Search found 1182 matches

by Bob Scott
Tue Aug 07, 2012 7:45 am
Forum: General Discussion
Topic: Fan motor running on half wave ?
Replies: 11
Views: 1926

Re: Fan motor running on half wave ?

Hi, This isnt something i'd want to try either. The windings are inductive but with DC the inductance has no effect so you are left with only the resistance of the winding that limits current. If you do have to try this for some reason it would be good to start with a resistance in series with the ...
by Bob Scott
Thu Aug 02, 2012 4:56 pm
Forum: General Discussion
Topic: Fan motor running on half wave ?
Replies: 11
Views: 1926

Re: Fan motor running on half wave ?

I tried this experiment a long time ago with an old AC shaded pole phono motor. I created a DC brake. The motor will oppose rotation. If you try to turn it by hand, it resists your rotational force. Sony used this principle in its old '60s and 70's half inch video recorders. (eg: AV-3600) The head d...
by Bob Scott
Wed Aug 01, 2012 3:43 pm
Forum: General Discussion
Topic: Scope question...
Replies: 7
Views: 2180

Re: Scope question...

the system risetime (input to CRT) will be the square root of the sum of the squares of the individual risetimes. ------------------------------------------------------------- 500 [1/X] [X²] + 250 [1/X] [X²] + 350 [1/X] [X²] = [1/X] [SQR X] Thanks Dean! I learned something new today. The equation l...
by Bob Scott
Fri Jul 27, 2012 6:16 pm
Forum: General Discussion
Topic: Scope question...
Replies: 7
Views: 2180

Re: Scope question...

Anyway, my main question is... In both of the manuals I noticed a little note that says if you have the probe set for 1x (vs. 10x), the max speed it NOT 100MHz but rather 5MHz (OWON) or 6MHz (Rigol). What gives? Kevin There is a resistive attenuator inserted into the probe circuit when it is switch...
by Bob Scott
Wed Jul 18, 2012 1:13 pm
Forum: General Discussion
Topic: UL listing...dubious assurance
Replies: 5
Views: 1289

Re: UL listing...dubious assurance

As long as manufacturers and regulatory agencies sleep together, there will be questionable decisions and rulings. As I read in Wikipedia, UL is no longer a non-profit independent lab. UL testing is now done for profit since 2007. That is a big problem for their credibility. For-profit companies ru...
by Bob Scott
Thu Jul 12, 2012 5:23 pm
Forum: General Discussion
Topic: Shocking News Report
Replies: 9
Views: 1744

Re: Shocking News Report

Hi Bob, Because the secondary of the transformer is a 'derived' or isolated source, it should logically have a GFCI on that side. Yes, I believe that the design engineer was not aware that a second GFCI would be necessary to protect the 120VAC outlets. He made a few mistakes in the design of the re...
by Bob Scott
Wed Jul 11, 2012 2:18 pm
Forum: General Discussion
Topic: Shocking News Report
Replies: 9
Views: 1744

Re: Shocking News Report

Interesting note: A GFCI breaker may sometimes be incapable of tripping even if a ground fault exists. I was familiarising myself with the electricals of a giant wafer inspection machine in San Jose. This monster used LOTS of power, so uses 208V 3 phase Delta AC for power (note: no neutral wire on i...
by Bob Scott
Mon Jul 09, 2012 6:19 pm
Forum: General Discussion
Topic: Lost my solder pads need help
Replies: 10
Views: 2350

Re: Lost my solder pads need help

What are vias? This is a MPU from a 1978 Bally Pinball machine. Had some corrosion from a leaky battery. Oh wow, corrosion is bad news. I would not have to much confidence in a successful repair. Battery acid contamination in the PCB is probably present and will continue to corrode any new repairs....
by Bob Scott
Sat Jul 07, 2012 5:07 pm
Forum: General Discussion
Topic: Shocking News Report
Replies: 9
Views: 1744

Re: Shocking News Report

Yes. There may have been an electrical fault with one of the houseboats if it is hooked up to shore electrical power. All I can think of that could conduct AC current enough to kill a human would be if there is a fault conducting current > 100mA through the water to ground or to the AC round on the ...
by Bob Scott
Wed Jul 04, 2012 2:57 pm
Forum: General Discussion
Topic: Free Energy Is Here Again!
Replies: 9
Views: 1698

Re: Free Energy Is Here Again!

Lenp wrote:Sit back, relax and view this http://nikolatesla.pl.tc
Enjoy,
Len
(PS if there is any interest, I'll sell it as a kit :idea: )
My computer won't load that posted URL. I get a virus warning from the Trend micro protection software that I bought and run.
by Bob Scott
Thu Jun 21, 2012 4:42 pm
Forum: General Discussion
Topic: Magnet in conductive media...
Replies: 21
Views: 5262

Re: Magnet in conductive media...

I did not try to state that a dead short is not close to some small value of resistance, i meant to try to draw attention to the voltage drop as being non zero. If we have a zero voltage drop then we have no field to analyze, but if we assume at least some voltage drop then we have a field and thus...
by Bob Scott
Thu Jun 21, 2012 4:07 pm
Forum: General Discussion
Topic: Magnet in conductive media...
Replies: 21
Views: 5262

Re: Magnet in conductive media...

If the magnet is submerged in a conductive fluid, call it mercury, seawater... Will the fluid bear currents around the moving magnet ? I remember the design of a turntable braking mechanism (1950?) for speed control, from one of those online old Popular Science magazines at books.google.com... Unde...
by Bob Scott
Sat Jun 02, 2012 10:33 am
Forum: General Discussion
Topic: Tell something you did not know until recently...
Replies: 6
Views: 1487

Re: Tell something you did not know until recently...

Here is a start: http://en.wikipedia.org/wiki/Capacitance_Electronic_Disc I remember those! The shop I worked for had the warranty repair contract for RCA Capacitive disks. All I remember is: There was no modulation in the groove. The only purpose for the stylus and the groove was to keep the picku...
by Bob Scott
Sat May 19, 2012 8:20 am
Forum: General Discussion
Topic: Another substitution needed...
Replies: 12
Views: 1835

Re: Another substitution needed...

Robert, I want to run a sim on it and my software does not have the TL0** series in the "parts bin" and I don't have any real way to add in a macro to model it/them. If it performs/sims as advertised, I have no problem ordering the actual parts list. Heck, Jameco has the TL062 at a price of 10/$2.5...
by Bob Scott
Wed Apr 25, 2012 3:15 pm
Forum: General Discussion
Topic: Name of transistor
Replies: 6
Views: 1391

Re: Name of transistor

I agree with Caesar. Looking at what I can see of the diagram, I believe that this (these) are constant current sources. This is a schematic of an IC. There has never been a discrete single transistor device sold that is wired like this, but you can make one. For this purpose, you can make a transis...