# Interest group forums > Energy and Resource Conservation Forum >  Ampere/hour battery rating.

## Derlyn

I understand that, lets say a 100A/H battery can supply 100 amps for 1 hour, or, 50 amps for 2 hrs etc.

Is the above rating for 50% dod or 30% dod or 100% dod ?

Cannot seem to find this info anywhere.

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## Isetech

> I understand that, lets say a 100A/H battery can supply 100 amps for 1 hour, or, 50 amps for 2 hrs etc.
> 
> Is the above rating for 50% dod or 30% dod or 100% dod ?
> 
> Cannot seem to find this info anywhere.


The DoD will determine how fast you destroy the battery, that is why it is so important to understand the C rate of the battery. 

IF you discharge a lead acid battery at 1 C to 100 % DoD, chances are it will becomes a door stop in 5 cycles (added the cycles just to confuse you even more) 

the life span cycles of a battery is determined by the 

C rating and the DoD (depth of discharge) 

Old lead acid batteries used hi cycle and deep cycle as a means to select batteries for applications.

Hi cycle for starting cars etc.

Deep cycle to use for camping, trolling motors on boats etc (they had thicker lead cells and a thicker base so you could put them direct on the concrete) That is how I understood it. 

Lithium batteries are very different, and it is important to understand what makes a good lithium battery. Hence all the threads and questions, trying to make sense of it all throw the mine field of bullshit in features to make one battery look better than the others.

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## Derlyn

Let me re phrase the question.

For how many hrs can one draw 10 amps from a fully charged 100ah battery before 50% dod is reached ?

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## Isetech

> Let me re phrase the question.
> 
> For how many hrs can one draw 10 amps from a fully charged 100ah battery before 50% dod is reached ?


A good question, it depends of the type of battery. 


In "theory" it would take 5 hours.

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## Derlyn

Ok.

So if one doesn't want to discharge a battery past a 30% dod, then you will require a 100ah battery to get a usefull 30ah.

That's what I needed to know.

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## Isetech

The SOC is the state of charge

The DOD is the depth of discharge

If your SOC is 20 % then your DOD is 80% 

IF means your battery only has 20 amp/hr left in the 100 amp/hr battery.

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## Derlyn

Understand.

They sell you a 100ah battery but you've only got 30ah if you dont want to exceed a 30% dod or 70% soc(take your pick ) and destroy it quickly.

Now I can start doing realistic calculations without sucking anything out my thumb.

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## Isetech

> Understand.
> 
> They sell you a 100ah battery but you've only got 30ah if you dont want to exceed a 30% dod or 70% soc(take your pick ) and destroy it quickly.
> 
> Now I can start doing realistic calculations without sucking anything out my thumb.


That is why blowing R10-15 k on a 3.6 kva with 2 x gel batteries is a joke. You lucky to get 4 hours with a 400watts of the 36000watts. I never set the cut out lower than 11.5 V. 

People get desperate with these ridiculous load shedding stages and hammer the batteries to try keep the lights on, which results in a decline in life cycle to a couple of months. I have batteries on my work bench that are not even 2 years old and cant hold a charge longer than 15 minutes.

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## Isetech

By the way, dont forget to throw in the peukert effect when you do your calculation once you start loading the battery (high discharge rate)   :Wink:  

At least we can look forward to the new plan to start a "second" Eskom  :Smile:

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## Derlyn

No high discharge rate this side, brother.  Maximum peak about 2 amps output. Less than 1amp 80% of the time.

I'm gonna double those currents for the calculations. Don't wanna discharge more than 30% so I'll be needing maningi batteries

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## Derlyn

Am I right so far.
Not worried about charging the batteries YET.

Calculating how many batteries I need to pull 2A for 24Hrs.

on 24V side current is 20A

20A for 24 Hrs = 480Ah.

Now we dont want to go beyond 30% DOD so the 480Ah is 30% of the total battery capacity.

If 480Ah is 30% then 100% will be 1600Ah.  ( 19.2Kw )


16 of 100Ah batteries should suffice.

That's a giant battery bank. Are my calculations correct ?  

PS.  We will worry about the charging later.   :Big Grin:  :Big Grin: 


Don't know if it's worth it after reading the following.
https://mybroadband.co.za/news/energ...ity-eskom.html

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## GCE

> Am I right so far.
> Not worried about charging the batteries YET.
> 
> Calculating how many batteries I need to pull 2A for 24Hrs.
> 
> on 24V side current is 20A
> 
> 20A for 24 Hrs = 480Ah.


