Quote:
Originally Posted by gpsman1
Willard, I'm 100% sure about this, and I would like you to perhaps edit your post to delete the part that may confuse novice readers. Then I'll delete this to tidy up.
With 100% certainty, once the 12v battery closes the contacts on the HV battery, the HV battery, via DC/DC stepdown converter powers everything. I'm 100% sure about this, it has been tested and proven correct time and time again.
The proof is in the pudding, and electrons, like water, only flow downhill.
A 12v battery at rest under the hood has 12.5 to 13 volts.
AS SOON AS the HV battery contacts close, the DC/DC converter applies 14.4 volts to the "buss" as you put it.
Since this voltage potential is higher than the 12v battery potential, amperage may only flow into the battery, not out of it. And funny thing.... if you park with your headlamps on ( key in run ), the HV battery loses state of charge, and the 12v battery does not. The 12v battery can act like a capacitor to take out spikes in power demand, the inrush of current that happens like the instant you switch a load, like the fan on. Is the Prius substantially different in this regard?
Thanks.
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That would agree with both what I've seen and what I think it should do. I'm an electrical engineer so I have some experience. I've never worked with automotive systems but essentially all the mobile systems I have worked with use the battery simply as a capacitor when they are plugged in. They pull current from the other source. The handheld instrument I've designed for my company does the same. The converter powers the handheld.... the only time current would be pulled from the battery is if the converter voltage dropped below that of the battery. You use various mechanisms to prevent too much charge on the battery but I'm not sure thats much of a problem for a lead acid chemistry.
When the system is on you get about 14.4 V. With no load on the battery its probably higher than 12V, but less than 14.4V I'd have to check my scanguage but have no doubt of John's observation.