×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Calculating battery efficiency

Calculating battery efficiency

Calculating battery efficiency

(OP)
Hi,

I'm having questions about calculating the charge efficiency of electric batteries.

For example: A 100Ah battery in the 24V PV system setup is discharged with a current of 1A. So could last for 100 hours (if its new and allowed to discharge completely).

Now I thought it would be reasonable to use the avarage dischargevoltage of 23 volts. So thats 23Vx10Vx10h=2300Wh

Now I want to now the required amount of energy to charge the battery so a 100Ah will be available again.

So if I would want to charge it I will need more then the 2300Wh.

However the battery needs to be charged at about 28V. Assumed that the efficiency of the battery is 90% (I'm not taking the the effect of the state of charge on the efficiency in account for the sake of this example).
Now where I get stuck:

Do I need to correct the Energy in Wh or the Ah? In the case of Wh it would be 2300Wh/0.9 is about 2556Wh needs to be charged in to the battery. At 28V this is 2556/28 = 91Ah..

or...

Calculate the Ah going out first: 2300Wh/23V=100Ah. Increase the Ah number with the efficiency: 100Ah/0.9=111Ah. And calculate the Wh going in: 111Ah x 28V = 3111Wh.

This is quite a difference. In case 1 I need 2556Wh and in case 2 3111Wh. Because in case to the voltage difference between charging and discharging plays a role ass well.

What is the right way to do it.

Appreciate your comments.

regards Geert

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources