Forming a recent NiMH purchase on the Hitec X4 and other computerized chargers.

Ed writes me about properly forming a recent NiMH purchase.

Hi Dave,

I recently bought one of the FDK Twicell 6.0V 5-cell 2000mah NiMH AA Flat Pack and would like to try it in one of my airplanes . I read all your comments about this battery pack and I have the HiTec Multi-Charger X-4 and not sure what is the best way to charge it. The charger is fairly new in my collection and I am still learning the best way to use it any thoughts?




The best way to do it on most computerized chargers is:

General procedure,

1. Go into setup, make sure the mah limiter and time limiter are both off.

2. Put charger in PB mode, yes for Lead acid.

3. Set charge rate to 100mah, any more will ruin the battery eventually.

4. Set voltage of battery to 8V

5. Start charger.

If it refuses to start, set voltage to 6V and let it run a minute or two, the go back and restart with setting at 8V

“Generally” Eneloop’s (Twicell’s) come to you about 1/2 charged. So, the hole your filling is about 1000mah. (Hole * 1.4) / charge rate in mah = time in hours. 14 hours in this case.

What we are doing with the procedure above is tricking the charger into functioning like a dumb wall wart where it will just plod along indefinitely until we disconnect the battery.

The best practice would be to connect the cells to a dumb charger that charges at 50mah for about 30 to 40 hours and is the ONLY method for which I would ever consider warranting a pack. People try to break in new batteries in peak detection modes all the time which is the cause of my slightly “acidic” warnings against such acts on my website. One issue is there are no makers of chargers like that that I know of in the hobby world today. The last one (Sirius) seems to have become inactive. The best chargers to own for this forming purpose at this time are an ACE DDVC, ACE Digipulse or Sirius Pro-Former. Should you run across one at a swap meet or on Ebay, snap it up.



Forming Charge On Peak Charger Email Question

Hi Dave;
Firstly- thank you for your quality battery packs. I received my recent purchase- your 1650mah NiMH 8 cell 9.6 tx pack, plugged it in to my tx just to see what it was at, it started at 8.9 but quickly went to 8.5 where I pulled it out. So on to the first break in charge at 0.1A- on a Triton 2 with a thermal probe connected. The pack temp was at 79 degrees, so I set the cutoff temp at 88 (about 10 degrees higher) The charge lasted 16 hours with a delivery of 1670ma- terminated by the temp sensor. I had anticipated a longer charge time but am happy with the results- My question is: should I expect even higher mA delivery?
Matt K.


Your charge time at 100mah would be a bit short for a completely empty 1650 pack. I’d suspect it might not cycle as full but it could. I’ve never checked a Triton to see how accurate that number might be at low charge rates. Normally you have to put in 140% at low charge rates to get a full pack. A NiCad or NiMH has a lot of resistance to accepting a charge.

I would never expect the chosen procedure to work properly and consistently. There is not enough temp rise. The peak in a first charge is more of a “several peaks” along they to the final peak. One of those peaks is often large enough to trick the charger into declaring the pack full. On virgin packs, it will happen about 60% of the time when you use normal rates like Cx.5 to Cx2 (C=capacity). I’ve never run a study on doing it at 1/8th the minimum peak charge rate but I’d expect the results to be very poor. The temp will fluctuate with room temp also. All this is not to say you should have charged the pack faster as an initial peak charge. It is to say never use peak detection on an initial charge, never on a pack coming out of storage. There is no way to have the screen of your charger (or any other) showing NiMH or NiCad mode and not be in peak detection mode.

The best way to form (initial break in charge to complete manufacturing of the cells) on a computerized charger; Put the charger in PB (lead acid) mode, set the rate to .1, the voltage or cell count to a 12v pack (6 PB cells). Make sure all time limits and capacity input limits are turned off. This will get the charger to plod along slavishly well past when the first couple of cells fill. The point is to fill all the cells (which are initially of unequal charge) to overflowing at a very slow rate with gentle overcharge at the end. Peak detection will not get in the way by reacting to any false peaks. Peak detection is not reliable unless the charge rate is about 1/2 pack capacity or more. A new battery might have several peaks before it gets full. Calculating charge time when forming or slow charging (not using peak detection) is; (Capacity (or empty hole in the battery) x 1.4) / Charger output = hours to full. Let it run that long. Rates should never be above 10% of cells capacity. If it’s a AA cell above 1700mah, the rate should never be above 100mah, 50mah is even better.

