Batteries byJohn Joyce Tel. 07890 227981

Introduction
Batteries cause a disproportionately large number of problems for such an apparently simple device. A little rudimentary maintenance can prevent most problems, although it should be realised that batteries have a finite lifespan, which will be shortened if they are not maintained correctly.

A Few Myths
DMUs are 24 volt. All vehicles I've ever seen have two sets of cells, one on each side, connected in series to provide this, and both are required to provide any power. Both sets are needed to start either engine!

A set of cells with one dud one will never start an engine reliably, however much the others are charged.

Batteries with two negative terminals and two positive terminals have them connected internally, and do not require all four to be connected to work. However, connecting all four terminals provides a degree of redundancy and reduces problems with bad connections.

Starting engines with 'boost' chargers will only work if the batteries are in fair condition anyway. A charger won't start anything unassisted. Jump starting from a couple of large lorry batteries (with suitably heavy jump leads) does work but car batteries aren't usually up to it.

I have yet to hear of any success with the 'Battery aid' tablets sold by various places. At the outset, DMU batteries are much larger than the car batteries these tablets are intended for, so a correspondingly large number would be required. As to what they are supposed to do - I don't know. Suffice it to say that attempts to revive a couple of dead car batteries with them proved futile and I've not tried again.

Types
Assorted types of batteries have been used over the years on DMUs, mostly lead acid but with a few nickel-iron ('NiFe'). I've little experience of the NiFe ones other than replacing them with lead acids! They are the same types as fitted to the 24volt hauled coaching stock, eg mark 1s.

The earliest type was the black rubber-cased BRA2, with two filler caps, four terminals, and a float to indicate electrolyte level. Few of these remain today as they appear to have been superseded in the late 1980s by plastic-cased cells in wooden crates. Early types of these retained the handy float level indicators, although they had to be removed for topping-up purposes. These appear to have been discontinued and replaced by simple lids, making topping-up a bit of a hit and miss affair. Later still came flip-cap fillers, which do have level markings, but these are often difficult to see without lifting the cells out.

The original type black rubber type, very old now (these dating from around 1978). These were under a Mark 1 and are the smaller 'BRA1' type (235amp-hour nominal) whereas DMU vehicles had the larger (395amp-hour) BRA2 type. The first two pics illustrate the float, first at empty and then at full, and also the filler caps. The third pic shows the cells all coupled. The first pic also shows the top lifting away as they tend to do when they get towards the end of their life. Not pleasant as the acid starts to escape!

Click on the images for a bigger picture.

These Crompton flip-cap batteries were found fitted to one of the 115 power cars at the Colne Valley Railway
Above: Plate on battery box
Top Right : close-up of filler cap. Hopefully what I assume are the level marks are obvious - at the bottom of the filler, and the step part way up.
Middle Right : A single cell, Crompton manufacture
Bottom Right : set of Crompton flip-cap cells

Click on the images on the right for a bigger picture.

top left : earlier Crompton type which replaced the BRA2. No filler levels at all which isn't very useful.

2nd left : 'Oakdale' type which look similar to the Crompton ones, but don't have the filler levels either.

3rd left : another view

bottom left : set of above.

Click on the images for a bigger picture.

Tools Required
Digital multimeter - as noted under 'alternators and generators' these are much more robust and accurate than analogue ones. Hydrometer - for checking electrolyte strength. I bought one from Halfords for £2.99 (it should be next to the batteries!), and it has proved a very useful acquisition. Demineralised /deionised / distilled water - for topping up. Spanners (preferably insulated!).

Health Warning
Battery electrolyte (sulphuric acid) is extremely corrosive. It will eat its way through most things (including metal, wood, clothes, people) given time. Avoid getting it on your clothes on pain of finding holes in them next time you wash them! On skin it starts to sting after a minute or so, but can be washed off with little ill effect, although experience shows that it is rather more unpleasant if it finds a cut. Don't try making up your own electrolyte from neat acid unless you know what you're doing; neat acid is very dangerous to the uninitiated. Note also that the charging process generates quantities of hydrogen and oxygen; theoretically these can explode if a spark or naked flame is nearby but I've not managed it (yet).

Maintenance

Electrolyte should only be topped up with demineralised / deionised or distilled water; tap water (soft or hard) will shorten battery life. The damage isn't obvious but the cells will fail prematurely. Use dedicated plastic storage and topping-up containers to avoid contamination; a plastic milk bottle or similar is handy for the latter.

Typical electrolyte level float. The red band indicates 'minimum' when it is about to disappear; the yellow area indicates 'maximum when it appears. This leaves enough space in the cell for it to gas during use without splashing electrolyte everywhere.

The electrolyte level needs to be above the top of the plates and some way below the top of the case - too high and it will splash out during charging and when the vehicle is moving; too low and the battery will lose capacity as the plates become exposed. Most types have some form of indication of maximum / minimum indication, earlier types having a float and later types having markings under the filler cap.

