How I Have Been Zip Charging a 3S1P ANR26650M1 (2300mAh) A123 System, Inc. Pack
By Ken Myers - March 2008

     This article first appeared in the April 2008 Ampeer.

     Warning: What you are about to read is what I am doing, NOT what I am recommending anyone else to do! Under NO CIRCUMSTANCES should you consider doing the following unless you have the proper electronic tools, skills and knowledge! This is not a how-to but a how I did it. Improper use of this information could lead to personal injury and property damage.

     "Zip Charging" is a term coined by Charles (everydayflyer) on RC groups to describe the charging method where a length of 16/17/18 gauge "zip cord/lamp cord" is used to directly charge a 3S pack of ANR26650M1 or APR18650M1 cells from A123 Systems, Inc. with a direct connection to a 12v Marine/RV battery. A meter, like the Astro Flight Whattmeter, is inserted inline to monitor the charge.

     This method may ONLY BE USED with 3-cell packs (or combinations thereof) of the aforementioned cells. Under no circumstances should this method be used with any other battery type or cell chemistry.

     This type of charge can be terminated automatically. Dan Baldwin has plans for the "Terminator" on RC Groups. It is a DIY project. ( For now, I manually terminate.
     On Sunday, March 2, I charged the 3S pack for the Son of Swallow for the first time using my unmodified Astro Flight 109 charger. Once I felt it was charged, I started discharging. While doing the initial charge, I used my very old Astro Flight Whattmeter inline with the charger and battery to see how it reacted to the charge.
     One interesting observation was that during Mode 1 of the AF 109 charger the Whattmeter averages the numbers as the charger does its "checking." Once in Mode 2, the charger numbers did not agree with the numbers displayed on the Whattmeter. To get the AF Whattmeter to "read" 2.3 amps during the charge, I had to set the charger to 2.5 amps. Also, the voltages displayed on the two devices were quite a bit different, with the Whattmeter being 0.2 of a volt or more lower. While investigating the charge, I also tried my Hyperion Emeter, but wasn't quite sure what I was doing with it being used this way.
     I then discharged the charged pack using the AF 109. During the discharge, I attached the CellMeter-8 from Hobby Lobby and found that once discharging, all three cells of the pack were reading exactly the same voltage, whenever I measured them, even though the individual cells had not read exactly the same before the discharge started. The discharge took about an hour and fifty minutes. I did not record the mAh taken from the pack, as I had stopped the discharge and "played" with the different meters a bit.
     I then charged up the pack again and let it set over night. The voltage readings in the morning were 3.45v, 3.54v and 3.54v. I topped off each cell individually using the unmodified AF 109 until they all read 3.74 while resting.
     I set up a discharge of the pack using the AF 109. I left the knob zeroed, as it has no affect on the discharge, hooked the charger up to the 12v Marine/RV battery and then hooked up the 3S pack for discharging. I went upstairs and set the timer for twenty minutes, as I wanted to monitor the pack during the discharge.
     If you own an AF 109, you know what I did wrong. To discharge a pack using the AF 109 you hook up the battery pack to be discharged FIRST, not the Marine/RV battery! That's right, I charged it for another 20 minutes! Yikes.
     When I discovered my error, I used the CellMeter-8 and found all three cells to have a "surface" charge of just over 4v. After an hour, they had settled down to about 3.85v per cell. They sat for another 15 minutes and then I put my AF 123 Blinky on the pack for 10 minutes. At the end of the ten minutes the CellMeter-8 read the voltages as 3.677v, 3.691v and 3.655v. When hooked up correctly in Discharge mode, the AF 109 read an initial 10.84v.
     It took 110 minutes to discharge 2220mAh. The "bounce back" voltages after resting for a while after the discharge were 3.148v, 3.163v and 3.161v.
     For the first Zip Charge the total length of the cord and AF Whattmeter was 18 ft., as this is what I had remembered the length being from the discussion of in "$10 3S A123 charger" on RC Groups. (
     Apparently, I had remembered incorrectly.
     During the first charge, I panicked a little and didn't really let it complete the charge. When I saw the Whattmeter reach 11.4v, I terminated the charge. I should not have terminated it at that point because only about 2085mAh had been returned to the pack. The highest amp draw that I saw near the beginning of the charge was somewhere just over 10 amps, and it went down to about 2.9 amps just before the early termination. For about twelve minutes of the charge the amperage was between 7.4 and 5.0 amps. That was much lower than I had hoped for. The cell voltages, after resting a half hour, were only 3.429v, 3.438v and 3.424v, which is not really a full charge, but close. I "A123 Blinkied" to equalize the pack and then started another discharge.
     I shortened the Zip Cord/lamp cord by three feet, to fifteen feet total including the Whattmeter, for the second Zip Charge. I also kept better records during the charge process. The second charge ran sixteen minutes and put in 2145mAh, according to the Whattmeter. That is an average of about 8 amps during the charge, or about a 3.5C charge rate. The highest amp reading I saw at the beginning of the charge was a little over 13 amps, but it went down quickly to the 9-amp range with the amp reading being 9.4 amps at two minutes into the charge. Even though the charge was terminated at 11.9v on the Whattmeter and at the sixteen minute mark, I am not sure that I actually filled the pack because a half an hour after the charge was terminated, the cells read, 3.583v, 3.534v and 3.551v on the CellMeter-8. The cells were barely warm to the touch immediately after the charge.
     The battery was equalized to 3.52 volts per cell, and once again discharged. Another three feet was clipped off the Zip Cord/lamp cord, making the total 12 feet. The battery was "Blinkied" after the discharge to about 3.12v per cell.
     The pack was recharged. The voltage on the Whattmeter read 10.2v when plugged in and showed 16.3 amps. After two minutes of charging, the voltage was up to 10.4v and amperage down to 11.2. The amps declined from 11.2 at 2 minutes to 7.4 at the end of 12 minutes and 2078mAh had been returned to the pack. Not wanting to terminate too soon, I allowed the pack to stay connected for another 3 minutes, during which time the amps went from 3.2 to 0.8 and 132mAh was added to the pack for a total of 2210mAh. The "surface" voltage read by the CellMeter-8 immediately after the charge was approximately 4.0v per cell.
     After the charge, the pack was warmer than the second charge, but it definitely was not hot!
     The pack was left to rest overnight and then the CellMeter-8 read the voltages as 3.761v, 3.690v and 3.691v while my Radio Shack #22-168A multimeter read them as 3.76v, 3.69v, and 3.69v. The Astro Flight Blinky for A123 cells was used to balance the pack before discharging again. 2245mAh was discharged from the pack.
     I cut another three feet from the zip cord/lamp cord and started another charge. Since this is where I've decided to leave the length, the following data from the AF Whattmeter describes the charge.

