• 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.

Begginer question

Status
Not open for further replies.

Njguy

Member
Say you wanted to hook up an electromagnet to a car battery. What would be the best way to "throttle" so to speak the power going to the magnet? How could you reduce or increase the current going to the magnet from the battery at will. Similar to how you can increase the power going to an rc car motor. This is for control and saftey. Start off with low power and increase slowly. Thanks guys.
 

Njguy

Member
Ok, so I found out that I need a Rheostat/potentiometer. Does anyone know where i can get one that would be safe on a car battery?
 
Last edited:

audioguru

Well-Known Member
Most Helpful Member
100 years ago a huge expensive rheostat was used. A Pulse-Width-Modulation circuit is a modern way to control the speed of a DC motor, dim a light or adjust the power to an electromagnet withot anything getting hot and wasting a lot of power.

Do the light dimmers in your home use a huge expensive rheostat? No, they use a cheap little "volume control" and form of PWM.
 

Njguy

Member
100 years ago a huge expensive rheostat was used. A Pulse-Width-Modulation circuit is a modern way to control the speed of a DC motor, dim a light or adjust the power to an electromagnet withot anything getting hot and wasting a lot of power.

Do the light dimmers in your home use a huge expensive rheostat? No, they use a cheap little "volume control" and form of PWM.
Only thing I can find on that is this pre-fabricated kit. DC to Pulse Width Modulator
Would this work on a 12V car battery? And if anyone knows of anything better, that would be good too.
 

audioguru

Well-Known Member
Most Helpful Member
Yes, that is a PWM circuit. But I have seen much simpler less expensive ones that have the same ratings. Maybe they made that one cost as much as they can.

You did not mention the current of your electromagnet. It must not use more than the max allowed current of the driver circuit.
 

RCinFLA

Well-Known Member
That module looks good.

The electro-magnetic is going to be an inductive load. This means you can get a high kick-back voltage that could blow out the PWM module.

At minimum put a diode in parallel with the coil, cathode to PWM output, anode to ground. This would be normally non-conducting unless a negative voltage kick-back is produced by coil which it will clamp near ground.

The PWM module may already have this but better safe then sorry.
 

Njguy

Member
That module looks good.

The electro-magnetic is going to be an inductive load. This means you can get a high kick-back voltage that could blow out the PWM module.

At minimum put a diode in parallel with the coil, cathode to PWM output, anode to ground. This would be normally non-conducting unless a negative voltage kick-back is produced by coil which it will clamp near ground.

The PWM module may already have this but better safe then sorry.
Well it takes up to 35V so I don't see how it could be blown out
 

audioguru

Well-Known Member
Most Helpful Member
Well it takes up to 35V so I don't see how it could be blown out
The kick back voltage of an inductor is hundreds of volts without a diode to arrest it.

Hold the two wires of your inductor in one hand and turn it on and off to feel the kick back voltage. ZAP! You will never do it again.
 

Njguy

Member
I understand that an electromagnet is an inductive load, but they also generate heat? So aren't they partially Resistive? Also how do you know what kind of diode to get?
 
Last edited:
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top