Sciencemadness Discussion Board - What dimmer to use with Glas-Col heating mantle in Europe

What dimmer to use with Glas-Col heating mantle in Europe

derk19 - 3-7-2019 at 12:41

Hi all,

I am buying a 380W 110V Glas Col heating mantle, with cable ending in a US plug, and then a US to EU adapter plug.
I want to use a light dimmer to regulate the current.

I suppose I need to use a dimmer for 110V, and then place it between the mantle and the US plug? Is this correct?

Thanks in advance.

Btw great forum, lurking for a while and learned a lot from you guys.

Ubya - 3-7-2019 at 12:55

you could get a 0-220v dimmer and never going over half of its range

Funkerman23 - 3-7-2019 at 14:48

A couple words of advice I pray you follow: When converting voltages; follow the 1/3 rule. The 1/3 rule is buy a transformer rates for 3 times the max wattage of the heating appliance you are using.
When using devices that heat, do not use anything but a actual transformer, and do not use a switching power supply.
For this task , something like this: https://www.ebay.com/itm/NEW-Pyle-PVTC2020-Step-Up-Down-2000... is what you should use, although 2000W is more than 3 times the 380W your mantle needs. This is a good thing.
After that, a dimmer switch CAN work but you will get better results with a proper variac. I understand these things are expensive, but if you plan to stay with chemistry you will find it is a good investment.

I disagree ...

Sulaiman - 3-7-2019 at 18:24

Although it is 'nice' to have spare capacity,
the load is resistive - the easiest type of load for a transformer to handle.
A 380 VA transformer is designed for 380 W output into a resistive load.
or only about 330W if full-wave rectified and smoothed for a dc output using bridge rectifier and capacitor(s)
If transformers were cheap then I would advise a large safety margin ... but they are not cheap.

You could use 230 (240) Vrms and a dimmer that you NEVER turn fully up
(doubling the voltage would quadruple the power = bye bye heating element)
but a 230:110 (or similar) transformer followed by a dimmer would be safer.
As dimmers are cheap (and much more prone to failure than a transformer) I do recommend using a very conservatively rated dimmer.
e.g. use one of the eBay 4000W or even 10000W dimmer modules.
https://www.ebay.co.uk/itm/4000W-AC-220V-SCR-Voltage-Regulat...
or https://www.ebay.co.uk/itm/High-Power-10000W-220V-SCR-Voltag...

Many 240V (230V, 220V) transformers have dual primary windings,
e.g. 120 + 120 (115 +115, 110 +110)
so they can be wired as an autotransformer, https://en.wikipedia.org/wiki/Autotransformer
leaving any secondary windings unused.

P.S. as far as I am aware, the main differences between using a variac or a dimmer for heating control are;
. cost ... variacs are much more expensive
. dimmers can cause radio frequency interference
. a complete new dimmer is cheaper than a new brush set for a variac

I have a few 240V rated variacs (1A, 3A, 16A etc.) but I use the eBay 4000W dimmers to control my hotplates and heating mantle.

If you have spare cash then rather than a voltage converting (step-up or step-down) transformer use an isolating transformer for added safety.

[Edited on 4-7-2019 by Sulaiman]

Heptylene - 4-7-2019 at 00:39

For my tube furnace with a similar power output I'm using one of those ebay dimmers, supposedly rated for 4 kW. You just have to be careful to not turn the potentiometer all the way up. If you know a thing or two about electronics, you could try to replace the original potentiometer with another one that cannot phyically go above midpoint.

Also include a thermal fuse in your design! The heating mantle might get hot enough to start a fire without tripping the breaker.

Funkerman23 - 4-7-2019 at 11:09

Quote: Originally posted by Sulaiman

Although it is 'nice' to have spare capacity,
the load is resistive - the easiest type of load for a transformer to handle.
A 380 VA transformer is designed for 380 W output into a resistive load.
or only about 330W if full-wave rectified and smoothed for a dc output using bridge rectifier and capacitor(s)
If transformers were cheap then I would advise a large safety margin ... but they are not cheap.

