Dual voltage controller

[Steve Broady]

I finally got around to building my heating element controller yesterday. Nothing special, but a couple people have said they wanted to see it when it’s done, so I’m sharing what I did.

It’s built around a 40A SSR, with a 30A rating on most of the components since that’s the largest circuit I expect to have access to for the time being.

I added a power switch in the potential water circuit, since 30A 220V switches are expensive, and I realized that most of them are 40A SSRs anyway.

The bus bars are rated for 150A, so even if the stated rating is 400% exaggeration, it should still be safe. I opted for bus bars for two reasons. For one, it made connecting things like the potentiometer ground and fan (110/220v rated) leads clean and easy. More importantly, it made it easy to connect both a 110 and 220 power cord.

All power wires have solid copper ring terminals crimped on and heat shrink tubing over the joint. I’m relying on the ratings on the terminals I bought, but they definitely seem heavy enough to do the job, and far heavier than the typical hardware store items.

I designed this to run on either voltage, depending on where I’m working and what I have available. Obviously, it’ll be severely limited on 110, but I think it’ll still be more power than I have been using for a spirit run, so hopefully still well within the usable range. There are two power cords, and the plan is to have whichever one is in use extend through a hole in the side of the lid while the other stays neatly and safely cooled inside. That’s the primary reason for putting this inside a plastic tool box, as the top tray and lid serve as an effective enclosure for the exposed pins.

While I realize that there are ways I could electrocute myself by being ridiculously careless and stupid, that risk also apples equally to most of the rest of the hobby, including drinking the final product. By only having one cord exposed at a time, and by ensuring that the case is latched before plugging in, I consider it a reasonably mitigated risk.

I have yet to test it under load. It does work to heat the element in free air, and the power switch does work. So at least I know I’ve got that part right. Hopefully, if I’ve missed anything obvious or serious, someone will point it out here. I’m always willing to learn.

[Wildcats]

Looking good man. I like the use of the tool box.

[Steve Broady]

I suggest adding a real safety power off switch in addition to your SSR switch.
The SSR may fail and provide full power, not reacting anymore to your little switch.
You will use that safety power off only in case of a malfunction. So a 30 Amp circuitbreaker (like in your breaker box) should be cheap enough. You surely will find a way to mount it to your toolbox.

I suspect you meant to post this here instead of the other thread. Good point, and I’ll definitely look for a practical way to do that. One of the reasons for the tool box was that I knew it would be large enough to accommodate any changes.

[kennstminet]

You are right. I intended to post here.
However, it seems to help at the other topic as well. Sorry for the mix up.

[shadylane]

That's a fine job.
But I didn't show us any vent holes.

[Steve Broady]

That's a fine job.
But I didn't show us any vent holes.

Is that better?

When I started looking for a safety cutoff switch, one of the things that popped up was a three position rotary selector, rated for 32A. I realized that I could use it as a master power switch and also to isolate the two power cords. And it was cheaper than a 30A double pole light switch. So that was a no brainer. All I had to do was make up a couple short leads, and drill the holes in the case for the switch. Easy modification.

[shadylane]

[kennstminet]

[Steve Broady]

I finally used this thing for the first time today. Other than the fact that I wired the potentiometer backwards, so that full on is to the left, I love it! I am stunned at how quickly it brought the boiler up to temperature, and how easily I could control the heat. I put a sight glass on top of the still, and I could literally adjust how high up the glass it was boiling.

Thank you to everyone who has posted their builds, given advice, encouragement, and other help. I don’t think I could have had the nerve to design and build something like this without you guys.

[Steve Broady]

If anyone has any suggestions on some kind of meter that I could add to this, I’d be happy to hear about it. It would be nice to have at least a rough idea what kind of power I’m using for a given result.

[Wildcats]

I finally used this thing for the first time today. Other than the fact that I wired the potentiometer backwards, so that full on is to the left, I love it! I am stunned at how quickly it brought the boiler up to temperature, and how easily I could control the heat. I put a sight glass on top of the still, and I could literally adjust how high up the glass it was boiling.

Thank you to everyone who has posted their builds, given advice, encouragement, and other help. I don’t think I could have had the nerve to design and build something like this without you guys.

