I have flown the A123 cells (the larger 2300mah) and I was able to draw down to about 90% before it would drop off and voltage was down to 2.8V per cell. One thing to check is the low voltage cutoff setting in the ESC. It could be set up for lipoly's that cut off at around 3.2V per cell. Since the A123's start at 3.4V (maybe a little higher off the charger but they quickly settle to 3.26V) it might be that under load you hit this quickly and it cuts off. For the A123's you can safely set the cutoff at 2.5V per cell.

Best,        Dennis

I don't know yet how much I'll put back in after a full run, I need to recharge them after yesterdays flight.  It takes me about an hour to charge them at 1.2 A after a 2 and 1/2 minute run.  How many amps are you charging at to be able to do it in 15 minutes?  I was able to charge the 3 cell pace with a zip charger in about 8 minutes but was told you can't zip charge 4 cell packs.

Yeah, a 15 minute capable charger is not something you find cheap -

I use an old Astro 112 - it will charge up to 43 volts at 5 amps (actually runs at about 4.5 amps) from a 12 volt source.  I have it running through a (LiPo)Dapter to cut off the charge at full charge. 

If you could find a power supply with a 15 or 16 volt - 5 amp capability, you could zip charge with that.  Otherwise, your options are pretty limited.

I charged my 4 cell pack this afternoon using 5A and it did charge to full in 12 minutes.  It took 866 mah.  I wonder if part of the reason I'm not getting more time is that the pack is unbalanced.  I added a new cell to a 3 cell pack and then charged it.  Just now, after charging the pack I checked the individual cells and I get 3.4, 3.4, 3.4 and 4.0 for a total of 14.2.  When I check at the connector it shows between 14.3 and 14.4.   I checked it before the charge as well and got readings of 2.9, 2.9, 2.9 and 3.2.  Even at 1100 mah capacity you would think I should get a little more out of these batteries.  I seem to be leaving about 250 mah "in the tank".

Jim, it is ALL WRONG. you cannot have 4.0V on one cell, the pack is unballanced. The 3.4V is usual voltage when charging, the battery has that voltage almost all time of charging, so it does not indicate the capacity already in. The voltage jumps up very quicly on end of charging, so that last cell is more charged and the voltage quicly jumps up and prevents proper charging of those others. Try to charge it with ballancer and if you do not have, then charge all cells separately. I note end voltage is 3.6V ... 4V is bad for your cells.

From my experience, if you once ballance the battery well and if you extensively use it, it not needs any ballancing anymore. But it if you store it for longer time, you will need to ballace it again before usage. So I reccoment either to use ballancer, or to check votlage time to time immediatelly after charging.

the situation is it just runs down or poops out over about 5 laps until there's not enough power to keep it up in the air.  I was afraid that the unbalanced cell would be a problem.  I don't have it wired for a balancer although my charger will balance a pack wired for it.  I think I'm going to rewire the pack so it will balance.  Maybe that will solve the problem.  By the way Igor, I really like the timers.  Will Hubin set them up for me.  Are they supposed to spool up the engine after only 5 or 6 seconds?

That does not sound like the batteries - A123 cells have a very distinct "Knee" in the discharge curve if the load is constant.  I suspect that your speed control is programmed to "decrease power" rather than to "hard cutoff".  Additionally, if you have the ESC programmed for LiPo's, then they will look like weak LiPo's very soon to the ESC.  Be sure that you program a hard cutoff and if your ESC "auto sense" s the number of cells, then set it up for NiCd/NiMH, rather than LiPos.  If you can program a cutoff voltage, rather than a number of cells, then program it for about 2.75 volts / cell or so.  Really, with A123's, you can't really hurt them by setting the cutoff too low, because they will very quickly fall through the cutoff voltage at the end of the capacity.  The real answer is to have the timer shut things off before the ESC senses the cutoff voltage.  That is the key to protecting your battery, whether it is LiPo or A123.

