I came across this idea - to power an induction motor from the mains which will drive an AC generator giving mains to my system. This should be equal to almost pure AC. Noise of the motor is not a problem, because I can put it far away from my listening place. It will power up my entire system including PC, DAC, amp.
But I think of a main problem - how to control the frequency to be steady (50HZ)? And what if the generator turns off due to a misfunction - this would progressively lower the frequency. Would this damage equipment?
But I think of a main problem - how to control the frequency to be steady (50HZ)? And what if the generator turns off due to a misfunction - this would progressively lower the frequency. Would this damage equipment?
You are certainly considering a very large project with a number of obstacles to overcome. The concept of 'pure ac' is overrated in my opinion. You should start by asking yourself what portion of my system is suffering due to non-pure ac. I would correct that equipment so that it can operate more robustly in the presence of harmonic distortion, waveform notching, and noise.
After all, most audio equipment operates off dc, so all you end up doing is rectifying the ac, whether it be distorted or not really has little effect. The exception would be ac heating of vacuum tubes, but there are simpler (and better) ways of addressing this.
To answer your question (but I don't condone the implementation) the optimal method would be to run a small motor off an ac drive. The drive controls the frequency (speed) of the motor very well, even in the presence of load changes and line voltage variation. It will eliminate the need for a flywheel, and provides a degree of protection for the motor. Best solution would be a vector drive, which has an encoder connected to the motor shaft. The drive directly controls the speed of the motor shaft in closed loop.
The motor drives a synchronous alternator with the same number of poles as your motor. You control the field of the alternator with a voltage regulator, which senses the output of the alternator. Many choices of regulator, and usually not very cheap, especially if you want good transient performance and solid regulation.
Then you need to consider winding pitch of the alternator. Depending on the pitch, each will provide different amounts and number of harmonics, so don't think for a minute a generator produces 'pure ac', it certainly does not.
All of this is pretty much geared toward three phase operation, but I am sure you can find equipment suitable for single phase.
My suggestion is to go with a ferroresonant transformer and be done with it. Regulation is excellent, and the harmonics produced are benign, even for ac heating vacuum tubes. Common mode rejection is very high; you can almost survive a lightning strike with those units. Zero noise let-through, although it does produce audible ambient noise that must be dealt with.
After all, most audio equipment operates off dc, so all you end up doing is rectifying the ac, whether it be distorted or not really has little effect. The exception would be ac heating of vacuum tubes, but there are simpler (and better) ways of addressing this.
To answer your question (but I don't condone the implementation) the optimal method would be to run a small motor off an ac drive. The drive controls the frequency (speed) of the motor very well, even in the presence of load changes and line voltage variation. It will eliminate the need for a flywheel, and provides a degree of protection for the motor. Best solution would be a vector drive, which has an encoder connected to the motor shaft. The drive directly controls the speed of the motor shaft in closed loop.
The motor drives a synchronous alternator with the same number of poles as your motor. You control the field of the alternator with a voltage regulator, which senses the output of the alternator. Many choices of regulator, and usually not very cheap, especially if you want good transient performance and solid regulation.
Then you need to consider winding pitch of the alternator. Depending on the pitch, each will provide different amounts and number of harmonics, so don't think for a minute a generator produces 'pure ac', it certainly does not.
All of this is pretty much geared toward three phase operation, but I am sure you can find equipment suitable for single phase.
My suggestion is to go with a ferroresonant transformer and be done with it. Regulation is excellent, and the harmonics produced are benign, even for ac heating vacuum tubes. Common mode rejection is very high; you can almost survive a lightning strike with those units. Zero noise let-through, although it does produce audible ambient noise that must be dealt with.
I have a gas (city gas) powered 12KW generator at home. More than enough for the whole house. Let me tell you, the AC out of that thing is the ugliest, dirtiest power I have ever seen. Not great for audio, but it keeps the lights on and the HVAC running when power is out.
If you choose to do this, as some high end Japanese installations have, you had better choose your alternator very carefully. It will probably be expensive. I have seen military surplus motor generator units that converted 60Hz AC to 400Hz AC. They may be pretty clean. Don't know about 60-60 or 0-60. Maybe. As ZigZag say, there are better, cheaper ways to do this.
If you choose to do this, as some high end Japanese installations have, you had better choose your alternator very carefully. It will probably be expensive. I have seen military surplus motor generator units that converted 60Hz AC to 400Hz AC. They may be pretty clean. Don't know about 60-60 or 0-60. Maybe. As ZigZag say, there are better, cheaper ways to do this.
