AC motor speed controller for washing machine motors. (US-52) - Page 1
Forum section: electronics / beginners

author: ktulu
author_rank: Regular Contributor
timestamp: January 08, 2024, 02:02:11 pm
content: There are a couple of chinese made devices for controlling the speed of washing machine motors with tacho generators.One of them is a cheap, OP amp based unit called US-52.I've found a russian site with schematics which I link in:https://cxem-net.translate.goog/remont/remont89.php?_x_tr_sl=auto&_x_tr_tl=en&_x_tr_hl=en&_x_tr_pto=wappI am interested in how exactly this is working?A few remarks: TJx connections match the numbering printed on the box.TJ6-TJ3 potentiometerTJ4-TJ5 tachogeneratorTJ2-TJ7 mains ACI am confused what that upper diode bridge - opto coupler and OP1.2 are doing? Some sort of feedbackwith gating circuit? The output of the opto is a PWM signal maybe?OP1.1 looks like some sort of integrator or PI controller?I am also confused of what is referenced to what here? On the non inverting input there are 2 zeners creating a +- 6V supply.What is the purpose of D11 and T4 emmitter follower?Weirdly the value of C9 smoothing cap is the same as C9' coupling (or derivating) capacitor?Both inpuths of the first op-amp are also connected to the filtered tacho output.A more detailed explanation would be very helpful.Thank you.

author: ktulu
author_rank: Regular Contributor
timestamp: January 11, 2024, 08:31:51 am
content: Anybody?

author: Benta
author_rank: Super Contributor
timestamp: January 11, 2024, 12:16:45 pm
content: Look for the Motorola data sheet for TDA1085C..This was the classic part for controlling washing machine motors (universal motors).It might give you some ideas on how the discrete circuit works.TDA1085C is long obsolete, unfortunately.

author: jwet
author_rank: Frequent Contributor
timestamp: January 11, 2024, 05:19:26 pm
content: First, be careful poking around in circuits like this. Its all floating- use an iso tranformer and establish a ground for your testing. Deadly, test equipment destroying stuff.The top bridge is across the motor and gives a line sync'd pwm of the motor on/off. It gives the opto a full wave rectified version of this for main feedback. T1 squares this up and pumps C5 though R9 to give a kind of triangle wave reference for OP2- this will create a pwm to drive the triac through T2, etc. There is a bit of schmidt trigger feedback going on with T3 and T1 to make sure switching only happens on edges. The pin3 link is the out When it turns on the triac, it blanks T1, etc. The pin 3 link is the "positive supply" but is chopped based on opto feedback. The "negative" voltage derived from the line is at T4 with filtering by C2. It is arbitrarily tied to one side of the motor.You can look at the lower bridge, T4 and OP1 as signal conditioning for the tach input. The bridge rectifies the tach and provides DC feedback thought the R24 string to OP1. OP1 's + input is held at zero by the two zeners which also provide a total of 12v across the amp. T4 sums in a bit of the ripple from the Tach and give a bit of "derivative" in a PID sense that is summed in to OP1. The pot at W allows you to vary how much D gain you want for stability (feedforward). OP1 is a shaped gain stage (almost an integrator) with a low freq roll off that feeds a conditioned input to OP2 that represents tach feeback.The pot across the lower bridge reduces feedback to set motor speed by lowering feeback. Finally the Triac is driven by T2 and the loop is closed.These circuits are devlishly clever (and cheap). Its fun to analyze them. The old IC solution that Benta pointed you to was created because all the old dudes that could design this kind of discrete stuff died off. My career spanned the 70's to current and I watched this transition. What this really is a fairly sophisticated control system designed by a sharp guy probably refined over a lot of years. Today this circuit would be done with a small microcontroller, a triac, opto and a couple of discretes. The simplest micro with some well written code could to a nice job of this and even offer enhancements like load compensation, stall detection and protection. ST has some app notes (google ST6210) about applying their micros this way. Microchip might too but the cheapest will use chinese no name uP's.Again- be careful.

author: ktulu
author_rank: Regular Contributor
timestamp: January 12, 2024, 01:55:43 pm
content: Thanks for the explanation. I might do some Tina simulations to clarify things up more.There is a much more simpler version.Can you please help me understand this circuit as well?I don't know why they are forcing the use of diode bridges? Here it is used in a more weirder way.

