fluid level

schreef in bericht news: snipped-for-privacy@l53g2000cwa.googlegroups.com...

Hmm... At first glance it looks like the latest perpetuum motion. (Did not give a second glance.)

petrus bitbyter

Ground point A at the bottom of R2. If the pump doesn't turn off and all your parts are good, you have wired something wrong.

Ed

Hi, Martin. Sorry for your troubles. If you're talking about the circuit on page 12, it's definitely less than ideal. First off, even if everything's working OK, the voltage at the base of Q3 won't go below 4V. That means your "turnoff" voltage at your relay coil could be as much as 3.3V, which just might not turn it off, anyway. And if you're using an automotive electrical system (nominal 13.8V or so), "turnoff" voltage could be as high as 4.6V or more. Not good, because a relay requires a lot less voltage to stay pulled in once it's there. If you were to ask if a 12V relay, once energized, would stay closed if 4.6V were applied, I'd have to say, "probably".

Second, I didn't look exhaustively at the article, so I'm not sure what relay you're using. But I can tell you that the poor Tr3 is probably overstressed unless it's a very high resistance relay coil. It might have smoked, and since transistors frequently fail shorted, that might also be responsible for your miseries.

Just for grins and giggles, I'd start by replacing Q3 with a beefier TIP31 (can handle 3 amps load current), and try replacing R4 with a

180 ohm resistor instead of 1.8K. That will allow Q3 to turn off for real. I'd also make sure I wasn't using a relay that required more than 1/2A or so when fully energized.

Actually, poking around with this simple switching circuit is good practice in basic electronics, but this should be a cautionary note about the level of technical expertise in the whole article. I'm not sure you want to go down this primrose path, sir. Note that the autor specifically says in the first paragraph that he is not recommending you actually build anything he's describing. I'd suggest that might be good advice from him, even if nothing else is.

Good luck Chris

thanks all for all your help, the resistor was the culpret also was connected to grid 7 not 6. thanks again to all who helped martin