A retired Broadcast Engineer here from the USA. Most transmitters had between 5KV and 12KV DC for the plate supply for tubes. There were automatic circuits built into most transmitters that helped with safety. There are a few working procedures that also helped. Keep one hand in a pocket or behind you. Remove all jewelry [watch, rings, necklaces, etc.] Always check that the mains breaker or power switch is off. Doing this twice is not overkill. Almost all transmitters have a grounding stick. Use it liberally. This ensures that capacitors are bled off. Know the equipment you are working on. Are there any other sources of voltages that might zap you? I have even received burns from solid state transmitters employing less than 100VDC for the supply. THE most important rule is: NEVER LET YOUR GUARD DOWN.
Your advise is crucial for safety. I think the most dangerous aspect of working with high voltages is complacency. One can sometimes get so accustomed to doing things that stupid mistakes can be made. It’s happened to me. The times I’ve experienced a shock have always been in situations that I can only attribute to distraction. After the shock I’ve stood there (and I’ve been lucky to still be standing), and thought: “how could I have been so stupid?”.
I built an isolation transformer out of a discarded 20A 240V-120V step-down autotransformer by completely rewiring it using its original single core winding to make two isolated windings. I later added a 100 W dim bulb, a 2A circuit breaker and a temp controlled fan. It worked well enough but it is inefficient due to the windings being made of aluminum rather than copper, so I added a 22uf AC motor capacitor which helped a little. True isolation transformers are expensive and hard to come by in my area. Your earth/lift switch is a good idea and I may incorporate it next. It reminded me of a low-voltage situation I once ran into as a teenager many moons ago. Not dangerous in an electrical sort of way but could possibly have caused a fire if I had not caught it. I was driving home one night in my father's 1973 Dodge Dart, when I noticed the dashboard lights dimming mysteriously. I then noticed that one screw holding the plastic dashboard speedometer bezel in place was turning red-hot. I could actually see it glow. Obviously the ground was faulty and that screw was acting as a resistor to ground. Tightening up all the screws fixed the problem but it taught me to not take grounds for granted even in low voltage circuits.
This example with the scratched plastic on the elko and a short to ground, not to the oher main line, opens my eyes. Veeery good. Never had such a case. But it can be. This tip comes to the right time, the material for my iso-transformer is nearly complete. The problem with to less current i will not have, the transformer hast 1,2KW. But the possibility, to test with and without isolation, must be addressed. You are right!
A Variac would be a nice addition to that test fixture. I'm about to rebuild my little setup. I got a Variac, Isolation Transformer, Dim Bulb with a 100watt bulb and a Kill-a-Watt meter. I'm planning to copy the setup of different light bulb ranges like you got and a switch to Earth Ground. I might add a bypass to Main switch as well.
Nice !! What you could add to make it even safer is by adding a diode ,a 5 -15K (depends on the led used) resistor dropper and an led in series , positioned at the front and connected to the secondary. This way when the secondary is NOT in use (when the mains are), the led will light bright but when you do use the isolation ,you're supplying current from the secondary to the DUT ,starving the led , so the led will be dimmer. You could label the led as "MAINS IN USE" or something... Just a thought because the added switches are on the side and not easily vissible...
Your story of the ground fault made me realize that none of these setups that I have seen on UA-cam (or built myself) to-date has a GFCI in it. I think I will rework mine to at least sense a current imbalance. That would be useful. On the isolation transformer issue, it it possible that you are saturating the core and losing the 1:1 coupling? Smaller isolation transformers with less "iron" will do that... Thanks for the video. Cheers, - Eddy
I love your videos, I have been out of the electric repair for a long time, been thinking of getting back into it again. I plan on building your device for testing, but there is one thing I will add to it. on the output side I am going to add 2 neon lights between the earth and line and the other neon light from earth and neutral. this will tell me if I have a dead short to earth ground under mains or isolation as well as what side of the output it is shorting to.
I was thinking, if you replaces your first switch with a 3 way 2 pole switch. Off in the middle, then one side is mains power, other side is isolation transformer. And it will turn off the isolation transformer, when switched to mains power.
Hi, thanks for the video. With the lamps in parallel, isn't the max limit with just the lowest power lamp (highest resistance) switched in? As you add more lamps in parallel the overall resistance to current flow drops, as with resistors in parallel?
