Benm
0
- Joined
- Aug 16, 2007
- Messages
- 7,896
- Points
- 113
A polarity indication by sticker or other marking is obviously a good idea.
As for the spring being the negative contact: That is indeed very often the case, for the whole flat negative / nipple positive thing on -commonly used- batteries.
But as always there are exceptions and problems with this: You do get those 18650 (and probably other) lithium batteries that have a flat top, probably intended to be used in battery packs where the contact is spot welded.
To have those replaceable an make reliable a contact, a spring on both sides is sometimes used, and in that case you could easily put it in the wrong way around AND make electrical contact.
Polarity marking and/or reverse polarity protection would be very good ideas in such designs. In that case the only motivation not do to it is financial: even putting on a sticker costs a few cents that come from a very small profit margin. Actual electrical protection using a mosfet would probably cost a dime or two, and a few mm3 of envelope space.
As for the spring being the negative contact: That is indeed very often the case, for the whole flat negative / nipple positive thing on -commonly used- batteries.
But as always there are exceptions and problems with this: You do get those 18650 (and probably other) lithium batteries that have a flat top, probably intended to be used in battery packs where the contact is spot welded.
To have those replaceable an make reliable a contact, a spring on both sides is sometimes used, and in that case you could easily put it in the wrong way around AND make electrical contact.
Polarity marking and/or reverse polarity protection would be very good ideas in such designs. In that case the only motivation not do to it is financial: even putting on a sticker costs a few cents that come from a very small profit margin. Actual electrical protection using a mosfet would probably cost a dime or two, and a few mm3 of envelope space.