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
What does the spec for the SSR say?
Control voltage range: 4 - 6vdc
Max. input current 20mA
Load voltage 3 - 52.8VDC
Load current 0.01
Control voltage range: 4 - 6 VDC
Damn just looked up a bit more info apart from what was supplied with ssr which was above. ssr is the
http://www.google.com.au/url?sa=t&rct=j&q=hfs40%20solid%20state%20relay&source=web&cd=1&ved=0CHAQFjAA&url=http%3A%2F%2Fwww.hongfa.com%2Fpro%2Fpdf%2FHFS40_en.pdf&ei=fYjNT7yUHcGuiQez3LWvBg&usg=AFQjCNHg3i-uRloK7b5ndvTHGJoVmSvQ6A&cad=rja
The drawing at the bottom of this product sheet has a number of diodes etc in circuit, oops
What do you think.
Cheers
The 'diode' across the SSR is a tranzorb it's a zener made with silicon carbide. The part I remember was a 1.5KE33. Look those parts up, they will save you a lot of trouble. They are invaluable for many inductive switching 'situations'... If you were really worried you "Could" use the SSR to drive a small relay to control the pump and that would require a single diode across the relay coil and totally eliminate back emf issues from damaging the SSR when the pump was activated and also a great deal more isolation from the load. I used them across the output of a bridge rectifier to keep line transients 'manageable' and where I used them they were really required. Also use the diode across the load... like a 1N54XX series diode use one with at least 100V PIV. The 540X series diodes are pretty hardy devices, I used a lot of them and they rarely failed. Did though blow a bunch of KE33's though... Cheap insurance, I think.
IMO
Doc
Thanks for that, I would prefer not to be adding more relays but considering the load (pump) has a usual draw of around 1 amp and I have variable voltage input from solar panel (+- 12 - 36v) any other surgestions for
I have a few 1n4007 's around, any good?
Just be aware I am not exactly an electronic guru (far from in fact)
This is what I believe I have to achieve.
Personally, I have difficulty calling this an SSR. It is a power opto-coupler. All standard transistor driver precautions should be followed. A 1N4007 would do ok for the diode at the load.
Yes, you need a diode across the pump to catch the back emf when the SSR turns off. If the pump takes no more than 1A then a 1N4007 will do. You don't need the zener diode unless you are expecting large voltage transients on the power supply.
Thank you all for your help, 1n4007 across load and all working ok