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Electric Stunt => Gettin all AMP'ed up! => Topic started by: Howard Rush on January 07, 2021, 10:54:31 PM
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I'm involved on the periphery of a small, full-scale electric airplane project. This airplane will fly for an hour or so, and takeoff will use more power than cruise. For a given battery capacity, battery weight increases with max discharge rate (number of C's). Weight is a big deal for this airplane. Should we consider having a supplementary (or complementary) high-C battery for takeoff?
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Potentially. What battery chemistry do you plan on using? For weight savings, I am finding NMC li-ion to have amazing Wh/kg. Depending on how quickly you're needing to finish the project, Molicel is introducing some amazing large products (individual cells) at the end of this year or q1 2022. There's also the larger cells with high ah ratings with 300a individual discharge rates. If you had a decent estimation on max kw or a few other base numbers, I could throw in an estimation for a battery spec.
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As an example, NASA is currently Molicel's largest customer for the P28B cell, for its unprecedented discharge capability in a 2.8ah cell. Just as an example of current battery trends.
So, a 420 pound calb lifepo4 pack (30s2p) can yield a maximum of 154kw with a 200ah rating. That could possibly give you something to think about.
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25 kW-hr, 40 kW max. That's not very many C's. Candidate battery is two Zero motorcycle batteries.
Thanks.
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Howard,
Will you be flying it?
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I was in the neighborhood with the voltage then. You'd be looking at a nominal 104.4v, or a 29sXp pack. Depending on cell size will give us the required "p" stack number. You'd be looking at a custom pack, plus BMS and charger. Seemingly simple enough.
The pros of the zero pack: very well tested, great information out there, very safe. The weight is nice, but could be lower without their proprietary case.
Pros of a custom pack: getting the kWh you need, and building in safety percentages. Getting the lighter weight. Ability to run any type of connection to the motor controller, meaning flexible mounting options.. Most likely, a lower start up cost. The zero packs are almost $3000 each plus a $600 charger. Which the charger price is actually pretty decent. In aviation, I'm sure this point on price is the least weighted for a decision, though.
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There is some stuff on you tube. I will occasionally watch stuff on homebuilt electric this is one i saw recently https://www.youtube.com/watch?v=hp7JcmwKQcU&list=PLAIipq7EZswu1yOYyeFLZ0QKvx8sPOCvA&index=1
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I assume you are using some kind of a brushless out runner motor with a 3 lead speed controller. Therefore you have throttle control. I would think that full throttle is takeoff power. Once airborne you go to cruse power. Battery, motor, prop, and speed controller needs to handle take off power and will surly handle cruse. Any other setup will add complexity and reduce reliability. The best approach is always the KISS approach. LL~