What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Alternators and Amps

bjdecker

Well Known Member
Ambassador
After receiving my first EarthX battery, I immediately noticed the large amount of current produced by the alternator to recharge the battery right after cranking the engine.

This is normal & expected behavior for LiFePo+ batteries.

What I couldn't explain was how the current reported by the EFIS exceeded that which the Alternator was supposed to be capable. I had rationalized that a few amps over the rating was within spec, but I was seeing more than 10% on occasion.

Turns out that the Plane Power Alternator that I have, model #99-1012, which is included in the AL12-60B/C kits, is in actuality a 70 amp model. This is documented on the data sheet/test report (attached).

Note the output curve; this alternator is capable of 60A at 3100RPM, 70A at 4100RPM and so on. This means it is capable of 70A at engine idle, and ~80A at cruise RPM, assuming you are using relatively stock pulley arrangement.

So, is >60A ok to dump into an EarthX battery rated for 60A? Is a 60A CB or 60A ANL sufficient to protect this Alternator? Should we resize the CB / ANL to a larger value? Should we keep the engine < 700RPM right after start to keep the output below 60A?

Time for more coffee...
 

Attachments

  • IMG_1941.jpg
    IMG_1941.jpg
    477.2 KB · Views: 257
So, is >60A ok to dump into an EarthX battery rated for 60A?

That's a question for EarthX.

Is a 60A CB or 60A ANL sufficient to protect this Alternator?

A fuse or breaker does not protect the alternator. It protects wiring. Specific to an alternator ANL or breaker, it protects the aircraft from an electrical fire (melting wire and burning insulation) due to available battery amperage, given a B-lead short among the collection of hot, vibrating parts in the engine compartment.

Should we resize the CB / ANL to a larger value?

To keep the planets in alignment, the B-lead is sized for an amperage higher than the expected alternator output, with a fuse or ANL rated less than the wire, and => that expected output.
 
bigger pulley

Slowing down the alternator output is one of the reasons I added a bigger pulley. Went from 3" to 4" to slow it down a little. No idea if it will help with the long term life of the alternator, and I do still see peaks of about 50-60 amps on a similar 60A PP/Hartzell alternator (http://www.rv8.ch/plane-power-alternator/) with the EarthX 680c battery.

I'm guessing the alternator output could go higher if I was at higher RPM after start, but I'm just above idle until the oil warms up.

IMG_1641.jpg

http://www.rv8.ch/alternator-pulley-change/
 
Last edited:
Some Daytime Running Lights (DRL) and the low speed of automotive cooling fans run thru a low resistance / high wattage resistor to drop the voltage and amps running thru them.

I suppose someone could come up with a circuit that does the same thing to slow down the charging of the alternator after startup. A large capacity diode on the battery would let the battery supply volts and amps if it had too, and the starter would have a direct connection to the battery.
 
My way

Some Daytime Running Lights (DRL) and the low speed of automotive cooling fans run thru a low resistance / high wattage resistor to drop the voltage and amps running thru them.

I suppose someone could come up with a circuit that does the same thing to slow down the charging of the alternator after startup. A large capacity diode on the battery would let the battery supply volts and amps if it had too, and the starter would have a direct connection to the battery.

The easier way to do this would probably involve tweaking the field current to limit the alternator output.
 
The easier way to do this would probably involve tweaking the field current to limit the alternator output.

Then the whole electrical system will have low voltage, not just lower voltage to the battery to slow down the charging rate.
 
The IR of the EarthX and similar lithium batteries is much lower than lead acid batteries. This low IR lets them pull much higher current. EarthX specs the max alternator size for each of their batteries. This seems to be their method of limiting the max charge current. The BMS does not factor into this. Normally I see approx 30 amps just after a start and it drops significantly by the time I finish the run up. Recently I had run the EarthX down pretty low (12.9v) playing with some setup stuff in the avionics. It still cranked ok but it completely maxed out the alternator (B&C 40 amp) to the point where the regulator (B&C) could not maintain the normal 14.5v set point. Took considerably longer to top off. I don’t see an issue with this. The system worked as designed and I would not want to introduce more components.
 
