Power Load Determination

[Marauder]

Hi All. I am in the middle of an avionics upgrade on my F model. I believe my airplane has a 60 amp alternator. I just started reading up on the power draw for my new avionics and wondered if anyone upgraded their alternators due to the expected power draw of new equipment.

Any advice?

[carusoam]

Modern tech often has a lower power requirement....

Electric motors, old landing lights, and pitot heaters probably use the most. Motors are usually not a continuous load.

Converting to digital, or LED usually uses less than anything with tubes or the word analog???

Does your POH indicate what you have for an alternator? It should be mentioned in the W&B section as well.

Just sayin'

-a-

[Steve Dawson]

I converted to a plane power for a couple of reasons. First because the original altenator produced noise on my new GTN 750 and it needed work to fix it ($), Secondly I wanted something dependable, proven and that wouldn't breakdown at an unknown airport were it would delay my trip and the cost for repair from an unknown mechanic would drain my credit card.

[Jerry 5TJ]

I installed a LED landing light on the "C" and now the highest remaining electrical load is the pitot heat. The 50A generator is loafing at about 20A total with everything switched on. As several people have suggested on this board load shedding is probably easier (and cheaper) on these old birds than a power source upgrade.

[1964-M20E]

Generally on the older models the ammeter is set up to measure the amount of power the alternator or generator is producing. Therefore when everything is on and the engine is running you can you can determine you maximum power requirements for you plane. As others have stated newer electronic radios and LED lights reduce the overall load on the system that is why when I replace my generator on my former plane I did not bother to replace the CB since I was already using much less than 50A with everything running.

[1964-M20E]

You could try these Whelen part numbers

P46FLC, 1800 lumens, 30W, 8 degree PAR46 spot light

P46SLC, 2000 lumens, 30W, 2 degree PAR46 spot light

PLED461L, , 30W, 10 degree PAR46 spot light

[Marauder]

Thanks everyone for the replies. What got me down this questioning path was, like you, I was under the impression that newer electronics should equate to lower current draw. I was a bit surprised to see that one of my KX170B radios had a similar power draw to one Aspen PFD. Granted what actually is drawn is a different topic but I think the higher watt output of the transmitters (like on a GTN650) and the associated cooling fans on the Garmins/Aspens, I am beginning to wonder if the draws are not a lot closer. Since I am adding more power drawing equipment than I am taking out, I am curious how much power draw I will be creating with the new equipment.

King KX-170B Receive Mode: 1.1 amp Transmit: 3.0 amp with a max draw of 5.1 amps with all the lamps on both the com and the nav

Aspen

Max Current 2.4 Amps @ 28 Vdc / 4.8 Amps @ 14 Vdc

I also agree that unloading power eaters is probably a better way of going about this. I have see the PAR46 lights in action. For 2.6 amps, it certainly outperforms the 10+ amp old lamps. I can also beginning replacing all of those little GE330 bulbs with LED equivalent. What other things have you replaced to lighten the load?

[Marauder]

Modern tech often has a lower power requirement....

Electric motors, old landing lights, and pitot heaters probably use the most. Motors are usually not a continuous load.

Converting to digital, or LED usually uses less than anything with tubes or the word analog???

Does your POH indicate what you have for an alternator? It should be mentioned in the W&B section as well.

Just sayin'

-a-

My plane has a 60 amp alternator. I did have it rebuilt probably 12 or so years ago. Since we are talking about alternators and their output, is there a better way of looking at the power draw than the factory installed ammeter? Mine has +60 to -60 amp window. Other than showing when I have a positive or negative draw, is there a cheap way to get the actual electrical draw in numerical format for what is on the bus?

[Hector]

It is important to determine your continuous power requirements vs intermittent loading. Below is a load chart for my M20C. My continuous power requirement is at near 50% of my 50 amp generator capacity. With EVERYTHING on I'm getting close to full rated capacity. I'm thinking about LED lights as well for the interim, with an alternator conversion down the road.

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[N601RX]

There is an AC on power analysis, I don't remember the number. They(FAA) only want you to use 80% of your alternator output, and assume a worse case which they define at night in freezing conditions ( All lights and pitot heat on). They also say assume the battery is partially discharged and some of the alternator output is being used to charge the battery. They do give a little break for temp loads like landing gear and radio transmissions. Also remember only one radio at time can transmitt.

[philipneeper]

What about the regulator? I know mine says max continuous duty 4 amps. Would that be something g to looking into?

[orionflt]

I have an old C model that had a 50 amp generator installed when i bought it, I upgraded to an alternator but left the system rated at 50 amps, during my latest panel and wiring upgrade i looked at my electrical loading and found that it wasn't worth it to me to upgrade my current breaker to 70 amps (the capacity of my alternator and wiring) due to the fact that my max load was well below the 80% load limit. my max draw with everything turned on is about 33 amps continuous, 37 peak, if I wasn't running a LED landing light my numbers would have been right at the 80% figure but since your set up with a 60 amp system yours probably wouldn't be an issue,

 

list of equipment:

Garmin 430W

Garmin 330

KY-97

KMA 20 audio/mrkr

Narco Nav 14

Narco DGO-10 HSI

electric T&B

MVP-50 Engine monitor

Whelen strobes with nav lights

Whelen LED landing light

Pitot heat

 

Brian

[Mooneymite]

It is important to determine your continuous power requirements vs intermittent loading. Below is a load chart for my M20C. My continuous power requirement is at near 50% of my 50 amp generator capacity. With EVERYTHING on I'm getting close to full rated capacity. I'm thinking about LED lights as well for the interim, with an alternator conversion down the road.