Black rubber cells (BRA2 type) and the early plastic cells (the ones in wooden crates) have floats which have markings for maximum and minimum. Do beware, as occasionally the float will stick or even break; this tends to become obvious when the battery is full and the float still hasn't moved! Later plastic cells (with the flip-cap filler) have a plastic moulding inside the filler neck, with the bottom of the moulding being 'minimum' and the ridge part way up being 'maximum'. These can be filled without removal from the battery box with a bit of ingenuity - use something clean and plastic (eg a drinking straw) as a 'dipstick'.

My interpretation of the markings on the flip-cap type filler; the bottom of the plastic moulding is 'minimum' and the ridge part way up is 'maximum'. If anybody knows different then do let me know!

A final word - top up batteries before charging them, not afterwards. The water will tend to sit on top of the existing electrolyte, and in frosty weather it can then freeze and split the case. Charging for a few hours will cause the batteries to gas a little and mix it in.

This should be checked from time to time, depending on the usage cycle of the batteries. It can also be checked more often to give some indication of whether a particular usage cycle is keeping them charged sufficiently. A further use is for identifying failing cells. (see 'fault finding', below) N.B. Don't try to use a hydrometer straight after topping up; as noted above, the water tends to sit on top for a while. Charge until the cells have been bubbling for an hour or two.

Take a sample of electrolyte from a cell; sufficient so that the float actually moves, but not so much that it hits the top of the hydrometer. Hold the hydrometer vertically and tap it gently to settle the float, but beware of acid dripping from the nozzle in the process. A reading of 1.250-1.275 seems to be a typical result for a charged cell, at least with the hydrometer I have. Below 1.225 and charging is required or the electrolyte is weak; below 1.150 and the cell is flat or failing. Of particular interest is differences between cells or over time.

The basic instruction is a day's charging every month or two should keep a healthy set of batteries in good shape. If they are in regular use on a trailer or generator-fitted power car then more regular recharging will be needed, perhaps even daily if heaters are in use. Alternator-fitted power cars should need no charging provided that they are used reasonably often. The worst thing to do is to undercharge.

Chargers need careful selection - ignore the 'boost' rating as this is largely irrelevant. A continuous output current capability of 30amps is satisfactory. Such an item will probably cost £100 or so - Machine Mart offer (or at least, used to offer) a suitable one (Rally 250 or something like that).

All kinds of arrangements are made for charging, with leads of one kind or another, often made with inadequately sized cable. The rule here is that the longer the charging cable, and the smaller the cable diameter, the longer it will take to charge properly. It is much better to take the charger to the vehicle with mains extension leads as problems with voltage drops are much less severe. If running long leads, aim for 25mm^2 (ie welding cable size) for at least the majority of the cable, perhaps with a short length of thinner cable to actually connect to the vehicle. Although the current is easily handled by smaller cable, it will have a substantial voltage drop which will slow charging down.

Check all connections in both battery boxes, the battery switch / fuse box ("BIS box" or "Electrical Control Box") are tight. If in doubt, remove, clean, and reassemble tightly with a thin smear of grease on everything. It is wise during overhaul to spend a couple of hours doing this to all the connections. Look out for corrosion on the cell terminals inside the battery boxes, evident as a white or blue powder. This is caused by a little of the acid in the cells escaping during charging, corroding anything nearby. Clean the affected parts thoroughly and smear lightly with grease to prevent a reoccurrence.

Fault Finding

These produce symptoms similar to a dead cell - the lights and heaters work reasonably well, but no amount of charging will get the engines turning over briskly. Check connections in the battery boxes, the battery switch / fuse box, and on the starters themselves. Immediately after trying to start an engine (ie within a few seconds) Feel all the connections with your hand to find any warm ones - bad connections can generate a lot of heat. In extreme cases, sparking can be seen / heard. Yours truly has learned the hard way that bad connections or one kind and another are a major cause of problems!

The biggest problem is caused when a cell goes 'dead' and will not hold any charge. This can be caused by the plates warping and shorting out, which tends to happen on the old black rubber cells, often accompanied by the top of the cell lifting away. Other failures include sedimentation at the bottom of the cell shorting the plates out and / or the active material on the plates being destroyed. Repeatedly running a set of batteries flat is a good way to kill one or more cells by over-discharging it; regular overcharging can loosen the active material, which then falls to the bottom of the cells and shorts them out.

A totally dead cell is usually obvious using a hydrometer or multimeter; what you should look for is one or more 'odd ones out' in a set. The dead cell will have a much lower voltage after charging than the others (or even a reverse voltage - beware with a digital meter, it is easy to miss this), a much lower hydrometer reading, and may get warm during charging. It will also use little electrolyte, and the other cells in the set will use more than usual. Cloudy (ie muddy-looking) electrolyte is another bad sign.