What I’m going for here is a system that works 100% of the time. Every other kind of form charge is just fraught with problems. Using a peak type charger in PB mode (not in peak detection mode) is the only way to make them work reliably as a forming charger.

Once the pack is broken in, and it’s in regular use, I wouldn’t Peak charge it slower than .8 amps. The slower you go below this the slower it heats up after it’s full, the slower the peak detection happens, the more you hold the pack in an overcharge condition. Heating up is what happens when it can no longer store the energy your putting in it. This causes a slight voltage reduction. The charger knows the pack is full because the voltage is dropping, there for it has detected that it must have “peaked”. Peak charging is a form of detecting heat indirectly by watching for the voltage to drop which can only because the pack is full and heating up. (The exception is virgin packs which may reduce in voltage very slightly during the first charge.)

Never peak a pack that’s been in storage. This kind of charging is only for packs in regular use. After it’s set in storage a few months, the cells could contain unequal states of charge. As the fullest (best cell) is peaking (heating up and dropping in voltage), the others may still be rising (as they do as they are filling). This can mask the peak and apply a damaging overcharge current to the first cell(s) to fill.

I know these steps will prove to get your pack into most reliable service for you.


Balancing Severely Out of Balance A123 Pack

The following is a recent exchange discussing some charging logic that is impacted often by time-out settings in chargers. Not a bad thing all in all. The same logic can be applied to Lipo packs as well.

Hi, Dave:
Here’s my situation: All of my A123 batteries came from you and I’ve got several. All of them (except 1) work perfectly and I enjoy being able to take advantage of all that A123 batteries have to offer. My one that doesn’t work properly is a 2300mah, 2S receiver battery that I can’t get to balance. I charge it on a Turnigy Accucell-6 with the cutoff voltage set at 7.2 volts. My charger timed out at 120 minutes with one cell at 3.6 volts and the other at 3.25 volts. When I first started using these batteries, I was negligent about balance charging and would as often as not, just quick charge them and go fly. So, this is not a warranty question at all, but one as much for my knowledge as anything. First of all, is this battery safe to use (as a receiver battery), and second, is there anyway to get the second cell back up to voltage? I’ve cycled and balance charged it probably 3 times trying to get it to respond, but nothing I know to do has worked. I guess I could used it on an electronic ignition where sudden failure wouldn’t likely be as catastrophic as losing receiver power. What is your recommendation?

When balance charging, the first cell getting up to 3.6V causes the charger to start stepping down the charge rate. Ultimately, the charger cannot go over the maximum dissipation rate of your balancer. In other words, if it can only dissipate 100 mah, then the charger will drop back to 100 mah. It’s charging the pack at 100 mah but at the same time discharging the full cell at 100 mah to keep it from going over 3.6v. If the low cell is 1000 mah behind, in the two hours of the time out, it will only be able to bring the lagging cell up about 200 mah. It will still be lagging by 800 mah and some measurable voltage difference will be the evidence. Because the charger times out and stops working, your still out of balance.

Procedure options:

A. You could just keep repeating a 100 mah charge rate and let it time out 4 or 5 times.

B. You could also go into the setup and disable the time out.

C. There are some safety concerns with both “A” and “B” above. The best and quickest method that we use at our shop is to connect the charger through the balance port to only the low cell. You can do this through the standard XH balance connector by taking a JR or Futaba RX charge cord, crack off the outer shroud exposing the two pins. These two pins will be .100″ apart, just like those in the balance harness. Plug the bullet end of the cord into a volt meter, plug the business end into the balance harness, probing the different combinations. In the case of a 2 cell RX pack, you’ll only find 2 combinations. Offset to the black wire and offset to the red wire. One of these will read about 3.6v (the full cell) the other will read 3.25v (in your example, it’s the low cell). When you find the low voltage position, carefully pull the banana plugs out of your volt meter and plug into your charger. Set the charger to charge 1 LIFE cell. Set the rate (for a 2300 A123) to something between 1 and 2 amps (we don’t want to overheat the delicate balance connector) and let it charge that individual cell through the balance harness until it’s full.

