cletus monroe

G9 Heatsinks and More Questions!
« on: April 25, 2005, 08:43:46 PM »
I found the thread, "Help!!! with G9 Power Transformers", and used straycat's post to decipher the code.  Yeah!! The G9 lights up.  Wait!
She's fading captain.

So, more reading and it would seem that I am overheating my 7812 chasis mounted regulator (but I'm not sure).  I noticed some pretty big heatsinks in finished G9 pics.

Question 1:  How big, or how small, can the chasis mounted heatsink be?
I'm using an aluminum anodized cheapy from the Shack.  It's 1 inch wide
by 1.18 inches long and .05 thick.  Is that sufficent?

Question 2: Does electrically insulating the regulator from the heatsink
require two washers?  One between the heatsink and regulator and one
between the nut and regulator?

And one more:

Question 3:  At one point I had hooked the trannies up wrong and the
G9 powered up.  If I blew components, does anyone know the usual suspects?  Like, "Dude.  I'd be suprised if you didn't fry all those diodes."

Thanks for taking the time to read this.  If anyone could help with any of
these questions I'd be mighty tickled.
take care,
cletus


cletus monroe

G9 Heatsinks and More Questions!
« Reply #1 on: April 26, 2005, 03:08:08 AM »
Alright,
My man Tom came over and we two headed the G9.
I went to Radio Shack today and bought mounting hardware
for $1.29 that included a clear thin plastic back and a fiber
washer with a bottom ridge that fit into the hole of the 7812
regulator.  She works!  She doesn't work! She works! She doesn't!
I know the power trannies are hooked up correctly thanks to Straycat's
post, so why is the G9 powering up and then slowly dying with my
third replaced regulator and my new exciting isolation hardware?
Well my friends, make sure you mount the regulator as flat as a pancake.  I had, but somehow, screwing with it led to power on success.
Now, no signal.  So I will continue my fault checking journey and keep
you posted.  No more power supply problems but now the proverbial "rent" is due.
take care,
cletus

louder

G9 Heatsinks and More Questions!
« Reply #2 on: April 26, 2005, 04:16:14 AM »
alo cletus
did you use 7812(1amp),or 78s12(1,5amp)?.
i used 78s12,and worked okay,altough the voltage reg had to be connected and insulated to the chassis.
best regards
pedro

electronaut

G9 Heatsinks and More Questions!
« Reply #3 on: April 26, 2005, 10:49:02 AM »
Hey Cletus,

I've had similar problems with 78XX regulators in the past, and they were always due to insufficient heatsinking.  That little heatsink sounds like it's probably way too small.  If your chassis is aluminum, find a place on the chassis and mount it there.  Steel doesn't make the greatest heatsink.  
Heatsinks are rated in watts, so make sure the one you're using can handle the current through the regulator.

When in doubt, go totally overboard.

cletus monroe

G9 Heatsinks and More Questions!
« Reply #4 on: April 26, 2005, 01:47:04 PM »
I'm using the 78s12.  The unti stays powered on and has not faded.
I kept it on for about 3 hours last night and it stayed strong.    Now
I figure out why no signal.  Hopefully I'll be able to figure it out
today.  
take care,
cletus

cletus monroe

G9 Heatsinks and More Questions!
« Reply #5 on: April 26, 2005, 01:47:30 PM »
I'm using the 78s12.  The unti stays powered on and has not faded.
I kept it on for about 3 hours last night and it stayed strong.    Now
I figure out why no signal.  Hopefully I'll be able to figure it out
today.  
take care,
cletus

peterc

G9 Heatsinks and More Questions!
« Reply #6 on: April 26, 2005, 01:52:27 PM »
Cletus, make sure you use silicon grease on both sides of the flat washer. It's that horrible white sh*te that sticks to everything...

Scrape the paint off the case so the reg mounts directly to the bare metal as well.

Regards
Peter
If opportunity doesn't knock, build a door.

cletus monroe

G9 Heatsinks and More Questions!
« Reply #7 on: April 27, 2005, 12:10:33 AM »
Thanks for the advice.  As of now, the regulator is mounted
to a 1.18 inch long heatsink that is chasis mounted. The unit
has stayed on now for up to about 4 hours without dying.

Do you think it will eventually if I don't chasis mount the heatsink?
I've read that even with that plastic film that it could be dangerous?
What do you think?
take care,
cletus

madreza

G9 Heatsinks and More Questions!
« Reply #8 on: April 27, 2005, 05:08:18 AM »
Hi All

Would this heatsink be enough for the 7812 ?
http://uk.farnell.com/jsp/endecaSearch/partDetail.jsp?SKU=170073&N=401
Knight 1: We are now no longer the Knights who say Ni.
Knight 2: NI.
Other Knights: Shh...
Knight 1: We are now the Knights who say... "Ekki-Ekki-Ekki-Ekki-PTANG. Zoom-Boing. Z'nourrwringmm.

gyraf

G9 Heatsinks and More Questions!
« Reply #9 on: April 27, 2005, 05:33:12 AM »
It is rated 30°C/W.

Calculate yourself: the G9 heaters draws some 600mA at 12V. measure the input DC voltage to the 78S12. This voltage minus the 12V output is your regulator voltage drop. Multiply this by your current draw (0.6A) and you have your dissipation in Watts. The mentioned heatsink will have a temperature that rises 30°C for each Watt you dissipate. Multiply your regulator loss (in W) by these 30°C, and you have predicted heatsink temperature expressed in °C. Don't allow for a heatsink temperature over say 90 or 100°C - the 78S12 shuts down around 120°C.

So to sum up - that heatsink is probably much too small. But calculate backwards, and you can figure out what size °C/W heatsink you'll need...

Jakob E.
..note to self: don't let Harman run your company..


madreza

G9 Heatsinks and More Questions!
« Reply #10 on: April 27, 2005, 06:35:57 AM »
OK !
I always wondered how it worked !
THanks Jakob

I guess I should go for another heatsink
Knight 1: We are now no longer the Knights who say Ni.
Knight 2: NI.
Other Knights: Shh...
Knight 1: We are now the Knights who say... "Ekki-Ekki-Ekki-Ekki-PTANG. Zoom-Boing. Z'nourrwringmm.

Hulk

G9 Heatsinks and More Questions!
« Reply #11 on: May 17, 2005, 12:34:30 PM »
Is a temperature of 70C acceptable for the 78S12???
Hulk

gyraf

G9 Heatsinks and More Questions!
« Reply #12 on: May 17, 2005, 12:52:35 PM »
yes.

If you're in doubt, consult the data sheet..
..note to self: don't let Harman run your company..

Hulk

G9 Heatsinks and More Questions!
« Reply #13 on: May 17, 2005, 12:56:18 PM »
Great!

Thanks Jakob!!
Hulk


 

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