I can’t speak for everyone but my electrical knowlege is pretty sparse. I think most of us could learn more in this area. I’ve been looking a low voltage lighting and it is difficult to figure what is what out there. There are a lot of low voltage DC lights out there with different energy requirements. Many of them have a transformer that converts 120V AC to different low votage DC. These lights might not be that effecient. Just easy to instal. Some are solar lights so I can be pretty sure they are DC and effeceint. The question I have is…. If the voltage is low and DC does it matter if the voltage is exact? There are a lot of light fixtures that are DC low voltage but the voltage supplied or used varies. Let’s say I have a DC 12V power supply and hook up a DC light to it that wasn’t 12V. Maybe 6V or 3V. The bulb would put out more light. But how much would it shorten the life span of the bulb? And can I drop the voltage with a resistor? I’ve been looking at stand alone solar security lights. They come with a collector, lights, motion sensor, and photo cell to turn it on and off. Can I take off the lights and power my own lights? If my lights are small it should be fine. Right? If I put to many or to large of DC lights on it they would be dim. One of the pros of low voltage lighting is the extremely long life of some bulbs. I don’t want to be replacing bulbs all the time. Thanks for helping!
Discussion Forum
Discussion Forum
Up Next
Video Shorts
Featured Story
Old masonry may look tough, but the wrong mortar can destroy it—here's how to choose the right mix for lasting repairs.
Featured Video
Highlights
"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.
Fine Homebuilding Magazine
Fine Home Building
Follow
-
Fine Homebuilding
Dig into cutting-edge approaches and decades of proven solutions with total access to our experts and tradespeople.
Start Free Trial Now -
GBA Prime
Get instant access to the latest developments in green building, research, and reports from the field.
Start Free Trial Now
- Home Group
- Antique Trader
- Arts & Crafts Homes
- Bank Note Reporter
- Cabin Life
- Cuisine at Home
- Fine Gardening
- Fine Woodworking
- Green Building Advisor
- Garden Gate
- Horticulture
- Keep Craft Alive
- Log Home Living
- Military Trader/Vehicles
- Numismatic News
- Numismaster
- Old Cars Weekly
- Old House Journal
- Period Homes
- Popular Woodworking
- Script
- ShopNotes
- Sports Collectors Digest
- Threads
- Timber Home Living
- Traditional Building
- Woodsmith
- World Coin News
- Writer's Digest
Replies
Most common "consumer" solar powered light is near worthless.
You may try looking around this site http://www.realgoods.com/
But the cost will be in the hundreds of dollars. Not $39.95
Let's say I have a DC 12V power supply and hook up a DC light to it that wasn't 12V. Maybe 6V or 3V. The bulb would put out more light. But how much would it shorten the life span of the bulb?
Yes, they will be brighter, but only for a few minutes or even seconds before they burn out.
And can I drop the voltage with a resistor?
Yes, BUT! You don't want to.
You will waste 2 or 4 times the amount of energy as heat rather than light.
This is like trying to control the speed of a car by applying the brakes rather than taking the foot off the gas.
Most bulbs you can find similar ones in any voltage. Or at worse change out the sockets.
I did contact Realgoods/solar before Christmas but they haven't gotten back to me yet.
I also contacted Backwoods solar. They look like a better fit for me. They asked me to count up the watts of the lights I will be powering and for how long each evening.
Based on that number they can size the collectors and batteries for the system. It shouldn't be much.
I've already bought a few 12V Dc fixtures so I'm commited to 12V.
I figured that a lot of low voltage landscape lighting is 12V so it was good voltage to go with. Plus the auto industry uses 12V.
I just picked up a landscape light yesterday that is 12V.
It came with an 18W bulb. I can bump up the watts if I need to.
Bill's advice is right on (as
Bill's advice is right on (as always), plus I have some things to add.
-- low-voltage landscape lighting is typically 12V alternating current, not DC. Why AC? Because you're starting with 120V AC power, and transforming it (stepping it down) to 12V. There's no practical reason to convert the AC to DC.
-- The advantage of using 12V is that it's safer, there's little chance of shock or electrocution.
-- Keep in mind that UL-listed landscape lighting transformers are limited to 300 watts per circuit. This is because it's safer to have limited power in the circuit. Even though the voltage (pressure) is low, you don't want the power (wattage) to be so high that the amperage (flow) is enough to readily cause a fire at a bad connection.
--There are light fixtures for landscape lighting systems that use LED light sources, which are extremely efficient and last a long time (50,000 hours average life). These LEDs are a semiconductor that turns electrical power into light without using a white-hot tungsten filament, which is how incandescent light bulbs (including halogen and xenon) work. Most landscape lighting fixtures use incandescent light sources, but LED sources are commercially available, and expensive. There are no conversion lamps (to allow LEDs to be used in fixtures designed for incandescent lamps available yet), but there may be in a few years. You can now buy LED light sources to replace PR-style flashlight bulbs.
