Hi.
I want to power a motor and some electrically operated valves along with it (all rated at 220Vac 50Hz. single phase). I want to power up the devices (using a momentary push switch - NO to NC to NO) so that the motor comes on and the Valves open 30 secs later. When a momentary switch is pushed (NC to NO to NC), the valves should close but the motor should continue to operate for another 30 seconds before it turns off. Please someone help me design the circuit and tell me what type of timer etc. should I use.
Thankyou

 

You can use solid-state-relays (SSR) to control the valves and motor. The 30 second delays can be generated by a 555 circuit. The alternate action can be provided by a flip-flop such as a CD4013 with the D input connected to the /Q output. The FF output is used to control the 555 timers in response to the push-button signal.

Do you have one push-button or two?

 

Thanks for the reply. I am using two push buttons. This is a good way to go but I need to get it done using industrial grade stuff (the motor operates a forced iar burner and the valves are for controlling the gas input to the burner. the 30 second delay is for purging the funace.

 

You could also look at using a SmartRelay these are miniature PLC's which have all the logic and timers you would need, for most the s/w is free and can be programmed on the unit or via the Win s/w.
There are quite a few that are relabeled under Idec, Siemens and a few others.
Max.

 

These are the types of posts that should just get locked IMO..
This is clearly a real world application where safety is easily involved and the person performing these modifications is clearly not competent on their own to perform said modifications.

people could get hurt.

 

A smart relay as suggested makes a lot of sense.

If you want simple relay/timer logic, then one control relay, one time on delay module, and one time off module is needed.

 

These are the types of posts that should just get locked IMO..
This is clearly a real world application where safety is easily involved and the person performing these modifications is clearly not competent on their own to perform said modifications.

Then the rules should specify what is considered dangerous, if you go by the safety body recommendations then all circuits here should be limited to 25VAC RMS or 60VDC.

Extra-low voltage is one of several means to protect against electrical shock.
The International ElectroTechnical Commission and its member organizations define an ELV circuit as one in which the electrical potential of any conductor against earth (ground) is not more than either 25 volts RMS (35 volts peak) for alternating current, or ripple-free 60 volts for direct current under dry conditions.
Lower numbers apply in wet conditions, or when large contact areas are exposed to contact with the human body.

The specification stating against earth does not preclude equal danger from ungrounded systems either if contact is made across the same potential.
Probably result in a 60% reduction in posts by deletion.
Also it could be said that someone with limited knowledge may be better off to come here to obtain advice from experienced users.
Human nature being what it is, most would not be deterred by any such warnings anyway and struggle on in their own uninformed fashion, with the added dangers?
Max.

 

Fair argument, Max, but...Is a beginner trying to attach a capacitor to the power line as dangerous as an amateur trying to control the purge function of a gas furnace?

I'm going to press the button and let the Mods decide.

 

Fair argument, Max, but...Is a beginner trying to attach a capacitor to the power line as dangerous as an amateur trying to control the purge function of a gas furnace?

.

Apparently the purge function is operating at 220vac?
Max.

 

Yeah I just think its one thing to blow a breaker/smoke some IC's.. Another to blow up a house/factory.

I'm just dumbfounded with the "projects" people who know very little to nothing about electronics/mechanics,etc.. actually attempt while hoping that providing sparse information on an internet forum will allow them to accomplish a task they shouldn't be attempting in the first place.

I've found that "the devil is in the details" is VERY true and you must be fairly proficient in something to even know half of the details.

Maybe I just need to learn to not care so much about peoples safety on the internet

 

I just now noticed it's for gas function. My bad.

That should be addressed.

Modifications to gas or burner controls are bad. mmkay.

 

Yes please. Can we add gas furnace/burner mods to the list of banned topics? That's as or more dangerous than automotive topics involving ABS system mods. And more dangerous still, than leds on mains, transformerless power supplies, and runaway overunity devices.

 

I don't think adding to the list of banned topics is necessary. IMHO, this situation is already covered in the ToS under "Appropriate Conduct". See the last paragraph in that section. I tried to cut and paste the text on my phone, but it includes providing information that may be injurious or destructive. So while the post may not be explicitly banned, responding to it may be.

Just my two cents.

 

Hi, MaxHeadRoom
Advice well taken. The system is well grounded and the only limitation is that the Gas Control Valves are already installed in the system and are rated at 110Vac, which I intend changing to 24Vdc, The forced air burner is rated at 220Vac, So I work with 220Vac for the time being and later the entire system will be converted to 24Vdc including the blower unit of the burner. Thanks anyway and I will look up and find a smart relay.

 

Hi 12,
The furnace manufacturer has specified a purge of 30 seconds prior to firing it up and 30 secs post shutting down the flame for the given burner (Manufactured by Olympia Burners, Korea).

 

Grounding, 24vdc vs. 120vac vs. 220vac, these electrical considerations are totally eclipsed by system considerations. You made no mention of things crucial to a burner system, like gas detection or cooling water verification or pilot verification or thermal runawa/overtemp shutdown.

A smart relay would be what I would have recommended had I not known the application. But in your case, a smart relay is NOT recomommended, rated, tested or approved. You need a safety rated device, a purpose made burner controller from the likes of Honeywell.

Please do not carry out your smart relay plans. You could lose your job, or worse kill someone.

 

http://www.ab.com/en/epub/catalogs/3377539/5866177/3377549/6547815/Introduction.html