A123 Lithium Ion Battery

UPDATE November 2007! - ALL is well, using on three gasser setups, using single 2S123 to power all servos and ignitions. NO problems.

Recently, I decided to follow Dick Hanson's lead and go down the A123 road. Buying the batteries on e-bay was easy enough, again following others' suggestions and buying a DeWalt 36v "A123" Pack.

From the same author, this MOST EXCELLENT "How To", courtesy of "RC GROUPS".... it is worth the reading, believe me..... (thanks to RCU's "Bubbagates" for suggesting the link!)....go here -----

1. Reduce possibility, as completely as practical, that the Spektrum Rx will see "brown out" voltage drop and reboot, causing a "low voltage" crash. (A123 cells remain voltage stable through about 95% of total ampacity, 3.3v per cell)

2. Increase total current available throughout the airborne total system without using heavier, higher capacity, and higher voltage, more expensive batteries. (A123 cells are good for 30A constant, much more in peaks, without voltage depression)

3. Reduce complexity of airborne configurations; less hardware, no regulators, etc.

4. Eliminate the ignition battery (meets 3. above) and reduces airborne weight. IN my case, took 5.6 oz out of airplane. Would be less with lower capacity ignition cells, of course.

5. Permit "one source" charging and voltage monitoring. This is accomplished by single balance charging lead to the RX A123 2S pack and using the FMA Cell Pro balance charger.

With the A123 being field tested, and proven strong and reliable, I had only to duplicate everyone else's pioneering, so off I went. I bought the FMA "Cell Pro" 4S charger, (http://www.fmadirect.com/detail.htm?item=2218&section=45), which is an intelligent charger which carefully monitors the A123 cell voltage and charge current. One of only a few at this time that have a dedicated A123 mode. Charges up to a 3A rate, and does a fantastic job.

After disassembly, I made up my own 2S packs, choosing to add dual output connections, and a "charge balance" lead that would connect to the Cell Pro. Here's the configuration:

Here is my "two switch" setup, with the charging wiring omitted so the drawing isn't too cluttered. One switch goes into the normal "Battery" connector on the Rx, the other switch can go into any unused channel. If no spare channels, just use a HD "Y" like the Hitec Short Y (20ga wire), and plug into a channel other than a primary flight control, like Gear or "Aux 4". Works just fine. Two switches permits lower current load per switch, per setup, and provides redundancy of the mechanical switch, if that's a concern.

This configuration permits me to do the charging safely, and also permits me to leave the "third wire" in the MPI switches so that I can "bind" my Spektrum AR-series receivers from the switch. This is an important feature for me, so I had to figure out how to make that happen.

The weekend of August 11/12, 2007 found me doing all the testing. First, we had to learn if the DL (RC-EXL) ignition would do okay with unregulated A123 output voltage. So, we installed a A123 pack as the ignition battery, and flew the snot outta that configuration. Handy feature of the CellPro is the display that reads out exactly how many milliamps it took to top it off.... so I was able to determine a good "baseline" of current draw on the DL (RC-EXL) ignitions (two different ones were used; both are version 2.0, with mid 2007 manufacture dates).

Second, was to determine "normal" current draw of the RX/Servo setup. I did this on two different A123-equipped setups to establish a rough baseline of current drawn in the space of my "normal" aerobatic routines. With this information, I had a good reference point to evaluate how things would go when I ran everything on one pack.

Airborne Battery Total Capacity before and after – Before, using two 5 cell 1500mah NiMh. After, one, two cell, A123, 2300mah

Ampacity before and after – Before, using two 5 cells, two switches, at about 3 A, voltage depression could be seen. After, with A123 pack, two switches, no measureable voltage change at all during loaded operation.

Weight before and after – Before, two 5 cell NiMh, 13.5 oz... After, one 2S A123, 5.6oz. If also replacing the ignition, as in my case, reduced another 5.1oz... so my bird dropped almost 12 oz total weight!!!!!!!!

Cost before and after – Before, low-impedance Hangtimes batteries, $45 per pack ( x2 for 30%'ers).... After, do-it-yourself DeWalt battery disassembly....$22 for 2 cells, $9 for leads, $1 shrink wrap, so $32 total. So an airplane with ONE A123 represents $32 in "total" battery expense, versus over $110 per airplane using 3 packs. A good discovery!!!

