Keyboard Shortcuts
ctrl + shift + ? :
Show all keyboard shortcuts
ctrl + g :
Navigate to a group
ctrl + shift + f :
Find
ctrl + / :
Quick actions
esc to dismiss
Likes
- TekScopes
- Messages
Search
|
Re: OT- question relating to DC shunt motor schematics
Chuck Harris
It really doesn't matter. Because both the field, and the
toggle quoted message
Show quoted text
armature change polarity, when you change supply polarity, the motor will continue to spin the same direction. Back in the days of yor, when there were competing AC and DC power generation systems, a universal motor was imagined, that would run on either AC or DC equally well. It is just a DC motor with the field and armature in series or shunt. To reverse a series, or shunt motor, you have to swap the field connections relative to the armature connections. -Chuck Harris Dave Seiter wrote: On the schematics pertaining to DC shunt/series motor starters, is there any naming convention relating to L1 and L2 being positive/negative? I ask because I'm used to DC systems specifying polarity, and the only "polarity" mentioned on the schematic I have is the name "D.C. Automatic Starter". |
|
Re: OT- question relating to DC shunt motor schematics
Hi Bruce, thanks for the input!
toggle quoted message
Show quoted text
If I sent you a photo of the schematic off list, could you make an educated guess (or perhaps see something I've missed?).? I've read schematics since my Radio Shack 101 kit, but power control, especially 3PH, is all new to me.? Vintage makes it even more interesting.?? Regards, -Dave On Wednesday, August 28, 2019, 07:57:58 PM PDT, greenboxmaven via Groups.Io <ka2ivy@...> wrote:
In my 30 plus years in the elevator craft, I have never seen or heard of any standard of L1 and L2, and I have worked on many DC motor starter/reverser panels. Different manufacturers used whatever designation they wanted to, every print I ever saw made it clear which? input terminal was to be positive and which was negative. Polarity is very important, large contactors have "blowout" coils or magnets, improper polarity can prevent the arc formed when a contact opens from being snuffed.? A flashover between contacts is a sensory experience you will not forget! It is great to hear someone discussing old control gear, learning about it is vital for proficiency with newer controls, and there is a surprising amount of that gear still in use today. ? ? ? Bruce Gentry, KA2IVY International Union of Elevator Constructors, Local 62, Retired On 8/28/19 10:03 PM, Dave Seiter wrote: On the schematics pertaining to DC shunt/series motor starters, is there any naming convention relating to L1 and L2 being positive/negative?? I ask because I'm used to DC systems specifying polarity, and the only "polarity" mentioned on the schematic I have is the name "D.C. Automatic Starter". |
|
Re: TDS 694C CRT screech
My favourite scope, a TDS 694C, has developed a nasty screeching sound when The downside is that you may feel compelled to kick yourself for not ditching the CRT earlier. Also, no more trippy head spinning when your gaze accidentally sweeps past the color shutter! -- john, KE5FX |
|
Re: Need Help Troubleshooting Tektronix PS280
Chuck Harris
I have fixed a lot of this family of supplies, and never had the luxury of
toggle quoted message
Show quoted text
a schematic. One really isn't necessary... sometimes it just adds confusion. Most of the problems are simple, and the result of GoodWill using cheap parts. The two variable supplies are carbon copies of each other... identical circuitry, that is floating so they can be connected in series or parallel aiding, or opposing. These supplies give you an excellent platform for debugging, as they give you two identical examples of the supply to check and compare. Put that to use... it is far more effective than having some one else walk you through it. Set them to track, look at the bad side, look at the same part in the good side, find where they behave the same, and where they don't, and that is the location of the problem. If the relays are a chattering, 9 times out of 10, it will be a bad filter cap that is creating a motorboat condition. The bad filter cap allows such deep ripple that the 15V regulator is just barely able to regulate, when you add in the load of the relay coil, it drops out of regulation, causing the relay to cut out, which brings the regulator back into regulation, which causes the relay to cut in... wash rinse repeat ad nauseum... If you had a scope, I would suggest you look at the two +15V supplies for ripple, but, that just adds needless complexity to the job. Look at the two 470uf 35V caps at the input to the 7815, 15V regulator, and the two 100uf caps at the output. My favorite tool for checking capacitors in circuit is an ESR meter. I use a cheap unit made by EVB in Portugal. I would bet that you find the 470uf caps on the bad side are showing 10x the ESR of the good side. You can make your own out of cheap parts... Search "Homo Ludens ESR Meter" for a design by one of our more creative members. Problems in the transistor switching area are not likely to have a period of several cycles per second... there are no capacitors to slow them down. That is why I think it is the filters... That and I have found too many of these supplies with a bad filter cap on one or more of their internal supplies. -Chuck Harris daven9ooq via Groups.Io wrote: Chuck ,Sorry to disagree with you, have you even taken the time to look at the schematic, In principle yesI agree with you but this supply is different than what you described. It uses a multitap transformer to minimize dissapation and a comparator thand maze of switching transistors that is where I suspest the problem lies or the feedback circuit. |
|
Re: OT- question relating to DC shunt motor schematics
In my 30 plus years in the elevator craft, I have never seen or heard of any standard of L1 and L2, and I have worked on many DC motor starter/reverser panels. Different manufacturers used whatever designation they wanted to, every print I ever saw made it clear which input terminal was to be positive and which was negative. Polarity is very important, large contactors have "blowout" coils or magnets, improper polarity can prevent the arc formed when a contact opens from being snuffed. A flashover between contacts is a sensory experience you will not forget! It is great to hear someone discussing old control gear, learning about it is vital for proficiency with newer controls, and there is a surprising amount of that gear still in use today.
