Kegconnection Complete Starter Kit and More Giveaway!


Home Brew Forums > Home Brewing Beer > Electric Brewing > Question on PWM

Reply
 
LinkBack Thread Tools
Old 03-27-2012, 04:00 PM   #1
GregKelley
Feedback Score: 0 reviews
Recipes 
 
Join Date: Feb 2006
Location: North Royalton, OH
Posts: 125
Default Question on PWM

I built my PWM using the information in this post. Instead of the 33μF cap, I'm using a 22 (because that was what I found).

When I connect everything up and I put my voltmeter on the output, I get 0v when the pot is turned all the way counterclockwise. Great, power is out. However, when I turn it all the way clockwise, I see my voltmeter cycle between 5v and 0v. I thought I should get 5v the entire time. Am I wrong?

__________________
GregKelley is offline
 
Reply With Quote Quick reply to this message
Old 03-29-2012, 02:56 AM   #2
Swib
Feedback Score: 0 reviews
Recipes 
 
Join Date: Feb 2011
Location: Durham, NC
Posts: 53
Liked 3 Times on 3 Posts
Likes Given: 3

Default

I would suggest posting this question in the thread you referenced, and if that doesn't work PM Walker.

My understanding of the PWM is that it basically cycles the power to the element on and off. The more you turn up the potentiometer, the more time the element spends "on". I can't speak to specific voltages, but the fact that it's cycling doesn't seem odd.

__________________
Swib is offline
 
Reply With Quote Quick reply to this message
Old 03-29-2012, 04:32 AM   #3
thargrav
Registered User
Feedback Score: 0 reviews
Recipes 
 
Join Date: Dec 2009
Location: Huntsville, Alabama
Posts: 821
Liked 38 Times on 35 Posts
Likes Given: 2

Default

Quote:
Originally Posted by GregKelley View Post
I built my PWM using the information in this post. Instead of the 33μF cap, I'm using a 22 (because that was what I found).

When I connect everything up and I put my voltmeter on the output, I get 0v when the pot is turned all the way counterclockwise. Great, power is out. However, when I turn it all the way clockwise, I see my voltmeter cycle between 5v and 0v. I thought I should get 5v the entire time. Am I wrong?
Cycling between 0V and 5V would be correct and the percent time it's at 5V represents the PWM duration.

But I would expect to see 5 V all the time when full on and varying PWM depending on where the pot is set.
__________________
thargrav is offline
 
Reply With Quote Quick reply to this message
Old 03-29-2012, 01:04 PM   #4
GregKelley
Feedback Score: 0 reviews
Recipes 
 
Join Date: Feb 2006
Location: North Royalton, OH
Posts: 125
Default

Thanks guys. I know it is supposed to cycle but from what I read last night on some other sites, it should be 5v all the time when full on. I'm going to add this question to the PWM thread.

__________________
GregKelley is offline
 
Reply With Quote Quick reply to this message
Old 03-29-2012, 01:16 PM   #5
JKoravos
Feedback Score: 0 reviews
Recipes 
 
Join Date: Jul 2009
Location: Chelmsford, MA
Posts: 964
Liked 18 Times on 14 Posts
Likes Given: 3

Default

I think even at full-on it still cycles but it's like 99% on vs. 1% off. I don't think a typical multimeter will really give you a good sense of the on/off time unless your cycle time is really slow, like >2-3s. I think I have my cycle time set around 0.5s and the multimeter doesn't give me anything indicative.

__________________
JKoravos is offline
 
Reply With Quote Quick reply to this message
Old 03-29-2012, 01:24 PM   #6
GregKelley
Feedback Score: 0 reviews
Recipes 
 
Join Date: Feb 2006
Location: North Royalton, OH
Posts: 125
Default

Quote:
Originally Posted by JKoravos View Post
I think even at full-on it still cycles but it's like 99% on vs. 1% off. I don't think a typical multimeter will really give you a good sense of the on/off time unless your cycle time is really slow, like >2-3s. I think I have my cycle time set around 0.5s and the multimeter doesn't give me anything indicative.
My cycle time is around 1.52 seconds. The "off" time is also enough to blink the LED on the SSR.
__________________
GregKelley is offline
 
Reply With Quote Quick reply to this message
Old 03-29-2012, 02:08 PM   #7
mredge73
HBT_SUPPORTER.png
Feedback Score: 0 reviews
 
mredge73's Avatar
Recipes 
 
Join Date: May 2011
Location: La Porte, TX
Posts: 618
Liked 30 Times on 30 Posts

Default

The 555 IC is a neat little device. I did a presentation on it in high school and wrote a long paper on it. When wired as a PWM it is an astable circuit; has no stable state.
The Pot will control your duty cycle; 100% will not be reachable with this circuit (0% will not be reachable either).
The frequency will be set by the capacitor that you choose. The smaller the Cap the higher the frequency. You can replace the cap with a variable capacitor to help dial in your system if you wish.
Another tip is to check the resistance of your Pot in the clockwise position where you expect the PWM to be at 100%; should be near 0 ohms.

This is a good site:
http://www.kpsec.freeuk.com/555timer.htm

__________________
mredge73 is offline
 
Reply With Quote Quick reply to this message
Old 03-30-2012, 02:20 AM   #8
pvtschultz
Feedback Score: 0 reviews
Recipes 
 
Join Date: Feb 2010
Location: West Allis (Milwaukee), WI, Wisconsin
Posts: 443
Liked 6 Times on 6 Posts
Likes Given: 13

Default

Like mredge73 mentioned, you'll never get a full off or full on with a 555 timer based PWM unless your trim pot has an "off" setting. The circuit that I used is very similar. When all the way "off", I get a very faint flicker on an LED that I wired into the output; all the way on results in a very brief dimming of the LED. Hooking up an LED on the output (or use the one on the SSR) will give you a better idea as to what your duty cycle is.

__________________
Brewing: BM's Centennial Blonde
Drinking: Brown Ale, Cherry Smoked Robust Porter (way too much smoke!)
On Deck: Dunkel, CAP, Berliner Weiss, Bock, Sour Raspberry Brown, APA...
2014 Gallons Brewed: 19
Gallons Brewed '11-'13: 250


http://www.homebrewtalk.com/f170/pvt...inally-298407/
pvtschultz is offline
 
Reply With Quote Quick reply to this message
Old 03-30-2012, 05:15 PM   #9
GregKelley
Feedback Score: 0 reviews
Recipes 
 
Join Date: Feb 2006
Location: North Royalton, OH
Posts: 125
Default

Thanks guys. I'm thinking about getting a little toggle switch and adding it to the PWM circuit. Flip it one way and ground is fed to the PWM and the PWM controls the circuit. Flip it the other way and ground is fed directly to the SSR bypassing the PWM. That way I can get 100% on until the BK reaches boiling.

__________________
GregKelley is offline
 
Reply With Quote Quick reply to this message
Old 03-30-2012, 07:13 PM   #10
mredge73
HBT_SUPPORTER.png
Feedback Score: 0 reviews
 
mredge73's Avatar
Recipes 
 
Join Date: May 2011
Location: La Porte, TX
Posts: 618
Liked 30 Times on 30 Posts

Default

Sounds like a plan.
I would use a 3 position switch so you can have ON, OFF, PWM.

__________________
mredge73 is offline
 
Reply With Quote Quick reply to this message
Reply


Quick Reply
Message:
Options
Thread Tools