Re: (ET) Retofit a moderm Electric riding mower Battery pack to fit an ET

["David Roden" <etpost drmm net>]

On 10 Feb 2023 at 0:37, David Tiefenbrunn wrote:

> I would not ever run lithium batteries, especially the size needed for
> an ET[,] without a BMS.  

Agree 100%.  There are folks out there who omit the BMS and "bottom
balance."  In effect, the owner is the BMS.  This works - until it doesn't.

Lead batteries are quite forgiving of careless treatment and nevertheless
can have some rather noisy accidents.  There is a stunning amount of both
power and energy in most lithium batteries.  And with the exception of
LiFePO4 they are far more volatile than lead when mistreated.

Can you say "flammable electrolyte" and "self-oxygenating fire"?  You
cannot put out a lithium battery fire with a foam extinguisher, only by
cooling it with thousands of gallons of water.

Every lithium powered device made by a responsible manufacturer has some
kind of BMS.  Maybe sensible manufacturers know something that the bottom-
balancers choose to ignore, eh?  Unlike the ones that made some of the
infamous hoverboards.  The hoverboards that caught fire didn't have BMSes.

Yeah.  Use a good BMS.  Or park your EV outside, well away from structures.

> With Lithium, you can use almost all of the capacity, unlike
> LA, which varies widely on the load current.   LA AH ratings are for a
> 20Hr rate, which is a lot less than an ET draw at. 

True, but the C20 lead capacity isn't the number ot compare.  You want to
use the reserve capacity for comparison.  For golf car batteries, this is
the capacity at 75 amps

> Lion are also a lot
> more efficient as far as the power lost in the charge / discharge cycle.

Lead battery charging is veryclose to 100% efficient between 0% and 80%
SOC.  You do lose some energy to electrolysis and heating in that last 20%.

> For the batteries and BMS, I spent around what it would cost for a set
> of high end LA batteries. 

That really surprises me, but then today's lead batteries cost a lot more
than they used to.

> But these should outlast them by quite a bit.

That probably matters more in a road EV, which stresses its battery more. 
>From what I hear, flooded golf car batteries last about 10 years in an EV.
The Deka Dominator gel batteries in my ET were 25 years old when I sold it.
 They were declining by then, but still had about 1/2 to 2/3 original
capacity.


> No messing with refilling water.  No more acid mist eating the
> steel, and my floors when the LA get older, and the mist collects and
> drips out the drains.

Also true of gel and AGM lead.  Admittedly, those cost more than flooded
batteries.

> The batteries, I bought from Batteryhookup.com.  They get surplus /
> used, and test them before listing them, so you know how they perform..

Interesting.  But do you know how many cycles are on them, and how long
they're likely to keep working for you?  Used batteries can be a real
gamble.

> Remember how you ET runs for the first 15 minutes or so with a brand new
> set of fully charged LA batteries just off the charger? With the 10
> series Lion cells, it runs like that for about 80% of the full charge,
> and only barely starts to slow a little near the end. 

This is also true of nickel cadmium batteries, such as Christopher Zack's
BB600s.

> I have the BMS
> set to cutoff with a good margin before the bottom, to extend life, and
> also, as a "get back to the charger" warning, so I can get a couple
> minutes more run if I loose track of time / charge.

Sensible.

> If extreme temperatures are a problem, LTO would be the best option -
> but they are a lot more $.

I don't know what LTO is.  Can you explain please?  Thanks.

To be clear, I'm not dismissing lithium batteries.  I've used them for some
projects and they've served well.  They are outstanding where minimal
weight is critical.  I'm just not totally convinced that they confer that
much benefit over lead batteries in an ET.


David Roden - Akron, Ohio, USA

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