None in town - Page 1
Forum section: electronics / general

author: Paul Price
author_rank: Super Contributor
timestamp: May 22, 2013, 05:58:12 pm
content: I am no longer interested in this thread.

author: SeanB
author_rank: Super Contributor
timestamp: May 22, 2013, 06:07:42 pm
content: Do not use the tacho below 20Hz and just use a simple linear relationship. That is what the machine does in the micro anyway, the taco is just being used once it is running to close the loop. Motor will be noisy as you do cycle skipping to make it run slow, but that is unavoidable.

author: SeanB
author_rank: Super Contributor
timestamp: May 22, 2013, 06:22:40 pm
content: Take the PIc and reverse engineer it then, you will find a very heavy digital filter there then, probably as a part of a look up table. So it starts then slow, and only starts to use tacho when it detects reliable speed input. moving a motor slowly is easy with no tacho feedback, it will have speed variations but will still run smoothly, it then probably only is using the tacho to give a signal that the drum is actually moving rather than a speed loop.Then again my machine has 2 speeds, and a gearbox for the spin cycle. low speed is by cycle skipping and is a little noisy. Yours might not be using a triac, but rather an IGBT and using it to control both turn on and turn off of the motor to synthesise a lower frequency drive for the motor.

author: rsjsouza
author_rank: Super Contributor
timestamp: May 22, 2013, 08:22:49 pm
content: Maybe you could check the first two app notes linked inthis forum thread. They show induction motor control using thyristors, which is far from ideal but surely doable for such small motors.

author: Harvs
author_rank: Super Contributor
timestamp: May 22, 2013, 10:49:13 pm
content: QuoteThe solution to that one is to use fixed point algorithms (It's pretty rare I use floating point for anything in an MCU unless the outputs can genuinely accept a range of values outside of a 32bit precision, such as a display.)The motor's not by chance a "smart drive" unit? Doesn't really sound like it from your description, but I believe they're very wide spread now (across many brands.) If it happens to be, Silicon Chip magazine have an project on driving one with a dsPIC.

author: Rufus
author_rank: Super Contributor
timestamp: May 22, 2013, 11:34:20 pm
content: Quote from: Paul Price on May 22, 2013, 10:57:37 pmThere is no such thing as a brush induction motor. It will be some variation of universal motor with tapped and possibly split field coils. You need to understand what the motor is and what the connections are before you can understand how to drive it properly at low and high speeds.

author: Harvs
author_rank: Super Contributor
timestamp: May 23, 2013, 12:08:00 am
content: Quote from: Rufus on May 22, 2013, 11:34:20 pmWhilst off topic, couldn't a wound rotor induction motor be called "brushed"?

author: Harvs
author_rank: Super Contributor
timestamp: May 23, 2013, 12:29:10 am
content: Quote from: Paul Price on May 23, 2013, 12:22:17 amA wound rotor (aka doubly feed) induction machine has slip-rings and brushes.Whilst I know it's not typically called a brushed induction machine in the west, is it not technically possible that somewhere in the world it might be called that?

author: Harvs
author_rank: Super Contributor
timestamp: May 23, 2013, 12:34:10 am
content: Quote from: Paul Price on May 22, 2013, 10:57:37 pmThe original "smart drive" motor is from fisher and paykel, it's basically an oversized stepper motor. They are very commonly re-purposed for generators in small scale wind and hydro turbines.But a similar system is used in a lot of washing machines now.

author: Rufus
author_rank: Super Contributor
timestamp: May 23, 2013, 12:40:11 am
content: Quote from: Harvs on May 23, 2013, 12:08:00 amOr ringed? Or slipped?Brushed and brushless seem to be reserved for commutation by armature or lack of it. Probably because having to replace worn out brushes (or not) is the most notable feature of the motor.

author: Balaur
author_rank: Unknown
timestamp: May 23, 2013, 05:41:38 am
content: Quote from: Paul Price on May 23, 2013, 01:25:18 amNever had any issues with the motors nor electronics on my washing machines. What broke are some rather low-tech parts: drum pulley and the stabilizing concrete block.

author: SeanB
author_rank: Super Contributor
timestamp: May 23, 2013, 05:34:05 pm
content: My AEG went to the scrapyard because a new set of bearings was more than the machine that replaced it. Only reason why, otherwise it was working well, just the really noisy bearings ( got to the point where the neighbours 2 floors down could hear it spin) and needing a newer motor for the pump, though it was working well with the one I Frankensteined onto the pump shaft quite well. Was over 30 years old at the time. AEG Lavamat Deluxe Electronic, used a 4 bit microcontroller inside.........

author: M. András
author_rank: Super Contributor
timestamp: May 23, 2013, 09:22:33 pm
content: maybe some pictures?

author: Kremmen
author_rank: Super Contributor
timestamp: May 23, 2013, 09:31:09 pm
content: Quote from: Paul Price on May 23, 2013, 09:02:47 pmWhile not addressed to me, let me just note that a couple months ago i had to let the old washer go precisely because of the brushes. Or actually the commutator. A pity really, because it was a quality piece of hardware ( a Cylinda - maybe unknown brand to most, but a Swedish all steel construction and as such none the worse for 12 years of nearly continuous duty).The weak point was the commutator in the end. I replaced the brushes 3 times in all (surprising that they even were available after that long a time). I suspect there was some undetected external root cause for the brush problem but the end result was that it got progressively worse, the last set of brushes working just a few days followed by a near fire (the maintenance room was full of magic smoke and the motor was _real_ hot when i tore the thing open to see.So yes, brush motors can serve reliably for years but in the end the mechanical commutator is a weak point. Accordingly the new washer is a brushless motor one. We'll see how that manages...

author: SeanB
author_rank: Super Contributor
timestamp: May 24, 2013, 03:47:36 pm
content: You had a partial short in the rotor, that caused the brushes to wear. This got worse with time until it eventually shorted out the whole turn and then the brush life was measured in minutes.Here I can buy washing machine spares, the units are expensive enough that repair is worthwhile, and a lot of machines use a common set of wear parts that are available. The old Hoover twin tub units are still around even though some are over 40 years old, and you can still get the whole range of spares, from seals to the drums, along with the motors as spare parts. About the only thing not available are the labels. We had one made by Hoover in Merthyr Tydfil in the pre war days, and used it till the 1990's. also had the matching upright cleaner, though that eventually was not repairable as they no longer stocked the case castings it needed. They had the rest though, just not the alloy case casting.