Keep in mind automotive power busses can and do have steady state voltages over 15V and even 16V when you include allowable ripple. Power busses are a terrible terrible place.
Assuming the K3 designers' had in mind a car's electrical system, the choice of the BZW50-15 (in the QRP version) puts the effective clamping voltage above 16.6 volts and even then it is a gradual rise in clamping action vs. voltage. Then if you take away the 1/2 volt or so drop from the reverse protection, the net bus voltage inside can be more than 16V steady state and even higher for brief surges. Yuck. Clearly the designers' know about real-life DC power busses and designed the rest of the radio to take the abuse with some margin and rely on that clamp diode to blow the fuse should things get hopelessly ridiculous on the power source. So the good news is the K3 should be able to take the smack in the face from what I assume is a PWM style battery charger when in trickle mode. However, I would not make a habit of it and heed others' advice about staying within the 15V limit with a good DC power supply or charge with the radio disconnected. It should have less electrical noise as a side benefit. John > Dick, > > Yes, 16 volts is too high. There is a 15 volt zener diode right at the > DC input of the K3 which should limit the voltage to the K3 at 15 volts > (or until that zener diode is damaged). > > The charger may be dropping into the bulk charge output rather than > staying in the trickle charge state. > You may be better off with a simple trickle charger than a 2 or 3 state > battery charger. > > 73, > Don W3FPR > > On 5/26/2011 1:58 PM, r...@aol.com wrote: >> Hi Guys, >> >> I'm operating from a portable location and using a 12-volt automobile >> battery with my K3. To keep the battery charged I'm using a Schumacher >> 15-Amp >> Charger/Maintainer that automatically switches to "Trickle Charge" when >> the >> battery is charged. My concern is that when the charger is connected >> the >> battery voltage is peaking at 16.0 volts. The K3 manual says "maximum >> voltage is 15 volts". >> >> Do I need to be concerned about powering the K3 with 16.0 volts? >> >> > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
