When an electric forklift is not performing as it should, a number of possible causes need to be explored.
The battery/charger package is definitely a good place to start troubleshooting, as any problem here shows up quickly in the behavior of the forklift.
If a forklift has shown a gradual decline in its ability to do the work at hand, and charging practices and workload have remained constant, then the evidence points to an aging battery. Any battery five years old or more is likely to show signs of age-related loss of capacity. It is also at this point that you are more likely to encounter individual cell failures that can suddenly disable the battery.
Failures can occur at any age, however, and this is especially true of batteries that have been abused (improper watering, improper charging or operation at high temperatures, for example). The following steps will guide you through a suggested battery checkout procedure.
It is important to get a clear look at the top of the battery, its cables and connector. Remove accumulations of corrosion products and while the battery is disconnected from its charger and the forklift, test the cable connections by tugging on them and flexing the cable. If anything comes loose, you’ve found at least one problem that must be fixed immediately.
Likewise, if cables are swollen or stiff (often noticeable at the battery connection point), they must be replaced. Replacement is a job for a professional. The only proper way to attach cables to a battery involves fusing (“lead burning”) the lead cable terminations directly to the cell post, which can be a dangerous job because of the explosion hazard caused by oxygen and hydrogen gases often present near each cell vent opening. The presence of explosive gas is also the reason that mechanical, temporary, cable-to-battery attachment methods are out of the question. Sooner or later such a connection will produce a dangerous spark under load.
Corroded, heating or damaged connectors (plugs) are another problem area that must be fixed immediately. Poor contact by the spring-loaded connector tips can interfere not only with transmission of power from battery to forklift, but also with charging. Check the connector assemblies on the charger cables and the lift truck as well.
There are two measurements commonly used to determine the state of charge as well as the electrochemical health of a battery: voltage and specific gravity. An ordinary DC voltmeter can be used to check voltages (cell voltages can range from 2.75 to 1.70 volts during a charge/discharge cycle). But be aware that open voltage readings only give the crudest of indications about the cell. Voltage readings are most meaningful under a specific (rated) current load, or when taken at a known point in the charge cycle.
You can tell if a cell is in bad shape, however, if its voltage is significantly below its neighbors when the battery is at rest. Start your check by using sharp probes to get good contact with each cell’s posts (lead connector straps connect one cell’s posts to its neighbors in the circuit – plastic covers commonly cover these straps and may interfere with readings unless you temporarily remove them). You may find it faster to take readings of a whole row of cells at a time to check for unusual voltages. For comparison purposes, make sure you include the same number of cells in each reading. Typically, lead-acid cells at rest are approximately 2 volts, so each 6-cell row in a typical 18-cell (36-volt) battery will show 12 volts or thereabouts. The exact voltage for a row is not important, but the difference from one row to another provides information. If you notice a difference of a volt or more, the battery may have problems.
More meaningful is a similar voltage reading under load. If the battery is installed in a lift truck, this is fairly easy to do. Some lift truck masts can be safely tilted back against the stop to provide a brief high-amperage load on the battery – or the lift mechanism may be operated under load. Do this while observing the voltage behavior of each cell or selected groups of cells. Cells which drop below 1.70 volts, or those that drop significantly lower than the others, are suspect. If most of the cells in the battery drop below this level, make sure that the battery is fully charged before trying again.
This quick exam is a troubleshooting aid only. Such voltage checks in no way substitute for a standard capacity discharge test which provides a complete picture of the battery’s condition during a 6-hour load cycle. Anyone who bases a forklift or battery transaction on the findings revealed in a few minutes of voltage readings is not being wise. A capacity discharge test often overturns the findings of such brief exams, especially when the battery in question has been sitting unused for an extended period, has had a history of improper charging or has been operating with diluted electrolyte in one or more cells.
Hydrometer readings provide clues
If the battery has an adequate level of electrolyte visible in all cells, and has been fully charged since it was last watered, a hydrometer can be used to check the specific gravity and determine the status of the battery. An ordinary auto battery hydrometer can be used if it provides numerical readings.
Once again, what you are looking for are readings of individual cells that depart from that of the rest of the battery. Specific gravity in a normal battery ranges from 1.150 (“1150”) discharged to 1.275 (“1275”) charged. Some high-performance batteries have a fully charged specific gravity in excess of 1300 (the battery should be labeled accordingly). If an individual cell in the battery shows a considerably lower specific gravity than the rest (more than 25 points difference), a potential problem has been identified.
If you are examining a battery with an unknown history, you will not be able to tell whether a cell or cells have been operating with diluted electrolyte due to overfilling and subsequent flushing out of the acid over time (extreme corrosion around the battery’s steel case and in the bottom of the truck compartment can give a strong clue, however.). This is a correctable problem, unlike a cell that has a depressed specific gravity due to internal failure. Questions like this, as above, can be resolved with certainty only by a battery technician.
Some problems are obvious enough to tell you that a battery needs substantial work before it can be used. A cell that issues a jet of steam with a strong hydrogen sulfide (rotten egg) odor has certainly failed, and more than a couple such cells in an older battery almost always means : “damaged beyond economical repair”. Physical damage (from dropping the battery or other impact) that has resulted in cracked or distorted individual cell jars (cell containers) or cell covers within the battery always means a visit to the battery shop.
Once again, the above exam can only give you a general impression about the health of a battery. The best guidance is provided by a complete capacity discharge test and evaluation by a trained battery technician.
For more information, contact Arcon Equipment Inc. (440) 232-1422.