B Lead AWG??

To keep the planets in alignment, the B-lead is sized for an amperage higher than the expected alternator output, with a fuse or ANL rated less than the wire, and => that expected output.


I'm trying to figure what AWG to use as B-Lead. I understand bigger is prefered to too small but don't want overkill and wish to keep some flex because of vibration etc...

I have a B&C 60A, and if I switch everything "on", I will draw more or less 60A. There is a 60A ANL near the main contactor.
My biggest energy hogs are Pitot heat, HID 75W Taxi & LND lights and Heated and lights can be managed to help lower power needs.


Search in different threads came up with a range of 2AWG down to 8AWG, that's quite a spread...
Bob Nuckol's book suggest 4AWG or 6AWG, and I understand that it' not a definite number because of varying needs.


I was tending towards 6AWG, but fearing it might be smallish to support 60A loads, compared to 4AWG???


What did you guys having possible loads nearing 60A install as B-Lead and what are your observations/comments/findings???


Thanks !!!
 
60 Amp ANL current limiter

I had the exact same issue, a P-P 60 amp alternator and a Earth -X alternator that would charge at 55 to 63 amps right after each engine start up at 1000 RPM. After about 10-15 flights, I noticed that the 60 amp ANL current limiter was black brown, but still working. I talked to P-P and B&C engineers and they both said that pulling nearly maximum amps at a low RPM is not healthy for the alternator...or the wiring. Earth X recommended putting in a higher rated ANL current limiter. I could only find an 80 amp ANL current limiter, but then that defeats the purpose of protecting my wiring to a 60 amp short to ground on the B-lead. I went back to a 60 amp ANL current limiter and the PC-680.
 
I'm trying to figure what AWG to use as B-Lead. I understand bigger is prefered to too small but don't want overkill and wish to keep some flex because of vibration etc...

I have a B&C 60A, and if I switch everything "on", I will draw more or less 60A. There is a 60A ANL near the main contactor.
My biggest energy hogs are Pitot heat, HID 75W Taxi & LND lights and Heated and lights can be managed to help lower power needs.


Search in different threads came up with a range of 2AWG down to 8AWG, that's quite a spread...
Bob Nuckol's book suggest 4AWG or 6AWG, and I understand that it' not a definite number because of varying needs.


I was tending towards 6AWG, but fearing it might be smallish to support 60A loads, compared to 4AWG???


What did you guys having possible loads nearing 60A install as B-Lead and what are your observations/comments/findings???
Hi Eric, I think you would be fine with #8 or fatter, depending on the length. I have a 60A PP alternator and the B lead length is about 24 inches - basically straight from the alternator back to the firewall. I went with some #4 welding wire which is strong, flexible, fat, and orange. I had a ton of it laying around. I also used an 80 amp littelfuse, although I can't imagine that it will ever do anything for me, since the alternator can't put out enough juice to hurt that short, fat welding cable. Some pics here. So far the smoke is still in the wire!

http://www.rv8.ch/alternator-b-lead-install-with-littelfuse-midi-inline-80amp-fuse/
 
BC voltage regulator

As I understand it the Earth X has a BMS but it can not limit the charging current. A BMS built in current limiter cost money.
The BC voltage regulator LR3D has an input for a temperature probe.
It seems to me that this input (1) can be used to manually adjust charging voltage using a variable resistance control.
A call to BC may give some more info.

https://bandc.com/wp-content/uploads/2020/05/LR3D-Technical-Manual_RevIR_5-13-20.pdf

Good luck
 
Brainstorm result?

Thanks guys for your replies !!!
It's amazing the amount of time spent to review/(over)think stuff just for what seems trivial between 2 wire sizes... arghhhhh :eek:
...No wonder this project is taking me soooooo long...:rolleyes:

Here's what I deduct from mulling over this and fishing aroud.
Hope this seems right...!!!

