Kegconnection Complete Starter Kit and More Giveaway!


Home Brew Forums > Home Brewing Beer > Electric Brewing > Variable speed controller

Reply
 
LinkBack Thread Tools
Old 03-07-2013, 07:35 PM   #11
millsware
Feedback Score: 0 reviews
Recipes 
 
Join Date: May 2010
Location: Pittsburgh
Posts: 210
Liked 12 Times on 7 Posts

Default

So "*Sensitive potentiometer for precise heater control" is not what I'm looking for? What is the difference between a potentiometer and rheostat?

__________________
beerapprentice.blogspot.com
millsware is offline
 
Reply With Quote Quick reply to this message
Old 03-08-2013, 12:37 PM   #12
millsware
Feedback Score: 0 reviews
Recipes 
 
Join Date: May 2010
Location: Pittsburgh
Posts: 210
Liked 12 Times on 7 Posts

Default

Bump

__________________
beerapprentice.blogspot.com
millsware is offline
 
Reply With Quote Quick reply to this message
Old 03-08-2013, 01:07 PM   #13
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 millsware View Post
So "*Sensitive potentiometer for precise heater control" is not what I'm looking for? What is the difference between a potentiometer and rheostat?
A rheostat is a higher wattage potentiometer.
__________________
thargrav is offline
 
Reply With Quote Quick reply to this message
Old 03-08-2013, 01:07 PM   #14
fermenter
Feedback Score: 0 reviews
Recipes 
 
Join Date: Jul 2011
Location: lakeville, mn
Posts: 30
Likes Given: 6

Default

Quote:
Originally Posted by millsware View Post
So "*Sensitive potentiometer for precise heater control" is not what I'm looking for? What is the difference between a potentiometer and rheostat?
I suppose we should step back, what is your goal? It seems to me that you just want the ability to control your boil rate correct?

If so it seems to me your cheapest option is to go with a potentiometer/SSR (Solid State Relay) setup

They way this works is the power is routed through the SSR. The potentiometer also attaches to this SSR, you can use the knob on the potentiometer to control how often the SSR allows power to flow to your element. So at potentiometer level 50 your element is OFF 50% of the time and ON 50% of the time. It does not lower the voltage going to the element, but no matter I can attest that that method does work just fine. As far as I know if you want to lower the voltage (power level of the element) you will need something like a rheostat and that will get more pricey.

The link you posted for $144 HERE seems to also be a SSR setup, but I am not sure without looking inside the device. I went with THIS one as it was the cheapest package without buying my own parts separately.

So yes a potentiometer is what you want but that is just part of it, what it controls is what makes the difference such as a SSR, rheostat or something else.

I hope I am being clear if not please let me know! Or if someone else has ideas please feel free to share.
__________________
fermenter is offline
 
Reply With Quote Quick reply to this message
Old 03-08-2013, 01:36 PM   #15
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 fermenter View Post
The link you posted for $144 HERE seems to also be a SSR setup, but I am not sure without looking inside the device.
This is a SSR phase angle type device.
__________________
thargrav is offline
 
Reply With Quote Quick reply to this message
Old 03-08-2013, 01:53 PM   #16
ajdelange
Senior Member
HBT_SUPPORTER.png
Feedback Score: 0 reviews
Recipes 
 
Join Date: Aug 2010
Location: McLean/Ogden, Virginia/Quebec
Posts: 5,657
Liked 536 Times on 439 Posts
Likes Given: 15

Default

A rheostat is usually an adjustable series resistor. Wire is wound on a torroidal support and a wiper, rotating on an axle through the center of the doughnut can be rotated to contact the more or less of the wire according to the angle to which it is set. The further from the hot end the wiper makes contact the more resistance is in the circuit. A rheostat has two connections. One end of the coil and the wiper.

A potentiometer is the same thing except that both ends of the coil are connected as is the wiper so there are 3 terminals. In the usual setup a reference voltage is applied across the ends of the coil (which in the small units you are talking about isn't made of wire at all but a flat, circular strip of some resistive material) and a desired 'potential', determined by the wiper position, taken off from the wiper terminal. For example, if a 12 volt source is placed across the resistor's terminals, 3 volts will appear on the wiper if it's position is such that 25% of the resistance is between the wiper and the ground terminal, 6 volts if the wiper is half way...

Thus a potentiometer and rheostat are really the same thing with the differences being in the role they are intended to play and the size which has to do with how much current is involved. Potentiometers (pots) are usually much smaller. Think volume control from the old days when radios had knobs.

