# In this formula, what is &quot;absolute maximum DOD&quot;?

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Solar Expert Posts: 364 ✭✭
system voltage x 1/2 the AH rating of your batteries = absolute maximum DOD

I mean, what is the result? Is it watt hours?
Paul

• Solar Expert Posts: 1,571 ✭✭
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Re: In this formula, what is "absolute maximum DOD"?
ILFE wrote: »
I mean, what is the result? Is it watt hours?

V x AH = VAH = WH, so yes

I.e. you have 12v x 100Ah battery which is 1200Wh of stored energy, but to discharge to 50% DoD you can only use 600Wh of energy from it.
• Solar Expert Posts: 3,741 ✭✭✭✭
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Re: In this formula, what is "absolute maximum DOD"?
ILFE wrote: »
I mean, what is the result? Is it watt hours?

I see your confusion... DOD is usually expressed as a percentage. In the formula, as stephendv points out, it is watthours.

--vtMaps
4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
• Solar Expert Posts: 364 ✭✭
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Re: In this formula, what is "absolute maximum DOD"?

I was pretty sure it was watt hours. I just wanted to verify it. I keep a list of useful formulas that I have been compiling for some time. I just noticed that I had not clarified that on that list.

Thanks, men.
Paul
• Solar Expert Posts: 50 ✭✭
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Re: In this formula, what is "absolute maximum DOD"?
ILFE wrote: »
I was pretty sure it was watt hours. I just wanted to verify it. I keep a list of useful formulas that I have been compiling for some time. I just noticed that I had not clarified that on that list.

Thanks, men.

Why not post your list for all to see? I'm sure it would be very helpful.
• Solar Expert Posts: 364 ✭✭
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Re: In this formula, what is "absolute maximum DOD"?
K4KMG wrote: »
Why not post your list for all to see? I'm sure it would be very helpful.

Well, it isn't exactly top secret:
volts / ohms = ampsvolts x amps = watts
MPPT: Output Current = Panel Wattage / Battery Voltage
PWM: Input Current = Output Current
To determine breaker / fuse size for panels: Take the Isc, multiplied by 1.56. Round up to the next available breaker / fuse size.
AH x battery voltage = total capacity in kWh.
system voltage x 1/2 the AH rating of your batteries = absolute maximum DOD (in watt hours)
(absolute maximum DOD should be less than 50%, for longevity of your battery bank, though)
watt rating x hours powered = watt hours per day
watt hours per day / system voltage = amp hours per day
rated array watts x hours of good sun x .52 = usable AC watt hours
(end-to-end efficiency of a battery system / inverter consumption and conversion is included in the rating)
rated array watts x 77% x hours of good sun = DC kWh
(important to note that as it is not the same as you get in AC what with inverter consumption and conversion efficiency)
Paul
• Banned Posts: 17,615 ✭✭✭
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Re: In this formula, what is "absolute maximum DOD"?
ILFE wrote: »
Well, it isn't exactly top secret:

And it is somewhat inaccurate. A little re-write:

Volts / Ohms = Amps (Ohm's Law).
Volts * Amps = Watts (Power Formula without power factor correction).
MPPT output current = panel Wattage * 0.77 efficiency / nominal battery Voltage.
PWM output current = input current.
To determine breaker or fuse size for panels: multiply Isc by 1.56 and round up to the next available size.
Amp hours * battery Voltage = nominal total capacity in Watt hours.
Watt rating * hours of use = Watt hours consumed.
Watt hours per day / system Voltage = Amp hours per day (nominal).
Rated array Watts x hours of good sun * 0.52 over-all efficiency = usable AC Watt hours.
Rated array Watts x 0.77 efficiency * hours of good sun = expected grid-tie system production.

There are some caveats that need to be included, such as real Amp hour capacity varying with rate of use and the fact the efficiency deratings are variable.

I've been meaning to do a sticky on this for some time. You may have just pushed me in to it. Thanks, I think.
• Solar Expert Posts: 364 ✭✭
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Re: In this formula, what is "absolute maximum DOD"?

Anything, to give you something else to do, Coot. You are welcome, sir.

Boy, am I glad I live half way around the world. You can't kick me so easily from this distance.

Thanks for the corrections.
Paul
• Solar Expert Posts: 50 ✭✭
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Re: In this formula, what is "absolute maximum DOD"?

Thanks. A sticky would be good! Although none of it is 'secret', it's not all in one place for quick reference.
• Solar Expert Posts: 492 ✭✭✭
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Re: In this formula, what is "absolute maximum DOD"?

And WHY there is NOT a sticky !! IS Unbelievable above me !!!!!!!!!!!!!!!!!! Start HERE : Solar Beginners Corner !! Read and follow links !!!
Same questions , same replys , same regurgitated info , This is GROUND HOG DAY !

So easy to build one with the amount of Folks who are in the Know to the MOD'S to put in a presentation trial & help sell NAW's Watt-0 meters to the correct widgets..
Nothing is secret , but all is lost in the mumble grumble of spewed dribble , same items with different terms. Nothing is as it is stated for real life power , but in a lab it works . Solar 101 , start here . Then maybe the mods / replying folks would not need to ask the same questions of whats your loads.
Maybe then more folks could also "raise the bar".

Just typing out loud.

VT
• Super Moderators, Administrators Posts: 33,541 admin
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Re: In this formula, what is "absolute maximum DOD"?

Hi VT,

I have added Marc's (cariboocoot) post to a Glossary Sticky over here:

Take care,
-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 364 ✭✭
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Re: In this formula, what is "absolute maximum DOD"?
BB. wrote: »
From another thread, ILFE and Caribootcoot:

Woo! Hoo! My name will live forever! I'm famous. I'm in a sticky! It's because of me! Me! All me!

Sorry, fellers, not signing any autographs today. Maybe tomorrow.

Okay, maybe I was a little bored. Sorry.
Paul