When it’s done, both cells should be at similar voltage.

If you want to get really fine, there could be a slight calibration difference between your charger charging a single and a two cell pack. To really refine it, reconnect the pack to the charger as a 2 cell pack in the conventional way. Put the charger in discharge mode set at 2 amps. Let it take our 100 mah or so out of the pack. Then, switch back to Balance Charge mode and charge at 2 amps. Now the charger will put the 100 mah or so back in and at the same time balance both cells to each other. Since the pack is almost full, it won’t actually charge at 2 amps, it will read something lower. When complete, if the cells are good and the charger is working properly both cells should be very close.

It is possible the cell is bad. If this is the case, the above procedures and logic won’t result in a balanced pack. (presuming the charger is working correctly) It’s OK to repeat the procedure if you want to try again however, it’s likely your results will be the same.

If you are able to balance it successfully, do a discharge on the pack at capacity/2 or near. This is the standard for testing lithium type cells. So, a discharge rate of about 1.1 amps would be correct. Realistically the A123 2300’s should test within 50 mah of 2200 if they are in perfect condition. If the pack tests below 80% of 2200 (below 1760 mah) it should be replaced.

As to safety, I hesitate to ever say any battery is “safe”. I would say that if I could not get the pack behaving properly, I’d replace it. The cost of any pack is always a tiny fraction of the value of a model. It never makes you feel like a winner to put one in the dirt over saving a few bucks on a simple part, especially if you were suspect of it before you flew. Get it right, get confident or replace it.

Another safety warning here is you should be extra diligent when working with any battery where it’s condition is suspect. Do it outside and/or supervise closely. Never charge unattended inside a structure or vehicle. Always use a fireproof container for charging, especially when dealing with anything suspect.

If you follow through those procedures and that logic, you should be able to rule the pack in or out and have good confidence in your decision. Hope this helps you sleuth out the pack. Dave


Is Daily Low Self Discharge Rate and Important Factor in RC?

A customer asking about an unusual cell size of ours asks: “Are they are low self discharge?”

They are not Eneloops which would be the only NiMH I would classify as Low self discharge. This is almost a silly thing to consider because we come off the charger and go to the field in this hobby. We do not charge a battery, then start a 1 week hike at the end of which we fly the model. That specification makes sense for a flashlight or an emergency radio, not an RC aircraft. Others may have a different view. I don’t fly unless I’m coming off a fresh charge at the beginning of the day. Other systems are to the choice of the users but reckless in my view. Yet I offer the Eneloops for those seeking this value. There are no Eneloops this small. Also, I don’t like the Eneloop under fast charge “ever” conditions.

For RC, lets go over how silly this is;

Standard self discharge x 2 would be only 2% per day.

After charging, if we let a 500mah pack set for 2 days before flying, it would lose (500x.01) 10mah the first day, (490 x .01) 9.8mah the second day. Value at end of 2 days 500-10-9.8=480.2mah. 19.8ma lost over 48 hours or about .416mah per hour dissipated.

If we come off the charger and go to the field, a trip that takes 2 hours, the same rate of loss would mean our pack would be about 499mah since we loose about .416mah per hour.

So, perhaps, a low discharge pack is good for about a .2% advantage when you get to the field. And, to come up with that .2% I had to exaggerate the loss by double and suggest a very long trip to the flying field.

This is why this specification is essentially moot when it comes to normal day in and day out use of receiver packs in RC aircraft. Is it better? We’ll yes in some microscopic way, but to get it, what are you going to have to do? Accept an Eneloop you can never fast charge? Use a non-Sanyo cell? I see a lot of effort hunting something that has no real measurable benefit in our application.

