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Re: calculating bps for sync rsg

Hi Bill,

My comments interspersed.

> Original Poster: "William Parn" <parn-at-fgm-dot-com>
Snip
> By the way calculating bps for a 50hz sync motor is
> the same as a 60hz rated motor when given the rpms.
> Just because it is 50hz doesn't mean there is only
> 50 seconds in a minute.  :-)  Oops.

Hey, that is a subtle mistake. It can happen to anyone. You just
used the 50 in the wrong place. The 50 or 60 (Hz) will already
be accounted for in the motor rpm, which brings me to your
next question:

> I have a question though.  Can a 60hz motor run on
> 50hz current?  If yes then I would presume that a
> 1800 60hz motor would spin at 1500 rpm, is that correct?

Yes, most can, but you will also have to take the voltage into
account. I have a Sears air compressor, which we took with
us on our move from the States. This compressor has a dual
voltage, dual frequency motor and it runs great on 230V &
*our* 50Hz ;o)). Of course, a little re-wiring was necessary,
but no big thing. The only time you will run into big time troubles,
is if the rated and used frequency are far apart. Like running a
400Hz (motor, xformer, whatever) on 50/60Hz. The other way
around should work, tho. For example, our trains run on high
voltage and 16 2/3 Hz. One could (yup, I already tried this
source to get a pig ;o}) easily run this xformer on 50/60Hz, but
back to your question: The compressor motor now runs a little
bit slower, so it takes a (wee) bit longer to fill the air tank,
which brings then brings me to your last question:

> And if one would want to simulate 120bps at 60hz, with
> one bang for every peak in an area running at 50hz then
> they would shoot for 100bps?

Right on !! Now you have it. Any motor designed for 60Hz
use, will run on 50 Hz at 50/60 or 5/6 of the original speed,
so a 1800 rpm motor will run at 1500 rpm on 50Hz. Using
the given example above, the SRSG for:

50 Hz would be: 1500/60*4 or 100 bps
60 Hz would be 1800/60*4 or 120 bps

Check: 5/6*120 = 100 bps (yup, works out ;o)

Just remember what Bart said in the other post about stationary
electrodes. Picture a disk (from the front) with four rotating and
two stationary electrodes. Every 1/4 of a turn a set of electrodes
(the two stationary and two rotating) line up and the gap fires (if
syncīd correctly), so you get 4 bangs per revolution. Any gaps
I add in series (schematic) will not increase the bang rate (it will
help quench, tho). But, now picture the disk with 4 rotating electrodes
and 4 stationary electrodes, which are paralleled into two sets.
This get pretty complicated, so lets use some variables:

The stationary electrodes are numbered 1, 2, 3, 4 going
clockwise. Electrodes 1 & 2 are connected together and so
are 3 & 4. The rotating electrodes are labeled A, B, C, D,
where, on start, the rotating electrode A faces stationary
electrode 1. The rotating electrodes are spaced in 90°
intervals:

A at 0°
B at 90°
C at 180°
D at 270°

The stationary electrodes are spaced a bit differently:

#1 at 0°
#2 at 45°
#3 at 180°
#4 at 225°

Best to draw yourself a picture to see what I mean. Now let
us look at what happens at certain degrees:

Gap fires at 0°, using the 1 & 3 and A & C electrodes.
Gap fires at 45°, using the 2 & 4 and A & C electrodes.
Gap fires at 90°, using the 1 & 3 and D & B electrodes.
Gap fires at 135°, using the 2 & 4 and B & D electrodes.
Gap fires at 180°, using the 1 & 3 and C & A electrodes.
Gap fires at 225°, using the 2 & 4 and A & C electrodes.
Gap fires at 270°, using the 1 & 3 and B & D electrodes.
Gap fires at 315°, using the 2 & 4 and D & B electrodes.
------------------------------------------------------------------------
Gap fires at 360°=0°, using the 1 & 3 and A & C electrodes.

In other words, this gap makes & breaks the circuit 8 times
per revolution and so running:

- on 60 Hz, this gap fires at: 1800/60* x(=8) = 240 bps
- and on 50 Hz this gap fires at: 1500/60* x(=8) = 200 bps

Okay, I hear you, what the heck is "x" in the above equation?
Well, I define  "x"  as follows:

The number of degrees in a circular disk divided by the angle
between the (two) paralleled electrodes. In our case this
would be 360°/ 45° = 8

Now what would happen if we added two more stationary
electrodes, say one electrode 45° clockwise of electrode #2
(call it 2a) and other one 45° after electrode #4 (call it 4a).
The electrodes would be once again paralleled into two sets
consisting of:

Stationary connection one -> 1, 2, 2a (the new one)
Stationary connection two -> 3, 4, 4a (the new one)

on 60 Hz this gap fires at: 1800/60* (360°/45°) = 240 bps
and on 50 Hz this gap fires at: 1500/60* (360°/45°) = 200 bps

Oops, doesnīt look right (the breakrate didnīt increase) at first
glance, but it is correct ;o)).

Let me take out one set of numbers from above:

Gap fires at 360°=0°, using the 1 & 3 and A & C electrodes.
However, at the SAME time the stationary electrodes 4a & 2a
and the rotating electrodes D & B align, so the spark either
travels from 1 to 3 (across rotating electrodes A & C) or the
path that 4a & 2a (in connection with D & B) form. Which way
the spark goes is a matter of breakdown voltage as you will
never get both 1000% equal, but this isnīt the point anyway.

As you can see, the breakrate cannot increase, so our above
calculations are true. The angle between the electrodes didnīt
change. It is still a minimum of 45°, even though I added two
additional electrodes, so the BPS didnīt change. Believe me,
a drawing will show you much more clearly what I am talking
about.

I hope this didnīt get you to pull out your hair in further confusion,
tho ;o)). Of course, it would have been MUCH easier to build a
240 / 200 bps gap by just using two stationary electrodes and
8 rotating ones ;o)).

> I better quit before I get in over my head again

Well, I hope I didnīt screw up above anywhere ;o))

> still trying to get my right shoe out of my mouth.  :-)
> It doesn't taste so good.  :-)

Yeah, and a shoe doesnīt have much nutritional value, either.
Better go get a hot dog or a hamburger. Tastes MUCH better
and gives the brain cells new fuel for thought ;o))))

Coiler greets from Germany,
Reinhard