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

You may want to look at some info available from some of the LV mfgs. I preferred RUUD Lighting out of Racine Wi. ''

They used to have (and probably still do) have distance & vd calcs tables to help with layouts, and they had a 3 conductor system.

Wire gauge is an important factor in voltage drop. What ga. wire exists?

That is the problem with low voltage. What wiring method do you have there? Is there any chance to run 120v down there?

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.

Multi-Tap Transformer

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!!

Am I wrong about the DC?

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.

I remember a few things from the RUUD methods, transformer location preferred in the 'middle' of the layout, 3 wire system, and HEAVY gauge cable.

They also had (have?) a really great application engineering dept. that provided a lot of layout help to me for sports and site lighting design/build jobs.

Soon as the weather breaks here, I have to redo my dock lighting.

I am not really much of a low voltage fan. If I was trenching wire in very far, it would be a chapter 3 method. Even if I was running it on low voltage, I would still have the option of cranking it up to 120 or even 240 later.
Wire is cheap compared to labor. (pavement cuts, landscape repair etc)

Converting VAC to VDC in no way increases the net deliverable power for a circuit of this type.

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It should be apparent that without further specific details from the OP everyone is left guessing -- too much.

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The odds favor a solution that requires no digging to speak of.

But, it's impossible to solve anything working blind.

I think most of the bulbs and a lot of the newer low voltage LED lamps are rated both AC/DC, so looks like a conversion would mainly involve finding a suitable power supply.

Thanks for all the input. As far as all the specific information, I cannot give ALL of it, since it will take quiet a bit more labor to determine all this, and that the customer has already stated that they want to go the "economical" way. I probably will not get paid for the amount of time I've already got involved. But discounting all of that, in my original post, I ask about the possibility of a booster. If there is not one available, then I'm just waiting for the customer to get back with me on their decision to let met run 120 volts up to the sign. The wiring is already there, looks like they got #8 coming out of the transformers. They are 300 watt multitap transformers, with 13 volts being the highest tap. There are other lights on this circuit, but not too sure how many. The 4 lights at the sign are on separate circuits, in other words, 2 are on one of the circuits, and the other two are on another circuit. As far as my experience, I have installed quite a few low voltage systems, though not as thorough as the "Low Voltage" specialist that runs landscape lighting to "Hollywood houses" etc., etc...
I changed probably 40 bulbs at this place around 1 1/2 years ago, and there are spot lights that are even farther away from the transformer than these sign lights. So, in summary, all I need to know was about the "booster" possibilities for the existing lights. I am not trying to re-design the wiring system. That's out of the question, too much money involved. Thanks for all your input. I did look on the Kichler site, but have not looked on the "Ruud"site or "Hadco", or the other brand name manufacturers. Also, I gave them the option of changing transformers, but to do that, especially with one that has only 14 volt taps, would be probably around $1100.00 or so, and still not sure it will get the voltage where it needs to be. Now, I have NOT looked into any with higher voltage taps, such as 22 volts etc. That may get them high enough, if it don't make it too high for any that is closer and are on the same circuit as the sign lights.
Anyway, it's been about 3 weeks now, and the customer has not got in contact with me, so they may have decided to leave it the way it is:( Thanks again for all your input though. Steve...

I was just wondering if you could increase the apparent voltage by exploiting the peak to peak.

Maybe this is another experiment for me. Put a 12v AC load out there with enough resistance to drop the volts to 8 and then do the rectifier thing. I have a hockey puck sized wire wound pot that is good for this kind of thing.

Greg, I don't know about that. Might work, I don't know. I have found a transformer with up to 22 volt taps, at a reasonable price($523.00), but now I can't find the right size low voltage LED flood lights that I think would do the job. If I can find them, I may submit another price to my customer. Thanks

Steve:
$1100 sounds really outrageous for a transformer.

I did a quick look at the landscape lighting site connected to RUUD and a 600 watt, timeclock & photo cell is a wopping $209.00

I did not dig into the specs, but their transformers used to be two circuit.

Just an FYI in case you get into landscape lighting in the future

Edit to add link:
http://www.e-conolight.com/landscape/transformers.html

Yea, John that figure was just off the top of my head from what I thought I saw from previous searches a few years ago. I haven't done a thorough search recently. I thought the multitap transformers were much more than the Lowes or Home Depot transformers.... Also I think I was pricing Kichler,Hadco, and more "upscale" manufacturers...
The transformers at "Econo-light" don't look to have as many taps as one of the "higher name brands" do.

Greg,

When I did LV landscape lights, I would always run 10-2 LV wire to help with the voltage drop. Even so, you would still have to calculate distance, # of lights, wattage of lights and voltage output of transformer. The lights I used where Hadco lighting and their transformers had several output voltages. You could crank it up (If I remember correctly) maybe 2-4 volts higher so that your output was 14-15 VAC.

Sparky, that 300W multi-tap trany in the link I posted is currently only $197.00 on sale and has 9 tap levels from 12V all the way up to 22V. It looks like the customer reviews for it are all positive, so that might be a pretty cheap alternative to explore before any major excavation and trenching.

What is the far end load (watts)?

Greg,

I dug out an old LV lighting book. There was a formula for landscape lighting that I used to use. it was:

Total Watts X Cable Length
--------------------------
Cable Constant

The above formula equals the voltage drop


Lets see if this comes out. The cable constant was depending on size of cable.
The different wires sizes. All copper UL listed for landscape lighting. i.e. #18 = 1380, #16= 220, #14=3500, #12=7500, and #10=11920

So a circuit 80 foot long with 6 lights of 25 watt each: 6 X 25 = 150 total watts X 80' run = 27000

So 27000 using #18 ga wire at 1380 = 19.56 voltage drop OR

27000 using #10 ga wire at 11920 = 2.265 voltage drop

All of these calcs. would be at 12 volt. You can also up the voltage a wee bit if needed.

I also should have added that back a few years 'RUUD' was just that, there was no 'Econolight' subsidiary! They had quality materials, sold direct to ECs.

KJay, thanks for the link. I didn't see it at first. I've done business with "Volt" before. I got some low voltage pathway lights from them. Was good quality, and a good price. I sent my customer another quote for replacing the transformer and installing some 30 watt LED flood lights (equivalent lumens to 150 watt. halogen). The existing flood lights they have, are either 50 watt. or 100 watt. halogen, I think.// Only problem I see though, is that that transformer only has 1 circuit. The transformer I will be replacing has 4 circuits

Rethunk my last post. If they call me, I can leave the existing transformer there with the other circuits in it, and just mount the new one beside it, and feed it from another breaker that is next to the transformers. There's 2 or 3 more spaces there:)

You could also run another 10 guage out there and make it a loop circuit. I know it requires digging but you wouldn't have to dig up or change any of the existing lighting, just hook on near or at the end of the existing run and choose any easy route back to the transformer. That's how we usually fix VD problems when we are called in after the lanscapers tried first.

Big B, unfortunately there is no easy route back to the transformer; 2 drive ways and 100ft. of trenching involved. Anyway, they haven't called me back yet. I think they are still pondering over the situation. Thanks anyway.