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Worth Upgrading Alternator?

CharlieWaffles

CharlieWaffles

Well Known Member
I have heard that a good planning base line is that your amperage load shouldn't exceed 80% of the Alternator output. According to the Vertical Power planning tool my load is at 52.6 Amps and the stock alternator on my engine is 60A. The 80% puts the max at 48A.

However, my load includes several ACCESSORIES that will not necessarily be used regularly or for extended period of time. For instance, I have two accessory power plugs (cigarette power plugs) to be able to charge a phone, ipod, etc... I have those down for 2 Amps each. So right there I'm at 48A if they arent used. While other things are short period - landing lights, taxi lights, etc... But they are not truly intermittant (flap motor, trim servos, etc...)

So, is it worth selling the stock alternator and buying a 70A alternator to cover ALL these items and assume they are in use at all times?
 
CharlieWaffles said:
So, is it worth selling the stock alternator and buying a 70A alternator to cover ALL these items and assume they are in use at all times?
Click to expand...

Mark,

Very doubtful if ever you would run out of electrons. Plus, you have a battery, right? Fly it and you will soon know. Stuff like this got me off track a lot, maybe that's why my RV build took six years.. :=)

.
 
Thanks Jerry. The benefit of traveling for work is it makes me think ahead in my build. If I know I am going to need more amps now, I can sell the unit as new. If I wait and fly it and find I am too low, then I have to sell as used.
 
With out seeing your entire list, it's hard to give a specific recommendation. I'm in a very similiar situation, as I suspect many RV-10 drivers are too. I decided to stay with the 60a for awhile.

This decision was reached by talking with other flying RV-10 builders to understand their average flying current draw as oppose to their predicted current draw per their plans. I think some of the ratings may be conservative and will yield more headroom.
 
I don't remember what my calculated load was, but my all electric panel with most of the bells & whistles draws 28-30A with everything running, including heated pitot and tablet pc. A little higher when actuating flaps and/or landing lights.

Jim Berry
RV-10
 
I was worried too

I thought I had a lot of amps being used and was worried about the alternator but after 200 hours I never see more than 32 amps and I have two cig. adapter chargers, heated seats, pitot, (4) HID lights, full IFR panel and so fourth. Normal cruise I see about 18, If I turn a bunch of stuff on I will see around 32. I wouldn't worry about a 60 amp like mine.
 
"Mark"

The final test when you're doing your phase 1 flying is to turn everything on and watch the voltage. If it stays steady over time, then your alternator can provide the necessary current. If it starts to drop then it can't provide all the power and you need to upgrade (or just don't turn everything on).

Each alternator vendor rates the alternators a bit differently, and some will certainly provide the full rated power. So I agree that waiting until you're flying and testing before making a trade-out decision is the way to go. :)
 
Thanks Marc, it was your presentation at OSH last year I even learned about the 80% guideline. If I have learned anything during the course of my build is if it's anything electrical, your opinion is the one I trust.
 
60 amp alternator, 70 amp, or more?

OK, I'm in the same boat. Having planned out my mostly electric aircraft, I'm looking at about 69 total CONTINUOUS amps if everything's turned on:

SYSTEM -- Continuous Draw amps
Cockpit
Left Skyview EFIS -- 2.5
Right Skyview EFIS-- 2.5
PAR100EX Audio Panel-- 1
PAR100EX Remote VHF--1
Skyview Transponder Remote--1.6
LED light strip--1
eyeball lights-- 2.5
avionics internal lighting--1
cabin map lights (pilot)--1
cabin map lights (copilot)--1
seat heater (pilot)--5
seat heater (copilot)--5
Fuel boost pump--5
Alternator Field--2.5
Alternator Vsense--0.1
Left Wing
nav lights--0.4
nav strobe--2.25
landing light--10
stall warning-- 2
Right Wing
nav lights--0.4
nav strobe--2.25
taxi light --10
Fuselage
Top Anti-Collision Beacon (Red Baron Mini) --1.85
Bottom Anti-Collision Beacon (Red Baron) --3.7
Tail
position light--0.4
position strobe--2.25
-TOTAL CONTINUOUS AMPERAGE DRAW--68.20 amps


Several things mitigate this total amp draw. For example, the landing/taxi lights are set to wig-wag any time they're both turned on (VP-X). Naturally, the total draw depends on worst-case night winter flight. Clearly the 60 amp alternator isn't good enough.

My quandry: Whether to upgrade to the 70 amp Plane Power alternator, or go higher (Hartzell makes an 80 amp gear-drive unit). I hate to remove the seat heaters...that was one of Kelli's going-in requirements (she loves traveling on "bun warmers"). Or am I over-thinking this?
 
