Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › 9V battery charger schematic?
New Posts  All Forums:Forum Nav:

9V battery charger schematic? - Page 2

post #16 of 23
Thread Starter 
Quote:
Originally Posted by Avro_Arrow View Post
 


Do you know how many cells are in the battery?

 

It could be 6, 7 or 8.

It might say something like 7.2 volts, 8.4 volts

or 9.6 volts on the battery.

 

For 200mA charging current, R11 would be about 3.25 ohms.

If the battery has 7 cells, charging voltage should be set to 10.5 volts.

It is an 8.4V battery. Would that means 7 cells?

post #17 of 23
Quote:
Originally Posted by drabina View Post
 

Thanks for replies. The battery I am going to be using is Rayovac 9V 200mA NiMH rechargeable battery.

 

Incidentally, what will the battery be used for?

 

As other posters explained, for NiMH batteries the method for determining charge cutt-off is important.  However, I have found it much more problematic to find an easy way for properly terminating discharge.  As these batteries internally tend to have a number of NiMH button-cells welded in series, discharging them too deeply will cause the remaining stack of cells to reverse-charge the first cell to become fully discharged.  They don't like that AT ALL!  If your circuit is designed to still operate quite happily at 5V for example, you won't notice the battery is slowly being killed.

post #18 of 23
Quote:
Originally Posted by drabina View Post
 

It is an 8.4V battery. Would that means 7 cells?


Yes, 1.2 volts x 7 cells = 8.4 volts.

post #19 of 23
Thread Starter 
Quote:
Originally Posted by 2leftears View Post
 

 

Incidentally, what will the battery be used for?

 

The battery is going to power a headphone amplifier.

post #20 of 23
Quote:
Originally Posted by drabina View Post

The battery is going to power a headphone amplifier.

Thought it might biggrin.gif

Then you may want to check the amplifier shuts the power down when the battery is down to 7V or so. Alternatively fit a LED which switches off at 7V. Not as reliable but better than no indication at all.

Most likely if you continue to use the amp until the sound starts to distort, your NiMH battery will be very unhappy indeed. It won't break immediately, but you will seriously reduce the number of times you can recharge it.

Depending on how you use it, buying a load of Alkaline 9V PP3 batteries may turn out cheaper in the long run.

Unfortunately PP3 style 7.2, 8.4 and 9.6 V batteries are a poor configuration for NiMH and NiCd rechargeables as the internal cells are not individually monitored during charging and discharging. They mostly find use as backup batteries on a very low trickle charge. They are still fairly cheap batteries and I do not know of a supplier which fits polarity reversal protection diodes for each cell in this battery format.
post #21 of 23
Thread Starter 

I was thinking of using a circuit like that to charge the battery by a manual ON/OFF/CHARGE switch. In ON position, the amp would run from the battery (no charge), OFF - everything is off, and CHARGE would enable the trickle charging circuit.

post #22 of 23

1. IMHO, what Tangent has shown you is optimum.

 

2. Check my signature for a humble, but simple design for a trickle charger.  It was originally proposed by _redruM, but had significant input from Tangent. I would change the 100 ohm resistor to a 75 ohm resistor, but other than that, it's worked for almost 7 years (well, I had to replace the batteries once).

 

http://www.head-fi.org/t/185377/trickle-chargers


Edited by tomb - 2/14/14 at 6:40pm
post #23 of 23
Quote:
Originally Posted by tomb View Post
 

1. IMHO, what Tangent has shown you is optimum.

 

2. Check my signature for a humble, but simple design for a trickle charger.  It was originally proposed by _redruM, but had significant input from Tangent. I would change the 100 ohm resistor to a 75 ohm resistor, but other than that, it's worked for almost 7 years (well, I had to replace the batteries once).

 

http://www.head-fi.org/t/185377/trickle-chargers

I have used tombs charger for years without a single problem

New Posts  All Forums:Forum Nav:
  Return Home
Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › 9V battery charger schematic?