Well, just an update on my Skeypad. I used the 18650 cells with the built in circuit protection. They were okay, but I never got the full charge that I liked. then I went back to the external charger, and that worked great, but I had to take the batteries in and out, in and out, in and out...and that got old too.
Well last week I cut the opening to my Skeyepapd a little larger and discovered that the recessed area where the square type batteries once were is actually large enough to hold an 18650 and still have a little room left over.
So I taped up a series-parallel group of 4 batteries. They fit very nicely
Finally I got on eBay and ordered a circuit protection board for 7.2V cells. It is really tiny. Actually they were only $4 each, delivered from China, so I ordered 3 of them. First time I wired them up, they Skeypad kept trying to turn on and then it turned off. It kept repeating that cycle. It was like the protection circuit cutoff was engaging and not letting power run through board.
Well, that was exactly what it was. The current of two 18650 cells was too much for the circuit. So then I separated out the cells into two separate circuits, using two of the boards. That solved everything. Now the cells charge up fine...when they get to 90% of their maximum charge, the circuit cuts in and stops the charging process.
With 2400mAh cells, that gives me just about 2100mAh of useful energy per pair of cells. Doubling that for the 4 cells, I get about 4200mAh of reserve power with this configuration. The original battery had 3600mAh of reserve. So with a full charge, my Skeyepad shows 100% charge for about 2 hours and then it starts dropping off at a normal rate. I can live with that, since it more than doubles my previous run time.
In the pictures below you can see the battery bay with just one 18650 cell laying in it. More than enough room for 4 of them. The next picture shows the protection circuit board. The last shows how I wired it to my Skeyepad.
(big enough.jpg) (protector.jpg) (chips.jpg) Attachments
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big enough.jpg (283KB - 0 downloads) protector.jpg (229KB - 0 downloads) chips.jpg (107KB - 1 downloads)