Help me design a LiFePO4 battery for my homebuilt airplane
- Thread starter cringely
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The main concern is having enough capacity to run critical systems if a main bus/alternator drops. Having a second smaller drop-in LFP (LOW c rate) may be called for. Set up the critical system to be powered by either battery. That avoids the need for a BMS bypass as you will hopefully have enough redundancy with two separate batteries.
Yep but there's a few big factors at play here: a second battery will weight more than a relay (or even two), it would make a more complex system (so more PoF, more possible human errors while doing maintenance, etc...) and I would not put a Li battery without a BMS so you're back to square one.
Also the starter is usually considered as a critical load so you'll need a battery big enough to handle that.
Also the starter is usually considered as a critical load so you'll need a battery big enough to handle that.
cringely
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I'm trying to absorb all of this (remember I'm an idiot) so this is really a place-keeper reply and I'll come back with something more substantial shortly.
My plane has foldable wings and will live in a 20-foot enclosed car carrier trailer with its own 12V solar system including a 30 amp-hour lithium iron phosphate battery and an MPPT charge controller, so maintaining the aircraft battery should be easy.
The alternator is a 35-amp Denso that is used on everything from Honda Civics to Kubota tractors. There is a 70-amp version of this same alternator that I have on the shelf and will probably install.
My Skytec starter is rated at 80 amps. Also, I now have the 100-amp BMS to go with these cells.
My plane has foldable wings and will live in a 20-foot enclosed car carrier trailer with its own 12V solar system including a 30 amp-hour lithium iron phosphate battery and an MPPT charge controller, so maintaining the aircraft battery should be easy.
The alternator is a 35-amp Denso that is used on everything from Honda Civics to Kubota tractors. There is a 70-amp version of this same alternator that I have on the shelf and will probably install.
My Skytec starter is rated at 80 amps. Also, I now have the 100-amp BMS to go with these cells.
WoodsieLord
New Member
[...]"my homebuilt airplane"[...]
I've just closed kerbal space program after playing for a little, I open the forums and there it is the picture of your own airplane... I'm in awe.
Sorry for the off-topic, I couldn't help it. Cheers!
Hedges
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Oh yea ... "airplane" means "altitude"
"altitude" means "cold"
"cold" used to mean icing of carburetor, so I used this thing called "carburetor heat"
... think you just might need to rig up "LiFePo4 heat"
Or is it going to be located somewhere warm and comfy? Do you have a climate-controlled cockpit?
Probably a thermostatically controlled, electrically powered heat tape is in order.
"altitude" means "cold"
"cold" used to mean icing of carburetor, so I used this thing called "carburetor heat"
... think you just might need to rig up "LiFePo4 heat"
Or is it going to be located somewhere warm and comfy? Do you have a climate-controlled cockpit?
Probably a thermostatically controlled, electrically powered heat tape is in order.
Having the ability to restart the engine while in flight is handy. I am not sure that a jump-starter would be ideal.
Yes you can build your own battery, but it does not mean it is a good idea. Too big of a risk. As you know you can't walk or swim home from 8000 feet.
Go with the Concorde battery and get a battery maintainer. If you can't afford to change a $260 battery every couple years you should get out of aviation and find a new hobby.
I know this sounds gruff, but too many people have died in aviation making poor choices. Yes, making your own battery would be a poor choice.
D
Deleted member 9967
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You might consider lifepo batteries for their safety.
Look at the videos in post number 10 here.
https://diysolarforum.com/threads/switching-to-lifepo4-advice-needed.13820/#post-155970
They won't catch fire.
They are good down to minus 20 Celsius for discharge.
And almost as small as the explosive regular lithium for the same charge.
Hopefully this helps.
Look at the videos in post number 10 here.
https://diysolarforum.com/threads/switching-to-lifepo4-advice-needed.13820/#post-155970
They won't catch fire.
They are good down to minus 20 Celsius for discharge.
And almost as small as the explosive regular lithium for the same charge.
Hopefully this helps.
D
Deleted member 9967
Guest
The batteries for my mobility scooter are 24 volt, 280 Ah and only weigh 90 lbs.
8 cells total.
Maybe this will help you decide.
8 cells total.
Maybe this will help you decide.
" IO-320-B1A" means Injected Opposing 320 cu-in (forgot the suffix stuff long ago), so no carbies there.
Carb heat, when applicable. is not done by the battery. You open a butterfly valve on the carb box that allows the carb to suck in air fed from a shroud around the exhaust.
Hedges
I See Electromagnetic Fields!
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I didn't recognize the engine designation.
The planes I flew were my age or older, and I haven't piloted a plane since grammar school.
Yes, I know carburetor heat is ducted air heated by exhaust to warm the carburetor, to prevent icing.
My point was his battery could become too cold during flight to accept recharging, so probably needs a method for heating. Not as many BTUs as a carburetor which has frigid air being sucked through it. Charging means alternator/generator is operating, so electric heating of battery seems most practical.
I think he was saying that regarding to the fact you can't charge LFP batteries under 0 °C.
But most GA airplanes aren't made to fly in icing conditions anyways. The carburator can ice even with well above 0 °C temps because it has a venturi which can drop the intake air temp by 20 to 30 °C in extreme cases.
Edit: @Hedges was faster... ^^
Well weight and balance are really important on a plane and the battery is a heavy and easy thing to move to adjust the W&B during the design stage
Indeed it is, but another factor in play in flight is the pitching moment created by the main wing. The tail is a favored place to put the heavy battery because it helps offset the pitching moment and requires less down force on the horizontal stabilizer and less total aerodynamic drag.
There is a lot of radiant heat from the engine, and all intake air is ducted through the baffles down through the open bottom of the engine and into the cowl. The cowl has a cooling air flow exit, but everything firewall forward gets plenty warm.
Doubt the aircraft in question has de-icing boots, so I don't think 0°C charging is an issue..
Doubt the aircraft in question has de-icing boots, so I don't think 0°C charging is an issue..
Hedges
I See Electromagnetic Fields!
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BiduleOhm's point was that carburetor gets much colder than ambient, so we could need carburetor heat to prevent icing but when else would get below 0C
I think a plane could operate well below that temperature (my car certainly does, just at 5000' in the winter) so long as moisture isn't causing icing of wings. If it does you'd have to drop to lower altitude. (If you don't, you will)
Here aircraft are allowed up to 20,000' without pressurized cabin or oxygen, I think. (no, that's apparently VFR limit)
Chart indicates standard temperature at 8000' is 0C:
www.engineeringtoolbox.com
I think a plane could operate well below that temperature (my car certainly does, just at 5000' in the winter) so long as moisture isn't causing icing of wings. If it does you'd have to drop to lower altitude. (If you don't, you will)
Here aircraft are allowed up to 20,000' without pressurized cabin or oxygen, I think. (no, that's apparently VFR limit)
Chart indicates standard temperature at 8000' is 0C:
Air Temperature, Pressure and Density vs. Altitude
Elevation above sea level and air temperature, pressure and density.
www.engineeringtoolbox.com
Last edited:
Now that was funny
That seems really high. Usually the max altitude is 12000 feet as it's the hypoxia limit.
12,500 is the unpressurized limit w/o oxygen. up to 14,000 ft with oxygen or 30 minutes max without. I ran at 13500 for 30 minutes between Vegas and PHX to test it. I didn't care for it. Plus, that high... 100kts feels like hovering.
EDIT: And yes. That was quite funny.
EDIT: And yes. That was quite funny.
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