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Mod #81: 12 Volt Fluorescent Lighting on the Cheap

Posted By ModMyRV On May 10, 2009 @ 12:31 pm In electrical, lighting | 12 Comments

This mod comes to us courtesy of RV.net senior member Gdetrailer, otherwise known as Gregg Berry, and is copyright with all rights reserved.

For boondockers and anyone who just wants more light than the typical RV incandescent lights you just can’t beat fluorescents. 12 volt RV fluorescents tend to cost an arm and leg, and for the most part look rather cheap, especially the economy versions (LOL they still cost $30+). This mod details a way to modify low cost fluorescent lighting fixtures to correctly work off your RV’s 12 volt power system.

Mod Difficulty:

While browsing around Home Depot, I found some battery powered single bulb fluorescents, 4w 6V DC ($5) and a 8W 12V DC ($9). Now you know the 6V ones will present a problem voltage-wise but most folks would think that the 12 volt models would be fine hooked up to a RV 12 volt system. Not so, this is a case were 12 volts may not be the same!

The 12 volt battery light takes 8 AA batteries. Dry cell batteries when new typically have 1.6 volts. So 8 new AA batteries would give 12.8 nominal voltage. Generally most devices will tolerate up to 10% over design voltage which would be 14.08V in this case.

Now in a RV with the advent of multistage charging your typical RV 12 volt system can see voltages as high as 15 volts. This will definitely let some smoke out of your low cost battery fluorescents.

Not to worry. I have a low cost solution to prevent damage and even be able to use the 6 volt versions. Even better yet is the cost, $1.50 per fixture (Radio Shack) or as low as $.50 per mail order. It is a voltage regulator IC, the LM78xx series, 3 pin, handles 1A of current, handles up to 35V DC on the input. This is more than enough to use with these battery powered fixtures. It is overload protected, in case of a short or overload on the output it will reduce the voltage down to 1.2V if needed.

The regulator does draw a small amount of power, typical 5ma which is a small price to pay to get low cost fixtures. I used a LM7806 for the 6V fixtures and LM7812 for the 12V fixtures.

Two possible combinations of mods, #1 easy mod, the regulator is used external to the light, basically regulator is mounted in a small box then output is plugged into the light. Note: you will need a small box to house the regulator and a coaxial power plug to fit the light. This also will allow fixture to still use batteries.

#2 Advanced mod: this is the one I have done. The regulator is mounted inside the battery compartment and hard wired to the internal inverter. This mod will prevent the use of internal batteries since the regulator is mounted in the battery compartment of the lighting fixture.

DISCLAIMER… The included photos and modifications only apply to the Amerelle brand lights I purchased at Home Depot. The design of the circuit boards is subject to change so you mileage may vary!

Warning! The inverters do generate HIGH VOLTAGES. Do not power up the light fixture while case is open.

Warning! Do not apply power to the fixture without the bulb installed, damage to the inverter may occur.

Comments: I’m adding some errata info missed from my draft of this section.

The lights used for these mods I purchased some time ago from Home Depot (6 months or more), in searching the Internet I noticed that these lights are selling about $9 for the 6” 4w ( model 73025) and $11 for the 12” 8W (model 73040) through Online stores. Still not a bad deal though.

American Tack is the import company.

It is possible to use LM7805 (might be able to still purchase at Radio Shack) for the 4W 6V light, this was what I used for my first conversions. It does work but I did notice one of the lights sometimes doesn’t get full brightness. For this reason I recommend the LM7806 (would need to special order at Radio shack or buy through mail order) which has a 6V output.

These mods could be done for other brands of lights but you would need to figure out how to connect the regulator to the inverter. In this case the simple route is to add regulator in between power jack and the inverter, no modifications to the circuit board would be needed.

You can also bypass the power jack and run the power leads out of the light body.

OK, lets get to the internal mods..

4W 6V DC light

  • To open, push in the tab at the battery compartment. The battery door end will swing away.
  • Remove the clear lens and bulb.
  • Remove the white plastic sticker which is under the bulb.
  • Once the plastic sticker is removed the main body should split in to two parts.
  • Carefully remove the opposite end from the body.
  • Once main body is apart you will see the inverter board.

Now I decided to make my modification insert the regulator after the switch, on the 6V inverter it is a little more involved.

Parts required: LM7806 – 6v@1A 3 terminal regulator Optional but recommended: Heatsink, can be a small piece of metal or actual purpose made heatsink that fits inside battery compartment.

