FSXA Starter AMPS issue

taguilo · 12 Jan 2017

Heretic said:
Tom is principally correct on the operation, with the exception that the battery charging bus is current limited to 275 amps.

I've mentioned the current limiter in post #21.
Actually the Battery Charging Bus in NOT current limited, otherwise a starter couldn't crank (initial draws can excess 800 Amps). Physical current limiters are placed between each generator bus and the Battery Charger bus to prevent excess workload on the generators, either for cross generator starts or battery charge.

Tom

ark1320 · 12 Jan 2017

This has been a very interesting and informative discussion. If you haven't seen something similar, the simplified diagram of the Lear 30 series electrical system at http://www.airplanedriver.net/study/lr30.htm (scroll down a bit) may be of some help in visualizing things. Note current limiter locations.
Al

delivery guy · 12 Jan 2017

Ok reading the last few posts now things are making sense as i was getting confused with the user manual explanation. So like the default system 2 generators will split the load.

This means i need to make my new coding have 2 rates based on how many generators are running.
Heretic is looking over my code today and i may not need to update if he does it first.

delivery guy · 12 Jan 2017

Heretic said:
Tom is principally correct on the operation, with the exception that the battery charging bus is current limited to 275 amps.

DG, can I have the updated .mdl file with the L: var driven ammeters?
I'd modify your electric system logic anyway, so I might as well code it for you in the first place.

This is now updated and splits the load if 2 generators are on.

Code:

<!--                      HIGHER CHARGING AMPS               -->
<Element>
   <Select>
     <Value>


<!--  1 GEN  -->

(A:GENERAL ENG GENERATOR SWITCH:1,bool) 1 ==
(A:GENERAL ENG GENERATOR SWITCH:2,bool) 1 == or
23.8 24 (A:ELECTRICAL BATTERY VOLTAGE:1,Volts) rng and

if{ (A:ELECTRICAL BATTERY VOLTAGE:1,Volts) 24 - -44.25 * 3.75 + (A:ELECTRICAL BATTERY VOLTAGE:1,Volts) * (>L:FSW LJ GENERATOR:1, NUMBER) }


(A:GENERAL ENG GENERATOR SWITCH:1,bool) 1 ==
(A:GENERAL ENG GENERATOR SWITCH:2,bool) 1 == or
23.8 24 (A:ELECTRICAL BATTERY VOLTAGE:1,Volts) rng and

if{ (A:ELECTRICAL BATTERY VOLTAGE:2,Volts) 24 - -44.25 * 3.75 + (A:ELECTRICAL BATTERY VOLTAGE:2,Volts) * (>L:FSW LJ GENERATOR:2, NUMBER) }


(A:GENERAL ENG GENERATOR SWITCH:1,bool) 1 ==
(A:GENERAL ENG GENERATOR SWITCH:2,bool) 1 == or
(A:ELECTRICAL BATTERY VOLTAGE:1,Volts) 23.8 &lt; and

if{ 300 (>L:FSW LJ GENERATOR:1, NUMBER) 300 (>L:FSW LJ GENERATOR:2, NUMBER) }



<!--  2 GEN  -->

(A:GENERAL ENG GENERATOR SWITCH:1,bool) 1 ==
(A:GENERAL ENG GENERATOR SWITCH:2,bool) 1 == and
23.8 24 (A:ELECTRICAL BATTERY VOLTAGE:1,Volts) rng and

if{ (A:ELECTRICAL BATTERY VOLTAGE:1,Volts) 24 - -22.12 * 1.87 + (A:ELECTRICAL BATTERY VOLTAGE:1,Volts) * (>L:FSW LJ GENERATOR:1, NUMBER) }


(A:GENERAL ENG GENERATOR SWITCH:1,bool) 1 ==
(A:GENERAL ENG GENERATOR SWITCH:2,bool) 1 == and
23.8 24 (A:ELECTRICAL BATTERY VOLTAGE:1,Volts) rng and

if{ (A:ELECTRICAL BATTERY VOLTAGE:2,Volts) 24 - -22.12 * 1.87 + (A:ELECTRICAL BATTERY VOLTAGE:2,Volts) * (>L:FSW LJ GENERATOR:2, NUMBER) }


(A:GENERAL ENG GENERATOR SWITCH:1,bool) 1 ==
(A:GENERAL ENG GENERATOR SWITCH:2,bool) 1 == and
(A:ELECTRICAL BATTERY VOLTAGE:1,Volts) 23.8 &lt; and

if{ 150 (>L:FSW LJ GENERATOR:1, NUMBER) 150 (>L:FSW LJ GENERATOR:2, NUMBER) }
 

<!--  GEN OFF  -->

(A:GENERAL ENG GENERATOR SWITCH:1,bool) 0 == if{ 0 (>L:FSW LJ GENERATOR:1, NUMBER) }
(A:GENERAL ENG GENERATOR SWITCH:2,bool) 0 == if{ 0 (>L:FSW LJ GENERATOR:2, NUMBER) }

     </Value>
   </Select>
</Element>

Heretic · 12 Jan 2017

delivery guy said:
Heretic is looking over my code today and i may not need to update if he does it first.