It’s more arguable in a TX battery because we often use that battery over a number of weeks between charges.



Crash Investigation, Why did it crash?

Just as in full scale aviation, crashes are often because of a sequence of things going wrong. I received a letter recently asking my opinion on a set of circumstances. At the time of this writing there is no 100% sure answer, not enough info is provided, however there is enough info to draw boil it down to a few likely reasons. It’s easier to take a cucumber cool Sherlock Holmes look at the facts when it’s not your own model. However, you should always investigate crashes and failures with cool logic looking for every possibility, particularly the human element. Read through John’s letter and see what idea’s you have based on the info provided

Hi Dave:

I have an Orbit Charger–up graded by you to accept A123 cells.–Number: 0650-05601OK

Until recently it has worked flawlessly–but that came to a “Crashing” end several weeks ago when I took of and immediately ran out of power, airspeed and ideas, all about the same time.

If you will bear with me I will run through the sequence of events:

*Prior to going to the Field I threw my Plane on Charge (6 x A123)–The Charger quickly indicated “Full and I assumed I had charged before leaving the field the previous day.

* Commenced T.O. and promptly BECed at about 15 ft–gliding smoothly into a vertical Metal Post just off the side of our runway—cleverly ripping the wing in two and tearing it off the Fuse.

*Checking the battery back at the Pits, with my Buddy’s similar Orbit Charger–the pack indicated full and would not accept any charge.

OK, that is what happened–here is the rest of the story:

On arrival at home–(I did not take my charger to the field as we have similar chargers and packs and intended to use my buddy’s) I put my Pack on MY charger–and was horrified to see, when it was turned on–“LiPo 4.2” instead of the usual 3.6!

So all was clear–somehow my Charger reverted to Lipo 4.2V/Cell, overcharged (very quickly I might add) and ruined my 6 cell pack. This without any abnormal heat or any indication (other than the initial charge settings–which I have never paid as much attention to, as obviously I should have– as it’s been “Bullet Proof” for years).

Battery Pack ruined–Airplane wing history, ego damaged–etc!

But what I would like to know–is WHY???–did my charger revert to 4.2V/Cell as I have never used Lipo Batteries with this charger since you upgraded it– and I must say it has preformed flawlessly–until now!!

I hope this ramble was understandable to you,

John, Canada

John, Sorry to hear of losing a favorite model. You say it ruined your pack, however, you don’t provide any cycle data or voltages to back that up. So, I’m going to make a guess or two to follow that presumes your pack is not ruined from over voltage charging.

You may not know, but when A123 first came out there were no chargers really. We all charged them with Lipo mode chargers. As long as they are perfectly in balance this can be done. The high voltage fuse does not open up and fail the cell until just a little bit over 4.2. So, if a fuse opened up (your pack would be reading zero) it would have to be out of balance to begin with. You don’t say your pack is reading zero, just throwing out there some information you may not be aware of. Obviously it is less risky to the HV fusing if charged to 3.6 per cell and as chargers (Orbit was one of the first) became available to do it correctly we started only charging them in A123 modes.

There is no capacity (or not much) above 3.6v so there is no advantage to charging them higher than 3.6v, just risk. They are not lipo which will puff or risk of fire if you charge them even a tiny bit above their max voltage of 4.2. A123 is a little more forgiving of it’s 3.6v cap. Not suggesting you take up this practice, just history to chew on which bears on your question.

No idea why it may have reverted. Have you run a test to satisfy yourself it is true? If it is, you could tell it that it was charging a Lipo pack of 1 cell less and it would stop at 4.2v x cell count. In this case, set to 5 cells it would stop at 21v on your 6S A123. This would prove for certain your correct.

Also, bear in mind you had some period of time of testing it and it worked perfectly. It’s possible something happened here that you may have not expected yet was exactly what was supposed to happen given the circumstances. Bear with me while I roll through the some possibilities. Anything is possible some some things are more likely than others.

