Weird power issue with dimmer and power splitter

[mikeosoft]

Hi, this is my first post here.
A little introduction of me: I started a small business in sound and lighting to produce shows and events in my local area. I try to get good gear but the very best is not reachable for me.

Recently, my local supplier got a bunch of used ETC Par EA 750w, so I bought 4 to start. They connect in twistlock. As they consume only about 6.5A each, I also bought 2 Stech twistlock splitter to be able to connect 2 pars on one power output.

Now the following must be read knowing this: I just want to test the pars and actually check if it can work using the power splitter. I know that the dimmer used is too small but it's the only one I have, and if I limit the output to 4-5A, it's supposed to work fine?

So I then connect the splitter to an Edison adapter to be able to plug it in an Elation DP-415 dimmer pack. I only want to send each 4 pars a little power each to stay below the limit of the dimmer but the problem is that as soon as I plug the cable to the dimmer (which is turned off), the par lighten up, and yes I checked the cabling and it's really plugged in the dimmer. Then if I remove the splitter in the chain, the par stays off. It's also the same thing when I turn the dimmer pack on.

So what I want to know is... is it a problem of the dimmer or the splitter?
Is it normal behaviour considering the low cost of the dimmer?

Here is a schema of the cabling as it is actually:

Thank you all!

 

[mikeosoft]

I am also open to suggestions on buying new quality dimmer pack of max 650$

Thanks

 

[derekleffew]

...Recently, my local supplier got a bunch of used ETC Par EA 750w, so I bought 4 to start. They connect in twistlock. As they consume only about 6.5A each, I also bought 2 Stech twistlock splitter to be able to connect 2 pars on one power output.

Now the following must be read knowing this: I just want to test the pars and actually check if it can work using the power splitter. I know that the dimmer used is too small but it's the only one I have, and if I limit the output to 4-5A, it's supposed to work fine?

So I then connect the splitter to an Edison adapter to be able to plug it in an Elation DP-415 dimmer pack. I only want to send each 4 pars a little power each to stay below the limit of the dimmer but the problem is that as soon as I plug the cable to the dimmer (which is turned off), the par lighten up, and yes I checked the cabling and it's really plugged in the dimmer. Then if I remove the splitter in the chain, the par stays off. It's also the same thing when I turn the dimmer pack on.

So what I want to know is... is it a problem of the dimmer or the splitter?
Is it normal behaviour considering the low cost of the dimmer?

First, have you verified what lamp is in the fixture s? Even though it says "750" right there on the back, the luminaire is capable of using (at 120V) 375W, 575W, and 750W lamps.

Second, what you call "Stech twistlock splitter" is better called a two-fer. "Twist-Lock" can be any number of plugs, but at 120V, NEMA L5-15 and L5-20 are the most common. Use a continuity tester/DMM to verify that the pins of the connector s are wired one-to-one: hot, the smallest blade, of the male to hot of the two females; neutral, the second smallest, may be be silver, to both females; and ground, the hooked blade, to both females. Same with your Edison-Twist adapter. Hot to hot, N to N, G to G.

I know that the dimmer used is too small but it's the only one I have, and if I limit the output to 4-5A, it's supposed to work fine?

Nope. Not going to work that way. The current draw of an incandescent lamp is not linear. If you want the actual math, see Mathematical Formulas for Lighting - ControlBooth . The dimmer's voltage output compared to console setting is also non-linear.

From the dimmer pack's manual:

The DP-415 is supplied with a 15 Amp, 12 gauge power line cord. Plug the line cord into a service capable of suppling up to 15 amps to the pack. Lamp loads should be plugged into the dual 15 Amp Edison sockets which are fitted on the sides of the pack and are clearly marked on the front panel. Each channel can accept a load of up to 5 Amps or 600 Watts. Be sure to not overload any channel as this may result in blown fuses and malfunction.

So even with one 750W lamp on a dimmer channel it's overloaded. Further, the total of all four dimmers on the pack cannot exceed 1800W, due to the plug and cord on the pack. Any dimmer, shoebox is going to have this limitation, although some 6 channel dimmer packs have two power cords.

Your existing dimmer pack would work fine with your four fixtures lamped at 375W, one per channel, and would require a line circuit of 12.5A. Probably a better setup if you are using them in non-professional venue s (bars, party rooms, ballroom s, and the like). Here's one source for one such lamp: StageSpot.com: HPL 375W 115V-Extended Life .

I can't address why you're getting lights coming on when the dimmer is off, depends on what your definition of "off" is.