toggle quoted message
Show quoted text
Bruce Gentry, KA2IVY International Union of Elevator Constructors, Local 62, Retired On 8/28/19 10:03 PM, Dave Seiter wrote:
On the schematics pertaining to DC shunt/series motor starters, is there any naming convention relating to L1 and L2 being positive/negative? I ask because I'm used to DC systems specifying polarity, and the only "polarity" mentioned on the schematic I have is the name "D.C. Automatic Starter". |
|
OT- question relating to DC shunt motor schematics
On the schematics pertaining to DC shunt/series motor starters, is there any naming convention relating to L1 and L2 being positive/negative?? I ask because I'm used to DC systems specifying polarity, and the only "polarity" mentioned on the schematic I have is the name "D.C. Automatic Starter".
I'm cross posting on Tekscopes2, where any discussion should take place, and adding more info there. -Dave |
|
WTB: Tektronix hand Held scopes
I am looking for Tektronix hand held scopes with CRTs, such as the 222, 224, 211, 213, 214 and others of those series. Need not be working, project units are more interesting, completeness is more important than anything else. Carrying bags, manuals, parts for these are also of interest. Thanks,
Bruce, KA2IVY |
|
Re: Need Help Troubleshooting Tektronix PS280
daven9ooq
Chuck ,Sorry to disagree with you, have you even taken the time to look at the schematic, In principle yesI agree with you but this supply is different than what you? described.? It uses a multitap transformer to minimize dissapation and a comparator thand maze of switching transistors that is where I suspest the problem lies or the feedback circuit.
Why does everyone state the obvious repeatedly and think I haven't checked it??? I think I metioned several times that I checked everything and cannot find any faults.I know when I turn the voltage up all the way I'm getting? about 15 volts and it should be 31 and the relay is oscillating on and off? about 2cycles a second , What is that, where to look. The problem lies in the op amp area . This is only the main side.what about the slave side which has little to know voltage. Chuck , I know you know your stuff, and I do very much Thank you fot your input,but I could use one person to walk me through the regulator,comparator error amp ,feedback and such to the output of the series pass transistors. There are dual fullwave bridges and filters ,bleeders? per side one low current feeding the references the other high current feeding the series pass transistor. Why isnt anyone talking about that! Im not an idiot! Many thanks! Dave |
|
Re: Plug for 7CT1N captive lead?
Hi Colin,
toggle quoted message
Show quoted text
Those 7CT1N captive leads are problematic. I've fixed several 7CT1Ns and they almost all had bad cables. By now most of insulation on the cables has gotten brittle and is cracking. The plug on the end gets banged around and twisted and/or bent which stresses the strands inside until they start breaking. I don't think the design engineers realized they would have a 50+ year useful life. Somewhere along the way I realized I was going to need those cables. I think I bought a bunch from Deane Kidd but it was so long ago that I can't recall where they came from for sure. Esmond's replacement cable is on the way to him. Dennis Tillman W7PF -----Original Message-----
From: Colin Herbert Sent: Wednesday, August 28, 2019 10:42 AM There appears to be two variants of this captive lead. The picture in my manual shows an in-line white plastic "plug", as does Tekwiki. It is given as p/n 195-0095-00 "Lead, test: BNC" and the manual also lists p/n 348-0301-00 "grommet: plastic, 0.312 ID x 0.43 inch OD" associated with the lead. However, my 7CT1N has a black lead with a double-ended connector forming a tee with the lead. One end mates with a BNC male, the other with a BNC female, but still only one connection, no shield. I might add that I purchased the 7CT1N from Dennis Tillman about a year ago. Colin. -----Original Message----- From: EJP Sent: 25 August 2019 07:21 The plug has finally broken off the captive lead on my 7CT1N, the one that goes out to a vertical amp or time-base depending on which side you have it installed. I'm sure I'm not the first victim of this. I can obviously replace it with an ordinary BNC plug, and am doing so temporarily (I hope), but it rattles around etc., and it also has a redundant earth connection. I'm wondering if there is something more suitable, short of the unobtainium (I presume) entire 195-0095-00 assembly, that is maybe made of plastic and/or only has the inner connecting ring. Thanks in advance EJP -- Dennis Tillman W7PF TekScopes Moderator |
|
Re: Upending a 7704, for the long run
If I had that need abd that concern, I¡¯d mill some wooden blocks to temporarity replace the feet and store the original feet away.
toggle quoted message
Show quoted text
DaveD Sent from a small flat thingy On Aug 28, 2019, at 19:06, Roy Thistle <roy.thistle@...> wrote: |
|
Upending a 7704, for the long run
Hi All!
