universal motor AC and DC power supply - Page 1
Forum section: electronics / beginners

author: lakis70
author_rank: Contributor
timestamp: June 06, 2025, 06:37:59 am
content: I have a universal ACC motor from a washing machinemotor specs are220-240V 50Hz1100/12500 rpm 210/320Wi meassured the field coils are 6.4 Ohm and 49mH and rotor coil 8 Ohm and 21mH.Q1: How i will calculate the DC voltage for same specs?is that right?AC calc70mH total at 50Hz has 22 Ohm reactance and the coils resistance 14.4 Ohm. From P=(U^2)/R => U = 87.7V rms and I = 2.7ADC calci need 2.7A for magnetic field so and i have 14.4 Ohm resistance so V = I*R = 38.9V but P=105Wor from P = (U^2)/R => U = 55V and I = 3.8AQ2: Why LTspice (R1=6.4 in series L1=49mH in series R2=8 in series L2=21mH) supplied by V1=130V (90Vrms) 50Hz meassures 3.4A rms so for 70mH coil takes 12 Ohm reactance?Q3: They said small motors has 30% efficiency, so from 210W i have 63W?

author: MariuszD
author_rank: Regular Contributor
timestamp: June 06, 2025, 08:37:45 am
content: You don't know important specs.You didn't include back-EMF in your calculations.Rated power is usually mechanical power. If that is true for this motor electrical power is unknown.I doubt this can be calculated with so little information. The rated power isn't continuous power, and cos ϕ (power factor) is always less than 1, so there's no way to precisely calculate current draw. You'll need to check how it heats up during tests. The voltage applied to the armature and the stator current determine the RPM. You'll need to find this experimentally. The motor should be mechanically loaded because series motors tend to over-speed.

author: Xena E
author_rank: Frequent Contributor
timestamp: June 06, 2025, 10:42:13 am
content: Washing machine universal wound motors are generally run series and the running of one will have to always be on load as otherwise they will overspeed and mechanically destroy themselves, even at small power levels.Depending on your application therefore, you may want to add some kind of closed loop speed controller/limiter. WM motors usually have a fitted tacho for this duty and a dedicated controller.The power they can run at will have been calculated by the manufacturer and for your purposes may be a function of the work dutycycle and cooling provided, I've seen them used intermittently at power rating•2Can you monitor the motor in the machine on a full load spin cycle to get an idea?TL DR.Electrically safe at peak AC value, mechanically and thermally not.What is your application? Are you repurposing this for another job other than a washing machine? Why DC?X

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 06, 2025, 11:30:49 pm
content: I once tried to blow up a universal motor. I took an old vacuum cleaner apart, removed the air pump, oiled the bearings and put 230VAC mains voltage on it. It survived a few minutes, and then I got disappointed and bored.

author: lakis70
author_rank: Contributor
timestamp: June 06, 2025, 11:40:22 pm
content: at first i want to learn how to calculate dc supply for the same efficiency and for power tools like drills etcalso i want to try it as bicycle generator. I separate the field coil and rotor, supply rotor or field with dc current, but i dont how much current it needs.

author: Benta
author_rank: Super Contributor
timestamp: June 06, 2025, 11:49:57 pm
content: Universal motors in power tools and washing machines etc. run miserably on DC. Inductance and commutator timing is laid out for mains AC.Separating field and rotor windings will bring you no joy, it will never work as well as a shunt motor/generator.But good luck.

author: Xena E
author_rank: Frequent Contributor
timestamp: June 07, 2025, 03:50:00 am
content: Quote from: Doctorandus_P on June 06, 2025, 11:30:49 pmSounds like you were already bored before you started.