transformer for landscape fixture with LED bulb

I have some Kim Lighting landscape fixtures along a driveway. They have small transformers imbedded in them similar to these:
http://usalight.com/sl-518-60w-electronic-transformer.html

In fact I have used a couple of the above transformers to replace ones that failed in the lights over the years.

I now have a couple of these that I put some LED bulbs into but they seems to misbehave from time to time (not come on, or come on for a while and then go off). I suspect it is because the minimum load on the transformer is 10W (as seen in the specs on the xfrmr above).

Does anyone know of a source of small transformers that can drive an LED load that might only be 7-8W or so? It would be nice if they could range from 5W up to drive a standard bulb just in case someone puts a halogen or incan. in one sometime....

Tom

{Scratches head}

Ok....so....you're running 120volt to each landscape fixture which in turn converts it to 12volt at the fixture so you can run low voltage bulbs?

Seems like it would be safer to run low voltage the whole way, especially when the sprinklers turn on, but I never claimed to be an electrician... Just curious what kind of 12volt LED bulbs you are using; MR-16, push in style, etc? I'm also noting the transformer you are using is just that - a transformer with no other DC conversion involved. Basically 12volt AC out-put and some LED supplies can't handle that.

Mean Well makes a whole slew of really nice AC / 12volt power supplies that will work a lot better with typical 12volt LED bulbs. I'd check their site first and then google the part number.

blasterman said:

{Scratches head}

Ok....so....you're running 120volt to each landscape fixture which in turn converts it to 12volt at the fixture so you can run low voltage bulbs?.

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Well, I didn't design or install them, but yes. They are landscape fixtures that are fed 120VAC and the transformer is in the fixture. They line a driveway and the distance is probably a couple hundred feet. Not sure if that is why they used line voltage.

blasterman said:

Seems like it would be safer to run low voltage the whole way, especially when the sprinklers turn on, but I never claimed to be an electrician...

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I thought it was odd too when I first realized, but that was how it was installed. Not sure why, but it was originally installed (12 years ago) by professional landscape developers and given the lights are designed this way, it must be common practice, or maybe not common, but practice...

blasterman said:

Just curious what kind of 12volt LED bulbs you are using; MR-16, push in style, etc? I'm also noting the transformer you are using is just that - a transformer with no other DC conversion involved. Basically 12volt AC out-put and some LED supplies can't handle that.

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They are MR-16 with the two pins on the bottom (push in style, I guess). So, if I had a transformer that specifically output DC it might work better you are saying? Perhaps I can install a small rectifier in there - not sure if there is room. Or find a different transformer. By the way, all my other landscape lights run off of a 12VAC. The big transformer in my garage that power various walk lights and tree/plant light are just step down - no rectifier. I also see that most of the bulbs (halogen/incandescants) that are used say: "12V AC/DC" on them.

Another oddity in this system, again Kim Lighting brand, is that some of the path lights use 25W 12V light bulbs with A19 (I think that is the right designation or Edison?) screw-in bases - just like your old style light bulb. Talk about weird! These are special order bulbs and are expensive and they go out all the time. I would really love to find a LED bulb that was shaped like a normal incandescent (because the fixtures are shaped to throw light from all around the bulb, with the same kind of screw in base. I haven't see any though.

blasterman said:

Mean Well makes a whole slew of really nice AC / 12volt power supplies that will work a lot better with typical 12volt LED bulbs. I'd check their site first and then google the part number.

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I thought I looked at Mean Well supplies before, but will look again to see if they make one that will fit.

Thanks!
Tom

PS: I just looked at Mean Well line and don't see any that are small enough and/or rated for outdoor use....

Wondering if it's possible to simply retrofit the 120VAC lights on the front end with a big 12volt supply kept indoors and solve it that way. Existing wiring would be over-kill, but it should work the same, and because it's 12volt there are really no safety or code issues to deal with. That way you don't have to do 12 volt conversion at each lamp and could simply bypass those pesky drivers. One big happy 12 volt circuit. Just thinking out loud.

This is similiar to a problem I solved last week in which I was trying to figure out how to retrofit some 24volt / 250watt halogen moving spots with LED. I'm totally befuddled as to why you'd go through the effort of sending 120volt to each fixture, then add the complexity and additional wiring of converting to 24volt. The 24volt bulbs are tougher to find, and don't last as long as 120VAC versions. The good news is that they were actually rectified, which means that a BuckPuck worked perfectly when plugged into the 24volt side..... which is also weird because there was no need for this in the case of halogen bulbs. Yeah....strange, but it fixed my problem :thumbsup:

I also see that most of the bulbs (halogen/incandescants) that are used say: "12V AC/DC" on them.

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I'm sure you already know this, but just for re-hash, incan light sources really don't distinguish between AC or DC sources nor polarity. As the current rapidly flips back and forth the filament doesn't cool down much so it appears like a constant light source. However, a DC input LED driver run off 12-24volt AC will detect the current change and try to switch on and off 50/60 times a second, and they will either keep up and produce an annoying fluorescent like flicker or simply burn out.

blasterman said:

Wondering if it's possible to simply retrofit the 120VAC lights on the front end with a big 12volt supply kept indoors and solve it that way. Existing wiring would be over-kill, but it should work the same, and because it's 12volt there are really no safety or code issues to deal with. That way you don't have to do 12 volt conversion at each lamp and could simply bypass those pesky drivers. One big happy 12 volt circuit. Just thinking out loud.

