Thursday, March 30, 2017

A quick introduction to batteries for model trains

Introduction

This page is designed to be a fairly simple and straightforward introduction to battery power for model trains. It is by no means a comprehensive or definitive guide. Hopefully there will be enough here to get you started and answer some of your basic questions.

I've covered the following:
  • Cells, batteries or packs - what's the difference?
  • Disposable or rechargeable?
  • Types of disposable battery
  • Types of rechargeable battery
  • Battery capacity
  • Battery packs
  • Connecting cells in series
  • Connecting cells in parallel
  • Combination packs
  • Choosing the right sized pack for your loco
  • Battery protection
  • Charging batteries
  • Battery chargers
  • Controlling speed
  • Manual control
  • Radio control
  • Radio control systems for model trains

Cells, Batteries or Packs - what's the difference?

To be pedantic, a battery is a collection of individual cells wired together - ie a 'battery' is really a 'pack' of 'cells'. However, it has now become common parlance to refer to 'cells' as 'batteries' so, when we refer to an AA 'battery', we are really describing a single 'cell'.

In this posting, will use both 'cell' and 'battery' to refer to cells, but will use 'pack' to refer to an interconnected collection of cells.

Disposable or rechargeable?

Disposable (or Primary) batteries

This is the simplest way to power your locos - insert some batteries into a battery box, connect the box through a reversing switch to your motor and away you go!
To be able to reverse the direction the loco travels, the DPDT (Double Pole Double Throw) switch would need to be wired-up like this:

When the switch is moved to the right, the motor leads are connected directly to the battery leads
and when it is moved to the left, the motor leads are swapped over, thus reversing the motor.

Types of disposable battery

The most effective disposable batteries for use in model trains are alkaline batteries. They are now the most readily available and tend to last longer than zinc carbon batteries. However, with more recent developments in battery technology, disposable lithium batteries are now becoming more common, though their price makes them less competitive than alkaline.
Zinc-carbon, also known as carbon-zinc or the Leclanché battery. These are the earliest and least expensive sorts of primary batteries. They deliver 1.5 volts but their capacity tends to be lower than alkaline batteries (ie they do not last as long before becoming depleted)

Alkaline. (Alkaline-manganese), is an improved version of the zinc-carbon battery and also delivers 1.5 volts. Generally longer-lasting than zinc-carbon and less prone to leakage.
Lithium (Lithium iron disulfide (Li-FeS2)) Normal lithium primary batteries deliver three or more volts, but Li-FeS2 batteries are usually rated at 1.5 volts to be compatible with AA and AAA formats. They are most often found as button cells (eg for use in hearing aids) but have a much longer life cycle than alkaline batteries (eg a heart pacemaker battery can last up to ten years). They are becoming more readily available and are beginning to drop in price. Some airlines do not allow any type of lithium battery to be carried on board planes.

Rechargeable (secondary) batteries

Rechargeable batteries can be used directly in place of disposable batteries, using the same wiring diagram as above. However, the batteries would need to be removed from the battery box to be charged. Alternatively, the batteries can be left in the loco and charged in-situ. If the  DPDT reversing switch does not have a 'centre off' position, an SPST (single pole, double throw) switch must be included in the circuit to switch between the motor circuit and a charging socket - to help ensure that the loco is not left on while it is being charged. 

As an additional precautionary measure, I usually use 2.1mm DC power sockets for charging which include an isolation switch. 



 When a plug is inserted into the socket, the connection between the battery and the motor (the blue wire in the above diagram) is cut-off. 

There are four main types of rechargeable battery available 'over the counter - Nicad/NiCd (Nickel Cadmium), NiMh (Nickel Metal Hydride), Lithium and Lead Acid. Nicads have now largely been replaced by NiMh. Lithium batteries are available in an increasingly baffling range of sub-types but are becoming a lot safer and more reliable. Lead acid batteries, as the name suggests, tend to be quite heavy and bulky.

I used to use NiMh batteries but now use lithium-ion batteries. These provide more power for their size than NiMh, but need to be handled with care.