1- The alternator might occasionnaly push close to 60A or, maybe for rare short time periods, slightly above 60A after startup because of the battery as per Eric H's obervation? (I'll have to monitor this and its Amperage).
2- Distance is about 3 feet from the alternator to the fuse before the contactor, where from there 2AWG runs to the battery, starter contactor and starter.
3- As a data point, the alternator has a .250" bolt to connect the B-Lead. That's roughly the diameter of 2AWG.
4- 4AWG is .204" in diameter, while 6 AWG is .162". (see screen shot)
5- At 60A and 14.4 Volts and 3 feet of wire, voltage drop is 0.62% or 14.31V with 4AWG and 0.99% or 14.26V with 6AWG. (surprisingly similar due to short run) (see screen shots)

In view of all this, I'll go with 4AWG for peace of mind.
I'm slightly concerned with the 60A ANL being close to the limit due to #1 remark above. Not knowing yet if I'll have peaks above 60A, a 80A ANL will be installed, (presuming that a 4AWG wire will handle up to 80A in this setup), until I can measure what's happening amperage-wise after startup.
EarthX specifies a maximum of 80A (from vehicule charging system) for my ETX900

Mickey, I love your LittelFuse solution!!! I didn't know about them, considering a swap...

Gustav, as for the input of the LR3D-14, if I read correctly, it adjusts the output voltage, not sure it will affect the amperage...??? I sent an email question to B&C.


I welcome any additionnal comments.
 

Attachments

  • Capture d’écran, le 2021-02-17 aÌ€ 10.05.21.png
    Capture d’écran, le 2021-02-17 aÌ€ 10.05.21.png
    147.6 KB · Views: 158
  • Capture d’écran, le 2021-02-17 aÌ€ 09.52.31.png
    Capture d’écran, le 2021-02-17 aÌ€ 09.52.31.png
    210.2 KB · Views: 172
  • Capture d’écran, le 2021-02-17 aÌ€ 09.51.53.png
    Capture d’écran, le 2021-02-17 aÌ€ 09.51.53.png
    208.1 KB · Views: 180
Last edited:
The ANL Fuse data indicates little difference between the ANL60 and ANL80 amp fuse, both will require a very high current event to fail.
 

Attachments

  • ANL Fuse Data Sheet.jpg
    ANL Fuse Data Sheet.jpg
    221.3 KB · Views: 173
  • ANL Fuse Data Sheet2.jpg
    ANL Fuse Data Sheet2.jpg
    298.5 KB · Views: 161
current limiter versus fuse

My thoughts:

  • A 60A alternator B lead can properly be protected with a 60A ANL current limiter. A 60A alternator B lead protected with a MIDI fuse should use a 100A MIDI according to my calculations ref the Littelfuse Fuseology document.
  • The B&C alternator stud is actually M6. Important to know if you need to replace the nut.
  • An external regulator will make up for the B lead voltage loss because it senses bus voltage. BTW, 60A thru a 100A MIDI drops ~.035 V.
  • IMO 6 awg B lead is good for a 60 A alternator. 60 A continuous thru a 6 awg wire will heat it ~12 C above ambient and a 4 awg wire ~8 C above ambient (still air, sea level, not in a bundle). M22759/16 Tefzel wire is rated to 150 C. EPDM insulated welding cable from what I have seen is rated to 105 C.
  • The online voltage drop calculator shown in post 12 assumes the ground return is the same gauge as the feeder.

