Circuit to operate a Relay

[Vladpl]

Hi All

I am trying to design a circuit that will operate a power relay(30A). Mains voltage in AUS is 240V 50Hz. I have tried to design few circuits but none of them worked. Then I went to google and that didn't help me very much. My problem is that I haven't used timing circuits for a long time.

What I need is to rectify the mains and step it down with a resistor to be able to run a 110VDC relay. Also the circuit needs a time delay of about 220ms on turn on and 220ms+ on turnoff (RC timeing circuit). I was thinking of using a 100V zenor diode, and a BF337 transistor to do the switching.

Can someone please help me with this. I know that it is meant to be a simple circuit and to some of you it would be the easiest thing to design. It has been a while since I did anything like this since I work with transformers.

Thanks in advance.

 

[Skogsgurra]

Vladpl,

You seem to be looking for a real cheap solution to a 100 dollar "problem". I have seen three postings asking similar questions the last six months.

I cannot believe that this is an engineering question - more a hobby project or something needed in the home. There is a policy regarding such postings, but since I am such a nice person, I will give you a few tips.

1 There are timers that do exactly what you want to do. A multifunction timer usually has both on delay and off delay available. They can be had with 230 V AC excitation voltage.

2 Any correctly rated surplus contactor an be used (provided this is a home/hobby project). There are junk yards for electric equipment. Try contacting/visiting one of those. Make sure that load and rating agree - inductive loads may need a higher rating. And DC loads are quite difficult to handle.


Gunnar Englund

http://www.gke.org

 

[Vladpl]

Thanks for your input skogurra

This is a serious project that I am undertaking at work. We had an engineer here who designed a similar circuit. Only problem is that it was drawing 14W and the 5W resistors he put in were very very hot, so I tried to alter the design. What goes after the circuit is easy for me to do. As I design transformers and not electronics circuits I have gone rusty on that side of electronics.

With the circuit side of it. I would just like to control a transistor switching power to the relay. Using RC timing circuit to control delays for on and off stages.

Since I am not the only one that has this problem it is not a hobby as you mentioned it. I am not gifted as many other people to be able to specilise in everithing.

 

[Skogsgurra]

If this is for professional use, then see AB, ABB, Siemens, Moeller or any such company. They will tell you exactly what you need and they will be happy to supply what you need.

Inventing delay circuits the zillionth time may be fun for a while, but is not the way to handle professional installations. There are standard solutions.

Gunnar Englund

http://www.gke.org

 

[itsmoked]

Here's an example of what skogs is talking about.

http://www.alliedelec.com/Images/Pr...c-Controls-LLC_Industrial-Control_8190003.pdf

 

[nbucska]

Vladpl:

I suggest using CMOS 555 and/or Cmos logic to redice the dissipation. You haven't described well enough the circuit
requirements to design it.


<nbucska@pc33peripherals.com> omit 33 Use subj: ENG-TIPS
Plesae read FAQ240-1032

 

[waross]

As I understand your posting, you have an existing circuit that works but the resistors overheat.
If that is the case, increase the wattage rating of the resistors you are using. if higher wattages are not availlable use resistors in series to increse the ratings.
Eg;
100 Ohms @ 5 Watts, 2 x 50 Ohms @ 5 Watts in series = 100 Ohms @ 10 watts.
I had a similar problem last year. The cheap, of the shelf two wire timers I was using needed more current than was drawn by my small relays to operate. I had to series up my loading resistors to get the wattage I needed for loading.
Note the series resaistors you are using work well with DC but there are other issues operating relays on AC with series resistors.