12V AC vs 12V DC

[HookWorse]

In theory...if a person is using 12V landscape lights, can he power them with a 12V car battery? Specifically, 12V MR16 halogen bulbs? The bulbs themselves don't say anything specific, just that they are 12V. I'm not knowledgeable enough about how a transformer converts 120V down to 12V and what the end result is. I do know if you hook a light up to a car battery, it lights up fine.

 

[rockwithjason]

not all lamps are created equal. some will work on either, some won't. you won't get tons of run time on a car battery in either case

 

[jetmech09]

It should work off a car battery. Not for very long. A transformer uses 2 coils to change the voltage and current, indirectly of each other. If voltage goes up, current goes down. Only works with AC. Google "Mutual inductance" for better reading material.

 

[HookWorse]

Wow, isn't there a "mutual inductance for dummies"? My head hurts

 

[Socophreak]

You shorten the life of the halogen bulb by running it on DC.

12V AC is the recommended method. You can pick up a 120v to 12v ac transformer quite easily from most electronics store. You just have to keep in mind that a 20W 12V ac bulb will, in theory, pull approx 1.7 amps.

 

[Kevin C]

Yes you can power them with 12 VDC. The effective power is the same. In theory, you can get better bulb life from AC, but bulbs are pretty cheep.

Headlights are typically halogen and are run on DC... apparently its a pretty common application.

http://www.htl.co.jp/english/p_pro1_info.html

 

[magova1104]

Absolutely yes. Actually those light bulbs are designed for 12VDC. You can use the 12 v battery for power them and and either a trickle charger for maintain the battery full or connect it to a solar charger for save energy.

 

[magova1104]

Yes you can power them with 12 VDC. The effective power is the same. In theory, you can get better bulb life from AC, but bulbs are pretty cheep.

Headlights are typically halogen and are run on DC... apparently its a pretty common application.

http://www.htl.co.jp/english/p_pro1_info.html

Wow! Great info.

 

[HookWorse]

Absolutely yes. Actually those light bulbs are designed for 12VDC. You can use the 12 v battery for power them and and either a trickle charger for maintain the battery full or connect it to a solar charger for save energy.

You and I are on the same wavelength, my friend. The application is not close to any power source, so my idea was IF the bulb worked with a car battery, to use a solar charger to maintain the charge of the battery. I had the option of using a 12V photocell or a 12 timer to turn the light on and off. I've found a timer inexpensively, so if I set it to run for 3-5 hours nightly instead of all night, the solar charger should have no trouble keeping the battery up...unless a serious cloudy spell happens. And, since the bulbs are under 5 bucks, if they don't last real long, its not a huge deal.

 

[larry_g]

the solar charger should have no trouble keeping the battery up...unless a serious cloudy spell happens. l.

Your going to have to pay attention to the watt-hours of the charger and the bulb. Batteries do not make electricity, they just store it. So you will have to figure the total load in watt hours and then make sure that the solar charger can provide more than you use.

lg
no neat sig line

 

[HookWorse]

Your going to have to pay attention to the watt-hours of the charger and the bulb. Batteries do not make electricity, they just store it. So you will have to figure the total load in watt hours and then make sure that the solar charger can provide more than you use.

lg
no neat sig line

Ok, if I'm going to run one 50W bulb for 5 hours max every night, how much charger would I need to keep the battery topped off? I see solar chargers rated in watts and others in amps, or mA, as it were. And I understand it will vary with length of daylight (seasonal), cloud cover, etc. Keep in mind, nothing depends on this light...so I don't need it 100% charged every day, rain or shine, summer or winter. I'm looking at an average.

 

[aandpdan]

Ok, if I'm going to run one 50W bulb for 5 hours max every night, how much charger would I need to keep the battery topped off? I see solar chargers rated in watts and others in amps, or mA, as it were. And I understand it will vary with length of daylight (seasonal), cloud cover, etc. Keep in mind, nothing depends on this light...so I don't need it 100% charged every day, rain or shine, summer or winter. I'm looking at an average.

50 watts at 12 volts is 4.16 amps. Multiply that by your 5 hours and your drawing about 20.8 amps out of the battery.

Assuming 10 hours of light/day, you need at least 2.1 amp/hr charge rate. Not including losses in the system.

A regular car battery won't last long either. You'll want a deep cycle battery for this and a charge controller.

 

[HookWorse]

Any way to convert amp/hrs to watts? The most common chargers seem to be 5-15 watts. One 5 watt one I found is advertised at 1.5 to 2.5 amps a day output (dependent on light conditions)

 

[Kevin C]

This is where an LED light source and a different battery chemistry would make a big improvement. As you may already know, LED's are a lot more efficient and there are other battery technologies that are a lot more tolerant to deep discharge cycles.

If you Google solar yard light you will find a pretty wide range of lights. Since the solar collector is the most expensive component they always use a very efficient light source (LED).

I have ten or so Home Depot LED stake lights in the garden thst is along the side of my garage. They light up the path pretty well and look really nice. I think I paid about $5 each. During the summer they are usually good until about 3 AM.

