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'[EE]Modified Senoidal Power Inverters and motors'
2007\07\20@131847 by rlistas

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Hi folks,

I need some literature about
the use of a modified senoidal
power inverter (DC > AC)
with motors, more especifically
small refrigerators.

I need some data about the reduction
of expected life for these motors when
compared to a normal senoidal power source.

Any suggestions ?

Thanks

Rubens

2007\07\20@162017 by Russell McMahon

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I have no experience of this but

- If lifetime really matters then use of an inductor as a prefilter is
liable to give an improved waveform, closer to true sinusoidal.


           Russell

> I need some literature about
> the use of a modified senoidal
> power inverter (DC > AC)
> with motors, more especifically
> small refrigerators.

2007\07\20@171156 by Herbert Graf

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On Sat, 2007-07-21 at 08:20 +1200, Russell McMahon wrote:
> I have no experience of this but
>
> - If lifetime really matters then use of an inductor as a prefilter is
> liable to give an improved waveform, closer to true sinusoidal.

Considering the motor is itself a very large inductor I'm not sure how
helpful it would be, without it also being very large.

On top of that I'd worry about the derating you'd have to do to the
inverter. It's already driving a very inductive load, that alone derates
it quite a bit, adding another inductor would probably mean having to
upsize the inverter even more.

Frankly, if it is a concern I'd leave towards getting an inverter that
outputs a true sine wave, it eliminates all these concerns. Yes, they
are more expensive, but if the chance of killing the motor is really a
concern it might be worth it.

Personally fridge compressors are so reliable these days I wouldn't
worry about this issue at all. I don't think I've ever seen a fridge
where the compression actually failed. TTYL

2007\07\20@203816 by rlistas

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There is a interesting "support doc"
from Xantrex about this.

One recomendation of Xantrex to help to start some motors is to
put a 5mH inductor in series with the motor.
http://www.xantrex.com/web/id/730/docserve.asp

Rubens

At 18:11 20/7/2007, you wrote:
{Quote hidden}

>-

2007\07\21@075913 by Bob Axtell

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rlistas wrote:
> There is a interesting "support doc"
> from Xantrex about this.
>
> One recomendation of Xantrex to help to start some motors is to
> put a 5mH inductor in series with the motor.
> http://www.xantrex.com/web/id/730/docserve.asp
>
> Rubens
>
>  
I have some experience with them, as one of my clients uses one to
convert 24V PV array
current into usable power.

I have my own office (a mobile home-type office) at my client's office
complex. It has a huge
fan and pump motor which runs at 115VAC 60Hz. It works perfectly. In
fact, the entire yard
is NOT connected in ANY way to the power company. My client, who will
sell solar tracking
systems, sells steel buildings. He has been in business for two years,
and not a single KW has
been purchased from the local power company, even though the steel
panels are WELDED
by solar power (yes, folks, if I had not seen it with my own eyes, I
would NEVER have believed
it).

He uses 3 large trackable arrays, approximately 14' x 16' in size. This
generates enough electricity
to:

1. Maintain and cool his office, which has a networked laser printer, a
fax, and two complete PC
systems.  Because the welding sometimes puts spikes into the raw battery
supply, The PCs, fax,
and printer are fed better quality power, and have a large independent
UPS system to keep it up.

2. Maintain a surveillance system of 20 cameras that watches his
property during the night and the
day. One of the PC's does NOTHING but record the surveillance.

3. I have an engineering office almost as large as his, cooled by the a
fan and "swamp cooler"  like
his. I have a WIN2K,  powered by the "clean " system from his office.
Sometimes I work late, VERY
late, and the flourescent and CF lights seem to work fine, and I've
never seen "dead" batteries. I
use my ICD2, but IT runs off the cleaner PC power. The soldering iron
runs off the raw inverter.

4. Operate two welders. These are DIRECT-CONNECTED to the battery
supply, which consists
of 4 HUGE 6V batteries. These are LEAD-ACID, and weight about 80 kgs each.

The PV arrays generate as much as 90A at 24V when tracked, less when not
tracked. My client
buys his solar cells USED from a surplus dealer, so they are weaker than
new cells, but it doesn't
matter as long as the cells match.

- - - -

The tracking system is my design and is not yet complete (delayed by
first my illness then my wife's
cancer surgery). But here are the specs:

1. The customer can choose to track the sun angle only, or the azimuth
as well.  The  two motors
are heavily geared and run at 24V, but the design can handle
12/24/36/48/96 volt systems easily.
Each motor has an accurate quadrature tachometer so the system knows
where it is pointed at all times.