DISCLAIMER: The report below represents MY individual results. In NO way am I recommending this to others. As installations vary greatly, both in principle and in practice, it is impossible for me to evaluate whether or not this configuration will give you the same results that I have. I assume NO responsibility for anyone’s decision to use all, or part, of the setup I detail below. I also assume NO responsibility for ANY results in performance, damage to equipment, property, or persons resulting from this configuration.

Now.... the “legal” stuff out of the way...

You all know I have been running the DL (RC-EXL) ignitions on both regulated 5.4v (from 6.6v A123 2S pack) and non-regulated, direct 6.6v direct from the A123, 2S ignition pack. Results have been excellent, and predictable, with total current draw per flight only increasing slightly from regulated to un-regulated, when compared to 4 cell NiMh.

In my setup, the RC-EXL ignition supplied by DL with my engine draws approx. 7 ma per minute, or about 420-450ma per hour. This is when operated over the power range of the engine, only at full throttle probably 2-3% of the flight. Majority of operation is at mid-throttle or below, representing 3500rpm and lower. Max throttle on the DL with the NX 22 x 8 at this point, 32:1 mix, Pennzoil, is 7260 rpm when hot.

I am also operating the Spektrum AR 7000 receiver, with one satellite receiver, stock. It is powered by the 2S A123, no-regulators, and is installed in a “stock” mid-ship configuration with the satellite receiver behind, above, and at 90* to main receiver. Satellite receiver is mounted approx. 9” aft and 6” above the main.

Ground range checks, engine off/on are nearly identical, being well over the 90 ft. Minimum, and closer to 125’ or more before the low throttle “fail-safe” kicks in.

My ground tests with engine on also were with the straight A123 connection, and today, connected to the MAIN 2S A123 battery powering the entire system. Performance was flawless; no differences observable, current drawn from the single 2S A123 pack agreed with the “normal” system draw, PLUS the anticipated ignition module current load.

Engine running, it went to fail-safe at the safe distance and antenna orientation as when configured with the normal 4 cell NiMh dedicated ignition pack.

Next is flight testing, and that should take place this evening. I will update when flights occur.

Braving 102*, and 15mph quartering blast-furnace hot gusts, I hauled the Cap out for the big non-event. Yep. That's right. NON-event.

NOTE: Original Radio in use was a Spektrum module in JR 9303, Spektrum AR 7000, single, stock satellite receiver. January 2008 using JR X9303, AR9000 and JR R921 Rx's.

UPDATE - November, 2007 - now also using with AR 9000 and dual remote receivers. Working very well. Have converted all airframes to "no ignition battery", adding additional pigtail output to A123 packs to connect to ignition. NO INTERFERENCE OR OTHER ISSUES using the Spektrum, RC-Excell ignitions, on three gassers!!!!!

A non-event because...
1. Ground range checking, engine on or off, not ANY difference from original install. 46 paces with the bind button depressed.
2. Try as I might, at the fringes of ground range... regardless of engine throttle setting.... everything worked perfectly normal.
3. Flights were picture perfect. Low, long, distant approaches, and departures.... rock solid. "Tracking" the airplane, with the antenna pointing right at it (worst signal condition for 2.4), even at the ends, and the TOP of the box.... solid.

Everything worked perfectly. Current draw per spec, performance of the ignition per spec.

My test - for me - is a success, and I will retrofit the balance of my planes to this single 2S A123 configuration for RX, servos, and ignition. Because it works.

The "gut check" was a low, distant, horizontal line, pulled to vertical, then accelerated straight up, rolling, until I literally could no longer see which way it was going. Wish my calibrated eyeballs would tell me how far, but it was up there a ways. Remained solid, and the throttle cut when *I* told it to.... This has been a good test, and I will continue with this configuration.

UPDATE January 26, 2008 - Flew my DL-50 powered Obsession, five Hitec 5985's, one JR4131. Single-power source of one 2S-A123-2300mah battery powering BOTH RX/servos and Ignition (no diodes in circuits). 40 minutes flying used 750ma, average of 20 ma/minute usage. No problems whatsoever, plenty of reserve power remained in 2300 pack. This is a JR X9303 w/ AR9000 2.4Ghz system.

UPDATE May 4, 2008 - Having put an additional 3 hours on two different setups where the single 2SA123 is powering BOTH ignition and RX/Servos, I can state that I have had no problems with this configuration of any kind, and that they are both rock-solid, glitch-free, and milliamp-hour frugal setups. Average running 5 Hitec 5955TG's and the DL 50 "RcExcel" ignition is costing 18 ma/minute, or just under 200 milliamps for a typical 10 minute flight.