--typical halogen incandescent wedge base T-3, 5 watt to 10 watt lamps (bulbs) for landscape lighting systems have a median life of 1000 to 1500 hours if run at 12-12.5 volts. That's 9 months if the lights are on an average of 5 hours a day. For a typical system, you're going to have to clean the fixture lenses of water scale deposits, dirt, leaves, etc., replace corroded sockets, and repair inadvertant damage, at least a couple of times a year. These fixtures need routine maintenance, unless you want to throw away the fixtures every couple of years. And that's what happens to most of the "Malibu" light kits that are installed and not maintained.
I've never seen a self-contained (solar-electric, or PV-based) fixture that was worth a hoot. The little mushroom-style or pagoda-style path lights with the solar cell on the top are worthless...they give an hours worth of feeble light after sundown, before the internal battery runs down.
Happy New Year,
Cliff
So the Malibu light I just bought that is 12V 18W is AC?
Nowhere on the package does it say it is AC or DC.
Can I power that with DC?
I have small 12V battery charger for auto batteries that lit it up.
One more thing. Could I replace the AC 12V 18W bulb in the Malibu light with a DC bulb? The bulb has a bayonet style base. I could pick up a DC bulb.
The bulbs don't care for if
The bulbs don't care for if it AC or DC. They work the same.
Without getting into too much confusing details since AC is a constantly varying value it is measured using a special averaging method (root mean square) so that with a resistive load (heaters or incandescent) it has the same wattage output as would DC of the same volts.
While an car battery has a nominal rating of 12 volts when it is fully charged it is a little higher. And a battery charge has to put out even high voltage to be able to "force" current into the battery.
With only a small load on it probably has an output of 15-20 volts.
Certainly OK to test some lights, but too high for long life.
Thanks! I wondered if the battery charger was really 12V.
It makes perfect sense that is is higher in order to charge a battery. I can switch it from 6V to 12V. I have hooked up the lights to a car battery as well. I was trying to see if the light fixture was going to put out enough light for the area.
If the light is to dim can I just up the bulb wattage? I really don't see how upping the bulb is going to be problem. Could I use a different or more effecient bulb?
I'm just trying to sort all this out.
I have another question. Lets say I have a string of Christmas lights that are leds. Some of these are power by AC and others (solar) are powered by DC.
The DC solar ones have batteries that are 1,2, or 3 rechargable AA batteries.
If I ran 12V through the string what would happen?
Do LEDs act like incandesent bulbs?
LED's are a typed of diode
LED's are a typed of diode and the characteristic is that that they have a certain voltage level that must be over come (.5 to 1.0 volts) and above that they allow more and more curent to flow through them.
But the current must be limited. There are many ways of doing that. Sometimes a resistor is used. That waste power and only works for a given design voltage.
There are electronic circuits that also are used. They will probably work at a higher voltage, but not unlimited voltage. And it depends on what the dsign is if they might overheat at higher voltages.
IE, no way of knowing what they will do at a higher voltage.
Yeah, all LEDs are DC, but they act as their own rectifiers to convert AC to DC, so they're to some degree "agnostic". But they have a (excuse the expression) "hockey stick" voltage/current curve, meaning that they don't conduct very much until about 1.2V, then they need to be protected from too much current above that, with a resistor or some sort of electronic constant-current source.
I googled constant-current source and found this.
http://www.constant-current.com/0704-02_MINIKON-L.pdf
And this one in elglish
http://www.constant-current.com/html/minikon.html
Just put it on the line in some sort of box.
Could I double them up? So it dropped twice?
Something like this would be easy to build:
http://delabs-circuits.com/cirdir/theory/tutors/doc00009.html
See now there you go confusing me. Not to hard to do, I know.
I just want to buy the component.
Can you recomend one that would serve my needs?
I chose the one I posted because it requires no soldering.
I'm just stepping 12V down to 1.5V.
Poppa, you're overthinking
Poppa, you're overthinking this. LEDs are current operated devices, it takes a certain current to turn them on, but the voltage is quite low across the LED. A very small increase in voltage across the led like say from 1.6 to 1.9 volts, a .3v difference, could increase the current 10 times and burn out the led.
That is why almost all led lights have a current limiter (resistor likely) to prevent the led from being destroyed. Thus, the wired led lights will probably be rated to work at a voltage like 12 volts and can be treated like a regular incandescent bulb.
MarkH, I am currently trying to figure out how to make my lighting in the front yard work out.
I contacted a solar supply company about panels, a controler, and batteries.
The first thing they need is the number of lights and their wattage in order to size the system correctly.
