Hi,
Do not ask me why, but after 10+ year an old obsession came back and I like to play with motors for turntables :- )
Maybe because I've recently acquired a Systemdek TT and want to improve.
Some 10+ years ago I wanted to play with 3 phase motors, I thought that should be the most smooth, silent but stable strong driving. Maybe THE ultimate driving. Since I had experience with DDS generators, to generate a precise, very close to sinewave (14bit, 400MSPS) what I can adjust each phase difference was not a problem.
Then I've started to search for motors. Had an expensive maxon and a lot of hard drive motors, some RC plane motors. None was good for being a TT motor, the reason was they liked to spin in high rpm, hated to spin in low rpm we need. Not only with my drive, I've acquired multiple divers too, result was the same.
A 2 phase driver derivated from that project, to drive the good old premotec/airpax/philips sycn motor - and that was great success. Especially with motors rewind to 24V. Sure it is overkill. Making 2 sinewave with 2 AD9954, than some signal conditioning and a power amp module (2x LM3886). I prefer it over the usual maxon 110191/110189 what I have to a friend.
I've used the DDSgen+LM3886 to 24V sync motor for a decade, I guess it will still win and will be my main driver, but I just can not stop playing with DC motors too, and now, I would ask YOU:
Do you have any tip, advice for a 3 phase motor suitable for TT, which may also accept (or even better is designed to) low rpm?
What is low rpm is relative I know. The sync motor spins 250 rpm, but with smaller pulley and driving on the outside of the platter we could go up somewhat (but for sure not to 3000+ RPM, where most motors started to shine what I've tested so far).
???
Thanks!
JG
Do not ask me why, but after 10+ year an old obsession came back and I like to play with motors for turntables :- )
Maybe because I've recently acquired a Systemdek TT and want to improve.
Some 10+ years ago I wanted to play with 3 phase motors, I thought that should be the most smooth, silent but stable strong driving. Maybe THE ultimate driving. Since I had experience with DDS generators, to generate a precise, very close to sinewave (14bit, 400MSPS) what I can adjust each phase difference was not a problem.
Then I've started to search for motors. Had an expensive maxon and a lot of hard drive motors, some RC plane motors. None was good for being a TT motor, the reason was they liked to spin in high rpm, hated to spin in low rpm we need. Not only with my drive, I've acquired multiple divers too, result was the same.
A 2 phase driver derivated from that project, to drive the good old premotec/airpax/philips sycn motor - and that was great success. Especially with motors rewind to 24V. Sure it is overkill. Making 2 sinewave with 2 AD9954, than some signal conditioning and a power amp module (2x LM3886). I prefer it over the usual maxon 110191/110189 what I have to a friend.
I've used the DDSgen+LM3886 to 24V sync motor for a decade, I guess it will still win and will be my main driver, but I just can not stop playing with DC motors too, and now, I would ask YOU:
Do you have any tip, advice for a 3 phase motor suitable for TT, which may also accept (or even better is designed to) low rpm?
What is low rpm is relative I know. The sync motor spins 250 rpm, but with smaller pulley and driving on the outside of the platter we could go up somewhat (but for sure not to 3000+ RPM, where most motors started to shine what I've tested so far).
???
Thanks!
JG
A car alternator is an inexpensive 3-phase machine that can drive directly with no gear/belt. It needs the rotor field coil (slip rings), connected to a small power like 6-12V.
Do not use toy RC plane / car BLDC controllers, just perform V/f control using a proper 3-phase inverter to reduce speed without reducing torque. With sinusoidal currents and reduced speeds the acoustic noise is also negligible.
In the video, read WFSM (wound field synchronous motor) instead of BLDC.
Do not use toy RC plane / car BLDC controllers, just perform V/f control using a proper 3-phase inverter to reduce speed without reducing torque. With sinusoidal currents and reduced speeds the acoustic noise is also negligible.
In the video, read WFSM (wound field synchronous motor) instead of BLDC.
Well, I just use ordinary turntables with up to, ~ 2 kg platter. Not those giants what turns 100+kg of mass.
On the other hand, it is interesting, I see that can rotate slow. I just need something a lot smaller. How many poles the car alternator has? Not that I would consider to put a car alternator beside my TT, but curious.
Thanks,
JG
On the other hand, it is interesting, I see that can rotate slow. I just need something a lot smaller. How many poles the car alternator has? Not that I would consider to put a car alternator beside my TT, but curious.
Thanks,
JG
An alternator is a synchronous machine and will turn at a speed related to the freq of the stator voltage as Ns = 120 f / P rpm, for example a 4-pole 50Hz motor will have 120x50/4 = 1500 rpm. If you feed it 5Hz from an inverter, then it would do 150rpm. However, you'd also have to reduce the voltage proportionally, to prevent magnetic flux saturation.
Car alternators are usually 4-pole. There're many videos that show the disassembled stator for example, the following video clearly shows a 4-pole 36-slot stator winding from a car alternator.
