>From: "Mike Gemeny" <MGemeny at pgcps.org>
>
---snip---
>
>Dwight mentioned RMS voltage when referring to a square wave. I was a bit
confused by that. My understanding of RMS is that it is a way of expressing the
energy under the curve of a sign wave such that the total energy was expressed
as that of the peek of a square wave with equivalent energy. If that is the case
then RMS and peek for a square wave would be the same but to convert between RMS
and peek for a sign wave you multiple or divide by the square root of 2 or
1.414. I???m not trying to criticize Dwight at all here, I suspect he makes a
good point, I???m just not sure I fully understood his post.
>
>Clarification and other opinions always welcome.
>
>Mike.
Hi Mike
I'll try to clarify.
RMS means that if you feed it into a resistor, it will
get as hot. Since a sine wave spends part of its time at
lower voltages, it has to have a higher peak voltage to get
the resistor as warm as an equivalent DC voltage. Now
when we get to a square wave, we see that it has exactly
the same voltage as DC for the same RMS level. It is just
that it switches polarity, but that doesn't effect the power
in the resistor.
Now, when looking at what we call 115VAC, we are referring
to its RMS level ( equivalent heating of a resistor ). A
115V square wave has a peak voltage of 115V as well as
an RMS of 115V.
This makes a difference when we use a load such as a rectifier.
It only looks at peak. On the sine wave, that was about 160V
while the square wave, it is still 115v.
So, something like a light bulb will but as bright on the
115V square wave as 115VAC but a power supply with a rectifier
will only see about the equivalent of 80VAC RMS sinewave source.
This is outside of most switchers operating range.
In other words, the square wave source would need to have
an output of 160V to be used correctly with power supplies
that have input rectifiers.
I hope that makes more sense.
Dwight
A few things I forgot to mention and then a couple of questions. Even though the caps were balanced for the lathe motor, when I start the grinder, the lathe motor gets even quieter. Does this mean that perhaps I should be dropping out the caps once I have a motor running? I don?t think so, because when I balanced the cap bank I was looking for the sweet spot in motor happiness. Perhaps its an indication that the more motors I have running the happier they all are, which has been my assumption.
If the latter were the case then a rotary approach would not have much in the way of limits for motors.
Also, the impression I have always had from machine shop circles was that commercial rotary phase converters were the same as motors as far as the stator and rotor were concerned. The only differences being that it has no output shaft and would have some other stuff (like my bank of caps) on the outside. But again, I don?t have experience with commercial rotary phase converters ether. If there were differences between the stator and rotor of a commercial rotary phase converter and a three-phase motor, I would love find out what they are.
Yes, Kevin is quite correct that solid-state phase converters are available. In fact some will even allow you to control the speed of the motors, although one that elaborate is most likely not what Brian would want.
I also agree with Paul that for a conventional power supply ?I would expect power supplies to be every bit as tolerant of distorted waveforms as motors are, even assuming that these converters produce major distortion.? And for switching computer power supplies I would bet that an old 3 phase motor idling in the corner would go a long way toward cleaning up any artifacts in the solid state converter output.
I would expect a solid-state approach to handle a wide range of loads, but I don?t have any experience with them. I would also expect a solid-state approach to have a strict upper limit on capacity. Is that the case? Perhaps Kevin could get his brother to share more information with us on his experiences.
On phase order I just want to point out what I hope is obvious to everyone but no one has said, if you swap any two phases you have reversed the phase order.
Jim brings up 208v, which brings up an issue not yet discussed, that is delta vs. Y.
My guess is that motors and generators are generally delta, and that most distribution systems are Y. I can accept being mistaken about this, and a rich discussion is sure to help us all.
Most of you must by now be familiar with the distribution systems used in the states as far as one leg being 110v and both legs giving you 220v on single phase service. With that in mind how can we best approximate that in a 3 phase building? We use a Y configuration of second windings on the last set of 3 transformers. If each secondary winding is set for 120v, and we combine 2 windings we don?t get 240v, we get 208v.
Given thusly:
(120+120)*sin(360/3)=207.85 (or 208)
If you wanted 220 or 230 or 240 you use a set of 3 transformers and most likely wire the primaries as Y and the secondaries as delta.
Dwight mentioned RMS voltage when referring to a square wave. I was a bit confused by that. My understanding of RMS is that it is a way of expressing the energy under the curve of a sign wave such that the total energy was expressed as that of the peek of a square wave with equivalent energy. If that is the case then RMS and peek for a square wave would be the same but to convert between RMS and peek for a sign wave you multiple or divide by the square root of 2 or 1.414. I?m not trying to criticize Dwight at all here, I suspect he makes a good point, I?m just not sure I fully understood his post.
Clarification and other opinions always welcome.
Mike.
