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Delayed live

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Scarr

Member
Hi all,

What is the best way of delaying a wire becoming LIVE (230v AC) the delay is 60ms, So I apply mains voltage to one end of a wire and 60ms later the other end becomes live.

Stevve
 

MikeMl

Well-Known Member
Most Helpful Member
60ms is just a bit longer than it takes a normal relay to pull-in. I would use a relay with a dc coil to switch the 240Vac line to the load, a diode, a resistor, and a capacitor across the relay coil. Juggle the R and C to get the desired delay.

I did something like this to create a delay in the primary of the high voltage power supply on my 1kW RF amp's HV power supply.
 
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spec

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Hy MikeMl,

Did you mean a relay with an AC coil.

spec
 

ronsimpson

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Because we can not see your entire system it is hard to say.
You could use a 230V coil.
OR
Some where in you system there is another voltage. Maybe 12VDC. The DC voltage very likely has some delay to it. You can us any voltage in the system.

Having built transmitters....a much longer delay will be fine.
 

MikeMl

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Most Helpful Member
Hy MikeMl,

Did you mean a relay with an AC coil.

spec
No, I used a relay with a ~100Vdc coil just so I could use a half-wave rectifier charging a capacitor (through a series resistor). The combination of the series resistor, the shunt capacitor, the relay coil resistance created (in my case) about a 1/4s delay till the relay closed, and applied the 240Vac to the primary of the HV transformer.
 

spec

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No, I used a relay with a ~100Vdc coil just so I could use a half-wave rectifier charging a capacitor (through a series resistor). The combination of the series resistor, the shunt capacitor, the relay coil resistance created (in my case) about a 1/4s delay till the relay closed, and applied the 240Vac to the primary of the HV transformer.
Oh I see- neat.

spec
 

Scarr

Member
Ron, There is no circuit or diagram I just wanted to know if / how it can be done, a relay sounds like good solution :).

Another question (been watching youtube videos and you know what it's like, you end up far from where you started!!) I have is on transformers, I was watching a video about isolation transformers and then thinking about live and neutral and when putting mains voltage through a transformer polarity no longer matters, I mean you can put the live + neutral either way around and get the same result on the output side of the transformer. I then thought I bet these are used on projects to keep people safe and so searched for PCB mounting 1:1 transformers, I did find some but noticed that none of the spec sheets quotes "max current" why do 1:1 transformers not have a current rating?

Sorry if these are noob questions, but I am interested.
 

ronsimpson

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This isolation transformer is rated at 300 watts.
Why not amps?
Inputs can be 110V at about 3A OR 220V at 1.5A = 300 watts.
The out puts can be 110 or 220 or some other choices.

So these transformers are usually rated on watts.
 

Scarr

Member
Ron,

First thanks for your guidance so far, I did also look for watts in the specs but didn't see anything. I think I know what your reply will be and that is "with the info given on the sheet you can work out the watts are" but I'm not that good yet ;-)

This is a pulse transformer (I know it's not strictly a isolation transformer but it is a 1:1) but I could not find PCB mount isolation transformers

http://uk.rs-online.com/web/p/telecom-transformers/6299177/

Steve
 

Nigel Goodwin

Super Moderator
Most Helpful Member
This is a pulse transformer (I know it's not strictly a isolation transformer but it is a 1:1) but I could not find PCB mount isolation transformers
That's no use to you, unless you're building a modem? (or similar).

As always in these kinds of posts, you're incredibly vague about what you're trying to do (and why). Give us exact details, and we can offer advice.
 

ronsimpson

Well-Known Member
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This is a pulse transformer (I know it's not strictly a isolation transformer but it is a 1:1) but I could not find PCB mount isolation transformers
This LITTLE transformer is for signals not really power.
The "76601/1C" version of the part has a resistance of 1.5 ohms so you will not get amps through it.
There is a number of 17.5V/uS. This is to say that you can put 17 volts across the primary for 1uS but any longer and the transformer stops being a transformer. (or 1.7V for 10uS) (or 0.17V for 100uS)
 

Scarr

Member
Nigel, as always your incredibly rude, firstly I was talking to another member not you, secondly, I am just watching videos and reading articles and when things don't make sense, asking questions on here, so I am not trying to do anything but learn, finally I did say it was a "pulse transformer" and these are used as I found out all by myself mainly for signal isolation, I did understand it was not for power isolation but wondered why I could not find small 1:1 isolation transformers as they look like a good idea for anyone who was to build a mains voltage circuit. Is that clear enough?

P.S. You have often commented on things I have asked and NEVER been helpful, so do me and you a favor and don't read or comment on my posts ever again, I can live without you as I am sure you can live without me and lets just leave it at that. (but I bet you can't!)
 
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