2. The main controller can control up to 8 UNIQUE arrays, and the size
of the array can be quite
different from another on the system.  Each array is controlled by an
bussed RS422 system, which
can be located as far away as 1000' (300m). It uses CAT5 cable, but the
connections are unique-
it only needs ONE pair, and the OTHER pair is for an independent source
of 15V power for all
the motor controllers (the independent power assures that the buss is
never "DOWN" due to some
outage or another).  So to make life easy, the CAT5 connections are
completely reversible, allowing
the use of the "indoor" type of RJ45 crimp if the client so chooses
(they look like telephone cords).

3. Every 15 minutes the main controller calculates where the sun is. It
does this by first knowing,
accurately, the time-of-day and day-of-year to within a second (It knows
the time because every
night at 2AM, when the system is not moving any motors, a WWVB system
[60khz time signal]
is turned on and the time is READ and stored before turning off). If
the  position is seen to be  far
enough "out of position" to warrant turning on the  tracking motor, it
does so and gently  moves
the array into the correct position. The WWVB system is at the FAR end
of the bus system.

4. When the installation is made, the latitude and longitude of the site
is entered into the main controller.
Knowing the TIME/DATE/LOCATION allows me to know exactly where the sun
is all the time, as
it can be precisely calculated. A cloudy day means nothing. The system
has NO photosensor for tracking,
but it DOES have a photosensor for adjusting the LCD Display Backlight
brightness.

5. The main controller has a wind speed indicator. When the wind becomes
too great, the arrays are
gently pointed straight up, presenting a minimum profile to the wind,
regardless of direction. When the
wind goes down enough, the array returns to its correct position.

6. The main controller has an accurate time/date clock, and the crystal
for it is maintained at a steady
temperature by a temperature-controlled heater. This allows the system
to work well even in locations
where time-code stations cannot be received every other night. But I
have been told that WWVB can
be heard almost all the way across Africa, so I suppose that the two
Japanese , one Swiss, and two
German stations should cover Europe well. In any case, we are allowing
an optional GPS system to
be connected instead of the WWVB receiver. It would still have a 2%
tracking accuracy even if the
date and time was entered once a week manually.

Flames welcomed.

--Bob

2007\07\21@081112 by Bob Axtell

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> where time-code stations cannot be received every other night. But I
> have been told that WWVB can
> be heard almost all the way across Africa, so I suppose that the two
> Japanese , one Swiss, and two
> German stations should cover Europe well. In any case, we are allowing
>  
Oops, the UK has a powerful station as well. Sorry.

--Bob A

2007\07\21@093507 by Russell McMahon

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All very impressive.
I'm jealous :-).

One  extremely minor note.

> and the crystal for it is maintained at a steady temperature by a
> temperature-controlled heater.

Your crystal oven seems to be overkill.
A wristwatch crystal "ovened" by operating on a person's wrist can
easily operate at under a second a day accuracy.
A system using that time source would maintain adequate tracking for
months.

One minute per day is about 700 ppm drift and one second per day is
about 10 ppm.

But I imagine that your temperature controlled heater is a minimal
addition to the expense.



       Russell

2007\07\21@095212 by Bob Axtell

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Russell McMahon wrote:
> All very impressive.
> I'm jealous :-).
>  

You can't be. Russell. You can easily do better. I have read your stuff
{Quote hidden}

Its not expensive, because in some locales the outside temperature is
-20C. I need it, really.
>
>
>         Russell
>
>  

2007\07\21@194717 by Howard Winter

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Bob,

On Sat, 21 Jul 2007 05:09:48 -0700, Bob Axtell wrote:

>
> > where time-code stations cannot be received every other night. But I
> > have been told that WWVB can
> > be heard almost all the way across Africa, so I suppose that the two
> > Japanese , one Swiss, and two
> > German stations should cover Europe well. In any case, we are allowing
> >  
> Oops, the UK has a powerful station as well. Sorry.

Yes MSF, on 60kHz covers most of Western Europe - I bought my first clock capable of receiving it about 15 years ago - cost about GB£60 (US$120) if I
remeber rightly!  I now have several clocks around the house which use MSF (plus a watch!),  and I have one that picks up the German DCF on 77kHz,
which cost UK£3 (US$6) on clearance in my local Staples.  This one only receives reliably in the front of the house - I assume the signal is a bit weak
by the time it gets here from Frankfurt, but for that price it's not a major problem.

