Replies

1. 
   UncleDunc | Mar 10, 2004 04:32pm | #1

   Can you find any latching relays at all? Or just not in 20A? If you can get lower amperage latching relays, it might make sense to run more but smaller circuits.

   What is the objection to having the relays energized all the time? Paying for the power? Overheating? Engineering elegance? :o)

   Do solid state relays even work for AC loads?

2. 
   Todd01 | Mar 10, 2004 04:49pm | #2

   One solution is to use a 120V coil multi-pole relay and parallel the poles.

   Another solution is to use a standard two or three pole contactor typically often used for starting motors.  In your application they are referred to as lighting contactors, and typically have 120V coils controlled by a photo cell.  The advantage of this solution is that a contactor is considerably more robust than a relay.

   In either case, a 120V coil would allow you to use a standard 120V circuit with three-way switches at either end.   (No transformers or power supplies to purchase.)  The coil current is very low, so the voltage drop in a long run of 12 AWG wire is small.

   Check the data sheet to confirm that the relay or contactor can support load of the circuit.  Relays and contactors usually have higher current ratings when used on resistive circuits (incandescent lighting).

   Todd

3. 
   TomMGTC | Mar 10, 2004 04:55pm | #3

   Have you checked grainger?

   Tom

   Douglasville, GA

4. 
   adamws | Mar 10, 2004 06:36pm | #4

   Don't know your exact situation, but depending on how the your shop is supplied with respect to your house you should be able to use a system called X-10.  This is the system that is used in home automation that communicates through the AC mains.  Do some searching at http://www.smarthome.com.

   The only requirement, I think, is that your shop and your house is wired from the same main transformer located, probably, on the pole outside your house somewhere.

   You'll need at least one controller switch and one receiver relay.

   Adam

5. 
   PlaneWood | Mar 10, 2004 06:40pm | #5

   I'm curious as to why you want to do this.  My shop is detached too.

   My outside decorative lights for the shop are on a daylight/dark switch.  I use the new 40 watt fluorescent bulbs (screw into a regular bulb socket) that claim an actual wattage of 9W.  They stay on all night.  They also last a long time.

   I have a separate circuit breaker for the shop that is wired directly to the house meter (through a 100 amp disconnect box), thus bypassing the house breaker box.  I did this because the shop machinery was putting to large a load on the house breaker box considering all the house stuff it was running too. 

   The shop light switch is just inside the shop door.

   PlaneWood by Mike_in_Katy (maker of fine sawdust!)
   PlaneWood

6. 
   daleduvall | Mar 10, 2004 07:04pm | #6

   Greg,

   ADAMWS23 has the right idea. If you can do this remotely by RF, it is probably the least costly, simplistic and most elegant solution. There are several brands of remote switchers on the market.

   If this is not practical, a direct wiring approach must be taken. If you want to PM me additional details, I can probably help.

   Dale

   P.S. Almost all solid state relays (whether triacs or back to back thyristors) are designed for AC.

1. 
   GregKopp | Mar 11, 2004 02:00am | #8

   Wow,

   What an excellent response, as usual you guys are great.

   I will try to respond to all of your questions and give you more information . The shop has a 100 amp sercive fed from a sub panel within the house.The reason it is fed this way is because the underground electrical service enters at the opposite end of the house. I have had no problems with service issues.

   My shop interior lights draw about 9 amps and are only used when I am in the shop. The shop is in a rather woody area and I have my exterior floodlights on motion/day/night sensors 24/7  except at holiday time and the odd need. The decorative light circuit is used only when guests are expected and at holiday time. I decorate with a lot of lights during the holidays and use both of these circuits for auxillary power. During these periods of use I am approaching maximum load on the circuits.I am concerned with overheat, voltage drop, and  power consumption along the traveller wires in a high demand situation. I also have another safety concern. The circuits are powered from the shop panel, I am uneasy sending 120v power into the swictch box in the house that is not breakered by the house panel, an unfortunate electrician might mistakenly think he had turned off the power when he would need to go to the shop to turn off the breaker. My thought is that if it is low voltage no one is going to get fried. That is why even though a 120 volt coil is attractive it just doesn't make me feel comfortable.

   Based upon my high current demand and safety concerns I figured low voltage must be the way to go. I am kind of old school and think if I can just locate the right relay/contactor I can make this work very nicely. I have seen the x10 but dont really want to have to learn a new system to make this work (If it is necessary I will). If I have latching relays the heat issue is minimized as well as long term power cost and device lifespan.

   My online research has included relay manufacturers, industrial supply houses, electronic suppliers,hours and hours of googling variations on low voltage and controls, etc. I have found plenty of latching relays that are below my current requirements, The only ones I have found so far that meet the current demand are multipole and pricey. During my research I came across solid state relays that met my current requirements. I don't have prior experience with  ssr's and attempted to learn more about their operation, receiving less than adequate help over the phone I ordered one  and tested it. I assumed it would function as a momentary contact flip-flop but I was incorrect, it is normally open, the contacts are only energized when the relay is powered. This is a heavy duty industrial ssr and I am confident that I could heat sink them and  the power supply, but it does not solve my fundamental objection to having the coil energized full time.

   I think Todd has a good point with motor/lighting contactors. I think of the contactors on  hvac equipment...... hmmm. I will have to do some more research. 

   I apologize for the length of my reply but there was alot to say, Thank you all for your responses they are all appreciated.

   I am off to do some googling,

   Thanks,

   Greg

1. 
   Jeff | Mar 11, 2004 02:57am | #9

   Greg

   Look for a ratcheting relay (sometimes called a Stepper relay).

   One pulse of power and it energizes one way, then the other on next pulse.

   I used to use them years ago for control circuits that I didn't want the coil energized  all the time.

