newbie help / suggestion

kc6cnn

Is there a sticky somewhere that explains all of the calculations needed to figure battery bank size, panel size, etc.
I was trying to figure out what my needs would be and how to meet them, but keep getting confused on watts, amps, voltage calculations.
Thanks
Gerald

BB.

Re: newbie help / suggestion

Gerald,

Just ask the question right here in your thread. I/we will go through the calculations based on your needs.

I think it will make more sense to you if we discuss your system vs a generic version. Many of the choices for battery voltage/hardware/etc. will be different based on system size/power needs/location of install. To discuss a "generic" installation will get even more confusing because of discussions of the options/variations.

-Bill

westbranch

Re: newbie help / suggestion

like they said on Dragnet Just the facts, M'am, just the facts... so start with a list of the items you want to run and the watts they use and the time (hrs) they are used
ie 4 CFL lights at 9 watts = 36w x 4 hours = 144 Whrs.

verdigo

Re: newbie help / suggestion

I am thinking that would be useful sticky as well. The general consensus is to buy a kill-a-watt meter and determine your load requirements, then do some conservation, then build a balanced system based on what you use with the idea that your gonna want to use more as time goes on. My problem is that as a DIYS kind of guy with limited time and resources I would never get anything done that way, so with the knowledge that almost all loads have an off and on switch I figured I would just shoot for a 3 KW or so system built with expandability in mind and just go for it all the while reading thousands of threads to hopefully apply all of that expertise to do what I have in mind, which might change at any given moment. A short concise sticky with formulas, rules of thumb, and safe practices would be great, but there would always be something left out. There just aren't any short answers with this stuff.

niel

Re: newbie help / suggestion

kc6cnn wrote: »

Is there a sticky somewhere that explains all of the calculations needed to figure battery bank size, panel size, etc.
I was trying to figure out what my needs would be and how to meet them, but keep getting confused on watts, amps, voltage calculations.
Thanks
Gerald

i don't mean to sound rude, but how did you get to be an extra class ham and say something like that?

BB.

Re: newbie help / suggestion

I was mildly dyslectic when I was a kid... So I know how the V/I/A/W etc. all floated around on the paper for me (as well as numbers and words).

I probably got much better in math from high school Chemistry (and Physics) classes when I was "forced" to carry units through all of my calculations. It made reading the equations much easier and understanding conversions/catching missing/wrong numbers&units much easier too.

I wrote a post recently about how I try to make the math more understandable on the forum.

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

-Bill

vtmaps

Re: newbie help / suggestion

BB. wrote: »

I was mildly dyslectic when I was a kid... So I know how the V/I/A/W etc. all floated around on the paper for me (as well as numbers and words).

I was also dyslexic as a kid. I owe my ability to read to the efforts of my mother who joined the support group D.A.M. (mothers against dyslexia).

--vtMaps

niel

Re: newbie help / suggestion

he can talk for himself and don't need the 2 of you to make up possible excuses for him.