The above screen shot is of the wiring harness in the Tam Valley Forney modified by Duncan McFee. His Company, Tam Valley Depot sells the DRS1 receiver. The receiver receives DCC signals via radio from the transmitter I will discuss a bit further down the page. Here is a screen shot of the receiver from the Tam Valley Depot web site. As you can see, it is quite small – 1 5/16″ x 3/4″.
Modelers source their own batteries, but Gordon makes a number of recommendations in his e-book. Individual Lithium Polymer battery cells have a nominal voltage of 3.7 volts. Two wired in series give you 7.4 volts (above image) and three give you 11.1 volts. I hope to standardize on 11.1 volts.
Basically, there are two choices. One is to buy a battery pack from a radio control dealer or hobby shop with the appropriate voltage. The second is to buy individual cells and assemble the packs yourself which gives more control over pack footprint. Wiring within a battery pack wired in series is not daunting (red to black, black to red, etc.) One of Duncan’s recommendations is of a Polymer Lithium Ion Battery – 400mAh from the SparkFun web site.
These 3.7 volt cells are around $7.00 apiece and include a PC that provides over current, over voltage and minimum voltage protection — the three conditions that are leading causes of Li-Po failure. Height is 35.5 mm, width is 25.5 mm and thickness is 6.7 mm. A stacked pack of three would have a thickness of a bit over 21 mm. For those of you that are metric impaired, there are 25.4 mm per inch.
SparkFun also offers a 3.7 Volt 110 mAh Li-Po battery. Its dimensions are 28 mm high by 12 mm wide by 5.7 mm thick. A stack of 3 would have a thickness of just under 18 mm. The pattern also has a PC that protects against ver current, over voltage, and minimum voltage.
A third option is a 240 mAh 3.7 volt Li-Po offered through All-Battery.com manufactured by Tenergy, It also has PC board protection, Dimensions are 25 mm high by 20 mm wide by 6 mm thick. A three battery stack would be just under 19mm thick,
In summary, three different batteries at three different footprints offer three different capacities. The best battery will be the one that offers the greatest run time given size constraints. Run times are very dependent on the current draw if the engine,.
One thing the above harness doesn’t show is a switch to turn the power off from the battery. Duncan recommends a switch that is displayed in the following modified harness image. The switch os from Polulu.com and includes a push button to toggle on and off. Gordon recommends substituting a reed switch which can be turned off by a magnet.
The Polulu.com switch shown in the harness is an earlier version. I plan to go with the later version which is the Mini Pushbutton Power Switch with Reverse Voltage Protection, LV. This switch is 0.6″ x 0.7″ x .0.12″. You can see the mini push button in the lower right portion of the board. The Polulu switches go for around $4.00. Depending on the Loco, I may use the mini push button switch and skip the reed switch which is available from DigiKey.com.
Transmitter Wiring – Existing DCC
Tam Valley Depot also sells the DRS1 MKIII Transmitter.
Transmitter Wiring – Full Wireless DCC
The disadvantage of the above approach is that the NCE throttle would be tethered at multiple points along the layout facia. While NCE offers a wireless radio throttle, it uses the same frequency as the DRS1 Transmitter.
A second option involves using a CVP Airwire T5000 wireless throttle. It sends a full DCC signal to the receiver and supports up to 16 channels and multiple engines per channel. Rather than using an existing DCC system, it functions totally independently of any form of track power. Apparently on Channel 16 it can communicate with the DRS1 Receiver. However, if multiple throttles are being used and ll set to Channel 16, there may be interference.
On the other hand CVP makes a receiver called the Convrtr that accepts signals from the T5000 and performs the same function as the DRS1 except it supports all 16 channels. The board is larger and nearly twice as expensive. Dimensions of the Convrtr are 0.8″ x 2″.
In theory a mix of both receivers could be used with the Airwire T5000 functioning as the transmitter.
Transmitter Wiring – Full Wireless Non-DCC
DelTang of the UK makes a system that transmits using the 2.4 Megahertz radio channel. It is a proprietary non-DCC system. The receiver costs $46. It is very small as shown in the following image.
The transmitter can be bound to up to 12 locomotives. It is available in kit form for $38.
This is a fairly ideal system for powering locomotives that are non-DCC, or for which only basic functionality is needed. One of my Shays is non-DCC. All of my garden railroad engines are non-DCC.
The fact it operates at 2.4 megahertz is also a major plus in that there would be no radio interference with either of the other two systems. It supports 2S and 3S Li-Po packs so my standard battery pack configurations would work with this setup.
Would it make sense to run a hybrid system? I think it might. Use the DelTang to power engines that are non-DCC or where bypassing DCC would still allow the level of functionality I desire, Also use it in situations where space to store a receiver and batteries is very limited. I think of the critters I want to run. Use a system like the NCE/Tam Valley Depot combination to power locomotives where more space is available and where the use of sound is a plus.
Of course, battery powered engines need to have their batteries charged periodically. Li-Po batteries are very sensitive to how they are charged. In addition, individual cells in multi-cell packs need to be balanced. There are three charging choices here.
- Charge through the track. This means at lest a portion of the track needs to be powered. It also means that track voltage would need to be rectified and the charge rates managed. I am not crazy about this option as I have no experience with Li-Pos and don’t want to be building circuits.
- Charge through a connector in the engine. This might be a viable long-range solution. But over the short haul I want to inspect the Li-Pos on a regular basis.
- Remove the batteries for charging. This is the approach I am going to take over the short haul. Thought needs to be put into how to make removal easy. But the advantage is that a discharged battery pack can be swapped quickly for a charged pack for longer sessions.
The above decision means considerable thought needs to be put into not only space for batteries and other components but ease of swapping. Duncan recommends going with a sophisticated battery charger. He likes the HiTek X1 but is not specific about the version. I like the HiTec H4 AC/DC. It is capable of balanced charging on 4 battery packs simultaneously. If I buy this $200 charger, I guess I’m pretty committed to battery power. However, I do have a garden railroad hiding under mulch in my back yard. That railroad will be brought on line this summer and will definitely be a battery powered railroad. Of course large scale locomotives have a lot more space to hide batteries that will need to be charged.
This page has laid out a number of available options. There are many others. As additional work is done on the approach I will take, links to those posts will be added below this post.