Having identified the failed cell(s), it / they should be replaced by one of a similar age and capacity. It is important that both the replacement cell(s) and the remaining good cells are fully charged before use - never put a flat cell into a charged set without an equalising charge, or it will never charge properly and soon fail.

This usually indicates a charging circuit fault or a failing cell - see 'dead cells' above, and also the fault-finding notes for alternators and generators. During charging from a battery charger, check the voltage of each cell individually with a digital multimeter - it must be at least 2.3volts, or the battery will not be fully charged. The charging current will drop to only a few amps once charging is complete. There may also be a continuous drain of some kind on the batteries - see below.

From a fully-charged state, there should be enough power left in a set to start engines after at least 3 months. If not, a slow discharge is usually indicated, often through earth faults. You do turn the battery isolating switch off at the end of the day, don't you? Not doing so can leave a small electrical load, even with the keyswitch turned off, depending on how the vehicle is wired.

With everything switched off and any charging lead unplugged, remove one of the battery connecting straps and connect an ammeter in its place. You will be pretty much guaranteed to get some reading, with most vehicles' wiring being many years old - perhaps 10 milliamps. (that's 0.01amps) Such a reading isn't a disaster; it will take many months to drain a battery at that rate, although it will shorten battery life a little. If it's much more than that, you need to start looking for the problem - 100 milliamps and your batteries won't start an engine after a month or two. If it's an amp or more you've either got problems, or somebody has left the cab light on or the charging lead plugged in!

To narrow down the problem, disconnect all jumpers from other vehicles - under some circumstances currents can circulate through the jumper connections. Note the ammeter reading, and then take a fuse at a time out of the distribution fuse box, checking the ammeter reading each time. This will obviously tell you which circuits you need to start investigating in detail to locate the problem(s). Heater glow plugs seem to be a favourite for producing earth faults.

Voltage
Voltage gives some idea as to how charged a cell is, although a hydrometer reading is more reliable if previous readings are available for comparison. As a rough guide, with the lights switched on and the charger unplugged for a few minutes:

Below 1.83V / cell: very flat, recharge as soon as possible
1.83V / cell or 22.0V total: flat
1.92V / cell or 23.0V total: nearly flat
2.0V / cell or 24.0V total: ought to start an engine but requires recharging
2.08V / cell or 25.0V total: OK
2.17V / cell or 26.0V total: good

Hydrometer Readings

Typical hydrometer. Dependent on the state of charge of the cell, the specific gravity (density) of the electrolyte changes, and the float sits higher or lower in it. (the grey bit is the electrolyte) Make sure that the float isn't hitting either end of its travel and giving false readings. Hold the hydrometer vertically and read from the lowest point of the meniscus (that's the curved surface you get on the top of a liquid) as shown.

Again these will vary from vehicle to vehicle, depending on battery age and so on. As a guide:

1.150 or below: flat or dead
1.200: nearly flat
1.250 or above: good. Most batteries don't get much above 1.250.

When trying to trace problems with poor starting, bear in mind that starter motors can get 'tired' for various reasons; for example, oil can contaminate the brushgear, and the motor will still work, but not very well. This can easily be misdiagnosed as flat batteries or poor connections. Such problems are often indicated when a vehicle has one engine which is 'easier' to start than the other.

Renovating Batteries
A problem which faces many owners is that a newly-acquired vehicle has been left to stand for months or even years, and the batteries are both well and truly flat, and reluctant to recharge. The advice in this case is simple: top up the electrolyte, attach a battery charger as soon as possible, and leave for a week or two. DMU batteries are remarkably resilient to being left for a long time, and will usually recover reasonably well. However, charging for odd days perhaps once a week when the owner is around is not a satisfactory substitute - if a continuous mains supply cannot be arranged for a week or two, take them off and recharge elsewhere.

Storage
New cells are fully charged, then emptied and sealed under a vacuum; they can be stored for years. Adding electrolyte produces a fully charged cell. This is difficult to do for most people. Emptying the electrolyte out from a fully-charged cell is unwise, as the plates will react with air which will destroy the active material. It has been suggested that discharged cells can be emptied and sealed, but I have not tried this - at a guess the sulphate coating on the plates will harden and recharging will become difficult.

Consequently I would recommend storage somewhere that recharging is easy, with a charger connected perhaps one day every month or two. We have stored some for several years and they appear not to be deteriorating badly.

Summary
Batteries cause far more problems than they should. Ideally all power cars should be alternator-fitted and all others charged regularly. As with so many other things, the proof of the pudding is in the eating - do your engines start or not? A reasonable life for an regularly-used power car is 5 years and for a trailer 10 years; start saving up the pennies as replacements are expensive at around £1000 a set!

Comments
As ever, direct comments / additions / hate mail to ... jcjoyce@iee.org