Some background:

  • Looking at the Bussmann ANL time/current curves, ANL current limiters labeled 100 A and less will carry about twice their nameplate rating indefinitely.
  • MIDIs are fuses and are not as robust as current limiters so should have a rating higher than the alternator.
    The Littelfuse MIDI spec sheet says a MIDI rated in the current ratings we are talking about will carry 110% for at least 4 hours and 150% for at least 90 seconds so you can see they are much faster than ANLs of the same numerical rating.
    Following the methodology in Littelfuse's Fuseology document, a fuse is always de-rated by 25%, then a temperature re-rating factor from the MIDI spec sheet is applied on top of that. 60 A alternator/(.75 * .95) = 84A rating for the MIDI fuse. This becomes a 101A MIDI rating if we assume the alternator is capable of 20% more than its rating and that we would actually load it to that level, close enough to 100 to choose a 100A MIDI fuse.
    For a 35A alternator such as B&C 462: (35 * 1.2)/(.75 * .95) = 59A so a MIDI 60 fuse is chosen.
    For a 32A alternator such as B&C 410 or 425: (32 * 1.2)/(.75 * .95) = 54A so a MIDI 60 fuse is chosen.
    Assumption: Fuse is on the firewall at 170 F.​
  • Looking at copper wire fusing (melting) currents, it seems like a 60 ANL is loosely equivalent to a 16 awg fuse link and an 80 ANL to a 14 awg fuse link. Seems like a 100A MIDI is loosely equivalent to a 16 awg fuse link. Fuse links more than 4 awg smaller than the protected wire would get dangerously hot in normal ops so this analogy should not be implemented!
  • If fuse links were used, as they are in the latest Z schematic (Z101), 6 awg would be conventionally protected by 10 awg which melts at 330 A and 4 awg would be protected by 8 awg which melts at 470 A. So you can see even the highly robust ANL current limiter will protect much sooner than a fuse link.

You heard it from some guy on the internet.
.
 
Last edited:
...
  • A 60A alternator B lead can properly be protected with a 60A ANL current limiter. A 60A alternator B lead protected with a MIDI fuse should use a 100A MIDI according to my calculations ref the Littelfuse Fuseology document.
    ...

Some background:


  • ...
  • MIDIs are fuses and are not as robust as current limiters so should have a rating higher than the alternator.
    The Littelfuse MIDI spec sheet says a MIDI rated in the current ratings we are talking about will carry 110% for at least 4 hours and 150% for at least 90 seconds so you can see they are much faster than ANLs of the same numerical rating.
    Following the methodology in Littelfuse's Fuseology document, a fuse is always de-rated by 25%, then a temperature re-rating factor from the MIDI spec sheet is applied on top of that. 60/(.75 * .95) = 84A rating for the MIDI fuse.
    This becomes a 93A midi rating if we assume the alternator is capable of 10% more than its rating and that we would actually load it to that level.
    So the next higher MIDI is chosen, 100A.
    Assumptions: Fuse is on the firewall at 170 F, sea level, still air, not in a bundle.​
    ...
You are right - I'm a bit tight with my 80A fuse according to the calculations for a continuous 60A load at typical under cowl temperatures. It has not blown yet, but I guess the lifetime will be reduced. Outside of the peaks of recharging the battery after startup, I rarely see even 15A. Can't hurt to bump it up to 100A - they are very cheap! Thanks for this analysis, John.
 
Just me

My thoughts:


[*]Looking at copper wire fusing (melting) currents, it seems like a 60 ANL is loosely equivalent to a 16 awg fuse link and an 80 ANL to a 14 awg fuse link. Seems like a 100A MIDI is loosely equivalent to a 16 awg fuse link. Such fuse links would get dangerously hot though so this is an analogy not to be implemented!

[*]If fuse links were used, as they are in the latest Z schematic (Z101), 6 awg would be conventionally protected by 10 awg which melts at 330 A and 4 awg would be protected by 8 awg which melts at 470 A. So you can see even the highly robust ANL current limiter will protect much sooner than a fuse link.
[/LIST]

This is why I dont believe in fusible links for large currents; they get really hot when they go. I think fusible links are find for lower current stuff, but when the fusible link gets larger than 20AWG, I get a little nervous. Serious smoke, fire and brimstone will be expelled when a 16 AWG fusible link goes. So for those cases, I like the ANL fuses. For anything in the cockpit, away from the engine compartment heat, a fuse or circuit breaker is my preference. The circuit breakers and fuses have structures in place to contain the failure events, so the pilot just goes, "Look dear, the blender stopped working?". When a fusible link goes, that is in the cockpit area, the wife goes, :" Like, oh my Gosh, we are all going to die!"
 