Car alternators are usually 4-pole. There're many videos that show the disassembled stator for example, the following video clearly shows a 4-pole 36-slot stator winding from a car alternator.
Please do not try to repurpose a car alternator to a turntable motor. the bearings, even if new are much too noisy.
A car alternator is designed to produce something in the order of 150A at 14V, around 2,100 VA; when used as a motor the vibration level
is orders of magnitude higher than could be tolerated in a belt drive motor, leave alone a direct drive.
Bill Carlin (Phoenix) recommends a 3 phase BLDC motor from Anaheim Automation; these are excellent if you are in the USA, for the rest of us
we have to find a similar product. These from China would appear to do a decent job, though you may have to replace the original bearings to obtain the best results.
https://www.ebay.co.uk/itm/204781686146?
A car alternator is designed to produce something in the order of 150A at 14V, around 2,100 VA; when used as a motor the vibration level
is orders of magnitude higher than could be tolerated in a belt drive motor, leave alone a direct drive.
Bill Carlin (Phoenix) recommends a 3 phase BLDC motor from Anaheim Automation; these are excellent if you are in the USA, for the rest of us
we have to find a similar product. These from China would appear to do a decent job, though you may have to replace the original bearings to obtain the best results.
https://www.ebay.co.uk/itm/204781686146?
Yes, but that was a great video, which I would never have seen otherwise.
I like the Anaheim Automation motors. I use this one: https://anaheimautomation.com/blws232d-12v-500.html
It is only 4pole. But very smooth under operation.
It is only 4pole. But very smooth under operation.
Yes, but unfortunately not easy to get outside of the USA. Another issue is that you need 'single ended' amplifiers in order to drive the motor. The vast majority of class D amplifiers have floating outputs meaning that you cannot connect any outputs to ground, this means there's no common point.
If you're driving higher voltage motors this doesn't matter as the transformers take care of the isolation.
What I have done before is to find the 'common' point inside the motor and separate the wires and bringing out the additional connections, so that each phase winding is 'on its own', thereby allowing the use of the common types of class D amp.
If you're driving higher voltage motors this doesn't matter as the transformers take care of the isolation.
What I have done before is to find the 'common' point inside the motor and separate the wires and bringing out the additional connections, so that each phase winding is 'on its own', thereby allowing the use of the common types of class D amp.
No, I haven't, but it might be worthwhile with an Arduino controller. I did note though that it's designed for small motors with an internal resistance of 10ohms or more; I'm not sure how that compares with the AA motors or equivalent
Hi jayme, this is very promising. It is specified for low rpm also. The 12V curve goes really low.
To order from US is expensive, it would land 2x the website cost, but this shows that a suitable motor actually exists. I'm looking for a NEMA23 BLDC now from Europe. Worst case I can order from US.
Thanks, JG
To order from US is expensive, it would land 2x the website cost, but this shows that a suitable motor actually exists. I'm looking for a NEMA23 BLDC now from Europe. Worst case I can order from US.
Thanks, JG
The delta wiring would not be a problem for me. I have 3 LM3886 amplifiers after the 3x AD9954 based generator,
I agree. I would not consider to use it for TT, but, good to learn. What is very interesting to me, we could adjust the "magnet" strength - which may greatly reduce cogging.
That is the problem with RC motors. For best efficiency they use very strong magnets and it is cogging very strongly. Otherwise, do not under estimate RC motors. Some are really high quality (and expensive). The problem is, only larger outrunners would do rpm under like 1000 per minute stable, but those are cogging like a rotary switch.
JG
That's why I'm so in favour of the Papst Aussenlaufer; zero cogging, can be found with as many as 12 poles running as low as 500 rpm, but only available on the 2nd hand market and getting rather old.
Best would be to get the same Papst what is (are) in the Voyd, I was looking a lot, but could not find. I was told they do not manufacture any more. Do you have a concrete type to search for?
Actually no, 3 phases are sufficient, the sum of the phases at any moment in time is equal to zero so theoretically there is no vibration. In practice imperfections in design or construction can allow for some vibration but this can be minimised by 'tweaking' the relative phase angle.
I am lucky enough to have one of the Papst motors that's used as the basis of that in the Techdas Airforce Zero, though without the air bearing or flywheel.
I am lucky enough to have one of the Papst motors that's used as the basis of that in the Techdas Airforce Zero, though without the air bearing or flywheel.
That's an open-end winding motor, but it has a large common-mode current flowing (labelled io in the picture below) directly across all 3 windings unless the inverter outputs are sinusoidal / LC filtered and sum exactly to zero.
This is because the 3-phase motor has no back-emf for CM voltages and therefore the only impedance seen by the inverter is the leakage inductance. However, if two separate DC sources are used i.e. one for each side, the CM current cannot flow (as there's no path) and the motor maybe driven without LC filters directly from the PWM, also shown below.
The solution for a non-zero CM voltage in a single-ended inverter is much much easier than that:
1) Connect the motor in the star configuration.
2) Remove the neutral connection through which the zero sequence current flows i.e. leave it open as shown below.
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