I have two small trees that I would like to light with string lights but I don't want them to be big or bright.
The ones I would like to use are these http://solarilluminations.com/acatalog/info_65.html
I've put some up so I am familiar with them.
I don't want the collector though so I'll pull the string off and power it with my 12V system.
Since they are powered by 2 AA bateries I figure I need to bring my power supply down to 1.5V.
There are other things I would like to do as well.
I would like to put a few lights on motion sensors.
Many of the motion sensors don't work on 12V.
So I'm trying to figure out how to lower my votage for these controls. There is a 12V motion sensor I found but it is $100.
Some of the things I want to do just doesn't exist as far as I know. So I can make them. But I need to do it right.
I think LEDS are great but many of the off the shelf ones won't work for me.
I think the constant current device should work but I need a source for the one that I can wire so my 12V system will deliver 1.5V to my lights. It's easy, inexspensive, and out there. All I need is source so I cna order a few.
I don't mean to get antsy about this. I'm not an electrical engineer or even an electrician. If you or some one here knows the part i need I would appeciate it.
I am a terrible typist and this is the second time I've written this because it all got errased the first time.
When you start talking about electrical stuff that is over my head my eyes glaze over and they roll back in my head.
This response is not under my control.
This new forum doesn't make this any easier. I never know who I'm talked to or answering.
It's like I'm in a room full of electrical engeneers that are talking at the smae time in a language that I don't understand.
To be completely frank, I think you have awfully ambitious plans for not knowing what the heck you're doing.
I agree. It is ambitous. I've
I agree. It is ambitous. I've found that usually if I study it for a while and get the right info I can do it.
It just takes a while. I don't have to know all about electronics. Just enough to do this job.
I went by Radio shack and they had 1/2 watt resistors.
I'm not sure what this means. " but for optimum brightness use two LEDs instead of one, wired in "parallel" but in opposite polarities, so one will be on when the other is off"
Did you mean two resistors? I'd need a drawing of the way you want it wired.
No, two LEDs.
Let's see if
No, two LEDs.
Let's see if this survives formatting:
---->|----
| |
--|<--
I guess it didn't survive.
I guess it didn't survive. (Sure would be nice if preview worked.)
OK, if you are cutting the string of leds loose from the box, There are 50 leds, I'm estimating .02 amps each, so the string is 1 amp. White leds require 3.4v approximately so the string is nominally about 3.5 watts.
This is a driver that would work, but the current is just a little low. It still would light up nicely. https://www.eio.com/p-2490-velleman-vm1433w-3w-power-led-driver-module.aspx
That driver would probably take 5 watts or less to work, since it is not 100% efficient.
Please remember that leds are not voltage operated devices, they are not like bulbs. They require a certain current to work correctly.
Thanks for the link. I read the description and it says, "Power up to two 3W high-power LED's".
Does that mean I can use this device for both strings of lights?
That would help with the cost.
All this equiptment adds up.
The strings would have to be connected in serial. I believe it would work.
for everyone here who has helped I just wanted to say thank you. I still have some questions but I'm a whole lot closer.
Here is a pic of the plan for the front yard. I still have to build the patio. It has been put on hold for now because of $$$. Or lack there of. So the landscaping is done and now I would like to have lighting. I just finished two more fence panels and three posts.
I've been working on this part time for about a year now.
Simplest is to use a resistor. Assuming you have 20mA LEDs, take your supply voltage, subtract off 1.5V, then multiply by 50 to get the proper resistor size. Eg, with a 12V supply subtract off 1.5 to get 10.5, multiply by 50 to get 502.5, pick the next larger standard resistor size (560 ohms), and wire that in series with the LED. Use at least a 1/4 watt resistor, preferably a 1/2 watt one. (Resistors available at Radio Shack, though you might have to buy a "variety pack".)
Note that the LED will conduct in only one direction, so if you have a DC voltage supply you may have to reverse directions on the supply to get the LED to light. For AC it won't matter, but for optimum brightness use two LEDs instead of one, wired in "parallel" but in opposite polarities, so one will be on when the other is off.
Thanks Dan. I'll try Radio
Thanks Dan. I'll try Radio shack.
-- low-voltage landscape lighting is typically 12V alternating current, not DC. Why AC? Because you're starting with 120V AC power, and transforming it (stepping it down) to 12V. There's no practical reason to convert the AC to DC.
*I plan on installing a stand alone solar system primarily for the lighting outside. Since the solar panels produce DC and the batteries store DC I figure I can just use the DC with no conversion.
-- Keep in mind that UL-listed landscape lighting transformers are limited to 300 watts per circuit.
*I understand about overloading. If anything I typically overbuild.
