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Bridging the power gap

Ordinarily, when a battery is removed from the computer to insert a new one, there is a brief power gap (a time gap between when the first battery is removed and the second is inserted). One or more large capacitors may be used to keep power to the circuit during this time period. However, I found a better alternative, which solved various problems:

  1. Allows new battery to be inserted before old battery removed, so that the power gap is bridged.
  2. Allows multiple batteries to be bridged together for increased power capacity.
  3. Protects against possible damage if battery polarity is incorrect.
  4. Allows mixed brands and capacities of batteries to be bridged together without damage resulting from one ``charging'' the other.
This alternative is implemented through the use of a unit comprised of diodes in series with each set of battery terminals, as depicted in Fig 1.

Figure 1: Combining the output of multiple batteries of possibly different types. (a) A large number of batteries may be combined, and in this way, there is also protection from accidental polarity reversal. (b) Where only two batteries are needed, a commercial bridge rectifier may be used. In this case, only 2 of the 4 internal diodes are used.

The diodes dissipate some heat, and must also carry the full current of the maximum anticipated load. Thus it was found that a bridge rectifier, by virtue of its larger surface area, etc., could dissipate the heat, and also be easily sewn into the clothing. The bridge rectifiers used by the author were salvaged from equipment in disposal sites (dumpsters). If a new purchase is being made, the following, diode pairs (rather than bridges which contain 4 diodes) are preferred. The author prefers 32CTQ030-ND which has enough reverse voltage in case 2 batteries in series are both inserted backwards, and enough forward current capacity for electronic flash (e.g. 12 volt Lumedyne which is fused at 30 amps). The following is a list of diode pairs that are satisfactory:

30a,  30vr,  .4vf,   32CTQ030-ND,  $35.04  for ten units
40a,  45vr,  .43vf,  40CPQ045-ND,  $103.76 for ten units
singles (remember: twice as expensive as listed since you need twice as many):
9a,   15vr,  .25vf,  95SQ015-ND,   $42.14  for ten units
19a,  15vr,  .32vf,  19TQ015-ND,   $37.13  for ten units

Steve Mann
Wed Dec 24 05:46:06 EST 1997