Also, havn’t used one lately in A123 mode but I am wondering if the screen reads differently? It’s late or I would check it, time to go home.

****For the benefit of readers, the Orbit charger starts the charge procedure as soon as you plug in the pack. Plugging in the pack is like hitting the “start” button on many chargers. It looks at the pack for a few seconds then displays on the screen the number of cells it “thinks” it’s connected to. The user then adjusts by hitting the up or down arrow and once you hit “start” and approve it, it starts applying current and charges the battery.****

Scenario’s I’d put forth:

1) If it were in fact in Lipo Mode, an A123 Discharged to 2.7v per cell would be only only be 16.2V, the charger would have guess it was only 4 cells and charged it to 16.8v. You’d be not fully charged and your flight would end very early. Your charger would “peak” out quickly. It would be very reasonable for you to fly the pack down to that level, so this scenario could hold some water. If your BEC voltage is hard set to something reasonable like 2.3v per cell or so, you can see how quickly putting a load on the partially charged pack would cause you to hit BEC cut out.

2) If it were a tad higher than 2.7v, lets say 2.9v, it might still only guess 4 cells. Same scenario as above, you’d be not fully charged and your flight would end very early. Your charger would “peak” out quickly.

3) If you had a short flight and the cells were at 3v+ then the total would have been 18+v. The Orbit tends to guess a tad low (to be fire/damage safer on your packs) at higher cell counts, so I’d expect it to count 5 cells in Lipo mode at 18v and only charge your pack to 21v. A full A123 would be 21.6v, it would have flown fine and you’d not have detected the slight short charge.

4) The charger could have been in A123 mode, the pack could have been discharged lower than normal. Did the last flight on the prior day end in a BEC cut out? Was it a great day, perfect conditions, where you reallying enjoying yourself extra well? Maybe you put a couple more minutes on it. Maybe it was discharged a little further than normal habits and counted 5 cells. Out of habit you approved it without looking and you had a short charge at 18v to start the flight.

My guess without having anything here to measure or double check is that scenario 4 happened It is even possible you could have had the pack so low (depending on BEC settings and nature of model) that the orbit only counted 4 cells and only charged to 14.4v. This kind of oversight when your distracted or in a hurry is very easy to make. And with a floaty model with very low cruise power requirements, it’s even easier to fly a pack very deep by mistake.

I would wager (unless there is mechanical damage) that your pack is just fine, just undercharged due to approving the charge at the wrong cell count and not hitting the up arrow to correct it.

If in fact it really and truly is in Lipo mode, I have no idea how that could have happened and it’s likely that scenario 1 describes the chain of events.

Some positive action to take:

When anything happens that is unexpected, it’s worth a closer look. You had the little red flag early on that the pack filled quicker than usual.

Really looking at that screen before you approve the charge is the first step in not having a problem. The second is looking at the finish voltage when you take the pack off. Your packs should be reading close to 3.6×6 or 21.6v. Seeing this end voltage is your second charging check and really your first step in pre-flight inspection of the model. The third check is listening to the ESC and make sure it’s counting 6 beeps. If it only beeped 4x or 5x when you plugged it up, it’s a big red flag something is amiss. If you pay careful attention to all three of these steps, it would be very difficult for something like this to slip by you again.

(You might actually be listening for 5 beeps as most ESC’s presume they are counting LIPO’s to set BEC Cut Off voltage. Being aware of the regular beep count that represents a full pack is the point, not the precise number in this case since your flying A123 cells and I dont’ know which ESC your using or it’s settings. So, correct could be 5 beeps, wrong could be 4.)

Hope those ideas will let you craw back through memory and your equipment and find a satisfactory explanation. Obviously, anything that goes unexplained can easily happen again so you want to figure out as much about it as you can. This should allow you to be alerted before flight if ever there should be a next time that circumstances stack up in a similar way.

If you did mechanically damage the battery, we can usually repair them. We keep cells on hand here.



High Cell Count Packs

Sonny P. Writes:

What is the proper way to charge a 14 cell A123 battery?

I take from your question that your concerned about the large cell count and not the rules of charging this particular chemistry of pack.