NiCd (Nicad - Nickel Cadmium) batteries were once the recommended rechargeable battery for models but they have largely been superseded by NiMh (Nickel Metal Hydride) batteries. NiCads are becoming increasingly difficult to find. Each battery delivers 1.2 volts.

 NiMh batteries do not suffer from the 'memory effect' which plagued NiCads - they can be recharged at any time, without the need to be fully discharged. As with NiCads, NiMh cells deliver 1.2 volts.


A major disadvantage of ordinary NiMh batteries is that they slowly become depleted when stored. It can be very frustrating to take your loco out into the garden only to find it needs recharging. Low Self Discharge (LSD) NiMh batteries (also known as Eneloop) overcome this problem. They tend to be slightly more expensive than ordinary NiMh batteries but, to my mind, they are well worth the extra expense.
Lithium-ion (Li-ion) and Lithium-Polymer (Lipo) are now being used more extensively but many modellers are cautious about using them as, if not handled correctly, they are more volatile and can burst into flames. Their main advantage over other sorts of rechargeable battery is their capacity. Whereas each NiMh cell delivers 1.2v, each lithium cell delivers 3.7v. Hence, li-ion and lipo batteries take up considerably less space inside a loco than NiMh batteries. 

 Li-ion batteries are inherently more stable and reliable than Lipos because of their chemistry and their construction. They are available in a range of cylindrical styles:

By far the most popular is the 18650 sized battery (18mm diameter x 65.0mm long). Most laptop computer battery packs comprise three or six 18650 li-ion cells, giving 11.1 volts. 14500 batteries (14mm diameter x 50.0mm long)  are the same size as AA cells.

Because of their durability, range of sizes and slower discharge rates, li-ions are better suited to battery powered locos than lipos. 

 Lipo batteries are generally favoured by model car and model plane enthusiasts because they are capable of delivering large bursts of power and can be recharged more quickly. However, these capabilities can make them less stable than cylindrical li-ion batteries. Lipos are generally constructed into flexible plastic pouches ........

.... though sometimes they can be further encased in rigid cardboard or plastic cases but generally retain their cuboid shape:

 Small sealed lead acid batteries, such as those used as back-up batteries for burglar alarms, can be used inside large scale locomotives but their major disadvantage is weight and size. 


 Their advantages are the ease with which they can be recharged and the relative simplicity of their wiring. 

 Battery capacity

The capacity of rechargeable batteries is measured in Amp Hours (Ah) or MilliAmp Hours (mAh). For example, this NiMh battery is rated at 2600mAh (or 2.6Ah).


In theory, roughly, this means that if the electric motor which powers your loco is drawing 1 amp, then a 2Ah (or 2000mAh) battery should be able to power it for two hours. However, many other factors will affect this rating and so it should be taken only as a guide. Furthermore, many of the cheap, 'bargain' batteries which  are offered for sale on eBay exaggerate their capacities. For example, a set of li-ion batteries which I bought cheaply on eBay were advertised as having a capacity of 3200mAh. I discovered their actual capacities were closer to 1600mAh - and one of them ceased working after less than a year and only three charges.

Ideally, you should choose the batteries with the highest Amp Hour rating you can squeeze into the available space in your loco. Larger batteries, as you would expect, tend to have higher capacities.


Battery packs

Ready-made battery packs can be purchased from specialist suppliers such as Strikalite, who will construct battery packs to your own specifications. However, it is possible to make your own.


Connecting batteries in series

When batteries are connected in series, the output voltage is increased in proportion to the number of cells in the pack. For example, three 1.2v NiMh batteries connected in series will give an output of 
3 x 1.2v = 3.6v.

If the three cells are li-ion, then the voltage of the pack would be:
3 x 3.7v = 11.1v

If the cells were alkaline disposable batteries the the voltage of the pack would be:
3 x 1.5v = 4.5v

However, the capacity of the pack would be the same as for one of the cells. For example, if the pack was made from three 1500mAh NiMh cells then the capacity of the whole pack would also be 1500mAh

It is not advisable to mix batteries with different Ah ratings in the same pack. You should only connect batteries of the same type together into packs - and in the case of Li-ion batteries, they should preferably be from the same manufactured batch to ensure the charging and discharging characteristics are the same as these can vary with the age of the battery.


