The following data is from my inverter manual for my inverter that is use at a
remote cabin here in Montana which uses the old EV battery from my EV which ran
8.5 years in the EV and another 10 years at the cabin.
The T-105's 200 AH battery has a usable AH of 100 AH at 50% SOC at the 20 hour
rating or 200 AH / 20 hrs = 10 amps. 50% SOC = 200 AH/2 = 100 AH.
We normally do not drive a EV at battery ampere of 10 amps unless it a bike
which has two 20 ah 12 volt batteries in my bike. They were on twenty something
dollars for them.
The Reserved Minutes of the T-105's is listed at 115 RS @ 75 Amps, therefore:
The Formula:
115 Reserved Minutes / 60 minutes = 1.916 hours
75 amps x 1.916 hrs = 143.7 ah
50% SOC = 143.7 / 2 = 71.35 ah
When I was using these batteries back in the 80's with a battery pack voltage
of 216 volts, my EV would use about 3 ah per mile using about 70 ah.
Roland
----- Original Message -----
From: Lee Hart via EV<mailto:[email protected]>
To: Electric Vehicle Discussion List<mailto:[email protected]>
Sent: Tuesday, July 28, 2015 11:00 AM
Subject: Re: [EVDL] Lead GC battery capacity
Willie2 via EV wrote:
> Somewhat against my will, I just did some lead battery shopping. T105s
> are about $150. The "minutes at 75 amps" rating seems most appropriate.
> That would be just under 100 ah. From what you say, it appears those are
> usable amphours. SAMs batteries, with presumably less capacity and
> longevity, are about $90. So, a pack of six T105s would be about $900.
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.
> Negatives: corrosion, watering, lower performance as SOC decreases,
> perhaps 1/3 the life of lithium, "all or nothing" major replacement.
Life would be about 800 cycles for the Trojans, and about half that for
the Sam's Club batteries (with a 75a load, discharged to 1.75v/cell,
barring any abuse from over-charging, over-discharging, or incorrect
watering).
I'm not sure what your "all or nothing" replacement means. You can
replace individual batteries if they fail early.
> 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.
> 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.
> Compare to 5 20ah ebike batteries @ $285. Total: $1425. Experience so
> far indicates as few as 2 20ah ebike batteries can be used at a cost of
> $570.
$1425/(5 x 36v x 20ah) = $0.40/wh. That's barely any cheaper than the
Thunderskys.
> The longevity of ebike batteries is a BIG unknown here.
Yes; you'd have to test to know for sure.
> I believe it is likely that the above can be scaled to larger vehicles.
> If the golf cart projects are successful, I will be exploring higher
> voltages and capacities on larger vehicles.
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!
> 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.
As you say, these Ebike batteries aren't all that expensive. Buy one,
and rig up a life tester. It would:
- Discharge the battery with a load representative of what your actual
load will be, until it reaches your desired "dead" cutoff voltage.
- For lead-acids, 1.75v per cell under load is usually used.
- For lithiums, there are no standards. Try 2.5v/cell as the cutoff.
Or go lower if you think life won't be reduced by deeper discharges.
- Charge the battery to whatever fully-charged criteria you expect
to use in your application.
- For lead-acids, "full" is typically when the current falls to 4%
of its amphour rating at 2.5v/cell.
- For lithiums, again there are no standards. Maybe use the "free"
charger/BMS that comes with the Ping cells? Or for LiFePO4 cells,
try 3.7v until the current falls under 4% of its rated AC capacity.
- Let it cycle, until the capacity falls to some reasonable fraction
of its original capacity.
- For lead-acid, 80% of original capacity is usually used. You can
obviously use them longer; but without a BMS, the capacity usually
falls fast once some cell starts getting weak.
- For lithiums, you can use the same 80% limit, or keep testing to
see what happens if you use them longer.
--
A truly excellent politician will tell you everything you want to hear.
A truly excellent engineer will tell you the truth. -- D.C. Weber
--
Lee Hart, 814 8th Ave N, Sartell MN 56377,
www.sunrise-ev.com<http://www.sunrise-ev.com/>
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