Need 240V timer with a programmable duty cycle

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  #1  
Old 01-20-13, 10:12 PM
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Need 240V timer with a programmable duty cycle

Hi.

Does anyone know where I can find a timer that can be programmed to turn ON for x minutes and off for y minutes? Needs to be 240V. The shorter the cycle period the better. I'd prefer to have the circuit ON for one minute and OFF for four minutes versus ON for 10 minutes and OFF for 40 minutes.

Thanks.
 
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  #2  
Old 01-20-13, 10:20 PM
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Electronic or mechanical ?
Output load ?
Duty cycle ?

Might have to use a generic timer board controlling a relay for load switching.
 
  #3  
Old 01-21-13, 07:28 AM
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"Electronic or mechanical ?"

I guess electronic because that would give me more flexibility in programming. Is it just a preference thing, or should I be leaning towards one or the other based on application?

"Output load ?"

30A

"Duty cycle ?"

I'd like it to be variable. Today I might want 80%, but next week I might only need 20%. It's to be used to turn on/off the heat tracing on my waterline. If the weather is calling for -30 degree temps then I'd want it to have a higher duty cycle. When it's just below freezing a lower duty cycle would be fine. A thermostat isn't possible at this time, so a timer is what I'm looking for.


"Might have to use a generic timer board controlling a relay for load switching."
That sounds beyond my abilities. Was hoping such a timer exists "off the shelf"

Thanks.

 
  #4  
Old 01-21-13, 07:42 AM
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A timer for heat trace cable ?

I'm just trying to figure how you could determine what timer settings to use.
Heat trace tape is for the most part a slow heat up process.
How can you randomly pick an on and off time without knowing what the actual pipe temperature is ?

I was looking for an off the shelf device for you. I did find some mechanical type repetitive
timers.....like the type that would be used in a lab.....but they are only 5-10 amps.

I'll keep looking.
 
  #5  
Old 01-21-13, 09:04 AM
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My current freeze protection is a system that can remain on all the time without risk of melting the pipe. It's currently on all the time, consuming about 1500W, which costs me about $150/month. I'd like to try having it ON for a period, then OFF for a period, with periods I could change based on the forcast and experience.
 
  #6  
Old 01-21-13, 01:58 PM
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The timer on my septic system recently died and I didn't like the cost of the replacement mechanical timers, so I purchased a simple digital timer like this:

Digital Quartic Timer Relay 100 240V Omron Relay CE B3S | eBay

then I wired in a contactor to handle the switching load. The on/off cycles can be set from a fraction of a second to 99 hours, each can be unique.
 
  #7  
Old 01-21-13, 04:43 PM
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Any chance of getting some pics of how you wired it? When you said "then I wired in a contactor to handle the switching load." I had no idea what would be needed. I have a friend whose hobby is electronics. He could help me out if I had a picture to show him what we're aiming for.

Thanks

 
  #8  
Old 01-21-13, 07:58 PM
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I don't have any pic's but here is a schematic. It's pretty simple. The SESTOS B2E timers(on ebay) have two timed intervals, A & B, or, on and off in this case. The timer has an internal relay, but it isn't robust enough to handle most loads, thus the need for a definite purpose contactor. A double pole contactor rated at or above the expected load, with a 240 volt coil is needed.

The timer has screw terminals on the rear side. Terminals 9 & 10 are the input power for the timer and can be fed 240 volt. Terminals 6, 7 and 8 are the output relay terminals for the timer. 7 is the common and gets a hot feed either direct or jumpered from one input terminal. Either terminal 6(NC) or 8(NO) can be used to feed one side of the contactor coil. It doesn't matter which you use as the intervals can be set according to your switching requirements. The other side of the contactor coil will need a direct feed.

The L1 and T1 and L2, T2 terminals of the contactor are wired based on the load.
 