Connecting batteries in parallel

If batteries are connected in parallel, then the overall voltage of the pack will remain the same as for one cell, but the capacity of the pack will increase. For example, if three 1500mAh NiMh batteries are connected in parallel, then the voltage of the pack will be 1.2 volts but the pack's capacity will be:
 3 x 1500mAh = 4500mAh
 Just as the pack of three cells in series is designated as 3S, a pack of three cells in parallel is designed as 3P

Composite packs

A 3S2P pack would comprise of six cells - three pairs of parallel wired cells in series. In other words, pairs of cells are wired in parallel and then the three pairs are connected in series:
As you can see, a 2S3P pack would comprise two sets of three cells connected in parallel, wired together in series.

Let's assume that the each cell in the packs above are 1.2v, 1200mAh NiMh. 
  • The output from the 3S2P pack would be 1.2v x 3 = 3.6v, 1200mAh x 2 = 2400mAh  
  • and the output from the 2S3P pack would be 1.2v x 2 = 2.4v, 3 x 1200mAh = 3600mAh.
So, the 3S2P arrangement would be used for a higher voltage, lower current motor  and the 2S3P for a lower voltage, higher current motor.

For more information on wiring up battery packs see - http://scriptasylum.com/rc_speed/lipo.html

Choosing the right sized pack for your loco 

 It can be quite confusing trying to decide what size of battery pack you need for your loco. For example, most of my battery locos use commercial motor blocks designed for track-powered locos running off a maximum of 24v. However, because I don't require express train top speeds, I use 12v battery packs. My modelling mate in Australia also uses 24v motor blocks and most of his locos are happily powered by 9.6v packs and has some powered with 7.2v packs.

Before cramming every nook and cranny in your loco with batteries, try out a few different configurations of battery pack sizes to determine what sort of top speed you want for your loco. There is not point in having an excess of volts if you never use them.
 

Battery protection

It is very important that lithium cells are protected with electronic circuitry to ensure they are not short-circuited or are over-charged. Most importantly, lithium cells must not be overly discharged. If their voltage level falls below 3 volts then the cells can become permanently damaged. Some li-ion batteries include miniature protective circuity to prevent this and are sold as 'protected' batteries. 
 However, individual 'protected' cells cannot be connected in series to form larger battery packs, 'Unprotected' li-ion cells can be connected into packs but it is highly advisable that protection circuit boards are used.

The wiring for the board is fairly straightforward. The board needs to monitor the condition of each battery in the pack and so connections need to be made between the board and the ends of each battery.
 Two further connections are then made from the board to the wiring and the charge socket in the rest of the loco as normal. 


Although the convention is for a two way switch to be used in locos to switch between powering the loco and connecting the batteries to the charge socket for charging, it is not essential. A simple on-off switch will suffice, provided you remember to turn the loco off when charging. One advantage of having the charge socket 'live' at all times is that a meter can be plugged into it to monitor voltage flow when the loco is in motion.

Charging batteries and battery packs

It is vitally important that you use the correct type of charger for the batteries you are intending to charge. A charger designed for NiMh batteries should NEVER be used to charge li-ion batteries and vice versa.

If your batteries can be removed from the loco then a standard 'wall' charger can be used provided you ensure that it is compatible with the type of battery which you are charging. 


If you are charging batteries and packs inside your loco then you need a charger which is specifically designed to charge the type of battery and the size of pack you are using. For example, if your loco is powered by a pack made up from three NiMh cells wired in series, then you need a charger capable of charging a 3.6v NiMh pack, such as this one which is designed to charge NiMh packs from 3.6v (3 cells) up to 12v (10 cells):

It is an 'intelligent' Delta charger which senses the state of charge of the cells and will automatically go into trickle charge mode when the batteries reach their full charge. As can be seen, it includes a range of connectors making it fairly universal.

Similar chargers can be bought for charging lithium-ion packs and lead acid batteries.

