Zonker's Railroad Lantern conversion to LEDs

If you try to use any of the white LED 6-volt replacement bulbs in your train lantern, the bulbs burn out quickly. Very quickly. (Think "flashbulb" here... a very EXPENSIVE flashbulb, if you try the MagLite LEDs at $20 US each!) This is because;

The problem lies between the way the lantern head is built, and the way the lantern batteries are designed. The regular incandescent bulbs (and I include halogen, Xenon, etc.) are designed, they don't care about polarity...so, there was no problem. But, LEDs do care about polarity... because they are Light Emitting Diodes, and a Diode is a one-way polarity device.

The image on the left below shows you the center and outside ring contacts of the lanern head, and the image on the right shows you the spring contacts on a rechargeable lantern battery, with the red circles showing you how the two contacts line up above the battery when the lantern head is attached.

Lantern batteries put (+) on the outside ring
Lantern head contacts
LED replacement bulbs need (+) on the center
Lantern battery polarity

The lantern battery shown in the image above shows how the positive ( + ) terminal touches the outside ring of the lantern head, while the ( - ) terminal of the battery touches the center ring.

When the LED makers looked at their market, they looked at flashlights using the "C" and "D"-type cells, with the positive voltage on the center pin, and the negative lead on the case, so that's the way the LED bulb-replacements were designed.

But, in a train lantern (using a normal lantern battery), the center pin contact is the negative lead, and the spring (which holds the case of the bulb) is the positive lead. You can see the bronze contacts down inside of the springs in this picture.

This is a typical lantern head, with the lenses and bulb holders removed. The left-hand contact is for the "spotlight" lens, and the right-hand contact is for the "flood" (wide area) lamp.
lantern head contacts

The REAL answer would be for the LED bulb makers to create parts which detect the polarity of the power source, and work no matter which polarity is presented. An acceptable alternative would be for the manufacturers to at least PROTECT the LEDs from incorrect polarity, instead of just burning out. (Or to make a replacement LED bulb just for train lanterns.)

In realty, the LED didn't burn out! It's the tiny circuitry inside that regulated the power to the LED which burns out, and then causes internal component damage. But, since you cannot service the micro-circuitry inside  these bulbs, they essentially become "disposable".

Initially, I tried to find a way to get into the lantern head, to try to change it (to swap the polarity), but I didn't have any luck. (Those things are TOUGH! And, if I had managed to get into them, I'd need to figure out how to seal them again to keep them dry and prevent corrosion. I didn't have any luck with hacking that hardware.

But, after working on one of the Train of Lights runs in 2007, I stopped at my local Fry's Electronics stores for batteries, and I found a lantern battery replacement that uses "D"-type cells for less than $3 US.

(Garrity Accessories, part number Z001G, shown at right.)

This was the answer...I could build a battery with reversed polarity! (It would be easier than hacking the lantern heads, and I could use it easily in any lantern!)

Since I had already burned out one MagLight LED bulb, I opted for a cheaper 1-watt LED from Nite-Ize, to go with the lantern battery insert, and I bought some 2500 mAh Ni-MH "AA" batteries, so I could hack!
Garrity battery replacement

The rest of the parts would be easy to acquire, but first I wanted to perform a test...how long would the 1-watt Nite Ize LED replacement bulb run using a four-"AA" Ni-MH (2.5 AH) battery pack under constant load. The answer was "more than 12 hours, with no visible difference in light output!", and that was good enough for me.

Parts needed:

Rough cost of the project: $42, plus about an hour of your time after shopping.

Battery notes:
  1. You can use alkaline cells with this project if you wish, but I prefer the rechargeable cells. Either of the LEDs mentioned above will put out sufficient light using Ni-MH cells.
  2. If you go to Fry's Electronics for your rechargeable cells, I have found that I REALLY prefer the Lenmar cells. They have a purple colored jacket, with a flame around the logo. These cells have much LESS internal resistance than others (which means that they hold their charge much better when they are sitting on the shelf, or in your grip) for a couple weeks.)
  3. If you decide to buy the Lenmar cells at Fry's, Look for the power capacity! Fry's charges the same for the 10-pack of "AA" cells, whether they are 2000, 2300, or 2500 milliamp-hours capacity. It's easy to tell the cell capacity with the Lenmar cells, as it is the LARGE NUMBER on the label of each cell. Look for 2500, or 2700 (2.5 and 2.7 amp-hours, respectively). The larger the number, the higher the capacity.
A side effect of this project is that the converted lantern weighs significantly LESS than a standard lantern!

