First start of day hard to turn over

Bill,

   With a factory "soft start" can I assume that starting with both mags is still correct?

Brian, I’ve had a lot of starting issues and the battery was one of the culprits for me. This chart shows that 12.2 volts on a 12-volt system is only 50% charged. That blew me away when I learned it. 

Tyler Asked:

With a factory "soft start" can I assume that starting with both mags is still correct?

 . . .

Commonly only the "A" Mag has the soft start feature. So starting on the singe "A" Mag would be the norm.

When it senses power is applied to the starting solenoid, the Soft-start delays the spark from 26° BTDC to 4° BTDC  making it easier for the starter to get the slow-moving piston Over-The-Top without the potential of a Prop Kick-Back.

This happens while the starter is engaged and for a few seconds more, After the Start, the "B" Mag is energized manually.

Starting on BOTH would allow the "B" Mag to light the fire at the normal 26° point, negating the whole Soft-Start function.

- - -

If you were to keep the battery on a Maintainer between flights, voltages in the lower 13's would be the norm before starting.

Hmm, I understand the concept, but I never heard that it applied to only one module.  I always start (912ULS) with both mags and the soft-start feature seems to work just fine every time.  The Rotax Operator's Manual (section 3.4) also says to use both.

1 Fuel valve open

2 Starting carb activated IF engine in operating temperature then start the engine without choke.

3 Throttle lever set on idle position

4 Master switch ON

5 Ignition both circuits switched on

6 Starter button actuate

Re determining state of charge solely from voltage:

"Measuring state-of-charge by voltage can be inaccurate because cell materials and temperature affect the voltage. The most blatant error of the voltage-based SoC occurs when disturbing a battery with a charge or discharge. The resulting agitation distorts the voltage and it no longer represents a correct SoC reference. To get accurate readings, the battery needs to rest in the open circuit state for at least four hours; battery manufacturers recommend 24 hours for lead acid. This makes the voltage-based SoC method impractical for a battery in active duty."