Originally Posted by Raiz
I really like the general concept with a high integrity essential bus that can be fed from the main bus, the battery and its own alternator. But, at a detailed level...
1. Have you considered placing the ANL 35 fuse between the battery contactor and the essential bus contactor. If you did that, you could use a smaller wire than 6 AWG for the feed to the ess bus and you could replace the ess bus contactor with a 40 amp relay - both worthwhile weight savings and also a useful reduction in the current consumption.
2. The ess bus backup feed has a 50 amp breaker on it, so the diode would need be capable of taking whatever the breaker lets through, so 50 amps continuously and probably rather more. If we assume a forward voltage of 0.5 volts, 50 amps will generate 25 watts of heat, which is a big heat sink (around 5" x 5" x 1" at a guess). Are you sure you need all those amps?
thank you for your comments!
1. Assume the ALT-2 develops a hard fault
If I placed the ANL 35 fuse between battery and the ess contactor -the 50Amp CB protecting the diode gets popped and the blown ANL35 would isolate the entire ESS bus. -the ESS bus is lost completely. -or maybe I overlooked something?
2. yes the heat sink is big, I expect (load analysis) the ESS BUS will take max 30amps at peak, 16 at normal. The 50 amps sized CB is there to avoid nuisance trips at spikes. Should the ESS BUS develop a hard fault, the CB would help with isolating the MAIN BUS from the ESS BUS.
The contactors (3x GX11-SA) I use need very little Amps to hold closed and they are all the same. I agree: there is added weight but they can be interchanged 'in the field' if needed. Thus, I could replace the main or ess contactors with the ext power contactor if needed (serves as spare part on board).