Why do I want all these?  I like to know *exactly* how late I am!  :-)

And I never have to put the clocks back or forward...

Cheers,


Howard Winter
St.Albans, England


2007\07\21@211209 by Sean Breheny

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Really impressive, Bob. Thanks for sharing the details!!!

Sean


On 7/21/07, Bob Axtell <spam_OUTengineerTakeThisOuTspamcotse.net> wrote:
>
> The tracking system is my design and is not yet complete (delayed by
> first my illness then my wife's
> cancer surgery). But here are the specs:
>

2007\07\21@235616 by Bob Axtell

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Howard Winter wrote:
>
> Yes MSF, on 60kHz covers most of Western Europe - I bought my first clock capable of receiving it about 15 years ago - cost about GB£60 (US$120) if I
> remeber rightly!  I now have several clocks around the house which use MSF (plus a watch!),  and I have one that picks up the German DCF on 77kHz,
> which cost UK£3 (US$6) on clearance in my local Staples.  This one only receives reliably in the front of the house - I assume the signal is a bit weak
> by the time it gets here from Frankfurt, but for that price it's not a major problem.
>
>  
I purchased one online about 14 months ago. It still has the same 1.5V
battery, and is placed in the jacuzzi room so I know what time it is, so
I won't be late in the morning. Very accurate.

BUT, the problem with MSF/DCF/WWVB is that each time code protocol is
slightly different. So my main controller sends the time code box a
command for the correct time code station.
The time code decoder is a small PIC (PIC12F629) but has enough space
for the 5 different types. The customer will specify which station is to
be used, and I will install the  correct fixed
receiver. But I have only extracted WWVB; I need to get a recording of
the others in order to develop the code. I am thinking that I can ask
some PIClisters to record the audio output from
their clocks and I can process it here into I/O.

Any interest? I need MSF, DCF, and the high freq Japanese station recorded.

Unless somebody has already done that...maybe I should ask the time
stations?

--Bob A

2007\07\22@014924 by Robert Rolf

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Bob Axtell wrote:
> the others in order to develop the code. I am thinking that I can ask
> some PIClisters to record the audio output from
> their clocks and I can process it here into I/O.
>
> Any interest? I need MSF, DCF, and the high freq Japanese station recorded.
>
> Unless somebody has already done that...maybe I should ask the time
> stations?

Err, yeah...
If their protocol is published (most are) you can 'fake it' with a PC.

http://en.wikipedia.org/wiki/Radio_clock

http://en.wikipedia.org/wiki/Time_from_NPL


http://en.wikipedia.org/wiki/DCF77
www.ptb.de/en/org/4/44/442/dcf77_1_e.htm
http://www.ptb.de/en/org/4/44/442/dcf77_kode_e.htm

etc.

Robert


2007\07\23@141906 by Howard Winter

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On Sat, 21 Jul 2007 23:49:21 -0600, Robert Rolf wrote:

> http://en.wikipedia.org/wiki/Time_from_NPL

Well there's my "You learn something new every day" item for today - I didn't know that MSF had moved from Rugby!  

I'm a tad surprised, because it was pretty-much in the centre of Britain where it was, and now it's way up North.  I had noticed at Rugby (which has
hundreds of aerial masts which you can see as you drive past on the motorway) that the VLF transmission towers, 12 of them in an oval about half a
mile across, had been taken down some time ago, but I never did know which of the rest was MSF.

I have to say that the move (at least 100 miles further away) doesn't seem to have affected any of my clocks, so presumably the signal strength is
still very good.  I do find that interference can stop them, though - too near a CRT television is a good one!

Cheers,



Howard Winter
St.Albans, England


2007\07\23@143348 by Howard Winter

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Bob,

On Sat, 21 Jul 2007 20:54:47 -0700, Bob Axtell wrote:

{Quote hidden}

Well you'd have a problem with audio on MSF - there isn't any!  It's carrier switched with variable-width bursts of carrier to convey the data (L1D to
give it its proper ITU designation), so I'm not sure how anyone could record it.  I suppose keying an audio oscillator would do it, but I'm not sure if that
would help you to simulate the signal for your decoder.