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the existing system probably ran in solid 14 or 12 ga. wire. solid conductor does not transmit as well as stranded signal wire. Voltage drop is "ALWAYS" a concern on low voltage systems!!! I would never run a 12 volt circuit 200 feet on a multi load system without considering voltage drop or alternate solutions.

Try running line voltage to a single Transformer(XMFR) near the first light in line and running signal wire between the lights?? You can get a XMFR designed for wet locations like these http://www.landscapelightingworld.c...-Outdoor-Lighting-Multi-tap-p/7300-1222-p.htm or use a outside J box and the XMFR's you have inside the box and feed your lights. there are a lot of ways to do this, but don't run low voltage 200 feet and feed these lights or your asking for problems if you do!
this is what I do when I do landscape lighting.

blasterman said:

Wondering if it's possible to simply retrofit the 120VAC lights on the front end with a big 12volt supply kept indoors and solve it that way. Existing wiring would be over-kill, but it should work the same, and because it's 12volt there are really no safety or code issues to deal with. That way you don't have to do 12 volt conversion at each lamp and could simply bypass those pesky drivers. One big happy 12 volt circuit. Just thinking out loud.

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Hmm, maybe worth considering. I will have to look at the wiring and see what else if anything is on that circuit.

blasterman said:

This is similiar to a problem I solved last week in which I was trying to figure out how to retrofit some 24volt / 250watt halogen moving spots with LED. I'm totally befuddled as to why you'd go through the effort of sending 120volt to each fixture, then add the complexity and additional wiring of converting to 24volt. The 24volt bulbs are tougher to find, and don't last as long as 120VAC versions. The good news is that they were actually rectified, which means that a BuckPuck worked perfectly when plugged into the 24volt side..... which is also weird because there was no need for this in the case of halogen bulbs. Yeah....strange, but it fixed my problem :thumbsup:

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It is interesting. Perhaps they sell more replacement parts that way ;-) Certainly more points of failure.

blasterman said:

I'm sure you already know this, but just for re-hash, incan light sources really don't distinguish between AC or DC sources nor polarity. As the current rapidly flips back and forth the filament doesn't cool down much so it appears like a constant light source. However, a DC input LED driver run off 12-24volt AC will detect the current change and try to switch on and off 50/60 times a second, and they will either keep up and produce an annoying fluorescent like flicker or simply burn out.

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Well, I'll keep looking for a DC xfmr that fits or a tiny rectifier I can put in there. Perhaps that will keep them on...

Thanks,
Tom

I would never run a 12 volt circuit 200 feet on a multi load system without considering voltage drop or alternate solutions.

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True....but....a current regulated LED driver at the ends will adjust accordingly. You lose a bit of efficiency with the long DC run, but more than make up for with improved LED efficiency.

blasterman said:

True....but....a current regulated LED driver at the ends will adjust accordingly. You lose a bit of efficiency with the long DC run, but more than make up for with improved LED efficiency.

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I agree. LED technology certainly has changed the way electricity works in a scenario like this, but as a Professional Electrician I have to follow the rules of the trade.

1. If you haven't already done so, contact Kim and ask if they can recommend an LED solution for those fixtures.
2. If Kim can't help, contact the mfg. of the LED lamps you chose and ask them if they can recommend an electronic transformer that works with their lamps. (Although, the great majority of LED MR16 retrofit mfgs. won't have a clue.)
3. A mismatched electronic transformer will fry your LED's. Two reasons: 1. As you note, most have a minimum wattage requirement; 2. Electronic transformers work by converting input voltage @ 60Hz to 12 or 24v ~30,000Hz. This, in essence, is taking a current that switches back and forth (from + to -) slowly (60 times per second) to one that switches rapidly (30,000 times per second). Every time the switch happens an inrush current (much higher than normal) hits the electronics. This puts extreme stress on the electronic components. The LED circuit needs a fast-switching rectifier to handle a fast-switching current, and it needs components that are rated for the high inrush, for it to work. Most cheap LED retrofits don't have this rectifier, not are the components rated for the inrush current.
4. Even if you found an electronic transformer that seems to work, chances are you'll burn out the LED circuit before long. The only way to be certain about the use of an electronic transformer is if the LED mfg. has specifically tested that transformer with that LED. The best LED mfgs. publish transformer compatibility charts.
5. The idea of using a single electronic transformer to power multiple lights could work, but those lights need to be within 10 ft. of each other. Electronic transformers with their high frequency currents loose voltage very rapidly over distance.
5. Regarding the use of existing 120V wiring to run low voltage - very bad idea. Another poster mentioned the voltage loss problem, this may or may not be problematic because many LED's have a wide range of acceptable voltage. The main problem is with the NEC. Most standard solid-core wire is not rated for low voltage. Also, you don't want to touch 120v wiring unless you're an electrician.
6. Having said all that, if I were you, I would either keep using incandescent MR-16's (they'll probably last almost as long as retrofit LED MR-16's when used in an enclosed fixture - maybe longer). Or, bite the bullet and replace the fixtures with units that use integrated (not retrofit) LED's - but you'll need to pay dearly for that change.

