Choosing a battery charger

There are many factors that determine the type of charger required for a particular application. Choosing the right charger is very important to insure not only all requirements are met but also the charger is not over specified resulting in a more costly solution than required. The primary factors in determining charger specifications can be divided into environmental and electrical categories.

Environmental factors

• Is a waterproof charger required? What are the temperature and humidity requirements? Will the charger be exposed to the element? Will it be used in a highly polluted environment where dust and grime are prevailing? Will it be used in environments where condensation can be produced? Is an extreme temperature range required for very cold environments? Chargetek has units with operation to -35C°. The waterproofing provides a hermetic seal that makes it impervious to these situations. In addition, Chargetek uses only UL94-V0 encapsulation material to insure that highest level of safety.
• Fan cooled pros and cons. There are many factors that determine the type of charger required for a particular application. Choosing the right charger is critical to ensure that all requirements are met and that the charger is not over specified. One of the primary factors in charger selection is the operating environment. Please review our waterproof page to determine what is appropriate for your application. If it is determined that a waterproof product is not required, then fan cooling can provide several advantages. The pros and cons of fan cooling or forced air cooling are described below.
  
Advantages
• Reduced component temperatures translate into higher reliability and lower MTBF
• Fans are very effective in forcing air through the unit and reducing internal temperatures
• Power output is 2-3 times greater than convection cooling
• Most restrictions on the system thermal design are eliminated
• The charger can be mounted in any orientation
• The physical size of the charger can be significantly reduced


Disadvantages
• Acoustic fan noise can be a negative for quiet environments
• Dust and other contaminants can be drawn into the unit
• Accumulation of contaminants on the fan and components reduces cooling effectiveness
• Air filters mitigate the negative effects but require maintenance to clear or change
• Fans are usually the least reliable component in the unit
  
  
• Vibration and shock requirements. Do you have a mobility, marine or industrial application where severe vibration can occur regularly? If so, you may want to consider the waterproof series. The encapsulation transforms your unit into a "brick" that allows no movement of external parts preventing things from shaking loose and resulting in failure.

System electrical factors

• Input AC voltage range. Will the charger be operating from 110VAC or 220VAC? Chargetek offers units in both input ranges.
• Number of battery banks required. How many batteries are required to be charged? Is it possible to save cost by using a multi-bank charger as opposed to a single output unit? For example, consider a 24V system comprised of two 12V batteries in series. The entire battery pack can be charged with a single 24V unit or the two 12 batteries can be individually charger using a CT 500 dual output units. Chargetek offers single, dual and triple output units that can be configured in many ways. See the charging system configuration page.
• Do the banks share a common negative or are all banks isolated? There will be a significant cost savings if the batteries share a common negative. If the batteries are stacked then the isolated output series are required.
• Battery stack considerations. If your application requires a stack of batteries to generate a 24/36/48V output then there are several factors to consider both in system design and choosing a charger.
  • Charge balancing. When batteries are charged in series by a single output charger, there is no way to determine if both batteries (24V system for example) are being equally charged. Although the current being applied to both batteries is identical, the capacity, age, specific gravity, etc. of the two batteries may not be close enough due to aging (assuming the batteries are an identical type) resulting in unequal battery voltages. For example, it may be possible for one battery to be at 16V and the other to be at 13V. The multi-output charger compensates for this by charging and monitoring each battery separately.
  • Tapped loads. A single output charger should not be used if the loading off the stack is not equal. For example, if there is a 12V load off the first battery and another from the entire stack, the discharge currents for the two batteries will not be equal and therefore equal charging currents will not provide a balanced charge to both batteries. Similarly, when building a stack all batteries should be the same type. Again, the multi-output charger compensates for tapped loads by charging and monitoring each battery separately. This could actually save the requirement for adding a third battery if a 12V load is required. In any case, the loads should be cut off if any battery voltage is less than 9.5V since this is a deep discharge and continually draining the battery at this point is not recommended.
• Type of battery chemistry. Chargetek offer chargers for several battery chemistries. While the standard units are lead-acid types, Chargetek has the capabilities do custom applications for other chemistries such as lithium Ion, Ni-Cd, Ni-MH, etc.
• Is a maintenance or three-state charger required?
  • Maintenance use. Will the charger be used to maintain the charge on a car, lawnmower or other personal craft that will not be used often and has its own charging system? A maintenance charger can be used for these types of applications.
  • Three state charger: If the charger will be the primary charger for the battery then the three state charger is what you need. This will return 100% capacity every time and reduce the voltage when complete to maintain the battery at full capacity indefinitely.
• UL/CSA or other safety agency requirements. Are there safety agency requirements that need to be complied with such as UL and CSA. Are there any particular specifications that need to be met? Chargetek products are being tested to CSA and UL specification 1236, which is a very stringent marine specification, which allows them to easily pass many other applications with little or no changes.

Battery characteristics

• Battery chemistry. Chargetek has products that can charge virtually any battery chemistry. Their chargers can be easily altered with simple flash programming at the factory to charge any battery and produce any charging algorithm to your specification. Please consult Chargetek Sales for any requirements you may have.
• Voltage rating. The battery must have the proper charging voltage applied. For example, it is acceptable to apply a 12V charger to two 6V batteries in series since this equals 12V but not to use the charger to charger the batteries individually.
• Charging current acceptance. The charging current is one of the most important criteria in choosing a charger. An excessive amount of current will overheat the battery resulting in reduced battery life and poor capacity. Some batteries are able to accept very large charging currents while others are more sensitive. You must check your battery specification to insure that you are not applying current in excess of the recommended amount.
• Depth of discharge. Is your application one where the battery is only moderately used or will it undergo deep discharges. Is it heavily discharged infrequently or very often? Is there a requirement to charge quickly or is there plenty of time. The following procedure will provide a good rule of thumb in determining your charger requirements:
  • Calculate the amount of drain on the battery in terms of amp hours. For example, if your battery is providing 10 amps for 3 hours this is equal to 30 amp hours (number of amps multiplied by number of hours). Similarly, 3 amps for 10 hours is also 30 Amp hours. However, this is not an exact equality since at the higher discharge currents more energy is lost in the battery during discharge due but it is close enough in most cases. For a more exact calculation, refer to the discharge curves of the battery specification where discharge time as a function of current is provided.
  • Now that the number of amp hours is calculated, divide this amount by the number of hours you have available to charge to determine charging current. For example, if you have only six hours to charge, you will require a 6 amp charger (30 amp hours divided by 6 hours = 5 Amps).
  • Multiply the number obtained in (3) by 1.3 to provide for charge acceptance and energy lost during charging: (5 Amps * 1.2= 6 Amps).
  • Now check the battery specification to insure that the battery can accept 6 amps and charge effectively. If not, the recharge time you allowed will have to be increased.

If you have any questions about your battery charger selection, please contact us by phone or at the email address given below.