[MOVED]Replace flashlight bulbs with LEDs?

[Jennifer Murphy]

Hi,

I am a new user. I have a little project I need help with. I am not sure which forum to post it in.

I want to replace the lights in a 60-year-old dollhouse. The current lighting uses flashlight bulbs run off a transformer. I want to use LEDs and I would like to replace the transformer with a battery pack. I have done quite a bit of research, but need help making sure the components are compatible.

I was about to post it to the Electronic Elementary Questions forum, but then I noticed the Analog Circuit Design forum. The latter seems more appropriate. Or is there a better place? Can someone direct me?

Thanks

 

[thylacine1975]

Re: Which forum (new user)

Heya Jennifer!

Well, here worked ...but probably the electronics elementary questions would be the better bet.
To your problem though - replacing the lamps with LEDs sounds like a good idea! What in particular can we help you with? Aside from being polarity sensitive (i.e. they only work one way around), LEDs differ from light bulbs in that they need the current to be controlled through them. In practice this is simply (and cheaply) achieved by a single series resistor of a value dependant on the a) battery voltage, b) number of LEDs, and c) type of LEDs.

So, the main things we need to know are:
* How many LEDs are you trying to light? What sort are they (e.g. individual coloured units or pre-packaged modules/lamps)?
* What type of battery did you have in mind (what fits?)

 

[Jennifer Murphy]

Thanks for moving this thread to the right forum. Here’s the project that I need help with.

We have an heirloom dollhouse built 60 years ago. It’s an amazing piece of work with incredible detail. It’s all in pretty good shape except for the lighting system. There is a little light bulb in the ceiling of each room and hallway. Most of the bulbs are burned out. I could only get one to work, and that was very dim. I spent a little time trying to see if I could get the other light to work without success. I ended up fixing up the rest of the dollhouse and giving it to my granddaughter for Christmas. I told her that I would fix the light later.

So now that’s what I’d like to do. I’ll first describe what I know about the current wiring, then explain what I propose to do. I would appreciate any suggestions or help in getting it right.

There are markings on the bulb bases, but they are almost impossible to read. As best I can tell, they say 2.5V and 0.3A. One says "GE50". Here are a couple of photos: Image - TinyPic - Free Image Hosting, Photo Sharing & Video Hosting & Image - TinyPic - Free Image Hosting, Photo Sharing & Video Hosting. After doing a little research, I believe them to be #14 bulbs with an E10 base like these: **broken link removed**. I tried to get a voltage reading at the light sockets, but there is barely enough space for the probes and my hands and I can’t see into the sockets. All of the sockets seem to be hot, but the readings were all over the place.

On one side of the house, there is a hole through which extends one of those very old cloth-covered 110VAC power cords. The cord does not appear to be damaged at all, but there is no strain relief around the hole.

The power cord goes into a sealed box underneath the house about 6" x 8" x 1". I assume it contains a transformer of some type. It is glued shut, probably to keep small fingers out. I haven’t broken into it yet. On the back wall of the transformer housing are 4 very old push-button style switches. I forgot to take a photo and I cannot find anything similar. They are black, with a round base, and a button that looks more like one of twist heat controls on old toasters. They are also loose. But they seem to work.

I would like to replace the power cord and the transformer with a battery pack (first choice) or one of those 12V wall wart transformers. I’d really prefer the battery pack to eliminate 100V entirely and then there would be no cord to trip over. Then I’d replace the #14 bulbs with E10 base LEDs.

I found the LEDs at LEDLight.com. A sales rep was very helpful. They make several versions. He said that the flat and concave models spread the light better. The round ones are more for flashlights. Here are the links:

• Flat: Flat LED E10 Screw Base LED Bulb - Automotive LED Lights - LEDLight
• Concave: Concave L.E.D. E10 Screw Base L.E.D. Lamp - Automotive LED Lights - LEDLight

And they come in 4-5 colors, which could be fin for the child.

They also sell battery packs. Most of them hold 4 AA or AAA (1.5V) batteries in series for a 6V power source. Here are a couple:

• 1x4 AA: Battery Holder AA 1x4 with Wires - Other LED Lights - LEDLight
• 2x2 AA: AA Battery Holder 2x2 with Wires - Other LED Lights - LEDLight
• 2x2 AAA: 4 AAA Battery Holder with wire 2x2 - Other LED Lights - LEDLight

Will this work? How many bulbs can I power with one setup using 8 AA batteries in series? The house has about 12 light fixtures in all. Can it handle a variable number of lights being on at the same time?

Is there a better way that doesn’t require 8 batteries? I have a little pocket flashlight with 9 LEDs that uses three AAAs and is so bright I cannot look directly at it. I also have a little keychain flashlight with one LED that runs on 1 AAA battery, also very bright. I see 1.5V LEDs from many sources, but none with E10 bases.

