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View Full Version : 169 Wh/kg batteries?!? That you can buy!?!



larryrose11
29 March 2012, 0856
All,
I was shopping for some batteries for an RC project, and I came across these

http://www.hobbyking.com/hobbyking/store/__21387__ZIPPY_Compact_5800mAh_10S_25C_Lipo_Pack.h tml

Spec.
Capacity: 5800mAh
Voltage: 10S1P / 10 Cell / 37V
Discharge: 25C Constant / 35C Burst
Weight: 1268g (including wire, plug & case)
Dimensions: 165x46x79mm
Balance Plug: JST-XH
Discharge Plug: 5.5mm Bullet
So,
37V*5.8ah-AH/1.268 kg = 169.24 wh/kg

Are the specks wrong?
Is there anyone out there with expirence with these Zippy Lipo?

frodus
29 March 2012, 0903
Search on endless-sphere forum. Plenty people use them.

liveforphysics
29 March 2012, 1002
Various HobbyKing RC LiPo has powered all of my bicycles over the years. I've also visited the factory that makes almost all RC LiPo brands, and enjoyed hanging out with the very cool owner.

There are some things to REALLY understand before choosing to go with RC LiPo. The power and energy density they claim, is 100% real. However, they also have a very real danger with them, and you should EXPECT to have random cells die in the first few dozen cycles, and its your job to find and replace them (with cells from that same lot, so buy about 10% more batts than you needed to build your pack). In some ways it's extremely simple pack construction, just plugging in wires, in other ways it's extremely careful complex work getting a pack dialed-in that will last and not burn your home down from the random infant mortality you get on cells that are impossible to find before they fail.

We've also had 2 reports now of packs just sitting unused that burst into flames... So, if you want the highest performance and energy density possible, they do deliver it, but it's not without it's drawbacks.

Nuts & Volts
29 March 2012, 1004
The weight may be wrong. I purchased one of these packs http://www.hobbyking.com/hobbyking/store/__21431__Turnigy_nano_tech_8000mAh_6S_25_50C_Lipo_ Pack_USA_Warehouse_.html

Instead of 159 wh/kg that you can calculate from their specs, I got more like 155 wh/kg. I don't have the actually weight measurement on hand sorry, but I will double check when I get home.

I have thought about making a small 20s pack with two of these. It would make a nice 10kW, 5 mile pack that I could just whip around on my bike with.

Sometimes the dimensions are a little bit off as well.

markcycle
29 March 2012, 1126
I'm going to add my experience with Lipo since I've built some fairly large packs with them
1) 25s 4p 20AH pack
2) 25s 2P 10 AH pack
3 28S 8P 40AH pack

Plus many other packs used in the shop for testing

What I have found and this isn't a certainty and Lipo has been reported to spontaneously go into combustion so be careful, but I've discovered it is important to monitor every string of parallel cells before every ride. i use a B6 from hobby king and have them always connected. I know they draw power and can cause cell imbalance but this is a small problem easily solved by doing occasional balancing. My procedure is this.

I charge as soon as I get home or right after a ride. i try and finish charging before I go to bed and most often do. If not I turn off and disconnect the chargers and never charge while asleep - never I also use a timer to assure this.
So my goal is to finish charging and let the batteries sit off the charger overnight. The next morning I observe the strings and compare them to each other. Most importantly I look at the self discharge of each "P" string.

When there is a bad or weak cell the "P" string will have a higher self discharge than other strings in the pack.
When things get bad enough a bad cell is obvious .5 volt drop in 7 to 8 hours for instance and immediate attention is required.
So far this method has worked well for me, finding two bad cells across three packs.

The thing is almost no BMS is going to give you this data as to which string of cells is lower than the others, and many will try and bring that string back up to voltage or lower all the other cell to that bad strings voltage level, causing a disaster.


There is the subject of pack building which i'm not going into here I just want to say many problems can be avoided - not all and I'll repeat Lipo has been reported to spontaneously go into combustion so be careful. by proper design of the pack and not over stressing the cells.