I have seen this used in a a large UPS installation. There was an enormous flywheel attached to the three phase motor-generator set - the idea being that when the mains was cut, the generator would keep going long enough for the backup batteries to kick in. These in turn would keep the electrons flowing while the diesel powered generator started up. Lots of control circuitry handled the switch-overs. Great for keeping sensitive laboratory equipment running, but I have no idea how squeaky clean the sine waves coming out the other end were.
You could build or buy a (very) large audio amplifier. Drive it with 50/60Hz generated by e.g. Audacity set to loop continuously driving a soundcard or get somebody to write you a program to send the values continuously from a lookup table.
Bear in mind that most people will regard what you propose as a complete waste of money and resources and likely to damage the environment, contribute to the extinction of species and the rise in worldwide temperature and sea level with a corresponding impact on 3rd. world human populations and even 1st. world prosperity, all for no audible result.
Why not just take the money it would cost and give it to charity? I suggest fusion power research. Plenty of time to take up your project again when that engineering challenge is met.
Bear in mind that most people will regard what you propose as a complete waste of money and resources and likely to damage the environment, contribute to the extinction of species and the rise in worldwide temperature and sea level with a corresponding impact on 3rd. world human populations and even 1st. world prosperity, all for no audible result.
Why not just take the money it would cost and give it to charity? I suggest fusion power research. Plenty of time to take up your project again when that engineering challenge is met.
Your local mains must be really bad if you think that a small motor-generator set will be better! 50/60Hz to 400Hz sets are probably intended for testing avionics on the ground; in the days before cheap reliable solid-state power electronics this was the best way of getting 'aircraft' power..
..or even a large motor-generator set. Recent project of mine involved a well-engineered 1.5MVA backup genset and even the output of that giant lump - specced to back-stop a hospital - is a mess compared with incoming HV.
Though the V-20 quad-turbo engine sounded great spooling-up under load...
Though the V-20 quad-turbo engine sounded great spooling-up under load...
I have seen a set-up at an EMI test facility (in the UK) and what they did was use an electric motor to mechanically drive another identical electric motor applied as the alternator. Frequency is maintained by the driving motor which is synchronized to the mains anyway and the regenerated ac is totally decoupled from any mains interference.
oh.. well now come on, pleaseee just a bit more common sense.
Audio equipment does NOT need AC.
riight? the PSU does supply DC.
You need clean DC.
surely one way is to get better DC is to have a better AC in the first place.
But let's just think a bit more.
There are quite nice electric fork lifters around, and those have heavy duty , low internal resistance deep cycle high current output batterys.
Actualy it is a cool idea to build an amplifier that runs on battery power.
Thats clean, it IS decoupled from mains noise.
A normal tractor battery, witch is not as good as a forklift battery has 12v @175 Ah here, and those can run standard 2Kw starter motors till discharged. That is well over 100A current handling ability. probably one would need quite a big amplifier to discharge it at a rate that yields a bigger voltage drop.
If someone is so into this clean power thingy, then get a handfull of bike batterys. Those are cheaper, and a nice dual 24 volt supply is actualy quite easy to make out of them.
One can go as far as adding even to this setup a voltage regulator to drive the source, and pre-amp, and even the voltage gain stage of a poweramp leaving only the output stage powered from unregulated battery power.
Actualy factory made of the shelf stuff can be modified too to work with this setup.
Ripping out everything before and including the rectifier, providing the unit with regulated power from a battery will yield a very clean DC supply.
But if You ask me it is overkill to a whole new level.
Audio equipment does NOT need AC.
riight? the PSU does supply DC.
You need clean DC.
surely one way is to get better DC is to have a better AC in the first place.
But let's just think a bit more.
There are quite nice electric fork lifters around, and those have heavy duty , low internal resistance deep cycle high current output batterys.
Actualy it is a cool idea to build an amplifier that runs on battery power.
Thats clean, it IS decoupled from mains noise.
A normal tractor battery, witch is not as good as a forklift battery has 12v @175 Ah here, and those can run standard 2Kw starter motors till discharged. That is well over 100A current handling ability. probably one would need quite a big amplifier to discharge it at a rate that yields a bigger voltage drop.
If someone is so into this clean power thingy, then get a handfull of bike batterys. Those are cheaper, and a nice dual 24 volt supply is actualy quite easy to make out of them.