As always, great video! qurious tho, why not put the "isolation\true mains" switch before the transformer, that way you won't have a potential on the tran when in "true mains" position.
Understood. I was under the (apparently wrong) impression that you were interested in having a true mains option to simulate a real life connection, instead of unplugging the DOT from the limiter and plugging it to a wall receptecle, once testing is done. @@electronicsoldandnew
A related idea I've been toying with recently is to maybe make the earth lift/passthrough temporary - basically, use a pushbutton to operate a self-latching relay that would reset to the default state* when the transformer was powered down. That said, my current isolation transformer is actually an ex-telco mains "earth isolation" unit - a weird device involving a mains contactor on the input, an isolation transformer, and both a core-balance relay on the A & N output and a low-current (3mA or so) AC sensing relay in the "Earth" output (actually a virtual earth derived from a resistor divider). Yeah, I know, sounds like chronic overkill and a complete "WTF??!!" - but in theory it'll protect any likely combination of shock/short dangers: ● A -> output-earthed chassis, ● N -> output-earthed chassis, or ● A/N/[output earth] -> mains earth, if the system ends up referenced to mains earth in some way (e.g. [output-earth] connected to mains earth through the antenna system). The more I think about it, the more inclined I am to leave it be... (* Either "mains earth through" or "mains earth disconnected", depending on one's PoV. It can be something of a religious argument amongst techs…)
Love the idea of a push button for the earth connection. Knowing myself and my lack of memory regarding this kind of stuff I’m sure I would mess it up, however just a quick push of a button to check for a couple of seconds if earth referencing makes a mess is good enough for me and yes jut the push button with no relay or anything. Great idea!
@@sstorholm The telco earth isolation unit? It's an ex-Telecom Australia (Telstra) QD750040 "Mains Earth Isolation Sub-Rack"; the "QD" marks it as a local design from Telstra's Queensland workshops. The workshops were all shut down ~20 years ago, and I don't know what happened to any of the local drawings - presumably, if they have been kept (a lot of them were for now very outdated one-off items), they'll be in Telstra's internal records only. Since I don't know anyone left in their engineering/drawings/records section (or even if there is!), I've been meaning to reverse-engineer the schematic. I might give it another go in the near future; if I do, I'll post a link here.
Jim S Nice, I’ll look forward to it, there’s very little information online about proper protection equipment for workshops dealing with hundreds of volts as nobody does any repair of high voltage equipment anymore!
12:00 Why placing the dual toggle switch behind the transformer and not before ? In the "bypass stand" of the transformer, the transformer is always powered and consumes power for doing nothing. Besides that, nice build.
Hi thanks for your very instructive videos. I would like to build a dim bulb limiter device but nowadays it is close to impossible to purchase incandescent light bulbs. The only of this kind I have found are small 230V 25W oven light bulbs. Can I use these as descent dim bulbs or is it a bad idea ? Thanks for any insight ...
Sure. Get 6 of them and you can then switch them in progressively in parallel with each other. That I would pair them and therefore have 50W, 100W and 150W to play with. They also take up less space.
I wanted a quick and easy way to check for normal operation so that I could be certain that there would be no surprises when plugged into the normal mains
Thanks but not my idea. I copied idea from Mr. Carlson Lab ua-cam.com/video/51mjt9nFoeA/v-deo.html but mods from other. His basically had it because of his transformer. I had to add step transformer to go from 125vac - 230 with euro plug. But still waiting on European plug in mail so not finished, but I am going to use your 4 bulb idea to make it even better. Also I am adopting other UA-cam ideas for under it. A Dc-Dc power supply 1.5, 3, 4.5, 5, 6, 7.5, 9, 12, 18 x2 from computer PS with variable 1.5v - 30v x2, and lastly 1v-42v variable voltage and current. 4 constant 5v USB. I have 90% finished, just waiting on shipping. You can use any ideas for yourself or videos. Because I am changing mine to adopt yours. Ambitious ideas but will be awesome when done.
to provide the limiting function NOT too provide the limiting function ; The second modification is to provide the limiting function - while ; being connected to the mains with the mains earth connection in place. ; This is especially important for the final testing - where some shorts ; to earth will only show when the device is earthed. STOP using the word YOU unless YOU are speaking with or directly to someone specific and not a general audience - meaning every'one' Use descriptive - grammatically correct language
Hi, thanks for the video. With the lamps in parallel, isn't the max limit with just the lowest power lamp (highest resistance) switched in? As you add more lamps in parallel the overall resistance to current flow drops, as with resistors in parallel?
