Help with 12v relay and transistor

[StealthRT]

And now re-testing with the 5v applied:

Base: 5.84v
Collector: 12.10v



David

 

[ccurtis]

Stealth, I want to commend you for a great job of describing the problem and annotating the photo!

 

[StealthRT]

Ha, thanks ccurtis.. i wish the problem was solved though

This is really bothering me why this is doing this!

David

 

[blueroomelectronics]

Real simple way to test.

With the AVR out of circuit, with a bit of wire bring the base resistor to GND (relay off) then to 5V (relay on)

If that doesn't work your transistor is either dead or incorrectly wired.

 

[duffy]

The emitter should be 0V (ground), sounds like there's 5V on it for some reason.

 

[StealthRT]

Real simple way to test.

With the AVR out of circuit, with a bit of wire bring the base resistor to GND (relay off) then to 5V (relay on)

If that doesn't work your transistor is either dead or incorrectly wired.

blueroomelectronics: As u can tell by the photos i posted on the first page, i have alagator clips supplying the volts. I am using the 5v off the ATMega stuff (without the chip in it of course).

To make sure I'm doing this correctly: Take the 5v and connect it to the base without a resistor? Straight 5v to base?

David

 

[StealthRT]

The emitter should be 0V (ground), sounds like there's 5V on it for some reason.

As the PDF for the transistor says:
https://www.electro-tech-online.com/custompdfs/2009/03/SS8050.pdf

Its an EBC and that's how i have it hooked up. The emitter is 0v.

David

 

[duffy]

DON'T HOOK 5V STRAIGHT TO THE BASE! You will burn it out.

You might want to try a 2N2222 transistor instead. The relay pulls 100ma or so, what you're using is an audio drive transistor.

 

[StealthRT]

DON'T HOOK 5V STRAIGHT TO THE BASE! You will burn it out.

You might want to try a 2N2222 transistor instead. The relay pulls 100ma or so, what you're using is an audio drive transistor.

I have an 1n4004 but not a 2n2222. I'm using the 1n4004 between the coil as u can tell on my drawing.

So, do u want me to use the 1k + 10k on the base with the 5v? If so, thats what im already doing.

David

 

[StealthRT]

However i do have a BC548 Small Signal Transistors NPN 30V 100mA HFE/8 i can try out if you think that would work better?

David

 

[audioguru]

The transistor is wired backwards.
You have the transistor connected like a European BC548 but you are using an American Fairchild transistor that has the collector and emitter pins reversed.

Look at the pins in the datasheet the next time.

 

[StealthRT]

The transistor is wired backwards.
You have the transistor connected like a European BC548 but you are using an American Fairchild transistor that has the collector and emitter pins reversed.

Look at the pins in the datasheet the next time.

I challenge your view, audioguru.

On the sheet it has:
1. Emitter
2. Base
3. Collector

and thats looking at the flat side.

Now look at my picture:
**broken link removed**

That is the correct order.

And here's the transistor showing u that it is, indeed, looking at it from the flat view.
**broken link removed**

Prove me wrong, please.

Davod

 

[StealthRT]

Ok i switch transistors to the BC548 Small Signal Transistors NPN 30V 100mA HFE/8 and almost burned my skin off!!!! (it got REALLLLLLLLLLLLLLLLLLY hot)

And yes i hooked it up correctly. It was backwards from what the other transistor was (CBE). So what did i do incorrectly with that??? When i was checking the volts, it had 0.70v on the base with the 5v connected... but then i started smelling "The smell" and yeah, thats when i almost burned my finger off.

David

 

[duffy]

Measure the current through the relay hooked straight to 12V and tell us what you get.

 

[StealthRT]

Measure the current through the relay hooked straight to 12V and tell us what you get.

Where its coming in 12v on one side and where i have the collector hooked to the other side?

 

[StealthRT]

Both sides are 12.10v without the 5v hooked up but with the 1n4004 between the two sides.

David

 

[audioguru]

Then your 1N4004 or relay coil is shorted.
A transisror that drives a short circuit gets extremely hot.

 

[StealthRT]

Then your 1N4004 or relay coil is shorted.
A transisror that drives a short circuit gets extremely hot.

How can either the 1n4004 or relay be shorted if the only thing connected to it is 12v on one side??

David

 

[StealthRT]

Ha, false alarm... my psu went off P

David

 

[audioguru]

You talk weird.
Relays do not open and close.
Instead they turn on and turn off.

EDIT:
Tell your professor that she (he or it) talks weird.