issue.
I would guess the battery is shot, but it could also just be that it's not charged. My kids will mess with theirs while it's plugged in, so it could be someone's pulled the charger out after you plugged it in, or unplugged it from the wall outlet or turned a power strip off, etc.
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$\begingroup$ Reading the battery voltage with an attempt at normal operation (motor connected, car turned on) while pressing on the "gas" should be informative -- if the battery sags under load, that's all she wrote -- you need a new battery. There could also be a loose connection between the battery and controller, or controller and motor; either of these would cause the symptoms seen. $\endgroup$ Mar 9, 2021 at 17:01
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$\begingroup$ @TimWescott - No voltage could also indicate a short, though, but I would expect something to start smoking if someone is shorting a 12V battery. $\endgroup$– ChuckMar 9, 2021 at 19:40
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$\begingroup$ It depends on the battery, but most lead-acid batteries will be able to supply substantial current if they're shorted -- I would expect that a fuse would blow or some other sort of protection circuitry would kick in if the motor were all the way shorted. $\endgroup$ Mar 9, 2021 at 19:56