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Last edited by ednu99; 01-21-13 at 08:16 PM.
  #9  
Old 01-22-13, 04:47 PM
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Wow. Thanks. The breaker on this 240V circuit is 20A, so I'd want a contactor slightly larger than that for safety. Any I find on eBay would be fine or do you recommend certain brands be avoided. Thanks again.
 
  #10  
Old 01-22-13, 04:54 PM
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This one's only $18.

Double 2 Pole 30 Amp 240 Volt Contactor Relay Siemens Furnas GE 61347 45EG20AG | eBay

For about $50 + the price of an enclosure I'd be in business. :-D
 
  #11  
Old 01-22-13, 06:04 PM
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Should work fine. I've been running a similar setup for around a year with no problems, 20 minutes on, 20 off.
 
  #12  
Old 02-11-13, 08:50 AM
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Hi again. I noticed that the timer isn't certified in Canada (only in EU). Since the timer will be inside my house I don't want to risk having my insurance being voided if I had a house fire due to the timer. I talked with a local electrician, and he said that if I could get a timer that runs on 24V or less, it doesn't need to be certified. I see that SESTOS has an identical timer (same base model) that runs on 12-24V. When I look at the specs for it, I don't see what the output (for operating the contactor) would be. I'm sure the info is there but I just don't know what I'm reading.

Can someone look at these links to confirm that it'll run a contactor?

SESTOS

or

http://www.sestos-hk.com/english/download/B3S-en.pdf

I would just need an adapter that outputs 12V to 24V, right?

Thanks so much. :-)
 
  #13  
Old 02-12-13, 06:11 AM
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These timers are available in several different input voltages as you have seen. The output relay contacts are rated the same for the various models. The timers output relay is rated at 3 amps, more than sufficient to drive a contactor.

If you purchase the 12-24 volt input model this is the one you would want:

Digital Twin Timer Relay Time Delay Relay 12 24V B2E | eBay

Then you would need a step down transformer such as those used in door bells.

It does change the schematic slightly however as you cannot now jumper the relay contact terminal from the timers input voltage terminal and would need to pigtail the wiring and provide the voltage direct to terminal #7.

There might be one other problem if your 240 circuit doesn't have a neutral you would need access to another 120 volt circuit for the transformer.
 
  #14  
Old 02-12-13, 02:13 PM
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Thanks, again, for the reply. :-)

Why would I want the B2E timer versus the B3S timer. Both have a 12V-24V model. The difference between the B2E and B3S is not apparent to me, so I'm curious why you suggested the B2E this time.

Both the B2E and B3S have either a "Two relay output" or a "Two SSR output". Which of those would I want?

For the schematic change, the 120V red and 120V black wires would connect directly to the L1 and L2 terminals on the contactor. The stepdown transformer would now provide the power to the timer, which would feed the contactor coil. Right? I have a 120V receptacle (to power the transformer) right beside my 240V receptacle (that powers my heat tracing line), so the lack of a neutral on the 240V circuit won't be a probelm.
 
  #15  
Old 02-12-13, 04:29 PM
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Go with the b2e timer. You need the relay version since you are using a contactor versus an ssr. There are many differences between the b2e and b3s with the b2e being somewhat simpler and for your application it's the right choice.

On the schematic the timer input voltage terminals 9 & 10 will now be fed from the step down transformer and the wires shown from the wirenuts going to terminals 9 & 10 removed. The Wire shown between terminals 10 & 7 is also removed and replaced with a wire from the red wirenut to timer terminal #7.
 
  #16  
Old 02-13-13, 08:38 AM
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Just a few more questions (hopefully ) for clarification.

The 120V lines now only connect to the L1 and L2 terminals on the contactor, right?

From the low voltage side the stepdown transformer, one wire will go to both 9 and one side of the contactor coil. The other transformer wire will go to both 10 and 7. A wire from 6 will go to the other side of the contactor coil. Is that all correct?

Thanks.
 
  #17  
Old 02-13-13, 08:59 AM
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No that's not correct at all. The step down transformer powers the timer, nothing else. The step down transformer was added because you didn't want to use a timer that required 240 volts.

