# Battery voltage change 3,7V to 3,0V

#### 552117348

Joined May 28, 2022
8
Hi,

I have a 3V laser and I need to connect it to 1x battery 18650B (3,7V)
What resistors should I use to change the voltage?

Thanks.

#### drjohsmith

Joined Dec 13, 2021
816
Hi,

I have a 3V laser and I need to connect it to 1x battery 18650B (3,7V)
What resistors should I use to change the voltage?

Thanks.
If you use a resistor,
the voltage drop across the resistor will depend upon the current drawn,
which as the current is not constant, then the voltage drop across the resistor is not constant

You need a voltage regulation of some sort
what current does the laser take ?
what is the voltage range / tolerance of the laser

#### ronsimpson

Joined Oct 7, 2019
2,797
You could use the forward drop of a diode to drop 0.65 volts.
Add a diode from battery to laser pointing so current flows. There will be a loss in the diode that will get you close.

#### MisterBill2

Joined Jan 23, 2018
16,598
Indeed the TS will need a resistance to drop the voltage a bit. And certainly that will depend on the current. A regulator will be overkill for the application, though. Select the resistor for 3.2 volts because the battery voltage will drop. To calculate the resistor, for that 0.68 volt drop R=V/I= 0.68/ (unknown laser diode current requirement)

#### dl324

Joined Mar 30, 2015
16,162
+1 for using a diode, e.g. 1N4001, to drop the voltage about 0.7V. That should be close enough for the laser if it's battery operated. Note that your 18650 voltage will be more like 4.2V when fully charged.

#### Ya’akov

Joined Jan 27, 2019
8,544
Hi,

I have a 3V laser and I need to connect it to 1x battery 18650B (3,7V)
What resistors should I use to change the voltage?

Thanks.
You might find the laser works just fine with the lithium cell and no regulator/diode/resistor. If you can get the datasheet, it will have absolute maximum rating information. If it is 5V (this is often the case) the lithium cell is OK as is.