Most standard solid-core wire is not rated for low voltage

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Again, what real issue is this and why does it matter given I'm skeptical if they are up to code now. Does the copper in the wire become radioactive and emit beta radiation when DC current is run down it? Do black dressed commandos rain down from helicopters with assault rifles? The last time I heard a debate regarding solid -vs- stranded core and power conduction it was between two audiophiles arguing about speaker cable and frequency attenuation.

Were moving from 120volt AC running several hundred watts to no more than 24volt DC running at tens of watts. The over-all current in use is going to be much lower when converted to DC although the percent of possible loss due to resistance might be higher. Big deal. 3watts of LED run to each fixture is enough to make your yard visible from low orbit. If 10% of that get's lost due to entropy big deal. I have buckpucks running at the end of hundred foot 12volt runs with zero issues. Don't recall if my wiring is stranded or solid core, and don't really care.

Also, 120/220 VAC from your breaker is enough to kill you - easily. Wires can get nicked by shovels, chewed by moles, or just plain rot. Touch a grounded metal stake and one of the shorted fixtures and you better have a neighbor that knows CPR. I realize most of our electrical codes were written according by depression era electricians but this one doesn't make sense.

The only way to be certain about the use of an electronic transformer is if the LED mfg. has specifically tested that transformer with that LED.

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The LED has nothing to do with it. It's the driver feeding the LED which tends to be China's finest and is rarely configured and tested with specific types of feed circuits. In the case of DC fed LED circuits it's typically switched or non switched or AC non AC. We can guess at if it's cap'd and rectified, but chances are if it's switched it likely is. Switch mode supplies are cheap and efficient for driving LED's, and have no issues. Transformers are big, heavy, and intended for driving halogen bulbs. The 'grey' area here is over hyped and mainly the fault of the consumer being cheap and not listening.

The problem with "rules of the trade" is that they are stuck in the 19th century, usually trying to make up for costing cutting cheapos and lack of common sense hacks from current and past eras. It takes too long for the "rules of the trade" to catch up with the current technology. Ask the solar guys that have been battling with AC codes in DC systems for years. There is some kind of chest thumping code battle going on among the AC electricians, DC electronic technicians, and those that are both.

If you're using LEDs, you need a driver.

You can run 120vac to all the lights and find a fixture sized AC-DC current limiting driver to provide the voltage and current that the LEDs need, and heed Blastermans warning.
Or, you can just get an appropriately powered AC-DC power supply and run that 6-24v DC to the lights with a DC-DC LED current limiting driver that works with the available fixture DC.

Btw, my 220v water well pump power line run was attacked by a mole. And, the circuit breaker is pretty big for a well. So, there was much sparking and cooking before it tripped. Its definitely not something that I'd like to bump into again with a shovel, tent stake, driveway marker, or other yard event. If/when my well pump dies, I'm switching to a DC pump for the same reason. I also lost pool, shed, and outdoor lighting power lines because of temporary 'party tents' and have had 'lawn sprinkler' issues because of the local utility company. Lets just say that other than the well, there are no more AC lines running in the yard. And, in a few years, the well will be DC too.

Indoor lighting, I'll always recommend an enclosed UL listed AC-DC LED driver(out of touch install and forget).

Since outdoor runs aren't always hidden, and can be dangerous(by accident, damn hole digging dog), keep the power supply at the house and run DC down your walkway/driveway/yard/garden for the 'LED accent lighting'. Lick a 9v battery. Tickles? Lick the 120v power outlet. How does it feel? Too much can happen when landscaping, gardening, or playing in the yard when you have available AC booby-traps running all over the yard.

I just worry about burning out the driver with a distance of 200 feet adding to the load.
I would place the Driver nearest possible to the load all the while keeping it hidden.

Don't worry. The 3.3v LED and its driver, using 6v-24v DC, is at the light or in the light housing. The transformer/powersupply/wall-wart/... is what is 200feet away and there is plenty of power if you pick the right one. Most common high power LED's require 3.3 volts and 350/700/1000mah, as in 1w, 2w, 3w... If you feed 100 watts of 24v DC power to that 200ft run, you might lose 20watts along with 5v to a bad wiring run. This still leaves 19v and 80w for that LED string.

The big issues that I see are people trying to pull 50w out of a 25w wall-wart and wonder why it doesn't work. And, there will always be someone using 40-gauge wiring and wonder why there is no power for anything but the 1st light. We created codes for them. Use common sense, and a DMM, and you'll be ok.

Found this thread concerning power loss over distance:
http://www.candlepowerforums.com/vb...-of-16-gauge-wire-with-four-402-LEDs-20-apart