 

[aandpdan]

Any way to convert amp/hrs to watts? The most common chargers seem to be 5-15 watts. One 5 watt one I found is advertised at 1.5 to 2.5 amps a day output (dependent on light conditions)

If the voltage stays at 12 volts:

5 watts/12 volts = .41 amps.

You're going to need a bigger panel, read that as $$$

 

[larry_g]

Any way to convert amp/hrs to watts? The most common chargers seem to be 5-15 watts. One 5 watt one I found is advertised at 1.5 to 2.5 amps a day output (dependent on light conditions)

Volts x amps=watts

so 12 v lamp
draws 1 amp

= 12watts. run the lamp for 1 hour and you have 12watt hour.

If your solar charger is a 1 amp charger (at 12v) it will have to run for 12 hours to recharge. If it is a 2 amp charger then it will only have to run 6 hours.

lg
no neat sig line

 

[HookWorse]

So, it sounds like if I ran it 3-5 hours, it sounds like I'd end up needing nearly 50 watts of charger to comfortably keep the battery up.

Lets visit what Kevin said. Are there any LED lights that will do 12V, put out the 850-900 lumens the halogen would, and have a wide flood pattern, such as 60 degrees?

Is something like this one feasable? And how many solar watt charger would this take to keep up with for 5 hours? The specs are a tad sketchy...

http://www.amazon.com/dp/B005MLXAF4/?tag=atomicindus08-20

 

[2manytoyz]

Keep the garden light fixtures, ditch the halogen bulbs. They consume far too much power for the light they produce.

A direct replacement for the MR11 halogen bulbs is this one, sold on Amazon for $8:

Instead of consuming 20W per bulb (halogen), each one will consume 2.1W, or 125mA at 12VDC or 12VAC. These can work with the original 12VAC transformer, or with any 12VDC supply (battery, solar, etc). They are also not polarity sensitive.

Here's where I bought mine:

http://www.amazon.com/gp/product/B002L4L606/ref=wms_ohs_product

Moved not long ago, haven't setup my solar array yet, but at my last house, all my garden lights were powered with energy captured during the day. The energy collected with the solar panels was stored in a battery bank, and at dusk, the charge controller (MorningStar Sunsaver) automatically turned on the lights at dusk, and off at dawn. This time is adjustable. Completely automatic.

One step led to another. Then made all my indoor lighting solar powered.

But alas, I have moved, and I'm still getting it all setup once again...

http://2manytoyz.com/altpowerboard.html

 

[kbs2244]

It would be a whole lot easier to just go to the local big box lighting department.
They have done all this for you.
You can get a solar powered, battery backed up, optional motion detector, LED night light in a box.
And cheaper than finding all the parts to do it your self.

I put one in my daughters barn last month.
Works great.

 

[2manytoyz]

BIG difference in a little low powered LED "night light" and one of these replacement MR11 LEDs.

Also the little wimpy stand alone LED garden marker lights, that barely put out enough light to even be seen, are a far cry from this 3W LED fixture.

I'll have to take some night pics of these LEDs. I've thrown away my solar garden lights from Home Depot. I've also thrown away the solar powered LED security light. It didn't last long before it failed.

I repaired it, and it lasted a few more months. But it was of poor quality. Bad solder joint on the circuit board, battery failed, then finally the photoresistor corroded. Neat idea, but only provides light during movement, and only for a couple of minutes at a time.

The MR11 LEDs provide decent light, and with the low power consumption, can run all night.

But this level of DIY is more than many are interested in. Just don't be surprised if the solar hardware you buy at the big box stores doesn't last long...

 

[gatchel]

You and I are on the same wavelength, my friend. The application is not close to any power source, so my idea was IF the bulb worked with a car battery, to use a solar charger to maintain the charge of the battery. I had the option of using a 12V photocell or a 12 timer to turn the light on and off. I've found a timer inexpensively, so if I set it to run for 3-5 hours nightly instead of all night, the solar charger should have no trouble keeping the battery up...unless a serious cloudy spell happens. And, since the bulbs are under 5 bucks, if they don't last real long, its not a huge deal.

I have used the 12vac hockey puck under-cabinet lights to light up enclosed trailers off of a deep cycle battery for years. They generate some heat but they are very bright and will work well.

If you are going to use solar to charge the battery I would highly recommend oversizing the solar panel by 1.5 times your estimate to replenish the battery and I would use a "smart" battery charge controller / maintainer. This will give you less of a chance of not being fully charged when you really need it and will prevent the battery from over charging.

 

[nuclearpete]

I have a 12v deep cycle battery to power my house in emergency. Would like to install 11 LED yard lights 10 watt ea. and 4 spots 40 watt ea. Am I on the right track or should I be installing a 12 v ac transformer.

 

[southalabama]

Looking around 2manys page. Good write ups on various projects.

 

[LS6 Tommy]

It should work off a car battery. Not for very long. A transformer uses 2 coils to change the voltage and current, indirectly of each other. If voltage goes up, current goes down. Only works with AC. Google "Mutual inductance" for better reading material.

Why bother with all the reading? You don't need the xformer to run on a car battery...

Tommy