With so many forklift battery charger manufacturers selling in the market, how is a savvy warehouse manager or purchasing agent supposed to know which charger is best for his or her company’s operation?
Below, Warehouse IQ has provided a simple guide to selecting the best forklift battery charger and power solutions for your operation.
Shift Work – How many hours does your lift truck work?
How many shifts are you working your electric forklift? If you answer one shift, then the usual combination for electric forklifts is:
- 1 lift truck
- 1 battery
- 1 charger
A shift is defined as 8 hours of paid work to a forklift operator. In that 8 hours, a forklift will likely work 5-6 pedal hours of work. That means, the lift has a motor running (lifting, lowering or traveling) for 5 or 6 of the 8 shift hours.
Single Shift Operation Battery Charger Recommendations
The charger recommended for this type of operation is a Conventional Overnight Charger. This means you will purchase a lift truck, a battery and a single dedicated conventional charger.
Conventional Overnight Battery Charger
A conventional overnight forklift battery charger charges a battery overnight for 8 full hours. The start rate of the charger is usually between 15% to 20%. That means the charger pushes 15% to 20% of the battery’s total rated ampere hours (energy) back into the battery in the first hour.
What does start rate mean? Imagine you are using a standard sized garden hose to fill a large forklift battery sized bucket. Now imagine the hose you are using has enough diameter and pressure to pour enough water in the first hour to fill 15% to 20% of the bucket. Therefore, the start rate at which the hose fills the bucket at the start of the filling session is 15-20%.
Does that mean the battery will be fully charged in 5 hours assuming a 20% start rate? Yes and no. Yes the battery would be full in 5 hours if a 20% start rate charger continued to charge a battery at 20% continuously. However chargers are designed to reduce the amount of charge over time so that a battery charges more at the start of the charging cycle and is reduced to a very small charge at the end of its charging cycle. This is why a battery takes 8 hours to charge on a conventional overnight battery charger.
Different types of conventional forklift battery chargers
There are multiple types of conventional (overnight) chargers for lift truck batteries. They include:
Multiple Shift Forklift Battery Charger Recommendations
You are probably considering higher output chargers because you run multiple shifts, you have a battery changer and you have more than one battery per lift truck. Your options are
- 1 lift truck
- 2 batteries
- 1 charger
- 1 battery changer
- 1 lift truck
- 1 battery
- 1 high output opportunity or fast charger
Price of Conventional vs Opportunity Chargers in a Two Shift Operation
If you have more than one shift, you will need to look at your battery charger infrastructure costs carefully . Consider the costs in the two scenarios:
(1) 18-125-13, 750 36 AH volt battery = $5,500 x (2) = $11,000 for two batteries
(1) conventional overnight charger = $2,000
(1) battery changer mounted to a pallet truck = $10,000
Total of $13,000 for power, plus a battery changer
Compare that to
(1) 18-125-13, 750 36 AH volt battery = $5,500
(1) Opportunity charger = $4,000
Total of $9,500 for power.
That can be a $3,500 savings.
The True Cost of Opportunity Charging
But be careful. It looks like by using high output opportunity chargers you are saving the price of a whole battery but you are not and this is why.
The average life of a forklift battery
By operating a forklift on a battery, you are taking ampere hours (amps) out of the battery and then replacing the amps through charging, then taking them out again until the battery stops working and is worn out. So let’s do the math:
(1) 750 AH battery has 600 useable amps because a lift truck takes only 80% of the amps out of a battery.
A standard battery warranty is guaranteed for 1500 cycles. Therefore,
(1) 750 AH at 80% = 600 AH x 1500 = 900,000 total amps to the end of it useful (warranted) life.
At 600 AH a day, the battery will run for 6 years.
Using a standard 750 AH battery and using 600 AH per shift, but replacing 25% of the total amps over a single hour of breaks (2 x 15 minutes plus 30 minutes meal break times two shifts) using an opportunity charger you will get 62% more shift life out of your batteries. This amounts to 975 amps per day. However, you will also lose battery life at the same rate.
How many shift hours will you get out of a 750 AH battery on opportunity charge? Well, 600 AH (which is 80% of the rated capacity of the battery) divided by 8 hours = 75 amps per hour. Now with 25% start rate opportunity charger, you will get 975 amps available divided by 75 amps per shift hour = 13 shift hours (not quite a full second shift).
As for the life span of the battery, we need to see how many years a battery will last with 975 AH being exchanged each day versus only 600 AH being used previously on a second shift. Let’s do the math:
900,000 total amps divided by 975 used per day = 3.69 years
Your forklift battery will now need to be replaced 2.31 years sooner than the original 6 year life expectancy.
Fast Charge Forklift Battery Chargers
Need more than 13 shift hours? You will need a higher output charger. Instead of a 25% start rate, lets use the highest start rate of 50%. Now a 750 AH battery will have 375 amps returned to the battery per hour of charging. Given the same number of hours to charge (2 hours), you can expect a full 1,350 AH available per day.
Divide 1350 AH by 75 amps per shift hour and you will get 18 hours of energy available in your batteries to run your lift trucks. That is 2.25 shifts.
If you use the full 1,350 amps per day, your battery will likely last only 2.66 years.
Differences between Standard Charging, Opportunity Charging and Fast Charging
So those are the differences between standard overnight charging, opportunity and fast charging a forklift battery. Put more amps into a battery based on the start rate of the charger will increase the available amps in the battery by replacing them in a meaningful way on breaks and at meal times. The more amps you need to work the increased number of hours due to longer shifts or more shifts will determine which charging method you will need to use.
However, the total life span of the battery will either be consumed in a shorter or longer time frame. With opportunity chargers and fast chargers, you will still need to buy extra batteries, just not all at the same time. You do not need to have extra batteries on hand, but you will need to buy batteries sooner rather than if you were using a standard overnight charging approach.
Lithium Ion Battery Chargers
Learn about lithium ion batteries and their chargers in this article: How viable are lithium ion batteries on forklifts?