Reposted to add info and a photos.
In reply to:
?? can someone provide me with some suggestions and recommandations on the Â´Â´additional SU power supply unit?? ( brand ect)
The “hard starting” problem is definitely not for all airplanes. I had trouble with mine only until I learned how to do it; I haven’t had a single hard start in the last 20 months or so. I learned a very specific technique that seems to work very well every time.
Perhaps the biggest factor, though, is that I try to avoid truly cold starts, by preheating the engine, which I do by switching on the Reiff oil preheating system that I had installed. I leave it on for seven or eight hours before I start. There have been a few occasions, though, when I’ve had to start the engine at around 0C with no preheating, and it started just as easily as normal with my “foolproof” starting method.
Of course, it’s entirely possible that I’m just lucky, and some engines may indeed be tough to start. For a real “Start-Up” supply, you want something that can deliver and sustain starting (cranking) current. That’s different than a Ground Power Unit that simply supplements the on-board battery power for e.g. charging it or allowing you to run avionics etc. without draining the battery. The difference is that cranking current is very high - often 100s of amps for a few seconds, and easily sixty or seventy amps while cranking, while normal loads for avionics etc. are typically no more than about 10.
So… for a real SU… use a 24 v battery (or better and cheaper - two 12 v batteries in series)… and a separate charger to keep them topped off. If you’re lucky enough to own a 24 v “tug” like the Aero-Tow, you can use its batteries.
For a GPU… any good 24 volt charger like e.g. the Schauer unit shown below will suffice - I’d recommend at least 10 amp capacity.
I use a combination – two 12 volt batteries AND a 12 Amp Schauer charger, and I keep them on a cart designed for moving boxes of paper. (Ignore the large white box on the left - that’s not part of it).
Whatever you use, you’ll need cable and the right connector to fit the airplane. If you plan to be able to start the engine using this as an SU, you need thick cable (heavy gauge).
The GPU alone is smaller and lighter, but it won’t crank the engine! Of course, you could buy an “industrial sized” GPU like the one pictured below, too. Lots of choices.