Excellent information !!!

  • The B&C alternator stud is actually M6. Important to know if you need to replace the nut.
  • IMO 6 awg B lead is good for a 60 A alternator. 60 A continuous thru a 6 awg wire will heat it ~12 C above ambient and a 4 awg wire ~8 C above ambient (still air, sea level, not in a bundle). M22759/16 Tefzel wire is rated to 150 C. EPDM insulated welding cable from what I have seen is rated to 105 C.


Thanks John, all your post is excellent !!!
You are correct, the stud is M6, not .25"

My concern is with the ANL60A in the long term. I know it's slow-blow and can handle more than 60A for short periods.

IF (as some have reported) the alternator is repeatedly producing 63-65A for short periods to satisfy the EarthX's initial demand following engine start, I wonder if over time, that fuse is going to weaken and blow.??
I have an electrical dependant engine and would like to avoid as much as possible a loss of main alternator in flight because of a tired ANL.
(I have backup alternator and battery BTW)

Is that a valid concern???
Otherwise, a bump to ANL80A with a 4AWG B-Lead wire??
The ETX900 is ok with a vehicule charging system up to 80A.
Not flying yet, but this will be monitored closely and if no peaks above 60A, I could revert back to ANL60A...

BTW, I'm still waiting to hear from B&C about the #1 terminal of the LR3D-14 and possible amperage control
 
Last edited:
hammer ANL current limiter?

... weaken and blow.??... Otherwise, a bump to ANL80A with a 4AWG B-Lead wire??...

Hi Eric,

One way to look at it is that conventionally a 6 awg wire could be protected by a 10 awg fuse link. 10 awg copper melts at ~330A. Since an 80A ANL current limiter melts at ~160A it must be OK to use it to protect a 6 awg B lead.

I don't think a 60A ANL current limiter will be hammered by 65A. It's easy to focus on the 60A rating of the ANL current limiter but if it were a fuse it would be called ~100A. I know there is more to fuse engineering than this but this is the basic situation.

There's room for opinion and comfort level here. Using 4 awg is simply a small weight penalty but IMO 6 awg is fine. An 80A ANL or 125A MIDI could be used but IMO a 60A ANL or 100A MIDI is fine. The lower rated protective devices would open sooner. Threats are internally shorted alternator, wire separating at alternator and contacting ground, and wire insulation failure. In crash or service scenarios, the master contactor should be off.

BTW
  • I've read that an alternator may put out up to 120% of placarded rating when it's cold (I don't have a source for this info), but it won't stay cold for long due to internal heating and you're not going to start the engine and go immediately to 1,800 RPM anyway.
  • In both ISO 8854 and SAE J 56, “rated output” is the current the alternator is capable of producing at 6,000 RPM, although they might typically produce more at higher RPM.
  • It's dangerous to jump start a dead battery aircraft and bring the alternator up to 6,000 rpm quickly, the battery will overheat. This includes jump starting and taking off promptly. I'm thinking you don't hear about this with cars because they have traditionally had larger batteries (greater thermal mass).
  • Lycoming alternator drive ratio is typically 3.25 with the 9-3/4" dia flywheel pulley so 1,850 RPM is needed for full alternator 6,000 RPM output. If you keep engine RPM down initially, alternator output is reduced.
  • I suggest flying with the main alternator off for periods of time to stress test the backup alternator. If you fly with both alternators on, the main alternator is being stress tested by default if the backup alternator is at a lower setpoint.

You could also inquire on the Aeroelectric List.
.
 
Last edited:
Thanks again!!

Thanks again John for your reply, really helpful.


I appreciate your data concerning ANL fuses. I'll stick for now with the ANL60A, and keep a close watch to the alternator behaviour and the ANL condition over time.