--There are light fixtures for landscape lighting systems that use LED light sources, which are extremely efficient and last a long time (50,000 hours average life). These LEDs are a semiconductor that turns electrical power into light without using a white-hot tungsten filament, which is how incandescent light bulbs (including halogen and xenon) work.
* I have installed 4 led lights already because I was building a lanscape wall. I bought another one that is a string light but haven't installed it yet. I guess I will have a mix of incandescent and led lights depending on usage and cost.
--typical halogen incandescent wedge base T-3, 5 watt to 10 watt lamps (bulbs) for landscape lighting systems have a median life of 1000 to 1500 hours if run at 12-12.5 volts. That's 9 months if the lights are on an average of 5 hours a day. For a typical system, you're going to have to clean the fixture lenses of water scale deposits, dirt, leaves, etc., replace corroded sockets, and repair inadvertant damage, at least a couple of times a year. These fixtures need routine maintenance, unless you want to throw away the fixtures every couple of years. And that's what happens to most of the "Malibu" light kits that are installed and not maintained.
* I understand how most lanscape lighting is poorly done.
Many, many well intentioned home owners just don't understand how poorly thought out and installed sytems look just like that. I don't want to get defensive about my work. But I felt you should know.
I'm not installing any kits. I am selecting lights that I like and will work for the given task. Some of the lights are in areas that aren't very important style wise so I get lights that cost less. There are some areas where I could install a stand alone system just for one small area. That's why I asked about the solar security lights.
-- I've never seen a self-contained (solar-electric, or PV-based) fixture that was worth a hoot. The little mushroom-style or pagoda-style path lights with the solar cell on the top are worthless...they give an hours worth of feeble light after sundown, before the internal battery runs down.
* Many of the lights I want to instal are curtessy lights that are desrete and only need to come on for a short time after the sun sets. I also want to control lights with motion sensors because I like the way they come on for the user automaticly. I would like to have the lights on the motion sensor come on gradually. I think that would be neat. But none of them will be very bright. Just pools of friendly inviting light in areas where people travel to and from the house. That's what I'm after.
I have six puck lights brightening my kitchen sink area from under a cabinet and a shelf, and they are 12v, 18w xenon bulbs with T5 bases. They're powered by a transformer under the sink. Been doing this for 13 years. Simple as that.
Minor detail: Virtually all of the low-voltage lighting system are AC.
AC to the transformer, DC thereafter. Where'd you get your electrical license?
barmil, with this new forum I'm not sure if you are addressing me or someone else. I don't have an electrical license.
No license, just a master's
No license, just a master's degree in EE.
Like I said, virtually all low-voltage lighting systems are AC.
to barmil--
Are you serious?
What's your experience with low-voltage landscape lighting systems?
They're AC, on the secondary side, too.
Don't believe me? Go measure the output of any landscape lighting transformer.
Go ahead. Make sure your DMM in on the right parameter, that'd be AC volts. Really, check it yourself. And report back, please.
Make my day.
Cliff
Here's a little diagram.
Here's a little diagram.
Thanks Mark. I can do that.
Probably not a good idea to wire them in parallel, since the LED with the lowest threshold voltage will draw the most current and the current won't "balance" between LEDs.
The leds are in parallel since they ran off batteries and the voltage is low and they have individual limiting resistors which I didn't draw that balance the current. These are premade strings that formerly had a solar cell and 2 AA chargeable batteries for power.
I picked that driver because it is more efficient than a simple resistor, and the big picture is there is going to be a large solar panel and battery powering the setup which includes a good bit more lighting.
The two strings have to be in series because the driver is designed to output a 700ma constant current, and is designed to drive two high current leds in series. There would be insufficient current and brightness if the strings were in parallel.
Minor quibble: Unless the driver is a chopper, it won't be more efficient than a resistor. It will, however, presumably have the advantage of maintaining a constant output voltage in spite of varying input voltage.
Here's a little diagram.
Here's a little diagram.
You could make this extremely simple or yourself by simply using batteries as the strings of lights are designed to use. Get some rechargable batteries and a charger. They sell sets at Costco and a lot of other stores. Yes, you'll always be having to change out and charge the batteries, but that could be made to be a rather simple task. And, you'd have it done.
But then I couldn't say it
But then I couldn't say it was solar ;^) And green.
Gilrs love it! Just kidding, I'm very married.
Unless I bought a solar battery charger.
I am and was tempted to put on cicuit on an inexspesive device. Put this up, take off the flood light, and connect my leds. http://www.buy.com/retail/product.asp?sku=212427150&listingid=57328722
Would it work?
One of the reasons for this thread is to find out more about electronics for everyone reading this. Lower energy systems controled by electronic devices are coming down the pike. Just look at cars.
I'd like to know more about them. Instead of just buying stuff form oversees.