One can go as far as adding even to this setup a voltage regulator to drive the source, and pre-amp, and even the voltage gain stage of a poweramp leaving only the output stage powered from unregulated battery power.
Actualy factory made of the shelf stuff can be modified too to work with this setup.
Ripping out everything before and including the rectifier, providing the unit with regulated power from a battery will yield a very clean DC supply.
But if You ask me it is overkill to a whole new level.
Hi Arty, a set of forklift batteries to derive say +-48VDC from will cost quite a bit more that the complete audio system. Yes it would be the ultimate power source. How would you handle the rest of the equipment, say the CD player, DAC, etc - remove each power supply and tap of the required voltage from the battery bank, i.e. 5V, +12V,-12V?
Hi Martin, the regulator is not really the issue here. I have been there tried it, saw the movie and got a T-shirt. To remove hash from incoming ac lines is not the easiest of tasks.
If it was the case there would have been no EMI/RFI regulations preventing equipment from contaminating the power and insist that equipment be non susceptible to hash on the lines or in the air. In Europe or any other part of the populated world regulation is quite severe.
I have in fact not seen any audio equipment that has been tested for compliance with the regulations.
Nico - I don't disagree. There are really obvious sources where HF noise and hash can propagate easily, even through 3-pin voltage regulators as I showed here:
Using 3-pin regulators off-piste: part 2
My point is that dealing with such noise is not actually difficult at all, and doing so is a lot more elegant than building your own power station. It might be a simple as choosing R-C values at the power input of every circuit. Some of this comes for free - for example, if you choose a power transformer that is not grossly oversized for a line level circuit the secondaries resistance and the leakage inductance can actually become very useful...
(and incidentally, the typical flat-topped mains input waveform is rather more efficient for charging reservoir caps than a pure sine... mop-up the harmonics if you need to)
Using 3-pin regulators off-piste: part 2
My point is that dealing with such noise is not actually difficult at all, and doing so is a lot more elegant than building your own power station. It might be a simple as choosing R-C values at the power input of every circuit. Some of this comes for free - for example, if you choose a power transformer that is not grossly oversized for a line level circuit the secondaries resistance and the leakage inductance can actually become very useful...
(and incidentally, the typical flat-topped mains input waveform is rather more efficient for charging reservoir caps than a pure sine... mop-up the harmonics if you need to)
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I don't argue about what you are saying, it is a bit of work to find and fix all there critters 
) go have a look here you will be entertained I guarantee that. But don't think I subscribe to this hokus pokus, but I am sure some with deep pockets does.
P10 | PS Audio
) go have a look here you will be entertained I guarantee that. But don't think I subscribe to this hokus pokus, but I am sure some with deep pockets does.P10 | PS Audio
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Hi Martin, the regulator is not really the issue here. I have been there tried it, saw the movie and got a T-shirt. To remove hash from incoming ac lines is not the easiest of tasks.
If it was the case there would have been no EMI/RFI regulations preventing equipment from contaminating the power and insist that equipment be non susceptible to hash on the lines or in the air. In Europe or any other part of the populated world regulation is quite server.
I have in fact not seen any audio equipment that has been tested for compliance with the regulations.
I was entertained Nico
Once upon a time I built myself a regenerator along similar lines to the original PS power plant - high quality oscillator, power amp, step-up transformer - for study purposes. Long story short: while it sounds like a good idea, delivering anything even as good as the raw mains supply once loaded is rather harder.
The latest PS units seem to take a different direction, borrowing from industry practice of active harmonic correction: which is to actively buck incoming %THD only. Much, much more efficient, but also inherently rather-to-very limited in terms of bandwidth for stability reasons. (the local poweramp only has to supply sum or difference components, while floating)
I'd still rather have my pile of boxes robustly indifferent to what they are fed. After a bit of effort , I think they are
Once upon a time I built myself a regenerator along similar lines to the original PS power plant - high quality oscillator, power amp, step-up transformer - for study purposes. Long story short: while it sounds like a good idea, delivering anything even as good as the raw mains supply once loaded is rather harder.
The latest PS units seem to take a different direction, borrowing from industry practice of active harmonic correction: which is to actively buck incoming %THD only. Much, much more efficient, but also inherently rather-to-very limited in terms of bandwidth for stability reasons. (the local poweramp only has to supply sum or difference components, while floating)
I'd still rather have my pile of boxes robustly indifferent to what they are fed. After a bit of effort , I think they are
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