Congratulations man. I bet you are super excited to be running on electric. Cheer's

[Setsumi]

I have this amp voltage meter.
https://www.aliexpress.com/item/4000029801048.html

Ampmeter

[Salt Must Flow]

I was nervous when I plugged in my first controller. I was even more nervous when I switched it on

[Steve Broady]

I was nervous when I plugged in my first controller. I was even more nervous when I switched it on

You’re not kidding! I plugged it in with more than a little trepidation, in case I had done something stupid (again). No smoke… flip it to the high voltage side.. no smoke…. Turn the power switch on, and we have heat! That was a relief.

[Steve Broady]

I wired in a meter today. Thanks for the recommendation, Setsumi. I found something nearly identical on Amazon that was a couple dollars cheaper with shipping, so I went with that.

I opted to connect it to the output of the SCR, since I didn’t know if the output voltage would vary or not. It does, at least according to the meter.

I needed a shim to get the meter to fit properly, so I opted to 3D print it. Since I was doing that, I figured I’d make myself a nicer knob as well. And I went ahead and rewired the potentiometer so that it turns the right way.

A quick test on 110V (with the element connected, so that there is a load on the system) seems to indicate that only the last 20% of the pot travel is actually useful. Is that common, or just a fluke of the meter I’m using? I noticed that when using this on 240V during a stripping run, I kept it at about 50%, so obviously there is SOME usability below the top 20%.

While obviously it would be nice to have accurate information, the primary reason I wanted the meter was for repeatability. And curiosity, of course.

[Yummyrum]

Steve, when using a SSRV , the Potentiometer value has to suit the Supply voltage otherwise you get range problems .

So for 240V you should use a 500kohm Pot , but on 120V , it should be 250kohms .
Sure , 500kohm will work on 120v , but the angle of control is quite reduced … IE , there is a lot of nothing happening , then it all happens at the end .

He’s some geeky stuff about it .

viewtopic.php?p=7570629&sid=2c881ae5c04 ... d#p7570629

[Steve Broady]

Steve, when using a SSRV , the Potentiometer value has to suit the Supply voltage otherwise you get range problems .

So for 240V you should use a 500kohm Pot , but on 120V , it should be 250kohms .

Very interesting! That explains why I got more range on the higher voltage. Thank you for sharing that, Yummyrum.

I’m using the pot that came with the SSR, and I expect that most of the time I’ll be using this on 240V anyway, so it should be fine as is. But now you’ve got me thinking about seeing if there are some unused contacts on the rotary switch that I could use to put a resistor in parallel with the pot when it’s on the lower voltage setting.

I should probably leave well enough alone…

[jonnys_spirit]

I fine tuned my kit that was intended for 240V operation yet destined for 120V - with some parallel resistors I had in the shop. A combination of some parallels and some series sorted it all out - the R changes as you turn the POT also with those in parallel... Couldn’t wait the two days for the different pot i’ll re-do it one day maybe..

Cheers,
-j

[Demy]

This is my ssr.va controller...I have another one (scr type) both work fine although ssr.va seems to be more robust.

[Buffalo]

Steve, Looks like a nice build. The wiring is neat and doesn't look like a plate of spaghetti. I do have a question though about the buss bars. I was trying to see if the bolts that hold the buss bars to the bottom of the box are common to the buss bar. It appears the hold down bolts that attach the buss bar to the box bottom might be common. Does the bottom of the box have a false bottom so the bolts that hold the SSR and buss bar bolts don't extend outside the enclosure? There are a lot of smart people on HD, I hadn't considered using a 240 volt SSR for a dual voltage controller.

[Steve Broady]

It appears the hold down bolts that attach the buss bar to the box bottom might be common. Does the bottom of the box have a false bottom so the bolts that hold the SSR and buss bar bolts don't extend outside the enclosure?

The bolts on the bus bars are insulated from the wiring. The last thing I want is a live 240V terminal exposed on the outside! I see why you’d think that, but in fact the bus pat is a piece of plastic, with a metal plate on top for the terminals to connect to.

There is no false bottom. The SSR is screwed to the heat sink, which in turn is bolted to the box. While I have not personally checked, I am operating under the assumption that the case of the SSR should be at ground potential, or at least not connected to one of the live terminals.

[Steve Broady]

I have two questions for the more experienced hobbyists out there.

1) Is it worth trying to add some kind of variable resistance to the potentiometer circuit, so that I can use more of the travel of the pot to control the power output? On 240V, I can use about half the travel, on 120V I can use less than a quarter. I’m not sure how I’d implement the idea yet. There are some unused contacts on the rotary switch, so I could use those to automate the selection between two different resistors which would be in parallel with the pot, values either determined by experiment, or just two internal trim pots.

