Dimmer switch repeat failures...need advice

First, I hate low voltage lighting. It is always more than a pain in the ass considering what you can do with line voltage.

Me thinks that the dimmer and transformer should be matched. It is possible that power is fed to the transformer and the dimmer acts as an regulator for the lights. Which means you need to replace like for like. You need to find out the manufacture of the dimmer you removed.

It is possible that the transformer/electronics are toast.

Why in gods name would you connect an neutral to an piece of conduit?

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pain in the ass

It is possible

an regulator for

You need to find

conduit?

Since neutral is grounded at the transformer, and the conduit is bonded to service box and that to ground...and the diagram called for a connected neutral...and all I had was the conduit... I connected to that..(which I realize is illegal) but its tempory until I figure out what the hell is going on.

I think your advice is correct.. the components need be matched...Im am not the original guy on this job, the previous dimmers were home depot stocked items, those lasted a year or two each by reports,,, the ones I bought lasted only weeks however.

I should call the mfgr.

One other question.. the bulbs in the three low voltage lights are rated for 50 watts... total thats 150 watts... so with say 90% minimum transformer efficiency.. the system should only draw 175 watts or so... yet it draws 3.1 amps at 120 volts.... about 360 watts....

that seems like it would point to a bad transformer / electronics package ..no? And one more questiong if you dont mind. Why to they need electronics on the lighting transformer ...why not just a straight wound coil by itself?

Phil Scott

9/6/2004

sounds to me like it is a regulated DC supply. the benefit here would be that if the load decreases (i.e. some lamps burn out) the remaining lamps do not get brighter and consequently shorten their lives.

some regulated DC supplies have something called a "crowbar circuit". this senses over voltage conditions and clamps the output. i would not expect to find one in a lighting circuit but i never expected to vote for a republican either. often the crowbar is a SCR that works once or twice then shorts internally. its supposed to blow a fuse.

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shorts internally.

This low voltage transformer lighting thing is a lot more complex than I had assumed.

thanks for your reply.

Phil Scott

Many LV lighting fixtures today use a switch mode electronic x-formers instead of a regular transformer. They do so because the SMPS is more compact than an ordinary transformer and, more importantly, silicon is cheaper than copper. These electronic transformers output an alternating current that's in the

100KHz range and bares no resemblance to a sine wave. The are sort of like a SMPS minus the hi-speed rectifier diodes and PWM regulator (there are no SCR crowbar circuits in these things either). This being the case, your clamp-on ammeter - which was designed to measure sinusoidal current - will not give you an accurate reading.

Paul

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I have been around for a long time, but had no clue about all these complexities with transoformer lighting... I still cant fathom why a simple 24 vac transformer at 60hz wouldnt work to run a string of parallel lights...its a constant 24 volts unless you add too many lights, then the transformer would get overloaded and a fuze would be fit to blow.

Obviously there are other issues.... but I sure as hell do not understand what they can possibly be.

As it happens I have another customer, billion dollar house over looking the ocean...and wants a lot of landscape lighting...untill this conversation developed I was just going buy a large 240v/24vac transformer and run light strings out from that on relays etc and put it all on a photo electric cell to start the lights and timer to shut them off at midnight or whatever.

So maybe there flaws in that plan... I have no clue at all whats up with the need for voltage and frequency control in this application.... I am looking for more insight on the over all scene with transformer lighting.

Thanks

Phil Scott

yes as long as the load is constant. all transformers have internal resistance (R int)

then the

and the voltage drop across the internal resistance has increased and the output voltage has decreased

use ohms law and standard wire gage tables.

low voltage (i e quartz lamps) tend to cost more then standard incadesents.

and frequency control in

use theater type dimmer packs to control banks of low voltage transformers. companys like this

offer quality long lasting products.

I am looking for more insight on the

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voltage transformers.

Thanks...thats what I needed...I was reading a book on these issues...dimming the bulbs makes them last a lot longer, and I want dim light anyway..so I will buy higher wattage lamps and run them at 50% or greater dimming for a reliable system.

Im also going to solder the landscape lighting splices.

Phil Scott

Are you sure this has a d.c. output? I have something that sounds quite similar (with a toroidal xmfr), but it runs the lamps with 12 vac.

