First CuMoCo C130 delivered to a customer.

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PJD
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Joined: 11/22/2006
Points: 1241
Calender Life of Thundersky Cells?

Since the success of CuMoCo scooters is hinging on the Thundersky cells, and this is the only currently active CuMoCo thread, I thought I would do this report here. It would likely just languish in the batteries and chargers forum. Unfortunately I never gathered hard data, so this report will be rather qualitative.

Since June 2008 and August 2008 respectively, I have been running two 48 volt LFP40AHA packs (with an additional 12 volts of lead acid for a switchable "boost" mode) in my two e-maxs. The cells themselves are older - probably manufactured sometime in 2007. The cells use a early version of the Goodrum/Fecher BMS (per the Endless Sphere Forum) and never saw any abuse. They were stored half-discharged in a minimally heated garage (above freezing) in the winter. The hottest summer temperatures are about 86-90F (30-33C) or so. Two cells in one scooter and three in the other failed prematurely (lost capacity) and were replaced.

As of this report, one scooter has about 4000 km on the pack, and the other has about 9500 km on the pack. The performance loss with aging has been exactly the same for both packs - there doesn't seem to be a noticeable capacity loss, but the increasing internal resistance in discharging is very obvious. The cells are subjected to about 95 amps maximum discharge - about 2.4C. When first put in service, at 60F, the voltage at max. discharge sagged to about 3.1 volts per cell or maybe a bit better. Now, at 60F, they sag to about 2.90 volts per cell. At colder temperatures, close to freezing, they perhaps sagged to 2.95 volts per cell, this spring, in near freezing temperatures they were sagging to 2.7 to 2.75 volts per cell or so. At higher temperatures, the mid 80's or so, the voltage sag is not still apparent.

I suspect the pack performance will probably be pretty marginal once cool weather returns this fall - which will mean i got 3 seasons of use - but the problem will be low voltages and reduced power output and speed, not necessarily reduced range.

So, here are my tentative conclusions:

1. The usable cell life of Thunderskys is going to be time, not cycle dependent for most users.

2. The usable cell life is highly dependent on the temperature the pack will be used at and the discharge rate. In a hot climate and lower current draw (2C or less) the pack life may be much longer than it is in my situation - then again, the cells may degrade faster if stored at higher temperatures.

3. From a design standpoint, designing for discharging at the lowest C-rate, and delivering new scooters with cells with the freshest manufacturing dates is going to be important for getting satisfactory life.

4. The history of Thundersky (and it's various licensees) has been of continuous improvement over their rather poor performing original products. So, it is a reasonable hope that quality continues to improve.

Mike or John, what is the max pack discharge rate on the CuMoCo scooters? What are your experiences with Thunderskys so far?

Matt, you probably have more experience with Thundersky as I do (and using them in a hotter climate). Any comments or experiences of your own?

- Paul D.
Pittsburgh, USA

Reid250
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Joined: 12/09/2009
Points: 107
Re: Calender Life of Thundersky Cells?

So, here are my tentative conclusions:

1. The usable cell life of Thunderskys is going to be time, not cycle dependent for most users.

2. The usable cell life is highly dependent on the temperature the pack will be used at and the discharge rate. In a hot climate and lower current draw (2C or less) the pack life may be much longer than it is in my situation - then again, the cells may degrade faster if stored at higher temperatures.

3. From a design standpoint, designing for discharging at the lowest C-rate, and delivering new scooters with cells with the freshest manufacturing dates is going to be important for getting satisfactory life.

4. The history of Thundersky (and it's various licensees) has been of continuous improvement over their rather poor performing original products. So, it is a reasonable hope that quality continues to improve.

Mike or John, what is the max pack discharge rate on the CuMoCo scooters? What are your experiences with Thunderskys so far?

Matt, you probably have more experience with Thundersky as I do (and using them in a hotter climate). Any comments or experiences of your own?