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Hector, I'm curious why you show landing light and pitot heat as "intermittent" on your spread sheet since there are certain conditions/phases of flight where they are continuous.  There might be some logic in showing that landing light and pitot heat might not be required at the same time.

 

To me, an intermittent load would be something like an electrical gear extension, or a radio transmission.

[Hector]

Hector, I'm curious why you show landing light and pitot heat as "intermittent" on your spread sheet since there are certain conditions/phases of flight where they are continuous. There might be some logic in showing that landing light and pitot heat might not be required at the same time.

To me, an intermittent load would be something like an electrical gear extension, or a radio transmission.

Yes, you can certainly look at it that way and there is nothing wrong with that. In my spreadsheet I was trying to distinguish more between my typical every flight current draw (things that are on all the time regardless of flight conditions), vs worse case condition. I was interested in knowing what percentage of my lowly generator capacity I was using during a typical flight as that has a bearing on generator longevity. Since I switched to an LED landing light, for example, it is now on the continuous column because I use it nearly all the time.

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[philipneeper]

Did you have to update your regulator as well?

[Bob - S50]

Thanks everyone for the replies. What got me down this questioning path was, like you, I was under the impression that newer electronics should equate to lower current draw. I was a bit surprised to see that one of my KX170B radios had a similar power draw to one Aspen PFD. Granted what actually is drawn is a different topic but I think the higher watt output of the transmitters (like on a GTN650) and the associated cooling fans on the Garmins/Aspens, I am beginning to wonder if the draws are not a lot closer. Since I am adding more power drawing equipment than I am taking out, I am curious how much power draw I will be creating with the new equipment.

King KX-170B Receive Mode: 1.1 amp Transmit: 3.0 amp with a max draw of 5.1 amps with all the lamps on both the com and the nav

Aspen

Max Current 2.4 Amps @ 28 Vdc / 4.8 Amps @ 14 Vdc

I also agree that unloading power eaters is probably a better way of going about this. I have see the PAR46 lights in action. For 2.6 amps, it certainly outperforms the 10+ amp old lamps. I can also beginning replacing all of those little GE330 bulbs with LED equivalent. What other things have you replaced to lighten the load?

I'm guessing the current draw is higher than you expected because of the glass.  Any glass instrument has to generate light so you can see it.  Old equipment did not, they only needed light at night.  The new equipment should draw less power for the functionality, but draw extra power for the lighting every time you use it.  If you compared an old transponder or comm radio to new ones, I think you'd find lower power consumption by the new ones.  Anything with a glass display though....

 

Bob

[N601RX]

What about the regulator? I know mine says max continuous duty 4 amps. Would that be something g to looking into?

4 Amps is the max current it provides  to the field of the alternator.  4 amps to the field is enough to get a full output on most alternators. 

[philipneeper]

Makes sense thank you

[Marauder]

I'm reviving this thread from the "dead thread" pile since I'm interested in knowing what amperage draw others are actually seeing in flight on a 14 volt system.

I got my first flights in on Saturday with the new 900 installed. I was really amazed to see that I was only drawing 3 amps for all the electrons I have moving around in my plane. Does that makes sense to see such a low draw?

I haven't noted the amperage draw when the gear is lowered or raised nor have I looked at what my Whelen LED landing light is drawing. Anyone have a "normal" draw for them?

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[ArtVandelay]

I have old fashion analog gauge, but it's not much unless my electric backup vacuum pump turns on, normally needle is just in the positive range. Modern avionics have low power draws.

You should test pitot heat and autopilot as these are extended power draws.

[carusoam]

Anything with an electric motor running will have high amperage draws...

Next in the line of high amperage would be known heat generators like standard lights or pitot heaters.

A stack of digital BK radios can get pretty hot.

A digital volt meter (aka JPI 900) across the shunt would be nice...

Best regards,

-a-

[orionflt]

Chris,

I am seeing a 12 -14 amp normal draw with my Mooney, I can attribute most of that to the strobes and position lights. the rest is radios and GPS. knowing what you are running for avionics I would say 4 amps just for that is reasonable.

Brian

[Marauder]

Chris,

I am seeing a 12 -14 amp normal draw with my Mooney, I can attribute most of that to the strobes and position lights. the rest is radios and GPS. knowing what you are running for avionics I would say 4 amps just for that is reasonable.

Brian

Thanks Brian. When I started this thread, I was worried that my 60 amp alternator was going to be given a workout with all that glass. I was just surprised to see it so low.

I'm going to be tracking some of the loads of the equipment I have onboard. Good to note what you need to shed in case you do lose the charging system.

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[Cruiser]

I searched for an FAA Circular on the subject but did not find any. There is an interesting one from Australian AC 21-38(0) MARCH 2005 AIRCRAFT ELECTRICAL LOAD ANALYSIS AND POWER SOURCE CAPACITY. Good information but advisory only, not regulatory.

 

The FAR refers to F2490-05(2013) Standard Guide for Aircraft Electrical Load and Power Source Capacity Analysis, 2013 which is an ASTM publication 

 

I thought I remember something about the maximum load not exceeding a certain percentage of the Alternator capacity but that might have been a daydream........ anyway I can't find it. 

[cliffy]

There is a requirement to do a "Load Analysis" after an electrical system change. The 80% figure is correct.

I think there is guidance in 43.13 on this but I too think there is an AC on it as well. If you re-equip your electronics

your shop should (is required) to do the load check before signing the install off and include it in the log book records.