   Potter & Brumfield made them.

   Jeff

1. 
   GregKopp | Mar 11, 2004 03:51pm | #13

   Hi Jeff,

   Thank you for your response. I will take a look for the relays you referred to it  sounds like they may be what I am after.

   Cheers,

   Greg

2. 
   adamws | Mar 11, 2004 04:52am | #10

   Greg,

   The Solid State Relay you have, I think, is one which does not operate like a standard relay.  That is, is doesn't have a coil that you would need to energize all the time.  If this is a true Solid State Relay the power you supply it operates a "Semiconductor version" of the coil in a typical relay.  This is good for you because there shouldn't be any heating due to the energy being supplied to the semiconductor version of the relay, it requires almost no energy compared to a typical relay.  A typical SSR may require 5mA of current at 12 Volts, that's only 60mW of power compared to a normal relay which requires about 500mA at 12 Volts, that's 6W of power.  In your application I would expect that the SSR won't heat up very much, but the heating will be due to the "On-Resistance" of the secondary on the relay.  If this "On-Resistance" is 0.2 Ohms and you are drawing 10 Amps through it then it will put off (0.1Ohms)*(10Amps(Squared)) or 10W, in the steady state.

   Hope that helps,

   Adam

1. 
   GregKopp | Mar 11, 2004 03:46pm | #12

   Hi Adam,

   Thanks for your response. I understand that the relay I bought for testing uses a semiconductor rather than a coil to operate the contacts and that the current draw is small(this one is rated at 16ma). Thus in operation the heat generated would be small. I have not run across any ssr's that indicate that they function like a latcher. I am going to do some more research on contactors today and see what I find. I really think an hvac contactor set might be the answer, thermostat wiring is low voltage controlling lots of amps. Like I said in my last post I am confident that the system will work with ssr's but don't want to rush into purchasing the components before I have explored a little further.

   In any case I will let you all know what happens.

   Thanks,

   Greg

1. 
   daleduvall | Mar 11, 2004 06:06pm | #14

   Greg,

   FYI, the SSR extinguishes (turns itself off) everytime the current passing through it goes to zero, which happens to be 120 times a second for domestic AC. That's why it requires a control voltage continuously applied; it basically is turned back on every half cycle. The control point is referred to as the gate of the device. This node generally requires a low voltage, low current DC signal for SSR activation (conduction). There is a nominal voltage drop across the SSR when it is turned on, so it usually requires some type of small heatsink.

   SSR's are quite simple to use, but how well the perform is application specific. They are subject to failure with large voltage transients, so unless they are internally protected, an additional device (usually a MOV)across the terminals is recommended for transient protection.

   MY first choice would still be a transmitter/receiver system like that used to remotely switch on a dust collector system. There is no learning curve and no additional wiring.

   All your approaches will work, and I agree with you that running 120 VAC back to the house to control few lights is not the way to go.

   Good luck with whatever you choose.

   Dale

2. 
   GregKopp | Mar 13, 2004 09:02pm | #15

   Dale ,

   Thanks for your reply and information on ssr operation. I did some further research online and didn't have much luck with other relay varieties. The ssr seems to be the best solution for me.

   Thank you all for your input.

   Cheers,

   Greg

3. 
   daleduvall | Mar 14, 2004 03:44am | #17

   Greg,

   If you desire additional assistance with your choice, feel free to PM me. I'll help you select the appropriate parts and confirm the wiring for you. I have designed and built numerous types of control systems when I used to own an custom electronics design and manufacturing firm (retired now).

   Dale

7. 
   proje | Mar 11, 2004 01:30am | #7

   I would also go with the X10 solution. It is not an RF solution, as described by another poster, but it actually works by transmitting short bursts of high frequency signals on your existing power lines. Invisible to your lights and appliances, the signals are interpreted by the X10 devices, and you have instant remote control with no new wiring.

   We have most of our house on X10, which means we can hop in the bed at night, hit one switch on the nightstand, and the whole house gets turned off.

   http://www.smarthome.com and http://www.x10.com are both good sources.

1. 
   daleduvall | Mar 11, 2004 05:49am | #11

   Proje,

   Not trying to get technical, but I believe many systems use a "short, high frequency burst" that is a RF signal. It just travels via wire, as opposed to wireless.

   Dale

8. 
   BarryO | Mar 13, 2004 09:31pm | #16

   You can use a standard relay to turn the lights on and off, one with a low-voltage coil (say, 12V).  Get a 12V power cube, and run that through the 3-way switches, with the relay coil as the load. 

   Or, just go the X-10 route.  Note, however, X-10 can be finicky.  Flourescent ballast can cause enough interference so that X-10 won't work, unless you add extra filters.

9. 
   FreeGee | Mar 14, 2004 10:59am | #18

   Hi,

   In an industrial environment it's common to have non-latching circuit breakers. It's probably also for safety. After a power down this prevents that machinery starts up spontaneously.

   This also applies to machines that somehow got switched on with the main power. They will start as soon as you switch on your main power !! In my country even the cheapest equipment (e.g. $50 dollar drill press) has non latching on/off switches proving that this doesn't have to cost much.

   Gert

1. 
   GregKopp | Mar 17, 2004 02:40pm | #19

   Thanks to all of you again for your input, I have learned a lot. In  my research I ran across some excellent manufacturer information on the ss relay I selected. I had always been concerned about power draw from  the relay coils being energized during circuit use. (500-600ma). I found that the ssr I  selected utilizes the light from the onboard LED to condition the control circuitry in the relay to engage the circuit (15ma). I no longer am worried about constant coil load. LED's have a long life and a failure will be easy to identify. Good point about not using latchers in industrial enviornments I should have thought of that

   Happy St. Patrick's Day!

   Greg