I've got a customer who has low voltage landscape lighting throughout their business facility. At one of the furthest points, they have 4 lights that shine on the "entrance sign" to their property. The lights only have around 8 volts at them, and need at least 10 volts or at the best 12 volts to make sure that the lights will put out optimal output. I've tried putting them on the 13 volt tap in the transformer, but at that distance, it only raises it about 1 volt. The customers are dissatisfied with the light output they have now. I have suggested going with LED lights, but unless I can get the right voltage there, they may not give the light they want(I've put that option before them to try out, but they have not decided yet). Does anyone know of a booster that can be put "in line" that will boost it up to at least 12 volts?? I'm talking 8 volts in and 12 volts out? I know I can get a transformer, but that requires 120 volts in, which is not available ( requires trenching under 2 (20) ft. driveways and about 100 ft. of dirt). I have gave an estimate for running 120 volts up to the sign, but they are wanting something "economical". I'm still waiting for their decision on the estimate, but thought I would do a little more research while I wait. I was told that Kichler use to make a booster, but no longer make it because of it's inefficiency to do the job. Anyone know of another? Thanks.. Steve
LEDs draw far less current, so the volt drop on existing cables would reduce accordingly. However, if there are multiple lights in a string ALL will be contributing to the volt drop so changing just the sign lights may have limited success. It all depends on relative cable lengths between lamps, number and wattage of lamps, etc Some rough volt drop calculations should be possible if you estimate the lengths of cables.
Provide all the specifics -- then a circuit design is possible that requires no trenching.
Total circuit load? Load of those last lights? Voltages? KVA of existing transformer? Low Voltage Amps from xfmr to light string? Fusing? Conductor size/ gauge? Insulation rating? Depth of cover? Opportunities for junction boxes along the load string? Price limits? Your experience with low voltage landscaping? (helpful) Your experience with buck-boost xfmrs and their calculations? E X A C T L Y what type of light fixture is at the end of the run? Does it have an internal, multi-tap, transformer, itself? Did you inspect its make-up for high resistance?
Are the last 4 lights on a ckt of there own or are there other lights in that string. If there are others, remove the bulbs and see what that does to the voltage. LED s will cut the current by a third, remove 3 of the 4 bulbs and check your voltage. If it is only the 4 bulbs you can use a buck-boost transformer wired as a transformer not autoformer. Use a 16/32 vmodel (sized for the load) wire it up 16 v sec. the only problem with this approach is is each bulb burns out it will increase the voltage to the remaining bulbs. causing them to fail early. Best solution is a bigger feeder (ga) or lower current lamps (LED)
Thinking outside the box, how about a full wave rectifier and a big capacitor. Make a DC voltage closer to the P/P instead of AC at RMS. The voltage drop may still be a problem but that might mitgate it a bit.
Supposedly they do make an in-line dc to dc booster for LV lighting applications, but I've never seen one and don't know who has them. The ones for PV's and such though seem to be everywhere. Is there any way to maybe separate the legs and step up the voltage to that leg using something like one of these 12-22V multi-tap transformers? Looks like they are also on sale at the moment, which is always nice.
You guys have me thinking now....LV landscape lighting is DC??
I was & am under the impression that the 12+/- volts is AC, from the 120 volt xfr. If my LV dock lights didn't get submerged, along with the xfr, I might go outside & check. Besides that it's <30 degrees with 25+ MPH wind!!
It is usually AC, 12v RMS. That is why I thought converting this to DC might actually bring up the voltage a bit. You lose .7v in the rectifier but you are then approaching the peak to peak instead of RMS. The voltage drop thing might still end up eating all of your gain (that is one of "them engineer'n" things).
A high tech solution would be a wide mouth 12v inverter power supply that works down to the 7-8 v the OP has.