| Electronics > Projects, Designs, and Technical Stuff |
| smps for dc motor |
| (1/4) > >> |
| daniel444:
i have acquired a 1kw 180v treadmill motor that im going to use a for a disc grinder project. im planning on using mean-well LRS-350-15 as the power supply i realize that its only 350w at 15v , that will give me the low speed i want with some torque too i dont need the full power of the motor for the type of grinder im building and ive already tested it on some 100w smps an it is almost powerful enough my question is do i have to put anything in between the motor and the meanwell smps to protect it ? thanks |
| beanflying:
The Meanwell is on the better end of the Cheap and Cheerful Chinese market and most likely has either an internal fuse (minimum but lift the lid and check or add one if not!) or short circuit protection. The problem you will face with any power supply (Linear or SMPS) and a DC motor is the inrush current on startup. If there is any sort of resistance to overcome initially the current will be way higher than a running current. |
| daniel444:
thanks , ive already tested the motor on a cheap 100w laptop supply and its almost powerful enough , so im thinking the meanwell should do the job |
| Siwastaja:
A quick approximation: 180V 1kW nominal = 5.5A nominal Stall current at 180V likely 10x that, so 55A. (A ballpark number.) Stall current at 15V = 15V/180V * 55A = 4.6A. Meanwell supply: 350W/15V = 23A. So it's more than enough. Of course, the RPM will be very low. Also, just 8% of nominal voltage is so low that it won't necessarily produce high enough torque, even at low RPM. An imaginary, ideal motor with zero equivalent DC resistance would give you full torque at zero RPM by just anything >0 voltage. Imotor = (Vsupply - Vbemf)/Rmotor, where Vbemf is the voltage the motor generates by rotating, linearly depending on the RPM. For example, a motor rated to run at 5000 rpm at 100V with no load, has approximately 0.02 V/rpm. At zero RPM, the current is simply Vsupply / Rmotor. And motor manufacturers want to minimize the R, because it's only causing losses. So now you see that an efficient motor, with almost zero Rmotor, absolutely requires being driven from an actual current source, not a voltage source, because driven from a voltage source, you get infinite current. The torque produced cannot be infinite, though; the iron saturates, and the efficiency plummets. Overcurrent protection is not needed - it just trips all the time - active current limiting is. (And with active limiting, you never get overcurrent.) It's exactly like driving an LED or charging a battery, voltage is secondary, current is controlled. Inrush is the wrong term. Of course there's inrush, because every motor sometimes starts at 0 RPM, but the same thing happens whenever you have a lot of mechanical load. Inrush only applies when the motor spins up on the lab bench, with no load. This model is too simplistic for real-world use. (It's like saying that LEDs need current limiting because of "inrush". No, current limiting is needed all the time.) Your case is an exception to the rule. You have such a ridiculously low voltage (8% nominal), that you are not going to have issues with too much current with any practical, less than perfect motor. Try it, and if you have enough torque for your task, you are fine. You can measure the worst case stall current, but I'm 100% positive it's going to be less than 23A (your supply rating), and it's very likely lower (or not too much higher) than the rated running current of the motor (around 5.5A we calculated as the first thing). But, running at low RPMs prevent the motor cooling (based on an internal fan, for example) from working properly. You may need to measure the winding and brush temperatures in extended high-torque use. |
| Siwastaja:
--- Quote from: daniel444 on July 28, 2019, 04:39:33 am ---thanks , ive already tested the motor on a cheap 100w laptop supply and its almost powerful enough , so im thinking the meanwell should do the job --- End quote --- Did you measure that the 100W supply voltage sags? It's highly likely that the voltage does not sag - if that's the case, a higher current rated power supply won't change anything. You may need to up the voltage instead of / in addition to power rating. But if you go too far, you may need to get into proper current limiting. Driven from a voltage source, your torque will fluctuate a lot depending on RPM, and you may have too high current at very low RPM, producing more torque than you need at the lowest speeds, and causing excessive motor heating. |
| Navigation |
| Message Index |
| Next page |