Hi,

I just bought an RD6000 with a 700 mah Ni-cad receiver pack. It came with a 75 mah wall charger, so this provides an almost perfect C/10 charge. I've used Radical R/C guidelines. For the most part, I've been charging it for (1.6*700)/75 = 15 hours, and I've cycled it half a dozen times with the following discharge readings: 338, 415, 461, 513, 542, 578 mah (in that order).

Is this an acceptable progression in mah increases? What causes some packs to "come up to snuff" so slowly? I've cycled "many" new packs, and I'm so used to them coming up to 90-110% in just a few cycles. I performed the last cycle this evening, and I'm starting to feel a little better now that I've broken the 80% mark (ie. 578/700 = 83%). This last cycle, I charged it for a little longer; say 18-19 hours. I also put it on a 125 mah charge for the last couple of hours.

What should I do now? I might add that I've been using a Hobbico Accucycle (I know, I know!). I'm thinking about trying a friend's Sirius discharger, so I can compare.

It's just that I'm so frustrated with this pack in particular. I've spent the last five days cycling it. I will not put a pack in a plane unless I'm 100% confident with it!

Robb

Something does not seem right. Since this pack is already 'suspect' try giving it a 24 hour charge at a 'known to be accurate' 70 milliamps rate. That should guarantee that ALL cells reach FULL charge. Then discharge it and see what you get.

Also make sure the new charger is REALLY giving it the charge indicated. Maybe the charger is bad.

If you cannot obtain very close to full rated capacity after the 24 hour slow charge at the proper rate, throw the cells out. It just is NOT worth the risk you would take if you decided to use them. You have the right attitude: if you do not have 100% confidence in a battery pack, get rid of it. You will probably save a LOT of money in the long run.

I would not use this pack. If you are right and the pack is good then no harm, no foul. If you are wrong, you will see quickly that the price of a new battery pack is a small price to pay for security

Thanks for the advice. One good thing is that it's a brand new radio, so the battery's covered under warranty.

I know a retired electrical engineer with some good testers, so we'll check out the wall charger to see if it's putting out 75 mah.
Till then, I'm going to put it on my Accucycle with the 125 mah charge for 15 hours. The Accucycle says this charge is good for 750-1875 mah batteries, so 700 mah isn't far off. I haven't gotten really aggressive with the pack just yet.

I had two Airtronics receiver packs that I used faithfully for 12 years. Even after all that time, they still discharged to 85-95% capacity. I finally threw them away, as I felt I cheated death long enough. I always charged them up good in the fall, and kept them in an unheated room off my porch durring the winter.

Robb

I always run 2 battery pack in my planes. Very simple and gives confidence.

I run two 5 cell packs as well. My thought is if one cell shorts, I have a 4 cell pack. If one cell opens, then I have the other pack. Either way, I can still fly until I can get the plane down on the ground!

I've never used 5. Does the higher voltage give longer flight times ?

The following is in regards to receiver flight packs:

Increasing the voltage by using 5 cells will sometimes provide faster servo response. Some flight systems do not accept 5 cells in the flight packs.

The milliamp-hour rating of the cells is what determines the number of flights you will obtain from a pack. If you have 4 cells of 500 milliamp-hour cells and you add a fifth cell to the pack you will still have a pack that will provide 500 milliamp-hours of energy but the voltage will increase from the nominal 4.8 volts of the 4 cell pack to a nominal 6 volts of the 5 cell pack.

Simply raising the voltage of the pack does not icrease the milliamp-hour rating of the cells involved.

There was a thread awhile ago that discussed the losing of one cell in a 5 cell pack. The consensus was that instead of acting like a 4 cell pack, the bad cell would quickly drag the four good ones down. Does anyone remember the thread, or know the "real deal" on that type of occurrence?

...a 5 cell pack will actually give shorter flight time than a 4 cell pack with the same mAh capacity, because the higher voltage will feed more current to the servos.

Given my limited electronics background I find that hard to comprehend. I flashlight with 5 cells will last longer than one with 4, given the same bulb. I might just give this a real bench test, simple enough. Anyone know if jr equip will function on 5 cells same as 4 ?

Sandal your comment was of interest. So I made a little Excel spreadsheet. What was not mentioned was that the 'resistance' is the same during the change from a four cell battery pack to a 5 cell battery pack, thus the current will increase. And an increase in current from a 'fixed' capacity cell will drain the available capacity in a shorter period of time.

