rotax 912 ul

Speculation:

The capacity of your charging system will reflect the demand ie if you have sufficient energy (electricity) hungry systems, that combined (all switched on) need 45 amps, then of course you will have to go this way.

I assume, a larger capacity generating system, will add weight & complexity. Both usually consider undesirable, in the sort of aircraft usually powered by a Rotax 912UL.

Pilot/owners are forever looking for ways to enhance their aircraft ie making flight more pleasurable for themselves. (they rarely improve the flight characteristics efficiency of the aircraft). We are offered ever more sophisticated/capable gizmos, mostly requiring electrical energy. At some point the fitting of all these devices may exceed the power supplied by the basic Rotax charging system - a larger charging system will be needed.

Ultimately this is a decision for you alone

hi James

Sean is correct.  Remember your existing system is a max of 250 watts, (18 amps) so a calculation of what is needed in normal flight would be a good idea.  if you are using LED strobes, normal radios and the basic day VFR things then it should be fine.  If for example you have a type 914 with dual electric pumps and the related TCU and servo motor, plus the lamps for the indicators for the TCU, load for that alone is about 7 to 8 amps.  Standard practice, according to the FAA are found here in

AC 43 13-1b: https://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.information/documentID/99861 common practices, states one should never load the electrical more than 80% of its total capacity.  So by that calculation 18 X .8 = 14.5 amps usable in normal flight.  It is a good practice to add up your consumable energy to see if you really need to add more.

Just my 25 cents worth.  (accounting for inflation) 

Cheers