Since you need to balance it from time to time, it should be charged as multiple lower cell count packs from time to time. All rules must be observed regardless of cell count or type of lithium chemistry. So, were I building a 14 cell aircraft pack for myself, I’d build it probably as two 5 cell and one 4 cell packs. In this way I could hook up to my balance charger and balance it. If you have a charger capable of balancing 8 cells, you could do two sevens. I am un-aware of any chargers capable of balancing more than 8 cells even though there probably are chargers that could manage a non-balance charge of 14 cells. Even if you owned one, you’d still want to be able to break the pack down (electronically) and charge it in shorter segments from time to time to maintain balance.

In the case of two 5 cell and one 4 cell packs for example, The pack could be literally 3 packs that are put in series in the model. You might use Anderson Power poles to do this to minimize the number of connectors needed. Each pack would of course have it’s own balance harness for plugging into the node port (balance port) of you charger.

It would also be possible to build the pack as one 14 cell block with one set of output wires for the ESC. However, you could put tap wires in that are heavy enough for charging at the union between the 5th/6th cells and 10th/11th cells. You would build in balance harness respecting this same cell spacing. So that “electronically” (if not physically) you have 3 battery packs, two 5’s and one 4. NOTE! This type of pack bould, the central tap wires would be positive or negative depending on which segment you were charging.

With a 14 cell charger you might be charging through the main output leads while your at the flying field. Yet, when your prepping the model for a trip to the field, you would be able to charge the pack in 3 steps (one step for each pack division 5 cell, 5 cell, 4 cell) with balance harnesses connected to your charger. In this way you’d be getting regular balance charges to keep all cells equalized.

Happy Flying!


Lipo Battery Disposal

Lipo Discharging
Warren Behymer asks and interesting question:

I need to know how to dispose of LiPo battery that has swollen due to an overcurrent.

There are two issues.

1. We want to discharge the battery in such a way as there is minimal risk of fire during the discharge and later when the battery is in the recycle or trash bin.

2. We want to dispose of the depleted pack in a recycling container.

The first thing to do is remove all potential from the battery. We do this with an 1157 light bulb (Brake/Marker type bulb). It’s handy to use because it gives an indication of ongoing discharge by emmitting light and doesn’t tie up one of my ever working chargers. We have our bulb wired with alligator clips and a switch to choose between one or both filaments. I don’t remember what the draw is per filament, but we considered that a small cell would be more safely discharged at a lower rate than a larger cell. When discharging a large cell, we set the switch so both filaments burn. We use an ammo box as an oxygen poor fire safe to do this, since we are indoors and we’re working with a suspect pack in the first place.

Lipo Discharged

This is allowed to burn until the bulb is out, then allowed to set connected to the bulb until the following day. This way we are 100% certain the pack is completely exhausted.

Lipo Leads Soldered Together

Next we solder together the leads on the pack. Just in case any recovery or bounce back of capacity in the pack were possible, it is constantly discharged through the short. There should now be no chance of any kind of arc or spark starting a fire in the recycling container. Being that the pack is completely empty, there should not be any energy present of any kind.

Battery Recycling Box
It’s now okay to discard /recycle the pack properly. We won’t have to worry about the pack accidentally being shorted and causing a fire in any container. It’s electronically inert.

Federal law (49 CFR 173.185) states lithium type batteries must be individually packaged in non-conductive material and transported to a “permitted” recycler. In our shop, we use Call2Recycle (also known as RBRC 1-877-723-1297). They provide free recycling materials and processing. A bag is provided for each pack, we wrap the back in the pack, seal it, drop it in the box. When the box is full, we contact UPS for a free pickup and delivery to the recycling station. Any local battery seller should have this capability on site. We accept lipos for recycling at Radical RC.

Help finding a Call2Recycle RBRC Recycling Location near you.

There may be other safe and accepted ways of doing this, the above is how we handle it at Radical RC.


