voltage regulator questions

Sean Griffin wrote:

I also have the OptiMate Lithium charger. The few times I have used it, it goes through its whole charging cycle, irrespective of initial battery charge condition. I have never timed it but it does take a long time😈

Sean,

Your observation was right on. After charging to a green light yesterday I connected the charger today and the charger took about 30 minutes to go to "green". I unplugged the charger and rebooted / and plugged in the battery and another 30 minutes for a green light, one more time I cycled it and again 30 minutes. Each time it started in blue 1/2 charge.

Looking back over the past 5 years of Dynon log files the Silent Hektic has been performing the same with different battery technologies AGM and now LiFePo4. Here is how it seems to be programmed. If after starting the engine the voltage on the system is 12.7 volts the SH will start charging at about the 30 second point, if the voltage is 12.6V or below it starts immediately. If the voltage is above 12.8V it starts at about the 11 minute mark, at any point in that 11 minute period it drops to 12.7V it starts charging. In a 1.5 hr flight it will charge to 13.7 volts, 20-30 minute flights typically only get to 13.3 volts. In the past when I had a AGM battery the voltage after start was usually 12.5 volts so I would never see negative amp draw since the charge was immediate. Now with the LiFeSo4 battery the voltage after start is 13.0 volts or more, the SH won’t start a charge and negative amps the showing on the Dynon.

I suppose a positive is with a good battery that holds a good voltage and doesn’t demand an immediate charge that the extra horsepower drain on the engine required for a charge is available for take off power.

The charging system load on the engine is insignificant. At 12 amps and 12.7 volts you’re drawing 152 watts or 1/5 HP. It sounds like your regulator is designed around a specific battery. Depleting the battery for a cold start and the first 10 minutes of the flight indicates the battery and regulator are a poor match. 

The legacy RV12 was spec’ed with the Odyssey PC680. Per the battery information manual it needs a changing system voltage between 14.2-14.5 volts. Apparently that regulator isn’t a good match for an AGM battery either 

Is it possible the alternator is not putting out the correct voltage?

Great question. If the stator were to have a an internal partial short, yes you would have reduced capacity.  Rotax doesn’t give us test data for the stator.  The only data provided is for the charging system as a whole, as designed. See the Rotax IM and HMM for rated output over the engines RPM range.  Load testing the system with the current SH regulator is problematic. The regulators stepped voltage profiles over a long time period combined with operating at higher engine RPM may make it impractical for ground testing.