Reversing polarity of an electromagnet.

Other Hardware General Electronics
1

Using PWM changing polarity of electromagnet.

I'm planning to use a L298n h-bridge to change the polarity of the electromagnet. My question is will I need to have rectifier diodes in the circuit connecting to the h-bridge or is that something that the h-bridge can handle.

The electromagnet has a 12v supply via the nano VIN and a resistance of 40ohm which should mean the current will be around 300mA.

Thanks :slight_smile:

2

It would appear from the datasheet that the L298N does require external clamp diodes.

It is considered by most here to be obsolete.

3

Rwj_1983:
Using PWM changing polarity of electromagnet.

I'm planning to use a L298n h-bridge to change the polarity of the electromagnet. My question is will I need to have rectifier diodes in the circuit connecting to the h-bridge or is that something that the h-bridge can handle.

The electromagnet has a 12v supply via the nano VIN and a resistance of 40ohm which should mean the current will be around 300mA.

Thanks :slight_smile:

Just a bit curious. What is the purpose of changing the polarity of your electromagnet?

Paul

4

Thanks for the replies.

Paul, I'm using the open source sketch available for Wonder Machine's Slow Dance frame and trying to build my own. The reversing polarity is basically to push/pull a magnet attached to a piece of spring metal at each end of the coil.

I'm very new to this kind of thing so it's been a real crash course trying to understand how everything works. Any advice or input is greatly appreciated.

I can attach a diagram later today of my circuit if anyone wants to critique or give suggestions.

Out of curiosity what h-bridge is considered current??

Thanks again.

5

Out of curiosity what h-bridge is considered current??

There are many. Buy one appropriate for the task at hand. Pololu has an excellent selection.

6

Here is my schematic. Does it look ok?

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7

Rwj_1983:
Here is my schematic. Does it look ok?

Not if you expect it to work... as there is no +12v supply on Vs.

Are you using a common L298N module? It looks that way as those are not the pin numbers for the bare chip. If so, the required snubber diodes are usually on the module.

D1 is not needed for a non-inductive load.

R2 is on the wrong side of R1. It drops the gate voltage that way. Not by much but details matter. Just like providing details/links to the actual parts you’re using as the help you get is only as good as the information you provide.

8

Try this part: http://www.ti.com/lit/ds/slvsac0f/slvsac0f.pdf a DRV8841 Dual H-Bridge Driver IC or this part: NCV7702B: Motor Driver, Dual H-Bridge, 1.0 A By On. These are MOSFET H bridges and will give you considerably more power and voltage at the motor terminals then the L298N. No external protection is required even though your load is inductive by definition. This response is to help you get started in solving your problem, not solve it for you.
Good Luck & Have Fun!
Gil

9

Thanks for your reply.

Regarding the 12v supply to the h-bridge being on vcc that's my error in the schematic, sorry.

I am using a module. This

I'll update my schematic. I wasn't able to find the exact module in kicad.

I'm also going to post elsewhere as I'm not sure this is the right spot with regard to the input I'm asking for.

Thanks again, much appreciated!

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10

Thanks Gil. I'll look at Those options! And thanks for the response regarding induction.

gilshultz:
Try this part: http://www.ti.com/lit/ds/slvsac0f/slvsac0f.pdf a DRV8841 Dual H-Bridge Driver IC or this part: NCV7702B: Motor Driver, Dual H-Bridge, 1.0 A By On. These are MOSFET H bridges and will give you considerably more power and voltage at the motor terminals then the L298N. No external protection is required even though your load is inductive by definition. This response is to help you get started in solving your problem, not solve it for you.
Good Luck & Have Fun!
Gil