On 07/28/2015 12:00 PM, Lee Hart via EV wrote:
So the T105 is $150/(6v x 75a x 1.75hr) = $0.19/wh.
The Sam's Club is $80/(6v x 75a x 1.75hr) = $0.10/wh.
I didn't check SAMs' battery claims. I had assumed less capacity than
T105s.
I'm not sure what your "all or nothing" replacement means. You can
replace individual batteries if they fail early.
It is pretty tedious to identify and change either a single lithium cell
or a lead battery. Also, if you have a bad lead battery or lithium
cell, you are likely to be near the end of it's mates. I am impressed
by how easy it is to add or replace ebike batteries. It is mainly a
matter of dealing with parallel rather than serial connections. With
serial, you break your pack to repair and you are down until you are
finished with your repair. You must have an entire working pack to be
functional. With parallel, you can likely "make do" with a single bad
battery and do the replacement much faster. Plug and un-plug SB50s or
similar.
Compare to 12 TS-LPF100s: about $1500 plus about $300 worth of BMS
stuff.
$1800/(12 x 3.2v x 100ah) = $0.47/wh. About 2.5 times the
cost/watthour of the Trojans, or 5 times the price of the Sam's Club.
They would have to last 2.5-5 times longer to reach the same cost/mile.
I used 100ah; but I doubt you can get even 75ah out of them with a 75a
load before the voltage falls under 2.5v/cell. I don't know how these
particular Thunderskys would test; but the older 90ah Thunderskys I
tested had significantly higher internal resistance than 6v golf cart
batteries. They weren't good for 75a continuous / 500a peaks; but more
like 25a continuous / 100a peaks.
I think you will find that more modern TSs are good for at least 2C.
Negative: nightmare of wiring maintenance, "all or nothing" major
replacement.
If you have a good BMS you should be able to replace individual cells.
Whether the BMS wiring is a "nightmare" depends on the situation.
I've been dealing with TS-LFP packs with miniBMS modules for many
years. I judge the whole thing to be a nightmare compared to the
integrated BMS/protection of an ebike battery.
$1425/(5 x 36v x 20ah) = $0.40/wh. That's barely any cheaper than the
Thunderskys.
The ebike batteries include integrated BMS/protection. Therefore, have
the possibility of being far more reliable/maintainable.
One unknown is the internal resistance of these small cell packs. Some
may be good; some horrible. Ebikes don't draw much current, but a golf
cart does!
The 20ah ebike batteries are SUPPOSED to be good for 30 amps. I
expected to need to use 3-5 in parallel. I was surprised to discover a
golf cart seems to run fine with 2. With the 12xTS-LFP100 pack, I've
observed a maximum 100-120 amps with non-alarming voltage sag. As
mentioned, I do not yet have an amphour counter on a ebike battery golf
cart.
I will not accept the contention that lithium batteries should be
limited to 50%.
OK; so that's your hypothesis. Now do the testing, and see if it's
correct.
That is outside my job description. If you wish to test, I am willing
to send you an ebike battery and one or two semi-good TS-LFP100s and/or
TS-LFP260s.
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