Shunt regulator running continusly

[JohnC]

High every one and Happy New Year.

Need some expert advice on trouble shooting a shunt regulator, Chris Greacin's design. http://www.homepower.com/files/shuntregulator18.pdf

It was working perfectly, then by accident I tried to show a friend my shunt.

I hooked it up to my power supply not checking my voltage setting and delivered 22 volts dc.  The problem now is even at 12 volts it stays on. Any suggestions where the problem may be, besides me being a idiot.

Thanks

John E Cox

Ottawa, ON

Canada

[kenputer]

 I learned a long time ago,never show a friend your shunt :-)

[JohnC]

Well I can tell you this kenputer, he wasn't impressed.

I looked on the board and found some info on some tests to do, still very lost.

Battery Voltage = 12V

Ground to fet gate 4.9V

Groung to drain =0 volts

Ground to collector of 2n222a = 10.8V

Voltage stays the same on pin 9 of LM 723 when adjusting the pot

Ground to emitter 10V

Positive to base = 11.3

Positive to 11.9

I sure this will help me.

THX

John

[drdongle]

I suspect that the 555 is DOA, their only rated to 18 V

[nothing to lose]

Hmm, never show your friends wife your shunt@!@

[Flux]

I would go for that for the first try as well, It's not a bad idea to fit the limit resistor and zener as intended for the 24v version although if you don't do silly things it's not necessary for 12v.

[amiklic1]

I think 555 is burned. In my regulator design, the only thing it ever goes wrong is 555. So, I sold some regulators and gave lifetime guaryntee. Noone has come back, but if someone brings it to me, just change the 555 and gave it back. All other components are sized for more abuse.

[JohnC]

THX guy's for advice.  Is there a sure blown test to run on the 555. As soon as I can get it up and working I will post a picture of me, oops, I mean my shunt.

THX

John E Cox

Ottawa, ON

Canada

[amiklic1]

I usually have lot of similar components, so I see the 555 is blown by replacing it. It's not soldered but inserted in a slot. It makes everything much simpler.My advice is to buy at least double components. They're so cheap, and it's more expensive to me to go in a shop (40 km), than to buy double components.

[BigBreaker]

This is excellent advice.

As a former electrical engeer I can tell you that all ICs should be in slots until mass production.  You should buy a dozen or so of each of the "generic" ICs - timers, op amps, voltage references, regulators, assortment of transistors, mosfets, diodes etc...  It'll cost you less than $50 and will save you a lot of headaches.

Spare components are perfect for testing against potentially broken ones.

Any electronics wonks should also check out the Atmel MEGA microcontrollers.  They have built in crystals, DACs and PWM controllers.  Each costs less than $5 and can be programmed in C code to do whatever you need.

[Opera House]

Remove the 100 ohm resistor from the 555 and tie it to ground to check the FET.  This will tell you if it has been damaged also.  It should not conduct with no gate drive.  I wish these archaic 555 circuits would disappear, you can do the same thing with a cheap switching regulator chip and about 5 resistors and caps.

[amiklic1]

I got some plans with Picaxe microprocessor, but my weak point is I'm beginner in programming. Really, I don't know a thing about it. So, I'll need to learn. I got charge regulator plans I begin to build, but I get the code from the owner, so it's simple.

[drdongle]

It's hard to beat the classic 555 for versitility, that why it lives on and on and on.......

[JohnC]

Did as you guy's suggested. Inserted a 8 pin socket and a new 555.

Low and behold it now is working again.

Thanks again gentelmen for your help.

As a treat you get to see my Shunt!

Thanks

John E Cox

Ottawa, Canada

[johnlm]

I realize its reflection from the flash on the plastic cover but I was going to add an additional joke and say

You shunt is glowing white hot.

John

[dinges]

G'day,

I have had my share of 555 problems the last few weeks too. A simple design, basically a 2-minute timer for a light in the shed. Small 12V/800mAh battery, solar charged. Press a button and a small 12V lamp (will be replaced by white LEDs) will light for 2 minutes and go automatically off.

Things I've learned:

1. a normal 555 draws about 10mA quiescent current; this discharges the battery in 80hrs! A cmos 555 draws only .1mA--> 8000 hrs (almost a year)!
   
2. IC sockets are evil. After a few evenings of intermittent faults (it worked on the desk, when installed in the (freezing) shed it worked for a 1/2 hour, then stopped (didn't automatically turn off). After having tried everything else (and suspecting the temp. range of the (commercial) 555 (not industrial temp.range) was the problem and exchanging for an industrial 555--> same problem. Finally, I deleted the IC socket and soldered it straight in: problem solved. So, the advice others (and I) gave you on using an IC socket may be a cause of problems ;-)
   
3. 'easy' projects usually cause much more problems and longer to get working than complex projects, that (in my case) usually work straightaway. It's when I think 'I'll quickly build this or that' that things go wrong...
   
   

Anyway, glad to see you your shunt is working again. But what is it with all this innuendo from other people that this innocent little shunt causes

Peter,

The Netherlands.

[dinges]

why,

are you ashamed of your shunt?

With shunts, bigger is better...

Peter,

The Netherlands.

[JohnC]

Hi Pete

Guess they are peni...I mean shunt envey.

Anyhow in a follow up posting "555 test circuit" I posted this tester is a good complement to using the socket. Allows me to do a quick swap if need be

Cheers

John E Cox

Ottawa, Canada