Solenid circuit modification

Siri

·In my project I would like to have LED show the state of the solenid so I plan in modifying the circuit which also
has a revrse biased diode to sub the spike generated by the collapsing magnetic field.
My question is can I add and LED(diode) in parallel in the other direction so it will light up when the solenoid is energised.
Is there any reason NOT to place the dioded in parallel.

The circuit diagrams are attached.

Bruce Bates

Siri -

No circuit diagram was attached, unfortunately.

Regards,

Bruce Bates

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skylight

As long as the LED has a current limiting Resistor in series with it then no problem, you'll need to select the value of resistor dependant on what voltage you are applying to the solenoid's coil.

Siri

Bruce,

I am sorry the attachment failed and I will try it again so you and others can see and help me out.

Siri

Siri

I would like·someone··to specifically address whether the reverse bias diode would work as intended· or the spike generated will by pass the the bias diode via the LED(diode) and compromise the snub.

Thanks,

Siri

phil kenny

Trust Skylight's response.

You must add a series resistor to limit the current through the LED.

With the circuit as you've shown it, the LED will glow brightly once
and the release all its magic smoke.

When you turn off the FET controlling the solenoid, the solenoid
current will try to continuing flowing. The only path available is
through the snubber diode you have connected across the solenoid.

When the snubber diode conducts, it will present a reverse voltage
of roughly 0.7 volts to the LED and associated resistor. I'm certain
that the LED can tolerate being reverse biased by 0.7 volts.

phil

Post Edited (phil kenny) : 6/10/2007 5:58:32 PM GMT

RinksCustoms

phil kenny said...
Trust Skylight's response.

You must add a series resistor to limit the current through the LED.

With the circuit as you've shown it, the LED will glow brightly once
and the release all its magic smoke.

When you turn off the FET controlling the solenoid, the solenoid
current will try to continuing flowing. The only path available is
through the snubber diode you have connected across the solenoid.

When the snubber diode conducts, it will present a reverse voltage
of roughly 0.7 volts to the LED and associated resistor. I'm certain
that the LED can tolerate being reverse biased by 0.7 volts.

phil

i don't mean to pick here, but i'd just like to clarify for integrity purposes...

This is the second time i've come across "magic smoke" in these forums. Rest assured there is no magic or wizardry involved herin.·I'm an Electronics engineer, simply put, when you present any electrical/electronic device with more electrical current and/or voltage than it's rated at it will generate more heat than it was designed·to dissipate·and will begin the thermal runaway process. Present too much electrical potential and it could explode! example would be a 2V LED vs a 12V battery, the result without a volt/current limit resistor? POP!

Reverse biasing a power diode on a coil of wire like a solenoid will protect the switching ciruitry from a potentially dangerous reverse polarity voltage spike. Keeping the LED in polarity with the solenoid will work fine as long as you use a resistor in series with the LED (not the protection diode). generally, use a 220-500 ohm for 5V devices, 500-1K ohm for 12V, 1K-2K ohm for 24V.

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Definetly a E³ (Electronics Engineer Extrodinare!)
"I laugh in the face of imposible,... not because i know it all, ... but because I don't know well enough!"

phil kenny

Wikpedia has an excellent description of the magic smoke installed
when integrated circuits are manufactured. Worth looking at.

http://en.wikipedia.org/wiki/Magic_smoke

phil

Post Edited (phil kenny) : 6/10/2007 6:54:36 PM GMT

RinksCustoms

umm, not sure how to tell you this, but wikipedia cannot be trusted as a source for valid and verified information as it is anonimously contributed to by ANYONE with internet access. In other words, it's more or less an online searchable database where "Mr. Anonnymous" creates an entry (definition) and when you search the web it sometimes comes up in the search results as what your looking for.

Thessaurus.com
Dictionary.com
Encyclopedia.com
Howstuffworks.com

Are examples of valid sources, i'm sure there are more, but Wikipedia is not one of them. I recall a few times loking for things on wikipedia and these are things i know in detail, search results came back as "scatterbrained" some definitions for my search terms look as if they were written by a 4th grader, bad grammar/spelling. I wouldn't trust it...

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Definetly a E³ (Electronics Engineer Extrodinare!)
"I laugh in the face of imposible,... not because i know it all, ... but because I don't know well enough!"

Siri

Thank you all - who replied to my question.

I have let everyone know that I was using an LED rated at 12V,20mA which has a built in resistor from Radio Shack - if anyone intersted in this part #276-209.That was why the resistor was omitted in the circuit.

I should have stated in the initial posting.

I am thankful to all of you who replied my posting and the explanations has taught me a little more.

Thanks once again to a nice bunch of electronic wizzards.

Siri