I've got a bare 7704 frame that's in the way, and I'd like to reposition it from the vertical, to the horizonal, to store it.... "upending" it, so to speak. I'm a little leary of doing it... because I think those plastic feet, and rubber pads, on the back, might not hold out, in the long run. Best regards and wishes. Roy |
|
Re: Tek 576 Curve Tracer HV Transformer winding
I just took apart the HV XFMR from my 561. The core is a ferrite or powdered iron E-E type. After removing the wrap around the core, the two E's separated easily at room temperature.
Still hoping someone has the winding data for a 120-225 or a 120-275 transformer. That data might confirm my reverse engineering of my 120-225. |
|
Re: Plug for 7CT1N captive lead?
There appears to be two variants of this captive lead. The picture in my manual shows an in-line white plastic "plug", as does Tekwiki. It is given as p/n 195-0095-00 "Lead, test: BNC" and the manual also lists p/n 348-0301-00 "grommet: plastic, 0.312 ID x 0.43 inch OD" associated with the lead. However, my 7CT1N has a black lead with a double-ended connector forming a tee with the lead. One end mates with a BNC male, the other with a BNC female, but still only one connection, no shield. I might add that I purchased the 7CT1N from Dennis Tillman about a year ago.
toggle quoted message
Show quoted text
Colin. -----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of EJP Sent: 25 August 2019 07:21 To: [email protected] Subject: [TekScopes] Plug for 7CT1N captive lead? The plug has finally broken off the captive lead on my 7CT1N, the one that goes out to a vertical amp or time-base depending on which side you have it installed. I'm sure I'm not the first victim of this. I can obviously replace it with an ordinary BNC plug, and am doing so temporarily (I hope), but it rattles around etc., and it also has a redundant earth connection. I'm wondering if there is something more suitable, short of the unobtainium (I presume) entire 195-0095-00 assembly, that is maybe made of plastic and/or only has the inner connecting ring. Thanks in advance EJP |
|
Re: Tek 576 Curve Tracer HV Transformer winding
Thanks Miguel,
That's what I was looking for - the info is now saved in my 576 notes. I like that little HV transformer in the picture. It's a fine example of a common method of attaining good HV performance by stacking the sections of winding. If one could be found in the right size range, and with a primary that can be readily modified, it may be the ideal solution for a drop-in replacement. This same sort of HV structure is used in transformers for LCD CCFL running, and in laser printer toner charging, etc. None that I've seen look quite "right" for a single-piece replacement, though. The next closest thing would be a two-transformer combo - a low voltage one for making the raw HF power and +225 V, and a small HV type that can tap the HF power and scale it up to the proper 4 kV range. With lots of winding flexibility in the first transformer, it should be doable, and attain the proper ratios and voltage regulation. I estimate that the +225 V and 4 kV each need about half of the total output power available - about 3W each. Ed |
|
Re: Tek 576 Curve Tracer HV Transformer winding
576 Transformer
Inductance Resistance AWG mm Turns AL=L/N^2 Pin 2-3 305,0E-6 22,0E+0 25 0,45 26 451,2E-9 Pin 7-8 918,0E-3 85,0E+3 40 0,08 1400 468,4E-9 Transformer core size 50mm 13mm 31mm Inductance 1khz 1mA 2-3 305uH 22R 7-8 918mH 85K Rubber potted /g/TekScopes/album?id=94656 I have the idea to use a pre made transformer and rewind it, reusing the HV coil. Something like this: But I think that¡¯s is a little bit smaller. Regards Miguel -----Mensaje original----- De: [email protected] [mailto:[email protected]] En nombre de Ed Breya via Groups.Io Enviado el: mi¨¦rcoles, 28 de agosto de 2019 3:40 Para: [email protected] Asunto: Re: [TekScopes] Tek 576 Curve Tracer HV Transformer winding Has anyone measured the low frequency (like 1 kHz) primary inductance of a normal, OK 576 HV transformer? I looked at the data sheets (at tekwiki) on the part, and none appear to show any inductance value. I've been pondering possible alternate solutions to the "bad epoxy" transformer problem. The first is a drop-in two-transformer (one to provide the HF power and +225V, the other to make the HV) scheme, to sub for only the original transformer. The other is a replacement for the HV supply section, basically an independent SMPS that can run from the +100V supply, like the original. My 576s are good, with the newer "black" transformers, but all the recent talk got me interested, and revisiting ideas I've been thinking about over the years. In case anything major should happen to the HV transformer or HV guts, I'd like to be ready to fix it, without resorting to rewinding the HV transformer. In either scenario, the plan is to use a "modern," off-shelf type small HF-HV transformer to provide the 4 kV. I'm picturing the little kind commonly used in Royer converters for LCD CCFL backlighting. I have many dozens of all sorts of these things. I'm sure that some types are just right for this particular setup, but would need a lot of experimenting to figure out. Anyway, if anyone has more info on the original transformer, please let me know. This is a low priority project, but I like to think about it. If I ever get around to actually making it, I'll put up the how-to info. Ed |
John Williams
Shaun M
Craig Cramb
to navigate to use esc to dismiss