The device with the pot consists of a couple of SCR's whose firing angles are controlled by a circuit which determines the firing angle from a voltage passed to it from the potentiometer. It is really PWM but the pulse is half a cycle of the line. For 50% power the SCR's each conduct 90 ° for a total of 180 ° which is half the 360 of a complete cycle.

Some systems will turn on for integer half cycle numbers to minimize noise and stress on the components. For 50% power they might be on for 50 half cycles and off for 50 the point being that they only turn on (or off) when they are not conducting (the voltage across them is 0). This is clearly just another implementation of PWM.

If all you want is 50 and 100% that is very easily arranged by putting a single diode in series with the power line with a switch across it. If the switch is closed the diode isn't there (shorted out) and power is transferred to the load on both half cycles. If the switch is open then power only flows on alternate half cycles and the power delivered is half.

The elegant way to do this is obtain a SCR/Triac.... system whose firing angle cycle ratio you can control via a 4-20 current loop or 0-5 volts and hook that up to a PID controller with 4-20 or 0-5 output. This gives you really smooth output power control. Much smoother than turning the power on for 50 seconds out of a hundred.

__________________
ajdelange is offline
 
Reply With Quote Quick reply to this message
Old 03-08-2013, 09:55 PM   #17
jCOSbrew
HBT_SUPPORTER.png
Feedback Score: 0 reviews
Recipes 
 
Join Date: Feb 2012
Location: Colorado Springs, CO
Posts: 606
Liked 36 Times on 32 Posts
Likes Given: 7

Default

Search for "voltage resistance SSR" on ebay or amazon to find the phase angle control.
Mine was about $12 shipped with a heat sink. Add the enclosure, pot, and power cords.

Make sure your power source has a GFCI for safety.

__________________
jCOSbrew is offline
 
Reply With Quote Quick reply to this message
Old 03-08-2013, 11:22 PM   #18
millsware
Feedback Score: 0 reviews
Recipes 
 
Join Date: May 2010
Location: Pittsburgh
Posts: 210
Liked 12 Times on 7 Posts

Default

Thanks for your input everyone. So what I'm looking for is a dial that I can set to a percentage, and the element will only output that much wattage. So a 5500W element set at 50% will "act like" a 2750W element. In older chemistry labs they have what are called variastats for controlling hotplates, and I was thinking of something like that. The variable speed router controls seem to do the same thing, but I can't find one at 240V and 20 amps.

For the SSR control, how fast is the switch between off and on? If I set it to 50%, does it switch on for 1 second, off for one second...millisecond...minute? If it is a fast switch, then it seems like it would effectively accomplish what I'm after.

__________________
beerapprentice.blogspot.com
millsware is offline
 
Reply With Quote Quick reply to this message
Old 03-09-2013, 12:24 AM   #19
alien
Feedback Score: 1 reviews
Recipes 
 
Join Date: Apr 2012
Location: Philadelphia, PA
Posts: 1,233
Liked 64 Times on 58 Posts
Likes Given: 61

Default

This one will handle 20 Amps, easy.

http://www.ebay.com/itm/10000W-220v-...-/181048405275

__________________
Magic Smoke brewhouse and grill

Arduino PID controller - Automatic Smoker - Cooler MLT - Counterflow Chiller - SSR demo - PWM timer - Folding Brew Table
alien is offline
 
Reply With Quote Quick reply to this message
Old 03-09-2013, 12:51 PM   #20
millsware
Feedback Score: 0 reviews
Recipes 
 
Join Date: May 2010
Location: Pittsburgh
Posts: 210
Liked 12 Times on 7 Posts

Default

Quote:
Originally Posted by alien View Post
Sounds a little too good to be true.

For the GFCI, can you just upgrade the outlet, or do you have to go all the way back to the circuit breaker?
__________________
beerapprentice.blogspot.com
millsware is offline
 
Reply With Quote Quick reply to this message
Reply


Quick Reply
Message:
Options
Thread Tools


Similar Threads
Thread Thread Starter Forum Replies Last Post
DIY variable speed grain mill ernestmyname DIY Projects 16 01-28-2012 10:35 PM
Inexpensive variable speed Keezer fan (stirplate?) pelipen DIY Projects 1 12-23-2011 04:46 PM
Harbor Freight Variable Speed Drill weirdboy Equipment/Sanitation 7 12-12-2011 05:23 PM
$18 Dual PWM Dimmer / Speed Controller CrazyP DIY Projects 1 05-14-2011 07:32 PM
What would MacGuyver do? - variable speed pump Gordie Equipment/Sanitation 7 04-11-2008 04:34 AM