Inrush current/"Bounce back" voltage 120/12v landscape transformer

[gar]

150307-0847 EST

grasfulls:

If your original motion sensors were Triac ouput, then for now we shall assume that the Triacs were inadequate for the load which consisted of the magnetic transformer and its LED loads.

Your modified circuit with the sensors connected to control an electro-magnetic relay is a good solution. You can select a relay of an appropriate size for your load. The relay coil of any reasonable size relay will not overload the the Triac switches in typical sensors. Your only problem with driving the relay coil is providing sufficient load to keep the Triac on. A 2000 ohm 20 or 25 W Ohmite resistor in parallel with the relay coil is probably sufficient. This wasted power is no problem because the lights are not on for a long time.

You do need to make sure the output relay is large enough for the load.

You don't need separate AC supplies for different parts of your circuit.

.

 

[grasfulls]

Transfromer always on/switch secondary

Transfromer always on/switch secondary

Electricians installing capacitors in lighting control circuits?

This sounds absolutely nuts to me.
.
If you are worried that transformer inrush will kill the relay my suggestions would be to use a larger relay or simple leave the transformer on 24/7 and switch the secondary side.

In my personal opinion reinventing the wheel is a disservice to the customer because in the future people will not understand the reasons or the methods.

Keep it simple, keep it consistent with the other eight billion lighting control circuits.

To each their own.

That is a great option (duh), I may need to tag the trans with "Caution, Always Energized" but I can easily just break the secondary with the relay and the LED loads should have no impact at that point?

The only time this might be tough is when a client wants dimming ability via a lighting system like SAVANT or whoever, but this is not that case. Sometimes I cannot see the forest because of a singular tree.

thanks!

 

[grasfulls]

wasted power

wasted power

150307-0847 EST

grasfulls:

If your original motion sensors were Triac ouput, then for now we shall assume that the Triacs were inadequate for the load which consisted of the magnetic transformer and its LED loads.

Your modified circuit with the sensors connected to control an electro-magnetic relay is a good solution. You can select a relay of an appropriate size for your load. The relay coil of any reasonable size relay will not overload the the Triac switches in typical sensors. Your only problem with driving the relay coil is providing sufficient load to keep the Triac on. A 2000 ohm 20 or 25 W Ohmite resistor in parallel with the relay coil is probably sufficient. This wasted power is no problem because the lights are not on for a long time.

You do need to make sure the output relay is large enough for the load.

You don't need separate AC supplies for different parts of your circuit.

.

I just saw this post after commenting on leaving the transformer on all the time, but no load 99% of the time. I need to ask the client his preference at this stage: keep pursuing what I think will ultimately be a good solution with the capacitor or resistor across the coil, or an ok solution with a constantly powered transformer. I can almost guarantee that late at night if they are out there, he will ask me why the transformer always has a slight hum, followed by "what is this costing me?" Leaving it up to him relieves me of possible repercussions.

So, what might an unloaded MLV 300 watt transformer consume so I can put that into my question to the client? I guess I can measure that as well.

 

[gar]

150307-1006 EST

grasfulls:

The unloaded power dissipation of a 300 W magnetic transformer is possibly in the 10 W range.

If your transformer output voltage is 12 V and the input is 120 V, then switching the load on the secondary side compared to switching on the primary side requires a relay contact capability of about 10 times that of the primary side.

A 2000 ohm resistor at 120 V dissipates 120^2/2000 = 14,400/2000 = 7.2 W. This is only dissipated when the relay is energized. Even if you switched the load on the secondary side instead of the primary this would not change the fact that something has to be done to make Triac switches control the relay coil.

.

 

[grasfulls]

10x current on secondary

10x current on secondary

150307-1006 EST

grasfulls:

The unloaded power dissipation of a 300 W magnetic transformer is possibly in the 10 W range.

If your transformer output voltage is 12 V and the input is 120 V, then switching the load on the secondary side compared to switching on the primary side requires a relay contact capability of about 10 times that of the primary side.

A 2000 ohm resistor at 120 V dissipates 120^2/2000 = 14,400/2000 = 7.2 W. This is only dissipated when the relay is energized. Even if you switched the load on the secondary side instead of the primary this would not change the fact that something has to be done to make Triac switches control the relay coil.

.

