After doing some research, I bought one of the new generation lightweight batteries for my 8A project, knowing that the e-bus performance would probably be poorer than the Odessey PC680 batteries that we currently use. Today I tested the duration of both the Odessey and the new Lithium Iron with a controlled 5.36 amp discharge to compare them side by side. Actually, the Odessey is a 3 year old battery with over 400 flight hours. The LiFePo is a Shorai LFX36A3-BS12, claiming "36 Ah Lead Equivalent". The Odessey is rated at 17 Ah. Here are the results:
The 3 year old Odessey survived 10 mins longer than the new LiFePo with twice the quoted Ah at this discharge rate.
My conclusion: the new gen Lithium batteries are light weight, crank the motor like crazy, but don't have the same capacity at low discharge rates, such as in an e-bus application. Per the graph, the are also less linear in their low current discharge characteristics than their lead acid bretheren, and tend to 'fall off the cliff' pretty quickly when they finally run out of juice.
Still, at 10 lbs weight savings and 90 minutes of e-bus performance, which I deem acceptable, it's going in the 8A.
About the test: to discharge the batteries I used a Optim Engineering CBAIII unit hooked to my laptop. This configuration allow one to precisely select a discharge current and a low voltage cutoff threshold; I chose 11v, which is where Garmin stuff tends to fall off. I charged both batteries fully before running the tests.
Here is a pic of the two batteries, close to the same size, the Shorai is slightlly smaller in height and length, but about 1/2" wider than the Odessey.
The weight difference is substantial: 15 lbs Odessey vs. 5 lbs for the shorai. The photo also shows the Shorai charger, a slick little unit that balances the individual cells as well as charges and stores the battery. My overall impression of the Shorai quality is good: well built, lots of hardware and self adhesive foam pads included. I''ll probably use some of this foam to dampen vibration. Total cost of the battery and charger is under $300 online.
The 3 year old Odessey survived 10 mins longer than the new LiFePo with twice the quoted Ah at this discharge rate.
My conclusion: the new gen Lithium batteries are light weight, crank the motor like crazy, but don't have the same capacity at low discharge rates, such as in an e-bus application. Per the graph, the are also less linear in their low current discharge characteristics than their lead acid bretheren, and tend to 'fall off the cliff' pretty quickly when they finally run out of juice.
Still, at 10 lbs weight savings and 90 minutes of e-bus performance, which I deem acceptable, it's going in the 8A.
About the test: to discharge the batteries I used a Optim Engineering CBAIII unit hooked to my laptop. This configuration allow one to precisely select a discharge current and a low voltage cutoff threshold; I chose 11v, which is where Garmin stuff tends to fall off. I charged both batteries fully before running the tests.
Here is a pic of the two batteries, close to the same size, the Shorai is slightlly smaller in height and length, but about 1/2" wider than the Odessey.
The weight difference is substantial: 15 lbs Odessey vs. 5 lbs for the shorai. The photo also shows the Shorai charger, a slick little unit that balances the individual cells as well as charges and stores the battery. My overall impression of the Shorai quality is good: well built, lots of hardware and self adhesive foam pads included. I''ll probably use some of this foam to dampen vibration. Total cost of the battery and charger is under $300 online.