Page 40: of Marine Technology Magazine (November 2022)

LANDER LAB #5 BATTERIES o (Charge battery, then discharge with CBA V Pro and tested them to 18,000-psi. They held up ? ne.

to this value. Explained below.) Placing a pressure compensated LiPo battery outside the hull ? Shipping voltage (30% of full charge): 3.71V/cell means you only subtract the water weight from the buoyancy (6S x 3.71v/cell = 22.26vdc) budget, rather than the air weight when it’s inside the hull. o (Charge battery, then discharge with CBA V Pro Just a SWAG, but for the same amount of buoyancy, a craft to this value. Explained below.) may be able to carry an additional 25% power.

? Min voltage (Absolute): 2.9V/cell For more background details on LiPo’s, see Battery Uni- (6S x 2.9v/cell = 17.4vdc) versity ; “A Guide to Under- o (Managed by the BMS, explained below) standing LiPo Batteries”

com/lipoguide>; and “The care and feeding of LiPo packs”

Using a 10” polyamide sphere, I’ve made a positively buoy- . battery that ? oats. Follow your curiosity and you’ll ? nd others.

LiPo quality varies between consumer and commercial grade batteries. Commercial grade batteries are made by paying at- LIPO PROTECTION CIRCUITRY tention to quality at every step, including selecting cells that Here’s where I diverge from normal RC practice. match the characteristics of others in a stack. Consumer grade It is very important to balance charge a LiPo battery. This is batteries are made by paying attention to cost. The difference because some cells have slightly higher internal resistance than is like buying batteries from Duracell versus Harbor Freight. others, allowing some to overcharge, while others undercharge,

Two commercial brands I tend to use are Gens Ace Tattu and if not regulated. You’ll ? nd a plethora of “balance chargers”

Turnigy Graphene. One list of the top LiPo manufacturers can that work ? ne. BUT, it is also important to balance discharge be found at . same reasons, and plunging too low. A low voltage cut-out is

Because prismatic cells are vacuum sealed in a soft plastic not enough, as that measures the total voltage of the pack. One pouch, they are pressure tolerant. There are no compressible cell, hiding within the total voltage of the battery pack, can be materials on the interior so the rate of chemical reaction is un- depleted to the point of ruin, taking the whole battery with it. affected by pressure. The matching BMS protection circuitry When that battery is placed on a balance charger next time, it is likewise made of pressure tolerant components (See next will ? nd the one that’s bad, and cancel the charge. section). I have immersed both in bags ? lled with mineral oil The solution is a BMS: Battery Management System, a board

Figure 5

A LiPo protective circuit “Battery Management

System” (BMS), protects individual cells in a LiPo pack during charge and discharge.

A 5S LiPo battery is shown.

QSKJ Power Module Experts 40 November/December 2022

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