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-   -   12 Volt Heating Element control (http://www.homebrewtalk.com/f170/12-volt-heating-element-control-366333/)

scottkct 11-08-2012 05:38 PM

12 Volt Heating Element control
 
First of all, I am an all grain home brewer for many years but this isn't for home brewing. I hope this is okay as I'm trying to translate some home brewing techniques into cheese making.

I am trying to build a RIMS setup using 12V to precisely control and maintain water bath temperatures that range between 80F-130F for long periods of time, up to 8 hours.

My reasoning to go with 12V is my need to quickly raise temps is not necessary. I can heat water on stove and add to bath to start with desired temps, I just need to hold the temp and raise very slowly.

My thought was to use a RIMS design but with a 12V element. I'm having a hard time though translating everything out there on RIMS designs for 120/240V applications down to 12V.

Some questions I have:
-Do I have to use a 12V element or can I use a 120V one and feed it low voltage? I'm pretty sure I can't but I thought I'd ask since 12V elements are more expensive.

-Do I have to use a SSR or can I power the 12V element straight from a 12V PID Temp Controller? I'm thinking I still need to SSR but though there's a chance since we're dealing with 12V.

-Is it really worth it to go 12V? I'm thinking while it would be logical for 12V to cost less since it's less voltage but I'm seeing it's actually not.


Thanks ahead of time.

BadNewsBrewery 11-08-2012 07:12 PM

The biggest problem you'll have is that (and I'm guessing here) the 12v elements you're looking at are DC, and most of the products you'll find discussed on these boards are for AC. I have no idea what would happen to a 120vAC element powered at 12vDC, but it probably won't be what you hope for. If you're already considering an SSR and running a 120v element, why not just run it at 120? Seems like extra effort to put in all the equipment and then step it down to 12v and figure that out.
-Kevin

crcusmonky 11-08-2012 07:26 PM

Also If u are using a pid just manually turn down output to the element save money and still maintain slow temp changes

Tinga 11-08-2012 11:04 PM

how much water are you keeping up to temp? you could get a low watt 110v water heater element. it would be much easier and you would have more heating power besides.

scottkct 11-08-2012 11:20 PM

Probably anywhere from 2-3 gallons. It's a good sized tub used for restaurant food storage that I will have a steam tray sitting inside so there will be displacement. Pretty much a sous-vide type setup but controlled by a RIMS design.

Yeah I'm thinking 120V is the way to go. I started with 12V because I'm using a 12V water pump that I'm controlling with a PWM/Speed Controller that runs at 108 GPH to circulate the water through the RIMS.

I'm thinking that having the additional heating ability on hand might be nice anyway.

Chad_Young 11-08-2012 11:46 PM

How about using an aquarium heater? Those still require 120V but usually have a built-in thermostat ready-made for 80-ish degree temperatures. I'm not sure you can find one that adjusts to 130F though.

Some sous-vide setups are using low-cost 120V immersion heaters for tea cups. I got one for about $5 online. Combine that with a PID or thermostat and SSR.

audger 11-19-2012 05:11 PM

voltage doesnt indicate "heating power"; Watts do.

and since "amps" is the rating that dictates how large your wiring must be (and larger = more expensive), its in your interest to use the highest voltage available which in turn minimizes the number of amps needed.

for example- say it takes 500 watts to heat your water bath to the temp you want.
a 500watt 120v heater will take one hour to do that, and will require 4.1 amps for one hour (which is negligable, all household wiring will support 4 amps). to get the same performance out of a 12v heater, the circuit would need to handle 41 amps for an hour. 41 amps requires 6 gauge wiring, and similarly rated plugs fuses, and connectors..... and then you need a 12v power supply that will output 41 amps.

you can use 120v heaters on 12v circuits, you just have to do the math. a 2000w 120v rated element would output only 20w of power at 12v. there is no reason to hamstring yourself by using only 12v.


Quote:

Also If u are using a pid just manually turn down output to the element save money and still maintain slow temp changes
slower output will ultimately cost you more. heat loss is a function of time. the longer it goes on, the more is lost. delaying reaching your goal will only cost you more money (though saving money isnt the intention here)

ajdelange 11-19-2012 05:45 PM

Quote:

Originally Posted by scottkct (Post 4570193)
I am trying to build a RIMS setup using 12V to precisely control and maintain water bath temperatures that range between 80F-130F for long periods of time, up to 8 hours.

AC or DC?

Quote:

Originally Posted by scottkct (Post 4570193)
-Do I have to use a 12V element or can I use a 120V one and feed it low voltage? I'm pretty sure I can't but I thought I'd ask since 12V elements are more expensive.

You definitely can but it might not be practical. A heater that produces 1000 watts when connected to 120 V will produce 1000*(12/120)^2 = 10 Watts when connected to 12 Volts DC or 12V rms AC.

Quote:

Originally Posted by scottkct (Post 4570193)
-Do I have to use a SSR or can I power the 12V element straight from a 12V PID Temp Controller? I'm thinking I still need to SSR but though there's a chance since we're dealing with 12V.

The 12 volts from a PID controller is intended for control. It is only capable of sourcing a few milliamperes. To get 12 watts from a 12 V heater you would need an amp.

So you would need a relay. Note that some PID controllers have relay outputs capable of handling an amp or 2. Using such a controller you would not need an external relay (provided, of course, that the heater load is less than the rating for the relay's contacts). The SSR would have to be an unusual one. Many are just back to back SCR's which cannot be used with DC as they would not turn off (commutate) when the control signal was removed unless they were especially designed for a DC application. A mechanical relay would do.

[QUOTE=scottkct;4570193Is it really worth it to go 12V? I'm thinking while it would be logical for 12V to cost less since it's less voltage but I'm seeing it's actually not.[/QUOTE]

Not if it costs more. The only advantage to a lower voltage, that I can think of off hand, is safety. OTOH 24 VAC transformers are widely used for control circuits. If you can find 24 V heaters you could use those. Note that a 24 ohm resistor with 24 volts across it will dissipate 24 watts (V*V/R) etc. If you can think of some way to protect them from liquid you can kluge up all sorts of heaters from readily available resistors.


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