Finding an ESC for a LiFePo4 Battery

Question

I have a project that uses 12S LiFePo4 batteries, and I need an electronic speed controller. The main problem I have is that pretty much all the existing ones I've found are designed to work with Li-poly batteries.

I've seen this post: Will LiFePo4 work with ESC for LiPo?

But the concern I have is that will Li-poly ESC's actually work for LiFePo4's when you consider that they have different cutoff voltage's.

Li-poly has shouldn't be discharged at anything less than 3.0V, where as LiFe's should go to 2.8V and that's a major bottleneck considering that they have a nominal voltage of 3.3-3.2V.

If someone could point out to me how I can make this work, or if I'm wrong / recommend an ESC, etc. It would be greatly appreciated.

Any answer helps!

Answer 1

It is generally a bad idea to let a motor/speed control decide when your batteries need protecting, even if you use a LiPo ESC on LiPo batteries, the monitoring should be separate and inside the battery pack.

For a couple of simple reasons:

1. On a collision you want any shorts to be protected from the battery outward, even if LiFePO4 is much safer vis-a-vis explosions.
2. A "remote drain" deciding to throttle or shut off can cause oscillations through wire resistance and inductance that end up being more harmful.
3. A power drain deciding to shut off creates the invalid "feeling" everything is protected, when other devices can drain enough to finally kill the battery.
4. When a battery is replaced by another chemistry you don't have to change every other component (the only non-safety-related point).

No project, ever, anywhere using a rechargeable battery somewhat smartly or professionally should off-load the UVLO (under-voltage lock-out) detection to individual devices, but have it at the battery. The one exception is a single bespoke PCB in a fully qualified housing with a rechargeable battery, such as tiny Bluetooth headsets, where the constitution of the innards will not change outside of a complete design path with meetings and verifications.

So, do as aDub says: Get battery protection and turn off the UVLO in the controller.

Answer 2

Many ESC can have the auto shutdown switched off, and battery level can be ignored in the FC - this function can be moved to a separate voltage monitor for auto-land etc, or to a purely audio/HUD for the pilot to respond to.

You can of course flash most ESCs and use your own code, or as many do, SimonK's "stripped down, and quicker response code", lots of info on this on the web. Try places like the Hobby King forum.

[edit] The link you posted seems to confuse the additional function of a BEC (battery eliminator) with the ESC itself: many purest will use ESCs without a BEC and use a separate BEC for powering other onboard equipment. He is generally right about linear and switching BEC's though.

ESC's don't really care what power source you use providing you do not exceed voltages specified - you could use a bench power-supply rather than a battery. The 3S etc. naming convention is just an idiots guide