• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Help please

Status
Not open for further replies.

JimB

Super Moderator
Most Helpful Member
If you mean the little 9v batteries used for radios and smoke alarms, there is your problem.

The battery is far too small, and will not last long when powering a motor.

Using several AA size batteries may be a better option.
How much current does the motor take?

JimB
 

gophert

Well-Known Member
Most Helpful Member
Hi I have built the circuit below, I am using a 9v battery as the power supply, unfortunately when the motor is running the battery gets extremely hot, how could I prevent this from happening please? Any help will be extremely appreciated

You may have something wired incorrectly (a short or improper resistor value). But, as Jim said, the little 9V battery is not intended for large loads. Typically, loads under 100 mA should be used with 9V batteries.
 

ronsimpson

Well-Known Member
Most Helpful Member
With a 9 volt supply there is not a problem.
BUT "5-30v BATTERY/SUPPLY" It is possible to get more than 20 volts on the gate of the MOSFET with a 30V supply. Most all MOSFETs should not see more than 20V Gate-Source.
 

alec_t

Well-Known Member
Most Helpful Member
You need a reverse-biased power diode across the motor to protect the FET from the voltage spike which occurs when the FET switches off.
 

Tony Stewart

Well-Known Member
Most Helpful Member
Battery ESR must be much lower than motor DCR and FET RdsOn

A better way is divide down a stable Vref to 50mV with LM358 or sense to ground OpAmp then sense current with max expected surge 10x? And choose R sense.

Then torque control is 0 to 50mV

Avalanche diode protected FET is needed.
 
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top