# TS 100A LiFePO4 Sag



## T1 Terry (Jan 29, 2011)

I think Thundersky cells drop to 3v as soon as any load hits, at least according to their charts anyway, anything above that appears to be a surface charge. So dropping from 3v to 2.84v isn't a big drop.

T1 Terry


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## EVfun (Mar 14, 2010)

bruceme said:


> Setup: 44 x 100AH Thundersky
> 
> Per cell that's 2.8v from 3.2v average. At 2.5C does that sound right?
> 
> I know my max current isn't over 250A as that's the breaker I run, and never over 300A as that's the fuse I run.


It sounds a little high for 2.5C, but older TS cells sag more than newer ones. I think that is true for all the makers of large format LiFePO4 cells. The manufacturing process has been improving over time, resulting in more capacity, longer cycle life, and decreased internal resistance.

Don't be so sure you aren't drawing over 250 amps based on your breaker. A 250 amp breaker is likely to pass 500 amps for 30 seconds before letting go. A 300 amp fuse is likely to pass 600 amps for 30 seconds before opening. 

If you are drawing 250 amps at 125 volts you have about 36 horsepower on tap.


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## bruceme (Dec 10, 2008)

Yup, I know that about breakers and fuses. I suspect i'm pulling perhaps up to 300amps absolute ceiling. All my components are rated for 500amps, but my controller has a reputation for smoking before it's spec'd limits (DCP Raptor 600) 600 amps/156V. So I dial down the limits to 250A @ 140V. I'm not sure how my Warp 9" does with these numbers. I could look it up, but I suspect it's right in-line.

-Bruce


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## dimitri (May 16, 2008)

In my experience its not unusual for TS cells to dip to 2.8 under 3C load in the middle of SOC range. I limit my battery current to 2.5C to prevent deep sags and associated heat accumulation.


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## corbin (Apr 6, 2010)

dimitri said:


> In my experience its not unusual for TS cells to dip to 2.8 under 3C load in the middle of SOC range. I limit my battery current to 2.5C to prevent deep sags and associated heat accumulation.


Hey dimitri -- Do you have any data on how this might affect cycle life to have the cells regularly dip to 2.8v?

I'm in a similar boat with my 200Ah cells; they tend to dip quite low (probably 2.8) when at 50% SOC, AND if it is cold out (i.e.: 40-50F). This morning it was probably about 35F and my cells were not as happy (the Elithion BMS was giving low voltage lights). I may have to heat my cells at night to keep the resistance down when I drive away in the morning.

-corbin


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## pm_dawn (Sep 14, 2009)

Hi !

I have had my 40 TS LFP160 down to 89v during extreme cold. -27degC and 1.7C load.

Today I measured 124v at 50A load and 108v at 270A load.
It was about 0 degC.

They really like warmer weather!!

Anyone knows about if the LYP are performing better ?

Regards
/Per


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## corbin (Apr 6, 2010)

pm_dawn said:


> Hi !
> 
> I have had my 40 TS LFP160 down to 89v during extreme cold. -27degC and 1.7C load.
> 
> ...


I don't run in that cold of weather, but my LYP cells also don't like the cold weather. I have my BMS to give a voltage warning when less than 3.0v, and to hit a buzzer when it is less than 2.8v. I hit the buzzer once (for half a second) on an early cold morning accelerating rather softly up a hill (~200amps?). 

I need to drive with a computer attached to the BMS and log some values. 

-corbin


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## bruceme (Dec 10, 2008)

corbin said:


> Hey dimitri -- Do you have any data on how this might affect cycle life to have the cells regularly dip to 2.8v?


I suspect you won't find such data... but if you running a BMS that disengages at that limit probably helps a lot.



corbin said:


> I'm in a similar boat with my 200Ah cells; they tend to dip quite low (probably 2.8) when at 50% SOC, AND if it is cold out (i.e.: 40-50F).


That's my whole winter... Bellow about 40F, they just act "limp", voltage sags under even light loads and amps must go up to compensate. They're better than Lead, but I was hoping for more myself. 

So realizing I hit a wall a couple weeks ago I finished moving my batteries into a sealed, insulated and heated box in the floor of the trunk. It's a 36"x28"x10" cavity cut into the floor made of aluminum sheet. I insulated the bottom and sides with 1" foundation insulation. I took an additional aluminum sheet and RTV(high temp silicone) glued to it a 800-watt "soil heater" which has a preset 70F thermostat built-in the loop. This extra floor sheet supports the batteries and keeps them from crushing the foam and it spreads the heat of the cable. I had a lot of logistical problems with the OO-Gauge cabling, local battery shop was awesome! Total project cost was about $150 and it took about 40hrs of work.


Here's a link to get the heater cabling, I've tried many options here, I like this the best as it's simple and low-power:

http://growerssolution.com/page/GS/PROD/econcables

I bought the 6' length, plenty long. I currently have it dangling out to be plugged in the wall at night, but I could easily connect a female NEMA connector so it could be attached to the 144v pack as well.

-Bruce


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## corbin (Apr 6, 2010)

bruceme said:


> I suspect you won't find such data... but if you running a BMS that disengages at that limit probably helps a lot.
> 
> 
> 
> ...


Cool Bruce! do you have any pictures?

corbin


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## bruceme (Dec 10, 2008)

corbin said:


> Cool Bruce! do you have any pictures?


Yup, I updated my garage entry last week.

http://www.diyelectriccar.com/garage/cars/274


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## tomofreno (Mar 3, 2009)

> So realizing I hit a wall a couple weeks ago I finished moving my batteries into a sealed, insulated and heated box in the floor of the trunk. It's a 36"x28"x10" cavity cut into the floor made of aluminum sheet. I insulated the bottom and sides with 1" foundation insulation. I took an additional aluminum sheet and RTV(high temp silicone) glued to it a 800-watt "soil heater" which has a preset 70F thermostat built-in the loop. This extra floor sheet supports the batteries and keeps them from crushing the foam and it spreads the heat of the cable. I had a lot of logistical problems with the OO-Gauge cabling, local battery shop was awesome! Total project cost was about $150 and it took about 40hrs of work.


 That should do it. I use the Farnum heater pads, have only 1/2" insulation, keep the heaters plugged in to AC and set at 65 F when parked in my unheated unattached garage, otherwise off, and have noticed little difference summer to winter. Typical temperatures are teens to 20's at night, high 20's to high 30's during the day. The cells remain above around 50 F when left outside for about 4 hours with temperatures in the high 20's. Yours should do better with more insulation and all in one box - I have 3 boxes.


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