- Paul D.
Pittsburgh, USA

Hi Paul;
My scooter was manufactured 15/11/2008 so we can assume the TS cells are older than that. I have 20 X 40Ah Cells. NO BMS. 3 of them were much lower than the other 17 when I first got the scooter. As instructed by friends who have been playing EV for 20+ years, I individually charged the 3 up to the discharged voltage of the 17 and then charged the entire battery. They were all very close, @ 3.75V. After 10 cycles, the charger started giving errors and on checking the discharged state, I found the same sick 3 cell were 2.7V while the 17 were @ 3.45V. Not to worry I was advised, so I again brought the 3 up to 3.45V and put the pack on the charger. They all came up to @3.75V again. Three more cycles and the 3 are down to 2.7V with the rest @ 3.45V. I am too busy to fool with it right now, so I sit and ponder which BMS to purchase or to purchase 3 new TS cells, or to keep playing the musical cell tune until we have a cost effective BMS solution ($100) available in the US, as is now available in China and being shipped with all TS and GBS cells. A rather strange fact, is I was warned by the supplier of my TS cells, not to buy TS cells on eBay or from any HK seller as he told me sick TS cells (seconds) do not get scrapped, but are sold off at lower prices and end up who knows where. This from the guy who supplied my 3 sick TS cells. Inscrutable Ornamental! A further puzzle is I now note many of the US suppliers of TS cells last year, no longer carry them, but have GBS instead. Much better they tell me. Much better what? Quality? Or in the grand fashion of free enterprise, greater MARGIN? EV's will remain a joke, with too many disappointed experimenters until such basic problems are solved. Larry Lunchbucket, who never checked his engine coolant or transmission fluid, will not find an EV of any description, even a fun hobby, never mind useful transportation, until it becomes "plug & play". Computers did not fly on DOS. It wasn't until Mac and Windoz came along that they took off. As a guy who learned to wire racks on punch card sorters in 1958 and was forced back to college by the invention of the keyboard and a CPU, I think EV's are a fun hobby so far.

Mik
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Joined: 12/11/2007
Points: 3726
Re: Calender Life of Thundersky Cells?

PJD wrote:

Since the success of CuMoCo scooters is hinging on the Thundersky cells, and this is the only currently active CuMoCo thread, I thought I would do this report here. ...
...
...

Bad idea IMHO!

Good to report and discuss it, of course, but not in this thread. It has a specific topic and you are hijacking it!

Your post about the batteries is however good enough to attract some attention and replies on it's own merit, I would think. I don't think it would wither away unnoticed if you posted it somewhere more appropriate.

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antiscab
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Joined: 07/07/2007
Points: 1598
Re: Calender Life of Thundersky Cells?

PJD wrote:

Matt, you probably have more experience with Thundersky as I do (and using them in a hotter climate). Any comments or experiences of your own?

Hi Paul,

I haven't heard from you in a long time.
My own Emax is now out of service.
I took all the goodies off it, and sold the frame and body on.

my 40Ah TS cells are down to around half of original capacity (after 22'000km of use).

This is in contrast to the 200Ah cells (manufactured 2006) in my friends mustang which have lost around 10-15% of original capacity.

a few things i noticed:
during dissasembly of my 40Ah pack, I noticed the surfaces between the interconnects and the cell terminal had surface corrosion.
after sanding them off, I noticed reduced sag. (I now use noalox to stop that surface corrosion happening again).

when I was playing with my newer cells, I accidentally left it floating on a charger at 3.8v for ~55 hrs, and it leaked.
I suspect that leaving cells at float for extended periods is bad for them.
This was another difference between my pack and my friend 200Ah cells.

thinking back, the chargers I used for my pack were intended of lead acid, so would float at the end of charge.
I suspect that may have played a part in the packs capacity reduction.

my discharge rate was ~55A (1.4C) continuous and 200A (5C) peak.
my friends discharge rate was 50-100A (0.25C - 0.5C) continuous and 600A peak (3C)
he too is noticing increased sag, however, since nothing was really recorded back in 2006 this is just by feel.
a brand new cell manufactured today does seem to sag less than a brand new cell manufactured back in 2007.

neither of us worried about temperature, so I don't have any data there.

Matt

__________________

Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah
Vectrix 60Ah Lithium Tyres Fuel Registration Insurance cycle analyst replacement TC Charger
conversion
Spent so far: $5800 + $7000 + $1720 + $960 + $320 + $720 + $140 + $600
Cost to do it again: $2500 + $5600 + $1720 + $960 + $320 + $720 + $140 + $600
Cost for a Petrol bike:$6000 + + $1440 + $6000 + $800 + $1400 + $3200 servicing
Total spent: $17260
Total to do again: $12560
Total to have used a petrol bike: $18840
Total distance travelled so far: 79'120km

PJD
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Joined: 11/22/2006
Points: 1241
Re: Calender Life of Thundersky Cells?

OK, at risk of double posting, I will post this in batteries and chargers.

I wanted to get John H's attention, he really needs to be careful about promising longer battery pack life in the CuMoCo products than they will really get. TS cells continue to go down in price, but replacing the pack every 3-4 years or so is still a hefty expense.

jdh2550_1
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Joined: 07/17/2007
Points: 2338
Re: Calender Life of Thundersky Cells?

Hi All,

I'm actually on vacation in the UK at the moment (visiting the folks in Shrewsbury) and so I've missed this entire set of new posts. I fly home tomorrow and so you can expect a post from Erik or I in the next couple of days.

All the best,
John H.

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Remember: " 'lectric for local. diesel for distance" - JTH, Amp Bros || "No Gas. No Worries." - JDH, CuMoCo || "Make Volts Not War" - anon.

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