# 9volt Ni-MH battery charger circuit diagram

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#### sshahid

##### New Member
dear sir

i need 9volt 200ma Ni-MH low coast battery charger circuit diagram

note: the input dc votage range 8volt to 40volt.

thanks

shahid hussain

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##### Banned
9 volt Ni-Mh battery? The nominal voltage for a Ni-MH cell is 1.2 volts, that would mean you have a 7.5 cell battery pack?

#### chris54

##### New Member
what he means Is that you have 7.5 cells (batterys) times 1.2 volts per cell equals 9 volts.

##### Banned
I'm not sure what you have arhi but are you sure it's a NiMH? If that battery pack is 7 NiMH cells in series 9.1 volts is overcharged. 7 cells nominal voltage would be 8.4 volts 8 cells would be 9.6 volts. There are more than enough battery charging schematics you can find via Google or searching the forums here, just look.

#### blueroomelectronics

##### Well-Known Member
9v NiMH batteries usually have 6 internal cells. 7.2v fully charged.

#### arhi

##### Member
chris, 7.5 cells ??? how do you implement half a cell ?

bill, I was 100% sure of that until I checked with voltmeter .... 2 nimh 9V batteries

on the sticker say: 250mAh nimh 6f22 8.4V rh-9V250

both fully charged and voltmenter show: 9.10 on one and 9.13 on another ... will try now with osc ... 9.28V avg on one and 9.27V avg on another - using x10 probe - ....

now .. the batt states 8.4, I measured 9.2V ... that's way over 7.2 (and I expected 7.2 when I purchased them)

##### Banned
8.4V's woohoo we have an answer! It's a 7 cell pack =) I'm not sure why you're using such a battery pack, lithium batteries are better in every respect of operations for small packs like that. Seeing a battery voltage over 8.4 volts on a freshly charged NiMh pack is perfectly normal, that 'surface charge' quickly goes away when the battery is actually loaded. Use google to search the net or the forums here, there are MANY threads for charging battery packs that include charger schematics.

#### audioguru

##### Well-Known Member
My Energizer 9V Ni-MH battery is 1 year old. It charges to 1.44V per cell. It has 6 cells so its fully charged voltage is 8.64V. Its voltage quickly drops to 1.2V per cell which is a total of 7.2V at a load current less than 10mA. It is marked "7.2V".
Fully charged, its voltage immediately drops to 6.8V with a load current of 230mA then keeps dropping more.

Today on Energizer's site they show a new 9V Ni-MH battery marked "8.4V" and the graphs show that it charges to over 9V and its voltage is a little higher than 8V for a discharge at currents less than 35mA.

My electric model airplane uses a Ni-MH battery with 7 AAA cells. It is marked "8.4V". I charge it to 10.25V when it becomes warm.

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##### Banned
You should use two or three cell Lithium pack audioguru, less than half the weight of the nimh setup you're using on packaging space alone.

#### Hero999

##### Banned
All of my 9V NiMH batteries are 7 cells, they have a nominal voltage of 8.4V and measure over 10V hot off the charger.

#### sshahid

##### New Member
8.4volt Ni-MH battery charging circuit diagram

dear sir
i need low coast 8.4volt 200 ma Ni-MH battery charger circuit diagram with over charging protection.

note: input dc voltage range 8volt to 40volt

thanks
shahid hussain

Last edited:

#### sshahid

##### New Member
8.4volt Ni-MH battery charging circuit diagram

sir
i need 8.4volt 200mh Ni-MH low coast battery charger circuit diagram with
over charging protcetion.

thanks

shahid hussain

#### arhi

##### Banned
I never understood why they made 9V rechargeables, the energy density is horrible, use a real pack =\ Or lithiums.

#### audioguru

##### Well-Known Member
I never understood why they made 9V rechargeables, the energy density is horrible, use a real pack =\ Or lithiums.
I use a "9V" (actually 7.2V) Ni-MH battery in my Sound Level Indicator project. It can supply 230mA to light all 10 LEDs for a few minutes so I can show it to visitors. It is charged from a current-limited constant voltage which delivers a very low trickle charge current. My old Ni-Cad 9V battery failed (it was about 12 years old) and this "new" one is about 1 year old.

#### HarveyH42

##### Banned
The two batteries I got from the link posted earlier, still read slightly over 9 volts, and have been sitting for about a month.

#### blueroomelectronics

##### Well-Known Member
I always get a kick out of "dear sir" it's usually a hoplessly clueless student.

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