Preparing the Garrity lantern battery replacement

Step 1, Trim the top springs

The springs on the Garrity lantern battery inserts are very stiff, and they are very tall. (The springs are nearly twice as tall as the springs on a normal lantern battery, and much stiffer then a regular lantern battery.)

Because the springs are so tall, and so stiff, you will have trouble twisting your lantern head back on if you do NOT trim the springs, and you risk shorting the Ni-MH batteries as well.

This is one of the hardest steps. I used a pair of tin-snips, but you may have OK luck with heavy wire cutters, or a dremel tool with a cut-off disc. Remove the top half of each spring.

Mark the top of the battery replacement, as shown in the image here. I used a silver Sharpie marker, since the case is black. This was to help me remember which leads should be which polarity.
Trim the springs

Step 2, remove one contact spring

The top spring (connected to what holds the normally negtive battery terminal) will make it hard to insert the "AA" battery pack. It is 'crimped' into the metal contact, but it can be removed. With some firm twisting, you can 'unscrew' this spring from the metal contact.

I discarded the spring, but some 'hardware hackers' may find a use for them.

The lower terminals on this side of the insert will support the "AA" battery pack, but will not be used electrically.
remove this spring

prepare the contacts While I'm in here, I also marked the polarity of these two tabs, which are riveted to the two springs, to remind me where to solder the wires from the "AA" battery pack. The silver Sharpie marker really makes a good contrast against the black plastic.

I also used some 600-grit sandpaper to rough-up the surfaces of the contacts where the leads will be soldered, and then I pre-tin them. Be careful abut the heat of the soldering iron, since the metal is riveted through the plastic. If you heat the contacts too much, you will melt the plastic and weaken it.

I also pre-tin the leads from the "AA" battery pack. This further reduces how much heat will be needed to connect the wires to the battery contacts of the insert.

Step 3, Solder in the "AA" battery pack

Solder the leads as shown here, and let the contacts cool.

NOTE:The polarity of this connection is extremely important when you are going to use LED bulbs in the lantern!
  • The normal polarity of this battery insert is marked on the top of the case, near the springs. You can see the silver Sharpie marker polarity reminders near the solder connections in the photo to the right.
The leads are dressed 'towards the center' of the lantern battery replacement. This will reduce tension on the leads during installation and removal of the "AA" battery pack.
solder the battery pack

Step 4, Install and secure the AA batteries

Install the "AA" batteries into the "AA" battery pack now, with the pack laying on it's side next to the Lantern Battery replacement.

Install the AA cells

Install the "AA" batteries into the "AA" battery pack now, with the pack laying on it's side next to the Lantern Battery replacement. Make sure you get the polarity of all of the "AA" cells correct.


position the AA battery pack

Position the AA battery pack on the lantern battery replacement, so that the end of the AA battery pack with the leads coming from the pack is positioned up against the lower spring of the lantern battery replacement. Then you can push the other end of the AA battery pack (indicated by the green arrow), pushing down against the spring. Tuck your leads under the AA battery pack.


Seat the AA bettery pack While still pushing the AA battery pack against the lower spring of the lantern battery replacement, also push the AA battery pack down into the lantern battery replacement, so that it is nestled against the lantern battery replacement.
the insert and the NiMH pack

velcro strap on battery pack

Securing the battery pack

Because of the "spine" in the lantern battery replacement, the "AA" battery pack will tend to rock a little bit, so I use a strap of hook-and-loop Velcro to strap the "AA" battery pack to the lantern battery replacement. This also serves to keep the "AA" cells in the battery pack during rough handling of the lantern.

In this picture, you can also see the purple Lenmar Ni-MH "AA" cells, and you can see the 2500 mAh capacity information on the label. (I have found the Lenmar Ni-MH batteries have been much better at holding their charge for weeks at a time than 6 other brands that I have tried. Your mileage may vary.)

