# Help needed working out resistor/voltages for a costume.

Discussion in 'The Projects Forum' started by Landstalker, Sep 20, 2012.

1. ### Landstalker Thread Starter New Member

Sep 20, 2012
6
0
Hello.

I'm making a gun from a videogame for a consume which has a motor, lasers and LEDs.

The LEDs and lasers are 3v
The motor is 4.5v (though it will turn at 3v)
The torch on the side is 4.5v too.

Is there any advantage to using 9v battery with resistors in place rather than using a voltage closer to the required voltages? Will a 9v last longer?

Also I have no idea how many milliamps the motor is drawing so I'm unsure which resistor value to use.

Any help would be much appreciated.

Thanks.

2. ### debjit625 Well-Known Member

Apr 17, 2010
790
186
With a resistor you can limit current ,you can't regulate voltage. If you are thinking about getting the required voltage from a voltage divider network (many noobs think so) then forget it.

As it’s a toy gun, and remote you have to use batteries, using a 9V battery is good idea but can't say how long it will run as you didn’t mention the total current consumption of your system.

To regulate the voltage, linear regulator will be not good as you are using a 9V battery and your required voltage is 4.5V half of the battery's voltage, you will end up with a huge power loss. A DC-DC converter will be good if using 9V battery...
Or you can use 4.5V rechargeable Li-ion battery it will be the best option...

To know how much current your motor is sinking, connect an ammeter in series with the motor with 4.5V.

Good Luck

3. ### Landstalker Thread Starter New Member

Sep 20, 2012
6
0
The plan was to have the battery providing a positive 'rail' down one side of the gun (inside) and a negative rail down the other, then use those to power the various items along the length. Take the feed for an LED and use a resistor to wire it up. Further along take the power to the motor with the relevant resistor in place etc etc.

Would that not work?

4. ### Landstalker Thread Starter New Member

Sep 20, 2012
6
0
Aaaah right. I've just done some reading on this.

So a resistor would waste a load of through battery energy as heat?
That would be pointless.

Maybe a 4.5v supply which would run torch and motor. Then a resistor to each LED. If it's only dropping the power to 3v (a 1.5v reduction) then that would be better.

Yes? No?

5. ### MrChips Moderator

Oct 2, 2009
16,745
5,135
A 9V battery is a convenient size but would not last long. If it is for something like a Halloween costume it might work. Carry spare batteries.

What is the motor for? Can you use two motors.

Don't use resistors. They waste energy.
Wire components in series to add up to 9v if they take the same current.
For example wire two 4.5v motors in series, or two 4.5v torches or three 3v LEDs.
If the motor and the torch take the same current, wire the two in series.
Experiment.

6. ### Landstalker Thread Starter New Member

Sep 20, 2012
6
0
Aaaah right. I've just done some reading on this.

So a resistor would waste a load of through battery energy as heat?
That would be pointless.

Maybe a 4.5v supply which would run torch and motor. Then a resistor to each LED. If it's only dropping the power to 3v (a 1.5v reduction) then that would be better.

Yes? No?

7. ### debjit625 Well-Known Member

Apr 17, 2010
790
186
Yes.
You can use cell phone's 4.5V Li-ion battery. You can recharge them too, but remember recharging Li-ion needs special care use proper recharging circuit.

Good Luck

Sep 20, 2012
6
0
9. ### Landstalker Thread Starter New Member

Sep 20, 2012
6
0
Thanks for your help. I think I have a plan now.

10. ### debjit625 Well-Known Member

Apr 17, 2010
790
186
You are welcome.
LEDs are current control device, you provide them with a proper current (by connecting them with a resistor in series known as current limiting resistor) and they regulate the voltage themselves, the regulated voltage will be the forward voltage drop of the LED. As the LEDs needs very small amount of current, the power loss through the current limiting resistor is also small enough in most case if properly designed.

If you don’t know how to calculate the current limiting resistor for the LED we can help.

Good Luck