voltage dominance

daguuy · Post by **daguuy** » Sun Apr 23, 2006 1:04 pm

if i have a 8.4v battery and a 9v (yes, psone screen can run on 9v) car adapter both plugged in at the same time (with diodes of course), would the N64p draw power from the battery or the car adapter?

codeman · Post by **codeman** » Sun Apr 23, 2006 2:17 pm

If put a diode on the positive line of both the battery and 9v supply, it i will only draw current from the 9v, the battery won't do anything.

Post by **gannon** » Sun Apr 23, 2006 2:19 pm

The car adapter would pump the extra voltage into the battery as well making it heat up and explode

codeman · Post by **codeman** » Sun Apr 23, 2006 2:34 pm

gannon wrote:The car adapter would pump the extra voltage into the battery as well making it heat up and explode

that would be pretty awesome, but that's not what would happen. If there is a diode on the positive line of the battery and the car adapter, and the "opposite side" of both diodes are connected together at node 'X'...then only the car adapter will provide any current.

Say you used silicon diodes with a forward drop of 0.7v. Both the battery and the adapter will try to drive node 'X' to (8.4v-0.7v) and (9v-0.7v) respectively. Obviously, one node cannot be at two different potentials at the same time. The adapter will drive 'X' to be 8.3v, causing the battery diode to be reverse biased. If it's reverse biased it'll prevent any current from flowing into the battery, and current is what causes batteries to explode, not voltage.

This is basically a logical OR circuit using diodes.

Post by **gannon** » Sun Apr 23, 2006 2:41 pm

Oh yeah, I kinda skipped over this part, "(with diodes of course)"

codeman · Post by **codeman** » Sun Apr 23, 2006 2:51 pm

yeah..well maybe my explanation will help someone else crazy enough to read the whole thing