The equipment I use to run Lithium Polymer batteries with my LEGO® trains. From top-to-bottom, left-to-right: The LEGO® Train itself (of course), a reputable battery charger, a custom-soldered Power Functions to JST battery lead, a LiPo battery (yellow) that is plugged into a Low Battery Alarm (red circuit board with green lights) and a “fireproof” bag to store the batteries when they are charging or not in use.
DISCLAIMERS:
First of all, I am not an electronics expert. For anyone interested in using LiPo batteries who is as unfamiliar with the topic as I was, I STRONGLY advise you to do some research on the matter. This article by a Canadian hobby shop is a great introductory guide, and even though they do mention that there isn’t anything to worry about if you handle your LiPo batteries with care, I will loudly repeat the “with care” part, and urge you to exercise caution. When you read up on the subject, you’ll surely find at least a few horror stories about these batteries exploding. A forum post I saw put it very succinctly: “Only a few factories in the world produce these batteries, and the quality control just isn’t there.” In short, never leave LiPo batteries unattended while they are in use or charging, store them safely and securely, and check their health as often as you charge them.
In fact, I might go as far as to recommend NOT using LiPo batteries if your trains are at risk of being dismantled by children. I would only recommend this power system for “serious” adult LEGO® train hobbyists who are already well-invested in the hobby, and find themselves at a point when the readily available power options are no longer working for them.
Next, this is not a final, absolute, way-and-the-light guide. This is just what I’ve found to work for me, if you ask another LEGO® train builder you might get different answers. Your Mileage May Vary.
Third, this is not an endorsement of any particular product. Again, these are just the products I’ve found that work for me.
Fourth, running your LEGO® trains on RC hobby batteries means a bit of modifying parts, which some LEGO® purists frown upon.
Fifth, Lithium Polymer is not the only battery chemistry available for rechargeable hobby batteries. Some folks use Lithium Ion, there’s also Nickel-Cadmium, Nickel-Metal-Hydride, and more! Even if you select a different type of rechargeable battery to use, this guide may still be useful to you.
Finally, now that I’ve given you all these warnings, you understand that you’re not allowed to blame me if the batteries burn your house down. Good? Right, let’s continue!
My first attempt at using a LiPo battery with one of my trains. As you can see, the battery was MUCH too large!
My journey towards Lithium Polymer batteries began when I found that conventional/disposable 9 volt batteries were not enough to keep my new 8-wide locomotives moving. I was using a custom cable that had two 9V battery leads connected to a Power Functions plug, but the two Power Functions “L” motors in most of my diesels demanded more juice than the 9V batteries were prepared to give (My one locomotive that used a single PF train motor did run comparatively well on a pair of 9V batteries, but by no means am I looking to power ALL my trains with the train motor). The “L” motors would prefer something like 850mAh, and most 9V batteries only put out around 500mAh. Some might say “Well just use the Power Functions AAA battery box, or the official LEGO® rechargeable battery!” Perhaps, but the way I build my 8-wide locomotives makes it quite difficult to fit a 4-stud-wide battery box in a 5-stud-wide locomotive hood. Doing so with the two official LEGO® LiPo battery boxes I owned made those two locomotives quite fragile, and charging them took FAR too long! At most shows, I could only run those locomotives for about an hour a day. As though that isn’t frustrating enough, using the Power Functions AAA battery box would mean the train has to be built in such a way that the box can be removed for battery changes, and even if you’re successful with that aspect of the construction, conventional rechargeable AAAs can take multiple hours to finish charging. For all these reasons, the readily available methods of providing power to my trains were unsatisfactory, so I decided to get my feet wet with more advanced power options!
After misunderstanding the power ratings of these LiPo batteries intended for RC hobby equipment, I bought a 3S 2200mAh 35C model. Roughly translated, that’s a 3-cell (the S means the cells are wired in Series) longer-life (2200 Milli-Amp Hours), high-discharge (The “C” rating refers to how quickly the battery can be drained of its charge) battery. It did work, but the train was going faster than I thought the motors were happy with, and I was warned by my LEGO® train colleagues that I could damage the LEGO® electronics with that much power. So, for round two, I purchased a 2S 850mAh 25C LiPo battery, which only puts out a maximum of 8.4 volts, but the milli-amperage is more than enough to keep a train moving at full speed for well over an hour. As a friend said, mAh is the “gas in your tank” rating. I could have selected a 2S LiPo battery with a higher mAh rating, but most of the higher-rated batteries use an XT60 discharge plug, with wire much thicker than that of the Power Functions wiring. The smallest LiPo batteries use a JST discharge plug, which is much easier to cram inside a LEGO® train. Also, note that the “C” rating isn’t really important for use with LEGO® trains. RC hobby equipment like model aircraft or miniature off-roading vehicles can discharge a battery in minutes because of their high power usage (hence the thick cable of the XT60 plug), whereas the power demands of LEGO® motors are comparably low. Even a 20C battery has many times more discharge-over-time capacity than what a LEGO® motor actually needs!
