Michael K Johnson wrote:
I already went with the ME1004 so I'm pretty much committed to a 48V system
for the soon-upcoming lawn mowing season; too late to start over.
Makes sense. Do what you can with what you've got (Teddy Rooseveldt, I
think). :-)
If I can't mow the whole lawn in one session, I can do front and back
yards on separate days.
OK; that can work. Depending on your mechanical situation, it may also
be possible to have two battery packs, and swap them. One charges, while
the other is in use. Kinda heavy; but it could be done like they do with
fork lifts: Batteries sit in a tray. Make two cart of exactly the same
height with a second tray of batteries. Slide the new set in, and the
old set slides out the other side. Latch it in place, and away you go. :-)
Thanks for pointing me back to AGM for heavier load tolerance, and to the
poster who mentioned Deka.
Deka (East Penn Mfg. Co.) makes fairly good batteries; but be warned
that they are expensive. I think David Roden mentioned their gel
batteries (Deka Dominator). Gels are great for long life, but poor for
high currents.
Their AGMs are the Deka Intimidator series. These are the ones you'd
want to use for high currents and short discharge times.
Lithium looks like it would be about $3K for cells alone, not
counting BMS or lithium charger. Looks like 4 Deka AGM Group 27s would be
about $1K. AGM would allow me to alter orientation so I could be more
flexible about placement. I imagine the AGMs will last at least 400 cycles,
200 cycles is a more typical life for AGMs. To get 400 cycles, you'd
have to restrict your depth of discharge to 50% or so per cycle.
which the Deka AGM is rated for at relatively deep discharge. I expect a
max of 40 full lawn mowing sessions per year, so depending on whether I
have to take one or two charge cycles per full lawn mowing, that's 5-10
years, conservatively. I'll accept that.
Just note that long life assumes that you don't do anything wrong in all
that time. Never run them completely dead, never overcharge them (which
most cheap chargers will do), etc.
Do I correctly understand that the SOC voltage levels for AGM and flooded
PbA batteries are the same, since the fundamental chemistry is the same?
Not exactly the same, but close. The biggest problem is that any sealed
battery has a very low tolerance for being overcharged. Once full, they
have no choice but to gas. In a sealed AGM, the gas has no place to go;
so it pressurizes the case. This opens the vents, and you lose water.
Water lost cannot be replaced. The more water that is lost, the shorter
the remaining life. When it runs out of water, the battery dies.
It is pretty common for commercial chargers to deliberately overcharge
the batteries. This maximizes the amphours you get per cycle; but also
shortens life. Thus, you find all sorts of UPS, alarm systems, etc. with
AGM batteries that only last 2-3 years. That's how long it took their
cheap chargers to dry out the battery.
And, responding to other posts... The trailer idea won't work for me
Ah well. Another great idea dashed to pieces by reality. :-)
--
We live in a society exquisitely dependent on science and technology,
in which hardly anyone knows anything about science and technology.
-- Carl Sagan
--
Lee Hart -- See my Xmas projects at www.sunrise-ev.com/projects.htm
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