Cheers,


Howard Winter
St.Albans, England


2007\07\23@152358 by Bob Axtell

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Howard Winter wrote:
> On Sat, 21 Jul 2007 23:49:21 -0600, Robert Rolf wrote:
>
>  
>> http://en.wikipedia.org/wiki/Time_from_NPL
>>    
>
> Well there's my "You learn something new every day" item for today - I didn't know that MSF had moved from Rugby!  
>
> I'm a tad surprised, because it was pretty-much in the centre of Britain where it was, and now it's way up North.  I had noticed at Rugby (which has
> hundreds of aerial masts which you can see as you drive past on the motorway) that the VLF transmission towers, 12 of them in an oval about half a
> mile across, had been taken down some time ago, but I never did know which of the rest was MSF.
>
> I have to say that the move (at least 100 miles further away) doesn't seem to have affected any of my clocks, so presumably the signal strength is
> still very good.  I do find that interference can stop them, though - too near a CRT television is a good one!
>  
yes, motor noise and signals from cellphones seem to cause some signal loss.

My solar tracker will ONLY obtain a time/date fix in the middle of the
night; i.e. NO tracking system movement or charger noise.
That is accurate enough.

--Bob Axtell
> Cheers,
>
>
>
> Howard Winter
> St.Albans, England
>
>
>  

2007\07\24@072639 by Russell McMahon

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>> Any interest? I need MSF, DCF, and the high freq Japanese station
>> recorded.

> Well you'd have a problem with audio on MSF - there isn't any!  It's
> carrier switched with variable-width bursts of carrier to convey the
> data (L1D to
> give it its proper ITU designation), so I'm not sure how anyone
> could record it.  I suppose keying an audio oscillator would do it,
> but I'm not sure if that
> would help you to simulate the signal for your decoder.

Sounds suspiciously like "Morse Code" :-) (but the code isn't Morse's
one).

A heterodyne oscillator will give you a beat note of your choice for
recording. Or, as you say, you can use the carrier to key any tone or
pair of tones of your choice.


       Russell


2007\07\24@082549 by Bob Axtell

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Russell McMahon wrote:
{Quote hidden}

Russell, what timecode source can you guys get down under? If I sent you
a test clock (1-line
LCD display) could you simply use it for a coupla weeks to make sure I
wrote the  decoder
right? You can keep it, or toss it, as you wish thereafter...

--Bob

2007\07\25@160646 by Richard Prosser

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Bob,
I haven't seen Russell reply to this so I'll add my comments.

AFAIK the only LF time signal we can get down here is the Japanese one
- and even then I think it is somewhat sporadic. Building a receiver
for it is on my long-term list of projects.


We can get the HF time signals (I assume they're still operating) but
again, somewhat subject to conditions. I used to use the Hawaian VOA
(?) signal to set my clocks, many years ago, although the local
broadcast "pips" would have been more than adequate, if less
convienient.

Richard P


On 25/07/07, Bob Axtell <.....engineerKILLspamspam@spam@cotse.net> wrote:
{Quote hidden}

> -

2007\07\26@020932 by Nate Duehr

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On Jul 25, 2007, at 2:06 PM, Richard Prosser wrote:

> We can get the HF time signals (I assume they're still operating) but
> again, somewhat subject to conditions. I used to use the Hawaian VOA
> (?) signal to set my clocks, many years ago, although the local
> broadcast "pips" would have been more than adequate, if less
> convienient.

That's WWVH, not VOA.

http://tf.nist.gov/timefreq/stations/wwvh.htm

LOTS of detailed documentation on their website.  They're part of NIST.

--
Nate Duehr
natespamKILLspamnatetech.com



2007\07\26@032256 by Richard Prosser

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Yep.
I knew I'd got that bit wrong - just couldn't remember the right callsign.
RP

On 26/07/07, Nate Duehr <.....nateKILLspamspam.....natetech.com> wrote:
{Quote hidden}

> -

2007\07\26@100330 by David VanHorn

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>
> That's WWVH, not VOA.
>
> http://tf.nist.gov/timefreq/stations/wwvh.htm

You notice on the timeslicing, that the lady gets to speak first?  :)

2007\07\29@054506 by Howard Winter

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Dave,

On Thu, 26 Jul 2007 10:03:25 -0400, David VanHorn wrote:

> >
> > That's WWVH, not VOA.
> >
> > http://tf.nist.gov/timefreq/stations/wwvh.htm
>
> You notice on the timeslicing, that the lady gets to speak first?  :)

I don't notice this, because I'm getting "Connection Refused" when I try this URL.  I wonder if they don't want us foreigners seeing what they're up to?  
:-)

Cheers,


Howard Winter
St.Albans, England


2007\07\30@043052 by Alan B. Pearce

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>Well there's my "You learn something new every day" item
>for today - I didn't know that MSF had moved from Rugby!

Yeah, happened about 6 months ago. Someone else 'got the contract' in this
privatised world.

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