G+_Rud Dog Posted August 21, 2016 Share Posted August 21, 2016 What are the consequences of running a 24VDC motor at 12VDC? Link to comment Share on other sites More sharing options...
G+_Eddie Foy Posted August 21, 2016 Share Posted August 21, 2016 They can smoke. The insulation (enamel coating) on the coils is not rated for the extra voltage. If run for short periods of time may be OK. But even with a PWM @50%, its not gonna last long. Link to comment Share on other sites More sharing options...
G+_martin rednal Posted August 21, 2016 Share Posted August 21, 2016 Should be fine as your putting half the voltage thru it, will run approx half the speed Link to comment Share on other sites More sharing options...
G+_Rud Dog Posted August 21, 2016 Author Share Posted August 21, 2016 Eddie Foy Think or I could wrong you read my voltages backwards? Link to comment Share on other sites More sharing options...
G+_Jason Marsh Posted August 21, 2016 Share Posted August 21, 2016 Speed and torque will be slow and low. Link to comment Share on other sites More sharing options...
G+_Eddie Foy Posted August 21, 2016 Share Posted August 21, 2016 Oh crap! Jason Marsh Yup. My LexDicisia prevails. :P Current will rise too. Link to comment Share on other sites More sharing options...
G+_Golden Retriever Posted August 21, 2016 Share Posted August 21, 2016 Smoke, tipically a 24 v DC motor will have windings at 1/2 the diameter of a 12 v DC motor so they will heat up like a toaster. Link to comment Share on other sites More sharing options...
G+_Fr. Robert Ballecer, SJ Posted August 21, 2016 Share Posted August 21, 2016 Electric motors can tolerate voltage other than their design voltage, but it can be very inefficient. They're designed for a particular voltage/current and undervolting tends to draw more current, which increases the amount of waste heat and can lead to premature failure or straight-out smoking. Link to comment Share on other sites More sharing options...
G+_Eddie Foy Posted August 21, 2016 Share Posted August 21, 2016 On another note: Not all motors are designed for continual run. I offered that up to a guy who wanted to use a garage door opener motor to run his mill grinder (for beer brewing) He tried it anyway and it died in a minute. Link to comment Share on other sites More sharing options...
G+_Eddie Foy Posted August 21, 2016 Share Posted August 21, 2016 Mark W it should hold it well. The current won't be via ohm's law (aka: double, since its not a direct resistive load) and and the wattage stays the same. Link to comment Share on other sites More sharing options...
G+_Rud Dog Posted August 21, 2016 Author Share Posted August 21, 2016 My take away, short term testing OK long term, create smoke generator. Link to comment Share on other sites More sharing options...
G+_Eddie Foy Posted August 21, 2016 Share Posted August 21, 2016 At 1/2 voltage it won't smoke. Might screw up the PS. You also never said the motor type: brushed, stepper, brushless, 3 pole brushless, etc. Link to comment Share on other sites More sharing options...
G+_Jason Marsh Posted August 21, 2016 Share Posted August 21, 2016 Dang that Ohm and his crazy law! Didn't he get banned from G+ a while back? Link to comment Share on other sites More sharing options...
G+_Rud Dog Posted August 22, 2016 Author Share Posted August 22, 2016 Eddie Foy Was gonna post a pic then I remembered you can't attach a pic here. Here is what was on the case. ELECTRIC MOBILITY - MOTOR 24V DC CIM EM801-003 Link to comment Share on other sites More sharing options...
G+_Jason Marsh Posted August 22, 2016 Share Posted August 22, 2016 Rud Dog Just run it. It'll be fine. Steve Wolf What? Link to comment Share on other sites More sharing options...