Converting A Model From Lipo to A123 (LIFE) Cells

Chris from Michigan Asks;

Hello Dave,
I would like to power my Ryan with A123 cells. I have been using a 9s 4p 6000mah Lipo pack to power a Hacker C50 motor.
If I understand things correctly, I believe that I need 4packs 6s 2300mah to equal the same watts and flight duration as the Thunder Power packs that I have been running.
Because of the cost of these A123’s, I want to be sure that what I am ordering is correct!


To match duration of a 6000mah Lipo, you’ll need at least 6000mah in A123 which will be 3P. You’ll actually be a little over as the 2300mah A123 cells actually test most of the time around 2200, at 3P you’ll have 6600mah which should result in slightly more flying time.

I assume your 6000mah lipo is made up of 1500mah Parallel packs. So, 4 1500’s in parallel = 6000mah.

If what you really meant was your running 6000mah cells, 4 in parallel, then your pack size is 24000mah which would be about 11P or 11 A123 in parallel. I am not thinking you meant you had a 24000mah pack.

If your running 6000mah total in the airplane, and are thinking of running A123 in 2P for about 4400mah real world, this may be just fine. I generally only use the top 60% of a Lipo (70% max) on a routine basis. 60% of 6000 3600mah, 70% is 4200mah. I’m more comfortable running A123 cells a little deeper than Lipo’s as the risk of hitting BEC cut off cause me less worry. (Hitting BEC cut off is hard on Lipo’s) So, running a 4400 A123 down 80% is 3200mah. So, a 2P A123 should get close to the Lipo in actual use. However, your not running as much cushion between a solid end of flight habit and the bottom of the battery.

For matching running voltage, you’ll need 10 to 11S A123. I’d probably go to 11. At 12S, you’ll definitely have 3-4 more running volts. It will be like 9.8 Lipo or something like that.

To do conversion at nominal voltage, (# Lipos * 3.7) / 3.3 nominal of A123 = cell count.
To do conversion at full voltage: (# Lipos * 4.2) / 3.6 full voltage of A123 = cell count.

Nominal conversion is: 9 Lipo = 10.09 A123 cells

Full voltage Conversion is: 9 Lipo = 10.5 A123 cells.

Since you do most of your flying between full and nominal voltage I lean towards the full number for this estimation. 11 is the best choice. 10 you might notice a slight decrease in performance by your motors KV * volt reduction of the 10S pack. Right in the front of the pack, the 9S Lipo is 37.8v. Right in the front of a 10S A123 your full voltage will be 36v. So, KV X 1.8 = drop in top rpm. If your running a 500kv motor, that’s 900 rpm.

If you go with 11 cells, you’ll be starting out at 40.4v meaning your over the Lipo voltage by about 2.6v. So, you pick up (with 500kv motor) 1300 prop rpm.

Either choice means to get back to exact performance you had on Lipo you may need to alter the prop slightly, maybe an inch more pitch for the 10S A123 and an Inch less pitch for the 11S A123 or something similar to re balance things back out.

So, on balance, not knowing everything about the model and power system, I’d lean towards 11S. If you go 12S as your proposing, you’ll likely end up way over on RPM and Watts from where you were with the 9S Lipo pack. Important considerations here are if you mind a little more or a little less power (if the ESC minds more amps/voltage) and if you would need to change props, is there a convenient prop up or down that would suit the model and flying preferences. For example, if your running right at the edge of the ESC at this time and didn’t want to upgrade it, a slight decrease in power is acceptable, 10S becomes the obvious choice.

Another consideration not taken into account above is there can be a wide variation in quality of Lipo’s people are using out there. (not picking on Thunder Power, remarks for general readers of this post) Your current pack which may be performing just fine for the application may be worn and not really up to snuff compared to the original new condition. Thus if the current lipo has more voltage depression than it should, an A123 10S pack depressing less by some significant amount, could end up taching and watt metering out higher than the battery you are now using.


