Bus Voltage

ArlingtonRV · #1 10-02-2015, 03:25 PM

This should be a simple answer, but I am having a great deal of difficulty in finding it.

I am trying to find out what "normal" bus voltage should be in a 12 volt system that is functioning properly. The reason that I ask is that I have a Dynon Skyview and with the engine running (alternator supplying power to the bus) it reads 14.4 volts and shows in the yellow range. It is easy enough to change the color coding of the "gauges" in the Skyview so that it isn't yellow, but before doing that I though I should find what "normal" is.

Do I need to worry about 14.4 volts? Is that good, bad, or indifferent? If it is not good, is there any way to adjust it?

Thanks

terrye · #2 10-02-2015, 05:08 PM

14.4 volts is a good number for an alternator supplied 12 volt system. That's what my C-150 has always read since I put a voltmeter in the panel. That's also what you get if you check an automobile system when the engine is running. The reason it's called a "12 volt" system is that's what the battery voltage is.

Mich48041 · #3 10-02-2015, 05:49 PM

Yes, 14.4 is OK. Many voltage regulators are set at 14.2
The ideal voltage depends on battery temperature. But I think that anything between 14 and 14.5 is OK.

f14av8r · #4 10-03-2015, 12:46 AM

My AGM battery, an Odyssey PC680, manual says it requires 14.1 to 14.7 volts for proper charging. Other sources I've read say the high end is better. So, I have my B&C regulator set for 14.7 volts and my Vertical Power/SkyView/PC680 system very happy.

larrynew · #5 10-03-2015, 05:19 AM

Quote:

Originally Posted by f14av8r

my Vertical Power/SkyView/PC680 system is very happy.

+1 at 14.4 volts.

f1rocket · #6 10-03-2015, 05:53 AM

Modify your Skyiew settings to bump the yellow lowew limit up a couple of tenths. It gets rid of the pesky warning when everything is really operating normally.

gasman · #7 10-03-2015, 03:41 PM

I set High side 14.5 yellow, 15 red. Low side 13.5 yellow and 12.8 red. The upper end is covered with crow bar. The lower end tells you that you have only a full battery left and the alternator is offline.

ArlingtonRV · #8 10-03-2015, 08:20 PM

Thanks for the replies.

A friend provided this information on general alternator theory.

http://ronkilber.tripod.com/alternat/alternat.htm

It contained the paragraph below which provided the magic numbers I was looking for.

"The regulated voltage (14.2) to the system bus is somewhat higher than the battery voltage (12 volts) so that alternator current flows to the battery to charge it. If the regulated output were, say, only 11 volts, battery current would flow to the bus instead, eventually discharging it. So to keep a full charge, the regulator must clamp at something greater than 12 volts, but not so high as to boil the battery or damage onboard electrical equipment. Thus, 14.2 volts (+/- .4 volts) is the industry standard for charging systems using 12-volt batteries."

He also provided the below information from the B&C web site which was most helpful.

http://www.bandc.biz/pdfs/quickfacts_lr3c.pdf

http://www.bandc.biz/pdfs/LR3C_Installation_Manual.pdf

From which came the following quote:

"The LR3C is pre-set at 14.4v (28.8v on the LR3C-28). If adjustment of alternator output voltage is needed, remove the 3/4" round plug from the side of the LR3C and use a small screwdriver to turn the small adjustment screw (clockwise to increase voltage, counterclockwise to decrease voltage; approximately 1/2 turn per .1 volt). Use a digital voltmeter at the battery for this measurement."

This was exactly the information I was looking for. Thanks to all who participated.