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Forum Index : Electronics : Solid state relay and reverse biased diod

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Rubes
Newbie

Joined: 01/05/2009
Location:
Posts: 36

Posted: 06:12pm 04 Jun 2012

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Attached is my circuit, consisting of 12v dc pump drawing +- 1amp run directly from 40w solar panel which has it own protection diode, pump is switched by optically isolated ssr controlled by arduino my question is, is a reverse biased diode across the load nessasary to protect the power FET in the SSR output from any inductive "Back EMF" pulse that is produced when the pump is switched off, and if so what sort of diode. Currently up and running as is but a bit worried about this issue.

Project is DIY solar hot water heater that is now getting bigger than ben hur, datalogging, ethernet, differential control (freeze protection to be added) etc.
Thanks for any help.

Dinosaur

Guru

Joined: 12/08/2011
Location: Australia
Posts: 338

Posted: 07:29pm 11 Jun 2012

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Hi All

Most SSR's have a reverse protection diode built in.
If you nominate the model and make, or Google the relay
it will be easy to confirm.

Regards

Regards
Hervey Bay Qld.

sPuDd

Senior Member

Joined: 10/07/2007
Location: Australia
Posts: 251

Posted: 01:23am 12 Jun 2012

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I would expect the diode to be across the motor. Its the cause of the back EMF.

sPuDd..

It should work ...in theory

CraziestOzzy

Senior Member

Joined: 11/07/2008
Location: Australia
Posts: 135

Posted: 08:08pm 29 Jul 2012

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if this was my project, throw a schottky diode (rated 3-4 times peak voltage/current dished out by your panels) at the motor, bung in some ceramic cap between the -/+ terminal at your motor and for good measure, toss in an electrolytic at the high voltage end of your relay.

...and a big g'day to all

http://cr4.globalspec.com/member?u=25757

http://www.instructables.com/member/OzzyRoo/

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