Should we be charging at a higher voltage?

[ScottSchmidt]

Is there any adjustment to the output voltage? If you read this from Odyssey they recommend charging the batteries with closer to 14.7 volts to maximize their use. I heard the same thing from a gentleman at Oshkosh this year when we were talking about charging our -10 batteries since I have the same batteries in my -10 that is in the -12.
Does anyone have any experience with this?

My voltage says 13.8 volts in flight.

 

[Mich48041]

I interpret the charging instructions to apply to discharged batteries. Since the RV-12 battery seldom gets discharged, I think that the trickle charge rates apply.
Odyssey Publication No: US-ODY-AM-001 - April 2006 page 14 says: The trickle charge voltage should be 13.5V to 13.8V.
Figure 6 of Publication No: US-ODY-TM-001 - April 2011 shows a Continuous float charge of 13.6V.
Charging at a higher voltage than needed can do more harm than good. In this case, more is not necessarily better. A battery maintainer like this http://www.walmart.com/ip/Schumacher-SpeedCharge-Battery-Maintainer-and-Charger/13005742
will keep the battery charged when not flying.
Unless RV-12 owners start reporting problems keeping the battery charged, I will assume that Rotax designed the voltage regulator to maintain optimum voltage.
Joe Gores

 

[Wayne Gillispie]

My -10 runs 14.2-14.3 V.

 

[Alschief]

Battery Charge Rate

Our UL Power Engine charging system charges at 14.6 to 14.7 volts

 

[Mich48041]

The Rotax Voltage Regulator is a sealed unit. There is no adjustment. I have not tried this, but think it will work: put a diode in series with the small yellow wire with the diode banded end towards terminal "C". Depending on the type of diode used, the regulator output should be raised about a half of a volt. Before making any changes, measure the battery voltage to see if any changes are needed.
Go flying for an hour or longer. Then next day and before turning on the master switch, measure battery voltage. If it is 12.8 or higher, then the charging circuit is working fine. If the battery voltage is less than 12.8, then changes are warranted.
Below is a quote from the Odyssey battery manual.
Joe Gores

The only tool needed
is a good quality digital voltmeter to measure its open
circuit voltage (OCV)1. The graph shows that a healthy,
fully charged ODYSSEY battery will have an OCV of
12.84V or higher at 25?C (77?F)
The OCV of a battery is the voltage measured between its positive and negative terminals without the battery connected to
an external circuit (load). It is very important to take OCV reading only when the battery has been off charge for at least 6-8
hours, preferably overnight.

 

[dmaib]

My -10 runs 14.2-14.3 V.

Same here. 14.2 - 14.3 volts

 

[Mich48041]

I charged up my PC680, and then disconnected the battery charger on Tuesday. On Wednesday I measured the battery voltage with no load. My cheap meter read 3.01 volts and my Fluke read 13.09 volts. Then I went flying, did some touch & goes and gave a couple of rides. A total of 1.75 hours accumulated on the Hobbs and the engine was started a total of 6 times during the day. The starter uses very little power because the engine starts with only one revolution of the prop. The longest flight was about 30 minutes. At cruise, the Dynon D-180 indicated the normal 13.6 volts (which is 0.2 less than what my handheld voltmeter reads.)
The next day, Thursday, I measured the no-load PC680 voltage: my cheap meter read 12.98 and the Fluke read 13.06 volts. The Odyssey Owner's Manual http://www.odysseybattery.com/documents/US-ODY-OM-010_0412.pdf
says that the battery is 100 percent fully charged when the open circuit voltage is 12.84 or higher. Since my battery voltage is above 12.84, I have come to the conclusion that the Rotax voltage regulator setting of 13.6 - 13.8 is adequate for normal operations. If the battery is ever discharged for some reason, I intend to fully charge it before flying.
Joe Gores

Bob Nuckolls, who wrote the book on aircraft wiring, commented:

Yes. A SVLA battery will always charge to 100% of capacity
with a 13.6 to 13.8 volt bus. The reason bus voltages are
set higher is to shorten a cycle time for recharge after
a deep discharge.

But if you always take off with a very lightly taxed
battery then the lower set point is fine.

Bob . . .