For maximum flexibility, I would recommend the iMax B6 charger. This is capable of intelligently charging NCad, NiMh, Li-ion and lead-acid batteries. It seems to have become the most popular smart charger available and as a consequence has dropped in price. Its disadvantage is that it looks very complicated to use when it is first taken out of the box, compounded by a largely incomprehensible handbook, but one its basic features have been grasped it is surprisingly easy to use and is very versatile. (see How to use an iMax B6 charger - pending)

These can be purchased quite reasonably on eBay. I prefer the original version of the charger as Version 2 requires obligatory connection of a balance charge lead when charging li-ion batteries.

Balance charging ensures that the level of charge in each cell in a pack is the same. If the charge becomes unbalanced then the efficiency of the pack is reduced. If the imbalance becomes too acute then the cells can become damaged beyond repair and so it is advisable to balance charge any pack from time to time. Again, the wiring for this is fairly logical - just as the protection board needs to be able to monitor the condition of each pack, the charger needs to do the same. Consequently, the connection to a charge plug - usually a JST multi-pin plug - is the same as that needed for the protection board.

The loco is then connected to the charger through an additional balance charge lead....

....connected to the balance charge sockets on the side of the charger.
Once in balance charge mode, the charger will automatically sense and manage the charging of each individual cell.

 Controlling speed

Manual controllers

A manual speed controller uses a potentiometer to adjust the voltage supplied from the battery to the motor. You could use a wire wound potentiometer to adjust the voltage, but there are more elegant and efficient ways to control the speed. Speed controllers can be bought in kit form from online suppliers such as IP Engineering or Cambrian Models or, if you are competent with a soldering iron, then you can make your own using a potentiometer and a single component such as the IRF3205 MOSFET (Metal Oxide Semi-conductor Field Effect Transistor).

 You may need to bolt the MOSFET to a heat-sink (eg a small piece of aluminium sheet) if the motor is put under a moderate load as it will generate heat which will need to be disipated.

Alternatively, you can buy a PWM (Pulse Width Modulated) motor controller circuit board quite reasonably on eBay, such as this:


The speed control knob can be disguised as a chimney, brake handle or wheel, or even a bucket.

Radio control

Radio control enabled you to control the speed and direction of your loco remotely from a distance. More sophisticated radio control systems allow you to control additional features such as lighting, sound and other gadgets such as remote uncoupling.

A traditional radio control system uses a transmitter, receiver and an electronic speed controller (ESC).

Most ESCs designed for model railway locos control speed and direction (eg Brian Jones' Mac5)


or the MTroniks Viper 10 Loco,

 - but some of the less expensive ESCs control only speed and so a separate radio controlled direction switch is needed. If looking for low-cost ESCs, make sure you buy one advertised as controlling 'brushed' motors.

Any standard radio control system can be used to operate the loco. I have used a cheap transmitter designed for use with those tiny battery powered helicopters and a standard receiver, into which is plugged the ESC (in this case a Brian Jones Mac5)

It is possible to get receivers which have an ESC built-in (eg the Deltang / RC Trains Rx65b).


These tend to be more compact and so will fit into smaller locos (eg the IP Engineering Plate Frame Simplex) and. of course, the wiring is simplified.

Radio control systems designed for use with model trains

 The disadvantage of standard radio control systems is that they are primarily designed for use with model planes, boats or cars and so tend to have joysticks or levers to control speed. If the joystick is sprung-loaded then a finger or thumb has to be held on the joystick continuously while the loco is in motion. Fortunately, there is a range of radio control systems available designed specifically for model trains. Here is a small selection:

Timpdon Ultrarad
http://www.timpdon.co.uk/timpdon/telec/products/products_urc.php

RC Trains / Deltang
http://rctrains.co.uk/Transmitters.htm

Yatton Engineering / Deltang
http://www.yattonmodelengineering.co.uk/radiocontrolsystem.html

LocoLinc

http://www.locolinc.com/locolinc.html

I have only had direct experience with Deltang and RC Trains equipment and also, as I used to construct and sell RC Trains transmitters, it would be unfair of me to offer opinions on the relative merits of each system. Over the years (well before I set up RC Trains), I have accumulated considerable knowledge of the Deltang system - just enter Deltang into the search box at the top of the page or browse through the radio control section in the blog contents for more information.

For general information on radio control in large scale garden trains see my blog entry on getting started with radio control.




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