I'm equipped with a VPX and it doesn't permit having both alternators on at the same time. It' one or the other, and both have their own LR3 voltage regulator set at 14.4v.
 
Reduce Charging Current

I am offering this circuit for your entertainment. I am not necessarily recommending
it because adding components increases the chances of failure.
EarthX recommends adding a diode to limit charging current.
https://earthxbatteries.com/dual-bus-lithium-battery-design
enhance
 
Diodes

Joe, that's very interesting.
As far as I understand, and I may be wrong, the article you are refering to recommends a diode for those using a 6Ah backup battery for an essential bus??
While this may be useful/essential for that setup, it doesn't apply to mine.

My main battery is a ETX900 (16Ah), connected to a B&C LX60 alternator.
My backup battery is a ETX680 (12.4Ah) connected to a B&C BC410-H 40A alternator.

Each can accept 20A more charging current than their related alternator rated output.
Each have their respective voltage regulator set at 14.4v.
Only one alternator can function at a time (VPX-PRO)
I don't expect issues with excessive current to the batteries. :)
 
Update for those interested

Thought I could share feedback received from B&C and EarthX concerning the use of the #1 input of the LR3D voltage regulator (temperature probe) and the charging rate of the LX60 v.s. EarthX batteries.

As per B&C, the temperature probe adjusts the charging voltage, not the alternator output (read amps). They don't recommend a variable resistor on terminal 1.
Also, for the vast majority of installations, they don't recommend using the temperature probe, it is a rarely used feature for aircraft operating in Artic temperatures.

About the observed surges from alternators, because EarthX batteries recharge at a significantly higher rate, combined with the increased efficiency of the alternator at lower temperature, allows for an output slightly above the rated 60 amps and is completly normal.
They have no reports of degrading ANL current limiters, being slow blow fuses, by temporary excursions above 60 amps.

They also say that some have adjusted the charging voltage down a few tenths, resulting in lower charging rates.

As per EarthX, lowering the voltage setpoint to 14.2V (instead of factory set 14.4V), would make a big change in peak recharge current.

Both mentionned that there is no down-side to slightly reduce the voltage.
 
Also, for the vast majority of installations, they don't recommend using the temperature probe, it is a rarely used feature for aircraft operating in Artic temperatures.

Can you more closely define "arctic temperatures"? While not real arctic cold, I plan to operate my aircraft to at least -30*c (-25*f), maybe colder, and would like to avoid as many cold weather problems as possible.
 
LR3 regulator temperature probe

... B&C... for the vast majority of installations, they don't recommend using the temperature probe, it is a rarely used feature for aircraft operating in Artic temperatures...

I see B&C does not stock the temperature sensor.

  • "built to order".
  • "This temperature sensor offers linear charging voltage increase as the battery ambient temperature decreases below approximately 80 degrees F. If the battery is in the passenger or engine compartments, it is sufficiently warmed to make this sensor of little value. If the battery is in a compartment with no environmental control, on an aircraft that flies in very cold environments (extreme latitudes or high altitudes), then this sensor is recommended."
  • "There is no temperature voltage correction above 80 degrees F."

From Bob Nuckolls, who designed the LR3 regulator: link

Battery University has detailed info about charging here and here.
.
 
Last edited:
Can you more closely define "arctic temperatures"? While not real arctic cold, I plan to operate my aircraft to at least -30*c (-25*f), maybe colder, and would like to avoid as many cold weather problems as possible.

David,
I won't or can't define Artic temperatures as it's what B&C replied to my question about the usefulness or operation of the #1 terminal.

I presume that it could be useful to regulate the charging v.s. the battery's temperature when it is in a cold, unheated location in the aircraft.
For example, in my Cutlass, the battery is in the tailcone, no heat there...
Flying in winter at -20C, I know what it's like, for long periods could affect the recharge of a non-heated battery.
Outside of the initial startup, a battery on a firewall will be in a warm environment while in flight even in winter.
 
Back
Top