Heating Element Control

[rad14701]

Hi folks,

Ive bought a PSR-25, a 250K 2ohm Linear Taper Pot and i plan on using it together with a 3KW immersion heater. I have seen the images and schematics posted by Mulekicker and i notice that the majority of posts are relating to domestic power supply from the US or Aus. I am in the UK and as you probably know we use 230V single phase AC, Single live, neutral and earth (twin & earth). Can anyone confirm if Mules schematic instructions are safe to use with our system. I have looked at the PSR schematic and i am pretty happy myself that it is safe to use as follows.

Live from switch to PSR pin 1, live out of PSR pin 2 to immersion heater, pot across PSR pins 3 & 4, neutral from ringmain to immersion heater. PSR earth tab to earth in ringmain as well as earth tab on barrel.

That should work fine... Essentially, wired like US 120V...

[Anthoney]

Yes your fine electrically for our power but you will find putting plugs and sockets in there will help the make the physical reality easier.

[frodo]

I do not know shit, i know less than shit.

actually, i am a plumber, i know my shit, It is Electricity i do not know shit about

i was looking at the Ski-matic for the element. Copied it

and showed it to a sur nuff electrician.buddy of mine.

this is his thoughts an comments.

Frodo. It seems to me that the original schematic - less the dimmer switch - is the factory wiring diagram for the heating element circuit. Is that correct?

If so, then the gated, switchable diode (fuse) directs the amperage flow through the circuit. In one setting [gate] it directs flow through the resistor to choke down the amp flow to prevent overheating of the element and maintain the factory set temperature. In the other setting [MT1], flow is unrestricted and allows the element to heat up rapidly, but when the flow drops to a certain level (the heating element is also a resistor), the diode switches to the gate setting.

If it were me, I would put the rheostat in the power cord itself. The reason being is that if it were installed in the circuit loop next to the resistor the adjustments by the switch to restrict the amp flow could trigger the diode by the reduction of the element temperature and cause it to switch from "gate" to "MT1" to raise the temp and thereby overheat.

I'm an electrician, not an electronics tech, but that's how it looks to me.
"I'd love to spit some Beech-Nut in that dude's eyes, and shoot him with my ol' .45 'cause a Country Boy can survive!" - Hank Williams, Jr.
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anybody agree/disagree or want to add to this idea?

[rad14701]

frodo, for a 120V circuit you don't need that 75 Ohm 25 Watt resistor... I have built several controllers with just a dimmer, resistor, and triac... I'm pretty sure there are pics of it in this or another controller topic... That resistor can be a whole lot smaller... I'll see what I use and report back... That circuit is also wired improperly... All current cannot go through the dimmer, it only samples voltage from MT2 and passes it on to the Gate... MT1 is connected directly to the Hot and MT2 is for output...

Edited to add: HERE is a post I made in THIS topic... And the proper circuit is the one below...

The dimmer supplies the diac function as well, so the circuit is very simple with no diac or led pair required... The lower mains feed is Hot and the upper is Neutral...

[frodo]

anyone look into using a water heater lower element control for your boiler?

http://screencast.com/t/GdPskZGkITol" onclick="window.open(this.href);return false;" rel="nofollow

[still_stirrin]

It's a thermostat control. Not what you need to run a boiler. Wrong tool for the job.
ss

[frodo]

ok,,,found a hot plate, took the switch out of it, no t-stat

simple rheo stat. will i need a resister or anything else?

this was wired with just the switch

[still_stirrin]

Frodo,

A rheostat is a variable resistor (a high current potentiometer).

So, if that's the only device you're using to regulate the heat element, it is essentially a voltage divider circuit...where the voltage is proportional to the ratio of the resistances of the heater element and the rheostat. With the potentiometer (rheostat) turned up (way up), the voltage would be sunk mostly in the potentiometer and the resulting current flow would be minimal. The power would be consumed by the potentiometer in this case and not much heat would be generated in the heater element (essentially turned off). The rheostat could, and likely would heat up however because of the resistance and what current would be flowing.

Now, turn the rheostat the other way, and the voltage is primarily on the heater element. The resistance of the element and the voltage would allow a current to flow through the (whole) circuit...heater element AND rheostat. Since heater elements are typically very low resistances, turning the rheostat down would possibly allow a large current to flow, generating a lot of heat in the heater element....and a lot of heat in the rheostat. If the rheostat is properly designed and manufactured to pass those high current loads, and also operate safely that way, then you may not need any other elements in your heater circuit.

Personally, I wouldn't like this type of circuit (although it is a simple circuit) because of the reliability concern for the rheostat...whether or not it can tolerate the type of service you're putting it into. But if the hotplate worked with it...and you haven't put any bigger heater element in your hotplate...it should work.

