Tech Tuesday: Depth of Discharge, State of Charge & Capacity

Posted October 15, 2019

Welcome to this week’s edition of Tech Tuesday. The topic this week is depth of discharge, or DOD, state of charge, or SOC, and how it effects a lithium battery. We'll cover how to calculate DOD, which is important to know because the numbers of cycles will vary based on your depth of discharge. We'll also discuss the differences between lithium and lead-acid batteries when it comes rate of discharge and capacity.

Screen-Shot-2019-10-07-at-3.27.34-PM.png#asset:10340:blog


Transcript

Hi everyone, this is Simon with RELiON Battery. Welcome to this week’s edition of Tech Tuesday. The topic this week is depth of discharge, or DOD, state of charge, or SOC, and how it effects a lithium battery. A battery’s depth of discharge indicates the percentage of the battery that has been discharged relative to the overall capacity of the battery. For example, if you have a 100 amp-hour battery and use only 20 amp-hours you have discharged your battery 20%, which means your depth of discharge is 20%, and your state of charge is 80%. If you took that same 100 amp-hour battery and discharged it 70% your DOD would be 70% and your SOC 30%. It’s important to know DOD calculations because depending on your battery, the number of cycles will vary based on your DOD. Most lead acid batteries experience significantly reduced cycle life if they are discharged below 50% DOD. LiFePO4 batteries can be continually discharged to 100% DOD and there is no long-term effect. However, we recommend you only discharge down to 80% to maintain battery life.

Another great thing about LiFePO4 batteries is that the rate of discharge has virtually no effect on the delivered capacity. This is also not the case with lead-acid batteries which have significantly reduced capacity of up to 50% as the rate of discharge increases. Lithium batteries provide 100% of their rated capacity, regardless of the rate of discharge, while lead-acid batteries typically provide less usable energy with higher rates of discharge. What does this mean for you? Ultimately you get more hours of power with a lithium battery. That’s it for this week’s Tech Tuesday. Don’t forget to subscribe and leave us your comments in the section below. See you next week.

SUBSCRIBE

COMMENTS