What this motor type? - Page 1
Forum section: electronics / beginners

author: Cos-Phi
author_rank: Newbie
timestamp: November 13, 2018, 08:51:44 am
content: Dear Guys,I have a motor from my washing machine. I don't know what kind of this motor. Is it induction motor or Synchronous motor? and why the rotor's winding is serially connected to the stator's winding? and i can change the rotation direction by exchanging the rotor's winding.i have googling for find what type of this motor, but i haven't sure. Thankyou for your answering

author: Zero999
author_rank: Super Contributor
timestamp: November 13, 2018, 09:00:47 am
content: It's neither an induction motor nor a synchronous motor. It's a universal motor.https://en.wikipedia.org/wiki/Universal_motorYes, the direction can be changed by reversing the connections to the armature (not rotor), but it might not run as efficiently, if it's only designed to run in one direction.

author: langwadt
author_rank: Super Contributor
timestamp: November 13, 2018, 09:01:16 am
content: universalhttps://www.testandmeasurementtips.com/basics-of-universal-electric-motors/

author: Cos-Phi
author_rank: Newbie
timestamp: November 13, 2018, 09:07:13 am
content: Thank you very much for answering.so, it is better to run in DC?in the washing machine, this motor was controlled by TRIAC BTB12-600 Series.well, thank you very much..

author: Benta
author_rank: Super Contributor
timestamp: November 13, 2018, 09:53:49 am
content: As people say, a universal motor.Note the round thing on the end (left side of the photo)? That's the tacho generator, which you'll need for speed control.It was very usual to use the TDA1085C IC (now obsolete) together with a triac to control this type of motor.

author: Zero999
author_rank: Super Contributor
timestamp: November 13, 2018, 11:56:35 am
content: Quote from: Cos-Phi on November 13, 2018, 09:07:13 amThe motor might work slightly more efficiently from DC, but a TRIAC speed controller requires AC. I doubt you'll see any gain in efficiency from using a rectifier to get DC and a MOSFET or IGBT to control the speed, as the total voltage drop due to the rectifier & MOSFET or IGBT will be higher, than a TRIAC. Using a bridge rectifier with SCRs to control the speed, might give some increase in efficiency, at the expense of additional complexity.It might not be safe to operate the motor unloaded, with no speed controller, as it could over-speed, causing damage to the bearings, brushes and commutator.

author: james_s
author_rank: Super Contributor
timestamp: November 13, 2018, 10:22:50 pm
content: It will work on either AC or DC, hence being called a "universal" motor. It will run a bit quieter and smoother on DC though.

author: Cos-Phi
author_rank: Newbie
timestamp: November 13, 2018, 10:34:45 pm
content: Quote from: Hero999 on November 13, 2018, 11:56:35 amQuote from: Benta on November 13, 2018, 09:53:49 amThankyou for the advice..i was design speed controller using this schematic.the "SPEED" input is time-based signal from uC. Micro controller use a Zero Cross Detection circuit to synchronize on and off pulses with the AC input periods. The AC input period is 20mS in 1 cycle (50 Hz). so, i can delay from 0 (100% power) to 10mS (0%).What do you think about my design? is there any something to be corrected? Your advice, please (Please ignore the "Rotor" type. it is mean the armature).

author: Benta
author_rank: Super Contributor
timestamp: November 14, 2018, 09:40:57 am
content: Why do you want to reverse both armature and field? It's only necessary to reverse one to change direction.And you really need to use the tacho feedback, otherwise your speed control will be very unstable.

author: Brumby
author_rank: Unknown
timestamp: November 14, 2018, 10:28:16 am
content: Indeed. Reverse both and the motor will rotate in the original direction.

author: james_s
author_rank: Super Contributor
timestamp: November 14, 2018, 04:24:44 pm
content: Who is talking about reversing both? The schematic I see is only reversing the power to the armature.

author: Benta
author_rank: Super Contributor
timestamp: November 14, 2018, 05:04:34 pm
content: Yeah you're almost right, but not quite. What I see is short-circuiting the armature (schematic error).But using a double-pole relay would be simpler and safer. Who knows what's happening as the MCU boots?

author: Cos-Phi
author_rank: Newbie
timestamp: November 14, 2018, 10:39:26 pm
content: Quote from: james_s on November 14, 2018, 04:24:44 pmQuote from: Benta on November 14, 2018, 09:40:57 amYes, of course.I need changing the direction of rotation.i wrote a program for my uC that will run in 2 mode. Free running and speed-based mode.in the free-running mode, the user is only enter the direction (CW or CCW), and the speed can be adjusted by pressing button up and down. start point is 10% (by firing TRIAC delayed 9mS after my ZCD detected crossing position of AC Line input. my AC lIne period is 20mS). And then the speed of motor will be showed in the LCD Display.And, in the speed -based mode, user will enter the direction (CW or CCW) and the speed. and then,microcontroller will start and controll the motor rotation speed automatically.of course, both mode (free-running and Speed-based) maximal speed was set due to over speed protection. I was use the LM393 Comparator chip to convert sinewave tacho signal to TTL Level pulse, and then read by uC useing Timer0 module. on full power, i got 16.000 pulse every 1minut (may be it is refer to 16000RPM. because i have no data about the tacho). SO i was limit to 10.000 pulse / minut only.tnxcos-phi

author: perieanuo
author_rank: Frequent Contributor
timestamp: November 15, 2018, 04:01:05 pm
content: Don't reinvent the wheel,put triacs,pwm control on them if you want,triac for direction change.quick,easy to control.Envoyé de mon iPad en utilisant Tapatalk

author: Zero999
author_rank: Super Contributor
timestamp: November 15, 2018, 04:12:35 pm
content: Quote from: perieanuo on November 15, 2018, 04:01:05 pmUsing a TRIAC for direction change seems a bit odd. I'd be inclined to use the TRIAC for speed control and an old fashioned relay to change the direction.

