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Anyone else got more information on how the diode thing works?


As you said, just a bunch of diodes in series... Each drops about 0.7V depending on exact current draw. Also to consider is the varying voltage in the car, about 12.6V with engine off and no [big, like amps] consumers on and up to 14.4V with the engine running, possibly even higher if the regulator isn't performing as it should.

That it works for so many gadgets is the fact that the gadget normally runs off batteries which lose voltage (especially normal non-rechargeables) as they are used, and the gadget must be designed to cope with that...

But a 7805 regulator and 2 caps will provide a vastly more stable voltage.

The Karma power supply says it can give 2A, which will cause a fair bit of heat (around )14-5)*2=18W) for any linear way of dropping the voltage(if it really draws that much), so a bit of heatsink is called form or at least don't bunch the diodes all up tight together.
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/Michael