newbie help / suggestion

BB. wrote: »

Thank you Rob... I really did try and figure out how to make the equations "readable"... To compare other ways of writing equations:

174 Watts * 5 hours per day * 1/0.85 inverter eff * 1/24 volt battery bus = 42.6 Amp*Hours @ 24 VDC

Why do I use 1/0.85 and 1/24? Because we recognize the numbers... Plugging in straight numbers would look like:

174 Watts * 5 hours per day * 1.17647 inverter fudge factor * 0.04167 volt^-1 battery bus = 42.6 Amp*Hours @ 24 VDC

That is a silly representation. Another would be:

(174 Watts * 5 hours per day) / (0.85 inverter eff * 24 volt battery bus) = 42.6 Amp*Hours @ 24 VDC

Which is the correct way to write the equation--With Parens to ensure the correct order of operations. But I think it sort of "groups" variables together in non-useful relationships (i.e., is Inverter Eff and Battery Bus Voltage somehow related--Not really).

And if I took out the "words" and did it the way my Math and Science Teachers taught:

(174W * 5H) / (0.85 * 24V) = 42.6 AH

It gets the units right (always useful cross check for engineering/sciences)--But sort of difficult to really get a "feel" of what is happening in "real life" system.

Then there is the "algebra" version:

P = Average power in Watts
T = Hours per day of average power
E = Typical inverter efficiency (in percent)
B = Battery Bank Nominal Voltage
C = Bank capacity in AH @ battery voltage

C=(P*T)/[(E/100)*B]

Where:

P=174 Watts
T=5 Hours
E=85%
B=24 volts
C=Results in AH

C=(174W*5h)/[(85/100)*24V]=42.6AH

Liking my "English Math" sentences any better yet?

Equations written as above are much easier to put in a spread sheet--But I think do a poor job of conveying the ideas behind why the equation does what it does.

And I now see way I was a "C" student in middle school math. :roll: English too... Another story (or not).

-Bill