A few months ago, your plant got a new plant manager. During his first week, he ordered the warehouse department to replace six of its 10 LP gas lift trucks with electric. This brought the total number of electric lift trucks from two to eight. He also ordered the production department to replace four of its eight LP gas lift trucks with electric, bringing their total number of electric lift trucks from two to six.
The purchasing department ensured that each of the replacements had at least the same lifting capacity as the truck it replaced. Chargers were bought and installed prior to delivery of the lift trucks, and a charging scheme was implemented to rotate all electric lift trucks in and out of charging throughout each shift.
But now there are problems, such as not enough lift trucks available when needed, lift trucks stranded on ramps, and lift trucks unable to lift the loads they were intended for. The plant manager is blaming the maintenance department for not properly charging the lift trucks and says if the problem isn’t fixed soon some heads will roll.
Your boss, ever confident in your abilities, wants you to look into it and write a report of your findings. What is wrong here?
Answer to Quiz. It is possible (but unlikely) that the chargers are putting out the wrong voltage (too high will degrade the battery while too low will fail to charge it). So check the battery charger outputs, and check that the charging schedule is being followed.
Despite the plant manager’s suspicions, it is almost certain that nobody in maintenance or engineering is to blame. The most likely culprit is the new trucks were not the right choice. Since the plant had electric trucks before the replacements were brought in, the problem isn’t electric trucks per se. It’s a mismatch between trucks and operational needs. Deciding on the right truck is not just a matter of considering the lifting capacity.
It helps to think of an electric lift truck as a battery-powered one because the battery is the limiting factor when it comes to how long that truck can last on the plant floor. This limiting factor sometimes escapes consideration when a decision-maker believes that a battery-powered vehicle is emissions-free. It’s not. Aside from battery gassing, the emissions occur at the power plant instead of locally, and LP is a much cleaner power source than coal is. Plus with LP, you don’t have the big transmission losses involved in getting the electric power from the generating station to the battery charger. Yet in a given environment, LP might be the wrong choice because of its localized emissions. On the other hand, factories are typically designed with LP lift trucks in mind and ventilated accordingly.
So in the typical factory, LP lift trucks are generally advantageous over battery-powered ones. If the gas cylinder for an LP truck starts to run low, the gas isn’t any less potent, so the engine doesn’t strain or overheat due to being low on gas. But when a battery-powered truck has a low battery, the voltage is also low. That causes the motor to strain when doing the same lift it could easily handle on a full charge. As the motor gets hotter, it draws more current from an already weak battery. This is why battery-powered lift trucks can “mysteriously” die when going up a ramp while carrying a load.
There’s not a cheap way to solve this problem, but here are some solutions to explore:
- Buy back some of the LP trucks that were replaced. Adding some of these back to the mix could alleviate the pressure on the battery-powered trucks enough to end the complaints.
- If possible, upgrade the batteries on the existing battery-powered trucks to higher capacity ones, and upgrade the chargers and charging schedule accordingly. Note that the insurer or fire marshall may pose limits on how big these batteries can be, so check with all authorities having jurisdiction first. The same applies to total battery capacity (balanced against fire suppression and related systems) in a given area such as the truck depot.
- Install additional, remote charging stations. These can be used when a truck is temporarily idled (e.g., between dropoff and pickup) away from the main charging area (e.g., the truck depot). Also invest in some portable chargers for when a truck is stranded.
- Instruct battery-powered lift drivers to reduce pallet loads by 20% wherever practical. Even though the truck can lift X weight, the problem is the stored energy required to carry that much weight from Point A to Point B. Speed reduction can also make a huge difference. However, these solutions might not be compatible with operational needs.
- Try to design work flows and truck paths so battery-powered lift trucks don’t have to change elevations as much. Going up and down ramps uses a lot of stored energy. You can also consider installing machinery (conveyors, robotic arms, etc.) that will move the intended loads closer to the main truck paths especially in terms of elevation.
If the plant is laid out and organized by functional cells instead of production flow, changing the layout to production flow will eliminate the need for so many lift trucks. This would be the most cost-effective solution in the long run. The seminal book on this topic was published decades ago, and the concept has since been widely adopted. The book is The Goal by management guru Eliyahu Goldratt. The decision to implement production flow layout is outside the scope of maintenance or even the plant engineer. But if the plant manager wants to reduce waste and pollution, this would be the way to go. Plus, it has the “side benefit” of increasing production significantly. Have a friendly chat and suggest it.
