NiMh Battery Charger?

SkinnyBoy · 12th January 2003, 11:45 PM

I have two 5volt @ 2amp switchmode plugpacks and would like to make a battery charger able to charge 2 AA NiMh batteries, They are 1.6amps each.. I would also like to include a feature to be able to select the charge rate (slow/normal/fast) anyone know of a circuit?? I have looked EVERYWHERE for a circuit.. well, nearly... also, a timer would be good... a simple one to select the charge time.. anyhelp would be GREAT!!

jackinnj · 12th January 2003, 11:50 PM

a circuit featuring these MAX712, 713 etc. chips was a staple in the ARRL Handbook, you can find it here at Maxim's site:
http://www.maxim-ic.com/quick_view2.cfm?qv_pk=1666

SkinnyBoy · 12th January 2003, 11:54 PM

Ok thanx, I think I saw it before... or maybe not... Anyway, my problem is (I have many, but not relevent to this project

) is that I am not sure if I can connect the cells in series due to the lowish input... one schematic I saw needed 7 volts I think to charge to cells in series...

dkemppai · 14th January 2003, 12:49 AM

NiMh can be tricky to charge properly. Usually they use a microcontroller, and monitor voltage, current and temperature. They are very sensitive... ...you can charge them with a simple power supply, but will shorten the life/capacity of the cells.

-Dan

Havoc · 14th January 2003, 09:27 PM

The max713 is very foolproof. Monitors dv/dt, Icharge, switches to trickle charge and has a timeout. If I remember you need 2V more than the max voltage during charge. So for 2 cells that would be 2V+2V+2V=6V. So a 7V adapter would be right.

Never charge cells in parallel! They will always charge uneven.

SkinnyBoy · 14th January 2003, 09:34 PM

Quote:

Originally posted by Havoc
The max713 is very foolproof. Monitors dv/dt, Icharge, switches to trickle charge and has a timeout. If I remember you need 2V more than the max voltage during charge. So for 2 cells that would be 2V+2V+2V=6V. So a 7V adapter would be right.

Never charge cells in parallel! They will always charge uneven.

Could I use 2 controller ICs and have a seperate circuit for each cell... I only have a 5volt plugpack.... I bought it with teh hope of making a battery charger..

I already had the batteries... I bought then 2 years ago, but had no way of charging them...

The reason I want to use the 5volt plugpacks is bacause they are small, very small, and give 2amps out, which is good.... I suppose I may be able to modify one to get 7volts, rather that 5.... A voltage divider on the feedback line.... but I can't even get it open.. :P lol

They are well regulated, they still give "5 volts" (about 5.2volts) even with a 2.1amp load..... So, I think these were a good find at only $5.50AU...

I only bought 2.... I was going to buy 5.... or... what else could I do with them?

jackinnj · 14th January 2003, 09:59 PM

the MAX713 is a little expensive to use 2 of them -- about $7 -- but with Maxim you get a lot of utility for the USD or AUD.

12th January 2003, 11:45 PM	#1
SkinnyBoy Banned Join Date: Nov 2002 Location: Adelaide, Australia	NiMh Battery Charger? I have two 5volt @ 2amp switchmode plugpacks and would like to make a battery charger able to charge 2 AA NiMh batteries, They are 1.6amps each.. I would also like to include a feature to be able to select the charge rate (slow/normal/fast) anyone know of a circuit?? I have looked EVERYWHERE for a circuit.. well, nearly... also, a timer would be good... a simple one to select the charge time.. anyhelp would be GREAT!!

12th January 2003, 11:50 PM	#2
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	Try Maxim a circuit featuring these MAX712, 713 etc. chips was a staple in the ARRL Handbook, you can find it here at Maxim's site: http://www.maxim-ic.com/quick_view2.cfm?qv_pk=1666

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Battery Charger for 15V Li-ION Battery Pack ???	Jan Dupont	Parts	2	11th April 2009 02:18 PM
R/C battery and charger	jaudio	Power Supplies	3	18th February 2009 07:27 PM
Simple and safe NiMH charger?	antomas	Power Supplies	21	28th March 2008 05:38 PM
Battery Charger	ThSpeakerDude88	Everything Else	13	6th September 2006 10:40 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

12th January 2003, 11:54 PM	#3
SkinnyBoy Banned Join Date: Nov 2002 Location: Adelaide, Australia	Ok thanx, I think I saw it before... or maybe not... Anyway, my problem is (I have many, but not relevent to this project ) is that I am not sure if I can connect the cells in series due to the lowish input... one schematic I saw needed 7 volts I think to charge to cells in series...

14th January 2003, 12:49 AM	#4
dkemppai diyAudio Member Join Date: Nov 2002 Location: Michigan, USA	NiMh can be tricky to charge properly. Usually they use a microcontroller, and monitor voltage, current and temperature. They are very sensitive... ...you can charge them with a simple power supply, but will shorten the life/capacity of the cells. -Dan

14th January 2003, 09:27 PM	#5
Havoc diyAudio Member Join Date: Feb 2002 Location: Belgium	The max713 is very foolproof. Monitors dv/dt, Icharge, switches to trickle charge and has a timeout. If I remember you need 2V more than the max voltage during charge. So for 2 cells that would be 2V+2V+2V=6V. So a 7V adapter would be right. Never charge cells in parallel! They will always charge uneven.

14th January 2003, 09:59 PM	#7
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	the MAX713 is a little expensive to use 2 of them -- about $7 -- but with Maxim you get a lot of utility for the USD or AUD.