Subject:
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New Battery Hack + Charger
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Mon, 15 Apr 1996 18:35:15 GMT
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Original-From:
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Larry Randall <lrand@cts.SAYNOTOSPAMcom>
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Viewed:
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2103 times
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This is in reference to the Motor Voltage Hack on the HandyBoard.
In considering the prospect of including the new battery pack in the
charge circuit, we should consider the following.
1) The machanics of charging a NiCad is to force a voltage that is higher
than normal into the battery. Usually about 30 volts from a wall brick.
2) Because of #1 a regulator would not work because it's job is to
maintain a set voltage, dispite the input.
3) A series of 1n4002/3/4 diodes seems the best choice, though, a bit
impracticle.
As an example: if you use 6 nicad's in series for a voltage of 7.2 volts,
and the HB's battery output is 10 volts, you would need 5 diodes in
series for an output of 7.0 volts. These diodes would be in series with
the cut on the HB. Anode to the left (HB's batter pack '+' terminal) and
cathode to the right (right hand side of the cut / new battery packs '+'
terminal). With this arrangement there would be no interaction between
the two battery packs.
The slightly negative aspect of this method is as follows:
3a) If the new battery voltage drops below 7.0 volts there will be
current flow from the HB battery to the motor circuit. This won't hurt
anything except to drain the HB battery during motor operation.
3b) It will take considerably longer to charge the batterys and the
supplied wall brick may overheat if both battery packs are very low. The
charge time will depend on the size (AA / C ect) of the new pack. To
determine this put a current monitor into the charge line and when the
charge current drops to approx 50 milliamps, the packs are charged.
The main thing to remember with Nicad batteries is that HEAT KILLS.
Normally they get 'warm' to the touch when charging. NOT HOT. Any
stress to the Nicad's will be noticed with in the first few seconds of
connection. Put your hand on the batteries, if they began to get warm
right away, DISCONNECT right away.
It is my opinion that the very best bet is a second charger jack, and a
second wall brick.
Good Luck
Larry
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