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Author Topic: 3-phase power demonstration  (Read 5036 times)

Chris Hindle

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Re: 3-phase power demonstration
« Reply #20 on: December 07, 2018, 02:51:56 pm »

I disagree. Automotive ALTERNATORS, in my experience, use a field winding on the rotor powered through slip rings. The output voltage, derived from the 3-phase stator and a 3-phase rectifier, is controlled by varying the field current.  They could use a permanent magnet field but would need to apply voltage regulation downstream, as by PWM.

The GENERATORS of yesteryear had a field winding in the stator, and took the output from multiple windings on the rotor through a commutator.

The whole nomenclature of what constitutes an AC or DC machine has become blurry in recent years with the widespread use of electronic motor/generator drives.  -F
Agreed to your points Frank.
As I retired mechanic, Generators were 50's, and Alternators 60's and newer.
Never had to rebuild a Genny, but have done a shit load of Delco's over the years. Mostly brushes and/or Modules. Those diodes were indestructible.

That they COULD have used PM instead of windings would have just made them heavier, and didn't PWM controls start in the 80's ?
Chris.
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Frank Koenig

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Re: 3-phase power demonstration
« Reply #21 on: December 07, 2018, 03:21:48 pm »

That they COULD have used PM instead of windings would have just made them heavier, and didn't PWM controls start in the 80's ?

Yes. Heavier, probably more expensive, maybe thermal issues, and auto manufacturers hate to change anything that's still getting product out the door unless they find a far cheaper way to make it. (Why are there still drum brakes in 2018?)

As an aside, last winter I visited both hydroelectric plants at Bonneville on the Columbia River. In the older plant they had replaced the exciter generators with semiconductor rectifiers. The exciter rectifiers for an alternator the size of a small house are air cooled and fit in an ~15 ft wide standing height cabinet.

-Frank
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Mike Sokol

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Re: 3-phase power demonstration
« Reply #22 on: December 07, 2018, 04:06:30 pm »

Just talked to their training manager and they’re excited about the possibility of having real 3-phase power in all the flavors to measure. And I get to do a full 8-hour training day. This could be a lot of fun.
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Mike Sokol
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Mike Sokol

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Re: 3-phase power demonstration
« Reply #23 on: December 07, 2018, 04:10:10 pm »

You need to add an islated neutral bus to do this right.-as it is pictued that panel is only acceptable for delta connected loads.
Yeah, that wouldn’t be too difficult considering there will only be a few hundred mA of current. Or I could bring a rack of MacroTech amplifiers and make some real juice.
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Mike Sokol
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Chris Hindle

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Re: 3-phase power demonstration
« Reply #24 on: December 07, 2018, 05:44:20 pm »

Yeah, that wouldn’t be too difficult considering there will only be a few hundred mA of current. Or I could bring a rack of MacroTech amplifiers and make some real juice.
And here I was thinking 3 sine wave oscillators and 3 DC-300's  ::)
Chris.
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Mike Sokol

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Re: 3-phase power demonstration
« Reply #25 on: December 09, 2018, 07:41:19 am »

And here I was thinking 3 sine wave oscillators and 3 DC-300's  ::)
Chris.

IIRC decades ago one of the companies I worked with used a Crown DC300 to drive big servo motors on a vibration platform. Don’t they go down to actual DC output because their’s no HPF in their signal path? Bad for speakers, good for servo motors...
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Mike Sokol
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Chris Hindle

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Re: 3-phase power demonstration
« Reply #26 on: December 10, 2018, 08:39:42 am »

IIRC decades ago one of the companies I worked with used a Crown DC300 to drive big servo motors on a vibration platform. Don’t they go down to actual DC output because their’s no HPF in their signal path? Bad for speakers, good for servo motors...
I believe that was the DC in the product name. They WOULD go to DC.
That was the default failure mode, and would wipe out a batch of drivers in a real hurry. Not as spectacular as a Flame Linear, but just as damaging....
On 1 rig, we lost 3 of 12 2441's when a DC300 took a dump.
Ahhh, the good old dayze....
Chris.
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Mike Sokol

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Re: 3-phase power demonstration
« Reply #27 on: December 11, 2018, 08:33:20 am »

I believe that was the DC in the product name. They WOULD go to DC.
That was the default failure mode, and would wipe out a batch of drivers in a real hurry. Not as spectacular as a Flame Linear, but just as damaging....
On 1 rig, we lost 3 of 12 2441's when a DC300 took a dump.
Ahhh, the good old dayze....
Chris.

I'm going to talk to my contact at Crown and see if they'll loan me a CT475 amp for the class: https://www.crownaudio.com/en/products/ct-475

This is a quad 1RU amp that outputs 75 watts per channel into 8 ohms, so it would match up nicely with air conditioner transformers that are 120/240-volts to 24-volts. And these transformers come in 40 or 50VA size which would match up nicely with the amplifier outputs. The only advantage of using a bigger amplifier would be that I could do a few current experiments that would be iffy on a little 10-watt amplifier. In any event, I'm going to draw up a schematic and block diagram in a few days to make sure I'm not missing anything. It's all in my head right now, so it's time to put this down on paper.
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Mike Sokol
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Chris Hindle

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Re: 3-phase power demonstration
« Reply #28 on: December 11, 2018, 08:54:20 am »

I'm going to talk to my contact at Crown and see if they'll loan me a CT475 amp for the class: https://www.crownaudio.com/en/products/ct-475

This is a quad 1RU amp that outputs 75 watts per channel into 8 ohms, so it would match up nicely with air conditioner transformers that are 120/240-volts to 24-volts. And these transformers come in 40 or 50VA size which would match up nicely with the amplifier outputs. The only advantage of using a bigger amplifier would be that I could do a few current experiments that would be iffy on a little 10-watt amplifier. In any event, I'm going to draw up a schematic and block diagram in a few days to make sure I'm not missing anything. It's all in my head right now, so it's time to put this down on paper.
Gotta say Mike, you sure get to theorize and build some pretty cool "stuff".
Good on ya, and the education you spread to others. (me included).
I got to blow up a lot of shit learning what I know...
Long before this interwebby thing came along....
Chris.
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Mike Sokol

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Re: 3-phase power demonstration
« Reply #29 on: December 11, 2018, 09:37:19 am »

Gotta say Mike, you sure get to theorize and build some pretty cool "stuff".
Good on ya, and the education you spread to others. (me included).
I got to blow up a lot of shit learning what I know...
Long before this interwebby thing came along....
Chris.

This really is too much fun!

Now what I need to consider is how to take the three transformer secondaries and rewire them as WYE, Delta or High-Leg Delta services at the flip of a switch. I'm not sure I trust myself to use banana plugs to rewire the various configurations while simultaneously teaching a seminar. Of course I could do the Rick Wakeman brute force method and have 9 transformers feeding 3 different service panels with everything wired at once, but that seems like cheating and too heavy to take on a plane. Looks like I need to remember Boolean Algebra and Karnaugh maps like I used in the 70's for machine control design, and get a really big rotary switch. My head hurts already just thinking about it. 
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Mike Sokol
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