I'll look at it when I'll be home tomorrow.

taguilo said:
I've mentioned the current limiter in post #21.
Actually the Battery Charging Bus in NOT current limited, otherwise a starter couldn't crank (initial draws can excess 800 Amps). Physical current limiters are placed between each generator bus and the Battery Charger bus to prevent excess workload on the generators, either for cross generator starts or battery charge.

Quote from the LJ31 systems description*:

The voltage on the generator buses is applied to the battery charging bus through 275-amp current limiters. Battery charge is maintained from the battery charging bus through the battery relays and battery buses

Confirmed by the diagram:
http://www.airplanedriver.net/acpix/LR20_Elect.jpg

The 275 A limitation is not in effect during cross-starts. Quote LJ31 again:

A cross start relay box is installed which enables an operating generator to assist in providing power to start the opposite engine. If one generator is on-line and a start of the opposite engine is initiated, the cross start relay circuits will cause both left and right starter relays to close. In effect, this will bypass both battery charging bus 275-amp current limiters and the output of the operating generator will supplement the aircraft batteries in providing power for the starter.

*http://www.smartcockpit.com/aircraft-ressources/LR-1A-Electrical_and_Lighting.html

taguilo · 13 Jan 2017

Heretic said:
Quote from the LJ31 systems description*:

Bjoern,

That is for the Lear 31. The Lear 35 is different. You can check it here:

https://books.google.com.ar/books?id=Ne3YWS9Iy3EC&pg=PA5&lpg=PA5&dq=learjet+35a+manual&source=bl&ots=q9tS7uBsMW&sig=GgULJFlkzibJ7aKAaGB7H_xNots&hl=es&sa=X&ved=0ahUKEwjY3Y20kr_RAhVGfZAKHWKuAyMQ6AEIZTAM#v=onepage&q=learjet 35a manual&f=false

Search for Electrics section, there is also a diagram of power distribution.

It works more like I described on my former posts.

Tom

Heretic · 13 Jan 2017

taguilo said:
Bjoern,

That is for the Lear 31. The Lear 35 is different. You can check it here:

https://books.google.com.ar/books?id=Ne3YWS9Iy3EC&pg=PA5&lpg=PA5&dq=learjet+35a+manual&source=bl&ots=q9tS7uBsMW&sig=GgULJFlkzibJ7aKAaGB7H_xNots&hl=es&sa=X&ved=0ahUKEwjY3Y20kr_RAhVGfZAKHWKuAyMQ6AEIZTAM#v=onepage&q=learjet 35a manual&f=false

Search for Electrics section, there is also a diagram of power distribution.

It works more like I described on my former posts.

That chapter is blocked out for me.

According to that encyclopedia everybody uses, the Lear 31 is essentially a Lear 35 with the Lear 29's wings. I also read somewhere that the electrical system aries with customer, series and whatnot.
If the only accessible piece of hard information about the electrical system of an aircraft is that for a very similar model (which is confirmed by a drawing somewhere else), I am going to model that system according to these specs. If people complain about the lack of realism due to necessary compriomises on my part, they have to ensure that the specific documentation is provided online and freely accessible. Not "I'mma send it to you via e-mail" online and accessble, but "Aircraft documentation for pilots in pdf", Smartcockpit or "Google page 2, open directory listing on a flight school web server" online and accessible.

If you still think your approach would be the better one, give me a shout and I'll let you do the coding. But as long as I'm the one to throw around L: vars, I get to decide how it's done.

taguilo · 13 Jan 2017

Heretic said:
If you still think your approach would be the better one, give me a shout and I'll let you do the coding. But as long as I'm the one to throw around L: vars, I get to decide how it's done.

Be my guest, code it as you wish.
I only made reference to what is included in the info I have for the 35a, which, btw and somehow agreeing with you, may be different depending on model versions and configurations.

Here is another link to a 35/36 manual that can be freely downloaded. Very good and complete documentation:

http://www.arquivosaeronauticos.com.br/2012/08/manual-operacional-learjet-3536.html

Tom

Heretic · 13 Jan 2017

taguilo said:
Be my guest, code it as you wish.
I only made reference to what is included in the info I have for the 35a, which, btw and somehow agreeing with you, may be different depending on model versions and configurations.

Here is another link to a 35/36 manual that can be freely downloaded. Very good and complete documentation:

http://www.arquivosaeronauticos.com.br/2012/08/manual-operacional-learjet-3536.html

Thanks!
(Every version of the electrical system - four in total - contained in the POH features a current limiter for the battery charging bus.)

Do you per chance know how much of a given circuit breaker current limit is usually used by a component (assume a simple on/off toggle with fixed power requirements)? 50%? 80%?
The Lear 31 handbook is the only one featuring circuit breaker limits for a given subsystem or instrument, but it never lists the actual current in use.

taguilo · 14 Jan 2017

Heretic said:
The Lear 31 handbook is the only one featuring circuit breaker limits for a given subsystem or instrument, but it never lists the actual current in use.