This picture also shows you "storage compartment" built into the base of these Garrity lantern battery replacements. With some light-weight foam, or some tissue, you can store a couple extra LEDs or incandescent bulbs in the storage drawer.

Install the "AA" batteries into the "AA" battery pack now, with the pack laying on it's side next to the Lantern Battery replacement.

Next, pick up the "AA" battery pack, and tuck the end of the "AA" battery pack against the spring below the negative lead. (This is the spring opposite from the one you removed earlier.) As you press the other end of the "AA" pack, so that you are compressing that lower spring, You should be able to lay the "AA" battery pack flat within the body of the lantern battery replacement.

Incandescent bulbs

Preparing the Lantern Head

Shown to the left are a Halogen bulb (left side) and a normal incandescent bulb (right side). This halogen buld is from MagLight, and includes a focused lens at the top of the bulb.

This is relatively easy if you are only using the Nite-Ize 1-watt LED replacement bulb, because it really is the same size as a normal incandescent bulb, in all of the dimensions that matter.

The case diameter on the Nite Ize (the left-hand bulb in the image at the right, with the large dome lens) is the same as for standard bulbs (0.365"), while the MagLite bulb case (far right) is 0.450". (See the micrometer images below.)

LED bulb case diameter differences

Normal bulb diameter

The micrometer readings tell the story. The MagLight LED in the picture to the right has a slightly larger diameter, which is why it is harder to install in the spring of the Spot position.

It will be hard to put the MagLight LED into the Flood spring as well, but not nearly as hard as the Spot spring.

You can also see the center contact on the Nite-Ize LED, but the center contact on the MagLight LED is recessed in the black ring in some versions of this LED. If yours is recessed, you will need to sand down that black lip a but, since the contact for some lantern heads is a flat contact, instead of a round pin.

MagLite bulb diameter

Not all LEDs are created equal

I've said this a number of different ways on this page, but only because I think it's important to consider the pros and cons of the different LED choices.

Because the MagLite 3-watt LED has a noticeably wider case diameter, it does not fit well into most of the lantern head springs that I've tried. (See the fuzzy image here I'll try to get a better picture when I do my next conversion. The Nite Ize LED drops right into the springs. but the MagLite wants to sit on top.)

Since the springs do not come out of the lantern, you're stuck trying to twist and grab the spring by reaching around the polycarbonate frame of the lantern head. It's a tough task, especially with only two hands. You might want to keep the head on a lantern without a battery to hold the head still. (If your lantern has a flat contact for the bulb position, you should trim the black lip of the MagLight LED before installing it in the lantern.)

You should probably try your MagLite LED bulb in a 4-cell flashlight before you attempt this next step, just to make sure the bulb is working, before you go to too much trouble.

LED fit in lantern head

This is the MOST difficult step of this conversion!

If you want to use the MagLite 3-watt LED bulb replacement, you cannot just force the spring down under the bulb case, because you will short out the terminals below the springs. What you need to do (PATIENTLY!) is try to widen the spring diameter by twisting it, or you can try to 'spin' the MagLite bulb into the spring. This is difficult work, and it will take time, and patience. (But the work is worth the effort. I use a MagLite 3-w LED in the Spot reflector, and a Nite Ize 1-w LED in the Flood position. The 3-watt doesn't work well as a flodlight.)

If you can, hold the MagLite bulb above the spring with your thumbs, and then use your fingernails (or small screwdrivers) to try to pull the edge of the spring up the outside of the MagLite bulb case. You only need to get the bulb down a couple of layers into the spring, and then it will twist down more easily. Did I mention this trick takes a LOT of patience?

When you are done mounting your LEDs into their springs, place the bulb covers on them, and then make sure that the power switch is in the center ("off") position.

Reassembling your lantern

Once you have your LED bulbs installed, you are ready to put your new battery insert into the lantern body, and attach the lantern head. If you have trimmed the springs down (as noted in Step 1 above), this should all go together smoothly. Time for the 'smoke test'.

Do NOT stare into the LED bulbs! Even the 1-watt bulbs are very bright!

Move the switch to the either position, and see if the LED lights. If it doesn't light immediately, try the other switch position.

If neither LED lights, disassemble the lantern, and check the batteries in the "AA" battery pack...