This might be a dimmer circuit, or a protection circuit for shorts across the 12 lines (usually bare with these installations).

Its possible that the non-linear characteristics of the transformer plus electronics module is interfering with the operation of your dimmer module.

By this, you mean that there is a hot feeding in and a switched hot feeding back out through the same conduit, right? If so, this is OK for a plain old switch, but not correct for a dimmer (or other device) which requires a neutral.

some theatre lighting systems have a "dim" or "preheat" setting. once you power them on they turn on just enough for a faint glow. the theory is that when you run the show there is not a shock to a cold filament thereby extending bulb life.

ceiling

clamped to

sounds quite

12 vac.

Its vac im sure i dont know why i said dc.

toroidal

15 a

unit

shorts

it does have a fuse in it.

feeding

ground

sticking

full

transformer plus

dimmer

Something is screwed up thats for sure...since then I have gone to an old timer electric wholesaler and they said the home depot dimmers are notoriiously failure prone... they sold me one for twice the money they said should work...we will see.

The home depot dimmers were all arranged to run three way if you wanted to... the one I got from he electic supply was just two wires a simple one line dimmer of for low voltage transformer circuits (wired into the 110)

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its hot in and hot out... nothing through to the ground.. that dimmer lasted one day then went up in a puff of greenish blue smoke...with a faint tinge of brown according to reports..impressive. a mini mushroom cloud effect. It turned out not be a real electronic dimmer, but a regular wound transformer with some electonics added for reasons known only to god and some idiot who designed it.

I have the following clues now... dont use home depot dimmers, buy them from an electric wholesaler who understands the application to transformer lighting. Tell the customer that these can be a problem and to cross his fingers for you...that way if goes up in a puff of greenish blue smoke with sort of a brown tinge around the edges he wont become overly upset.

My nice big land scape lighting is going to use commercial transformers, one for each major circuit..with one commercial dimmer in the common 120v feed. and I am going to solder the splices then cover them in polyurethane roof sealant. I will buy the fixtures at twice the wattage I need, and dim them to the desired lighting level, extending the lamp life and socket connections dramatically.

I will run the thing with photo cell 'on'..and time clock 'off' at midnight.. and some remote areas will only operate when a proximity switch is activated...that will time out after half an hour or whatever. this landscape lighting is going to be a lot of fun I think, Also low voltage architectural lighting...

I think I can run 12vac wire where conduit etc would not be practical. Any comments on that aspect. It seems you could burn a building down with 12vac wire easily enough... yet I see it run exposed a lot tight against combustibles.

Phil Scott

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another good idea...thanks... I could wire that in with a timer and resistors for start up. for my landscape lighting job.

Phil Scott

And put the transformers and dimmers where a buzzing noise won't annoy anyone.

There are a few articles in the NEC that describe what is allowed for low voltage circuits, energy limited or signaling circuits and low voltage wiring specific to low voltage lighting.

Keep in mind that the two things that will 'burn down' a building are excessive conductor temperature in contact with combustible materials and arcing/overheating caused by a fault on the circuit. Appropriate overcurrent protection and sizing wire to the loads will minimize these problems.

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Good idea... what about running 12vac wire just stapled to the woodwork in a restuarant for instance... it seems you could toast the wire easily enough, short it across and cause a fire... what is accepted practice on running that wire...do you know?

Phil Scott

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You mean I actually have to go READ my NEC book? (gasp). one thing for sure most low voltage controls are energy limited due to very small transformers...etc.. but substantial low voltage lighting say 5ea 60 watt spot lights would not be very limited.

Phil Scott

Phil Scott

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You'll have to get Code comments from others. If I ever staple any kind of wire I use the staples that have the little stop mechanisms (tabs) halfway up their legs. The staples can only be driven in about half way. They will not pinch the wire. You may want more staples (for looks) this way as the wire will droop in between staples. A surface mount wiring system (Wiremold) may be usable but probably costs about 10000 times as much as a couple staples. The kinds of wire I have ever used staples for are, e.g. coax cable for television etc., not for any power application.

Make sure you don't do any work that requires an electrician and/or permit if you don't have an electrician and/or permit.