The other alternative is to use a wall wart transformer. LEDLight.com sells one for $15. Here’s the link: Power Supply LED Light 12 VDC 25 Watt - Low Voltage LED Lights - LEDLight. The sales rep said is it intended for LEDs. This doesn’t get rid of the power cord, but it does eliminate the need to replace batteries.

So, I’d appreciate suggestions for the best solution. The dollhouse is currently clear across the country, but we will be visiting in a few months. My plan is to make a bench top model and get it all working, then take it to install at the next visit.

What’s the vote: batteries or wall wart?

One final question. Is there some way to wire up 9V batteries to get close enough to 12V to light the LEDs?

Thanks in advance.

 

[thylacine1975]

You've certainly given it some serious prior planning!

OK, that info helps narrow the range of options a lot. Given that you're going to preserve the original wiring and screw bases, the choice is fairly clear: wall wart (alas?). I'll explain...

Those screw base LEDs are a nice (read: convenient) solution as they incorporate that additional current limiting resistor I mentioned earlier. Their web page states: ".02 mA@13.8VDC 345mW" which is in error, since the power (345mW) is given by the voltage (13.8VDC) multiplied by the current: .02mA is (significantly) suspiciously low. Working the numbers backwards yields a current of 25mA = 0.025A. I can see where their typo comes from

Since the actual light-emitting part (the diode) of each LED typically requires ~2V to operate, a common approach to (efficiently) lighting a large number of LEDs is to string them all in series such that: n (LEDs) x ~2 volts < the supply voltage, and set the current (via a resistor) accordingly. While this approach is efficient, it would also require you to rewire the light fixtures. Don't be alarmed though (!) - all this is moot since the resistors are integrated into the LED screw-bulb assemblies and you are denied the ability to adjust it. Consequently, *each* LED will consume ~25 mA from your 13.8 V supply (more on the supply in a sec...). N.B: This assumes your light fixtures are all presently connected in parallel and the house's integral transformer supplies 2.5V to each fixture. Since you mentioned that only one bulb works, that suggests a parallel connection... so we'll run with that.

12 lamps x 25 mA = 300 mA. [= the current for just one incandescant bulb. Heh ]

Batteries store a fixed amount of energy; specified in Ah (Amp hours) - which is the product of how many amps you can draw for how many hours before the battery is "flat". Even for a fixed battery size (bigger batteries generally have higher Ah ratings), the numbers vary all over the place depending upon the manufacturer, chemistry and cost. For AA's, I recall seeing values over a range of ~1 - 3 Ah, with a value of 2Ah being conservatively common. The battery life is then determined by:

Hours = Capacity (Ah) / Current (A)

For your application, this is: 2 / 0.3 = 6.7 hours. i.e. leaving the lights on will flatten 8 x AA's in one evening. This is probably too short.
Bigger batteries will certainly extend this time (D cells store ~ 12Ah), but raise the replacement cost. 9V batteries (due to their smaller size) only store ~ 0.5 Ah. Your call, but I'd probably lean towards the wall wart. (The unit you've cited is more than adequate, since it will supply 2 A and you only need 0.3A.)

As you've noted (in your flashlights etc), there *are* ways to eek greater efficiencies/battery configuration flexibilities out of LEDs but they all rely on having direct electrical access to the diode itself. 'Bare' LED diodes in screw bases seem to be hard to come by.

With regards to the power supply voltage, it's really quite non-critical. The LED lamps you found will likely start emitting light at some voltage above ~2-3 V and get progressively brighter as the supply is increased, reaching their specified intensity at the stated value of 13.8V. Aside from dimming the LEDs, decreasing the supply voltage will also reduce their current requirements. At 9V for example, I'd expect the current consumption to fall to ~15 mA per LED = 180 mA for all 12 bulbs. Hmm, that means ~2+ hours life from a 9V battery...

Finally, yes - since the lamps are all (assumed to be) connected in parallel, you can certainly light any number of them independantly.

I hope that helps! I know how much my daughter would enjoy a doll's house like that

 

[Jennifer Murphy]

Wow!!! That is exactly the kind of information that I was hoping to get. I never even hoped that it would be so detailed and clear. Thank you so much for taking the time to enter all that.

Now I just have to digest it all. It kinda makes me want to dig out my old college physics book and read up on the Wheatstone bridge!

One deterrent for the wall wart was the kids tripping over the power cord. But it I mount the plug on the side of the house, it can be easily unplugged.

One thing puzzles me. If 12 of these LEDs will drain 8 AAs in 6-7 hours, how can my little penlight generate enough light to blind me and run for hundreds of hours on one AAA?

If I get it all working. I'll post a photo of the dollhouse. LEDLight.com even sells some light strings that I may be able to mount under the eaves as Christmas lights. Here's a link: Flexible 12 Inch LED Light 1210 SMT Low Voltage 12 Volt DC - Low Voltage LED Lights - LEDLight

Again, many thanks for this amazing response. I'll have to buy you a Foster's (or a case).