TP-8000 Li-Poly Battery Pack Modifications

Last Updated: 04/04/2004

This page documents the change I made to my Thunder Power 3S4P (S=Serial, P=Parrellel)  TP-8000 Li-Poly battery pack. The modification was made so that each individual paralleled cell pack within the battery pack could be monitored or charged if needed. The reason for this is to keep the battery pack balanced. This is when each of the cells within the pack are charged to the same level. After usage the pack can become unbalanced if one or two of the cells discharge or charge at a different rate. By adding two wires to the pack you gain access to each cell pack within the battery pack. The image below shows the pack after removing the shrink wrap tubing.

Since I couldn't solder directly to the battery terminals I removed some insulation from the two wires within the pack. See photo below. 

I then soldered two 20 gage wires to the larger wires that connect the cells together inside the pack. 

The photos below shows the pack ready for the heat shrink wrap tubing and after tubing has been applied to the pack. The bottom pack is the TP8000. The top battery pack is a homemade 3S4P pack made using Kokam 1500 HD cells.

Below is a schematic of a 3S4P battery pack with the additional wires needed to monitor or charge each paralleled cell pack.

The weight of the battery after adding the extra wire and Deans Ultra Plug is 473 grams. The weight before the modification was 468 grams. The overall size of the battery is 1.95 inches (49.5 mm) wide, 1.15 inches (29 mm) deep and 7.65 inches (194 mm) long. With this pack I can hover and do slow forward flight with my ECO 8 #2 for 30+ minutes. As of 4/4/2004 I have 12 discharge/charge cycles on the pack. So far I have had no problems with the pack becoming unbalanced. On 4/2/04 I did a discharge test using my Great Planes Triton battery charger. This battery charger can discharge a 3 series cell pack between 1.6 to 1.8 amperes. The Triton charger was set to stop at 9 VDC. I was able to get 7709 mah (milliamp hours) out of the pack. The next charge replaced 7814 mah back into the pack.