# Another Newbie question about Power supplies

Mar 11, 2020
846

#### Bluejets

Oct 5, 2014
5,985
I have a 4 cylinder car so how fast will it go.
See the problem..??

Assumption is your 9v battery is a common smoke alarm battery so current in mA.
The internal structure of the battery limits the amount of current supply and the life span.
A site Battery University has a great deal of reliable information on battery specs.
https://batteryuniversity.com/learn/

#### Nanren888

Nov 8, 2015
623
Why?
If you are simply trying to power something that normally uses a nine volt battery, then set the voltage to 9 volts.
The current will just be what the circuit needs. Power supplies often offer a current limit that helps prevent accidents if connected incorrectly, or circuits are not as expected. You can set the supply up to limit the current to some sort of maximum that is expected from a nine volt battery. If as Bluejets asked, the battery is a standard 9V pack, then you can limit it to quite low.
suggests a peak current of about 600mA from such a battery.
Depends whether normally takes standard dry cell or alkaline.
.
If you are trying to emulate a battery over its lifetime, as it goes from new to depleted, then much more complicated.

#### Audioguru

Sep 24, 2016
3,649
Energizer makes 9V alkaline batteries and show a datasheet. It shows the voltage dropping with time when powering a 270 ohm load.
You can simply calculate the current that is also dropping by using Ohm's law.
If the resistance is lower then the current is higher and the time is shorter.

#### Attachments

• 9V battery.png
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#### Audioguru

Sep 24, 2016
3,649
This is from Duracell's datasheet:

#### Attachments

• Duracell 9V battery.png
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#### SparkyCal

Mar 11, 2020
846
Thank-you. That helped but I asked my question in a twisted fashion. I will be re-asking it on a new thread, as it is a different question. My fault.

#### bob.steel

Feb 27, 2020
16
Set amperage at 500 mA and set voltage at 9 volts . Watch the little light . If it is being current limited the light next to that value will be lit . If it is being voltage limited then its light will shine for all to see.

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