G+_Jason Marsh Posted August 22, 2016 Share Posted August 22, 2016 Steve Wolf It was likely a far heavier winch than the power supply (battery(ies) and alternator) could handle. If you halve the potential across a circuit, you will get less work out of it and dissipate less heat. People often think they understand Ohm's law, and assume that equal work will be done, so current must be increasing. Not so. The resistance doesn't quarter itself to increase current and maintain watts (work), at least not with inductive and resistive loads (motor, solenoid, speaker, lamp, heating coil, etc.). Now, look at an LED light bar, and the LED drivers are controlling current across the LEDs via high-speed switching or other current-limiting control mechanism. It isn't controlled by the voltage (potential, reason, EMF, whatever you wish to call it). With LED light bars and similar loads, you can observe an increase in current from the power source (battery) as the battery drains, because the driver is a buck-boost converter. Watts (measure of work) run constant as voltage dips and current increases. Current across the driven LED remains constant, though. Ohm's law/math has that covered nicely. If it worked any other way, "free energy" devices would be real and we wouldn't be pumping fossil fuels from the ground or irradiating ourselves in the name of progress. Link to comment Share on other sites More sharing options...
G+_Daniel Armstrong Posted August 23, 2016 Share Posted August 23, 2016 It sounds like the motor in question is a permanent magnet brushed DC unit from a medical mobility scooter or electric wheelchair. These are usually good quality and will usually run just fine on half voltage, obviously at half speed. They are normally controlled by a 4 quadrant full H bridge PWM driver that can run them either direction and do regenerative braking in either direction. The caveat is that they also have a spring applied electromagnetic parking brake that probably won't release when supplied with half voltage so it will have to be re-wound or removed from the motor. Link to comment Share on other sites More sharing options...
G+_Jason Marsh Posted August 23, 2016 Share Posted August 23, 2016 I hadn't considered a brake being built into the motor. 12V may be enough to energized it, though. Those powerchairs are probably built to accommodate running the batteries down pretty bad. When I was teaching, one of my favorite subsystems was a cupola that was driven by an H bridge and pretty stout 24v motor. Those were wicked fun to induce faults in. You could see the fear in a student's eyes when it went out of control, especially if you messed with the negative feedback. I nearly got swept off the top of my tank by the .50 cal mount a few times. Such troubleshoot. Very fault. Many fun. Link to comment Share on other sites More sharing options...
G+_Rud Dog Posted August 23, 2016 Author Share Posted August 23, 2016 Daniel Armstrong Great info been searching for more on this motor and past 2 days have not yielded what you discovered. That may be due to the brain lock on searches like Rascal, 24V, part number etc. Thank you really harvested some useful information. Link to comment Share on other sites More sharing options...
G+_Rud Dog Posted August 23, 2016 Author Share Posted August 23, 2016 Begs the next question can a pwm motor be connected to resistance controlled 24VDC voltage. Link to comment Share on other sites More sharing options...
G+_Eddie Foy Posted August 23, 2016 Share Posted August 23, 2016 So in a nutshell, you want to control a rascal/wheelchair motor meant for 24V, with 12V, and use a pot to control the PWN signal? Its a big motor, go 24V. Buy a motor controller deigned for the load. Remember the start up current will be large. Best to test max current draw at start up under load. (motors aren't PWM, the controllers are.) And its HIGHLY inefficient to regulate voltage via resistance.) Link to comment Share on other sites More sharing options...
G+_Rud Dog Posted August 23, 2016 Author Share Posted August 23, 2016 Eddie Foy Looking at the PWM controllers and they are crazy expensive hence the control using some sort of resistance control. As for the inefficiency not worried about that unless it either catches fire or drains the batteries excessively. Link to comment Share on other sites More sharing options...
G+_Eddie Foy Posted August 23, 2016 Share Posted August 23, 2016 Not gonna happen with a pot. Unless you start seeing 100+ watt pots. Those resistors (pot) will be dissipating a massive amount of power (aka: heat) You could experiment with building some MOSFET or IGBTs H-Bridges. (would be a good learning experience) Link to comment Share on other sites More sharing options...
G+_Eddie Foy Posted August 23, 2016 Share Posted August 23, 2016 If using an arduino/Pi/etc, do fully isolate it from the motor. Link to comment Share on other sites More sharing options...
G+_Rud Dog Posted August 23, 2016 Author Share Posted August 23, 2016 Looked at some bridges and might consider this option lots of research for parts but it might be my only option. Link to comment Share on other sites More sharing options...
Recommended Posts