Do A123 LIFE Packs Free Us From Cycling?

Dave
One more quick question. I ordered some 1100 2s A123 packs from you today.
Do these need to be cycled? I have a FMA 4S CellPro charger that is A123 compatible. It will charge and balance, but not cycle.
Thanks again.
IRL

 

Irl,

If you want to check them before flying, Yes.
If you want to find out when they go bad on the workbench rather than at the field, yes.

There is no skipping regular battery testing and maintenance regardless of battery chemistry. All battery types will fail eventually and discharge testing is the only chance to discover packs needing replacement before having an accident.

My answer might seem a bit strange, however, every time there is a new battery chemistry many modelers think the new “miracle chemistry” means the end of regular battery maintenance and testing. I got the question many times at the beginning of the NiMH revolution, the Lipo revolution and at the introduction of A123 Systems LIFE cells. There could be nothing further from the truth. There is never a time when battery maintenance and testing is not prudent.

No jab against the CellPro chargers is intended here. They are very good quality and I recommend them. I don’t know the specifications of all the models they sell but am aware some of them will discharge test packs. It is possible to discharge these in NiCad or NiMH mode on modern digital chargers as long as the mode has NO CHARGE at the end of discharge. In other words, as long as it’s not a “cycler”. A cycle is a full discharge then charge or full charge then discharge. To do this, we want to us a charger that simply does 1/2 the cycle, in other words we want it to discharge and that is all. Just set the (NiMH or NiCad) cell count to 4 for a 2 cell A123. Some let you set the cut off voltage directly and in that case, set it to 2v per cell or 4V for a 2cell A123 pack. The correct discharge rate for any kind of lithium is Capacity/2. They are rated over 2 hours. Since many chargers/dischargers only allow discharge rates at even .1 amp (100mah) increments, set discharge to 500 or 600mah (.5 or .6 amps) to do a reasonably accurate job on an 1100mah rated cell.

I’ve noticed over the years the 2300mah cell (26650 can size) generally cycles to 2100-2200 range. They seem slightly over rated. Don’t be alarmed if your 1100mah (18650 can size) pack tests to 1000 or 1050mah. It’s probably just about right.

Happy Flying
Dave,

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Battery Storage In Reverse

For many of us there is a winter storage season. How do we bring our fuel powered models out of storage confident our RX battery packs are up to snuff? Were they nearing the end of life at the end of last seasons flying? Did they survive being in the trailer or garage ceiling for a number of months? Here are important steps to greatly reduce your risk of shouting “I Ain’t Got It!” when you hit the field this spring. These recommendations are intended for NiMH and NiCad packs although the similar principals apply to any mission critical TX or RX pack regardless of chemistry.

1. You should have cycled your packs and noted the value on them when you put the model in storage. Did you do this? A simple round of cycling in the fall will help weed the weakest packs from the herd.

2. Check the purchase date on your pack prior to model reactivation. Did you date your packs? Noting the purchase date in permanent marker should be a routine with new packs. Has this pack made it 3 seasons already? If it has made it 3 seasons, it’s time to replace it with a fresh one even if it’s still cycling well. It never seems like a good deal to “squeeze one more season” out of a pack if a model is lost doing so. There are no battery experts in the industry, nor any magazine writers that are willing to dare recommending using packs beyond 3 years. Most recommend only 2 years. The incident of surprise failures increases with each season. It’s much cheaper “not” to find out how long it will take to have a failure. Think about it.

3. Similar to a new pack, a pack having been in storage for some time is in need of a slow “forming charge.” A forming charge is a simple full-to-overflowing charge on a non-peak detecting charger like your factory wall wart. While in storage the cells slowly discharge. Not every cell will discharge at the same speed. After a few months, you could have one cell at 80%, one at 60% and two at 50%. When form charging, It’s important the charge rate does not exceed 10% of the packs mili-amp-hour (mah) value when doing this procedure. This type of charge allows all the cells to fill fully and the first cells to fill won’t be overheated by the ongoing charge. The danger of peak charging a pack that has been in storage is the best cell (the 80% full one) can be ruined as it’s overcharged while the other 3 are still filling up. Also, your pack may false peak meaning that although the charger reports it is full, it really might not be. Re-equalize the cells with a good long slow wall charger charge prior to any peak charging to avoid most problems.

4. Test for Capacity. Discharge the pack on your favorite charger (with discharge function). For the purposes of this kind of test, the correct rate to test against factory rating is 20% or 1/5 of the rated capacity. It’s ok if you can’t get that setting exactly, just get it close. Example: A 1000mah pack would be tested at 200mah discharge. Most chargers will display this as .2A. Your pack should test at least 80% of it’s rated capacity. If it does not, then a few more charge / discharge cycles are in order. If you can’t get the pack to test above 80%, it’s time to replace it. Although it might seem like a money saver to succumb to temptation and overlook marginal packs, one crashed model will pay for a great many replacement battery packs. And that’s to say nothing of the risk to others when a model goes out of control. Good pack or no go!

5. When you recharge the pack after your final discharge test, check the charger input mah. Did it put in about the right amount? A pack that’s been in storage, particularly if you’ve skipped the step of re-forming it is very prone to a false peak. A great pack that tests perfect but only takes 50% of the expected recharge amount could cause some unwelcome excitement.

