need 24V to 115VAC 3 phase inverter for gyro

I've got an ARU 44 gyro and I'd like to power it off my 24VDC system.
It needs 115VAC 3 phase, and about 75W to 100W. Is there an off the
shelf unit that can do this, or maybe someone knows of a schematic to
build my own? I'm an electronics engineer so I can do this, but
inverters are not my specialty so any guidance would be greatly
appreciated.

In article . com,
wrote:
I've got an ARU 44 gyro and I'd like to power it off my 24VDC system.
It needs 115VAC 3 phase, and about 75W to 100W. Is there an off the
shelf unit that can do this, or maybe someone knows of a schematic to
build my own? I'm an electronics engineer so I can do this, but
inverters are not my specialty so any guidance would be greatly
appreciated.


WAG says it's probably 400 cycle, as well. not 60Hz.

Design can be fairly simple, particularly if you use a micro-controller
for the 'logic' of phase generation.

start with a clock that is 2 X phases X frequency,
Feed it into a counter, that counts from 0 to (phases-1).
Hang a number of comparators on the counter outputs, one that
triggers for each value.
Send each comparator output through a flip-flop.
(this gives you a 50% duty-cycle output for each phase,
and at the right frequency.)

[now for the "analog stuff

low-pass filter to sine-wave.

Amplify to get the needed voltage/current levels.

Voila!


The digital part can be hard-wired with several discrete logic chips,
or via a cheap micro-processor.

I did something similar to this a while back to power an old military
artificial horizon. I don't think I ever actually drew out a schematic - too
simple; I just wired it up on a perf board.

Vcc was 5 volts, regulated by a 7805, from 12 volts in my case, but 24 volts
should work too. I used a 555 to generate the clock, which was 400 Hz *
9=3600 Hz. That clock was fed to a 4 bit counter. The output of that counter
was fed to the input lines of a 74154 decoder.


http://www.datasheet.in/datasheet-ht...uctor.pdf.html
http://www.datasheet.in/datasheet-ht...ilips.pdf.html
http://www.datasheet.in/datasheet-ht...ments.pdf.html
http://www.datasheet.in/datasheet-ht...uctor.pdf.html



On the output side of the decoder, 3 bits each were used for each phase.
Phase A was y0, y1 and y2 fed through 1n914 diodes as a "wired or" circuit.
Phase B was y3, y4, and y5. Phase C was y6, y7 and y8. Y9 went to reset on
the counter.

Now we have 3 phases of square waves at 5 volts. feed those phases backwards
through 3 small 120v to 5v transformers. Total cost - $10 or so at Radio
Shack.

The fact that they are square waves, not sine waves has no effect at all as
far as I could see. You are just running a tiny 3 phase synchronous motor.

3 phase, 400 cycle military instruments are super cheap on ebay. You can
mostly set up a complete IFR panel for really cheap!





"karel" wrote in message
...

"Robert Bonomi" wrote in message
...
In article . com,
wrote:
I've got an ARU 44 gyro and I'd like to power it off my 24VDC system.
It needs 115VAC 3 phase, and about 75W to 100W. Is there an off the
shelf unit that can do this, or maybe someone knows of a schematic to
build my own? I'm an electronics engineer so I can do this, but
inverters are not my specialty so any guidance would be greatly
appreciated.


WAG says it's probably 400 cycle, as well. not 60Hz.

Design can be fairly simple, particularly if you use a micro-controller
for the 'logic' of phase generation.

start with a clock that is 2 X phases X frequency,
Feed it into a counter, that counts from 0 to (phases-1).
Hang a number of comparators on the counter outputs, one that
triggers for each value.
Send each comparator output through a flip-flop.
(this gives you a 50% duty-cycle output for each phase,
and at the right frequency.)

[now for the "analog stuff

low-pass filter to sine-wave.

Amplify to get the needed voltage/current levels.

Voila!

And how does this manage to produce 110 volts from 24?
Some kind of transformer wil be required.
Step-up rectifying might be an option
but will be hard at these power levels,
i.e. require huge condensers.

But I'm afraid I am no more able than you
to really fill O/P's request for a schematic

PS does anyone know how important the true
sine wave is for this kind of equipment?

"karel" wrote

PS does anyone know how important the true
sine wave is for this kind of equipment?

Running a motor, such as on a gyro, is the least critical place for a sine
wave.
--
Jim in NC

wrote:
I've got an ARU 44 gyro and I'd like to power it off my 24VDC system.
It needs 115VAC 3 phase, and about 75W to 100W. Is there an off the
shelf unit that can do this, or maybe someone knows of a schematic to
build my own? I'm an electronics engineer so I can do this, but
inverters are not my specialty so any guidance would be greatly
appreciated.


I found a man named John Popelish in a ham or elctronics neswgroup a
couple of years ago who drew me up 3 schematics for various wattage 115
VAC 400 hz 3 phase power supplies. All three were based on the same
phase shift circuit. I lost the schematics in the Great Crash of '04. I
did bread board one and it did work. Give him a shout.

Dan, U.S. Air Force, retired

Hey, for all you folks talking about small transformers and signal diodes to
do the job, note the OP said he needed 75 watts. With normal conversion
efficiencies, this is about 4 or 5 AMPS from a 24 volt supply. We ain't in
small signal land any more, Toto.

Now, to the OP: What makes you think you need that much wattage to spin up
a small gyro motor?

