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Anelok: battery contacts (2/2)

Werner Almesberger werner at almesberger.net
Sun Mar 27 02:10:11 UTC 2016


Battery contacts come in many styles and sizes. In order to get a
quick overview of which ones might actually fit, I made some rough
outline drawings of the ones available from Digi-Key:

http://downloads.qi-hardware.com/people/werner/anelok/tmp/aaa-contacts.pdf

Each drawing shows two concentric circles, one for the nominal size
of the battery itself (it has a tolerance of +/- 0.5 mm) and one for
the "tube" the battery compartment forms.

The contacts are approximated with a rectangle and are shown roughly
where I'd expect them to be located relative to the battery. In some
cases, this is just a guess.

Contacts should be entirely within the "tube", except that they can
protrude on one side, where the face the PCB. Some contacts have
solder tabs that are not shown. They would be part of these allowed
protrusions.


So this leaves the following candidates that fit:

- Keystone 238 (+) and 204 (-/omni): snap-on, perfect fit.

- Keystone 1021-1 (-) and 1075-1 (+) would also fit, but the
  1075-1 seems be unsourceable.

- Keystone 5225 (+) and 5203 (-): slide-in. They appear to be
  slightly oversized, but the real parts have rounded corners and the
  diagonal is only about 10.6 mm, so they should actually fit in the
  11 mm tube.

- MPD BK-204 (-/omni): snap-on, perfect fit.

The MPD BK-204 has no positive counterpart, but could be used with
the Keystone 239. If trying to use mechanical battery polarity
reversal protection, we can't use an omnipolar contact for the plus
side.


Next, we have to look at how much length the contacts add on either
side of the battery.

- Keystone 238 (+):
  1.19 mm	solder eye
  1.26 mm	metal thickness, 3 x 100 mm
  1.7  mm	panel (1.52 - 1.78 mm)
  0.28 mm	nipple
  -------
  4.43 mm	total

- Keystone 204 (-):
  1.52 mm	solder eye + one layer of metal
  0.51 mm	metal thickness, 2 x 100 mil
  1.7  mm	panel
  2    mm	bend (guess)
  0.1  mm	bumps (guess)
  -------
  5.83 mm

- Keystone 5225 (+):
  0.51 mm	base plate (200 mil)
  0.2  mm	tolerance
  1.33 mm	wall	  1.44 mm total contact height
  -------		- 0.51 mm	base plate
  2.04 mm		+ 0.4  mm	nipple height / 2
			---------
			  1.33 mm

- Keystone 5203 (-):
  0.51 mm	base plate (200 mil)
  0.2  mm	tolerance
  1.33 mm	wall (see above)
  0.5  mm	slack
  -------
  2.54 mm

- Keystone 1021-1 (-):
   3.96 mm	uncompressed
  -1.4  mm	compression (wild guess)
  --------
   2.56 mm

The current Anelok case design has 2.05 mm (+) and 2.15 mm (-) of
space reserved for the contact, so that's pretty close to the
dimensions of the Keystone 5225 and 5203 pair.

Keystone 238 and 204 are far too big. The MPD BK-204 is similar
in size to the Keystone 204.

The Keystone 1021-1 (leaf spring) could be an alternative to the
Keystone 5203 (coil spring) and has only about half the cost.


In all these cases, the connection to the PCB would be with a wire,
either directly soldered to the PCB (making complete separation
difficult) or with connectors (a bit messy and possibly unreliable).

- Werner



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