You know, ni-cads are like computers
Anyone reading this must have at least a nodding acquaintance with computers (don't let it nod too vigorously, it might fall off the table) and you must be aware of the current trend whereby computers stay at roughly the same price, while the specification is steadily improved. The obvious question is, "Why not leave the specification alone and drop the price?" The answer, of course, is that it doesn't make sense commercially.
You must also be involved in the world of model helicopters and, therefore, aware that you need a higher capacity battery pack than that which is normally supplied with radio control equipment. If you look around at what is available, you soon come to the conclusion that you are being asked to pay through the nose for high capacity batteries that are the same size, or smaller, than those of lower capacity. If not, you are paying high prices for batteries that are higher in capacity, and have a higher specification than you really need.
For example, you are offered a pack of four 1700 mAh fast charge 'SCR' cells at anything up to �30 ($50). You don't need all that capacity and you don't NEED fast charge cells. Alternatively, you can obtain a smaller, lighter pack of 1300 mAh cells at a similar price, with some radio manufacturers name on it.
What we actually need for our average helicopter is a straightforward 'sub-C' 1200 mAh cell which, even in industrial quality, shouldn't cost more than about �2 per cell - �8 per pack! This is confirmed by our editor, who informs me that RS Components (A very large electronic component supplier in the UK) offer such cells at �2.20 each. This supplier offers a fine service, but they are far from being the cheapest around.
You could probably make out a similar case for just about everything that the current state of the art involves, particularly servos and gyros, but batteries seem to be a particular case. This may be due to the fact that, like computers, they are surrounded by a certain mystique. A case in point here is 'cycling'. This is a subject that, like silencer pressure, can lead to lots of argument. If you consult a user manual from a ni-cad manufacturer you will find that cycling is not recommended. Actually, they say that repeated deep charge/discharge cycles are harmful - something which any electric flight enthusiast can confirm. My own experience here suggests that the average electric flight battery is over the hill after 100 cycles or so.
These manuals will also tell you that any loss of capacity can be apparently restored by several charge/discharge cycles. They then go on to tell you that this increase in capacity will disappear after one cycle of normal use!
Another aspect of the ni-cad phenomenon is the legendary black wire corrosion. Much has been written on this subject without anyone really getting to grips with it. After some 30 years of experience with these cells, I can state categorically (that's such an authoritative word that I ran it through my spellchecker) that this corrosion will not appear if the cells are always kept with some charge in them. Other than that, I know nothing.
I was going to be even more outrageous and say that I have never seen this phenomenon in my own equipment, only in that belonging to others, but that would be really asking for it. One must be careful not to offend Messrs Sod, Murphy, Parkinson or Finagle!
Before leaving the subject, it might be worth adding a little on the subject of charging. Nickel Cadmium cells will take quite a lot of abuse without any real distress, but it will produce a cumulative effect of a loss of capacity. Overcharging can certainly do this, but there is another, lesser known, danger caused by undercharging. If you try to charge your expensive 1700 mAh battery from a charger designed for a 500 mAh, or 1000 mAh, type it will obviously take longer. However, another effect is that you will never actually fully charge it, and it will get used to that rate of charge. This is the only area in our sort of use where the so-called 'memory' effect comes into play.
You may sometimes see it advised that you keep your batteries on a permanent 'trickle' charge - say 10 to 20 milliamps, or so.. This will do serious damage over a period of time and the batteries may become virtually useless for our purposes. A far better idea is to charge them at the usual rate for one hour out of every 24 hours. This is not too difficult to arrange using a 'process timer' - you can get one that is built in to a mains plug - and has much to commend it. This way, your batteries are always ready and you are keeping them healthy.
Oh dear, I really could go on like this all day, but we will have to leave the subjects of PCM, computer transmitters, etc. for another time - not that they have any connection with the above opening remarks, of course.
As they say to the young lady with the large van which is running on three cylinders at the beginning of the week, Sick Transit Gloria Monday.