Landscape lighting bulbs burn out prematurely

[Ike]

We have Malibu landscape lighting and the bulbs burn out after only about two months of service. They are very bright compared to my neighbor's Malibu lights and he only replaces bulbs about once a year. When the landscapers installed our lights they did not use the wiring that came with the set. Instead, they used their own wiring which is a much larger gauge resulting in less voltage drop by the time the current reaches the lights. I am sure they thought they were doing me a favor, but their generosity appears to have worked against the life of the bulbs. Is there a simple solution to drop the voltage enough so these bulbs don't burn so hot? Would a standard light dimmer for 120 VAC work to adjust the 12 VDC voltage?

[Joseph Meehan]

Run them in to sets of series so each gets only half the voltage. You also may want to check the voltage they are really getting with a good meter. You may find over voltage.

[RickR]

They did do you a favor, your lights are brighter. BUT that probably doesn't have anything to do with the burn-out.

Check a couple of things;

1. What is the rated life of your bulbs?
2. How long are you running them? Timer or photocell or both? If your running them all night and your neighbor isn't your going to lose bulbs (and money) faster.
3. As below, check your incoming voltage. Are you getting 115-120V?
4. Check your out going voltage from the transformer. Many transformers have multiple taps to help overcome line losses. Check it at the closest fixture. If its over 11.5V you may want to drop it down.
5. Do you like having brighter lights? If so you may want to just live with it.

6!! Check for voltage spikes! This is probably your problem. A motor starting up or some other electrical problem (loose neutral, large factory near by) can give you a spike that will burn bulbs in a well designed system. This is the number one cause of premature failure.

1. Check for overheating in the fixtures. Not usually a problem outdoors but killer for lamps.

Putting a dimmer in *will* get you longer life.

1. Get a transformer rated dimmer!!!! You could lose both the dimmer and the transformer and that will cost far more than the extra bulbs.
2. Put it in the 120V side.

RickR

[Jeff Wisnia]

If you happen to have another transformer with a 120 volt primary and a

12 or 24 volt secondary lying around you could wire it up as an autotransformer to subtract 12 or 24 volts from the 120 volt line and use that reduced voltage as the supply voltage to the transformer feeding the lights.

The added transformer's secondary current rating has to be at least as large as the primary current the exixting transformer draws of course.

Jeff

[w_tom]

[Pop]

===> Uhh, in series, meaning half voltage for two of them, you'd be lucky if the bulb even glowed visibly in the dark of night! It required about 80% before you start to get usable light from them. Your dropped your teeth or something there!

Pop

: : -- : Joseph Meehan : : Dia duit : :

[Pop]

Where the hell did you go to school? There was no course on common sense or safety, was there? Or, umm, more likely you're "self" taught? Keep learning!

: : -- : Jeffry Wisnia : : (W1BSV + Brass Rat '57 EE) : : "Truth exists; only falsehood has to be invented."

[Jeff Wisnia]

If you knew anything about college education Pop, you'd recognize that my sig line indicates I'm an MIT electrical engineering grad without my screaming it out. (And FWIW I hold a masters in the same field from an Ivy League school to boot.)

You not even know what an autotransformer is Pop, but I can tell you that back in the '50s I installed at least ten of them ahead of TV sets and expensive home audio equipment to reduce the overly high line voltage present on the lower floors of a high rise apartment building in Cambridge, Taxachusetts. They were wired eggsackly the way I described in my post.

There was a lot of line drop in that building's wiring, and the owners had played with the supply transformer taps so the upper floor's line voltage wouldn't sag too low. That caused the voltage to be up around

135 volts on the lower floors ... The building's manager had a nice little side business going. He was stocking and selling high voltage light bulbs to the tenants on those floors.

That high line voltage raised hell with the filaments in the vacuum tube electronics of that era, just like it appears it might be doing with the OP's light bulbs.

If you think you're right about decrying my advice Pop, let's hear you tell us why you think it's unsafe if done in a workmanlike manner using a transformer with adequate winding insulation ratings.

Otherwise, kindly STFU.

Happy Holidays,

Jeff

[Norminn]

I don't know volts from ohms, but helped a friend shop for those dang Malibus. We had to select the right total watts to fit the transformer, as I recall. If a bulb burned out, it was supposed to be replaced quickly or the remaining bulbs got too much. Is the transformer right size for size/number of bulbs?

