A lot of effort, by all diy-ers, is put in getting a good, steady, DC- Rail voltage from a one-phase mains power supply.
If you spend that much amount of effort in reducing ripple why do we not switch to a three-phase mains supply.
iso getting one 300VA Toroid, you need three 100VA toriods, but the rectified voltage is far nearer to DC.
sure, you need a different wall-socket to plug in the amp. But 3-phase in-house is not that complicated.
I've not done it, but has somebody tried this??😕
If you spend that much amount of effort in reducing ripple why do we not switch to a three-phase mains supply.
iso getting one 300VA Toroid, you need three 100VA toriods, but the rectified voltage is far nearer to DC.
sure, you need a different wall-socket to plug in the amp. But 3-phase in-house is not that complicated.
I've not done it, but has somebody tried this??😕
I dont think a lot of us can get 3 phase in our homes without extreme construction costs from the utilaties, if they will even consider it.
I dont think Ive seen 3 phase primaries within 3 blocks of my home.
This is an area were living in an aprtment building can be a real advantage.
I always did want to live in a converted warehouse.
-Dave
I dont think Ive seen 3 phase primaries within 3 blocks of my home.
This is an area were living in an aprtment building can be a real advantage.
I always did want to live in a converted warehouse.
-Dave
3 phase amps
Hi,
I have worked with CROWN PA amps that run on 3 phase mains.
In denmark 3 phase mains are in most homes 🙂
When I was an apprentice somebody at work modified a "normal" power amp to run on 3 phases. The result was obvios - more power and more "kick"
I don't know if the same result - With kick - could be made by adding more caps to a singel phase amp
\Jens
Hi,
I have worked with CROWN PA amps that run on 3 phase mains.
In denmark 3 phase mains are in most homes 🙂
When I was an apprentice somebody at work modified a "normal" power amp to run on 3 phases. The result was obvios - more power and more "kick"
I don't know if the same result - With kick - could be made by adding more caps to a singel phase amp
\Jens
I have 3x 240v 60A at home 😀 but simply have it split to power, lights and oven. I always imagined I would do something 3-phase-ish but it never happened...
With a normal 3 transformer setup you can wire the 3 primaries from neutral to each phase and the secondaries in a star configuration. With a full wave rectifier this will give you 300/360Hz ripple.
If you add a second set of 3 transformers with secondaries 1.732 times the voltage of the other three (and current ratting 1/1.732 times) and connect these 3 secondaries in delta config and run them to their own full wave rectfier you will also get 300/360Hz ripple.
So what? The magic thing is that there is 30 degrees phase difference between star-star and star-delta, so if we parallel our two full wave bridges via an interphase reactor (google for details) then we have a dc supply with 600/720 Hz ripple. Not much ripple either for that matter. Very little choke and cap needed.
With a normal 3 transformer setup you can wire the 3 primaries from neutral to each phase and the secondaries in a star configuration. With a full wave rectifier this will give you 300/360Hz ripple.
If you add a second set of 3 transformers with secondaries 1.732 times the voltage of the other three (and current ratting 1/1.732 times) and connect these 3 secondaries in delta config and run them to their own full wave rectfier you will also get 300/360Hz ripple.
So what? The magic thing is that there is 30 degrees phase difference between star-star and star-delta, so if we parallel our two full wave bridges via an interphase reactor (google for details) then we have a dc supply with 600/720 Hz ripple. Not much ripple either for that matter. Very little choke and cap needed.
3 phase has always been great for motors.
I can see obvious similarities for amplifiers.
Your 3 phase Crown, was it one of the legendary MRI power supplies? (oops just read it was PA gear, there were legends here in the US about surplus magetic resonic imaging power suplies that were Crown Delt-O amps w/ 3 phase power suplies)
I'm envious of the 3 phase in the home.
I can see obvious similarities for amplifiers.
Your 3 phase Crown, was it one of the legendary MRI power supplies? (oops just read it was PA gear, there were legends here in the US about surplus magetic resonic imaging power suplies that were Crown Delt-O amps w/ 3 phase power suplies)
I'm envious of the 3 phase in the home.
hm.
I asked two electricians about this all. Both of them have already built several tube amps in the 80's. They think it's absolutely senseless for normal amplifiers. It just simply doesn't matter.
Now, what?
🙂
I asked two electricians about this all. Both of them have already built several tube amps in the 80's. They think it's absolutely senseless for normal amplifiers. It just simply doesn't matter.
Now, what?
🙂
For most people it is probably both cheaper and simpler to just
use larger capacitors than to use three-phase. There will still
be ripple also with the three-phase solution.
use larger capacitors than to use three-phase. There will still
be ripple also with the three-phase solution.
Da5id4Vz said:
Assuming you're in the US... Most electric dryer hookups are run from 220 Volt supplies. This is actually a 3-phase system. Actually the electric company should be sending 3-phase electricity down the wire to your junction box. I thought it was the standard. Your typical 110 is just 2 legs of the 3-phase.
not that you want to run a powercord from your garage to your living room.....
--
Danny
Christer said:
3 phase full wave rectified DC has only 5% ripple. If you use a regulated power supply, you may not even need input filter caps (assuming you regulate at a point below the valleys).
But for U.S. residential areas, 3 phase is not really available. It's an industrial thing.
3-phase is readily available here so that only introduces minor problems.
