# Potentiometer to Variable Resistor

#### bong

Joined May 20, 2013
5
Hi,

i want to change the exisiting resistor circuit (potentiometer) to a variable
type so that i can control the speed of the crane machine. I have attachment for clear illustrations and i would like to get ideas/advise on how to do it.
I would appreciate for any assistance.
regards,
bong

#### Attachments

• 350.3 KB Views: 46

#### Shagas

Joined May 13, 2013
804
By the resistor circuit are you talking about the 3,6k 10k and 5k?
You want to put variable resistors instead of the fixed ones?

#### bong

Joined May 20, 2013
5
yes. i want to change those three resistor if applicable to
variable type to limit the current flowing thus reducing the
speed of the motor.

#### wayneh

Joined Sep 9, 2010
17,498
Be sure to retain a fixed R1, to limit current and avoid a short at one end of the pot's rotation.

#### bong

Joined May 20, 2013
5
Thanks for the reply. So I should retain R1 (5kohms) and only
R2 and R3 to be variable type.
Also, this is the advise from the crane maker "Yes, you can replace the potentiometer to variable (volume) resistor.
However, that resistor will be required larger capacity (larger than 4 watt) because large current flows through it."
How can I calculate for the correct wattage? Can you please show me
(sketch) on how the variable resistor can be wired on the circuit?
I appreciate for any reply. Thank you very much.

#### wayneh

Joined Sep 9, 2010
17,498
... that resistor will be required larger capacity (larger than 4 watt) because large current flows through it."
That makes no sense until you consider those "bypass" switches. If the pot happened to be set near one end of its travel and the switch sends full voltage to the short, low ohms end, a high current might be possible. But even that depends on where Vout goes.

#### bong

Joined May 20, 2013
5
thanks for the reply.
will the attached makes sense?
please correct me if i am wrong.
any advise would be greatly appreciated.

#### Attachments

• 39.2 KB Views: 35

#### wayneh

Joined Sep 9, 2010
17,498
Your polarity reversal switch drawing doesn't make sense but yes, I think the way you have replaced the fixed resistors+switches with pots makes sense.

A single pot to replace the two would give the same functional result with just one knob to turn.

I really don't think the manufacturer's comment about high current makes any sense. But I'd sure want to be careful when experimenting, on the chance I'd misunderstood what they were trying to tell me.

#### bong

Joined May 20, 2013
5
"A single pot to replace the two would give the same functional result with just one knob to turn." ------
Hi Mr Wayneh. I appreciate all your inputs. May i request for a sketch to show single pot to replace the two that will yield the same result. Thanks a lot.

#### wayneh

Joined Sep 9, 2010
17,498
In your schematic, Vout depends on the sum total resistance of the two pots, not on the position of either of them specifically. So there's no need for two of them.