current regulation and batteries

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Forum Name: General Discussion
Forum Discription: General Mobile Electronics Questions and Answers
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=102199
Printed Date: May 13, 2024 at 5:00 AM

Topic: current regulation and batteries

Posted By: paddlenbike
Subject: current regulation and batteries
Date Posted: February 14, 2008 at 4:17 PM

Hi all,

I have a device that requires use of a 115V AC wall adapter and I want to make it run on a battery pack. The wall adapter steps power down to 5V DC and 200mA. The device the plug powers says "MAX INPUT 5.1V DC, 1 AMP." So, if I build a battery pack that either puts out 5V DC or I use a LM7805 to step the voltage down to 5 volts, do I also need to somehow limit the current to between 200mA and 1 amp or will the device only take what's needed?

Thanks!

Replies:

Posted By: i am an idiot
Date Posted: February 14, 2008 at 9:50 PM

You do not need to limit the current. A 7805 will work fine. You may need to mount it to a heat sink.

Posted By: paddlenbike
Date Posted: February 20, 2008 at 6:12 PM

Thank you for the reply.

Posted By: Ween
Date Posted: February 20, 2008 at 8:24 PM

hi,

and if you do use a regulator (7805 or ?), be sure the input voltage is two volts or higher than the output voltage.

the regulator won't work properly if it isn't. and be sure to heatsink the regulator properly. (Vin - Vout)/I = Pd.

I is current the load draws...Pd is power to be dissipated by the heatsink. a small piece of metal (aluminum or copper) will work just fine.

hope this helps.

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