Hi, thanks for the video. With the lamps in parallel, isn't the max limit with just the lowest power lamp (highest resistance) switched in? As you add more lamps in parallel the overall resistance to current flow drops, as with resistors in parallel?
Hi, thanks for the video. With the lamps in parallel, isn't the max limit with just the lowest power lamp (highest resistance) switched in? As you add more lamps in parallel the overall resistance to current flow drops, as with resistors in parallel?
A retired Broadcast Engineer here from the USA. Most transmitters had between 5KV and 12KV DC for the plate supply for tubes. There were automatic circuits built into most transmitters that helped with safety. There are a few working procedures that also helped. Keep one hand in a pocket or behind you. Remove all jewelry [watch, rings, necklaces, etc.] Always check that the mains breaker or power switch is off. Doing this twice is not overkill. Almost all transmitters have a grounding stick. Use it liberally. This ensures that capacitors are bled off. Know the equipment you are working on. Are there any other sources of voltages that might zap you? I have even received burns from solid state transmitters employing less than 100VDC for the supply. THE most important rule is: NEVER LET YOUR GUARD DOWN.
Your advise is crucial for safety. I think the most dangerous aspect of working with high voltages is complacency. One can sometimes get so accustomed to doing things that stupid mistakes can be made. It’s happened to me. The times I’ve experienced a shock have always been in situations that I can only attribute to distraction. After the shock I’ve stood there (and I’ve been lucky to still be standing), and thought: “how could I have been so stupid?”.
I built an isolation transformer out of a discarded 20A 240V-120V step-down autotransformer by completely rewiring it using its original single core winding to make two isolated windings. I later added a 100 W dim bulb, a 2A circuit breaker and a temp controlled fan. It worked well enough but it is inefficient due to the windings being made of aluminum rather than copper, so I added a 22uf AC motor capacitor which helped a little. True isolation transformers are expensive and hard to come by in my area.
Your earth/lift switch is a good idea and I may incorporate it next. It reminded me of a low-voltage situation I once ran into as a teenager many moons ago. Not dangerous in an electrical sort of way but could possibly have caused a fire if I had not caught it. I was driving home one night in my father's 1973 Dodge Dart, when I noticed the dashboard lights dimming mysteriously. I then noticed that one screw holding the plastic dashboard speedometer bezel in place was turning red-hot. I could actually see it glow. Obviously the ground was faulty and that screw was acting as a resistor to ground. Tightening up all the screws fixed the problem but it taught me to not take grounds for granted even in low voltage circuits.
Sincerely Yours : voltage stings, but the current is what really scares me. I always get a little nervous around transformers that weigh ton.
This example with the scratched plastic on the elko and a short to ground, not to the oher main line, opens my eyes. Veeery good. Never had such a case. But it can be.
This tip comes to the right time, the material for my iso-transformer is nearly complete. The problem with to less current i will not have, the transformer hast 1,2KW. But the possibility, to test with and without isolation, must be addressed. You are right!
Glad to have posted this one in time for you to make any adjustments.
This is pretty much what I'm building, BUT I'm adding a Variac between the isolation transformer section and the limiter sections. Nice !
👍
I find the use of a variac very helpful.
A wafer switch from an old radio can be used in a similar manner if you have any on-hand. But I like the idea quite a bit.
👍
A Variac would be a nice addition to that test fixture.
I'm about to rebuild my little setup. I got a Variac, Isolation Transformer, Dim Bulb with a 100watt bulb and a Kill-a-Watt meter. I'm planning to copy the setup of different light bulb ranges like you got and a switch to Earth Ground. I might add a bypass to Main switch as well.
Leland Clayton : yes, I’ll probably add a variac next. Prototyping never ends!
