SD 240V Controller Pot: 50%=0, too sensitive

[pickled]

I have a SD 240V controller with a 6500W element. I've found that the controller will send no power to the element until the potentiometer knob is rotated to about 45%. From this point, the controller will start sending ~800W through the element. The control is extremely sensitive up to about 3500W.
Is there a way to reduce sensitivity and have the pot output be more linear? ie. 10% knob = 10% power, 80% knob = 80% power
I'd like to avoid adding another potentiometer because my box is a little crowded.

I read mention in another thread about putting some kind of resistor in parallel...

[Yummyrum]

Are you using it on 110V ? ... that will do it .

Have a read of this viewtopic.php?f=85&t=75372#p7570629.

Yes shunting the Pot with a resister will help but getting the More appropriate Pot in the first place will help with Linearity .

[pickled]

I'm using it with 240V.

[Crabmanstyle]

Hi Pickled. Is this a controller you purchased or made? I have a similar issue with mine (purchased and I've seen similar models here before) but it's very usable, regardless I'd like a bit more accurate control.

[pickled]

Crabman, I used the Still Dragon kit that many people seem to use on this forum. I wired it per their instructions with the exception of adding a cutoff switch, cooling fan and multimeter.

[ShineonCrazyDiamond]

FYI, it's not you. I have the same kit, 240, with a fan. No multi on mine, but I can tell you there is more precision I could use with the ccvm, as I spend more time adjusting between 50 and 51.5, then I'd like, as it bounces from flooding to dry on each end.

The kit is great, though. Got me to electric when I just couldn't understand any of it.

I also notice 40% before the element does anything noticeable. Never bothered me though.

[Yummyrum]

I'm using it with 240V.

OK well your , at least ahead of the game .... try running it on 110v and it will really suck .

The thing is that these controllers are analog and dependant on supply voltage and POT manufacturers ranges and tolerances .

Unfortunately there is not many Pot resistance choices to make . 50k , 100k, 200k , 250k, 500k, 1M etc

Or the Europeans seem to favour . 47k, 100k , 220k, 470k, 1M

Either way , theres not much choice In the critical area around the 400-600kOhms area that is needed . Combine that with 220, 230,240V supplies and you have a clusterfuck of combinations that culminate in a compromise over each scenario .

It is what it is ... the bottom of the scale will be a dead band . How much depends on the above .

If you want precise power control , consider something like Auberins DSPR 1 power controller. That will give 0-100% power control .
https://www.auberins.com/index.php?main ... cts_id=444

[Saltbush Bill]

I have a SD 240V controller with a 6500W element. I've found that the controller will send no power to the element until the potentiometer knob is rotated to about 45%.

Doubt that it makes much difference, I'm not a lectrickery geek, but those controllers are only rated to 5500w.
Quote: "this phase angle controller kit can be used to control electric elements up to 5500 watt at 240 volts."

[Yummyrum]

Good pickup Salty
If indeed pickled is using a 6500w element , thats exceeding the controllers ratings if he cranks it up full , ...He’ll cook that controller .... ...but regardless of element size ,it will not have any bearing on the control range . .. thats all to do with Pot value and Supply voltage.

[StillerBoy]

I have a SD 240V controller with a 6500W element. I've found that the controller will send no power to the element until the potentiometer knob is rotated to about 45%.

That statement is misleading, as there's a failure to understand that the potentiometer is only working on one line/wire of the 240v..

The other line/wire is life at all time once the power switch is on, cause it it connected straight to the element, so there is always power at the element..

As to it working on a 6500w element, other than the measurement being different, it should still work well but I've never tried it on such an element..

Mars

[shadylane]

I've found that the controller will send no power to the element until the potentiometer knob is rotated to about 45%.

I read mention in another thread about putting some kind of resistor in parallel...

Try putting a 500k 1/4w carbon resister in parallel with the pot
The value doesn't have to be exactly 500k just some were in the ball park

[pickled]

Try putting a 500k 1/4w carbon resister in parallel with the pot
The value doesn't have to be exactly 500k just some were in the ball park

Shady, what will that do?