If only one LED lit, check to make sure the other one is seated in the spring properly. (This can be a problem with the MagLite bulbs. They need to be pushed down well into the springs. Some versions of the MagLight LEDs have a lip around their center contact...if your lantern has a flat contact for the bulb position, you should shim the black lip before installing the LED.)

About the incandescant and LED choices

The halogen bulbs (from MagLight and other makers) use a LOT of power, approximately 2.5 times more power than the regular incandescant bulbs from Fry's and Radio Shack. You do get a lot more light from the halogen bulbs, at the cost of shortened battery life. This was the original reason that I looked into the LED options.

No matter what type of batteries you will use in your lantern, the batteries will last basically 3 times longer if you are only using the 1-watt Nite-Ize LED, versus the 3-watt MagLight. I found the Nite Ize LED provided a sufficient amount of white light to do my job as a brakeman, when using it in the Flood position. However, I wanted more light in the Spot position.

I should also note here that the Nite Ize LED that I used will work in any flashlight which has between 2 to 6 cells, automatically adjusting to the voltage (which means it will compensate for the lower voltage of the Ni-MH batteries).

I've used the MagLight LED in a 2-"D" cell MagLight flashlight, and I'm happy with the amount of light it gives off, as well as the beam pattern when used in the adjustable flashlight. So, I was willing to try spending another $20 to try it in the lantern project (because I needed a 4-"D" cell version for the lantern, and my original LED was for half the voltage.)

I threw away the package from the MagLight LED before I started taking pictures for this project, and I haven't been able to find the 4-cell versions in the local stores lately, so I haven't been able to buy another and tkae it's picture in the store packaging. Sorry.

Nite Ize LED

My first converstion

This lantern head has a few years of use, and there are some signs of rust around the edges, but the mirror surface is still in good shape, and the polycarbonate base is still intact.

The picture at the right shows my first lantern conversion, with a MagLight 3-watt LED in the Spot reflector lens (the 9-o'clock position) and a Nite Ize LED in the Flood socket (the 3-o'clock position), with a normal incandescent bulb as a back-up (6-o'clock potition), just in case.

You can sort-of see the difference of the LED elements under the different lenses of each LED. The smaller LED on the left is the one that throws the most light!

Lantern with 1-w and 3-w LEDs

Nite Ize Flood 
      light pattern

Here's how well it works

The image to the left is showing a stand, in my back yard, near midnight, on a cloudy, rainy night. The stand is holding the lantern 4 feet above the ground, simulating me carrying it on my arm.

The light is a 'cool white' (bluish, not yellowish), and the amount of light around you is slightly more to that of walking on a clear, full-moon night.

The idea for this photo was to show you the light pattern of the 1-watt LED being used in the Flood position. Notice the light in the nearby chair. You can tell the ring from the lantern base, but there is a fair bit of light even close to the 90-degree angle from the front of the LED lens. It also throws a good amount of light down, so you can see where you are walking. (Most of the light points down, you do NOT get a lot of light if the lantern is sitting on the ground.

Almost all of the light from the MagLite LED goes forward. It works well in the Spot position, but I don't recommend it in the Flood position.

The battery life running the 1-watt Nite-Ize LED, using 2 amp-hour (2000 mAh) Nickel-Metla-Hydride (Ni-Mh) AA batteries is over 18 hours(*) on a charge before you start to notice a loss of light output.

* Because the Nite-Ize 1-watt LED has a built-in regulator, and can run on only 2 cells, you won't see any light loss until the batteries are nearly completely used.


What's the difference between 1 and 3 watts?

Like I said, if you want to be able to sling some light a good distance, you will probably want to put the MagLite 3-watt LED into the Spot position...but you need to be prepared to work for it. Due to the larger case diameter, getting the case of the Mag-Lite LED into the spring will be the hardest part of (what I consider to be) a fairly easy project.

In the photo on the right, I pointed two lanterns at the fence 15 feet away. I used the Spot setting on both lanterns. The left side is the 1-watt Nite Ize, and the right side is the 3-watt MagLite LED.

Remember, that watts are a measurement of power. That means that the 3-watt LED will consume that much more power from your batteries (Which means your operating time on batteries will be reduced to 1/3 of the life you saw using the 1-watt LED.)

Spot LED comparison

David K. Z. Harris, copyright 2008