Garmin GTR 225 & 695 current draw

[Camillo]

Hallo.
I am deciding which alternator will suite my new aircraft.
Can't find on the web power consumption for two devices:
- Garmin new GTR 225A & 225B VHF (most interested in 10W transmitter unit current draw);
- Garmin 695.

Also, I would like to install a B&C SD-20 but can't easily determine which will be the current produced at a given engine RPM and the raccomended maximum continuous current which it can support. I found a table on bandc site at which alternator RPM will produce current, but it states 29 amperes @ 3.000 alternator RPM. On the brief description of their web it is said that it produces 20 amperes @ 3.500 alternator RPM. On the Aircraft Spruce site it is said 20 amperes @ 2.500 alternator RPM. It is a mess! Since engine RPM/alternator RPM is 1 to 1.3, at 2.350 engine RPM only 3000 alternator RPM may be produced. So if the correct output is 20 amperes @ 3.500 alternator RPM it may not be enough at 3.000.

Thanks.
Camillo

[Mich48041]

For sizing the alternator, do not consider the com radio current draw while transmitting. If the alternator is unable to supply enough current during transmit, current will be drawn from the battery. That is not a problem.
The nominal rating of the SD-20 is 20 amps. Its output is dependent on RPM. The faster it turns, the more current it is capable of producing. However, the limiting factor is temperature. The more current the alternator produces, the hotter it gets. Heat can damage diodes and windings. If the alternator is operated at maximum output, it should be provided extra cooling air. If the main alternator fails, unnecessary loads should be shut off so that a smaller backup alternator can handle the load without overheating.
Drawing less than 20 amps from the SD-20 should not overheat it. The temperature of the SD-20 could be monitored to ensure that it does not get too hot when operated at maximum output.
Joe Gores