6. Test your Switch. First, use a loaded tester to check your fully charged pack directly. Note the value then test it through the switch harness. If it tests good directly but marginal through the switch, it might be a sign the switch is getting dirty internally, worn or perhaps some connectors are going south. Like battery packs, finding out how long a switch will last is costly knowledge to acquire. It’s a good idea to replace the switch with every other new battery just to avoid trouble. Load testing your pack with and without the switch harness looking for any substantial difference is a good way to detect a problem before starting the season. Did you notice what I omitted? After checking the battery through your switches charge lead or charge jack, unplug it from the RX, turn the switch to the “ON” position and check it again. Is it load testing similar to the charge jack/charge pigtail? The most important place for your pack to deliver it’s energy is to the RX. Make sure it’s solid to this point, not just the charge harness.

Integrate these practices into your seasonal routines and many common pitfalls are avoided. Don’t forget to scrutinize your TX battery in similar fashion. Ongoing TX function is every bit as important as RX functionality.

Dave Thacker, Owner: RadicalRC.com
Blogsite: Radical RC Workbench

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The Texas Sharpshooter Fallacy

I wrote previously on the subject of “Confirmation Bias”. Sometimes it is difficult to discover the answer to a technical problem because the person bringing you the problem has a hitch, assumption, or faulty logic step in their diagnostic process. Often people draw conclusions from spotty evidence. For instance a customer shows me a receiver and say’s “This receiver is bad.” I ask: “Why do you think it is bad? The answer almost always comes back something like “I plugged it in and it does not work.” The person is saying from that one test or measurement they have drawn a conclusion. It seems reasonable doesn’t it? But, really it’s pretty silly when you think about all the things that can cause an RX not to respond to a TX. You see, the real and only conclusion you can draw from the customers test is this. “In one trial, the RX produced no apparent response.” That is quite a bit different from “This receiver is bad.” Understanding the difference in those two conclusions is why some people are good at diagnostics and others are not. To be good at figuring out a problem, you are greatly advantaged by not making any assumptions or broad conclusions.

In the case of a receiver, lets go over many measurements and tests that you might perform to decide if it is in fact “Bad”.

1. Has it ever functioned successfully?
2. Does it really match the Transmitter? (is it talking the right language DSMII vs DSMX or PCM vs FM vs AM and etc…)
3. Is it on the same channel? (in the case of non-2.4ghz gear)
4. Besides looking at the stickers, did you actually look at the tags on the TX and RX xtal?
5. Is the shift the same? For example, a positive shift JR TX is never going to drive a negative shift Hitec or Futaba RX.
6. Have you driven the servo you used on the tested RX with a servo tester to make sure it actually wiggles?
7. Have you load tested the battery your driving the RX with to see that it is high enough to actually turn on an RX?
8. Are you using a switch between the battery and RX? Plug the battery in directly so your not actually testing if the switch is good.
9. Can you demonstrate the TX driving another RX to establish that your testing with a working TX? One might complain, “I flew it a week ago!” However, we’re not testing the troubled RX a week ago, we’re testing it now. 😉
10. Have you plugged a voltmeter into an empty servo port to see if there really is voltage finding it’s way to the RX?
11. Is the crystal really fitting tightly in the socket or is it loose and wobbly?
12. Does the TX have the capability of being on for programming without broadcasting?
13. Is the meter on the TX a voltmeter or RF Output indicator? What does it say?

I’m sure a sharp thinker can come up with some more things to consider. Many of the things above we’ve found at one time or another to be the cause of a non-responsive RX. Assume nothing.

Recently we had an A123 RX pack returned by a customer. He said it tested poorly, only a few hundred mah. The customer appeared to be correct, it was testing bad after several charge/discharge cycles on our bench. And, the charger would increase in voltage rapidly when we applied charge current. Strange. However, even after several trials, a good mechanic still hasn’t drawn any conclusion. He may be moving towards condemning the battery but all tests were not complete. He cut the shrink off the pack. The tabs all looked fine. He re soldered the tabs anyway just in case there was an unseen cold joint. Note: He had originally built the pack, but without emotion, he redid his original work anyway. Many people fail at this step because “they couldn’t possibly have done anything wrong.” (yea right!). The pack was cycled again with the same poor result. Now, finding a bad battery pack is rare, exceedingly rare. We know this to be true from many years of experience. So, we keep looking. I examined the pack under magnification (even though it had been re soldered by a respected pro) and all looked good. I looked at the plug under magnification and found a thin transparent film on the plastic shell. The more I looked, the more I saw this film all over the shell. Is this paint? We decided to solder a second lead onto the pack and test again. The pack tested good. What was the problem you wonder? We can only conclude the film on the plug was thin CA the customer had somehow accidentally allowed to come into contact with the plug. It had a high resistance because one or more connector pins was evidently coated in glue. After replacing this plug, the apparently bad battery pack was proven that it was always as good as new.

So, if a battery pack fails a discharge test or an RX fails to respond, is it bad?

To read about The Texas Sharp Shooter Fallacy, check out this wiki link. Reading it is what inspired me to write today’s article. It describes in somewhat technical language a common way to foul up a test.
“Texas Sharpshooter Fallicy” Wiki Link.

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