Ever since I got the bug to build a garden railroad, I was certain of three things. One, that I would make as many mistakes as humanly possible; two, that those mistakes would cost me hundreds upon hundreds of wasted dollars; and three, I would use on-board batteries and radio control to power my trains. Sadly, my first two absolutes materialized in spades, but happily my foray into radio control was somewhat of a success.

There are several pure radio control systems out there, and they all have one thing in common. Namely, they all require the use of batteries to supply power to the locomotive. It doesn’t matter if it’s placed inside the locomotive, in a tender or trailing box car, you need a battery to supply power. I know many people consider Direct Cab Control (DCC) a viable alternative to track power, but it nevertheless uses power from the track to relay information back and forth to the locomotive. Pure radio control systems eliminate all electrical pickup from the track.

For anyone who cares, what follows is the step by step method I used to assemble a battery pack for a USA Trains GP 38-2 Locomotive. It’s not the only way to assemble a pack, and it may not even be the correct way. All I know is that it worked for me, and I think that anyone who is contemplating using battery powered radio control for their power source can apply a similar methodology to build their own pack for their particular engine.

STEP 1: Battery Choice
There are a few types of battery chemistries commonly used for radio control use. They are Lead Acid, Nickel Cadmium (NiCd), Nickel Metal Hydride (NiMH ), and the newer Lithium Ion and Lithium Ion Polymer cells. All of these batteries have one very important thing in common.... they all are rechargeable. Lead Acid and NiCd’s have been around since dirt under fingernails. They are relatively inexpensive and reliable. NiMH’s are also very reliable and now their cost rivals NiCds. Lithium Ion and Polymer cells are the latest and greatest, and if you live your life on the cutting edge, you’ll surly want to get your hands on these little gems.

For me, the best overall choice was the Nickel Metal Hydride cells. They come in familiar sizes such as AA, C, Sub-C, and D and do not exhibit the dreaded ‘memory loss’ affect associated with other chemistries. As an aside, Lead Acid and NiCd batteries tend to accept less and less of a charge if you don’t use them often, or if you forget to charge them after every use. Lithium cells were too expensive and charging them can be an adventure.

I decided to use the NiMH Sub-C size which is slightly smaller than the regular “C” size battery used in flashlights. Each cell is 1.2 volts and the radio control system I chose to use has a maximum input rating of 20 volts before blowing up. So, I thought that a 16.8 volt battery pack consisting of 14 Sub-C NiMH cells would be a safe bet (14x1.2 = 16.8 volts). Click on figure 1 to see a photo of the battery cell.

NiMH cells come in various strengths, expressed in milliamp hours (mAh). I chose 3300 mAh cells, which were middle of the road in cost and power. Larger ‘C’ and ‘D’ cells come in 5000 and 10000 mAh strengths and are fine for installing in trailing box cars but may be too large to fit in some locomotives. Anyway, I guessed that my 16.8 volt pack would produce an approximate run time of one and a half to two hours on a full charge. I ain’t complaining. For the record, I purchased my cells from Batteryspace.com at a cost of $3.86 per cell. Information about the exact cell can be found at: http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=1201

If all this talk about battery types has you rightfully confused, please remember this: No Matter What Type of Battery Cell You Use, Make Sure That You Purchase Cells with the Tabs Already Attached. Soldering tabs on a battery is more difficult than trying to get a Democrat elected in Utah. Save yourself a ton of trouble and order your cells with tabs.

STEP 2: Placement of Battery Pack
The GP38-2 is a relatively large locomotive, however its narrow body shell limits both placement and design of a battery pack (See Figure 2). The only place that seemed like a suitable location was at the rear end of the locomotive. The lead weight was removed from the rear end, (See Figure 3) and a battery holder box was constructed out of a spare piece of Masonite (See Figure 4). This box holds the battery pack in place and also doubles as a jig for pack assembly. Figure 5 shows the battery box in the locomotive. The weight of the battery pack is roughly equal to the lead weight that was removed, so no additional ballast had to be added.

STEP 3: Building The Pack
OK, now the fun begins. Given the narrow physical constraints of the locomotive, it was necessary to design the battery pack in layers. Figure 6 is a crude sketch representing the final design plan. The first ten cells are arranged horizontally in two rows (first layer), and the remaining four cells rest on top, perpendicular to the bottom cells (second layer).

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