question about discharging batteries

[snake21]

hi friends,i have a coupe of question concerning discharge of batteries.

i have a deep cycle batteries rated 12v and 100a/h and is connected to wind turbine and solar panels.
what i understand by 12v and 100a/h is that the battery will provide a max of 100amps in 1 hour at 12v and after 1 hour,the charge of the battery will be 0%.if i am wrong please correct

now make as if 1 day the battery is fully charged and i disconnect the charging source and intend use 80% of the battery power leaving 20%for the safety of the battery

80% of the battery charge is 960watts. if i connect my computer which consumes 320watts to the battery through the inverter,does it means that i will be able to use it for 3 hours (3x320=960) until the charge of the battery reaches 20% ?

another question,if the battery is rated 100amps /h at 12v,does it mean that it will give 100A in 1 second for 1 hour or does it mean that it will give a total of 100A in 1 hour at 12v?

the third question,for example a led bulb is rated at 3w,is it 3w per hour or 3w per second, making it to consume 3wx3600s=10800w?

thanks

[wooferhound]

You need to learn the difference between Watts and Watthours
100 watts for 1 hour is 100 watthours, for 2 hours it is 200 watthours

does it mean that it will give 100A in 1 second for 1 hour

What does that mean ?

[jayson]

It sounds like you were trying to convert to Coulombs per second? 

Battery capacity is usually labeled to the 80% discharged point, you can get a full 100ah out of your battery. A 3 watt led would draw a quarter amp at 12v, so you should have 400 hours or so of run time. This does not mean you will get 16 days off of a charge, lead acid batteries have a fairly high self discharge rate, and the older the battery, the higher the self discharge rate.

Have you measured your computer's amp draw? or is that what the computer's power supply is rated at? If you are measuring on the secondary side of your inverter, you are not getting a good picture of what's going on, as inverters are very inefficient.

[snake21]

all this confusion started when i was talking about my small system with my colleague who is a physics teacher.he asked me about the power storage and i told him that my battery is rated 12v and 100a/h.he then asked me what are the things that i can power with the system and for how long.i told him that i power ome bulbas and sometimes my computer for about 30 min a day.then he told me that this is impossible.the fact that he is a physics teacher,i couldnt argue with him.he just gave me an example about a bulb.he told me that if a bulb is rated 3w,it means that i will consume 3w per second.i was completely confused at that time.

then i told him that i will need to confirm with fieldlines member first.

thats wat i did

thanks for the reply

[ghurd]

I believe it is easier to think in amps than watts.
The first thing I do is get everything into amps.

3W is 0.25A.

0.25A / 100AH = 400H
G-

[TomW]

I believe it is easier to think in amps than watts.
The first thing I do is get everything into amps.

3W is 0.25A.

0.25A / 100AH = 400H
G-

Actually that is 100AH / 0.25A=400H

But you knew that.

Just for accuracy.

And now you know why they pushed Algebra on you as a kid.

Tom

[ghurd]

Oops.
G-

[snake21]

haha.......mistakes happens.lol

[ChrisOlson]

i couldnt argue with him.he just gave me an example about a bulb.he told me that if a bulb is rated 3w,it means that i will consume 3w per second.i was completely confused at that time.

Well, leave it to some college educated teacher to think that up and declare to the world that you do the impossible.

3 watts @ 12 volts is .25 amps, and 3 watts consumed for one hour is 3 watt hours or .25 amp-hours @ 12 volts.

If your computer pulls 320 watts for 30 minutes that's 160 watt-hours or 13.3 amp-hours @ 12 volts.  Assuming your inverter is 90% efficient that's about 14.8 amp-hours used out of your 100 Ah battery with plenty left over to run a few light bulbs in the house.

Not impossible at all.  You can tell your physics teacher friend I said so.
--
Chris

[Bruce S]

i couldnt argue with him.he just gave me an example about a bulb.he told me that if a bulb is rated 3w,it means that i will consume 3w per second.i was completely confused at that time.

Well, leave it to some college educated teacher to think that up and declare to the world that you do the impossible.

3 watts @ 12 volts is .25 amps, and 3 watts consumed for one hour is 3 watt hours or .25 amp-hours @ 12 volts.

If your computer pulls 320 watts for 30 minutes that's 160 watt-hours or 13.3 amp-hours @ 12 volts.  Assuming your inverter is 90% efficient that's about 14.8 amp-hours used out of your 100 Ah battery with plenty left over to run a few light bulbs in the house.

Not impossible at all.  You can tell your physics teacher friend I said so.
--
Chris

Chris, What you said. Physics teacher should join up here and let us help them understand battery stored energy

I'll add my name to the list of tell the physics teach he's wrong

[TomW]

Not impossible at all.  You can tell your physics teacher friend I said so.
--
Chris

Chris;

This brings to mind an old saying I have heard many times and it is not always true but often is.

Those who can, do. Those who can't, teach.


Tom

[kurt]

haha when i was 18  i asked 3 teachers how to do a math question that was on my sheet metal workers entrance exam every one of them told me wrong answers that did not pass the smell test.  i had to go ask my father how to do it and he gave me the correct answer. 

[Bruce S]

Not impossible at all.  You can tell your physics teacher friend I said so.
--
Chris

Chris;

This brings to mind an old saying I have heard many times and it is not always true but often is.

Those who can, do. Those who can't, teach.


Tom

Tom ;
I used to use that one too, until I started teaching  .
I still use it, but only when some smart a$$ teacher pipes up with a "Better than Thou" attitude 
HEY OP!! Can you bring the "physics" teacher to your computer so we can hep edumakate 'em  ?

It is possible he/she was having a bad day? I've had those 
Bruce S

[ChrisOlson]

Those who can, do. Those who can't, teach.

LOL!

On a more serious note, I have no time for teachers that tell somebody something is impossible.  If I had a nickel for every time that teachers explain why something won't work, that somebody with hands-on experience proves does, I could've bought me a brand new Jake 31-20 by now - with cash.
--
Chris

[rossw]

he told me that if a bulb is rated 3w,it means that i will consume 3w per second.i was completely confused at that time.

What he really meant was that *HE* was completely confused, and was doing his best to confuse you too.

As others have said, he's totally wrong. Even his basic understanding is WRONG.

Amps, volts (and therefore watts) are instantaneous units.

Volts are like water pressure. It's instant. Your meter may have a response time, but the unit itself is timeless.
Current is also instantantaneous. Watts are volts*amps, and are therefore also "timeless".

3 watts is 3 watts. All the time. 3 watts for an hour is simply 3 watt-hours.  3 watts for a whole day is 72 watt-hours. And finally, 3 watts for a second is (close enough to) 0.0008 watt-hours.

Send him back to skeewl.

[snake21]

i am a design and technology teacher but i am completely far from those teacher who learn only from books without experiencing things. in the college i teach,there is a small workshop where student doing design produce their own artefacts,i do help those students too but i am experiencing skills.by the way,this forum is great,i learn a lot here and this help me to help the students.

thanks for your support friends,you are all genius

[Bruce S]

i am a design and technology teacher but i am completely far from those teacher who learn only from books without experiencing things. in the college i teach,there is a small workshop where student doing design produce their own artefacts,i do help those students too but i am experiencing skills.by the way,this forum is great,i learn a lot here and this help me to help the students.

thanks for your support friends,you are all genius

We all started out not knowing any of this,BUT we didn't close our minds to new lessons either.
I believe learning should be a life long experience, otherwise what's the use 

Cheers
Bruce S