Reprinted from the JetProp Bulletin Board

 

Posted By: Chris Hollenberg <cwhollenbe@aol.com>
Date: 2/26/03

In Response To: deep cycle batteries (ken pritchett)

Technically, there is no such thing as a "deep cycle" on these batteries. Deepcycling is what you do to NiCad batteries to restore their capacity, but our batteries are lead acid type batteries. So your battery guy is partly correct.

What you must do with some regularity, however, is a conditioning procedure that removes sulphidation and gets the batteries to accept a charge more easily. It is very similar to a "deep cycle". Concorde, the manufacturer, is very specific about what needs to be done:

First, discharge the battery at the C1 rate (that is 12 amps for our model) until the voltage drops to 18 volts. Then, charge it with a constant current of 10% of the C1 rate, which is 1,2 amps, for a full 16 hours. The charging part is somewhat brutal, as you will end up with a charging voltage of around 31 volts towards the end of the 16 hour period, and the battery will be gassing a lot. But it is necessary to keep the battery in good shape.

Any good battery shop will have the necessary equipment. You can use chargers normally used for NiCad batteries. Alternatively, you can even do it yourself. I recently did it, and used a laboratory power supply for the constant current charge. The whole equipment cost me less than $ 200, and the results were just fine. You can probably even do it with the batteries installed in the aircraft, although Jetprop advises against doing it that way.

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UPDATE:

 

New technology has come a long way in conditioning lead acid batteries in the last few years. The most exciting to us is the disulfide/chargers. I have been using the BatteryMINDer (Cost about $140) for the past 4 years with great results. The basic principle is the disulfide pulse circuit changes the sulfide built up on the plates back into sulfuric acid, instead of the flakes dropping to the bottom and shorting out the plates. These flakes develop internal resistance and discharge the idle battery. The chargers also automatically float the battery after fully charging it.

 

I have the original batteries that came with my conversion in 2000. According to the Shadin, the starting voltage today in 2007 is the same as it was when they were new. I keep the charger on the batteries at all times when the airplane is in my hangar.

 

The batteries can be charged together in parallel.