how to cut off supply?

sid2286

Aug 24, 2011
102
I've a battery of 4.8v/350ma and a charger wit 6.8v and 1A
the problem is once the battery is charged , it heats up the battery and the charger and it heats real bad!
I want to cut off the battery supply once the battery is charged.

how should I do it?

regards,
Sid

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,509
Use a proper charger

sid2286

Aug 24, 2011
102
thanks Steve !
I'm aware of that solution, however I'm not able to find a proper charger! I've these chargers in stock so if I get a cut off circuit I can use them

thanks once again though!

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,509
OK, but you must tell us what sort of battery it is, what sort of charger you're using, and how you intend to determine that the charge is complete.

Otherwise all we can do is say things like I did above, or other (even less useful) things like "With a switch"

sid2286

Aug 24, 2011
102
the battery is nickelcadmium battery wit voltage 4.8v and 1600maH.

the charger I has got 7.5v 1amp rating on it!

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,509
Get a proper charger.

Alternatively you could turn off the charging when the cells get warm.

You really want to track the rate of change of temperature, but perhaps you can get away with detecting a temperature some number of degrees higher than ambient.

edit: Here is a fairly simple option.

Last edited:

sid2286

Aug 24, 2011
102
thanks Steve!

what I did now is connected a Zener of 4.7v between battery terminals.

I guess that should work, what is your suggestion?

Moderator
Jan 21, 2010
25,509
Last edited:

CocaCola

Apr 7, 2012
3,635
edit: Here is a fairly simple option.

It's links like that, that remind me that I need to build a new charger for my Paslode impulse nailer, there was always a vacant charger on the jobsite so I never bothered replacing my broken one... But, now when I want to use it around the house for a project I need the charger

Harald Kapp

Moderator
Moderator
Nov 17, 2011
13,337
Steve, that last link of yours is mean

CocaCola

Apr 7, 2012
3,635
Steve, that last link of yours is mean

Yeah the fact that you need to purchase the \$25 PIC chip kinda defeats any DIY cost effectiveness...

BobK

Jan 5, 2010
7,682
That is the very article that got me back into electronics. I had two drill drivers that kept wearing out their batteries with its dumb charger. I didn't want to pay for his PIC though, so I got my own and one plussed his design by using a buck converter controlled by the PIC. This was my first of many PIC projects.

Bob

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