LM393 with NE555

dl324

Joined Mar 30, 2015
16,846
The purpose of the circuit is to tell the pilot if they need to charge the battery before starting the system or if they can start the system and there will be no problem for 20min only using battery power.
I think you need something better than an "idiot" light. An LM3914 would give a better indication. You can make one or more LEDs yellow to indicate caution, some red to indicate dangerously low, and some green to indicate okay.

The IC can drive up to 10 LEDs.
 

crutschow

Joined Mar 14, 2008
34,285
Tolerance of detection should be 24V ± 0.2V
For that tight tolerance, you will likely need to add an adjustment potentiometer to allow for the tolerances of the reference voltage and the resistor values.
You will then need to adjust the pot to the desired voltage when the circuit is powered by an adjustable power supply.

A TL431 is an example of a inexpensive, programmable, precision voltage reference which should have sufficient stability for your requirements.
 
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LowQCab

Joined Nov 6, 2012
4,026
There should be no warning device.

If You need a warning device, the Battery has already sustained damage from Sulfation.

The Battery should be kept on a "Maintenance-Charger"
at all times when it is not in the Air.

Simply double the numbers in this Chart below ..........
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Lead-Acid Temp Graph .png
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WBahn

Joined Mar 31, 2012
29,978
There should be no warning device.

If You need a warning device, the Battery has already sustained damage from Sulfation.

The Battery should be kept on a "Maintenance-Charger"
at all times when it is not in the Air.

Simply double the numbers in this Chart below ..........
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.
.
View attachment 286664
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Should be on a maintenance charger and is practical to be on a maintenance charger are two very different things.

If the aircraft is in a hangar with power, that's one thing. But that's rare. If it's out on the line, or in an unpowered T-hangar, then that's just not practical.

What I don't understand is the need to draw 20 A from it for 20 minutes before engine start. The only thing I can think of is if this is in a very cold climate and the power is being used to heat the oil before cranking. Would be interested in knowing what the story it. Pulling a fourth of the battery's total capacity (from a full charge) before cranking doesn't seem like a good idea to begin with.
 

WBahn

Joined Mar 31, 2012
29,978
A Solar-Charger propped-up against the Windshield would be just fine.
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Possibly. Most aircraft isolate the battery with a master power switch. Would depend on the specifics of the aircraft how feasible it is to connect up without having to do something that would constitute an aircraft mod (the same might be true for what the TS has in mind, but that's something that could at least be done without any mods on most light aircraft by turning on the master power and then plugging the device into a power receptable (similar to the ole infamous cigarette lighter).

If I owned a single airplane I might consider it, but then again many planes sit on the ramp for weeks between flights with no problems. But if I had a fleet of planes, especially rentals, I'd have to really ponder the pros and cons. I've never seen a fleet that did anything like that, so it's unlikely the pros outweigh the cons by any significant amount, otherwise it would be common practice.
 

LowQCab

Joined Nov 6, 2012
4,026
Or, everybody is required to replace their Battery every Year,
or something to that effect,
then yeah,
there might not be much of an advantage to
making your ridiculously expensive Battery last for ~5-Years,
because it will be scheduled for automatic replacement before then.

I'd be willing to bet that the Battery has special required Specs,
and costs an arm and a leg.

And, there seems to be almost an "expectation" with Pilots .............
Oh, inspection date coming up ...........
that's going to be at least ~3-Grand ..........
I'll just start doing my bending-over-exercises right away.
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sghioto

Joined Dec 31, 2017
5,380
I am designing a small circuit which will compare a Voltage from a 24V battery with a reference Voltage
You can accomplish that with a single 555.
R1 selected for the low voltage activation required.
With component values listed LED is ON and OFF for 1 second when activated.
1675449045785.png
 

Thread Starter

slevesque

Joined Jan 31, 2023
43
Hello everyone,

Just to put you in context the battery is not the aircraft battery. The battery is a new battery added inside the aircraft to power a system that was also added in the aircraft. So the battery system is only use to power the system when the aircraft is off. The reason why the system needs to be powered when the aircraft engine is OFF is because the system need to warn up and to a couple check before flight.
 

sghioto

Joined Dec 31, 2017
5,380
Are you asking or telling me it will not exceed 15volts?
On a 12 volt supply the voltage on pin 2 was appx 11 volts when the output was high.
In this edited schematic I added R5 to reduce the max voltage on pin 2 at appx 10 volts.
Added Rv1 to fine tune the set point.
Changed values of C1 and C2 for more pleasing flash rate.
1675473543303.png
 
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