For practical purposes I use 30 % of CB nominal amperage for switches and 15 % for cockpit instrument lights. Motors (flaps, LGear,etc) at ~ 40-50 %.

Tom

EDIT: Regarding the 275 amps current limiters, those are a protection for the generators not delivering higher amperage to the Battery Charging Bus.
Indeed, when a starter motor cranks, instant power demand of 800+ amps is filled by the batteries through the BCBus.
Perhaps you are saying the same with other words?

Heretic · 14 Jan 2017

taguilo said:
For practical purposes I use 30 % of CB nominal amperage for switches and 15 % for cockpit instrument lights. Motors (flaps, LGear,etc) at ~ 40-50 %.

Maybe I'll lower the currents later on. For now, switching all consumers on (minus starters, flap, gear, spoiler circuit motors) yields 485 amps, which drains both batteries in 10 minutes (using a custom battery model).

Any idea how much of a voltage drop will be observable for a 24V (lead-acid) battery during a full discharge cycle?

taguilo · 17 Jan 2017

Heretic said:
Any idea how much of a voltage drop will be observable for a 24V (lead-acid) battery during a full discharge cycle?

I guess it would be similar in many turbine aircraft. I am using

- 23V minimum recommended for normal engine start.
- 22V min for hot start but within limits (emergency start).
- 20V starter won't crank.
- 10V all dark.

Tom

Heretic · 17 Jan 2017

taguilo said:
I guess it would be similar in many turbine aircraft. I am using

- 23V minimum recommended for normal engine start.
- 22V min for hot start but within limits (emergency start).
- 20V starter won't crank.
- 10V all dark.

Since asking, I've implemented a 1V drop across the entire capacity drop and even that seems to be a bit exaggerated when looking at some real figures.

But thanks for the reminder about the starters!

Roy Holmes · 20 Jan 2017

Here are some numbers about amps and discharge time.
150 7 mins
125 10 mins
100 15 mins
75 20 mins
50 30 mins
They are for the Hunter which had two 6000 watt engine driven generators charging two 24 volt batteries in parallel.
The load and times above were for both batteries after double generator failure.
Typical flight load was 105 amps.
The starter was energized by decomposition of isopropylnitrate liquid. Nasty stuff but it used no electric power, useful when parked in a remote dispersal.

I noticed umpteen references to amps and volts in this thread, but the basis of performance should be in watts (volts*amps), in my opinion.
Roy

WarpD · 20 Jan 2017

Electrical performance isn't usually described via watts, it's amps. I don't have a 1100 watt electrical outlet in my wall, it's a 10 amp outlet, etc.

Heretic · 20 Jan 2017

Roy Holmes said:
I noticed umpteen references to amps and volts in this thread, but the basis of performance should be in watts (volts*amps), in my opinion.

Generator performance, yes. But batteries are best judged by their capacity, which is measured in Ampere hours.
You can, of course, convert Ampere hours into Watt hours but I find the other unit much more convienient to work with.

If my math and your numbers are correct, the hunter used two 12.5 Ah (or 300 Wh) batteries.

Roy Holmes · 20 Jan 2017

WarpD said:
Electrical performance isn't usually described via watts, it's amps. I don't have a 1100 watt electrical outlet in my wall, it's a 10 amp outlet, etc.

Well I did say it was my opinion.
But your outlet does nothing, has no performance, just a maximum current limitation.
What you plug into the outlet does something like lights up the room and its performance is designated in Watts. An electric motor has power and it is designated in watts.
You might have something about volts and amps in the small print, but unless you are traveling to UK and worried about blowing up your hair dryer, you probably will not read it.
Roy

WarpD · 20 Jan 2017

Every aircraft manual in my possession uses the term amps and my electronics training also taught me to use the term amps to describe loads and load capacity. The aircraft indicates generator performance with an ammeter not a watt meter.

Roy Holmes · 20 Jan 2017

Aircraft have electrical power supplies usually generators and batteries.
The SI unit for electrical power is the watt.
Sometimes the term Volt Ampere VA, but more typically KVA Kilo Volt Amperes, is used instead of the watt or kilowatt, but they are the same thing.
Similarly, on the assumption that the electrical power will be supplied at a regulated voltage, it is more convenient to use amperes to describe the amount of power being consumed.

Since this thread is dealing with situations when the voltage is varying, using current only is missing half the point. No volts = no current because no electrical power.
Battery voltage usually decreases when high current is drawn because there is only so much electrical power. Generators replenish the electrical power of the batteries.

Roy

WarpD · 20 Jan 2017

The documentation for aircraft discuss the generator capacity in amps, not watts. If you have issue with that standard... take it up with the manufacturers... until the documentation is different... the values used are amps. Even the simulator uses amps, not watts. There is no variable in the sim for watts. The ammeter displays amps, not watts. Need I really go on as to why the proper value to discuss in this is amps not watts?

Doesn't matter what you want to call it... the rest of the industry isn't. Period.