12V LED lighting vs. Wire losses

Redford · January 2009

I really like the efficiency and selection of 12v lighting although a big problem with 12v lighting is the wire sizes required to handle even a few amps on longer runs.

I have one run that is 12 gauge romex that is a 75 foot long one way run.

Selecting a wire for 3 percent loss would require a substantial investment in 6 or better yet 4 gauge wire just to hook up 4 LED lights that draw a couple amps!

So I was wondering if anyone has used or knew the effeciency of 120vac/12v transformers.

I'm not sure that would be the most efficient method to retrofit wiring for 12v, I suspect some electricity would be lost as heat in the transformation process.

Right now I have a branch circut with 4 recessed lights in a room and I run them off a Morningstar SureSine, 300 W inverter.

I would think that adding a transformer on the circuit, 60 feet down the run would be adding to the losses already incurred by the inverter. But I don't know the kind of efficiency that transformers have.

I was looking to get IMTRA products
http://www.imtra.com/product/marine_lighting/transformers/voltage_regulated_led_converters/voltage_regulated_led_converters.htm

Then replace the 4 incandecents (15w, 120vac, each) with 4 dimmable LED spots that use 3.2 watts a piece.

In all the load wiring would need to be sized for about 20 watts for all 4 LED lights about 1 amp.

mike95490 · January 2009

Re: 12V LED lighting vs. Wire losses

My rule of thumb, is that transformers should be at least 95% efficient, and closer to 98% efficient. Of course, corners get cut, in both supplies and construction, so efficency goes down for each shortcut.

The IL-LED10WDC12V AC - DC LED supply, has no efficiency rating .

I would think that 70' of ac cord, to power 200W should be feasible with even 18 ga lamp cord, and a sure thing with 16 ga cord

BB. · January 2009

Re: 12V LED lighting vs. Wire losses

If using the minimum amount of power will be a "critical" requirement, then you should test the components yourself.

Unfortunately, this probably means that you will need to purchase at least one sample of each major component, a Kill-A-Watt meter, and a good DMM (Digital Multi-Meter and possibly a current shunt, depending on the amount of current under test) to measure the power draw/loss of each component (probably for both AC and DC devices). And, for example, evaluate the quality of light from each lamp.

The problem is there is no standard assumption you can make when trying to understand efficiencies of various components and they don't publish charts/graphs of how much power they lose.

Sending power longer distances, pretty much means higher voltages. In the "Olden Days", transformers where pretty much the only thing out there that could efficiently "transform" voltage/currents.

Now, we have lots of neat electronic DC to DC power converters that can (in some cases) give transformers a run for their money (here is an example of 12/24 volt up/down DC converter). A good 120 VAC inverter is probably more practical--easier/cheaper to find 120 VAC devices than the same things in 24 VDC.

And, we every component has its own limitations which can cause excessive power loss (to ensure cheap cost of manufacturing). For example, LED's are very efficient, but they require some sort of ballast to limit current flow. This can be done with a little DC switching power supply (efficient but expensive) or simply a resistor in series with the LED (lots of losses, but cheap).

To a degree you can read the specifications and get rough power requirements--but without doing your own measurements and evaluation (such as "quality of light").

And, how you use the components will also matter... Can you turn of the inverter when the 120 VAC power is not needed--or will it run 24x7 and waste power on standby.

-Bill

Brock · January 2009

Re: 12V LED lighting vs. Wire losses

Maybe I missed something, but you should easily be able to run 4 LED lamps 75 feet away on #12. Well maybe if they are 50w or more you will have an issue. What are the LED's? They would have to be 12w each to pull 4 amps at 12v, that would be HUGE for LED.

Now for the key point, most LED lamps are regulated back to the 4v range for the LED's so unless the voltage drop is more than 8 volts you should be fine. Of the two 12v medium base LED's I have both run exactly the same off my 12v battery or a simple tiny 9v alkaline battery. Again this is because the lights are regulating the voltage down to what the LED’s really want.

I would think the loss of converting the voltage up to 120 and move it and back down to 12v would be a lot more then just running it 12v the whole way.

icarus · January 2009

Re: 12V LED lighting vs. Wire losses

I'm with Brock on this one,,

We used to run the whole house (granted it was small) 150' from the batteries, feed by strand of # 10 wire. We had substantial line losses, but everything worked fine. We would draw ~ 40-50 watt max. Later, I added a #6 so it ran on the #6 and the# 10 and the line loss dropped considerably.

If all you are running is a couple of amp @12vdc you aren't going to have enough loss to worry about. The LEDs aren't going to care.

Tony

Moe · January 2009

Re: 12V LED lighting vs. Wire losses

Quality LED lamps use a current regulator rather than resistor ballasts and usually operate over a range of 8-32 VDC.

A couple of amps (and that would be a lot like for Luxeon Stars) on 75 feet (150 both ways) of 12AWG should be only about 1/2 volt drop.

Redford · January 2009

Re: 12V LED lighting vs. Wire losses

I was looking into getting 4 of these:
http://www.imtra.com/product/marine_lighting/spots/led_recessed_spots/hatteras_powerled_spring_mount/ilim31500.htm

They use 3.2 watts per light, but will be on a PWM dimmer so I would think the power consumption would be correlated to the lights intensity.

So I figured the wire size using 20 watts of power so that's under an amp @ 12 volts.

I used the wire size/loss chart in the SEI solar design book for 2 amps at 150 foot (2 way) run and I think it said 6 or 8 guage.

I couldn't believe it when I read it! The specs on the LED's say the operate between 10 to 32 volts so I imagine they wouldn't mind a 5 or 6 % voltage drop @ 75 feet.

n3qik · January 2009

Re: 12V LED lighting vs. Wire losses

Do the KISS thing, go with 12V wiring. I have 2 1W 1156 Auto LEDs and 1 3W MR16 16 LED on 18AWG at 50 and 75 foot from the battery. The voltage at each LED is 9-11 VDC. Also, by running the LEDs at 10-11 volts, I found the current dropped in half but the light output only dropped by 10%.

Redford · January 2009

Re: 12V LED lighting vs. Wire losses

The KISS rule is in effect for this problem!

I may have gone wrong using the SEI wire size chart (not because the chart is wrong) possibly because that chart is meant to properly size the wire from the solar panels to the combiner box then from the C.B. to the panel. I suppose this area is where losses would take the greatest toll.

BB. · January 2009

Re: 12V LED lighting vs. Wire losses

Our eyes do not see light in a linear fashion, but logarithmic.

So, our eyes barely perceive a difference when light output drops (or increases) by a factor of 2. If your light is 10x brighter, it swamps the lower output.

So, this make perfect sense in that if the power output (current) drops by 1/2, you will perceive hardly any difference at all.

-Bill

niel · January 2009

Re: 12V LED lighting vs. Wire losses

redford,
i too agree to go with the wiring you have. even with the losses you were getting with incandescents it would prove to have just as much or more losses to do the converting with ac power. if there's still a problem in the future (as in the case of longer runs or expanding the number of lights) then you may not get around getting more wire or larger wire to accommodate your lights.
one other possible solution is to up the voltage being presented to the lights. for 12v transistorized radio transmitters many are designed to output their power with the alternator's output, which is much higher in voltage than just with a battery alone. output suffers at 12v so some elect to up the voltage to imitate that of using an alternator. here is an example with the n8xjk boost regulator at www.tgelectronics.org mind you, this is not an endorsement as i have not tried this and i don't know of its cost or worthyness. this example is supposed to handle up to 40a and i would view that as overkill for your application.

12V LED lighting vs. Wire losses

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