>
>Subject: RE: kda50 manual and sdi cables & questions
> Date: Fri, 29 Apr 2005 18:35:49 +0100
> To: "'General Discussion: On-Topic and Off-Topic Posts'" <cctalk at classiccmp.org>
>
>John Allain wrote:
>
>> As discovered with the RA90 fitting in a SF200 rack.
>> DEC must have thought this out pretty well, but Wikipedia
>> actually credits the RA9 series for wrecking the company.
>
>> ref: http://en.wikipedia.org/wiki/Digital_Equipment_Corporation
That wikicrap again.
Actually one of the things that did hurt was the RA8x debacle.
Good drive but some dunderhead subbed a adhesive and usually within
a 100hrs they would headcrash. I believe the FA forcast on that was
101million to return and preplace all the damaged HDA and it was
more due to efforts resulting from crahses.
That and keeping PNO and ABQ open with staff no work.
Allison
If we're all going to do a "wish list", is there anyone in the UK with an
un-loved and un-wanted ASR33?
Jim.
Please see our website the " Vintage Communication Pages" at WWW.G1JBG.CO.UK
Hi
You can disconnect the motor and run it by hand, turning
the shaft. First after powering up, you need to turn the
shaft until the clutches release. You need to squeeze
the two tabs together that come from each clutch to
keep them from dragging when running slow. It is a little
hard to do while also holding the shaft. Once you've done
it, you'll understand.
Anyway, you should be able to walk it through a letter
>from the keyboard and you can watch to see what isn't
working right. Erratic operation is a little tougher
to find when running by hand because it tends to work
right at the slower speeds.
I hope you have a manual. If not download the stuff
>from the web page. You'll need the manual for adjustments
and disassembly.
Dwight
>From: "Bill Kotaska" <bkotaska at charter.net>
>
>I am looking for troubleshooting tips for a 33 teletype.
>
>I'm testing in local mode and am getting incorrect characters
>on (almost) every keypress. The characters will change even
>with repeated pressings of the same key. I am pretty sure the
>keyboard is outputting the correct codes.
>
>I wiped down the distributor surface (it was pretty grimy) and no change.
>I tried adjusting the range finder but could never find a point where the
>characters were consistent.
>
>Is it possible to disconnect the motor drive belt and rotate the shaft
>manually to get a closer look at what is happening mechanically?
>It's very hard to see what is going on in the selector area with the
>shaft spinning so fast.
>
>By the way, my drive belt is somewhat loose. Is there still a source
>for these? Or maybe an adjustment for tightening?
>
>Thanks,
>Bill
>
They used to be big in terminals and printers. They still have a lot of spare
parts for everything they serviced. Think they have a lot of pc's,xt's,at's,&
Teletypes still.You can e-mail them @dataterm.com
There is currently a discussion (argument?) on vmsnet.pdp-11
in respect of the media required for the TK70 tape drive.
Indeed, there is even a question of using the TK70 tape
drive on a PDP-11.
Has anyone any explicit knowledge and / or experience of a
TK70 tape drive on a PDP-11?
In respect of the media, does anyone know of any explicit
differences between a CompacTape and a CompacTape II?
Memorex used to have a page listing all DLT physical and
magnetic characteristics. At the time, I was unable to
see any differences.
Can anyone at classiccmp help answer these questions?
My personal experience over the last 15 years using a
TK70 on a PDP-11 under RT-11 is that regular TK50 media
(CompacTape) have always been successfully used (over
100 TK50 media) with the TK70 tape drive (after the TK50
media are bulk erased if they were ever placed into a
TK50 tape drive - if they were completely unused, they
worked immediately).
Sincerely yours,
Jerome Fine
--
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address has been discontinued due a high volume of junk
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>
>Subject: Re: Hacking the DECmate serial port
> From: Wai-Sun Chia <waisun.chia at gmail.com>
> Date: Fri, 29 Apr 2005 11:38:17 +0800
> To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at classiccmp.org>
>
>On 4/29/05, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
>> Not necesarily. The 6402 takes external transmit and receive clocks, at
>> 16 times the desirted baud rate. If the clock generator hardware can't go
>> faster than 16*4800 for some reason, then you won't get more than 4800
>> baud. This is probalby very easy to modify, though.
>
>Sorry to sound simplistic, but does that mean if I just whack in an
>appropriate crystal, then I'd magically get 9600? (haven't downloaded
>the prints yet)
>
>Recommendations for an appropriate crystal would be very much appreciated! :-)
>How much do you think I could up it to? 19k2?
The crystal would be 4x whats used for4800! There are a few yabuts.
One the crystal me DIP osc, two the end freq may exceed the divider
logics count speed and three the same rock may also supply other
logic that may not like being sped up like the cpu itself.
Look at the prints first befor you speculate. The UART itself can
easily go faster but it's never that easy.
Allison