I'll play with the idea for a while and do some googling.
thanx for the suggestions
😉
I'll play with the idea for a while and do some googling.
thanx for the suggestions
😉
dutch diy,
by "readily available" do you mean you actually have 3-phase
outlets in ordinary rooms, or just that you have 3-phase incoming
to the house/flat as here in Sweden? Here we usually have all
three phases coming in and then they are distributed between
the various one-phase outlets in the rooms to help even out
the load, so it would in principle be possible to get 3-phase by
finding three outlets wired to the different phases, but it would
be a bit awkward to have three long mains cables running between
the rooms. 🙂 The only things in a normal home that are sometimes
directly wired directly to a 3-pahse outlet are stoves and washing
machines, but I think that is getting rare too. It is more common
to have 3-pahse outlets outdoors, especially on farms, and
sometimes in garages.
by "readily available" do you mean you actually have 3-phase
outlets in ordinary rooms, or just that you have 3-phase incoming
to the house/flat as here in Sweden? Here we usually have all
three phases coming in and then they are distributed between
the various one-phase outlets in the rooms to help even out
the load, so it would in principle be possible to get 3-phase by
finding three outlets wired to the different phases, but it would
be a bit awkward to have three long mains cables running between
the rooms. 🙂 The only things in a normal home that are sometimes
directly wired directly to a 3-pahse outlet are stoves and washing
machines, but I think that is getting rare too. It is more common
to have 3-pahse outlets outdoors, especially on farms, and
sometimes in garages.
Hi Christer,
I live in a 3-story appartment building on the ground floor.
Normally each "floor"is run from one of the three phases.
In my situation readily available means that in my main switch board all three phases are available and I could have a 3-phase wall socket installed which is fed from the main switch board.
It's fairly normal business here: most electrical kitchen stoves run on a 3phase supply.
Although the current IEC connector / sockets do not have a design look and feel.
Jos
I live in a 3-story appartment building on the ground floor.
Normally each "floor"is run from one of the three phases.
In my situation readily available means that in my main switch board all three phases are available and I could have a 3-phase wall socket installed which is fed from the main switch board.
It's fairly normal business here: most electrical kitchen stoves run on a 3phase supply.
Although the current IEC connector / sockets do not have a design look and feel.
An externally hosted image should be here but it was not working when we last tested it.
Jos
Ground-floor marketing opportunity for someone.
Now just =where= are you going to get a 3-phase Magic Power Cord 🙄
Now just =where= are you going to get a 3-phase Magic Power Cord 🙄
I studied 3 phase diode bridges at scool.
For sure, the ripple is much smaller, the frequency is higher. That will be easier to filter.
But it also has drawbacks. I don't know the english word for this, but in french it's called "empietement" (an online translator gives me: encroachment)
This happens when diode N is at the end of it's conducting cycle, and that at the same time diode N+1 is at the beginning of it's conducting cycle. (This is when Vn=Vn+1)
Instead of having the same output voltage as the input voltage (-0.7V), you have (Vn+Vn+1)/2
As image tells more than a thousand words:
For sure, the ripple is much smaller, the frequency is higher. That will be easier to filter.
But it also has drawbacks. I don't know the english word for this, but in french it's called "empietement" (an online translator gives me: encroachment)
This happens when diode N is at the end of it's conducting cycle, and that at the same time diode N+1 is at the beginning of it's conducting cycle. (This is when Vn=Vn+1)
Instead of having the same output voltage as the input voltage (-0.7V), you have (Vn+Vn+1)/2
As image tells more than a thousand words:
Attachments
Sounds like slow recovery of the outgoing diode as the incoming diode forcibly reverse-biases it. Quite an issue for serious size rectifiers, but for us it's nothing that fast soft-recovery or especially schottky diodes won't fix.
Quick lesson on diodes -> normal diodes conduct a few hundred microseconds in reverse before they shut the current off *suddenly*. They have a "snappy" turn-off like a dry piece of wood that snaps or breaks very suddenly. Fast and especially ultra-fast soft recovery diodes conduct in reverse for 20-50 nanoseconds while the current reduces gently to zero. Like stretching bubble gum till it finally weakly breaks. 🙂 Schottky diodes simply don't have any reverse recovery time to speak of; just a little reverse current to charge the capacitance as the reverse voltage rises. Normal silicon schottky's till relatively recently could only stand about ~60 volts reverse max. Up to 200v ones are available now.
Quick lesson on diodes -> normal diodes conduct a few hundred microseconds in reverse before they shut the current off *suddenly*. They have a "snappy" turn-off like a dry piece of wood that snaps or breaks very suddenly. Fast and especially ultra-fast soft recovery diodes conduct in reverse for 20-50 nanoseconds while the current reduces gently to zero. Like stretching bubble gum till it finally weakly breaks. 🙂 Schottky diodes simply don't have any reverse recovery time to speak of; just a little reverse current to charge the capacitance as the reverse voltage rises. Normal silicon schottky's till relatively recently could only stand about ~60 volts reverse max. Up to 200v ones are available now.
Lower mains impedance!
I have tried it in a DIY 500W FET amplifier. The main advantage is not the lower ripple on the supply, but you have a lower impedance of the mains!! (by a factor root3) as the phases are not in series (in the netherlands) but parallel! Result, better impulse response.
I have tried it in a DIY 500W FET amplifier. The main advantage is not the lower ripple on the supply, but you have a lower impedance of the mains!! (by a factor root3) as the phases are not in series (in the netherlands) but parallel! Result, better impulse response.
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