One of my packs has a stubborn cell, like yours that shows 4.0 volts.  I had to leave it on the FMA Cellpro charger for quite awhile while it charged the other 3 cells and kept the higher one discharged.  When the charge was done, they all read 3.6 volts. It is really annoying, because it often sends the FMA into "Safety Charge" mode ( at .5 amp, rather than 3 amp).  There are other chargers that will balance charge without the "auto safety" features, which protect LiPo's but only slow down the charge on A123s.  I would also recommend that you get a balancing charger or a separate balancer that can be plugged in while you charge.  This will keep the stubborn cell under control.

I rewired the pack with a balancer pigtail and the charger balancer indicates it is connecting.  However it gets up to about 13.8 volts and gives me an unbalance warning 2.5 volts.  I discharged it for 10 minutes and started the charge again at .5 amps but it gave me the same warning at about the same voltage.  I though the whole purpose of the balancer was to prevent this and get all cells to balance.  What do I need to do to get this pack to balance?  Is one cell just so far out it won't balance or am I doing something wrong here?

Well it looks as if this pack is determined to be a problem child.  The technician in me says that something changed when you added the balance connector: before it charged up to 14.2 volts but the cells were not balanced; Now it charges to 13.8 volts and the charger pukes.  So the balance connector MAY not be correctly wired in (How many pins does it have?).  Your phrase "... gives me an unbalance warning 2.5 volts" isn't real clear to me what your observations are.  What charger do you have and do you have any packs that work correctly with it?  I assume you are aware that for a 4 cell, your balance tap must have 5 pins.  I also assume that since your charger tries to charge, you must have the polarity correct.

To check the pack, I would individually discharge each cell to 3.0 volts, if possible.  You would need some kind of "load resistance" that would handle a couple of amps - a couple of 1 ohm, 10 watt resistors in series would draw about 2 amps initially from a partially charge cell ( ~3.4 volts across 2 ohms = ~ 1.7 Amps @ ~6 watts or ~3 watts per resistor).  You would want to use a fairly heavy wire and alligator clips and be aware that the resistors will get pretty warm.  Put the load across one cell at a time and put a voltmeter across the load - watch for about 3.0 volts to go by and disconnect the load.

When you've "hand-balanced" all four cells, you can try to charge again, but frankly I would expect that it would act the same.  Things seem to be pointing to some kind of wiring problem or a problem in the charger itself.

Sorry I can't be more help long distance, but would be glad to get your pack and charger on my bench and check it out for you, if you wish to go through the hassle of sending it.  I've done lots of battery pack building and have the equipment to figure out which end is which.  There would be no charge, of course, except the cost of shipping it.  You can send me a pm or an email (mikeainia "at" iowatelecom.net) to arrange it if you decide to.

Well, success of a sort, at least with balancing.  After checking the pack all cells were indicating 3.4 volts.  I ran it down till the engine lost all power and rechecked and they had not all run down equally.  I then recharged at 2.5 A and got an error message at around 14.3 volts of charge.  I unhooked the balancer and started the charge again and was only able to put in another 25 mah before it indicated full.  Total mah input around 890.  Checking the individual cells they were all within .2 volts of each other.  Unfortunately I still don't get more than 3 and 1/2 minutes of run time out of the 4 cell pack.  This is not a real problem except I don't like coming down with the engine still running, I'd rather have a clean cut off.  I may just have to have the timer reprogrammed. 

Igor has it right - and he's been flying A123's longer than any of us.  And I still don't understand the error message your timer is putting out, but it seems that it is significant.  The new cell must still be a troublemaker as far as balancing goes.

Also, I would get a timer with an easier to adjust run-time - we've been flying half a dozen of Will Hubin's various timers around here all year - The ability to twiddle a pot for run-time and power level (rather than go into programming mode) has proven to be a real plus over the JMP.  I've got a z-tron, but haven't yet gotten it out and flown it.  I have flown the JMP, though, and find that rather than reprogram the run time at the field, I just put the plane away and try to remember to do it at home.  Usually I forget, so I get out to the field without having fixed anything.  The z-tron also has an easier to program run-time - just by flipping switches.

(Also, I thought that it was possible to reprogram Igor's timers for run-time ?? Not easy, maybe, but possible.)