0 min.10.2v20.1 amps0.000Ah
1 min.10.6v13.6 amps0.273Ah
2 min.10.6v13.1 amps0.500Ah
3 min.10.6v12.7 amps0.722Ah
4 min.10.6v12.5 amps0.940Ah
5 min.10.6v12.3 amps1.140Ah
6 min.10.6v11.8 amps1.350Ah
7 min.10.7v11.3 amps1.539Ah
8 min.10.7v11.1 amps1.737Ah
9 min.10.8v10.5 amps1.911Ah
10 min.11.0v8.2 amps2.079Ah
11 min.11.7v3.6 amps2.165Ah
12 min.12.0v1.5 amps2.208Ah

     The surface charge cell voltage readings immediately after the charge, using the CellMeter-8, were all around 4.0v, but quickly started to settle. The temperature of the pack had risen from 58-deg F to 80-deg F at the end of the charge. The pack felt significantly warmer than any of the previous charges, but not hot!
     During the charge, because I sometimes had my hand in the proximity of the zip cord and Anderson Power Pole connectors, I could feel them giving off some heat.
     Approximately six hours after the charge the CellMeter-8 showed the following; 3.732v, 3.638v and 3.682v. The AF "A123 Blinky" was used to bring the pack back into balance.
     Throughout the Zip Charger adjustment process, I noted that the most positive cell seemed quite different from the other two cells. It always discharged lower than the other two cells and charged higher than the other two cells.
     A twelve-minute charge is fast enough for me, so, for now, I'm leaving the total length of the Zip Charger at nine feet, which includes the length of the monitoring AF Whattmeter and Zip Cord/lamp cord wires.
     The pack was discharged on the morning of March 5 so that it could be charged at Midwest RC Society meeting that evening. I charged it during my A123 presentation, but, unfortunately, I didn't show the members the finishing voltage, as I was discussing the cells at the time the charge finished.
     On the morning of March 7, the resting cells read 3.581v, 3.475v and 3.546 on the CellMeter-8. The pack was AF 123 "Blinkied."
     In the warmer than my basement meeting room, the pack reached about 95.5F at the end of the charge, which is still not really hot. The voltages noted above, indicate that the "most positive" cell has fallen inline with the other cells.
     On the morning of March 11, I prepared to do some motor/prop testing for the Son of Swallow using this pack. The pack had not been touched since March 7. The CellMeter-8 read the resting voltages as 3.459, 3.458 and 3.451, which is pretty nicely balanced for just sitting around.
     I then used the pack, without recharging of any kind to warm up the motor with a prop on it and then take two no load readings and capture five reading per prop on my Emeter for four different props. The pack output held up very well through that first series of tests. It was then Zip Charged in a short time and a second series of tests run on the four props with it warm from the charge.
     The remaining charge was used to adjust the servos in the Son of Swallow and run up the motor several times to full power to see the cowl hold on method of magnets was working well.
     The rest of the pack was run out that afternoon before the Skymasters' meeting on April 12.
     During my presentation about the A123 Systems, Inc. cells at the Skymasters' meeting, I Zip Charged the pack, terminating the charge with the AF Whattmeter showing 12v. The pack temperature was 92.5F after the Zip Charge. The resting pack voltages were not measured that evening.
     On Saturday, March 15, the CellMeter-8 read the resting voltages as; 3.490v, 3.486v and 3.478v. The AF A123 Blinky was then used to bring down the "high" cell.
     It appears that these 2300mAh cells tend to "settle down" to about 3.45v to 3.5v after resting for a period of time, not the 3.6v as expected from the A123 Systems, Inc. data.

April 1 Update:
     I had not touched the pack since March 15. Using the Cellmeter-8, I checked the cell voltages this morning and found; 3.452v, 3.453v and 3.420v. I consider this to be still pretty well balanced since the last charge with only 0.03v being the greatest difference.

My Zip Chord Charger

WARNING! DO NOT use the type of terminal connectors that I used with exposed connectors, like a Deans, as they could be shorted by a metallic object! If you are using any type of exposed connector, like Deans, use alligator clips for the battery to cord connection so that a lead can be easily removed for safety!