Re: rec tech mower

On Mon, 14 Apr 2025 22:48:59 -0400, Frank Krygowski
<frkrygow@sbcglobal.net> wrote:

Again, I'd love an electric mower, but I'm not aware of one with
sufficient run time to do this lawn. Also, I've read some complaints
that the (rather expensive) batteries last only a few years (like 3
years in some cases) before needing replacement.

Battery life is a complex problem.  For LiIon, the more energy (in
joules or watt-hrs) you drain out of or charge into a battery, the
faster it deteriorates.  You can make a mower where the battery lasts
many years, but you'll need to stop draining the batter at about 25%
SoC (state of charge) as well as stop charging at about 85% of full
charge level (about 4.1VDC with no load).  You'll also need to charge
slower than what the battery is capable of handling and use a motor
that uses far less power (watts) than what the battery is capable of
delivering. 

Currently (pun intended), battery powered tools are designed to
operate at just below the point where something will fail, usually the
battery.  With LiIon, both over and under voltage will kill the
battery.  Fast charging and fast discharging will accelerate
deterioration.  When larger numbers on the spec sheet sells more
mowers, then manufacturers will do what is needed to produce those
large numbers, even if it prematurely kills the battery.  If they
produce a mower or tool that lacks power, takes forever to charge, and
requires a physically large battery, the typical consumer won't buy
it, even if it promises a battery that lasts forever.

There's also the matter of not providing features that will extend
battery life but are missing in order to provide a low selling price.
What is needed is something like what can be found in RV batteries.
For example (in order of importance):
- LiFePO4 instead of LiIon
- BMS to equalize the voltage of each cell in the battery.
- MPPT charging (usually external).
- BMS for over and under voltage protection.
- BMS with overcharge protection.
- BlueTooth wireless for battery on/off, telemetry, SoC, etc.
- Modular construction to aid in rebuilding battery.

Electric mowers and tools might have a few of these features, but I've
never seen one that has all of them.  LiFePO4 and a BMS that equalizes
the cell voltages are probably the most important for best battery
life.  I've only seen a few LiFePO4 tools.  None of my DeWalt tools
have a BMS with cell equalization.


--
Jeff Liebermann                 jeffl@cruzio.com
PO Box 272      http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann      AE6KS    831-336-2558