Rob

I am not an expert by any stretch, but the preferred method of cycling nicads is to bring them to around 1 volt because if you cycle them to zero, you risk the battery reversing which is generally considered "toasting" them.

Although having said that, you can frequently revive reversed cells by zapping them with a momentary 12 volt car battery attachment, and then recharging them normally afterwards. I have done this numerous times.

However I test them afterwards to verify they are not totalled. I test them on a loadmeter, because sometimes they will show a surface charge.

I have never actually noticed memory effects and I am not sure anyone would actually notice them except in a lab.

Having said all of this about that, nicads (1.2 volts topped off) start out after recharging having less voltage than regular batteries (1.5 volts) and they last considerably less time than regular batteries (in my experience) and the nickle metal hydride batteries that I used in my Walkman seemed to start out after a full charge with even less voltage and when in a cool environment seemed to last even less. (this will start a war of words)

That's why some electronic devices particularly ones that use a high number of cells will tell you not to use rechargeable batteries as their topped off voltage is not enough to cross the usefullness threshold.

ie. ten times 1.2 volts is only 12 whereas ten times 1.5 volts is 15.

So what I suggest is for anyone wishing to test it out, buy both batteries and test it in the the conditions (ie. temperatures) that you will be using them and you be the judge.

Very interesting Alan, thanks for that reply,

Reversing a cell is definately not desirable. When discussing this topic the distinction needs to be made between single cells and batteries, batteries of course being groups of cells in series and/or parallel.

If you take a single cell and discharge it by putting some sort of load across it there is no way to reverse it. However if you have a number of cells being used in a device (as is usually the case) and you attempt to fully discharge them there is a real risk of reversal as you have pointed out.

I was certainly giving bad advice by suggesting that you run the rechargables completely flat inside a device. I fully discharge my cells (on the rare occasion that I've needed to) by using a load on the individual cells. That method is a fair bit of mucking for the average user so I quickly tried to think of an easier alternative while I was writing the post above. You are quite correct that in this case it would be advisable to stay above a volt or so.

You may be interested to know that single Lithium Polymer cells are approximately 3.7V when fully charged and can be seriously damaged if they are discharged below about 3V!! Electric powered model aircraft which run on Lipos often have devices in them which disconnect the pack from the motor when the voltage reaches a certain level eg. 9V if you are using a pack of 3cells in series.

Rob.

Berthos

Thanks for the clarification! The maintenance guys on our aircraft always cycle cells individually and although I sort of understood what they were doing, now I completely understand why they do the cells individually.

I had an electric sailplane years ago and I guess the new technologies have certainly changed things.

Years ago in Canada the Department of Transport mandated "Emergency Locater Transmitters" in all aircraft. The mandated batteries were lithium. After some aircraft blew up, they rescinded the law. So whenever I hear Lithium I cringe. This reaction is based on really old thoughts.

At one time there was a serious problem with NiCads also in aircraft. Due to the enormous power drain that engine starts impose in a turbine aircraft, the nicads would get very hot and the plates inside would sometimes warp. When the plates warped enough they sometimes would touch the adjacent plates, which of course would short the battery and so when you turned off the battery, the battery was still generating power... unto itself. So it would get hotter and hotter and eventually ignite, and burn a hole in the aircraft. If a magnesium spar happened to be nearby... catastrophy.

Interesting thread!

I am getting completely off topic... Sorry Mary!

Alan,

Are you saying that NiCds were used to start (what we call in the model world) full scale aircraft!!

I never realised this was the case. Do you know what the current (no pun intended) technology is?

Rob.

We use a NiCad. That's not unusual, although nowadays people are buying Lead acid batteries because they have more juice, give cooler starts and after a number of years you just chuck em. They are cheap and don't have to be cycled etc.. ie no maintenance. We haven't gone that route because we operate in -40 degrees occasionally and we are not sure how that will effect them. Leave well enough alone.

The NiCad problem of years ago was solved by improved quality of plates. They don't warp as easily at high temperature and also better venting for the batteries has made this "Runaway Battery" problem history.

Actually full size aircraft don't get new technologies until they are old technologies. Our instruments although up to date are old news say compared to the computer world. The idea being that let the technologies settle down and we take the rock solid ones.

Can you imagine having Microsoft Word running an aircraft!!! Scary! Uh sorry folks but our instruments just crashed.

Thanks that is soo funny!!!

At least if Apple manufactured them you could get them in a variety of fruity colours. "Do you like my new Lime instrument panel?"

Rob.

Good heavens !

Another of my weaknesses. I have an iMac with OS 9.1.

I don't want it running my airplane either!

Howdy Rob,
What do you think about rechargable Alkaline batts?

D. Ho
TheMightyHobie18 1067

Alan,

I'm an iMac user as well although I am running OS10.

D.Ho, alkaline cells are primary cells. One use only, you cannot recharge them.

Rob.

Some are rechargeable and from what I have heard (untested and unsubstantiated) all are rechargeable to some degree but some are specifically made for recharging a certain # of times. Don't know the details. God is in the details...