  • To do this I had to cut two of the circuit board traces (#1) then run a jumper to connect the trace ends that was cut (#2).
  • Connect the input of the regulator (LM7806) to the pad that was isolated (#3), this is one end of the switch.
  • Ground of the regulator is connected to the incoming 12V neg (#4).
  • The output of the regulator (#5) is connected to the same trace as #2 red jumper.
  • Alternate connection before the switch, left photo, disconnect red wire from the center of the DC jack, connect regulator input to the jack.
  • Connect regulator output to the pad where the red lead connects.
  • Connect regulator ground to the black wire on the DC jack.

You can see the detail of regulator in the photos above:

#1 is the input. Middle pin is the DC ground, mounting tab is also DC ground. #3 is regulator output.

I also mounted the regulator on a heat sink, mine is salvaged from old obsolete equipment. You can buy small aluminum heat sinks or even use a short piece of aluminum, copper, or steel. The idea is to provide a way to keep the regulator cool.

I also used a plug method for connection. This was salvaged from a old PC. You can also buy these but in a pinch you can wrap the wire around the pins and solder the wire to the pin. Use a small soldering iron. Do not use a gun. The regulator and heatsink fit into the battery compartment.

I had to cut notches in the heat sink to get past some ribs molded in the plastic. This also helps to keep the heat sink from moving around.

The light is ready to reassemble and test.

12V 8W light

  • To open, remove the screws that are on each end.
  • Remove clear cover and bulb.
  • Carefully remove the white plastic that is under the bulb.
  • With both ends removed the two halves of the main body will separate. I did have one of mine that was glued at the battery compartment seam. Using a knife lightly cut the glue.

Parts Required: LM7812 – 12V@1A three terminal regulator, heat sink. This light will draw more than .5A so a heat sink is a must. This can be a piece of metal or purpose made that fits inside the battery compartment.

  • Be careful to not lose the two metal pieces (one on each end) since these are used by the screws to hold the ends on.
  • Remove the red wire (see pictures above), create a solder bridge from the center pad (where the red wire was) to the pad that is to the left (#1 of right picture).
  • Solder regulator (LM7812) output to the pad beside the two pads you bridged (#2)
  • Remove the old red wire from the power jack and solder the regulator input wire to the power jack (#3)
  • Solder the regulator ground wire to the black wire on the power jack (#4)

I re-purposed an old 3.5” floppy drive power connector. I rewired it so input is red, ground is black, output is yellow, and removed 4th wire (unneeded).

If you don’t have a connector, just solder wires to the regulator terminals. Use a small soldering iron. You might want to wrap some black tape on the terminals. Do not use a soldering gun!

See picture above of completed modifications with regulator installed in the battery compartment.

Reassemble light. Don’t forget to install the small metal pieces at each end.

One draw back to the switch modification is the fact that the light switch function has been changed. What was OFF is now the ON position. To get around this I peeled the switch sticker off and flipped it. I had to cut off one end of the label. Light is now ready to test!

TipNow that you have low cost fixtures, you can dress them up if the plain white plastic is not to your liking. You can make a small wood box (or metal box painted to your favorite color) to surround the light. Then take a piece of Plexiglas (1/8”or thinner would be fine) cut to the size of the box. To further hide the light, simply take sand paper and lightly sand one side only of the plexi, install with the sanded side in towards the light. You can do this by hand or with your electric sander. The sanding will make the plexi opaque which will hide the light and provide a professional touch.
TipHave one of those Thin Lites fixures with a dead inverter/ballast? Well it may be possible to use two of the inverters from these lights (one for each bulb) to replace those expensive Thin Lites inverter/ballast ($30 for one of those). I have not tried this idea but some of the Thin Lites do use 8W bulbs. A bonus to this is for boondockers, add extra on/off switch to the fixture and you can select one or both lights depending on your needs. I would however suggest if you decide to try this that you should still use a voltage regulator to prevent high DC voltage damaging the inverters (you would need one LM7812 for each inverter). To fit in the fixture you can unsolder the board with the battery terminals, then fabricate a insulated mount for the boards. In this case for longer life of the inverter (8W version) you can also add a small heat sink to the inverter power transistor if you have the space. The tab of the transistor may not be electrically insulated so you should ensure that the transistor heat sink can not touch any metal.

ModMyRV recommends these parts for this mod:
12V Fluorescent Lights
7805 +5V Voltage Regulator TO-220

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