[Yummyrum]

That statement is misleading, as there's a failure to understand that the potentiometer is only working on one line/wire of the 240v..

The other line/wire is life at all time once the power switch is on, cause it it connected straight to the element, so there is always power at the element..

Sorry Mars , that makes absolutely no sense at all.

by pickled » Tue Jun 16, 2020 5:20 am

shadylane wrote: ↑
Try putting a 500k 1/4w carbon resister in parallel with the pot
The value doesn't have to be exactly 500k just some were in the ball park
Shady, what will that do?

The short answer is it lowers the “effective resistance “ .

[Yummyrum]

Here’s the longer one .

You say that you get minimum power when the knob is at 40% . We could just measure that with an ohm meter and find out what it is .... but ... assuming the te pot is fairly well accurate ( which it wont be ) , we can calculate that at 40% , assuming you have a 500kohm Pot , the resistance will be 300kohms .

As I mentioned earlier , there is no such thing as that . The closest manufacturers make is a 470kOhm or a 250K ohm .... ones too big , ones to small .

So if we want the 500kend of the pot ( “0%” on the knob) to be 300kohms we can put a resistor in parallel .

Resistors in parallel can be calculated .

07D89039-BA39-4D5A-9682-EFC243F79D8E.jpeg (25.86 KiB) Viewed 4494 times

So if we connect a 750kohm resister across the Pot connections , it will make the Pot appear as if it only 300kohms when its turned right down and your controller will give 0 power at 0% on the knob . Unfortunately the scale will not match perfectly .

There is another problem . You can’t but a 750kohm resistor readily . Closest common ones a 680kohm and 820kohm.

But this can be fixed by adding a few resistors in series to make 750kohm

[RedwoodHillBilly]

You will also find that most of these cheap phase angle controllers have hysteresis. i.e. turn it up until you see some power and then you can turn it down and get a bit lower power.

[shadylane]

Try putting a 500k 1/4w carbon resister in parallel with the pot
The value doesn't have to be exactly 500k just some were in the ball park

Shady, what will that do?

It will make you controller work like you want it to.
Without having to buy another pot

The 500k pot and 500k resister in parallel will equal 250k
That's what the pot alone has mid scale when your SSVR begins conducting

Just so everyone understands the lower the resistance between terminals 3 and 4 on the SSVR the higher the output.
In other words the pots resistance value is inverse to the output.
If you short terminals 3 and 4 together the output is wide open
If there's nothing connecting 3 and 4 together the output is zero

I've been assuming the controller has a 500k pot already installed
That might not be the case, could you look and make sure before I make an ass of myself

[StillerBoy]

StillerBoy wrote: ↑Mon Jun 15, 2020 11:27 am
That statement is misleading, as there's a failure to understand that the potentiometer is only working on one line/wire of the 240v..

The other line/wire is life at all time once the power switch is on, cause it it connected straight to the element, so there is always power at the element..

Sorry Mars , that makes absolutely no sense at all.

240v work on two 120v wires, with the ground serving as neutral..

So on an SSR, only one of the 120v wire is connected to it and in turn managed or controlled by the potentiometer.. the other 120v wire is directly wired to the element and therefore life when the power switch is turned on..

Mars

[RedwoodHillBilly]

240v work on two 120v wires, with the ground serving as neutral.

Say what???? PE (ground) is NOT neutral. Neutral is a grounded conductor, but PE shouldn't conduct any power except in a fault condition.

So on an SSR, only one of the 120v wire is connected to it and in turn managed or controlled by the potentiometer.. the other 120v wire is directly wired to the element and therefore life when the power switch is turned on..

Not quite, on a 240v circuit with a 240v element, there is no 120v wire, there is L1 and L2, the 2 sides of the circuit. The switch (commonly a phase angle controller in our application) only needs to control one side of the circuit. Remember it is a loop.

Mars

[Yummyrum]

Mars
Sorry but this is wrong way to think about it.
Neither the Neutral or the Ground have anything to do with it . They are only for earth protection or to run auxillary curcuits but play no part in the actual control curcuit .