Sorry for the lengthy dissertation. But electricity has a lot of power in it...enough to kill. Safety is a motivational factor. Cutting corners in design to save a few pennies could undermine that safety.
ss

[shadylane]

Frodo
That's a thermostat. It's good for turning a heater on/off when the temp gets to the set point.
In other words it's good for controlling a heater on a fermenter but useless for controlling a heater on a boiler.
A rheostat can control the power on a heater but it needs to have a power rating similar to the heater.
And 5000 watt rheostats are rare and very expensive.

[frodo]

thanks guys.

NEXT!!! LOL

[frodo]

would you guys mind taking a look at my cart, let me know if i have the correct items or not?

http://screencast.com/t/nii4imOoA" onclick="window.open(this.href);return false;" rel="nofollow

[frodo]

i ordered my SS couplings, and elements

any one have opinions as to the optimum placement of the elements? in a 15 g keg

I am thinking if i split the tank into thirds, 15 gallon

install along the top of the first third. of about the 5 gallon mark

should i be lower?

[FreeMountainHermit]

I'm just a tad lower.

[jedneck]

I'm just a tad lower.

Same here I think it takes little better than 4 gallons to cover mine.

[frodo]

sounds good. right around the 4 gallon mark

thanks...sometimes i think about this stuff to much

[FreeMountainHermit]

Make sure your element is fully covered and then some. OTHERWISE !!!

bzzzzzzzzzzzzzzz,... TOAST !!

[frodo]

following in Crankys footsteps.

here is a wireing diagram of what i an going to do

5500watt element

using a ssr 40a ac24-380v

a..2pc b 500k ohm pot

cheap pos 120v fan

if anyone sees where i am fuuuup holler!!!

[likker liker]

I followed crankys build and it has worked out perfectly

[frodo]

disposal connector, plumbing dept. hardware store. 4 bucks


i am using it one go over the wire connection at the element

[pfshine]

Looks like a good plan frodo. Love that idea.

[frodo]

Thanks,, got all my crap ordered, playing the waiting game.

and watching tracking numbers.

[frodo]

Ordered material for my controller, Looking everywhere for a cheap metal box.
them damn things are expensive for a friggen box.
even pulled a cranky, went to the Goodwill.
Good idea Cranky, no box, but scored some other shit.
came home, bummed out. I walked in my shed, and their it is.
An old metal dewalt drill box.



do not have all my parts yet, they are slowly coming in the mail, one by one


I am fitting the components into the box, after I fit everything, finish drilling mounting holes
i will paint it.
using a gastite stub out as a mounting flange to the keg lip.
i will hide my wires buy running them thru the pipe

digital thermometer, fan, fan switch

[cranky]

Nice work Frodo. Goodwill is one of those places you never know what you will find or not but sometimes what you are looking for is already in your shop. A nice neat new box doesn't really seem your style anyway. I'm surprised you didn't make it out of copper scrap like you make so many other things.

[frodo]

Nice work Frodo. Goodwill is one of those places you never know what you will find or not but sometimes what you are looking for is already in your shop. A nice neat new box doesn't really seem your style anyway. I'm surprised you didn't make it out of copper scrap like you make so many other things.

believe me, it crossed my mind.
so did using some scrap aluminum siding.to flimsy
I like to repurpose stuff,
really appreciate your tutorial, helps out a lot

[cranky]

believe me, it crossed my mind.
so did using some scrap aluminum siding.to flimsy
I like to repurpose stuff,
really appreciate your tutorial, helps out a lot

I'm glad that tutorial helps people.
I like to repurpose too, I was looking at a bunch of air filters in a dumpster the other day that had aluminum frames and aluminum expanded metal front and back and was thinking that would be good for a controller box. I was thinking I could use one for the frame and cut the other frames into strips to make the front and back cover but since I don't need a box and couldn't think of anything else to do with them and the wife is pissy about me dragging home stuff, I left them there. Next time I see some I am going to grab them and hide them from the wife in the hopes that I will have a use for them, I need to make a recycling run to sell some old wheels and scrap stuff and more aluminum wouldn't hurt.

[frodo]

behind my barn looks like fred sanfords yard. i drag stuff home, then strip it down for the copper or aluminum. that is my gun powder, primer money for my reloading addiction

[cranky]

I would be that way myself if I had space to spread out.

[frodo]

still waiting on my POT, 220 switch, and volt/amp meter

heres what i have so far,,box is an old metal dewalt drill box. i primed painted it

I will paint it after i fit everything.

[Edwin Croissant]

Wood is not a very good insulator
I have seen vintage wooden switchboard panels but these were oven dried and painted with isolation varnish. I have also seen one of these panels with a hole burned through.
In my humble opinion I would consider a terminal block.

Is that your element on the other side of your buss bar?

[frodo]

that is a spare lower element for my water heater 3800 watt camco 02292
that will get used if the 5500w takes to long getting here

I will be using a camco uldw 5500w

the wood is not a "proper" buss bar, it actually acting as an insulator for the bolts

keeping them from touching anything metal. not good ?