Jim



In article . com,
wrote:
I've got an ARU 44 gyro and I'd like to power it off my 24VDC system.
It needs 115VAC 3 phase, and about 75W to 100W. Is there an off the
shelf unit that can do this, or maybe someone knows of a schematic to
build my own? I'm an electronics engineer so I can do this, but
inverters are not my specialty so any guidance would be greatly
appreciated.

"RST Engineering" wrote in message
...
Hey, for all you folks talking about small transformers and signal diodes
to do the job, note the OP said he needed 75 watts. With normal
conversion efficiencies, this is about 4 or 5 AMPS from a 24 volt supply.
We ain't in small signal land any more, Toto.

What makes you think you need that much wattage to spin up a small gyro
motor?

Jim


You are correct that the circuit I described will not supply more than a
watt or so, but it was enough for my application, which was what I was
describing. The original poster said he was an EE, so I did not feel the
need to elaborate.

If one were to add 3 driver transistors after the diodes (using the 24v
Vcc), and be sure to use at least 2 amp (low side) transformers, even this
75 watt load could be supplied.

karel wrote:
"RST Engineering" wrote in message
...


Hey, for all you folks talking about small transformers and signal diodes
to do the job, note the OP said he needed 75 watts. With normal
conversion efficiencies, this is about 4 or 5 AMPS from a 24 volt supply.
We ain't in small signal land any more, Toto.


A transformer big enough to transfer 75 W would weigh in at 2-3 lbs,
at a guess? Even them new-fangled toroidal thingies?
And then one apiece for each of them 3 phases?
Better use one 3-phase transformer, if the power requirement is for real.


Now, to the OP: What makes you think you need that much wattage to spin
up a small gyro motor?


Yep that's what I wondered, too.
But there's people round here more competent than myself
so I just waited a bit and sure enough the question come up!

Besides, I always understood these gyroscopes
do not take any real power
seeing they do not actually operate anything.
Just a gentle push to overcome friction, no?

Steady state, you are correct, however, the power required to spin up
the gyro can be significant for a few seconds at least.

Matt

In article ,
karel wrote:

"Robert Bonomi" wrote in message
...
In article . com,
wrote:
I've got an ARU 44 gyro and I'd like to power it off my 24VDC system.
It needs 115VAC 3 phase, and about 75W to 100W. Is there an off the
shelf unit that can do this, or maybe someone knows of a schematic to
build my own? I'm an electronics engineer so I can do this, but
inverters are not my specialty so any guidance would be greatly
appreciated.


WAG says it's probably 400 cycle, as well. not 60Hz.

Design can be fairly simple, particularly if you use a micro-controller
for the 'logic' of phase generation.

start with a clock that is 2 X phases X frequency,
Feed it into a counter, that counts from 0 to (phases-1).
Hang a number of comparators on the counter outputs, one that
triggers for each value.
Send each comparator output through a flip-flop.
(this gives you a 50% duty-cycle output for each phase,
and at the right frequency.)

[now for the "analog stuff

low-pass filter to sine-wave.

Amplify to get the needed voltage/current levels.

Voila!

And how does this manage to produce 110 volts from 24?

Note the last line: "amplify to get the needed voltage/current levels".

Original poster claimed to be an E.E., so I didn't feel it necessary
to go into all the gory details -- amplifiers that produce larger output
voltage swings than their supply voltage _are_ "well known" devices.

Some kind of transformer wil be required.

Indeed. the 'output transformer' of the powered-by-low-voltage amplifier.

Step-up rectifying might be an option
but will be hard at these power levels,
i.e. require huge condensers.

But I'm afraid I am no more able than you
to really fill O/P's request for a schematic

PS does anyone know how important the true
sine wave is for this kind of equipment?

Depends greatly on the device (I'm not familiar with the specific one the OP
names), and whether there is anything more to it than just the drive motor.
*MOST* motors could care less about the quality of the wave-form. 'smarts'
for attitude read-out are a whole 'nuther story.

There are various ways to build the voltage/current 'amplifier' stage:
1) use a switching-type power supply to 'up-vert' to a DC level adequate
to allow the use of an output-transformer-less power amp circuit.
2) take the square wave output from the phase generator directly into
a 'class C' amplifier, and feed that output into a step-up xformer.
(very good efficiency on the amplifier, lousy efficiency through
the transformer. corollary of lousy transformer efficiency -- need
a bigger transformer, and noticeably more power input to it.)
3) filter out (some/most/all of) the high-frequency components of the
waveform _before_ amplifying. then current-amplify, and transform.
(lower amplifier efficiency, but also lower losses in the xformer.)

trade-offs *galore* between the approaches.

The smallest lightest weight way it to do this is to generate 180
volts DC with a high frequency DC to DC converter then use a counter
to generate the three phases which drive a six FET three phase H
bridge to generate a modified sine wave using the 180 volts DC that
you generated with the HF transformer which is much lighter weight
than a 400 Hz transformer for the same wattage. This will give you
115 VAC at 400 Hz and eliminates the heavy 400 Hz transformer.
John

On 29 Oct 2005 01:20:54 -0700, wrote:

I've got an ARU 44 gyro and I'd like to power it off my 24VDC system.
It needs 115VAC 3 phase, and about 75W to 100W. Is there an off the
shelf unit that can do this, or maybe someone knows of a schematic to
build my own? I'm an electronics engineer so I can do this, but
inverters are not my specialty so any guidance would be greatly
appreciated.