SOC
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State of charge?
liveforphysics
Enlightened
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- Dec 4, 2006
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SOC = Stage of charge.
It's the resting voltage of a cell at 70degF.
It's a representation of a the state of the cells chemical energy storage state.
It's the resting voltage of a cell at 70degF.
It's a representation of a the state of the cells chemical energy storage state.
McAllan
Enlightened
Yeah. Figured the SOC out myself too 
However I'm having a bit of trouble with the HVC.
I figure the HVC is the final voltage of a cell. Ex. 4.2 for LiIon. However it bothers me not knowing what the precise words the abbreviation really stands for :thinking:
However I'm having a bit of trouble with the HVC.
I figure the HVC is the final voltage of a cell. Ex. 4.2 for LiIon. However it bothers me not knowing what the precise words the abbreviation really stands for :thinking:
I am guessing high volt cutoff.
liveforphysics
Enlightened
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- Dec 4, 2006
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HVC = High voltage cut-off
LVC = Low voltage cut-off
In a pack, it's the values you program into the BMS (battery management system) to cause some protective action to occur when the SOC voltages reach those set limits.
For example, in an EV pack, you set your LVC to the lowest point you wish your cells to be discharged to, and at this point, the BMS pulls the voltage low on the gates of the FETs on the discharge stage, so the pack can't continue to discharge. Or a multi-stage LVC, something that activates to tell the motor controller to only draw 1/2-1/3rd of it's normal current limit to give a warning to the user to get it to a place to charge soon.
Same with HVC during charging, or extreme re-gen braking events, like getting tow-charged, or starting out at the top of a big hill with a full pack. lol When the HVC is reached, it pulls the charging FET gates low, disconnecting the pack from the charge source until the voltage drops below the HVC threshold again. This makes for a natural oscillation for very simple SOC testing each time the current is cut to the pack, and a simple diode and cap on the input to the FET driver acts as the delay to enable a few seconds charge, a few mS to check SOC, a few seconds charge, etc etc.
Flashlights generally have slow CC/CV charging with no HVC (and often no BMS), because there is no reason to bother taking up extra space and hassle trying to protect a $5 pair of cells, and when dealing with energy amounts seldom even exceeding 20-50w-hrs, optimizing charging just isn't worth the expense. Working with $2,000-20,000 in Lithium cells, and needing to get them charged as rapidly as possible makes proper BMS designs with HVC/LVC settings a critical attribute. Attached a pic of a close friend's DIY BMS solution for up to 36 cells in series. There are setups commercially available for 144 cells in series (550v nominal packs).
Best Wishes,
-Luke
LVC = Low voltage cut-off
In a pack, it's the values you program into the BMS (battery management system) to cause some protective action to occur when the SOC voltages reach those set limits.
For example, in an EV pack, you set your LVC to the lowest point you wish your cells to be discharged to, and at this point, the BMS pulls the voltage low on the gates of the FETs on the discharge stage, so the pack can't continue to discharge. Or a multi-stage LVC, something that activates to tell the motor controller to only draw 1/2-1/3rd of it's normal current limit to give a warning to the user to get it to a place to charge soon.
Same with HVC during charging, or extreme re-gen braking events, like getting tow-charged, or starting out at the top of a big hill with a full pack. lol When the HVC is reached, it pulls the charging FET gates low, disconnecting the pack from the charge source until the voltage drops below the HVC threshold again. This makes for a natural oscillation for very simple SOC testing each time the current is cut to the pack, and a simple diode and cap on the input to the FET driver acts as the delay to enable a few seconds charge, a few mS to check SOC, a few seconds charge, etc etc. Flashlights generally have slow CC/CV charging with no HVC (and often no BMS), because there is no reason to bother taking up extra space and hassle trying to protect a $5 pair of cells, and when dealing with energy amounts seldom even exceeding 20-50w-hrs, optimizing charging just isn't worth the expense. Working with $2,000-20,000 in Lithium cells, and needing to get them charged as rapidly as possible makes proper BMS designs with HVC/LVC settings a critical attribute. Attached a pic of a close friend's DIY BMS solution for up to 36 cells in series. There are setups commercially available for 144 cells in series (550v nominal packs).
Best Wishes,
-Luke
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