Use of 18650 Batteries with ThunderBorg

Submitted by panayiotis on Mon, 09/19/2022 - 11:33

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Hi all,

A bit new to all of this and certainly to the electronics bit. I was building a robot with the thunderborg controller. If I am not mistaken the controller should be able to deal with up to 35v of power. I had decided to use 4 18650 batteries connected in parallel to power the controller and the Pi. However, when I did that both the thunderborg and the Pi got fried. I know this is part of the learning curve, but I am not sure where I went wrong. Can you pls advise?

Thank you

piborg's picture

piborg

Tue, 09/20/2022 - 09:44

It seems like there might be some confusion about wiring and battery voltages.

A single 18650 cell has a usable voltage range from 4.2V (fully charged) to 3.2V (basically flat).

If wired in parallel, all +s connected to each other and all -s connected to each other, the voltage would have the same range as a single 18650 cell, 3.2-4.2V. This is not enough to power the ThunderBorg as it needs a minimum of 7V to work.

If wired in serial, each + connected to the - of the next cell, the voltages would be 4x a 18650 cell, 12.8-16.8V. This voltage range is good for a ThunderBorg :)

Can you confirm how the 18650 cells were wired to the ThunderBorg?

panayiotis

Tue, 09/20/2022 - 10:09

Hello and thanks for your reply.
Indeed, I confused the terminology. Meant to say in serial, not parallel. I had 16.3V as measured by my multimeter, hence I was a bit surprised by the result. Maybe I shorted sth, but neither the pi nor tge controllers work any more.

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piborg

Tue, 09/20/2022 - 14:30

The most likely explanation is if the connections on the ThunderBorg were wrong, for example getting the V+ and GND connections swapped would damage the ThunderBorg and possibly the Pi as well. Connecting the batteries into the motor outputs instead of the power inputs could also cause damage.

The +ve from the batteries should have been connected to V+ and the -ve from the batteries should have been connected to GND.

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