The larger battery in the back is the first LiPo battery I purchased. It turned out to be much too large and much too powerful. The large cables leading to the yellow plug coming out of the 2200mAh battery are XT60 leads, which are MUCH thicker wires than Power Functions cables, and therefore not easy to bend around. The smaller battery in the foreground is one of the batteries I use now. Notice how small it is, barely six studs long not including cable leads, a little over 3 bricks high, and barely two studs wide. It will easily fit inside most MOCs, and the cables are thin enough that they can be easily manipulated to cram into your builds. The multicolored wires leading to the white plug on each battery are the “balance” leads, which allow the charger or the low battery alarm to determine how much charge is contained within each cell of the battery.
Now that we’ve established what these batteries are and what they do, let’s talk briefly about the major accessories needed to run them!
First, a quality charger. I chose a charger from a manufacturer that has a function on their website where you can enter the serial number of the product you’ve purchased to ensure that it’s a genuine model. There are a lot of “clone” chargers that may not be built with the best quality, do some research to ensure you select one that suits your needs and comes from a reputable company.
Second, you will need some low battery alarms. These are tiny circuit boards that plug into the balance lead on your batteries, with indicator lights to show the health of each battery cell. When the battery reaches a specified low voltage the alarm will sound, and it’s loud enough that you can hear it even in a crowded expo hall!
Third, you will need some JST plugs with leads. This is the part that requires soldering. Cut a Power Functions extension cable in two pieces, giving you two plugs with wires coming off of them. After cutting the wires to size, solder the JST leads to the Power Functions leads, as shown in the image below. Once the soldering is done, wrap electrical tape around each solder point individually before taping them together. The idea of wrapping them individually is to prevent the hot and ground wires from touching each other accidentally.
The process of making a custom battery lead involves cutting apart a Power Functions extension cable and soldering it to a JST battery plug. The one I’m making in the picture is very short, but I do have some longer ones. On a Power Functions plug seen on the right with the cable going left, the bottom wire is the Hot wire, and the top wire is the Ground. The two center wires are for control signals to be sent to the motors, and are not needed for making a battery lead. After soldering the wires together, tape them up, taking special care to ensure that there’s no way any of the bare wires could accidentally touch each other.
Lastly, I would recommend the “fireproof” bags available for LiPo batteries. I use these to store the batteries when I’m not using them. I’ve heard from some RC hobbyists that say you can leave a LiPo battery sitting on a shelf in the garage without issue, but I prefer to keep my batteries in the recommended temperature-controlled climate. Some outlets say you should put the battery inside one of these bags while it’s charging. Mind you, I doubt the bags are truly “explosion proof” but I figure that if you’re around when things go wrong, the bag should buy you some precious time to get the burning battery outside. On that note, I once again urge you to NEVER EVER EVER leave the batteries unattended while charging.
Here is the battery, low battery alarm, and battery lead all crammed into the body of one of my locomotives. Not visible are the two Power Functions “L” motors, and the IR receiver.
So what does a typical session of using these batteries look like? Well, it starts a couple of nights before a weekend train show. I will charge all my batteries to full power, which is 8.4 volts, or 4.2V per battery cell. I have all my batteries numbered, and throughout the show day, I will use them more or less in numerical order. When a battery sets off its low voltage alarm, I remove the battery from the locomotive, remove the low battery alarm from the balance lead, and set the battery to charge. Each battery gives me about 2 hours of train running time, and charging takes around 45 minutes per battery. By the end of a show day, I’ll usually have a backlog of batteries that need charging, so I’ll bring the charger and batteries home to finish topping them all off for the next day. When the show is over, I will charge the batteries only up to the “storage charge.” As mentioned earlier, the full charge for a 2-cell battery is 8.4 volts. The low-battery alarms will start flashing at under 7 volts, and the alarm will sound at 6.4 volts. The “storage” charge level is 7.4 volts (3.7 Volts per cell), because this is where the chemistry of the battery is most stable. After charging all my batteries back to “storage” charge, I will stow them in the fireproof bags until the next time I need to use them.
Finally, the big question of cost. How much does it cost to run these batteries compared to, say, disposable batteries? Well, the batteries themselves cost around $6 or $7 USD each. Compare that to a single pack of disposable 9V or AAA batteries that have to be discarded after one use (rechargeable AAAs or 9Vs will be more expensive, but worth it if you prefer to use those kinds of batteries for your trains). The charger rang up at about $60 USD, and the Low Battery Alarms are around $3 each. In my case, a charger, several alarms, a couple of “fireproof” bags and a dozen batteries brought my initial purchase price to a bit under $200 USD with tax and shipping and so forth (remember that I’m running a somewhat large show layout with over a dozen locomotives and two trains running at all times). After using these batteries for only three or four shows, I’d say they’ve MORE than paid for themselves over using disposable batteries. Oh, and did I mention that the LiPo batteries do not gradually slow the train down as they lose power like conventional batteries do? I get maximum power & speed from full charge all the way down to the alarm going off.
Cost aside, the performance is far superior to any other battery I’ve tried. I would even go as far as saying I prefer it to the 9 Volt metal-rail system. I would absolutely recommend these batteries to anyone who has a lot of trains to power and hasn’t been happy with the official LEGO® options. With the right caution and know-how, LiPo batteries are a fine solution to the problem of powering your MOCs. Good luck, happy building, and thank you for reading!