Analyzing Forklift Battery Charging & Discharging Patterns

Forklift power study data was acquired to analyze battery charging and discharging patterns. Data being analyzed is from  6/5/22 through 7/5/22 and was pulled from the existing battery modules. 

The graphs below show battery amps used and amps returned to the battery. The green line on the  graphs represents an 80% depth of discharge for a 750Ah battery. Flooded lead acid batteries are  allowed to use 80% of their total capacity in a typical 8 hour shift application.  

Battery Usage (Throughput)

Battery throughput on the graphs is represented in orange. Usage up to the green line is  consistent with a conventional application which is typically 6 hours of lift use (or an 8 hour shift) in a 24  hour day. Truck #1 does have few days where utilization was above the green line putting it into an  opportunity charge application. Those days also show that there wasn’t a sufficient amount of charge  returned back to the battery. 

Discharge.

Single shift application involves 6 hours of cumulative usage of equipment. Over 6 and less than  12 hours a day (2 shifts) is ideal for opportunity charge. More than 12 but less than 18 hours a day fast  charge is ideal. The data from this power study indicate this is a conventional charge application. If  production increases or an additional shift is put in place, opportunity charge may need to be  implemented.

Open (Idle) & Charge.

Idle time plus charge time is to be considered available time to recharge. This typically applies to  opportunity and fast charge. All graphs indicate that the batteries are being charged sufficiently for the  current application. Trucks #1 and #9 show days that the batteries didn’t get fully charged.

Daily Plug-In.

It is extremely important to make sure the batteries are being charged at the end of the shift. This is to  ensure that the batteries have enough charge to make it through the following day, but also the warranty  requires that the battery receive a full charge daily.

Truck #1

Truck #5

Truck #9

Areas of Improvement

• Depth of Discharge  
  Batteries should never get below a 20% state of charge. This is considered over discharged which can damage the battery and void the warranty. Over discharging causes  heat, and that heat causes the lead oxide to shed from the plates in each cell more  rapidly. As this happens the battery loses capacity and run time gets shorter and shorter.  Excessive shedding can also cause shorting inside the cells leading to premature failure.    
• Charging.
  Data shows that there are days that the batteries either didn’t get charged at the end of the  shift or wasn’t on charge long enough to return the amount of amperage that we used within that 24 hour period.  
• Battery and Charger PM’s.
  A visual inspection of the batteries reveal that they haven’t had a PM or battery wash in  quite a long time. Damp dirt and heavy corrosion conduct voltage across cells and also to  the steel case of the battery that bleeds over to the truck causing electrical issues and self discharging of the battery.
  
  The biggest threat to chargers is dust. Although the charger modules have cooling fans and a filter on the front, the fans introduce dust to the internal components which in turn  cause excessive heat and eventually failure.

  Neither of these are covered under warranty and can lead to the warranty being voided.