I am also open to suggestions on buying new quality dimmer pack of max 650$

ETC Smart Module 2 is only slightly above your price limit. But you're still going to have the issue of limited input power. One vendor: http://www.filmandvideolighting.com/etc-smart-module-dimmer-pack-sm4-6a-edison.html .

 

[JD]

To make matters worse, cold inrush current (when the lamp first comes on) is much higher then the rated draw of the lamp!

A 600 watt dimmer has taken this factor into design (hopefully) and is safe to operate at loads below 600 watts.

It might be noted that the most common failure of a triac dimmer (most shoebox dimmers are) is one that leaves the light on at 100%. This often will still be the case even when the power switch is off as often the power switch only powers the control circuit and does not interrupt the power feed to the triacs themselves.

If you dimmer works properly on all channels without the two-fers then this has not happened yet.

Have to agree with Derek above and suggest you limit the fixtures to 375w with one per channel.

 

[mikeosoft]

First, have you verified what lamp is in the fixture s? Even though it says "750" right there on the back, the luminaire is capable of using (at 120V) 375W, 575W, and 750W lamps.

Yes it's 750w on the lamp, wired in L5-20, as it is for the two-fer (thanks for the term).
I will check the continuity tomorrow, but I'm sure they are correct as the company I bought them from are a production company of many big shows.

Just to make sure I expressed myself well, what I wanted to say with "limiting the output of the dimmer" is: if I set the channel 1 to dmx value 15, even if the total lamp wattage is overloading the channel, the dimmer will only send a fraction of power to the lamp, right? Is it working? I have still to learn on that. But if it's like sound amplifiers, even if an amplifier is rated for 2000w, if the volume knob is at half, it won't draw 2000w. Can I think like that with lighting dimmer?

I can't address why you're getting lights coming on when the dimmer is off, depends on what your definition of "off" is.

Well I mean "off" as the physical switch on the pack is turned off and the red led that says "Power indicator" is not lid. It's very weird!

It might be noted that the most common failure of a triac dimmer (most shoebox dimmers are) is one that leaves the light on at 100%. This often will still be the case even when the power switch is off as often the power switch only powers the control circuit and does not interrupt the power feed to the triacs themselves.

This is exactly what it does when it's turned off, but if I remove the two-fer, it works like normal (when it's switched on naturally).

Thanks for the replies

 

[mikeosoft]

Another thing...
We know that the dimmer channel is overloaded by the lamp wattage. But when I test the par with the two-fer so it lights up, the breaker on the dimmer doesn't trip...
They supposed to be 6a breakers per channel. In my opinion, it should normally trip...?

 

[MNicolai]

Another thing...
We know that the dimmer channel is overloaded by the lamp wattage. But when I test the par with the two-fer so it lights up, the breaker on the dimmer doesn't trip...
They supposed to be 6a breakers per channel. In my opinion, it should normally trip...?

Circuit breakers do not necessarily trip immediately. If they are just slightly above the rated load, they can sustain the load a long time before tripping. Sometimes a circuit breaker can hold a load for over an hour before it trips (which means the load is very close to the load rating of the breaker; it could even be below the load rating of the breaker).

The more current, the faster the breaker will trip, as shown on this chart. This relationship is called a trip curve, and exists because of how the mechanisms function that cause circuit breakers to trip.

There are two mechanisms to the average thermal magnetic circuit breaker.

The first is a bimetallic strip that heats up over time. The more current flowing through it, the faster it heats up. As it heats, it bends, then comes in contact with another piece of metal, and once that happens the breaker trips.This is the thermal mechanism, which shows mercy to loads that are near the current rating of the breaker. The purpose of this mechanism is to prevent an overload on your wiring from lasting long enough to melt the insulation of the wires. Generally, this mechanism trips because you've accidentally turned on too many things at the same time.

The second mechanism is the magnetic component. The magnetic component will trip instantly as soon as a certain threshold of current is reached. Regardless of how high above the threshold the current draw is, this mechanism will kill the circuit in the same amount of time (unless you want to start arguing over differences of milliseconds) It's designed to keep your electronics from exploding in the event of an electrical surge, like that of a lightning strike or should two wires short across each other.

The summary is that the thermal component exists for situations where somebody turns too many appliances on at the same time and is forgiving because in cases like 1800-watt hair driers, they need lots of current but only for a couple minutes; either you'll dry your hair fast enough and without problems or the thermal component will eventually heat up (before your wires do) and turn the circuit off before damage occurs. Then the magnetic mechanism prevents damage/injury in the event of a catastrophic event (someone drops a toaster in the bathtub). At that point, there's so much current going through the wires that instead of an accidental overload, likely something has faulted at the device or the wires and if the circuit is not turned off immediately, there will be serious damages.

