Whether you are buying or replacing a fleet of batteries or electric forklifts this article may be for you.
Electric forklifts have been a thing for decades as well as lead acid batteries, and neither is going away anytime soon. Regardless of what technology is on the horizon and barring any unforeseen legislation; and the latter not being too far-fetched.
Many possible situations can cause a need for know-how on the topic of batteries, eg. purchasing new batteries for your fleet, a new fleet of trucks, converting from internal combustion, etc. and if you are in that then this article may help.
Battery Voltage
For whatever reason, there was at some point a belief that 48V on a size of truck that was traditionally 36V would be more efficient because of the lower use of “amps”. That may be why some forklift manufacturers, who previously made their sit-down type 36V lift trucks to a certain capacity convertible to 48V, or vice versa, now make those same trucks either 36V or 48V with an accommodating gear ratio and smaller motors for the higher voltages. This is because engineering caught up with fads and proves that electrical efficiency is not decided by how many amps are drawn, but by how much of the overall power consumed is used by the system.
For every change, there is a tradeoff. If you go higher on the voltage, then you have to use increased motor speed for your power. In other words, to get the efficiency, you have to compensate for every change made with a gear ratio, a smaller pump that turns faster, or electronics that convert the battery voltage so that the input marries up to the gear ratios. Either way, something has to be done to compensate for change from what was already found to be optimum. In the long run, no matter what voltage is used, Amps x volts = Watts, and watts is the “gas tank”.
A lead acid battery is made up of 2-volt cells, with a certain number of plates in each cell. The number of cells adds up to make the total voltage, so 18 cells make a 36V battery and a 24-cell battery produces 48V. The higher the voltage the more cells are required, and that means more plastic walls and less lead, usually less capacity. For instance, for both a 3-wheeled sit-down 4K capacity, and a 6500lb capacity, the 36V came out 2000 watts stronger. That means that the 36V for that size has more power than the 48V comparative.
Lead acid batteries also have the issue of water evaporation, and low water will wreak havoc on any battery, regardless of voltage. Higher voltage batteries, having smaller cells, will have less surface area in each cell and will need to be watered more frequently. This is especially true for hotter environments and more intense usage. And both will compound the issue.
In the end, the “traditional” is usually the safest and most efficient choice. The good thing is that there are traditional voltages for each size forklift, and that, in my experience, has always been the winning choice.
Battery Size
Electric lift trucks, excluding pallet jacks, typically have a minimum and maximum weight. Fortunately, on most trucks the box sizes are relatively common throughout the brands, although assumption is highly unwise. Sometimes there are batteries for certain model trucks that do not take up the whole compartment but meet the minimum battery weight, but typically need something to fill the extra space. Good practice in this regard is to “fill the box” of the forklift with a battery that is made to fit snugly in the battery compartment, without having to install stops and fillers. The compartments are typically sized to optimally fit the “traditional voltage” battery.
Getting smaller batteries for particular truck models, and certain models come with varying battery compartment sizes, is in some cases the right option. For instance, for some makers, a 3.5K sit-down three-wheeler can be spec’d with a 17 or 21-plate 36V battery compartment. The 17-plate battery is going to come with a smaller price tag and allow for an inch or two less turning radius overall, and maneuverability with intentionality can bring noticeable energy savings. All of that spells efficiency and can make a difference when properly applied.
However, using a larger battery may bring more run time and a little more lift capacity at higher levels due to the extra weight for counterbalancing. Not only that but a higher plate count has been known to be more reliable in the long run, although maybe a minor advantage added in, but that advantage does grow larger when compared to a higher voltage battery with significantly fewer plates in each cell.
Most battery manufacturers have what is called a battery selector guide, a tool that enables you to pick and choose a particular forklift, system voltage, and battery dimensions that can be somewhat helpful for ballparking specs. Typically, you can change the voltage and compare the wattage capacity and weight for the different sizes and voltages. In some cases, going up or down in voltage makes little difference, and is sometimes the same, but when there is a dichotomy between the two for a particular box size, the advantage is usually on the lower voltage. An example of the comparison is that with both a 3-wheeled sit-down 4K capacity, and a 6500 lb capacity, the 36V came out 2000 watts stronger. That means that the 36V for that size can transfer more power than the 48V comparative.
To summarize, most of this has been figured out for a long time and it is really simple, keeping it that way will likely make your next purchase a long-term win.
The good thing is that there are traditional voltages for each size forklift, and that, in my experience, has always been the winning choice.
By Dustin Link
