[TManiaci]

I thought it might be a good time to share making A123 Battery Packs.

I am running A123's in my 37.5% TOC Yak. I have the Powerbox Royal installed, and I am recording my flight data. I am using 700-1000 mAH per flight, average around 875 mAH. I am a novice 3D pilot, and generally fly mixed 3D and circle flying, so I don't tax them real hard. My flights are generally 10 minutes.

My current setup has twin 4800 mAH Iron Corps Fromeco (A123 copies). With this setup I can easily go 8+ flights, but my habits are to fly 3-4 flights on a typical outing.

I have bought all the materials to build two new 2S1P 2300 mAH A123 packs. This will give me 4 flights, and reduce battery weight by half. Saving almost 12 ozs (3/4 lb) in the bird, which is my goal.

The Parts Pile...


I also have a 2S1P 2300 mAH A123 pack on Ignition, and I'm changing that pack out for a home-made 2S1P 1100 mAH A123 Pack. I have a 3W157CS for power, and the typical 2 cylinder ignition system draws 650-800mA. My charge mAH agrees with that conservatively, and I use 100-130 mAH per flight. The 1100 mAH pack should have enough for 7+ flights. This will save another 3 ozs.

So, I will save almost 1 lb in the re-equip effort. I should be able to fly 4 flights before recharge. I will check voltage before each flight, and continue to record my mAH usage after each flight. I will probably build four 2300 mAH packs, and rather than charge at the Field, change the packs after 3 flights to be safe if I am having a busy day. I have my packs installed on Velcro pads and Velcro straps, so swapping is not trouble at all.

I love the A123 technology. With my own current draw recorded at over 20 amps peak with my conservative flying style, I feel much safer having a system that can actually deliver 3 times what I need. My batteries connect directly to the Powerbox, so there is no switch to choke current. All the servos connect directly to the Powerbox with one extension, so they all can pull as much as they need, and the only restriction is the capacity of the servo connection (generally said to be 3-4 amps on JR connectors). I have 13 high torque control surface servos (3 - JR8611A's and 10 - Futaba 9156's), along with throttle and choke servos. 13 big servos can potentially pull 39-52 amps if they are all loaded to the max (never happens when the way I fly). The twin shared A123 packs can service 120 amps peak in this setup. No brown-outs in this rig, that's for sure.

I like conservative. Even the smaller 2S1P A123 packs give me more than I will ever need. I am sacrificing by limiting to 3-4 flights, but the weight savings is worth it as I try to advance my lame 3D Skills.

Let the build begin...

[TManiaci]

These are authentic A123 cells I ordered from Hobby City. The are $14.95 each, and with all the little goodies I should have a 2-Cell pack for less than $32 each. Fromeco sells this pack (without balancer tap) for $50. The cell model number is 26650 is actually the size, 26mm diameter x 650 mm long.


These batteries came with solder tabs. This makes the soldering easy. When two cells are side-by-side you can line up a (+) end to a (-) as shown and they lay on each other nicely.


We want the packs to be tight together, so we will use the slot between the cells to route wires and make a neat package.


To do good soldering work, you need a good soldering iron. I use a Weller WTCPT which is 60 Watts. If you don't have at least a 40 watt unit, you will find it difficult to get solder to flow and heating times will be very long. First thing here is to "tin" the tabs. I use Rosin Paste Flux and 0.031 diameter 60/40 solder. Note that the tabs on the table are staggered when the end we are joining is connected. Be careful to avoid touching tabs at both ends, that is a meltdown you don't want to see.


Once the two tabs are lined up and tinned, apply heat until the solder flows between the tabs. Add a little solder as necessary to produce a good fillet around the joint.

[TManiaci]

I bought 6-conductor balance leads, so I cut them down to 3-conductor leads to keep them light. These were also from Hobby City, and have that really nice flexible silicone insulation.


First you need to tin the power leads as shown. A little flux, then apply heat and solder until the wire end wicks up the solder and makes a solid mass.


The Balancer leads connect in a simple fashion, negative (pole 1) goes to the negative pole. The second lead goes to pole 2, the connection between the cells, and the pole 3 goes to the Positive lead.

So here you solder pole 2 to the tab bridge between the cells.


Now solder the negative lead to the cell with the negative pole open, and include the pole 1 lead of the balancer.


Then solder the positive lead to the free positive cell tab along with the pole 3 of the balance leads.

[TManiaci]

At this point you have a "hot" pack. It's a good idea to put a bit of shrink tubing or tape on the free positive lead to prevent accidental shorting.


I connected the battery monitor toy to check the balancer lead wiring.


I routed the pole 3 balancer lead over the end of the pack so the balance leads all come out together as a set and still allow the cells to be touching full length.


Then I tuck in the leads so they all lay in the gap between the cells...


So , when the shrink wrap is applied you will have a tidy exit of the leads.

[TManiaci]

I cut a v-notch in the shrink wrap to allow the wires to exit. In retrospect, a deeper u-shape cut will be much better on the next one.


Holding all the wires in place and the cells together, heat the shrink wrap just like you do Ultracote with the hot air gun.


Now tin the female Deans connector...


and solder the leads one at a time, taking care to avoid shorting.


... and there you go. A home made A123 2300 mAH 2S1P 6.6V battery pack with balance lead ready for business.

[TADILLAC]

Sweet tman... Just a tip if you plug the female deans into a male while soldering it will keep it from warping and keep it from being a pain to unplug...

[Airbike]

Looks good Tony.

I use the same setup on my flag scheme compy, 2 packs of 2s 2300 mah A123, then swap out after 3 or 4 flights depending on type of flying. I used a 2s2300 on ignition so I don't have to swap that out. ( Ididn't have anymore 1100 mah size at the time, I use the 1100's for Rx packs for other smaller stuff)

One thing to note in the above pictures. On the A123 2300 size cell, the "button" end is the negative so pay attention when soldering up your packs!

[Rod Bender]

Great 'How To' Tony.. I will have to give this a try when my packs need changing...

[ScottZ]

TManiaci, I am using 2, 2cell A123's in my 37.5% TOC Yak at 36.5 lbs and fly aerobatics and 3D for 15 minutes and pull about 260mah per pack each flight. Thats only 520 total average per flight.Unless you fly really hard you might have a hinge binding or a servo fighting issue.Nobody out at my field is using that much. I have a Hobbico inline amp/voltmeter which I use to check every servo going through its travel. I have found that even a little buzzing can be a big amp draw. If you are running ignition through those packs then you are probably OK.

[TManiaci]

Originally Posted by Airbike

One thing to note in the above pictures. On the A123 2300 size cell, the "button" end is the negative so pay attention when soldering up your packs!

What do you see for charge mAH per flight?

That's right Airbike. The ends are the opposite of what we are used to in small cells. They also have a +/- laser burned on the case.