2) I would like to use this to control a 120V hot plate in order to run a small gin still. Would it make more sense to make an adapter to go from the twist lock on the power cable, or to wire in a receptacle mounted into the box? The adapter would require no modifications, but it’s another piece to make and store and it’s more expensive. The receptacle might look cleaner, but it would presumably be live at all times, regardless of the voltage that I’m running on. Just how far should I go in trying to idiot-proof this thing?

[elbono]

On 240V, I can use about half the travel

Do you mean that half travel on the pot goes from 0V to 240V? If so there is a problem.

I built the simple still dragon kit and I can adjust from nearly zero to 240V .with full travel . As designed it wouldn't go to dead zero (only a few volts don't remember exactly) but I added a 50k pot in series with the 500k pot for fine adjustment. With this change it goes to dead zero.

If you get something very different from close to zero to 240 in less than full travel there's a problem.and you should fix that first.

0 ohms on the pot should be 240v out, a bit over 500k should be 0v out.

Once 240v works correctly move on to 120v lots will be glad to help with that but as is that's difficult.

[Steve Broady]

On 240V, I can use about half the travel

Do you mean that half travel on the pot goes from 0V to 240V? If so there is a problem.

Exactly. Then usable range of travel of the pot is roughly 1/2 the total rotational travel. The first 120-135 degrees or so does nothing, and from there I go from zero to 240 volts. Based on that, I am guessing that the resistance is too high by roughly 50%, but I don’t know enough about these systems to do more than speculate at this point.

I will point out that I’m using the potentiometer which came with the SCR, but I have no reason to believe that it’s anything more than an off the shelf component which was close enough to work for a cheap Amazon part.

Based on that, my first thought was to get a second potentiometer which I could mount inside the case, and wore it in parallel. Adjust it such that the usable travel on the pot is more or less 100%, and then leave it alone. Maybe even lock it in place with a dab of hot glue or something. Then do the same for the 120V side of things.

[shadylane]

usable range of travel of the pot is roughly 1/2 the total rotational travel. The first 120-135 degrees or so does nothing, and from there I go from zero to 240 volts. Based on that, I am guessing that the resistance is too high by roughly 50%, but I don’t know enough about these systems to do more than speculate at this point.

Sounds like you're on the right path.
What is the pots ohm rating?

Plan A is to replace the pot being used with one of half the value.

Plan B is to slowly turn the pot until the controller shows an output.
Unplug the controller, disconnect one leg of the pot and measure it with an ohm meter.
Now you know what resistance the SSVR needs to begin turning on.

[Steve Broady]

What is the pots ohm rating?

I have not measured it yet. It should be about 500k, but I have not verified that.

FWIW, my usable range is very similar to what Yummyrum found in the thread he linked above.


If I assume the values he found will match mine, then I’ll need about 400k and 200k for the two voltages. Based on that, I’d need a 2.2m and 330k resistor, respectively. I might have to order a pack of resistors and give it a try.

[NormandieStill]

There is no false bottom. The SSR is screwed to the heat sink, which in turn is bolted to the box. While I have not personally checked, I am operating under the assumption that the case of the SSR should be at ground potential, or at least not connected to one of the live terminals.

Do you have a ground connection to the heatsink? My SSRs do not have a dedicated ground link so the heatsink will be floating. Depending on any number of variables you could potentially see a potential difference between the heatsink and ground. Personally I would explicitly the the heatsink to your ground connection for the box to prevent potential excitement (see what I did there?).

[shadylane]

What is the pots ohm rating?

I have not measured it yet. It should be about 500k, but I have not verified that.

Most likely its 470K
Just like resisters, pot's usually come in standard sizes.

[Yummyrum]

I think you could use a dual gang linear Pot .
If you have extra switch contacts available, parallel the pot contacts when in 120v and it should give the same range as on 240v with just a single gang used .
They look like this .

Use one pot as you normally would on 240v . Connect one end of Both pots together. Put a switch between the Wipers ( centre terminals ) and switch on for 120v .leave the unused ends of the pots not connected .

Sorry I’d draw a pic but I can’t find a pen or pencil here LOL

[shadylane]

That could be doable Yummy.
Stacked pots and a 120v - 240v selector switch.
The problem is finding a set that matches what the SSVR needs.

Plan B
Would be use a switch to add a fixed resister in parallel with the pot for 120vac operation.