If you look at that chart I linked to, you'll see the rounded part of the trip curve is the forgiving and merciful characteristic of the thermal mechanism, and the horizontal, straight section of the curve at the bottom of the graph is the instantaneous reaction of the magnetic component.

If you run 6.25A (750w) through a 6A breaker, you're running at a multiple of 1.04 of the current rating, which falls into that weird red part of the graph that pretty much means your circuit breaker may eventually trip but not necessarily and not after a consistent duration of time. (It's also worth noting that not all circuit breakers are made equal; some will handle a 100% load for 24/7 operation, but others will only handle 80% for 24/7 operation and loads in the 80-100% window can only be sustained for a short duration of time.)

Because you're so close to the current rating of the breakers, you could go anywhere between a couple minutes and couple hours of having your lights on before one of the 6A circuit breakers trip. That's good if you only need all of the lights on at the same time for a few seconds. What's not good is that you be 30 minutes into an event where the lighting seems to work and then suddenly have a circuit breaker trip unexpectedly.

Devices like Atomic 3000 strobes take advantage of trip curves. Their peak current draw is 33A, but they won't trip circuit breakers because the duration of time that they're pulling that much current is barely a fraction of a second. According to the chart I linked to, an average 20A circuit breaker would probably last about 60 seconds before tripping, so the fraction of a second that the fixtures draw 33A won't come close to tripping a circuit breaker.

EDIT: (all of this being a moot point because the Elation pack has fuses, not breakers)

 

[TimMiller]

I know for a fact that those cheap packs will self destruct before those cheap circuit breakers in them will trip.

 

[gafftaper]

The Elation DP-415 has four internal 6.3A 250 Volt normal blow fuses, not a breaker.

 

[FMEng]

But if it's like sound amplifiers, even if an amplifier is rated for 2000w, if the volume knob is at half, it won't draw 2000w. Can I think like that with lighting dimmer?

Basically, no you can't. The dimmer's rating needs to match or exceed the total wattage figure for all of the connected lamps. You might get away with it for awhile, but at some point you will fatally blow an SCR.

 

[shiben]

Basically, no you can't. The dimmer's rating needs to match or exceed the total wattage figure for all of the connected lamps. You might get away with it for awhile, but at some point you will fatally blow an SCR.

Also its gonna be really dim. A 375W lamp will be significantly brighter on full than a 750 at 15%. Actually a 750W S4 PAR with a Congo blue in it is going to literally not show up on the floor... Go the other rout, its just dim. So thats another factor. Lamps should run you about 60 bucks for 4 of them? Have not purchased lamps in lots of less than 50 recently, so not sure what they cost individually, guessing around 15 each?

 

[mikeosoft]

Ok I'll consider changing the lamps.
I just tested the cables and there is effectively a problem with the two-fer. One of the two female end has the connectors offset by one pin...
Time to visit the supplier

 

[JD]

I would also check to see if the H / N is reversed going into the dimmer pack. Measuring from the larger neutral pin on the channel output to ground should yield 0 volts. If it is 120 volts, then they are reversed. If reversed, all you need is the H / G to be switched in the two-fer (as you described) and the light will be on 100% even though there is no failure of any of the equipment.

 

[derekleffew]

Thank you, JD, for that scenario. I was wracking my brain, but stopped short of drawing it out, to figure a way a mis-wired female on the tufer could cause both lamps to come to full. Still not totally convinced; someone want to draw it out for me?

...I just tested the cables and there is effectively a problem with the two-fer. One of the two female end has the connectors offset by one pin...
Time to visit the supplier

You could, and maybe should, "visit the supplier," but any competent person can correct the problem in less than five minutes.

If you feel qualified, open all three connectors on the two-fer, and ensure:

Black (wire) to brass (hot terminal)
White (wire) to silver (neutral terminal)
Green (wire) to green (ground terminal).

Male, looking at blades


Female, looking at sockets

Having gone this far, you might want to consider changing all the L5-20's to 5-15 (Edison). It will eliminate the need for adapters and a stock of special cables.

 

[mikeosoft]

I would also check to see if the H / N is reversed going into the dimmer pack. Measuring from the larger neutral pin on the channel output to ground should yield 0 volts. If it is 120 volts, then they are reversed. If reversed, all you need is the H / G to be switched in the two-fer (as you described) and the light will be on 100% even though there is no failure of any of the equipment.

Thanks! You're the man!