2 Amps at 240V = 480Watts 
For 24 hours you will need 24 x 480watts = 11 520 watthours or as we are used to 11,5KWH  

From Battery side 
24V x 20 amps will give 480watts/hour x 24Hrs = 11 520 watt hours capacity = back to amp hours will be 11520/24 = 480Amphrs or 11520/12= 960Amphrs

Amp hours is similar to watts - The amp hour is what is available if used in an hour and then the DOD comes in and the C rating comes into play.

If you going gel batteries you are going to need lots of them - As a thumb suck I use 360watts or amp hours usable per 100amphr battery for each hour which will mean around 32 batteries 100Amphr or 16 x 200Amp hour batteries 

Besides charging you need to think of gas build up and ventilation

Lithium is the only way to go. 






> Don't know if it's worth it after reading the following.
> https://mybroadband.co.za/news/energ...ity-eskom.html


Sometimes think My Broadband should stick to IT issues and not create panic - It is not so much the extra cost that comes into play it is how you manage it - The majority of extra cost is due to TOU tariff

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## Derlyn

> 2 Amps at 240V = 480Watts 
> For 24 hours you will need 24 x 480watts = 11 520 watthours or as we are used to 11,5KWH.
> 
> If you going gel batteries you are going to need lots of them - As a thumb suck I use 360watts or amp hours usable per 100amphr battery for each hour which will mean around 32 batteries 100Amphr or 16 x 200Amp hour batteries


Thanks GCE.

Somewhere I'm making a mistake with the number of 100Ah batteries needed.
Maybe you can help me.
I come up with 16 of 100Ah batteries needed. You say 32 batteries needed.

We both agree that 480Ah is whats used over the 24 hr period.
You should then have 70% of your total battery capacity left if you disregard any charging during that time.

My maths is as follows:                  480  =  30%
                                    Therefore   X    =  100%

                                    Therefore 30x  =  48000

                                    Therefore  x     =  48000/30

                                    Therefore  x     =  1600

                                    Therefore 100% battery capacity = 1600Ah

                                    1600/100 = 16 of 100Ah batteries.

Where am I going wrong ?
Big difference between 16 and 32 batteries.

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## GCE

> We both agree that 480Ah is whats used over the 24 hr period.
> .


did some changes to calculation in original post I made - Our difference is due to battery voltages - you using 24v which means 100amphrs needs 2 batteries 
Still think I could be confusing myself , will need more coffee and a couple of cigs to wake up completely

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## Derlyn

Morning brother. 

I also need some coffee and gwaai's to wake up in the morning, otherwise I'm still  :Zzzzz:  

*You are correct*

Batteries in series do not increase the Ah rating. Only the voltage.

My battery bank has just increased from 16 to 32.

Will have to buy a new house now.   :Wink: 


Now to start working on how to charge these things. That should be fun.

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## Dylboy

Hello !

Didn't even know there was another section hahaha. 

If it is 12V and 100AH that is then 1200WH or 1.2KWH

Then if 

24 V and 100AH that is then 2400WH or 2.4KWH 

Is that correct ? 

Sent from my CPH2197 using Tapatalk

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## GCE

> Hello !
> 
> Didn't even know there was another section hahaha. 
> 
> If it is 12V and 100AH that is then 1200WH or 1.2KWH
> 
> Then if 
> 
> 24 V and 100AH that is then 2400WH or 2.4KWH 
> ...


That is correct - 
Battery in parallel - voltage will be added , amp hour stays the same 
In series - voltage stays constant , amp hours is added up

2 batteries in Series  = ( 2x12v) x 100Amphr = 2 400Whr 

2 in Parallel - = 12v x ( 2 x 100Amphr) = 2 400whr 

As a quick rule I just use a 100Amphr battery using only 30% will give me 360w usable energy - If the client wants to run a 1 Kw load for 2 hours then I say he needs 2Kw of energy divide by 360W = 6 Batteries - The configuration of batteries to suit the inverter voltage all works out the same , The bucket of water is still the same size.

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## Derlyn

> That is correct - 
> Battery in parallel - voltage will be added , amp hour stays the same 
> In series - voltage stays constant , amp hours is added up
> 
> 2 batteries in  Parallel  = ( 2x12v) x 100Amphr = 2 400Whr 
> 
> 2 in series - = 12v x ( 2 x 100Amphr) = 2 400whr



Hmmm   .....  Regarding series and parallel batteries, I think the above 2 statements are the wrong way round.

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## GCE

> Hmmm   .....  Regarding series and parallel batteries, I think the above 2 statements are the wrong way round.


You are correct did an edit on previous post- Still confusing myself even with coffee and cigs

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## Dylboy

Awesome ! That is how I have done it and always understood it but had to make sure as the above stuff has me questioning my self. Albeit I did read it quick but still.

Appreciate it as always  :Smile: 

I like your rule of thumb for the 100AH and 30%.



Sent from my CPH2197 using Tapatalk

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