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Smoking Heat Sensor
30 x NiCd cells would have a nominal pack voltage of 1.2V each x 30 = 36V (peak say 1.4V/cell so ~42V)
20 x 18650 Li-Ion cells in 10s2p would have a nominal pack voltage of 3.7V each x 10 = 37V so a good match (peak say 4.2V/cell so ~42V).

The STW40N65M2 is rated for 650V spikes (& is not damaged by spikes), 60V or more would be no issue for it. It's also rated for approx double the amps. It should be fine.

The drill might have some shorted windings, hence the smoking?
Have you tried measuring the current when it's running? If the current seems excessive, that would confirm this?
Does the motor spin freely? Shorted windings will cause resistance to free spin beyond eg brush friction.
18650 likes this post
Running off solar, DIY & electronics fan :-)
Thank you to all that contributed to this thread, the STW40N65M2 arrived and works a treat, I am now putting back the two cells I removed so it will be back to 42v/36v
Thanks, it's interesting

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