Battery Life

Is it a good idea to let the batteries of the RX and TX run down completely now and again before charging?

Mike

"Completely" implies running them until the voltage goes to zero. In a typical NiCd battery, that means that one or more of the cells (because they're not perfectly identical) will be reverse-charged, and probably destroyed. So no, it's not a good idea. It's O.K. to discharge a single NiCd cell to zero,* but not a battery.

With NiCds, it is a good idea often to use most of their capacity rather than constantly recharging, even though the "memory effect" is somewhat overrated.

the short answer is NO the long answer is,,, well check it out yourself at:

Your question deserves more than a mindless response. First we need to cover a couple of terms. The first is mAh (milli-amp hours) which is a measure of battery capacity. To understand this term, an analogy can be made between gallons of fuel in a gas tank and battery capacity. A 20 gallon gas tank has twice as much fuel capacity as a 10 gallon, and similarily, a 1000 mAh battery has twice the electrical fuel as a 500 mAh battery.

Voltage is a measure of pressure or force that pushes electricity through a wire. A NiCd used in a R/C radio has a typical voltage of

We want to know how much capacity the battery has down to the the point we call a dead battery. To do this, we need to recycle it. A typical recycler (Hobbico makes a couple) will discharge down to 1.05 Vs. To find out the voltage at which it is dangerous to operate your radio multipy the number of cells times 1.05: RX - 4.2 Vs, TX 8.4 Vs.

As the battery is discharged, it is losing electrical energy or capacity. The recycler will read the amount of lost energy in mAh. A typical R/C system uses electrical fuel at the rate of 250 mAh, so if your readout at the point the battery is fully discharged is 500 mAh, then it will theoretically operate your TX & RX for 2 hours. Note that you must always discharge a fully charged battery for this reading to have any sense.

Besides finding battery capacity, the main purpose of a recycler is to determine the condition of your batteries. The rule is that discharged capacity should equal 70% of the rated capacity. For example, if the battery's rated capacity is 1000 mAh and it's discharged from a fully charged condition, the mAh reading should be at least 70% or 700 mAh.

NiCds do develop memory and as a consequence they lose capacity. The only way to determine the health of them is to recycle. If the capacity has dropped to a dangerous point, recycling can salvage the battery, but you should expect to have to run it through several cycles.

I have switched to NiMhs simply because thay have greater capacity than NiCds (two to three times as much), and they don't develop memory. However, they won't provide the current flow (amperage) that NiCds will. Also when left unused, they discharge at a higher rate. Finally, if you store your batteries, always discharge them.

Ciao,

Mr Akimoto

Not to nit pick but 80% has been the number that is recommended.

The memory card has been the trump played by people peddling battery get well schemes for a long time. The Ni-Cd technolgy today has pretty well made memory a thing of the past.

It really does not matter what state of charge they are stored in, they will self discharge over several months anyway. Storing them discharged does give them a better chance of developing a short in a shorter time period if there has been separator deterioration. Regardless of how they are stored, they should be given an open circuit voltage measurement before charging, any cells that are less than 0.6 volts are suspect, particularly if all the others are above 0.9 volts. Then they should be given a slow charge (C/10) for 14-16 hours, cycled to check capacity (80% or rated or better) and then charged and put into use.

In fact, this is a good way to check to see if a cells developing shorts. Once you discharge it to zero volts, remove the load. If the battery does not recover SOME voltage after resting for 24 hours in all likely hood it is bad - as in separator failure.

The primary reason for shorting out aircraft cells is one of safety. When you consider exposed terminals can generate 800 amps or more if shorted it was a good practice to leave the cells completely discharged (flat) in storage or for transport. One slip in assembly them into a battery (usually

On a related topic, I read somewhere that connecting Tx and RX batteries and charger via a timer so that, after being given a full charge/discharge/charge cycle, an hour a day on charge would keep them always in a "fully charged ready to use" condition.

I was somewhat sceptical - especially when the so called memory effect is reputedly more pronounced when batteries are charged for exactly the same length of time every time.

What's your opinion Red?