Assume a 50 ohm load ('fixed' resistor):

Using four cells at a nominal 1.2 volts each, 500 mah capacity:
Current = (E/R) = .096 amps (96 milliamps)
Power dissipated = ((E^2)/R) = .4608 watts
Time to discharge battery pack = (500/Current) = 5.208 hours

Using five cells at a nominal 1.2 volts each, 500 mah capacity:
Current = (E/R) = .120 amps (120 milliamps)
Power dissipated ((E^2)/R) = .7200 watts
Time to discharge battery pack = (500/Current) = 4.166 hours

So your comment would appear to be correct. It would take less time to discharge the pack using a 5 cell pack.

I never thought about this before.

I have argued that higher voltages do give you shorter discharge times with the same capacity but when used in a flight pack, the increase speed and power of the servo should make the servo get the position 25% quicker on a 5 cell pack compared to a 4 cell pack. With this said, the flight time should be the same. Many people disagree but no-one has been able to take the realities of our flight dynamics and convince me any difference.

Geistware;
are you saying that the servos work harder, but shorter time intervals, making the current draw equal to a 4-cell pack? That is VERY interesting. I think you're right, but I guess it depends on flying too. If it is a fast airplane where you pull hard on the elevator through the turns, I think the total current will be higher for the 5-cell pack, because the servos are pushed hard. But with a "normal" airplane with gentle flying, your theory seems correct to me. It would have been great to use some sort of computer measuring equipment to log the current draw to a file and print the numbers. Then we could see not only which pack lasts longer, but also how different manoeuvres affect current draw.

Sandal, basically yes. The power output is higher by 25%, the speed is increased by 25% which should mean that the power draw of a 5 cell pack is 25% higher than a 4 cell pack. In balance, the flying time should be the same. The only exception to this is if the higher voltage reduces the dead-band of the servo. Then all bets are off.

Rob_H

Try putting the pack on a C/10 charge for about 4 days. I started doing this to form my battery packs. When I bought my Litco charger, the instruction book said to charge your new packs for several days using the N function (normal C/10 charge). Then I cycle the pack a couple of times.
All of the packs I've done this way have a good capacity, and last a long time.

Greg

Greg,

Since I last spoke, I put the pack on a 125 mah charge for 15 hours, using my Accucycle. I got 644 out of 700 (ie. 92%). I then put it on 75 mah for about 20 hours, and got 630 (ie. 90%). These are respectable numbers, and there might very well be nothing wrong with the pack; however, Airtronics said they'd gladly take the pack back under warranty. I think I'm going to take them up on the offer, as I still have the slightest bit of doubt. I was hoping to get close to 100%.

It's just that I've had so many packs come up to 90-110% capacity after a couple of cycles. This was after charging for 16-20 hours using the wall charger. I'm going to take your advice and start charging new packs for a little longer using the C/10 wall charger. They don't even get warm using this low of a charge, so it's probably hard to damage them.

On the other hand, I cycled the transmitter pack last night for the first time, and got 680 mah (ie. 97%). This was after charging for 18 hours using the 75 mah wall charger.


Robb

Robb may want to check that the Accu-Cycle is giving you good numbers. I just bought a used Accu-Cycle from a friend and he stated that it always read 15% short.

In a thread "Calibrating Accu-Cycle?" In this forum I’m waiting for an answer to possibly re-calibrate it myself.

Sdr,

I did see your thread, and am anxious to see if anyone replies. It's just that I've had so many packs read over 100% capacity with my Accucycle. However, I've also heard the debate that many battery manufacturers use larger capacity cells than what they advertise. This way, if someone's cycler is reading short, then it kinda fools them into thinking they're getting a 100% capacity pack or better.

I've been contemplating getting a Sirius discharger for $70. The giant scale guru in our club is an electronics expert, and he says Sirius products are well worth the money.

As an engineer, I tend to be overly conservative, almost too cautious. I've been helping a newbie, and I told him to charge his batteries at least overnight, as it was our first time out this year. I rarely check his batteries, but this time I did. They read 4.9 volts. One, maybe two flights, and that woulda been all she wrote. That pack was only 1 year old.


Robb

The transmitter pack that I just purchased, cycled the second time at 880Mah This is a 700mah pack made by Maxx. They use Sanyo cells in their packs. When I cycle I go right from trickle to discharge. This will give you a slightly higher reading than if you let the pack rest for a period of time before starting the cycling process. When my packs cycle at the same or less capacity than the pack is rated at, it is about time to replace it
If your packs cycle at less than the rated capacity, I would take them up on the pack replacement.

Greg