# Long Term Storage



## GerhardRP (Nov 17, 2009)

twright said:


> <snip>Does this mean that everything is OK with my storage? <snip>


Yes, it is fine.G.


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## Sunking (Aug 10, 2009)

Do not store LFP or any lithium battery at 100% SOC. Storing voltage for all lithium batteries is 60 to 70% SOC. Boost back to storage voltage every 6 months due to self discharge.


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## dougingraham (Jul 26, 2011)

Resting voltage is a good indication of state of charge. 144 volts and 44 cells = 3.27 volts per cell which is about 25% SOC based on the resting voltage. If you are certain you have no parasitic loads it will be fine for many years. Correctly functioning LiFe cells do not have a measurable self discharge. They do however appear to have a shelf life and lose about 1.5% of their capacity every year stored. If the car is going to remain in storage I would disconnect one end of the battery and if you have a BMS with a connection to each cell I would go ahead and charge it up some (or completely if a shunting type BMS) so you are not surprised. BMS's can be a parasitic load and in fact if poorly thought out will be an imbalancing parasitic load.

It is considered best to store around half charge. I would like to see a resting voltage of around 145.2 volts (plus or minus a few tenths) for the pack. Your 17AH used does not jibe with the resting voltage. Then again an inexpensive meter could be off by a couple of percent which would be as much as 2 or three volts at the 144 volt level. I think your pack should be much closer to 147 volts if only 17AH where used from a fully charged pack.

Hope you start driving your EV again soon!


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## twright (Aug 20, 2013)

I have a very inexpensive dashboard display of voltage. That's where the 144 volt number comes from. I'm sure it's inaccurate. However, it has not changed since I stored it, so I don't think anything's drawing it down.

I will put a more accurate meter on it to be sure.


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## Sunking (Aug 10, 2009)

twright said:


> I have a very inexpensive dashboard display of voltage. That's where the 144 volt number comes from. I'm sure it's inaccurate. However, it has not changed since I stored it, so I don't think anything's drawing it down.
> 
> I will put a more accurate meter on it to be sure.


Not really an issue for me, just giving you the heads up. Manufactures do not ship them fully charged for that very reason. In fact you can greatly extend any lithium battery life by never fully charging them up. Chevy Volt took note of that and thus will not allow you to fully charge the battery up, and also will not allow you to go below 10 or 20% SOC before the engine starts. You can double to triple cycle life by operating only between 10 to 90% SOC.


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## twright (Aug 20, 2013)

I have more accurate voltage measurements from my cells: My Orion BMS reports that all of the cells are between 3.25 and 3.27 volts.

Is that only 25% state of charge?


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## dougingraham (Jul 26, 2011)

twright said:


> I have more accurate voltage measurements from my cells: My Orion BMS reports that all of the cells are between 3.25 and 3.27 volts.
> 
> Is that only 25% state of charge?


It is a little less. Here is a link to my incidental testing on my GBS 100AH cells. SOC column and chart is compensated for capacity.

LiFe voltage vs SOC

My numbers are unloaded numbers. If the Orion places a load on the cells the SOC could be a little higher than that. Also you have no idea how accurate the Orion is. And 0.01 volts resolution is not enough to get you closer than 20% if it is close to the middle of the state of charge.


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## twright (Aug 20, 2013)

Doug,

The numbers that I have seen from driving my car about 4000 miles don't seem to match yours. My Orion will stop the charger from additional charging when the average cell voltage is about 3.35 volts. When I drive it, the voltage gets on the flat part of the curve pretty quickly and stays there for about 50 % of the capacity of the battery. This flat spot is about 3.23 volts. When I get down to about a 20% SOC, the voltage is about 3.18 volts.

I don't know if the differences are because of meter inaccuracy, different battery manufacturer or something else.

Is there a difference in voltage between resting for an hour and resting for a month?


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## dougingraham (Jul 26, 2011)

twright said:


> Doug,
> 
> The numbers that I have seen from driving my car about 4000 miles don't seem to match yours. My Orion will stop the charger from additional charging when the average cell voltage is about 3.35 volts. When I drive it, the voltage gets on the flat part of the curve pretty quickly and stays there for about 50 % of the capacity of the battery. This flat spot is about 3.23 volts. When I get down to about a 20% SOC, the voltage is about 3.18 volts.
> 
> ...


Unloaded resting voltage will creep for several days but 99.9% of it is done in 24 hours. An hour is not enough time for a resting voltage. If there is any kind of load more significant than a few micro amps the voltage will be lower than my chart. A DVM will present a load of 10 megaohms or less so the current on a 3 volt battery would be 0.3 microamps or less. A BMS could load several MA. Not saying yours does but they can. One thing everyone with a BMS should do is verify the accuracy. Buy or borrow a pretty good DVM and read the voltages of every cell. Then compare to what the BMS tells you. If they match that probably means the manufacturer bothered to calibrate the readings. If not it would be easy to have several percent error. The DVM is the same reference across all cells. You can compare the readings from the DVM. The BMS could be a different reference on every cell. Your DVM doesn't need to be a $450 Fluke like mine but it is a good idea to use something a little better than one of the free harbor freight DVM's <grin>.

There could be any number of reasons for you seeing a lower voltage. My guess is that most of it is because the cells have not rested long enough or there is a significant enough load on them that they will never spring back up to a resting state.

Resting voltage can tell you a lot but when you are driving your car it is a pretty useless thing.


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## Caps18 (Jun 8, 2008)

I have one of these in my conversion:










And with the battery disconnected, I have seen it drain from 124.7 VDC to 124.0 VDC (divide by 32 = 3.875 VDC) in the past 10 months with no use.


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## dougingraham (Jul 26, 2011)

Caps18 said:


> And with the battery disconnected, I have seen it drain from 124.7 VDC to 124.0 VDC (divide by 32 = 3.875 VDC) in the past 10 months with no use.


Isn't there some sort of BMS still connected to the cells even with the main power connector disconnected? That does not seem like an excessive voltage change for a 10 month period even if there is still a parasitic load from a BMS. A temperature change from warmer to colder could account for a voltage change of that amount.

LiPo pouch type cells are in distress when the resting voltage is much below three volts. I would be concerned if you see that pack voltage drop below 96 volts (for 32 cells).


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## Caps18 (Jun 8, 2008)

Nope, no BMS in my battery pack. And yes, it was colder when I measured 124.0 VDC than back in March '14 when it was 124.7 VDC

Dealing with the battery will come next month in my conversion. 
Lots more research into how to do it right, especially since I won't be able to access the batteries without removing the bed of the truck first.


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