U2008B - ac motor controller with soft start option - Page 1
Forum section: electronics / beginners

author: Lautrec
author_rank: Newbie
timestamp: October 28, 2017, 08:57:47 pm
content: Hi, everyone.I tried to make ac motor speed controller for my angle grinder.After bought U2008B chip I created PCB using circuit from datasheet of U2008B, but the controller doesn't work correct.The controller doesn't work in "soft-start" mode and it doesn't work in "current-sensing mode" at all.After I added capacitor 47µ/25V (I see this version in the WEB; look the pic.) the "soft-start" present, but in second mode the chip doesn't work at all, it behaves as if there is no power supply to the PCB.Can I have a bit of help. Thank you.

author: Benta
author_rank: Super Contributor
timestamp: October 28, 2017, 09:52:17 pm
content: Perhaps you should analyze the datasheet:"Variable soft-startorload-current sensing"You can't have both...And as to not working in current sense mode, no wonder: you removed the sense resistor.

author: oldway
author_rank: Super Contributor
timestamp: October 29, 2017, 06:49:02 am
content: A potentiometer with a metal shaft in a circuit connected to 230VYou want to commit suicide?Use ONLY potentiometer with PLASTIC shaft

author: Lautrec
author_rank: Newbie
timestamp: October 29, 2017, 06:39:37 pm
content: Quote from: Benta on October 28, 2017, 09:52:17 pmI understood that.Before I'm adding capacitor 25µ/25V between pin3 and pin5 the circuit work upside down. When power is turn on the bulb immediately lights up in full range for 2-3 second then light decrease to the set value.But now when chip start to work the bulb doesn't flashes immediately (which is incorrect). Light gradually increases for about 2-3 second to the set value.I think this IC is not very good for this project. Whatever I'm not good enough in electronics, so may be I wrong.Quote from: oldway on October 29, 2017, 06:49:02 amThank you for your advice but don't worry. I'm using a plastic knob when I use P1 because I haven't a potentiometer with a plastic shaft. And NO, I'm not planning suicide.Bye the way, what are you thinking about U211B3 for my project?

author: Zero999
author_rank: Super Contributor
timestamp: October 29, 2017, 06:49:51 pm
content: A plastic knob still won't give enough protection to comply with the safety regulations, in most countries: knobs can and do fall off. It the potentiometer is fixed to an earthed, metal panel then that might all right, depending on the creepage and clearances, inside the potentiometer.As far as your query to the U211B is concerned: it depends on the type of motor used. If it's a universal motor (brushed) then it will be fine. If it's an induction motor, then you might just about get away with it, for a grinder, requiring little torque, but it's not the correct way to do it. A variable speed inverter is the proper way to control the speed of an AC induction motor.

author: Benta
author_rank: Super Contributor
timestamp: October 29, 2017, 07:21:59 pm
content: It's an angle grinder, so the probability of it being a universal motor is around 98%.(The other 2 % would be BLDC for a high-end type).

author: Lautrec
author_rank: Newbie
timestamp: October 29, 2017, 08:03:34 pm
content: OK. Thank you.Obviously U2008 is not appropriate, U211B looks good for me. Actually I found another two scheme for AC Motor.With TDA1085C, but looks like not soft-start and LM358 with soft-start, I think.I didn't want to try more than one but obviously it'll have to.

author: Zero999
author_rank: Super Contributor
timestamp: October 29, 2017, 08:04:15 pm
content: Quote from: Benta on October 29, 2017, 07:21:59 pmI agree, I missed the angle part! If it's an angle grinder, it will have a universal motor. An induction motor would be far too big and bulky.

author: oldway
author_rank: Super Contributor
timestamp: October 29, 2017, 09:15:28 pm
content: Quote from: Lautrec on October 29, 2017, 06:39:37 pmThe most stupid thing you could answer....remenber: SAFETY FIRST.....Before you begin with project on 230V, you should learn first a little about safety.https://www.tme.eu/en/details/6pmi-2k2/carbon-single-turn-axial-potentiometers/piher/pc16sh10ip06222a2020ta/The only safe solution is this kind of potentiometer....It cost less than 2 US$ ....and you risk your life for 2 US$...

author: Benta
author_rank: Super Contributor
timestamp: October 29, 2017, 10:03:35 pm
content: The TDA1085 is obsolete since years. It's made for universal motors, but needs tacho feedback. It was mostly used in washing machines in the 80s/90s.

