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Engineering Series
EV ENGINEERING – BATTERY CHARGERS

Charger Output (VDC)
Quality batteries are fundamental to any reliable EV.  And not all batteries are created equal.  But just as important as the quality of the batteries is a good battery charger.  If the batteries do not receive a proper charge, they will not deliver the performance required of them.   

The basic equation is:
Watts = Volts x Amps or Amps = Watts/Volts

The most important requirement is to ensure that the battery charger meets the requirements of the battery manufacturer.   Typically, for a wet lead acid the manufacturer recommends that the charge rate be 10% of the 20 A-H Rate.  So for a 6V Trojan T-125 with a 235A-H rating, it should receive a 23 amps at charge.  If you have a 144V system, then the charger should be capable of 144V x 23 amps = 3312 watts.   A 3000 watt charger would be marginally acceptable.  A 1500 or 2000 watt charger would not be acceptable; it might result in long term degradation of the battery performance.
For Trojan AGM batteries, the charge rate is 20% of the 20 A-H Rate.  For the 6V AGM with 200A-H Rating, the charge rate should be 40 amps.  If you have a 144V system, then the charger should be capable of 144V x 40 amps = 5760 watts.  You can see that a 5000 or 6000 watt charge would be required.  So while you are evaluating batteries, also evaluate the battery charger and its cost.
This is even more critical if you consider lithium batteries.  Lithium batteries may require a Battery Management System in addition to a Battery Charger.

Charger Input (VAC)
Equally important is the input side.  Most AC outlets are designed for 115VAC and 15 amps.  That is only 1725 watts.  That will limit the both the input and output of the charger.  For 230VAC 20 amp service, the limit is 4600 watts.  It is clear that a 3000 watt battery charger will be under utilized on a 115VAC circuit because it is limited to only 1700 watts.
Sometimes a customer buys a 6V battery pack for a 120V truck and tries to charge it on a 115VAC circuit.  Consequently, the battery pack that should be charged at 23 amps is charged at only 12-14 amps.  In time, the range decreases significantly not because of battery life but because the batteries were never charged properly.  
Our rule of thumb is that if the battery pack weighs 1000 lbs or more, you need 230VAC for charging.   You can use 115VAC as an opportunity charge, but long term use is not recommended.

Charger Options

One of our suppliers Quick Charge Corporation (www.QuickCharge.com) provides battery chargers with a 3 year warranty.  Quick Charge has been a U.S. manufacturer of industrial chargers for over 30 years.  EVA assisted Quick Charge in entering the EV Market in 2007.  Quick Charge’s latest family of chargers are designed specifically for the EV market. Models include on-board, and stationary types, ranging from 72 to 156 volt, and 10 - 40 amp outputs as shown.   These chargers are User programmable for the type of battery (wet or AGM).  You simply push a button.  Now the programming includes lithium batteries.  For lithium applications, it's important to know the number of cells, nominal, and charge to voltage. With their transformer based technology, Quick Charge can quickly design and manufacture battery chargers for one-of-a-kind applications.

EVA also offers PFC battery chargers ranging from 1500 – 5000 watts.  These units are programmed by the importer, Electric Conversions, (www.zivanusa.com) for the specific voltage and battery manufacturer.  

Both of these manufacturers have good battery chargers.  The question is what is best for your specific application.  At EVA, we can help you select the right charger.  
April 2010