voltage drop

Thread Starter

levs

Joined Jun 17, 2009
2
hi, i dont know if anyone can help me out with this, i have a rc boat and the motor seems to work only on and off ( one speed for forwards) it is far to fast for what i need it for. is it possible to to slow it down by adding l.e.d's bulbs or anything to the +/- black/red wires on the motoers? it runs on 7.2v nicad , dropping the out put to the motor to drop it down, making it run slower?

thanks
levs
 

SgtWookie

Joined Jul 17, 2007
22,230
For an "easy fix", you could add some diodes in series with the motor.
1N5400 diodes are rated for 3 Amperes.

Each diode you put in series with the motor will drop the voltage by somewhere between 0.7v and 1v, depending on the load.

A more elegant solution would be to use PWM. Check out Bill Marsden's circuits, here:
http://forum.allaboutcircuits.com/showthread.php?t=24028

Note that you don't HAVE to have D1/D2/R1/R2 in the circuit, but they'll give you a rough visual indication of what the output duty cycle is - and whether it's working or not.
 
Last edited:
...I'm assuming that you are talking about a standard DC motor.
If you connect a resistor in serie with the motor you will get what you want.
...by the way some power will be dissipated on the resistor and the battery will not last more...

If you want to reduce the speed and increase the battery life, you should use a PWM technique.

Ciao,

Mauro
 

thingmaker3

Joined May 16, 2005
5,083
What you suggest will work, but will waste power. A more efficient method is to use a thing called "PWM" or "Pulse width modulation." Enter either term with the search function to learn more.
 

Thread Starter

levs

Joined Jun 17, 2009
2
thanks alot for those replys, very quick! you know what your on about! i will try these options out.

thanks again
levs

great forum
 
...now three people has suggested to use the PWM...

you should be convinced of using it...

I would suggest to use an NE555 (LM555) and a power mos for making the PWM generator you need.
It's simple and cheep.

You should easily find schematics on line.

Ciao,

Mauro
 

jpanhalt

Joined Jan 18, 2008
11,087
Here's a non-PWM method, assuming you do not need variable speed.

7.2V is 6 cells. Will it run on just 3 cells or 4 cells? If it runs on 3 cells, then your 6-cell pack can be reconfigured to two, 3-cell packs. Connect those in parallel for longer running time.

John
 
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