Battery Characteristics

Here is a little bit about batteries. It discusses several different types, identifying their pros and cons, uses, performance, etc. If you’ve ever wondered what kind of battery to use for your locomotive or building or water feature, this article might help you out. It was taken (with permission from Tom Gaps) from an article Tom Gaps wrote for the Garden Railways Magazine in August of 2016, so some of it might be a bit dated. If you think so, and have more recent information, please let us know .
Under construction/modification by DErik (talk) 15:11, 21 May 2023 (PDT) Source: Tom Gaps

Battery Types

Lead Acid, a.k.a. Gel Cell

There are several different battery chemistry's to choose from, each with their own pros and cons. A few years ago the primary chemistry was sealed lead acid, or Gel Cell. This chemistry produces a nominal 2 volts per cell. Gel Cell batteries are very reliable and can take a great deal of “electrical” and “physical” abuse but they are heavy and have a low energy density (little power for lots of weight). Putting Gel Cell batteries in a Diesel locomotive puts a lot of weight on the drivers which helps the pulling power of the locomotive. Putting Gel Cell batteries in the tender of a steam locomotive adds dead weight that has to be dragged around by the locomotive without doing anything to help it's pulling power since none of the additional weight is on the drivers. For this reason, some people like to make room for the batteries in the boiler by replacing the “lead” weight in the boiler with Gel Cell batteries. This tends to be a one for one weight replacement which means that it neither increases nor decreases the weight on the drivers so it has no impact on the pulling power of the locomotive but it does avoid adding the weight of the heavy Gel Cell batteries as dead weight that has to be pulled around by the locomotive.

Nickle Cadmium (NiCad) & Nickle Metal Hydride (NiMH)

The Gel Cell technology was eventually replaced by the Nickle Cadmium and later the Nickle Metal Hydride (NiMH) battery, both of which produce a nominal 1.2 volts per cell. Nickle based batteries have a higher energy density than the Gel Cell, which means more amp-hours for the same size cell, but their lower voltage output reduces the total power of the battery, power being the produce of amps and volts. Adding more cells in series to increased the voltage does not impact the total amp-hours available. Compared head-to-head, a Gel-Cell and a Nickle based battery configured to produce the same amount of power will always result in a smaller package or less weight for the Nickle based battery. Because the weight to volume ratio of Nickle based batteries is less than that of a Gel Cell, it no longer makes as much sense to put the batteries in the boiler of a steam locomotive because that would mean replacing a 5 lb lead weight with less than 5 lbs of battery of the same volume. While avoiding the introduction of dead weight in the tender, placing Nickle based batteries in the boiler reduces the total weight on the drivers thus negatively impacting the pulling power of the locomotive. Placing the batteries in the tender continues to mean adding dead weight to haul around but the NiCad and NiMH battery adds considerably less dead weight for the same amount of power when compared with the Gel Cell. Like the Gel Cell, nickle based batteries are also relatively immune to electrical and physical abuse but, when compared with Gel Cells, nickle based batteries come with a relatively high SDR (Self Discharge Rate). A Gel Cell can be charged to full capacity and still retain most of that charge a week later, which is why they make a very good standby battery. The NiCad and NiMH battery, on the other hand, has a SDR in the 3% to 5% range when fully charged. That means that every day they will have 3% to 5% less charge than they had the day before. At a 5% SDR, after a week (7 days) it will have lost almost 25% of it's charge and after two weeks (14 days) the charge can be down almost 50%. Luckily, this high SDR drops off as the battery discharges which means that the SDR slows over time so it's not quite as bad as it sounds. NiCad and NiMH batteries also have a tendency to develop a memory. If they are repeatedly partially discharged and then recharged, they will soon lock into that pattern and will not allow discharge below that point. To avoid this “memory” condition, they must regularly be fully discharged before recharging. This is often referred to as “conditioning” the battery.

