12V bulbs

kicknargel

kicknargel

Well-Known Member
I can't believe I'm struggling so hard with this.

I'm building props that need about 10 light bulbs. These need to be battery operated units. The bulbs want to be about 2" diameter clear. These will need to run for about 40 minutes on a charge.

So I'm looking at 12v, figuring that's the easiest to get batteries for. I'm figuring about 15w max to be able to run on a reasonably sized/priced battery (as is I'll need 18-20 Ah which is a high-end motorcycle battery). Trouble is, I can't find any 12v 15w clear bulbs in the 2" range.

Any suggestions on a source? Or another way to look at it? If I get a 24v 25w bulb and run it on 12v, will it be similar to 12v 15w?

Also, does wattage more-or-less equal brightness, regardless of voltage?
 
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Auto supply stores? Most RV interior Lights are 12v (if theyre not LEDs). Same with trailer lights. Should be able to find something that will work.
 
Motorcycle battery connected to an old computer UPS with the beeper removed. 7 watt 120 volt clear sign lamps plugged in. Plug the ups in for a second so it kicks on and you are set to go! (We all have a graveyard of old UPSs around!)
 
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Call911 said:
Auto supply stores? Most RV interior Lights are 12v (if theyre not LEDs). Same with trailer lights. Should be able to find something that will work.
Click to expand...

Funny enough you'll have more luck for 12v A Lamps at WalMart than auto supply stores.
 
There are lots of specialty lamp store online. I have found low voltage lamps from many different online suppliers. My go-to for 12V A-lamps is Grainger. Are you specifically looking for globe shaped lamps or would A-lamps work?
 
Thanks, folks. Dr. Pinto, those are better than any I found (internet searching can be fickle), although slightly small and bayonet sockets seem to be a pain. I also really like the idea of using a UPS.

However,

Looks like I'm going with a (nine, actually) 150W automotive inverter (the highest wattage than has no fan) (Buy.com - Tripp Lite PowerVerter 150-Watt Ultra-Compact Inverter). Then I can use 120v bulbs and have a lot more options. And the 15w, 120v globes are candelabra base, so the wiring is easy with a Christmas stringer (watching my rating, of course). My only worry and what I'll be testing is that the inverter will switch off when voltage drops, so if the batteries aren't fully charged, or aren't enough to make it, the thing will snap off rather than slowly fading out. But that might just mean I have to spend more on bigger batteries.
 
kicknargel said:
My only worry and what I'll be testing is that the inverter will switch off when voltage drops, so if the batteries aren't fully charged, or aren't enough to make it, the thing will snap off rather than slowly fading out. But that might just mean I have to spend more on bigger batteries.
Click to expand...

Find a friend who has a fishing boat and borrow his/her battery. Car and motorcycle batteries are designed to take a large load for a short amount of time, just long enough for the engine to start and the car's charging system to take over. You need a battery designed to take less of a load for a much longer time. The batteries used for electric trolling motors are known as "Deep Cycle Marine" batteries. They have a much higher reserve capacity than car batteries. Get your hands on one of these and you're all set.
 
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Slapping a big fat capacitor across the battery will also help a lot! A lot of car audio stores sell them for use on those insanely large car sound systems.

The reason they work is that as the battery voltage drops, a waveform appears on the battery DC from the draw of the driver on the inverter. The inverter kicks off when the bottom of the waveform crosses the threshold. (Usually about 10 to 11 volts.) The cap gets rid of the waveform so the inverter won't trip until the true battery voltage drops that low. Mount the cap as close to the inverter as possible and keep the leads between the inverter and cap as short as possible.

Although this is far more important a factor with the "Thumpa-Thump" eardrum bursting bass the car audio produces, it still helps a lot with flat draw loads.

Tons of the out there. Ebay sample here- http://www.ebay.com/itm/2-FARAD-CAR...818?pt=LH_DefaultDomain_0&hash=item20c50bcaba
 
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DrPinto said:
Find a friend who has a fishing boat and borrow his/her battery. Car and motorcycle batteries are designed to take a large load for a short amount of time, just long enough for the engine to start and the car's charging system to take over. You need a battery designed to take less of a load for a much longer time. The batteries used for electric trolling motors are known as "Deep Cycle Marine" batteries. They have a much higher reserve capacity than car batteries. Get your hands on one of these and you're all set.
Click to expand...
Golf cart batteries have tons of power too. They aren't sold specifically in the marine market but they are commonly used for inverter installations.
 
Gel-cell power chair batteries are my friend. I've been using them a couple of years now for lighted scenic pieces that need to be rolled on then turned on in place. a small inverter < cheap-o Harbor Freight style> will run a low wattage 120 v flicker bulb for a long time.
 
Many newbies are very surprised when they find out how much power is pulled from batteries with inverters. Here is an example . . .
You are running an inverter from a 12 volt battery and supplying 120volts to a Light Bulb that is pulling 120watts. So 120watts divided by 120volts equals 1 amp to power the Light. The inverter is putting out 120volts and the Light is using 1 amp of current. To go from 12volts up to 120volts the amps get multiplied by 10, so the 1 amp pulled by the Light at 120v will be 10 amps coming from the battery at 12volts. Any one battery will not last long when 10 amps is being drained out of it.

Now for the bad news, inverters need to use power too. They need some current to power the electronics that do the work of raising the voltage and converting it from DC to AC. This is in addition to the power needed to run your 120volt appliance. This is called the efficiency. Inverters run about 90% efficient, but under certain conditions can be as low as 80% efficient. It's been said that an inverter is the most efficient when it is operating at 1/3 of it's labeled capacity.
So we lose 10% of the power when it goes through an inverter, this changes the numbers a little bit. Instead of multiplying the 120volt amperage by 10, instead we multiply by 11 to account for the 10% inefficiency of the inverter.
The 1 amp Light Bulb is now pulling 11 amps from the battery

So if you want to use an inverter, you will need to plan your usage carefully in order to take care of your battery properly.
If you already use an inverter regularly, then you will already know all of this.

It is best not to let your battery get drained below 11.0 volts and always recharge batteries immediately to prolong their life.
Do it yourself alternative energy
 
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One last thought.... If you are near the time that you replace all the batteries on your emergency lights, you might want to order them a little early and kill two birds with one stone!

10 of them in series will give you 120 volts DC, which will operate 120 volt incandescent lamps just fine! This will eliminate the potential sudden drop-out. (You may only need 9 as a fully charged 12 gel cell runs at about 13.5 volts.)

When you are done, they can go into the emergency lights having undergone an extra "quality assurance test!"
 
I did not see anything that said size or weight was a concern. If that is true. Pick up a 8D battery. Most power gen dealers replace them every 2 years so you may be able to pick on up for cheap. An 8D runs on average 1300 CCA but are large enough to run lights for hours. I used to run a service truck radio, 1500 inverter, and work lamps for 8 hours on a single 8D.
 
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