Nice !! What you could add to make it even safer is by adding a diode ,a 5 -15K (depends on the led used) resistor dropper and an led in series , positioned at the front and connected to the secondary. This way when the secondary is NOT in use (when the mains are), the led will light bright but when you do use the isolation ,you're supplying current from the secondary to the DUT ,starving the led , so the led will be dimmer. You could label the led as "MAINS IN USE" or something... Just a thought because the added switches are on the side and not easily vissible...
That’s a good idea. Probably for the next iteration :)
Your story of the ground fault made me realize that none of these setups that I have seen on UA-cam (or built myself) to-date has a GFCI in it. I think I will rework mine to at least sense a current imbalance. That would be useful.
On the isolation transformer issue, it it possible that you are saturating the core and losing the 1:1 coupling? Smaller isolation transformers with less "iron" will do that...
Thanks for the video.
Cheers,
- Eddy
The transformer does “lose regulation” as the current rises, so not surprising.
I love your videos, I have been out of the electric repair for a long time, been thinking of getting back into it again. I plan on building your device for testing, but there is one thing I will add to it. on the output side I am going to add 2 neon lights between the earth and line and the other neon light from earth and neutral. this will tell me if I have a dead short to earth ground under mains or isolation as well as what side of the output it is shorting to.
I like the idea.
I was thinking, if you replaces your first switch with a 3 way 2 pole switch. Off in the middle, then one side is mains power, other side is isolation transformer. And it will turn off the isolation transformer, when switched to mains power.
Hi, thanks for the video. With the lamps in parallel, isn't the max limit with just the lowest power lamp (highest resistance) switched in? As you add more lamps in parallel the overall resistance to current flow drops, as with resistors in parallel?
As always, great video! qurious tho, why not put the "isolation\true mains" switch before the transformer, that way you won't have a potential on the tran when in "true mains" position.
I wanted the isolation transformer always in circuit for protection in the case of hot chassis sets.
Understood. I was under the (apparently wrong) impression that you were interested in having a true mains option to simulate a real life connection, instead of unplugging the DOT from the limiter and plugging it to a wall receptecle, once testing is done. @@electronicsoldandnew
A related idea I've been toying with recently is to maybe make the earth lift/passthrough temporary - basically, use a pushbutton to operate a self-latching relay that would reset to the default state* when the transformer was powered down.
That said, my current isolation transformer is actually an ex-telco mains "earth isolation" unit - a weird device involving a mains contactor on the input, an isolation transformer, and both a core-balance relay on the A & N output and a low-current (3mA or so) AC sensing relay in the "Earth" output (actually a virtual earth derived from a resistor divider). Yeah, I know, sounds like chronic overkill and a complete "WTF??!!" - but in theory it'll protect any likely combination of shock/short dangers:
● A -> output-earthed chassis,
● N -> output-earthed chassis, or
● A/N/[output earth] -> mains earth, if the system ends up referenced to mains earth in some way (e.g. [output-earth] connected to mains earth through the antenna system).
The more I think about it, the more inclined I am to leave it be...
(* Either "mains earth through" or "mains earth disconnected", depending on one's PoV. It can be something of a religious argument amongst techs…)
Love the idea of a push button for the earth connection. Knowing myself and my lack of memory regarding this kind of stuff I’m sure I would mess it up, however just a quick push of a button to check for a couple of seconds if earth referencing makes a mess is good enough for me and yes jut the push button with no relay or anything. Great idea!
I would love to see a diagram of how that device is wired, does it have a model number or anything equivalent?
@@sstorholm The telco earth isolation unit? It's an ex-Telecom Australia (Telstra) QD750040 "Mains Earth Isolation Sub-Rack"; the "QD" marks it as a local design from Telstra's Queensland workshops. The workshops were all shut down ~20 years ago, and I don't know what happened to any of the local drawings - presumably, if they have been kept (a lot of them were for now very outdated one-off items), they'll be in Telstra's internal records only.
Since I don't know anyone left in their engineering/drawings/records section (or even if there is!), I've been meaning to reverse-engineer the schematic. I might give it another go in the near future; if I do, I'll post a link here.
That would be great.
Jim S Nice, I’ll look forward to it, there’s very little information online about proper protection equipment for workshops dealing with hundreds of volts as nobody does any repair of high voltage equipment anymore!
