afreegreek wrote:total life of most deep cycle batteries is optimal at 50% DOD but still better at 80% DOD than 20%...
say a battery is 100 amp hours..
20% DOD @ 3000 cycles (3000 x 20 AH = 60,000 AH)
50% DOD @ 1500 cycles (1500 x 50 AH = 75,000 AH)
80% DOD @ 800 cycles (800 x 80 AH = 64,000 AH)
no sense in doubling the size of a battery bank to avoid a DOD greater than 20% when you can go to 80% DOD with a half as big, half as heavy, half as expensive battery bank that will give more hours of use over it's life....
MtnDon wrote:Maybe I am misinterpreting what you wrote.
I have read your post several times. When I read the last paragraph I understand you to mean that a deeper discharge is better ... "go to 80% DOD ..... .... will give more hours of use over it's life...."
If that is what you mean that flys in the face of what is generally accepted as truth. The depth of discharge chart in the OP above clearly indicates a lesser depth of discharge results in more cycles. As does the Trojan chart on this page.
You seem to be equating the theoretical amp-hour total as the criteria that make it better to discharge more deeply. I've never seen anyone calculate in that manner.
I am counting cycles not the amp or watt - hours of power withdrawn from the batteries.
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From a Trojan document. "Do not discharge your battery more than 80%. This safety factor will eliminate the chance
of over-discharging and damaging your battery"
This article states, "When using lead-acid batteries, one of the most common fatal mistakes is to discharge one's battery bank too deeply, causing permanent damage that impacts performance and reduces the life of the batteries"
And this site states "Battery life is directly related to how deep the battery is cycled each time. If a battery is discharged to 50% every day, it will last about twice as long as if it is cycled to 80% DOD. If cycled only 10% DOD, it will last about 5 times as long as one cycled to 50%. "
Trojan has a battery bank sizing calculator here. It uses DOD figures of 10% to 50%. It goes no higher than that.
That all indicates that it is better to cycle batteries somewhere between a DOD of 20 to 50% and to do your best to never discharge as deep as 80%. If that is what you mean I somehow have trouble understanding your writing and I apologize for that. However, if you mean we would all be better off to regularly discharge our lead acid batteries to 80%, I believe you are incorrect.
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