That's a good reminder, thank you. I have a 30 amp relay on the primary now, so changing over to the secondary should be ok. It is pretty neat, totally enclosed SPST, fits very easily into a single gang raintight box. Then, given your last comment...lol, I am right back at the same point, so primary or secondary is no big thing - chatter is chatter. I am going to install what I have ordered.

Now, I know the moderator may wish to see this thread out of here, and 8 billion people are doing it differently, but..

I see RAB has a 12v ac/dc sensor. I could take the 12vac invert it to run the sensor on dc then use a 12vdc relay, would that not also eliminate chatter? I am not trying to be difficult or make things complex, but making something work with less potential for problems is a goal. The few items involved is really not that complex at all.

 

[Electric-Light]

The problem with using a triac type motion detector with a transformer is that when the light shuts off, it produces a kick back. The energy isn't great, but the voltage is very high. which fries the triac unless it has a sufficiently high voltage rating to withstand it. If the sensor switch is only intended for incandescent lamp, using higher withstand voltage triac increases cost, so they probably won't. Electronic timer/sensors turning into a day burner is a common complaint involving their use with HIDs, which is highly inductive like a transformer.


Supporting documentation on the point I made on CFL inrush damaging mechanical contacts:

http://www.digikey.com/en/articles/techzone/2012/jan/compact-fluorescent-tribulations

I have personally tested quite a few Light Emitting Decora lamps and my testing finds that many have addressed inrush current issues while some are comparable to CFLs. This is just addressing the inrush current issues. LE Decoras have their own set of problems such as operating at PWM modulation that makes them more likely to cause RFI.

 

[gar]

150307-1915 EST

I am going to repeat that both of your circuits are logically correct. Thus, the lighting circuit is simple. The complexity comes from how the various components are interacting.

Because you ran into component failure problems with the non-relay circuit and that you may not easily find sensors that would work with high reliability I suggest you concentrate on the relay type circuit.

Why the relay chatters needs to be determined.

Is the relay truely an AC relay? Connect the relay coil directly to 120 V 60 Hz with the intended transformer and LED load. Does it chatter? If it does not chatter, then the entire problem is probably with the sensors.

I took a rather small 115 V AC relay, coil is about 1" in diameter and 1/2" high, too small for your application, (Potter & Brumfield KA14AY), and controlled it with a P&B OAC5 solid-state relay. No chatter and nothing in parallel with the coil. The OAC5 is probably a Triac switch.

I could control an AB #2 motor starter with the OAC5 and have no problem.

First, determine that your relay does not chatter with 120 VAC directly connected to the coil.

I see no reason to shift your power contact from the transformer primary to the secondary, and I believe to do so is a bad idea.

If the relay works as expected, then you need to investigate different motion sensors.

.

 

[gar]

150307-1951 EST

Electric-Light's reference is a very good discussion.

.

 

[grasfulls]

test with direct 120

test with direct 120

150307-1915 EST

First, determine that your relay does not chatter with 120 VAC directly connected to the coil.
.

No chatter

150307-1915 EST
I see no reason to shift your power contact from the transformer primary to the secondary, and I believe to do so is a bad idea.
If the relay works as expected, then you need to investigate different motion sensors.
.[/QUOTE

I will keep it as is.
Got 'em

 

[grasfulls]

Triac motion

Triac motion

The problem with using a triac type motion detector with a transformer is that when the light shuts off, it produces a kick back. The energy isn't great, but the voltage is very high. which fries the triac unless it has a sufficiently high voltage rating to withstand it. If the sensor switch is only intended for incandescent lamp, using higher withstand voltage triac increases cost, so they probably won't. Electronic timer/sensors turning into a day burner is a common complaint involving their use with HIDs, which is highly inductive like a transformer.

Thanks for the link, I will read it.
In the future I will ask manufacturers if they are using triacs. I knew they were used in forward phase dimming modules and have leakage at low wattage, now I know they are in motion sensors. All great info to keep in mind.

 

[grasfulls]

Coil too small

Coil too small

150307-1915 EST
.

I took a rather small 115 V AC relay, coil is about 1" in diameter and 1/2" high, too small for your application, (Potter & Brumfield KA14AY), and controlled it with a P&B OAC5 solid-state relay. No chatter and nothing in parallel with the coil. The OAC5 is probably a Triac switch.

.