author: Zero999
author_rank: Super Contributor
timestamp: October 29, 2017, 10:42:02 pm
content: How about using a microcontroller? A small 5VDC supply, made from a small mains transformer + rectifier, could be used to power the MCU and an opto-TRIAC isolator, such as the MOC3022, to fire the TRIAC. If sufficient creepage distances are used on the PCB, the control circuit and potentiometer will be safe to touch.

author: oldway
author_rank: Super Contributor
timestamp: October 30, 2017, 12:34:50 am
content: A fully isolated solution using a 555.NB: To work properly, the soft start must be after the on / off switch and not before.Since this switch is located in the angle grinder, the electronic circuit must also be incorporated in the angle grinder.

author: tooki
author_rank: Super Contributor
timestamp: October 30, 2017, 01:57:09 am
content: Quote from: oldway on October 29, 2017, 09:15:28 pmIs there a way to lubricate/dampen those pots? I know Piher is a quality brand, but the feel when turning them is just horrible.

author: Zero999
author_rank: Super Contributor
timestamp: October 30, 2017, 08:23:02 am
content: Quote from: oldway on October 30, 2017, 12:34:50 amThat looks similar to something I designed awhile ago, except I used pin 5 to control the delay, thus the output level and a comparator on the rectifier of the low voltage supply for zero crossing, rather than another opto-coupler.A large capacitor on pin 5 (the value and to where +V or 0V? That's for the original poster to figure out) can be added to implement a soft start.

author: oldway
author_rank: Super Contributor
timestamp: October 30, 2017, 10:04:48 am
content: For safety reasons, the on / off switch is mounted on the case of the angle grinder. This configuration can not be changed.If using an external dimmer, how to reset the soft start?The soft start reset is normally done by switching off the power supply of the dimmer.With an external dimmer, it is not possible.You can not add an additional wire to power the external dimmer.The only option in this case is to limit the starting current without any soft start.To mount the dimmer in the case of the angle grinder, it seems very difficult ... The grinder angle should be specifically designed for this.

author: nowlan
author_rank: Frequent Contributor
timestamp: October 30, 2017, 11:21:58 am
content: All the chips mentioned are obsolete. Are there any current replacements, or is it just microcontrollers now?

author: oldway
author_rank: Super Contributor
timestamp: October 30, 2017, 12:09:34 pm
content: Quote from: nowlan on October 30, 2017, 11:21:58 amIn the current devices that I know, (vacuum cleaners, kitchen robots, mixer, drill, ...) they are all microcontrollers now.If not, there are options to use an NE555 or a classic DIAC circuit.For an inductive load such as a universal motor, it is preferable to use a multi-pulses circuit with auxiliary low power triac.http://www.iascaled.com/docs/psu-400w/an308.pdfTo dim a transformer, the circuit must be modified to reset timing capacitor to 0V each cycle and to avoid asymetric drive of the triac. ( = DC current = saturating transformer)

author: Lautrec
author_rank: Newbie
timestamp: October 31, 2017, 02:43:42 pm
content: I don't understand the microcontrollers and I'm haven't any skills with the program languages. My experience with MSU ends with programming with hex file provided from cool and smart people in the WEB.I don't know...... perhaps the programm languages aren't so complicated but for me is quite difficult to learn some of them.Quote from: oldway on October 29, 2017, 09:15:28 pmChill Out man, I am still alive. There is nothing accidentally in that.

author: oldway
author_rank: Super Contributor
timestamp: October 31, 2017, 02:54:56 pm
content: Quote from: Lautrec on October 31, 2017, 02:43:42 pmBut the difference between you and me is that I have more than 30 years of experience working in electricity and power electronics and I'm still alive.You should learn to be a little more modest ... If you had real experience, you would be less sure of yourself, because accidents happen, and always in the most stupid way possibleAs I said, safety first, learn not to defy fate, don't play Crocodile Dundee with electricity....

author: Lautrec
author_rank: Newbie
timestamp: October 31, 2017, 03:40:05 pm
content: Quote from: oldway on October 31, 2017, 02:54:56 pmI have 12 years... it's not so bad.So, just like you man, just like you.Peace!

author: oldway
author_rank: Super Contributor
timestamp: October 31, 2017, 04:54:47 pm
content: Quote from: Lautrec on October 31, 2017, 03:40:05 pmIf you kill yourself, I do not care, you do what you want.But in a forum, you're on a public space and there are hundreds, if not thousands, of other people reading this topic, including beginners.So you behave as a responsible person and not as a kid ...And a responsible person sets a good example and follows the safety rules when working on 230V circuits.