author: perieanuo
author_rank: Frequent Contributor
timestamp: November 15, 2018, 04:19:12 pm
content: Relays are expensive,slow,not reliable.And big.Put a relay if you want.I'll prefer always triacs or ssr-sRegards,pierreEnvoyé de mon iPad en utilisant Tapatalk

author: Zero999
author_rank: Super Contributor
timestamp: November 16, 2018, 02:52:39 pm
content: Quote from: perieanuo on November 15, 2018, 04:19:12 pmI don't think I've ever seen TRIACs used for changing the direction of a universal motor, simple on off or speed control yes, but not directional. There would need to be four to make an h-bridge. I can't see how it would be cheaper or less reliable than a relay, since it won't be switched very often. TRIACs also are more sensitive to current surges, over-voltage and false triggering, compared to relays.

author: perieanuo
author_rank: Frequent Contributor
timestamp: November 16, 2018, 04:53:09 pm
content: Quote from: Hero999 on November 16, 2018, 02:52:39 pmOver voltage my a..ss,current BTA's have 600-800 Volts,over current if you have a shortcircuit both relay and triac dies.If it's not often put an inversion switch like in drilling machines.I like cause it's elegant.you put like you said a h-bridge of s202-s12 like ssd's and you're good.triacs are cheap for the currents they commute,relays not.false triggering never happens if you do your job right in command circuit.Anyway false command may happen with CW-ccw from microcontroller.I have one last argument :nobody uses mechanical relays anymore if you can do this with ssd's.even for slow commutation devices like valves and motors.His demand to invert rotation on a classical motor is not usual thoe.Anyway, I think I'm free to consider triac a better alternative, with respect others don'tRegards,pierreEnvoyé de mon iPad en utilisant Tapatalk

author: james_s
author_rank: Super Contributor
timestamp: November 16, 2018, 04:59:28 pm
content: Relays are more reliable than triacs generally speaking. There's a reason that even most modern iron transformer type xray machines have a mechanical relay for the secondary control. A triac or back to back SCRs handles the exposure timing but the relay is tested to verify it is open and then closes immediately prior to the exposure and opens once finished. Solid state devices usually fail shorted, adequately rated relays very rarely do.

author: perieanuo
author_rank: Frequent Contributor
timestamp: November 16, 2018, 05:22:06 pm
content: Quote from: james_s on November 16, 2018, 04:59:28 pmNo they are not.In terms of reliability electronics beats mechanics.If you don't know how to handle it it's another business.If some machine use mechanical relay,ok,I can enumerate many others that don't.Your example does't state a rule.It's just a simplier solution to securise an automation where hasard in commuting is disastrous.In the OP case, doesn't seems to be (in fact, it's not mentioned if direction reversal is critical).I will continue tu use ssr (just checked an 8amps 600 volts triac costs 0.3 euros in France from mouser).and if I need to deal with commutational hasard I'll just put electronical commutation verifications on triac involved.The protection will be much faster than mechanics.I saw already half a relay blocked (yes, welded contact) and the other relay contact who did his job.in this case, you're f..ed if you don't have hazard protection in place.I'm speaking from some years of research and dev in medical and general electronics where security matters and cost you patient's life.PierreEnvoyé de mon iPad en utilisant Tapatalk

author: james_s
author_rank: Super Contributor
timestamp: November 16, 2018, 06:45:25 pm
content: The issue is more complex than failure rate, failure mode also matters. A mechanical relay usually fails safe, a triac or other solid state device almost always fails shorted. Nobody in their right mind would rely on a SSR alone to cut off the power to something that could cause injury if it powers up unexpectedly or fails to shut off when commanded. When it comes to things like momentary overloads or electrical surges, a relay is much more likely to survive an event that would blow a triac. Under normal conditions both are quite reliable, I have equipment that is decades old using relays to control loads that all still work fine.Just one random example I've dealt with quite a lot is pinball machines, the solid state machines use transistors to control all the solenoid coils and those transistors are one of the most common failures in the machine. The old electromechanical machines use relays, I don't recall ever having to replace a relay in one despite the fact that the newest ones are now ~40 years old.Microwave ovens, dishwashers with electronic controls, clothes washers, that sort of stuff still often uses relays. Of the machines that use triacs to control motors and solenoids the triac is usually what fails, I can't remember having to ever replace a relay in anything like that.

author: Zero999
author_rank: Super Contributor
timestamp: November 16, 2018, 07:27:35 pm
content: Another issue with TRIACs is they have a much higher on loss, compared to relays which lose negligible power.Relays can also fail short circuit, but it's less common than TRIACs which nearly always fail short circuit.As far as reliability is concerned, there are some advantages TRIACs have over relays: they're less susceptible to vibration and the number of switching cycles is unlimited. In this case vibration can be mitigated by appropriate component selection and good mechanical design and the number switching cycles is a non-issue, as the motor won't be reversed frequently enough for that to matter.In the case of controlling both the speed and direction of a universal motor is concerned: use a TRIAC for the former and relay for the latter. Using four TRIACs to control both the direction and power makes it more difficult to control, results in double the power dissipation, compared to a TIRAC and relay and if one of them fails short circuit, the power supply will be short circuited when the other one turns on. In short, using TRIACs to control the direction of a universal motor is a bad idea. Different components have their strengths and weaknesses and good engineering is about knowing which component is best suited to a certain application.A latching relay for directional control is probably best, since there's no chance the motor can suddenly reverse, if the power to the relay coil fails. Reversing the motor when the shaft is moving at full speed, will result in an enormous peak current, nearly double the initial starting current which will cause total destruction of the driver circuitary.