Malcolm

From the Battery Clinic

Cadmium migration is a function of the time the charge current is flowing through the battery and less a function of the level of current. Therefore we have found that high pulses of charge current to maintain the charge state are better than a steady low rate (trickle) current. This is very difficult to quantify as their are many other factors contributing to the life equation but improvements in battery life of 10 to 20 percent by pulse charging vs trickle are not unrealistic.

Therefore we have found the sustaining a pack at the fully charged state by way of pulsing the charge is better than an continuous trickle charge.

Some charges employ this technique. You can do the essentially the same thing rather simply and at a very low cost.

Simply connect your regular wall module charger that came with your system to an appliance timer. Intermatic makes a good unit for around $5.00. Set the trigger pins on the timer so that it is on for 1 hour a day. When you return from a flying session turn the timer wheel so that the on off triggers come up in 14 to 16 hours. Then turn the timer knob to on. This will give your pack a full charge and then a sustaining charge for 1 hour a day. The battery can be left in this manner for a long time between flights and still be maintained at a fully charged state with minimal overcharge.

Red S. Red's R/C Battery Clinic

Thanks Red,

That confirms what I read, but as said in my earlier post I was not totally convinced, and concerned about the possible "memory" effect.

I'm now prepared to give it a try.

Malcolm

You might as well, 100s of modelers are using it with good results. :-)

Red S.

Jeez Red, when I refer folks to my website I just give 'em a link!

Sometimes the level of the question suggests giving them a link wouldn't get them anywhere. :-( If they get there they have difficulty locating the specific topic.

Red S.

I, for one, appreciate Red's responses - they save duffers such as me an awful amount of grief.

Malcolm

Red:

I often wonder where you old field geezers get your information. There hasn't been any major changes in NiCd battery chemistry that would preclude the memory problem. Although anecdotal, I have made purchases of recently manufactured NiCds only to discover they developed memory or low capacity problems.

Memory is usually the result of the flyer only putting a few minutes of flight time on his equipment each field session (he probably crashed due to his poor flying skills another common problems you old geezers have). He then returns to the field a week later after a full charge. Do this enough times and your batteries will develop memory.

The time read out on my 9C (when I was using NiCds) after a typical flying session was usually around 4.5 hours! My batteries don't develop memory problems. Like anything, to get your money's worth or useful life out of any appliance, you need to exercise it!

Ciao,

Mr Akimoto

As far as I can recall, "memory" on Nicads only develops if partially discharged batteries are recharged for exactly the same length of time every time.

Reduced capacity after a partial discharge is sometimes referred to as "recession".

A full charge/discharge/recharge cycle usually resolves this.

Malcolm

ROLF.

You really should make a habit of checking your assumptions. Your assertions about NiCd memory are no doubt as accurate as your pejoratives.

Hard-won experience. 30 years of carrying a NiCd-powered radio will do that for you. The "memory effect" is highly overrated.

But don't take my word for it. Contemplate for a moment the portable telephone in the typical household. Those cells could hardly have a more miserable existence (constant charging, only partial discharge), yet they hold up for years.

By the way, it would be just as well not to be too critical of a species of critter (geezer) that you're likely to join one day, if the world permits it.

With all due respects to Mr. Akimoto (very bright fellow, I have observed) and all others, I can tell you the Red Scholefield knows what he is talking about. He worked in the development lab of a Ni Cad manufacturer for some many years, I understand. I, myself, worked in a hobby shop that serviced radios (we were certified to gold sticker and modify radios to be certifiable). We never saw a battery pack that had any sort of memory and we saw over the years a thousand or more of them. Most NiCad packs usually last about 3 to five years and when we found any that cycled less than 80% of capacity, we replaced them. Much about the same as a good automobile battery...none last forever.' As for memory, I think I read it in a GE Technical Paper that memory COULD be established in a nicad pack by many hundred of cycles of the same discharge and discharge every time. Running them down to the cut off point (1.1V per cell) and then recharging them would erase the memory. We sold a lot of battery packs to those who subscribed to the false notion that they might get a memory in their pack and aftery flying went home and ran the pack down and then recharged it...they just wore them out before their time. Going back the the hundred of cycles of discharge and charge at precisely the same time every time..they found this out in satellites..the fix was easy. So, forget the old wives tale about memory...it is literally impossible to do it in the R/C world...most battery problems are due to either under charging or a pack that has lost its punch. Regards to all.. Frank Schwartz