A site visitor noted that Index for the Electrical System Diagrams had a Electrical Load Analysis listed, but the document was not available on-line. He asked if I could send him a copy, which I did. I hadn't posted it originally because it had too much missing info. It has been fleshed out a bit more now, so I will post it on-line. It is still not 100% complete however.
I used a spreadsheet to create the electrical load analysis. Each item is indicated as being on either the Battery Hot Bus (B), Main Bus (M) or Essential Bus (E). Also, the continuous and intermittent portions of each load are inserted in the corresponding columns. Note: continuous does not necessarily mean the item will be ON 100% of the time that I am flying, but it means that it may be used for long enough periods that the electrical system must be able to handle it continuously.
Read on to see the load analysis.
| Load | Bus | Continuous | Intermittent | Remarks |
| AI | E | 1.21 | from Kelly Gyro - see fax | |
| DG | E | 1.21 | from Kelly Gyro - see fax | |
| Turn Coord | B | 0.5 | from Bob Nuckolls | |
| Electronic Ignition | E | ??? | ??? | |
| Pitot Heat | M | ??? | ??? | |
| Engine Monitor | E | 0.15 | 0.25 | from Install Manual + e-mail from Grand Rapids |
| Microair 760 Com | M | 0.086 | 1.2 | from Install Manual |
| GNS-430 Com | E | 0.01 | 6 | |
| GNS-430 Flags | E | 0.1 | checked via ammeter. The Install Manual says the max value is 1a, but this would vary according to the CDI model) | |
| GNS-430 Main Pwr | E | 2.5 | checked via ammeter (no antennae connected - figure to be checked again once the whole system is operational) | |
| GI-106A CDI | E | 0.1 | from spec sheet - ammeter suggests less than this | |
| Ldg/Taxi lights | M | 9.2 | ||
| Strobes | M | 7 | from data plate on power supply | |
| Nav lights | M | 5.7 | from install manual, wing nav lights, 1.9a each | |
| Flood lights | M | ??? | ??? | |
| Map Light | E | ??? | ??? | |
| Pitch & Roll trim | E | ??? | ??? | |
| Trim + AFCS Disconnect Relay | E | 0.1 | ||
| Wing Leveler - TC Function | M | 0.8 | ||
| Wing Leveler - WL function | M | 1 | 1.5 | measured with ammeter |
| Battery Contactor | M | 0.8 | measured with ammeter - 0.66a at 11.8v thus assume 0.78a at 14v | |
| Flaps | M | ??? | ??? | |
| Boost Pump | M | 5 | ||
| Transponder | E | 1.1 | 1.6 | Where did these numbers come from? |
| Encoder | E | 0.18 | ||
| PMA-4000 Intercom | M | 0.1 | needs 13v for noise suppression - thus needs to be on Main bus | |
| Bus Totals | Continuous | Intermittent | Total | |
| Main | 24.7 | 7.7 | 32.4 | |
| Essential | 6.6 | 7.8 | 14.4 | |
| Battery Hot | 0.5 | 0.0 | 0.5 | |
| Grand Total | 31.8 | 15.5 | 47.3 |
Looking at the Electrical Load Analysis (which is still missing the amperages for a few loads), I see that the total of all continuous loads is 31.8 amps. My alternator is rated for 60 amps, so there is lots of margin there.
If the main alternator fails, I will be shed the Main Bus, leaving the Essential and Battery Hot Busses to be powered by the Standby Alternator. Those two busses have continuous loads of 6.6 and 0.5 amps, for a total of 7.1 amps. FAR 23 aircraft normally are required to have the continuous loads be no more than 80% of the alternator's capacity. The Standby Alternator is rated at 8 amps, but Bob Nuckolls has stated that B&C made design improvements that increased the capacity to 10 amps, but they did not change the documentation. So, I will treat it as a 10 amp alternator, which means I want to keep the continuous loads of the Essential and Battery Hot Busses to 8 amps total.
