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Post Info TOPIC: Best series/parellel set up for lipo pack


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Best series/parellel set up for lipo pack
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Hello racers,

Our battery charger had a moment and slightly overcharged our LiPo pack. I did not have quite enough spare cells to replace all the damaged ones, so the pack is down on capacity. It was originally rated at and tested at 945 Watt hours but shut down after 825 the first race and 801 Watt hours the second race.

Looking for a quick available replacement, I found these packs. They are each 6 cells in series and 108 Watt hours. If I wire 9 together , I will have 982 Watt hours and under 15 pounds: https://hobbyking.com/en_us/rhino-4900mah-6s-22-2v-25c-lipoly-pack.html

Cost is under $350, so about the same as 2 Optimas!

For the right voltage for the motor and controller, I want 18 cells in series.


So my set up will be 3P18S. The problem is the nicely sealed packs are 6S.

Does anyone know if there are any advantages or disadvantages to:

A. Running three seperate strings of 16S and only connecting them at total pack negative and total pack positive.

B. Connecting three of the purchased packs in parellel, so 6S connected 3P to make a bundle and then connecting each bundle in series.

C. Disassembling the packs, bundle each cell as 3P and then connected in series 18S. (which would require removing shrink material, disconnecting cells and regen sealing in shrink material).

The cells are rated for 25C but I will be discharging at max of 5C and an average of 1C. My goal is to get maximum energy capacity from the pack rather than maximum power.

 



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Cliff

www.ProEV.com



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ProEV wrote:

Hello racers,

Our battery charger had a moment and slightly overcharged our LiPo pack. I did not have quite enough spare cells to replace all the damaged ones, so the pack is down on capacity. It was originally rated at and tested at 945 Watt hours but shut down after 825 the first race and 801 Watt hours the second race.

Looking for a quick available replacement, I found these packs. They are each 6 cells in series and 108 Watt hours. If I wire 9 together , I will have 982 Watt hours and under 15 pounds: https://hobbyking.com/en_us/rhino-4900mah-6s-22-2v-25c-lipoly-pack.html

Cost is under $350, so about the same as 2 Optimas!

For the right voltage for the motor and controller, I want 18 cells in series.


So my set up will be 3P18S. The problem is the nicely sealed packs are 6S.

Does anyone know if there are any advantages or disadvantages to:

A. Running three seperate strings of 16S and only connecting them at total pack negative and total pack positive.

B. Connecting three of the purchased packs in parellel, so 6S connected 3P to make a bundle and then connecting each bundle in series.

C. Disassembling the packs, bundle each cell as 3P and then connected in series 18S. (which would require removing shrink material, disconnecting cells and regen sealing in shrink material).

The cells are rated for 25C but I will be discharging at max of 5C and an average of 1C. My goal is to get maximum energy capacity from the pack rather than maximum power.

 


 I realize you didn't get any response to your question (I had no intelligent input to offer), but what did you decide to do?



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Option B with some modifications suggested by endless-sphere forum. 

So connect the negative wires from 3 packs at one end and the positives wires at the other end.

Make three of these parallel bundles.

Connect them in series. Pos to neg, pos to neg. 

The additional trick is to take the balancing wires that connect to each cell and bundle them 3 into 1 in each bundle. That means each parallel cell is connected directly to the other two cells paralleled with them to give the benefits of Option C without disassembling the packs.

The additional advantage is that I can use 3 6S cell voltage readers rather than 9. I bought 3 of a $4 version with low voltage alarms that will warn me when any cell voltage goes low. These cheapo voltage readers are notorious for not being very accurate but I just need a warning.



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Cliff

www.ProEV.com



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Cool. Good luck with your new setup.

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