I have a zero time OH Hartzell ALX-8521-LS 70A Alternator I will swap for a 60A. Came on a new Lycoming engine. We didnt use it.
 
You guys are over engineering. I have all those things, includeing the seat heaters. during the daytime, I fly around with a load of ~15 amps, strobes, avionics and the 2 amps going to the battery. At night, the nav lights add 7 amps. If I turn EVERYRHING on, including Pitot heat and keying the transmitter, I am pulling 60 amps. The only time I will need EVERYTHING is on approach to land, at night, and in the soup. The battery is there to pick up the slack for that short amount of time. If that is not working, kill one landing light.
BTW, I have two amp meters: main bus and alternator (delta is going to the battery).
Keep it light.
 
60A is fine

I would stick with the 60A. PP said it was fine to pull full 60A load if needed. The only time I ever hit 60A is after running aux pc680 down for 30 min or more then start up with everything on except HID's(9A) and pitot heat(7A), flaps(4A), boost pump(4A). By the time I taxi out and do runup, I am down to 30A or so and still recharging batteries. Then power up HID's and boost pump. I continue charging aux bat until in cruise and leaned out, then disconnect until taxiing back to hangar. During cruise with EVERYTHING on except flaps, boost pump, but not transmitting I will be pulling around 40A. My normal cruise is about 21A. If you have two agm batteries to charge after start, just watch what you turn on initially. My voltage is always between 14.3-14.4.
 
scrollF4 said:
OK, I'm in the same boat. Having planned out my mostly electric aircraft, I'm looking at about 69 total CONTINUOUS amps if everything's turned on:

SYSTEM -- Continuous Draw amps
Cockpit
Left Skyview EFIS -- 2.5
Right Skyview EFIS-- 2.5
PAR100EX Audio Panel-- 1
PAR100EX Remote VHF--1
Skyview Transponder Remote--1.6
LED light strip--1
eyeball lights-- 2.5
avionics internal lighting--1
cabin map lights (pilot)--1
cabin map lights (copilot)--1
seat heater (pilot)--5
seat heater (copilot)--5
Fuel boost pump--5
Alternator Field--2.5
Alternator Vsense--0.1
Left Wing
nav lights--0.4
nav strobe--2.25
landing light--10
stall warning-- 2
Right Wing
nav lights--0.4
nav strobe--2.25
taxi light --10
Fuselage
Top Anti-Collision Beacon (Red Baron Mini) --1.85
Bottom Anti-Collision Beacon (Red Baron) --3.7
Tail
position light--0.4
position strobe--2.25
-TOTAL CONTINUOUS AMPERAGE DRAW--68.20 amps


Several things mitigate this total amp draw. For example, the landing/taxi lights are set to wig-wag any time they're both turned on (VP-X). Naturally, the total draw depends on worst-case night winter flight. Clearly the 60 amp alternator isn't good enough.

My quandry: Whether to upgrade to the 70 amp Plane Power alternator, or go higher (Hartzell makes an 80 amp gear-drive unit). I hate to remove the seat heaters...that was one of Kelli's going-in requirements (she loves traveling on "bun warmers"). Or am I over-thinking this?
Click to expand...

I had a conversation about this recently with Bill Bainbridge of B&C. His rule of thumb is 80% of continuous load, where continuous means only those things that you'll have turned all the time. For example, landing and taxi lights are not normally considered part of the continuous load, unless you're planning to fly with them on all the time (there's 20 amps right there).

It also appears that you may be rounding-up on some of the above items? LED light strip, eyeball lights, map lights, etc. should draw very little current, certainly less than the nav lights. On the other hand you do appear to have an unusually large list of electrical items (first time I've seen anyone install strobes AND two anti-collision beacons).
 
Playing it safe...going with 70 amp alternator

Gents,
I sure do appreciate the comments. Some said 60's fine, others said go toward 70. I'll go with the 70 amp alternator.

Alan, I've also been briefed on the 80% rule, and I originally intended to follow it. My mistake: I didn't do my math up front (lesson for the new builders?). And you're right: I added my amps based on worst case and rounded some values up.

JetD, thanks for the offer. I plan to see if the Mothership offers a 70 amp solution, and exchange my new-in-box 60 amp alternator. If not, I'll return it for full refund and buy the new-in-box solution from Spruce.

Wayne and Alton, thanks for the "you're doing fine" words. Being a flight safety professional, I'm going to do like Justin Wilson and add a belt to the suspenders. :D
 
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