Well, this is a new point. I am using a "American Zettler, Inc. AZ2280-1A-120AF RELAY; POWER; MINIATURE; 30A; SPST; 120VAC; 1 FORM A; SEALED" I will gamble that coil is smaller than the one you used. However, I also read something else in its description that piqued interest - it is non-latching. I mean, I knew that, but I had not given it any consideration. If I get any time I may try a latching relay. Well, no, if this new setup works, with the capacitor or a power resistor, I may not mess with the latching relay. But, if the chatter is from fluctuating voltage, it may not stay latched. I will forget that and refocus on the size of the coil in the Zettler relay. Should I get one that is physically larger?

 

[gar]

150307-1134 EST

grasfulls:

My guess is that you may have a wimpy relay for the job, but at least it is a separate part. Thus, independently identified if it fails.

Triacs, SCRs, and back-to-back SCRs are devices that if the gate control electrode is biased on, then will they conduct while the gate is on.

But also, if the gate is simply pulsed and if there is sufficient load current (greater than the holding current), then after removal of the gate pulse the device will remain on until the load current drops below the holding current. Thus, the device turns on following the gate pulse, and turns off at the next load current zero crossing.

We don't have sufficient information to know how the sensor switching device is controlled, thus, don't know why the relay chatters. Also at the moment we assume it is a solid-state switch.

My small P&B relay pulls in at about 90 V and drops out at about the same voltage. At this pull-in drop-out point the relay chatters. Just above this point, within about a volt, the relay closes in a solid fashion. This voltage is way below the voltage you should expect at the relay coil.

My son has several indoor motion sensors, from Lowes, that have a contact relay as their output switch. Look for weather proof sensors with a contact type output. You can hear the relay click. Try these to control your relay coil.

I doubt that you want a latching relay. But if you did go down this path I would try a GE RR relay. But we really don't know what you need in terms of relay contacts for good life. For most latching relays you need separate set and reset signals.

It is apparent that components are being put together to form systems that are really not appropriate for the application by many people because they have inadequate information about the components..

My comment on wimpy relay does not relate directly to coil size, but directly to contact capability.

If LED drivers are the cause of very excessive in-rush currents, then a solid-state relay with turn-on at a voltage zero crossing might be useful. You do not have instrumentation to tests for many of these questions and thus we have to guess on many aspects of the problem.

.

 

[grasfulls]

Hodge Podge systems

Hodge Podge systems

150307-1134 EST

My guess is that you may have a wimpy relay for the job, but at least it is a separate part. Thus, independently identified if it fails.
.

Probably

150307-1134 EST
We don't have sufficient information to know how the sensor switching device is controlled, thus, don't know why the relay chatters. Also at the moment we assume it is a solid-state switch.
.

I will find out, it is a RAB SMS500

150307-1134 EST
I doubt that you want a latching relay. But if you did go down this path I would try a GE RR relay. But we really don't know what you need in terms of relay contacts for good life. For most latching relays you need separate set and reset signals.

It is apparent that components are being put together to form systems that are really not appropriate for the application by many people because they have inadequate information about the components..

My comment on wimpy relay does not relate directly to coil size, but directly to contact capability.
.

OK
Yes, I am guilty of this
it is a 30amp rated contact, not sure what else I could do.

150307-1134 EST
If LED drivers are the cause of very excessive in-rush currents, then a solid-state relay with turn-on at a voltage zero crossing might be useful. You do not have instrumentation to tests for many of these questions and thus we have to guess on many aspects of the problem.
.

Correct, I do not have the test equipment and I would have little idea as to what to do with it. I also have no concept what a "turn-on at voltage crossing zero" means exactly.... I am one ignorant electrician.

I will let you know what happens when it all goes together. Sadly, due to its being pieced together via guessing, if it works, we can only guess at that as well. I appreciate our patience and thoroughness.

 

[gar]

150309-0938 EDT

A few quick comments.

I tried to look up the SDS500. It appears to be an indoor unit and there were no technical specifications.

I believe a purpose of this site is education. As such probing problems such as yours would seem to be appropriate.

With an electronic switch, such as an SCR or Triac it is possible control on and off times accurately relative to a 60 Hz sine wave. For an SCR or Triac turn on is determined by a trigger time, and off by when the current thru the device goes to 0. If instead of using a trigger pulse for turn on a sustained input signal is provided, then the device remains on until after the next current zero after the signal is removed.

An SCR only conducts in one direction so the above statement is not quite correct.

Have to leave. More later.

.

