Here's an example.· It's a controller I'm building to handle power outages by monitoring the power mains.· When the utility power goes off, as in a hurricane, the controller will wait ten seconds, start my Onan JC generator (three tries, if necessary, but it always starts), wait while it warms up, and switch the load (my house) to the generator.· Then when the mains come back on, it will wait 5 min to make sure the powe is really up, then switch the house back to the mains, then run the generator unloaded for three minutes as a cooldown, and shut the generator down.· It's all standard stuff except the main contactor, which is a great moose of a relay with two solenoids -- one pullis it this way, and the other pulls it the other way.· It is actuated by small relays that in turn are driven from p0 through p3 of a Stamp.
Uhhh -- I just looked again. That 10V C-E breakdown is worrisome. It will be fine, if you are feeding the relays from 5v, but if, say, you're running from a 12v supply, or even 9v, it may fail early. With a 9v supply you will get the 9v plus some kick voltage at turnoff (the "plus" amount will be the forwrd drop of the protection diode). I think I'd want a C-E beakdown spec at least twice the supply voltage.
i would like to say something and please i mean no disrespect as i say it.
when you start a thread you say "experts only please" I would like to venture to say. I watch several forum here i download all messages in most of them. I have archived over 15,000 posts. I have yet to see anyone try to answer a question that is out of there ability. Some may misunderstand or give personal experiences but no one here will try to lead you in the wrong direction. If they did that would kindly be let known that they were not correct and be corrected rather quickly. I just wanted to point that out.
No disrespect taken but there was no need to even address it.
"Experts only please" simply refers to anyone that knows what they are talking about.
It was not intended to offend and it appears that it offended you.
Thanks
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How can there be·nothing? Nothing is something!
Post Edited (beazleybub) : 10/28/2008 7:15:36 AM GMT
Comments
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· -- Carl
Thank you everyone for your help I now understand what I needed to know about hFE and transistor selection.
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How can there be·nothing? Nothing is something!
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· -- Carl, nn5i
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· -- Carl, nn5i
The relays are being fed 5V.
Thanks for the heads up, I may double it anyway just to be safe.
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How can there be·nothing? Nothing is something!
Post Edited (beazleybub) : 10/28/2008 7:34:32 AM GMT
i would like to say something and please i mean no disrespect as i say it.
when you start a thread you say "experts only please" I would like to venture to say. I watch several forum here i download all messages in most of them. I have archived over 15,000 posts. I have yet to see anyone try to answer a question that is out of there ability. Some may misunderstand or give personal experiences but no one here will try to lead you in the wrong direction. If they did that would kindly be let known that they were not correct and be corrected rather quickly. I just wanted to point that out.
as i said above not disrespect intended.
Badger
Badger,
No disrespect taken but there was no need to even address it.
"Experts only please" simply refers to anyone that knows what they are talking about.
It was not intended to offend and it appears that it offended you.
Thanks
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How can there be·nothing? Nothing is something!
Post Edited (beazleybub) : 10/28/2008 7:15:36 AM GMT
http://www.fairchildsemi.com/ds/PN/PN5134.pdf
Input
Rb (Base Resistor)·········· = 0.499K ohms·
Vin (Signal)··················· = 4.8V
Rc (Relay Coil Resistance)·= 0.055K ohms
VP (Relay)··················· · = 5V
hFE·(Min)·······················= 20
VBE·(Voltage Drop)········· = 0.7V
Results
Vc (Collector Voltage)····· = 0V·
Ve (Emitter Voltage)······· = 0V·
Vb (Base Voltage)···········= 0.7V·
Ic (Collector Voltage)······= 90.909mA·
Ib (Base Voltage)···········= 8.2164mA
Saturated
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How can there be·nothing? Nothing is something!
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Chris Savage
Parallax Engineering