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NiMH battery charger

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neil1221

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hi im trying to build a battery charger for my 9 volt NimH battery and fortunately I found a spec sheet of MAX712 which I think can apply to my project. but the problem is I found some confusing parts on the schematic of the specsheet. "the BATTERY part" I have attach the schematic diagram and pointing out the confusing part (im thinking that I would place a battery on that part)..can someone explain me what is this part. thank you so much people...
 

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kchriste

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That "part" is your 9 volt NimH battery which you wish to charge.
 

bountyhunter

Well-Known Member
hi im trying to build a battery charger for my 9 volt NimH battery and fortunately I found a spec sheet of MAX712 which I think can apply to my project. but the problem is I found some confusing parts on the schematic of the specsheet. "the BATTERY part" I have attach the schematic diagram and pointing out the confusing part (im thinking that I would place a battery on that part)..can someone explain me what is this part. thank you so much people...
A "9V" NI-MH is about 150 mA hour so you can just use a resistor and an unregulated voltage source to supply continuous current. If you use 10 - 15mA charge current, you can charge it continuously with no harm to the battery. You could use a "12V" wall wart that puts out maybe 15V no load and a resistor in series of about 470 Ohms.
 
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neil1221

New Member
hey guys thanks for the replies

@ kchriste and what am I suppose to place at the "load" part of the schematic..isn't that where I will place the battery that I will charge?

@ bountyhunter. for how many hours will I charge the battery if I will use an unregulated supply.On the spec sheet is says that the maximum charging time out for this is 264 minutes..
 

bountyhunter

Well-Known Member
@ bountyhunter. for how many hours will I charge the battery if I will use an unregulated supply.On the spec sheet is says that the maximum charging time out for this is 264 minutes..
If you use about 10 - 15 mA charging current , you can charge it as long as you like since you will be below 1/10C rate and the battery should handle that indefinitely without problem.
 

Chippie

Member
The load is whatever the battery is supply power to...However not all of the battery voltage is applied as there is a v drop across the current sensing resistor.

The charger is designed to charge a nimh chemistry battery and as such has a finite charge time...Unlike Nicads, nimhs do not like being overcharged, hence the timer function..
 

bountyhunter

Well-Known Member
The charger is designed to charge a nimh chemistry battery and as such has a finite charge time...Unlike Nicads, nimhs do not like being overcharged, hence the timer function..
Most NI-MH will accept C/10 charge rate continuously with no problem, but battery spec sheet will give that information so always check to make sure.
 
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