Electric Flight in Australia

 

Can I use any type of nicad cells?

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The answer to this is, no! Some ni-cad cells are designed only for trickle charge and low current drain. It is dangerous to fast charge this type of nicad cell, and, if you try to draw many AMPS from them they will become very hot, melt their plastic casing or even rupture.

You must make sure that you have vented ni-cad cells before you attempt a fast charge . The vent allows gases to escape. But there is still a great variation in vented (fast-charge) ni-cad cells. Some have to be handled with kid gloves and will not stand any abuse or they will fail. Commonly, they leak electrolyte out of the vents if they are charged too fast and this severely mars the performance of the cells.

I must say emphatically that electric fliers have found that the best type of ni-cad cells that will stand the sort or abuse we continually give them are Sanyo cells, and in particular the ‘R’ series temperature cut-off cells. These cells (the ‘R’ type) are meant to be charged until they are warm (45ºC) and will deliver high AMPS continuously without damage. My experience is that the Sanyo N800 AR and N1250 SCR cells will safely deliver up to 50 AMPS and the Sanyo CP1300 SCR and CP1700SCR will safely deliver up to 80 AMPS.

Now, many of you will not want to use currents anything like those quoted, but the message is that if you use these (better) cells for low current applications they will barely get warm and will not be in danger of failing – you can expect long life from them. I have heard of electric fliers using the same pack for eight years – it’s got to be cheaper than fuel!


What are the characteristics of Ni-cad cells? Read the introduction to the section on Chargers – this will give you some information.

Generally ni-cad cells discharge in a very flat curve – they give basically continuous current right to the end, and then droop off suddenly. By comparison, dry cell batteries give a very short burst of full power and then start dropping off in a steep curve all the way to the end. Dry cells have this “bounce back” capability when they seem to regain some of their charge when left to stand for a while – this is because they have time to expel some of the gases built up internally. Trickle charging is kinder to ni-cad cells than fast charging. It has been said that if you trickle charge ni-cads every time they are flat they will give up to 1,000 cycles. This is reduced to something like 400 cycles if you fast charge all the time (that is, if you can avoid the unevenness problem). The best compromise for electro-fliers is to fast charge in the field at up to 2 x the rated capacity of the cells (3 x for ‘R’ series), store your cells in ‘flat’ condition, then trickle charge before going flying again. Occasionally you may want to cycle your cells to ensure peak condition: trickle-discharge-trickle.

When you arrive at the field with your trickle charged cells you will notice on the first flight that the power output and engine run time will be reduced by about 25%. As you proceed with fast charging during the day the performance and engine run time will increase. The cells are said to “wake up”!

Competition fliers often cycle their cells before flying to ensure a good performance, but if you are sport flying you will fly them and use them anyway after trickle charging (but be aware of this characteristic).