12:00 Why placing the dual toggle switch behind the transformer and not before ?
In the "bypass stand" of the transformer, the transformer is always powered and consumes power for doing nothing.
Besides that, nice build.
Bjorn V : very good point Bjorn. Didn’t see it at the time. Thanks.
@@electronicsoldandnew it can be done with 2 double pole toggle switchen, one on the primair side and one on the secondaire side of the transformer.
Just use a '4 pole double throw' toggle switch ... no need for 2 toggle switches ... make it simple ;) ...
@@krellft , you're right ;-)
Great information and clear explaination,thank you!
My pleasure.
Hi thanks for your very instructive videos. I would like to build a dim bulb limiter device but nowadays it is close to impossible to purchase incandescent light bulbs. The only of this kind I have found are small 230V 25W oven light bulbs. Can I use these as descent dim bulbs or is it a bad idea ? Thanks for any insight ...
Sure. Get 6 of them and you can then switch them in progressively in parallel with each other. That I would pair them and therefore have 50W, 100W and 150W to play with. They also take up less space.
@@electronicsoldandnew Thanks for your fast reply !
Hello Sir,,I like your idea but why should you use the Bypass? Isn't it safer to work only with the isolation transformer
I wanted a quick and easy way to check for normal operation so that I could be certain that there would be no surprises when plugged into the normal mains
Great video. Explaining why the option of earthing the isolation is a very important point that is usually overlooked. Very thorough, thanks
mark buxton : you’re welcome.
Great design. But writing on the bulb may shorten its life depending on the ink used.
I guess it could, but it’s been fine for quite a few years so far.
Again a great video , I have also build one of these based on your schematic . Did you figure out the mystery of the neon switches yet ?
Bert Van Lokeren : not really. Some people have provided possible explanations in the comments. Mine just works.
So, if I want to add a variac to this circuit, where would it go? In the front, center, or rear, or doesn't it make a difference?
I would add it right up front, between the mains and the unit.
@@electronicsoldandnewI was thinking after the isolation transformer?
I built a 2 bulb one but mine has a variac transformer, thinking about making it 4 bulb
The variac is great. Be careful, as it’s not isolated. Have fun.
Thanks but not my idea. I copied idea from Mr. Carlson Lab ua-cam.com/video/51mjt9nFoeA/v-deo.html but mods from other. His basically had it because of his transformer. I had to add step transformer to go from 125vac - 230 with euro plug. But still waiting on European plug in mail so not finished, but I am going to use your 4 bulb idea to make it even better. Also I am adopting other UA-cam ideas for under it. A Dc-Dc power supply 1.5, 3, 4.5, 5, 6, 7.5, 9, 12, 18 x2 from computer PS with variable 1.5v - 30v x2, and lastly 1v-42v variable voltage and current. 4 constant 5v USB. I have 90% finished, just waiting on shipping. You can use any ideas for yourself or videos. Because I am changing mine to adopt yours. Ambitious ideas but will be awesome when done.
to provide the limiting function
NOT
too provide the limiting function
; The second modification is to provide the limiting function - while
; being connected to the mains with the mains earth connection in place.
; This is especially important for the final testing - where some shorts
; to earth will only show when the device is earthed.
STOP using the word YOU unless YOU are speaking with or directly
to someone specific and not a general audience - meaning every'one'
Use descriptive - grammatically correct language
Hi, thanks for the video. With the lamps in parallel, isn't the max limit with just the lowest power lamp (highest resistance) switched in? As you add more lamps in parallel the overall resistance to current flow drops, as with resistors in parallel?
Hi, thanks for the video. With the lamps in parallel, isn't the max limit with just the lowest power lamp (highest resistance) switched in? As you add more lamps in parallel the overall resistance to current flow drops, as with resistors in parallel?
Hi, thanks for the video. With the lamps in parallel, isn't the max limit with just the lowest power lamp (highest resistance) switched in? As you add more lamps in parallel the overall resistance to current flow drops, as with resistors in parallel?
Exactly. The more lamps in parallel, the lower the resistance and the higher the current possible. So, more lamps, more current.
@@electronicsoldandnew OK, thanks, when I first saw it I thought you were switching in more resistance with each lamp, as if in series. Cheers. M