author: jwet
author_rank: Frequent Contributor
timestamp: January 13, 2024, 12:47:22 am
content: Give me a thanks with the thank button. Its why I do this- its sad but all I've got.Second circuit is pretty rough and ready- almost just a lamp dimmer circuit, doesn't bother with zero crossings explicitly.The tach drives two opto led's thought a pot (speed control). The use of two antiparallel LED's is the alternative to using a bridge here as the last circuit did. The gen makes AC and this gives you "DC", one or the other optos is conducting. DB3 is a "diac"; kind of the solid state equivalent of a neon bulb. It gets up to a certain voltage and conducts in both directions, this turns on the big triac which drives the motor. The whole circuit to the right of the bridge is negative feedback and some frequency tailoring for stability. When you short out a bridge with the optos plus T1 and the LED, you lower the voltage seen at R2 which will make the triac conduct less and closes the loop.Bridges used to be used for a lot of clever things like this in circuits. Precision HP test equipment circa 1970 used this kind of stuff. You can make "switching" type circuits by manipulating the output side of a bridge. You can do thing like direct signals based on DC signals used on the ports of a FWB. This is why these little diodes like the 1N914 and 1N4148 are called "switching" diodes- lots of circuits used some clever schemes using diodes, pre logic. FET's and finally analog switches replaced a lot of this bridge stuff but its still clever. Might be worth googling or a simulation.This is mostly a bang-bang type controller I think- I haven't gone though in much detail but the RC/diode stuff around R5 looks like its trying to approximate some linear stuff but its pretty crude. . I think the motor would get turned on, the opto's would conduct based on the tach and pot setting and shunt the bridge, taking the Triac out of conduction and lowering speed. Those RC and diode circuits make it so it doesn't "breathe" too much- low frequency hunting. Probably requires tuning to the motor and final application.Its nice to run motors with zero crossing operation for EMI and brush life- hitting a motor with line peak is hard on things. There is a special optocouplers like the MOC3081 that is an opto coupler that drives a mini triac at zero crossings that can be used to drive a big triac in these kind of circuits. Before this, there were non zero crossing triac driver optos like the MOC3011. If you have a micro, you can fire these optos at zero crossings with a line freq interrupt to your micro. The MOC3081 does it in analog and probably better.Are you trying to make some motor controllers? Some of the better circuits that I've seen are treadmill motor controllers. They're pretty beefy and well designed, modern circuits. White goods (appliance apps) are very cost driven and tend to cut corners. Tread mills have good EMI and smooth operation due to their use.Have fun.

author: ktulu
author_rank: Regular Contributor
timestamp: January 13, 2024, 08:56:53 am
content: Yes.Probably C1 gets charged trough R1, the bridge, R3, C2a in each half period until the diac fires the triac. The motor starts spinning and gathers speed.Meantime C2a is slowly charging trough R3 while keeps T1 closed.The LED is there probably to lift the emitter of T1 to compensate for the voltage drop across VD4.When C2a gets charged enough, T1 will open and shunts the bridge, forcing the charge of C1 even faster.The voltage on the opto's influence the charge cycle of C2a providing negative feedback.I have some washing machine motors that I'd like to use in some equipment, like a concrete mixer.I couldn't really find any good microcontroller or analog project that could offer even close the functionalities of the TDA1085.

author: jwet
author_rank: Frequent Contributor
timestamp: January 13, 2024, 08:21:49 pm
content: I think you have a better handle on this thing than I do. It would be interesting to build some discretely like this.I've done a lot of power design but only a few motor drivers over the years- mostly steppers. As an FAE, I looked at a lot of these circuits from our customers.I do know you can have some exciting failures in these circuits just when you thought you were getting a handle on things.I don't think you'll find anything worth building in the hobby literature on line. I would look at commercial industrial guys like Teccor, Diodes Inc, Bosch and Vishay for driver circuits app notes and some of the uC guys like Renesas/Intersil, ST and Microchip for micro stuff.Have fun.

author: Benta
author_rank: Super Contributor
timestamp: January 13, 2024, 09:16:25 pm
content: If your project is a one-off, NOS TDA1085C can still be found.

author: Atlan
author_rank: Frequent Contributor
timestamp: January 14, 2024, 01:35:10 pm
content: Not the best regulation at low revs.There are solutions based on Arduino or uPhttps://forum.strojirenstvi.cz/viewtopic.php?t=34454