The circuit is a simple series one . A load ( element) in series with a switch ( the SSR) connected to a 220v supply .
It works exactly the same way whether you are using the European 220V Phase ( Live) and Nuetral System or the American bi-phase ( 2 110V live wires in anti-phase) System .

[StillerBoy]

Say what???? PE (ground) is NOT neutral. Neutral is a grounded conductor, but PE shouldn't conduct any power except in a fault condition.

In north america, 240v is 2 - 120v and the ground serves as the neutral.. check out your hot water tank element with a volt meter.. 240v across the red and black.. 120v across the red and green (ground) and the same on the black..

Mars

[RedwoodHillBilly]

Say what???? PE (ground) is NOT neutral. Neutral is a grounded conductor, but PE shouldn't conduct any power except in a fault condition.

In north america, 240v is 2 - 120v and the ground serves as the neutral.. check out your hot water tank element with a volt meter.. 240v across the red and black.. 120v across the red and green (ground) and the same on the black..

Mars

Ground is NOT neutral. Neutral is grounded at the service entrance. Ground is also called PE (protective earth) it is for fault protection, not for power delivery.

A little knowledge is a dangerous thing.

[StillerBoy]

Mars
Sorry but this is wrong way to think about it.

Do know about it being the wrong to think about it, but that's the way it was explain to me by a certified electrician that serve the community, when question why there was still power at the element, or one leg of the plug had power on it, yet the potentiometer was turned off..

Mars

[Yummyrum]

Mars , I get what you mean that one side of the element is “live “ with respect to Neutral , but as the Neutral is not connected to the the controller (SSR) , it is irrelevant to the issues the OP is having .

It is wrong terminology to say that “Power” is connected to one side of the element .

Not deliberately being pedantic , but some folk have a hard time understanding it at the best of times .

[pickled]

Try putting a 500k 1/4w carbon resister in parallel with the pot
The value doesn't have to be exactly 500k just some were in the ball park

Thanks for all the good info Shady.
How should I attach the resistor in the controller? Which terminal to which terminal?

[Yummyrum]

You solder it across the same two terminals that the wires are connected to ... or a simpler way is to stick it under the Pot connection screws on the SSR

Edit: 470k is an arbitrary ( or ball park ) value . You may find that you still are at 0% when your knob isn’t turned right down ... or you may find that you are turned right down but the power is still there .

In reality you may need a resistor anywhere from 470kohms to 1.5meg ohms .

When I looked back at my experiment , my 500K pot in reality measured 600K ... thats the manufacturers tolerances I was talking about .

The point at which my SSR reached 0% power was 400kohms @ 220V ... so the resistor I would have needed to give me full scale would have been 1.2Meg ohms .

Just say’n

[Yummyrum]

You will also find that most of these cheap phase angle controllers have hysteresis. i.e. turn it up until you see some power and then you can turn it down and get a bit lower power.

Redwood , you are bang on there . It makes the whole thing seen touchy as at the low end .

Guess its fortunate that most of us probably don’t need to use our controllers at the lower end of the range .

[MagicMan]

I’ve dabbled in electronics for years building old tube amplifiers. Most cheap off the shelf pots have a tolerance of +/- 20% or even 25%, the highest quality ones are still generally +/- 10%. What this means is that a cheap 500k pot could actually be anywhere from 375k to 625k. Resistors generally have a +/- 10% tolerance. Electronic parts aren’t a perfect science, lots of variables and sometimes it takes some time to find the right combination of parts needed to get to the value you are looking for.

[Odin]

Potentiometers suck and that seems to be the problem here. They result in square/root functions being introduced, thus making a 0-100% scale worthless (and explaining the "nothing happens until 40% power" and "between 50 and 51.5% is running good or flooding"), by making it exponential rather than percentual.

Odin.

[bluefish_dist]

I guess I don’t get too worked up about it. I run a power meter and put marks for every 500 watts. Don’t really care what % of the dial I am using, just what am I getting for output.

[LWTCS]

The POT is literally $2.75
Less than precise? Perhaps with out an amp meter to provide a window to understand the adjustment.
More precise than a typical propane regulator? Er,,,,yep.