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LiPo batteries and wiring

Lithium Polymer batteries are the revolution that makes portable e-vehicles possible.

In general, P = I V. So the same power can be achieved with high voltage or high current or medium both. Current incurs heat. Voltage incurs risk of electric shock.

Living human tissue can be protected from damage by the insulating characteristics of dry skin up to around 50 volts. U should ideally stay at or below 40V. That’s about 10S. With a 100A max ESC, I should be good.

Notation

Some batteries are designated as 3S, 10S, …, kS. The k here is the number of cells connected in series. Each cell is by convention 3.7V when fully charged, so 3S = 3.7 * 3 = 11.1V, and a 12S is equivalent to 44V.

Some batteries are designated 4S2P, 12s2p, …, iSjP. This means that there are a matrix of cells: j sets of i cells in series wired in parallel.

Remember: wiring in parallel increases capacity (measured in Ah). Wiring in series increases voltage. This notation is used less now since LiPo cells are greatly improving and you get more life from a single cell.

Other battery types

Original Solowheel had LiFePO batteries.

Dan (from Firefly SUP drives) original kit used LiNCM batteries.

High current wiring

There’s a thing called American Wire Gauge (AWG), which determines wire diameter and many other parameters of the wire. A lot of the stuff you find online is specific to electrical wiring in houses.

In general, the thicker the wire, the more current it can handle, the less it will heat up, etc. Insulation also matters in this department.

As a rule of thumb, it seems like 10AWG is working well on my current setup which is running at 12S, and not really exceeding 100A.

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