Look at the schematic and only make the changes I previously listed. Here it is again:

"On the schematic the timer input voltage terminals 9 & 10 will now be fed from the step down transformer and the wires shown from the wirenuts going to terminals 9 & 10 removed. The Wire shown between terminals 10 & 7 is also removed and replaced with a wire from the red wirenut to timer terminal #7."
 
  #18  
Old 02-13-13, 09:19 AM
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Here is a new schematic..................
 
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  #19  
Old 02-13-13, 09:34 AM
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That's what I thought you were saying, but it didn't seem right that I'd have a high-voltage line connected to the timer. I should have just stated it that way in previous post.

I was thinking I didn't want anything above 24V connected to the timer so that it would qualify for a low-voltage device (and not need certification). I'll have to check with the eletrical inspector to see if it would qualify with the 120V line on 7.

So I'm guessing the contactor requires 120V to energize its coil? If that's true, is there such a contactor that switches high-voltage but only require low voltage to energize the coil?

Thanks. Hope I'm not testing your patience. I really do appreciate the advice.
 
  #20  
Old 02-13-13, 09:41 AM
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Yes there are contactors that switch with 24V coils. If that is what you want then your previous post on wiring changes would be correct. Sorry for my misunderstanding.
 
  #21  
Old 02-13-13, 09:48 AM
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Schematic for 24V timer and Contactor Coil
 
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  #22  
Old 02-13-13, 10:52 AM
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"Sorry for my misunderstanding." <--- no need for that. I should have just voiced my confusion instead of of posting something that I knew didn't correspond with what you had said.

Do you happen to have a link to a 240V contactor that switches with a 24V coil? I'm not sure how to phrase that eBay search. I'm sure I'd get a many matches no matter how I phrased it, but it might not be what I need.

Thanks for the new schematic. It's clear to me now, and exactly what I want.
 
  #23  
Old 02-13-13, 11:59 AM
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Something like this:

Heating Air Conditioning Contactor 24 Volt Cutler Hammer | eBay

or here:

C25DND230T 2 Pole 30 Amp 24 Vac Coil $22.69

Both name manufacturers so I'm assuming UL or similar rating.
 
  #24  
Old 02-13-13, 01:36 PM
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Thanks for ALL the help.

Contactor and Timer ordered.
 
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Old 03-02-13, 02:01 PM
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Update

I've temporarily assembled all the components on a piece of plywood to make sure they were connected properly. Here's what it looks like. I'm watching eBay for an appropriate enclosure. Once I have that, everything gets moved to its new home and put into service. :-)

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I'm using SJ00W 14/3 cord for the power to the transformer and SJ00W 12/3 for the 240V lines that connect to the contactor. When I get the enclosure and drill holes in it for the 14/3 and 12/3 cords, is there some sort of grommet I should be using to protect the cord? Aside from a grommet (or whatever) how do I secure the cord inside the enclosure so if someone tugs on the cord outside the enclosure, they don't get pulled on the inside the enclosure? Is there a standard fastener for that job? Links to sources for any items greatly appreciated. Thanks.
 

Last edited by Solitude; 03-02-13 at 04:40 PM.
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Old 03-04-13, 05:53 AM
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  #27  
Old 03-04-13, 02:25 PM
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That would definitely work. Hadn't considered those, but it's the easiest solution. I guess in my head I was envisioning something cleaner looking, like the thing that connects the cord to a drill, but much shorter in length so it only sticks out 1/2" from enclosure. Thx.
 
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Old 03-04-13, 07:38 PM
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I guess in my head I was envisioning something cleaner looking, like the thing that connects the cord to a drill, but much shorter in length so it only sticks out 1/2" from enclosure.
Something like this? Halex 3/8 in. Hit Lock Cable Connectors
 
  #29  
Old 03-05-13, 09:59 AM
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Thanks. I don't think I've seen those before. They're certainly low profile. Just what I was looking for. :-)
 
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