# Can a 12 Volt 1.5 Amps AC to DC adapter be used to charge a 9 Volts battery?

#### Hooriya

Joined Oct 4, 2015
5
I am a student of Electrical Engineering. I am working on a circuit which requires a 9 volts 550mAh battery as a source. This battery source is a rechargeable one. Now, while going through some of the articles, I came to know that for recharging a 9 volts battery, we require a charger which has the output of at least 9.5 volts.
My question is that can I use a 12 volt 1.5 amps adapter to charge a 9 volt 550mAh battery? If yes, then should I make a resistor divider circuit to make it equal to 9.5 before connecting to battery or is charging the battery at 12 volts okay?
Also is a 9 volt 1.5A ac to dc adapter sufficient to charge a 9 volts battery? Some of the articles I read clearly stated that at the least 9.5 volts charger is required?
All suggestions are welcome.
Thank you.

#### GopherT

Joined Nov 23, 2012
8,009
I am a student of Electrical Engineering. I am working on a circuit which requires a 9 volts 550mAh battery as a source. This battery source is a rechargeable one. Now, while going through some of the articles, I came to know that for recharging a 9 volts battery, we require a charger which has the output of at least 9.5 volts.
My question is that can I use a 12 volt 1.5 amps adapter to charge a 9 volt 550mAh battery? If yes, then should I make a resistor divider circuit to make it equal to 9.5 before connecting to battery or is charging the battery at 12 volts okay?
Also is a 9 volt 1.5A ac to dc adapter sufficient to charge a 9 volts battery? Some of the articles I read clearly stated that at the least 9.5 volts charger is required?
All suggestions are welcome.
Thank you.
Charging batteries is usually a bit more complicated and you need to provide the battery chemistry and "C" rating of the battery. The "C" rating tells us the maximum charge rate and the chemistry tells how it should be charged - constant current, various rates at various levels of the charging cycle. Also, what is your goal, fastest possible charge, most possible charge cycles, most efficient charge, ...?

#### R!f@@

Joined Apr 2, 2009
9,916
You can, provided that the battery is charged according to the battery specification.
In short you need a charger that suites the battery chemistry and charging method

#### Dodgydave

Joined Jun 22, 2012
11,235
Depends on what type of battery it is, if its a nicad/nimhi or sla type you can put 12v in series with a resistor, or direct onto the battery, if is a li-on lifepo you need a charger chip.

#### wayneh

Joined Sep 9, 2010
17,493
As DD just said, it's all about the battery. You might use just a current limiting resistor, or a voltage regulator, or a dedicated charge controller, maybe even including temperature monitoring. The choice depends on the battery chemistry, which dictates the charging strategy.

A 9V adaptor is indeed very likely able to charge a 9V battery but to be certain you need more details. Is it an old-fashioned wall-wart adaptor or a small, modern type? The old ones would have a voltage well over the rating when the current draw was less than the rated max. And not all 9V batteries are equal.

#### Hooriya

Joined Oct 4, 2015
5
Charging batteries is usually a bit more complicated and you need to provide the battery chemistry and "C" rating of the battery. The "C" rating tells us the maximum charge rate and the chemistry tells how it should be charged - constant current, various rates at various levels of the charging cycle. Also, what is your goal, fastest possible charge, most possible charge cycles, most efficient charge, ...?
Thank you for your answer. I am using a 9 volts, 550mAh Li-ion battery. I am not sure about the C rating though, although, I have searched on the batteries and have found out that my battery will have the maximum of 3C. My goal is most possible charge cycles. So, could you kindly guide me whether to go for the 12 V 1.5 Amps adapter or not?

#### Hooriya

Joined Oct 4, 2015
5
Depends on what type of battery it is, if its a nicad/nimhi or sla type you can put 12v in series with a resistor, or direct onto the battery, if is a li-on lifepo you need a charger chip.
I'm using a Li-ion battery. Could you elaborate on the charger chip that you mentioned? Thank you.

#### Alec_t

Joined Sep 17, 2013
14,210
Charging Lithium batteries is dangerous if not done properly. I suggest you read this.

#### Hooriya

Joined Oct 4, 2015
5
As DD just said, it's all about the battery. You might use just a current limiting resistor, or a voltage regulator, or a dedicated charge controller, maybe even including temperature monitoring. The choice depends on the battery chemistry, which dictates the charging strategy.

A 9V adaptor is indeed very likely able to charge a 9V battery but to be certain you need more details. Is it an old-fashioned wall-wart adaptor or a small, modern type? The old ones would have a voltage well over the rating when the current draw was less than the rated max. And not all 9V batteries are equal.
I'm using a Li-ion battery with a max rating of 3C. The 12 Volt adaptor that I'm using is: http://www.evselectro.com/power-supply/ac-to-dc/12v-dc-1.5-amp-3801
The 9Volts adapter is this one:
http://www.evselectro.com/power-supply/ac-to-dc/9v-dc-2.0-amp-3868

#### Kermit2

Joined Feb 5, 2010
4,162
Unless you stand there and monitor the charging process and keep a vigil on the volt meter in order to stop the charging process, while also monitoring the temperature of the battery, you WILL eventually overcharge the battery. Maybe not the first few times, but sooner or later it WILL happen.
Hope you have good liability and fire insurance policies.

http://www.batteryjunction.com/9v-lithium.html

#### wayneh

Joined Sep 9, 2010
17,493
I'm using a Li-ion battery with a max rating of 3C. The 12 Volt adaptor that I'm using is: http://www.evselectro.com/power-supply/ac-to-dc/12v-dc-1.5-amp-3801
The 9Volts adapter is this one:
http://www.evselectro.com/power-supply/ac-to-dc/9v-dc-2.0-amp-3868
OK, those both appear to be modern adapters and the output voltage is probably quite close to the nominal value.

For Li-ion, you need a charge controller chip. The requirements of that chip will determine whether you can use the 9V adapter. My guess is that you will not be able to use it and will need the 12V one.

#### Dodgydave

Joined Jun 22, 2012
11,235
Try the Ltc1732 chip, there are others.