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

My situation - I can store the tractor in my garage or basement.  Both are temperature controlled. Basement is about 70-75 year round.  Garage gets into the 80s in summer, rarely below 70s in winter.  I'm in CT.  For snow, I use my Dynahoe, because it has a heated cab, and it's not great to let it sit all winter either.  The snow thrower also doesn't like a stone driveway much.  I imagine it would work great with the lithium batteries.
I would not ever run lithium batteries, especially the size needed for an ET without a BMS.   The BMS monitors temp, current, voltage [under, over, and difference] of each cell, state of charge, and cuts out if anything goes out of range.   I charge before I plan on running the machine, and if I run it down below 50%, just put enough back in to get to around 50%.   I have fans that run at temps above 85 degrees, mostly just for if I run it outside on a hot & sunny summer day.  The load an ET puts on the batteries I have is nothing for them, one set can supply 150 Amps continuous, 600A for 10 seconds.  I am running 2 sets in parallel, for more run time, and shallower cycling.   About 140 AH capacity.  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.  Lion are also a lot more efficient as far as the power lost in the charge / discharge cycle.
For the batteries and BMS, I spent around what it would cost for a set of high end LA batteries.  But these should outlast them by quite a bit.  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.
The batteries, I bought from Batteryhookup.com.  They get surplus / used, and test them before listing them, so you know how they perform..
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.  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.
If extreme temperatures are a problem, LTO would be the best option - but they are a lot more $. 

Dave


On 2/9/2023 8:26 AM, David Roden wrote:

For those who've done this, it would be interesting to hear what advantages
a lithium conversion confers.  I can see some advantage, but not nearly as
much as in a road EV, and some possible negatives.

I guess you'd get significantly more running time for a given battery
volume, if that's something you need.

In exchange you get a battery that requires a much more sophisticated
charger and cell-level management - not just for cycle life, but for
*safety*.  All that gear is pricey.

You also have to pay more attention to temperature.  Lithium batteries
degrade faster at full charge than when they're around 50% charge or less.
And the higher the temperature, the worse this effect.

So you want to charge just before using the tractor, rather than just
after.  And what's the summer temperature in your garage?

Lithium will also degrade, maybe be damaged, if it's charged when it's
below freezing.  That's not such good news for winter snow moving.  A
battery that's been used hard will be warm internally -  but if you charge
it right after plowing or snow throwing, then you have to store it at or
near full charge, also not so good for it.

Factory EVs handle the temperature restrictions with micro-controlled
thermal management systems, many times using liquid coolant.  What
equivalent are you going to build for your ET?

IMO, lithium in an ET would be a better choice in a temperate region - that
is, one with winters that seldom get below freezing, and summers that don't
often exceed 80 deg F or so.

Finally, you *want* weight in a tractor, n'est-ce pas?  So the weight
reduction would actually be another downside.

My lithium info is a few years old, so maybe modern batteries have fewer
restrictions.  But I would suggest doing some further research and
consideration.


David Roden - Akron, Ohio, USA

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