 

[grasfulls]

wrong sensor ID

wrong sensor ID

150309-0938 EDT

I tried to look up the SDS500. It appears to be an indoor unit and there were no technical specifications.
Have to leave. More later.

Sorry: rab sms500

 

[gar]

150408-2151 EDT

grasfulls:

I found the specifications for the SMS500.

From those specifications I can see why you expected your first circuit to work. There is insufficient information for you to understand why the first circuit failed. I am still assuming that the sensors use a solid-state output switch.

See:
http://en.wikipedia.org/wiki/Thyristor

http://en.wikipedia.org/wiki/Thyristor search for Triac failure modes.

A good early reference is the first edition of Controlled Rectifier Manual by GE circa 1960.

Since we do not know much about the internal circuit design of your sensor the next step seems to be to put the 0.1 ufd capacitor across the relay coil as suggested by RAB. See if this solves the problem with the relay. i don't know if a shunt resistor across the relay coil would be any better than the suggested 0.1 ufd capacitor.

Your discussion has been good because you don't just drop things and never respond. There are many discussions on this site where someone wants help and never responds afterwards with any feedback on results.

.

 

[grasfulls]

Internal components Sensors

Internal components Sensors

gar:

Thank you! I would consider it rather callous/rude to ask for help, have intelligent people get involved, then abandon the discussion. I also consider the wealth of information a cash free education that many might pay for to get. However, I think it has been like throwing water at a dry sponge, some is absorbed, most splashes off.

The first failed unit is a heath zenith, scavenged from brand new bronze fixtures from Lowes, because I needed bronze and they were closest - I threw the fixture components away. They worked for a bit. The closest failed first.

Then I installed the relay and was waiting on the RAB but the client was anxious.

So I got the second set - DEFIANT from Home Depot, off the shelf bronze replacement sensors.
The Heath Zenith is 4.2 amps, the DEFIANT is 2.2 (I did not care because it is just a relay). I noted no restrictions on its use

The RAB are here, waiting on the capacitors

I am going to try the HZ and the DEF on a 60w incandescent bulb, if they function I will chalk it up to bad choices of pairing - they may even work with the capacitor. I will hang onto them for future needs. If any/all do not function, I will open at least one up to look at it and see if I can visually see a potential point of failure.

Disregarding all of the above, I will post whether I finally attain a functional/reliable Lighting Control assembly to validate its being in the forum and all of the time you in particular have devoted to it.

I also like not having to quote you each time, see, I do learn some - the water that soaked in.

 

[grasfulls]

RAB does not know why its driections are like they are

RAB does not know why its driections are like they are

I had contacted RAB about the spec for a VDC capacitor with no indication of where the + or - should go:
REPLY
Thank you for contacting RAB Lighting regarding your capacitor question. Im not sure why it would not specifically state that information, but one thing I can tell you is that AC is not biased. Meaning it should not matter whether you are on positive or negative. Just try it both ways and one way should work. You will not be damaging the capacitor in anyway by doing this. If you have any further questions please don?t hesitate to ask.
END REPLY

So I asked if we can use non-polarized. - waiting on an answer

I need to know because both sets of capacitors I ordered were shown as 400VDC but they have no + or -....sheesh. Can I stick an ohmeter across them and figure them out out?

 

[gar]

150309-20410 EDT

grasfulls:

Most capacitors are non-polar. Meaning that either lead can can be connected to either a +/- voltage relative to the other lead. Capacitors with materials such as air, paper, mica, glass, Mylar, other plastics, oil, water, and many other insulators are non-polar. These should never have a + or - on the capacitor package. Some non-polar capacitors may have a solid bar or band on or around one end of the capacitor to indicate which lead is connected to the outer foil of the capacitor.

Electrolytic capacitors are normally polar unless specially made. Those that are polar will have a + and/or - on the capacitor package. Plus needs to go to the more positive voltage. Never apply a changing polarity voltage to a polar capacitor.

The top capacitor is a tantalum electrolytic with positive identified by the package shape with the tapered end being positive.

The next two are Mylar.

The last two are electrolytic.

 

[grasfulls]

This is what I got

This is what I got

gar:

So if it has any indication of a positive and a negative I should never use them on an AC circuit? It contradicts the RAB tech's recommendation.

I received these. They look non-polar. I am going to check them tomorrow with an ohm-meter, just to see if I can measure anything and if the measurement changes relative to meter leads.