Alternator simulator circuit - Page 2 - Electronic Circuits Projects Diagrams Free

kchriste · 19th March 2009, 05:53 AM

If you had 400Hz 3Φ in your shop it would be easy.

tcmtech · 19th March 2009, 10:17 AM

I still say filter the alternator. Kill the noise at its source. why prune each leaf of a weed every time it grows a new one? Kill the root at its source. Still just a thought.

If the system is a 30 amp. the capacitor values could only need to be a few 1000 uf and possibly not need a filter choke.
Still just a thought.
------------------------------------------------------------------
True lazyness is the real motivator to do it right the first time!
Doing it wrong, then doing it over is just misguided ambition!

MikeMl · 19th March 2009, 05:25 PM

Quote:

Originally Posted by tcmtech

I still say filter the alternator. Kill the noise at its source...

If the system is a 30 amp. the capacitor values could only need to be a few 1000 uf and possibly not need a filter choke.
Still just a thought.

I have tried "filtering" an alternator with just a large 47,000uF "computer grade" electrolytic capacitor, and it does NOT work. The effective series resistance of a large electrolytic capacitor is more than 10mOhms at 120Hz. I suspect that the ESR is much higher at kHz frequencies. The impedance being bypassed (30A loads, the battery) is much less than 10mOhms, so most of the ripple current still flows along the airframe to the loads and battery.

It would require putting a series choke of more than 100uH (that will not saturate at the max alternator current of 60A) between the alternator and the loads and battery.

Electrically that might help, but practically, it would never fly. It raises all kinds of FAA certification issues due to modifying an existing design, and introduces several failure modes. Those large electrolytics hate elevated temperatures (engine compartment is over 130degF), and they hate vibration. Fusing the path to the electrolytic wont work because the resistance of the fuse is a few hundred mOhms, which kills its effectiveness as a bypass for the ripple currents.

tcmtech · 19th March 2009, 05:59 PM

Ah. computer caps do have rather poor high frequency response.
Good point on the FAA regs though.
Chase the ground loops it is!
sure its just alternator? No feed back from the duel ignition circuits?

crutschow · 19th March 2009, 06:01 PM

Quote:

Originally Posted by Sceadwian

I guess it would be down to which is harder. Removing the prop without disconnecting said pitch control hydraulics and loading the main output shaft to allow the engine to run, or disconnecting the drive belt to the alternator and putting in an electric motor to drive it. It's starting to sound like simply electrically disconnecting the alternator and putting in some kind of direct electric simulation would be smarter, if not easier. Honestly, I'd just come up with a practical way of working around the aircraft while running, even if you need a separate person for safety alone it sounds more practical than most methods so far, unless you plan on doing this repeatedly.

The intention of my suggestion (which apparently was not clear) was to use a separate external alternator and motor, not to drive the alternator in the aircraft.

It probably isn't necessary to disconnect the aircraft alternator when you connect up the external unit since the alternator is already looking at the battery voltage anyway.

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19th March 2009, 05:53 AM	#16
kchriste	If you had 400Hz 3Φ in your shop it would be easy. __________________ Inside every little problem, is a big problem trying to get out.

19th March 2009, 10:17 AM	#17
tcmtech	I still say filter the alternator. Kill the noise at its source. why prune each leaf of a weed every time it grows a new one? Kill the root at its source. Still just a thought. If the system is a 30 amp. the capacitor values could only need to be a few 1000 uf and possibly not need a filter choke. Still just a thought. ------------------------------------------------------------------ True lazyness is the real motivator to do it right the first time! Doing it wrong, then doing it over is just misguided ambition!

19th March 2009, 05:59 PM	#19
tcmtech	Ah. computer caps do have rather poor high frequency response. Good point on the FAA regs though. Chase the ground loops it is! sure its just alternator? No feed back from the duel ignition circuits?