NiMH battery recharger schematic needed

[boylesg]

http://digital-diy.com/general-electronics/227-float-charging-nimh-cells.html

I have found this one but to charge both 4 x series AA cells and a 9V battery I would pretty much need to create two seperate circuits with two different plug packs to power them.

Does anyone know of a single schematic that can charge both AAs and the 9V batteries?

I am thinking along the lines of two seperate points at which you attach the different battery types but that don't function unless you do complete the circuit with a discharged battery.

 

[tpetar]

For charging NiMh monitoring and controlling current is important.

See this circuit, works nice :



Two diodes make constant 1.3V at the transistor base and constant 0.65V on emitter.

R2 sets the charge current 0.65/R2. 0.65/10 make 65mA on emitter output.

;-)

 

[boylesg]

For charging NiMh monitoring and controlling current is important.

See this circuit, works nice :

View attachment 85475

Two diodes make constant 1.3V at the transistor base and constant 0.65V on emitter.

R2 sets the charge current 0.65/R2. 0.65/10 make 65mA on emitter output.

;-)

Well that one is nice and simple - thanks.

What does 12ishV mean? What is the maximum you would want to apply to the circuit?

I take it there is no reason I couldn't charge 4 x 1.2V cells in series? That would make 5.2ishV which is within the range.

What slows or stops the charge current when the battery reaches full charge?

I might be able to put an LED in here some where to indicate full charge.

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I suspect it wouldn't be a bad idea to put a forward biased diode in series with the battery to prevent it discharging if you remove power from the circuit.

Let me think here......

As the battery reaches full charge it would oppose the voltage of the power source and as a result the transistor would see a lower voltage.

That would mean the current through R2 would fall for starters. The current flowing through R1 and the diodes would fall also.

What is the purpose of R1 exactly?

Could you replace D1 or D2 with a LED as an indicator? Does the current through these diodes fall enough, as the battery reaches full charge, to cause an LED to turn off?

 

[tpetar]

12 on top of circuit is 12V input voltage.

You can monitor voltages of NiMh batteries in range of 1,4V-1,6V.

Also when battery voltage reach that full of charge level, you can disconnect battery from charger.

If you look better without R1 positive is direct connected to ground over these two diodes, high current will start to flow and diodes will explode.

I try this circuit to charge Alkaline and NiMh batteries successfully.

To this circuit you can add voltage monitoring and switch off based on full voltage level and timer.
After that next version can have temperature monitoring and automatic adjustment of current Lo/Hi, and fan control.

 

[boylesg]

To this circuit you can add voltage monitoring and switch off based on full voltage level and timer.
After that next version can have temperature monitoring and automatic adjustment of current Lo/Hi, and fan control.

Any schematics for these?

 

[tpetar]

Any schematics for these?

See this multi-battery charger/tester.

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English translation

**broken link removed**