Battery chargers are an overlooked element of electric forklift operation.
Chargers are often overlooked by end-users. I’m sure your customers know what brand of lift truck you sell. They might know what battery you’re selling. But they almost never know much about the battery charger.
The battery charger plays a critical role in the whole material handling process, yet many lift truck salespeople spend lots of time selling the qualities and features of their lift truck and almost none with the battery charger.
In their zeal to sell an electric lift truck, many salespeople cut corners when it comes to the charger. Keep in mind, a battery that is charged improperly or inadequately will reflect negatively on the truck’s performance. It may not be evident immediately, but eventually, the operation of your truck will be affected. So, what should you and your customers know about chargers?
Types of Chargers
There are multiple types of chargers available today for a wide range of applications. Ferroresonant chargers are still the most popular because of their simple yet rugged design. This type of charger must be matched to the battery by ampere-hour (AH) capacity and voltage.
Another type is a Silicon Controlled Rectifier (SCR) charger. It can offer greater flexibility than a ferroresonant charger, but it is typically more complex and slightly more expensive. The biggest advantage of SCR chargers is that they can be designed so that one charger can charge flooded or valve-regulated lead acid (VRLA) batteries with a wide range of voltages and AH capacities.
The newest charging technology is Isolated Gate Bipolar Transistor (IGBT). This type of charger has many of the same characteristics as SCR, but is more complex and more expensive. However, there are definite advantages with the input power characteristics, such as efficiency, power factor and harmonic distortion. In addition, because of the high-frequency switching of this charger, there may also be significant reduction in physical size and weight. IGBT chargers are primarily targeted for opportunity or rapid charging, but may be programmed to fit nearly any type of charging application.
Within all the different types of chargers are a variety of ratings—100 percent, 80 percent, 60 percent, single shift chargers, rapid chargers, opportunity chargers, and the list keeps growing.
Before the days of lift interrupts and battery gauges, many batteries were discharged beyond 80 percent. Therefore, it was necessary to provide a charger capable of fully charging the battery from 0 percent to 100 percent in eight hours. These chargers typically will have a maximum output current of 19-21 percent of start rate for a ferroresonant charger, or 16-18 percent for a SCR charger. These are still the preferred chargers for many customers because they allow for fluctuations in work schedule.
To compare chargers, make sure the maximum output currents are close to the same. Typically, the higher the output current, the faster the charge. This holds true only when comparing a ferroresonant charger to another ferroresonant, and an SCR charger to another SCR.
Naturally you want to match the charger to the battery as closely as possible. So if you are quoting your truck with an 18-85-21 battery, your charger should be an 850 ampere hour, 36-volt charger. The ampere hour rating of the charger should vary no more than +/- 10 percent from that of the battery it will be charging.
Next, consider the power availability of your customer. Do they have single-phase or three-phase? Many high output chargers are only available in three-phase, so your customer must have this power available. But a single-phase charger can be connected to a three-phase line, and when properly installed, there is no difference in operating costs of single-phase versus three-phase.
For the last 20 years, truck manufacturers have provided the customer with the tools to control depth of discharge, and the number of batteries that get discharged beyond 80 percent has been drastically reduced. This is why most charger manufacturers offer chargers that are designed and rated to only return 80 percent of the battery’s rated capacity in eight hours.
Another consideration is the application. How many shifts do the trucks operate? If your customer is truly operating a single shift operation, with no intention of adding additional shifts, they can get by with a charger designed specifically for this type of application. These chargers are typically identified as single-shift chargers or extended charge time. The recharge time for these chargers is 10 to 16 hours and will have a 10 percent to 16 percent start rate.
What is the ambient temperature of the area in which the trucks operate? This is typically the concern for cold storage application. The amount of time the trucks spend in the cold environment will determine the actual electrolyte temperature. Charging batteries with electrolyte temperatures below 70 degrees Fahrenheit presents a special application and is best addressed with a charger that can measure electrolyte temperature and adjust its output profile accordingly. At a minimum, oversize the charger to compensate for the lower temperature battery.
How much time is available for charging? How many batteries per truck is the customer purchasing? What are their future growth plans? (A well-designed charger will last 15-20 years.) All these things affect the type and size of charger you should quote.
Probably the biggest mistake a new lift truck salesperson will make when selecting a charger is undersizing. Regardless of the charger type, it will create problems if it is not large enough to fully charge the battery in the allotted amount of time. You may be saving your customer a few bucks in the short-term, but you will cost your customer and yourself much more in the long run than you initially saved.
An undersized battery charger will eventually lead to battery sulfation, which reduces the battery ampere-hour capacity. This means that the lower voltage of the battery causes all the components on the truck to draw higher currents and run hotter, shortening the life of those components and increasing lift truck maintenance costs. The battery won’t last its maximum life, and the warranty may be voided as a result of improper battery charging.
Listen to your battery and charger experts. They want their equipment to look good, and if they look good, so will your lift truck!
|Meet the Author
Jim Keyser is business manager at AMETEK Prestolite Power, located in Troy, Ohio, and on the Web at www.prestolitepower.com.