Bayou Bert

Bayou Bert

Well Known Member
The RV9A project I bought in July was at, my guess, the 80% range.
Lots of stuff already installed.
Stein has the panel and equipment on the way so thinking shifted to
electrical. I went through everything electrical that is either installed now,
or will be. That's when the flags went up. I used the max rating for each
item. Some I just don't know, like the ElectroAir Ign, not installed yet except
timing unit for right mag. It shows two power needs, one fused for 2A and
the other for 10A...wow. I have tried to call them but with holidays, no go.
Here is how I show the load, tell me what I am missing or have wrong.
The plane has a B&C L-40 alternator. My brain says no way, but will the
L-60 clear the cowl? These are max numbers, what do they really pull in operation?

Amps
12 2 Seat heaters 6amps each
4 Nav Lights
7 Strobes
20 Landing Lights 2 100W at 10 each
7 AP and servos
5 Boost Pump
12 ElectroAir Ign 1 at 2, 1 at 10
8 Avionics
10 Dynon heated pitot
2 Trim servos, 2 at 1amp each
5 Flap Motor

82 Total

Please, all comments and info appreciated. Is this in line with other
RV's? Talked to Greg at B&C about swap for L-60, but want forum
input on this before proceeding.
 
It sounds like you are basing your loads on circuit breaker sizes. CB are sized to protect the wiring, not the device. The actual load of the device should not be even close to the CB size.

Also you are including landing lights, boost pump, and flaps. These are not normally considered within "continuous" load unless you plan to fly with them on all the time.
 
Last edited:
What I Used

I went through all spec sheets for each device.
If it stated, like heated pitot, max amps 10,
that's what I used.
 
Mel said:
It sounds like you are basing your loads on circuit breaker sizes. CB are sized to protect the wiring, not the device. The actual load of the device should not be even close to the CB size.

Also you are including landing lights, boost pump, and flaps. These are not normally considered within "continuous" load unless you plan to fly with them on all the time.
Click to expand...

Mel, I think one question might be ( I have had this too) what happens when the intermittent loads exceed the alternator rating. Does it blow the 5 amp field fuse? And we just continue to landing?

The next question would be how to mitigate the peak draws, when they might occur and how they could be managed.
 
BillL said:
Mel, I think one question might be ( I have had this too) what happens when the intermittent loads exceed the alternator rating. Does it blow the 5 amp field fuse? And we just continue to landing?

The next question would be how to mitigate the peak draws, when they might occur and how they could be managed.
Click to expand...

The load can exceed the alternator capacity. That's what the battery is for. You will simply not be charging the battery during this short time. It will not blow the field fuse.
 
I, pretty much, have all the loads listed, and a few more (including the heated seats. If I turn everything on, I am pulling 55 amps on the meter. With strobes on, during theday, I cruise around pulling ~15 amps. Like Mel said, the fuse rating is not an indication of load amps. If I have a load that pull 5 amps, I am not going to put a 5 amp fuse in the circuit, I would expect it to pop. The fuse is there to protect the wire and avoid a fire, not protect the load.
 
BB: Take it from another Louisiana guy, you don't have a problem. I have just about exactly the same potential loads you do; perfectly typical for these airplanes. My 60 amp Plane Power has never broken a sweat---all per design. Typical/actual in-flight loads are about a quarter of the numbers you listed and as Mel says, the 800 pound gorilla in the corner is your battery. It's the big load moderator/damper in the circuit, but it rarely even gets involved after engine start. The alternator can handle it all except in the rarest of cases, then the battery "automatically" jumps in to bat cleanup.

Geaux Tigers!


Lee...
 
It wouldn't surprise me that you will be pushing your alternator pretty hard if you are out flying with the heated pitot on, the seat warmers on, the strobes and nav lights on, plus the EI, avionics, and AP.

You'll probably want to think about load shedding in those circumstances. Based on your location, why not give up the heated seats?
 
I think your numbers are way high

200W of landing lights will probably pull 14A max (but will be off most of the time)
AP will pull 1 or 2 most of the time
Boost pump & flap motor & trim servos can be ignored - intermittent loads only
Ignition - 10A? are you sure?
8A for avionics is a lot of electro whizzes

I would guess at 40A max with seat heaters and pitot heat on. As others have said, the battery will soak up any remaining demand.

Pete
 
LEDS

Consider using LED lights for landing and/or strobes if you are concerned about your load. That alone will eliminate a lot of amperage.

Gordon

Super ES N144GP
 
That's a Fact

You are right Gil, ElectroAir called me this morning and told me to
count on .75amp draw at 2700. I forget the fellow's name that called,
but very nice and WOW, I lost 12amps with on phone call.
Now on to TruTrak to see about some operational numbers
from them.
 
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