Lithium-Ion (Li-Ion)

Relatively new to the hobby market is Li-Ion (Lithium-Ion) batteries. This chemistry produces 3.7 volts per cell and has a very high energy density, i.e. it packs a lot of power in a small package. In addition, it has a very low SDR and is not prone to developing a memory if only partially discharged before recharging. However, the Li-Ion and the other Lithium based chemistry's do not handle electrical or physical abuse very well. In fact, they don't tolerate either type of abuse at all. If they are over charged, over discharged, charged too fast or discharged too fast they are very prone to over heat and in many cases, catch fire or explode. A sudden shock, like dropping them on a hard surface has been known to start a bad chemical reaction in the battery. For this reason, Li-Ion batteries (and their other Li based cousins) should always be used with a monitoring circuit which controls the charge and discharge levels and rates to ensure they are not electrically abused. They also should only be recharged by a charger designed to deal with Lithium based batteries. These chargers are some times referred to as CC-CV chargers (constant current – constant voltage). Virtually all manufacturer supplied Li-Ion battery packs come with a built in monitor circuit designed to ensure that the battery pack is not electrically abused. This is where the major down side comes with Li-Ion battery packs. With Gel Cells and Nickle based batteries, as the battery becomes discharged, it is no longer able to provide full voltage which means a locomotive will begin to slow down and have less and less power as the battery becomes discharged. An early indicator that a battery is reaching the end of it's charge occurs when the voltage output drops below the level needed to operate the electronics in the sound card. This will cause the locomotive to go into “stealth mode” where it stops making any sounds. If a Li-Ion battery is allowed to discharge until the voltage drops way off, it will damage the battery. To avoid this possibility, the monitor circuit will cut off output (stop the discharge) when it detects that the battery is starting to show a significant voltage drop, and it does this with NO WARNING. That means that the locomotive will suddenly stop, also with no warning, when the Li-Ion monitor circuit decides that the battery has been used enough. This can prove to be a real problem if the locomotive happens to be in a tunnel or in some other hard to reach location at the time that the protection circuit cuts off battery output. One solution to this problem is to monitor your run time. The typical locomotive draws 0.5-to-1.0 amp per hour. If you want to run for 4 hours between re-charges, then you must use a battery with a minimum rating of 4 ah (4,000 mah) and then monitor the number of hours of run time since the last charge, keeping in mind that excessive load (long, heavy trains), excessive grades and excessive speed will reduce this total available run time.

Battery Size vs Recharging Cycles

Since batteries have a limited capacity, they will have to be recharge after a period of usage. If the battery is permanently installed in the locomotive (i.e. hard to get out), recharging the battery means taking the entire locomotive off line while it's battery is recharged. This could prove to be a bit annoying. If the battery is (easily) removable, when it runs low, it can (quickly) be swapped for a freshly charged battery while the discharged battery is recharged off-line. Here again., there are trade offs. Making the battery easily replaceable generally means using a smaller battery. The bigger the battery, the harder it becomes to easily remove it from the locomotive. Constantly having to stop and replace a relatively small battery pack can also be annoying. So, the decision becomes - “Can I put enough permanent battery in the locomotive to ensure that it will make it all the way through a session without having to be taken off line for a recharge, or do I need to go with (smaller) removable batteries that may need to be swapped several times during a session”.

On the subject of recharging permanently installed batteries, it is a good idea to include an isolation switch that disconnects the battery from the locomotive while it is being charged. This can be done with a double pole – double throw (DPDT) switch that either connects the battery to the locomotive or to a charger. The down side to this method is that even though the charger is plugged into the locomotive, nothing will happen until the battery isolation switch is activated. Plugging in the charger while failing to set the battery isolation switch will result in a lot of time spent waiting for a charge cycle to complete when it is not actually charging. A better solution is to connect the charger to the battery via a charging jack with a built in isolation switch. When the charger is plugged into the charging jack it will automatically isolate the battery. The positive (+) connection between the battery and the locomotive feeds “through” the charging jack. When the barrel of the charging plug is inserted into the charging jack, it opens the connection to the rest of the locomotive so that the battery is connected to only the charging jack and thus only to the charger.