Author Topic: MOSFETS and relays  (Read 3067 times)

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Offline airman00Topic starter

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MOSFETS and relays
« on: July 27, 2007, 03:32:55 PM »
Where can I get relays for a motor that is 24VDC @ 11 amps? I can't find it anywhere. It should be cheap and should be switched by 4 AA batteries.

If there are any cheap H bridges or motor controllers that fit my requirements, please tell me about it!
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Offline Bajanick

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Re: Powerful Relays - LOOK
« Reply #1 on: July 27, 2007, 05:18:16 PM »
Try http://www.allelectronics.com/ They have a 3-15 volt, 18amp SSR.

and theres this one also.....
http://www.allelectronics.com/cgi-bin/item/SRLY-26/100/40_AMP_SOLID_STATE_RELAY_.html


For H-bridges theres lots of places........

Parallax
Pololu
Robotmarket place sells quite a few different makes and models.
« Last Edit: July 27, 2007, 05:44:40 PM by Bajanick »

Offline airman00Topic starter

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MOSFETS and relays
« Reply #2 on: July 28, 2007, 07:22:36 PM »
How can I wire a mosfet so that is works like a relay.?

Can I wire a MOSFET so that 5V@300mA switches 24V@11A like in a relay?

What are the advantages of using a MOSFET over a relay?
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Offline airman00Topic starter

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Re: MOSFETS and relays
« Reply #3 on: July 28, 2007, 07:46:49 PM »
Should I use 2 DPDT relays to control the motor to be bidirectional or can I use MOSFETs to do this? Will the MOSFET be cheap if I need one for 11 A?
Please Help
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Offline HDL_CinC_Dragon

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Re: MOSFETS and relays
« Reply #4 on: July 28, 2007, 11:52:20 PM »
You could use a mosfet to trigger a relay im sure, but 11A through a mosfet im sure would achieve but a pretty picture... pretty and painful if your close enough
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Offline airman00Topic starter

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Re: Powerful Relays - LOOK
« Reply #5 on: July 29, 2007, 05:19:12 AM »
If it says 40 amps @ 24-280 VAC does that mean it would work with 24 VDC. I don't know because I have no idea how solid state works.
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Offline Bajanick

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Re: Powerful Relays - LOOK
« Reply #6 on: July 29, 2007, 09:28:28 AM »
If it says 40 amps @ 24-280 VAC does that mean it would work with 24 VDC. I don't know because I have no idea how solid state works.


I posted the wrong link, sorry. Search the site for solid state relays and you will find one you need. Heres a good one.
You can switch this one with up to 18 amps between the voltages of 3 and 15 volts. I am not sure why they are showing AC being switched.
http://www.allelectronics.com/cgi-bin/item/SRLY-18/search/18_AMP_SOLID-STATE_RELAY,_3-15VDC_CONTROL_.html
« Last Edit: July 29, 2007, 09:33:10 AM by Bajanick »

Offline zamboniman60

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Re: MOSFETS and relays
« Reply #7 on: July 29, 2007, 06:04:34 PM »
To make a motor bidirectional using a DPDT relay, just have the motor attached one way to one pair of nonmoving contacts, and have the motor attached with the leads flipped to the other pair of nonmoving contacts. That way, turning on or off the relay will cause the way the motor is connected to switch -- reversing its direction.

Offline Admin

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Re: MOSFETS and relays
« Reply #8 on: July 31, 2007, 07:00:26 AM »
Probably one of my worst tutorials . . . but still a good quick summary for you:
http://www.societyofrobots.com/electronics_advanced_components_tutorial.shtml#mosfet

One day Ill write a full MOSFET tutorial . . .

Quote
What are the advantages of using a MOSFET over a relay?

size, switching speed . . . and the fact that you still need a MOSFET to control a relay.

Offline airman00Topic starter

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Re: MOSFETS and relays
« Reply #9 on: July 31, 2007, 02:41:08 PM »
why would you need a mosfet to control the relay?
Wouldn't any switch work as well?
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Re: MOSFETS and relays
« Reply #10 on: August 03, 2007, 09:52:59 AM »
How would you control the relay otherwise?

Offline airman00Topic starter

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Re: MOSFETS and relays
« Reply #11 on: August 03, 2007, 10:08:51 AM »
Just connect a regular pushbutton switch or a logic signal to the relay coil. Thats it.
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Re: MOSFETS and relays
« Reply #12 on: August 03, 2007, 10:12:36 AM »
Quote
logic signal to the relay coil
Wont work :P

A microcontroller can only supply a few milliamps. A relay requires 100x that amount to work. This is why you need a MOSFET as it only requires a few milliamps (or less) to control.

 


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