Align 6S2P 4200 16C

The following is a review of the Align 6S 4200 16C lithium polymer battery pack. This pack was provided courtesy of www.grandrc.com as part of the standard T-Rex 600 package.

The pack consists of 12 cells arranged in a 6S2P configuration. The cells themselves are 2100 mAh cells which have been configured in parallel to produce 4200 mAh packs. Six of these have then been placed in series to produce the 22.2 V endproduct. The entire pack comes shrink-wrapped in black plastic and each set of parallel cells is separated from the next via an air gap. This is good practice as it allows air to flow around the cells in the pack which helps with cooling. The pack comes fitted with a balancing cable and the main power connector was already soldered onto the pack.

Given the large capacity of this pack it is not very practical to try to test it using a constant current discharge as a huge number of Watts is required to do the higher amperage discharges. The T-Rex 600 serves much better in this capacity as a high amperage load for the battery. Therefore we will use in-flight data to test this pack.

I used an in-flight data logger in order to gather the loading information for the pack. An infrared temperature monitor (gun) was used to measure the pack temperatures at the end of the flight.

 

Before moving into the review proper, here are some pictures of the pack under review.

 

 

Flight Testing

The flight testing has been conducted using a standard T-Rex 600 with the default T-Rex 600 motor. The flight style adopted for the review has been a 3-D flying session. Within the 3-D flying session I perform loops, rolls, tic tocs and some inverted and backwards flight, plus the flight ends with an autorotation.

First and foremost this pack does provide the necessary punch to do some very nice tic tocs. The pack is relatively light weight and this lends itself to a light disc loading. The pack provides enough for about seven minutes of 3-D flying and then it is time to land. Pack temperature was measured using a Tenma infrared thermometer gun.

After completing the flight the pack temperature had risen to 70°C. This is most definitely over temperature and will lead to short cycle life due to the pack overheating. Five minutes later and the pack had risen to 72°C. This is typical of lithium polymer batteries in that they will get hotter even after the flight has ended.

If we analyse the flight that produced this excessive temperature we can see the following statistics. The average amp draw across the entire flight was 34.4 amps which equates to an average discharge of 8C. the maximum amperage at any point in the flight was 78.8 amps. This equates to an amp draw of around 18C this is slightly beyond specification and might account for some of the excessive temperature experienced (but I doubt this contributes greatly).

If we now look at voltage the minimum was 19.8 V which equates to 3.3 V per cell. This is not too bad considering that the pack has been run beyond specification. Included below is the full discharge data for the 3-D flight.

 

 

Note that I have not shown the autorotation at the end of this flight in this graph as the period of time with no amp draw skews the information showing pack performance.

Conclusion

The standard Align pack can be sourced very cheaply and it does provide a reasonably exciting flight performance. I am not keen on the configuration of cells particularly using parallel cells in order to get the 4200 mAh capacity rating. The reason is that the more cells you put in a pack the more critical it becomes in terms of balance and it also introduces more points of failure.

I am not particularly aggressive with my 3-D flying and yet this pack is still going way over temperature at 70°C. This will lead to a short lifetime. I am tracking every charge and discharge on this pack and will update this review once the pack has reached its end of life.

I feel this pack would suit a beginner or intermediate flyer who is not going to push it very hard. For anybody doing any kind of 3-D this pack is not suitable. 3-D flying is clearly pushing it beyond its temperature limit and would make the pack a poor investment in terms of its cost per flight (due to reduction in charge cycles).

The pack going over temperature also raises other questions in that the average amp draw across this flight was only 8C (half the rating of the pack) and yet it still managed to go over temperature. This would lead me to believe that this pack is not correctly rated in terms of its discharge capabilities. A pack rated at 16C should be capable of doing a 16C (67.2A) discharge for the entire pack without going over 60°C. I have serious doubts that this pack could actually achieve that based on the in-flight data.

Overall I would NOT be happy to recommend this pack for use in the T-Rex 600 unless it was just for a beginner where cheap packs are desirable due to the high incidence of crashing and the possibility of the pack being damaged/destroyed. For 3-D flight this pack seems entirely unsuitable and I believe far less than 50 cycles is likely due to the overheating.