[Roger Taylor]

Some of the technical answers are indeed good advice, especially the ones advocating measuring voltage at key points from transformer to light sockets. I have had a cheapo 12v malibu system for 8 years, with 10 lights on the string. Over that time, only one of the ten has blown. There is likely a serious overvoltage on your system, or you have been using the wrong bulbs. Check to see that they are rated at 11-12 v.

[Mark Lloyd]

The voltage is probably 12VAC not 12VDC. Rectifying it would add to the cost of the power supply unit, with no benefit. Incandescent lights work just as well on either AC or DC.

A dimmer won't work on 12VDC, but it MIGHT work on 12VAC.

One thing you might do is install a diode (half wave rectifier) in the line to get half power. Make sure it can handle the current. I've done that before, to make lights dimmer.

[mm]

Bigger wires have advantages, but I don't think there should be any measureable voltage drop even with your neighbor's smaller wires.

Your neighbor's certainly wouldn't have been designed to work that way.

Remove NOPSAM to email me. Please let me know if you have posted also.

[Jmagerl]

You didnt say what model you had but check for plugged vent holes. USually caused by bugs building nests in them. Mine was caused by ants. I doubt that thats it though just because you say the lights are noticably brighter. You really do need a voltmeter to measure the AC voltage at the bulbs.

[Ike]

2000 hours and they are rated for 12 volts.

5 to 8 hours per night, depending upon the time of year. This means I should be replacing them about once per year. The first bulb in the set will burn out in as little as two weeks and will last as long as two months.

Yes.

I am getting 12 VAC on the output side, plus or minus a few hundreds of a volt. It was my error to think it was 12 VDC.

Yes, but not at the expense of such short bulb life.

Unknown if I have spikes.

The transformers are well ventilated inside our garage.

I tried putting a regular incandescent dimmer on the 12 VAC side but the lights did not work at all. Oh well, it only cost $5 for the dimmer to try it out.

I looked for a low voltage transformer dimmer and here is what I found: there are two types of low voltage dimmers - magnetic low voltage and electronic low voltage. I don't know which type the Malibu transformers are. I am not sure what to do to get the voltage down another volt or two so the bulbs last longer.

[w_tom]

Tenths of volts on 12 volt output is be important. For example, voltage at 12.2 may shorten life expectancy by 50% compared to a voltage of 11.8. Little voltage increase can to cause a significant reduction in bulb life expectancy. Important here is the 120 VAC voltage. What is that - to three digits?

Reducing 12.0 volts to about 11.0 volts will increase bulb life expectancy by a factor of three times.

Voltage is also how one can change bulb life expectancy. One important factor - how many amps are being drawn from the transformer. A two digit number is good for this. A device that drops 12 volts by say 0.3 volts would consume how much power? A calculation necessary before lowering voltage on the

12 volt side. Even a couple of diodes placed reversed and in parallel on transformer output would limit voltage from 12.0 volts to about 11.3 volts. But 0.7 volts times that ballpark current is how many watts - to estimate how hot those diodes may become.

The answer of 115 to 120 volts tells little. What is that number accurate to three digits. And how does it vary? Does line voltage increase to 126 volts?

Voltage spikes would have little to do with bulb failure.

Regular incandescent dimmer must be on the 120 VAC side of transformer.

BTW transformer output voltage dr> >> ...

[Ike]

When checked under load this morning the input side was 119.4 VAC. The output side was 11.38 VAC for the 200 watt Malibu transformer and

11.68 VAC for the 300 watt Malibu transformer. (I have two separate strings of lights.) These figures appear to be completely within reasonable tolerances. It is the 200 watt transformer that has the closest bulb (about a 12 foot run) and that is the bulb I have the most problem with. I have had to replace this bulb on the average of once per month.

It sounds like the idea of the two diodes in parallel to drop the voltage slightly would work well. If my math in right, 200 watts divided by 12 volts gives me 16.6 amps. I would need to find two 20 amp diodes to meet these specs and probably a heat sink for them, too. Alternatively, maybe the best and cheapest solution would be to drop the voltage on the closest light on the 200 watt transformer that is giving me the biggest problem. That way I would only need to buy 2 amp diodes and may get by without the heat sink. Your thoughts on this idea?

I have no method to constantly monitor line voltage.

I understand that, but I did not want to risk damaging the transformer and I thought there might be a small chance the dimmer might work on the 12 VAC side considering it was AC current. My understanding of how light dimmers work is limited only in that I know they are not just a big variable resistor.

The 200 watt transformer has eight 20W lights for a total of 160 watts. The 300 watt transformer has two 20W lights and four 50 watt lights for a total of 240 watts. I would say each has an appropriate load for its rating.

Thanks, Ike