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1. 08:54 PM - Battery capacity tester- Why isn't there a flyback diode? (Mark Todd)
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Subject: | Battery capacity tester- Why isn't there a flyback |
diode?
I finally got around to building Bob's battery capacity tester and, as a
long-time lurker on the Aeroelectric list, I'm primed to slap a
'flyback' diode on every switched inductive load I find. But, the
schematic for the battery capacity tester (
http://www.aeroelectric.com/articles/battest.pdf ) doesn't appear to
have one. My understanding of semiconductors is pretty weak but the
datasheet for the NPN transistor I happen to be using (2N5961) says the
max collector-base voltage allowed is 60V. Although the inductive load
in this case doesn't appear to be huge (my relay coil draws about 36mA
at 12.4 V), it seems to me like I might be able to do some damage to my
transistor. Is there something about the behavior of the Zener or the
transistor that moderates the flyback voltage effect?
I don't see any harm in adding a diode, but I'm just trying to learn.
Do I need to a diode across my coil before I actually use this thing?
Mark
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