keskiviikko 17. helmikuuta 2016 19.17.54 UTC+2 Steve Koerner kirjoitti:
On Wednesday, February 17, 2016 at 5:15:06 AM UTC-7, Jim White wrote:
At 09:16 17 February 2016, Tim Newport-Peace wrote:
At 07:49 17 February 2016, krasw wrote:
Adding 1 amp switch/breaker for 200mA instrument draws 10% more powe
from
battery because breakers have internal resistance. That may or may not
be
significant. If you have 10 hrs battery capacity, you will loose on
hour.

I doubt that.

10% of 200mA is 20mA, or 0,02A.
It would then take 50 Hours to reduce the charge by 1AH.

Is that a problem?



I replaced all the circuit breakers with fuses in my ship. I reason that
circuit breakers cause a voltage drop and use unnecessary power.
I did not see any benefit in being able to reset a breaker in flight as I
wouldn't do it. If a breaker trips it is usually for good reason and
should, therefore, stay that way until you are safely on the ground.

I think the right way to look at this is to take a gander at the spec sheet of the referenced part. At the top of the sheet is a table showing the resistance that the breaker introduces for varying current ratings. It shows for example that a 5A breaker introduces 0.03 ohms. Next, consider the peak load of the device that you're powering. If it's a radio, for example, look at its transmit current. Let's say the peak current is 1 amp. Then the voltage drop across the breaker is: V = iR = (1)(.03) = 30 mV. That's insignificant. The actual effect on battery life is that it will more likely be extended by the introduction of the additional load; it's just that the drop out point for the connected instrument will be 30mV lower. For a lithium battery with a fairly sharp fall off, I think you'll normally end up net positive to battery life by the introduction of the small series load (as long as the connected instrument works down to the steep part of the battery discharge curve).

And, BTW, fuses have resistance too -- it's the same game with a fuse.

I was looking at 1 amp breaker specs, there the resistance is 0,61 ohms. Trip time for 10 times nominal trip current is 0,4-2,5 secs, which is quite slow. Of course for radio or xpdr you would probably use 5 amp switch with lower voltage drop.