Checking A123 RX Packs For Recharge Point

Radical RC A123 2300 2S RX Pack Example
Radical RC A123 2300 2S RX Pack Example

A123 RX Packs can be tricky to deturming how much is left in the pack by checking voltage alone. Variations in connectors and length of wire can have a big impact on actual volt readings when loaded. Using an RRC1000 digital voltmeter with load capability of 0.0A, .5A, 1A and 1.5A we get the following results measuring a 2300 2S RX pack with 6″ 20 g silicone JR pigtail and the included 22 guage battery checker pigail with the meter. Note: the meter (which ever you are using) is reading the voltage on it’s board, not at the pack. The voltage at the pack will actually be higher by the voltage drop across your checkers connector, pigtail, checker/pack connector and the pigtail on the pack. Here are the results we measured at varous loads. Room temperature was 74 degrees F, each load held aproximately 5 seconds before reading taken.

RRC1001 Voltmeter Image
RRC1001 Voltmeter Image
State Of Charge No Load Resting Voltage .5 Amp Load 1.0 Amp Load 1.5 Amp Load
40% 6.58v 6.37v 6.18v 6.09v
30% 6.52v 6.38v 6.17v 6.06v
20% 6.45v 6.32v 6.19v 6.08v
10% 6.38v 6.25v 6.14v 6.04v
0% 5.43v 5.19v 5.08v 4.98v

As can be seen from the data above, at some loads, the pack actually increased slightly in voltage as we went down even though the overall trend was lower in voltage. Note this test was not over a multitude of packs which would be more accurate and likely nuetralize the unexpected results mentioned.

Notice how little the pack is falling off in voltage and that the biggest consistant drop is in the resting voltage column, not a result I expected.

Notice the results at 0% capacity remaining as measured by my charger/discharger. As it is important to understand the context of the data and how I was checking the voltages, it is also important to understand the context of the data and how I was discharging the pack in 10% steps until empty (more explanined below) All discharges to make this chart after the initial 60% discharge were at 1.1A and in 230mah steps. The discharge harness was made from 22guage wire, 24″ long and plugged only into the JR output lead on the pack. Even though after 5 seconds of holding the load, I got the voltages above on the 0% line, putting the pack back on the discharger and trying to discahrge it some more resulted in the pack falling off to the 4V cut off (the empty point) in only about 10 to 15 seconds. Yet, I was still able to measure almost 1.5 higher than that when the pack had come off the first discharge to empty and been allowed to set for only 10 minutes before I measured anything. We can see that a wide range of voltages over 5 to 15 seconds with differing loads were all the same thing – EMPTY! Pay attention to the context of everything or you’ll get fooled! Because the context of how you are checking the voltage has such an impact on the reading, you should check your packs the same way every time with religious zeal.

A123 Systems cells ability to hold a strong voltage under load all the way until they are empty is one of the primary reasons they are so popular as RX packs, yet it is the very reason they are somewhat more challenging to voltmeter check from flight to flight.

To devise your own chart, cycle the pack to deturmine it’s actual value (ours was 2250), recharge, then set your chargers limiter to 60% of the actual value (ours was set to 1350) and discharge at capacity/2 (we used 1.1amp for our pack). After you’ve discharged it to this point, take the reading with the equipment and through the switches or whatever you have installed in your ship. Now you will know the readings at the 60% discharged (40% remaining) point. This is where you should be recharging any mission critical pack such as a TX or RX pack. To arrive at another row of data aproximately 10% further down in the pack, we simply set the limiter to 230mah and repeated the discharge. Repeat for each line of data you’d like to collect. You could start from full and discharge in 230mah steps generating data for 100%,90%,80% & etc….. Science, don’t you love it!

It would be my advice to think about making your own chart so you can learn something and become firmiliar with the voltage drop across all the gear in your model. You’ll be measuring the pack across a switch harness in most cases which will give you lower voltage readings than these.

General practice should be to taxi the model back to the pits, and before you’ve turned it off, plug your loaded volt meter in, turn off the model and take your reading immeadiately. Note your own chart for the correct cut off voltage and always recharge at the 40% remaining point. Flying below 40% is dipping into your reserves and should be avoided for any mission critical pack.


Do A123 LIFE Packs Free Us From Cycling?

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.



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