You could use 230 (240) Vrms and a dimmer that you NEVER turn fully up
(doubling the voltage would quadruple the power = bye bye heating element)
but a 230:110 (or similar) transformer followed by a dimmer would be safer.
As dimmers are cheap (and much more prone to failure than a transformer) I do recommend using a very conservatively rated dimmer.
e.g. use one of the eBay 4000W or even 10000W dimmer modules.
https://www.ebay.co.uk/itm/4000W-AC-220V-SCR-Voltage-Regulat...
or https://www.ebay.co.uk/itm/High-Power-10000W-220V-SCR-Voltag...

Many 240V (230V, 220V) transformers have dual primary windings,
e.g. 120 + 120 (115 +115, 110 +110)
so they can be wired as an autotransformer, https://en.wikipedia.org/wiki/Autotransformer
leaving any secondary windings unused.

P.S. as far as I am aware, the main differences between using a variac or a dimmer for heating control are;
. cost ... variacs are much more expensive
. dimmers can cause radio frequency interference
. a complete new dimmer is cheaper than a new brush set for a variac

I have a few 240V rated variacs (1A, 3A, 16A etc.) but I use the eBay 4000W dimmers to control my hotplates and heating mantle.

If you have spare cash then rather than a voltage converting (step-up or step-down) transformer use an isolating transformer for added safety.

[Edited on 4-7-2019 by Sulaiman]

I stand happily corrected. I was also not aware of the dual windings feature on the 220V transformers. Because I repair vacuum tube electronics, I have always had a variac on hand to slowly bring up the voltage. Sometimes older capacitors can be saved this way (though I prefer to replace every one that I can, save for silver micas in IF circuits where the risk of the 'repair' destroying the If transformer is much greater, then I replace as needed). I have always tried to give as much room as I could. Once bitten twice shy and all that.

I still stand by my statement regarding heating loads on a switching power supply. It is possible to do, but I have had no end of Radio frequency interference from switching power supplies. Never mind the rhythmic dimming if its a large mantle and the noise it can add to the outlet. From my experience, appliance makers make thier circuits as cheaply, and as lazily as they can. Very few appliances will think to filter power from the mains.

As far as the 220:110 dimmer theory you are right, but in my mind I was more worried about the current differences. Again, I admit I go out of my way not to tax the circuit after losing a few experimental devices early on in my work. For me I own ,and would buy a varaic and a dedicated transformer as an investment, as I use these things enough to justify the cost over the long term. but in any case I salute you Sulaiman!!

[Edited on 4-7-2019 by Funkerman23]

Sulaiman - 4-7-2019 at 18:09

"Because I repair vacuum tube electronics, I have always had a variac on hand to slowly bring up the voltage. Sometimes older capacitors can be saved this way"

a successful time-tested procedure, very useful when powering up old electrolytic capacitors,
most of my repairs have been on equipment that has a switching power supply,
many switchmode power supplies can be killed by slowly increasing the ac input voltage,
so I prefer a switch and a filament lamp in series with the supply,
the lamp flashes brightly at switch-on and fades to very dim if there is negligible load on the power supply (linear or switchmode),
if the equipment is faulty then the lamp continuously illuminates fully - limiting the current to a usually non-destructive level
or at least to a non-explosive level

"I still stand by my statement regarding heating loads on a switching power supply. It is possible to do, but I have had no end of Radio frequency interference from switching power supplies. "

I can not argue with that
(but in industry virtually all heating devices are powered by some sort of switching power supply/controller, mainly due to the cost of the copper and steel used in transformers)
I once had to replace my new soldering iron with a more expensive one because the internal 'dimmer' caused so much rfi
(I have an amateur radio license)

"Very few appliances will think to filter power from the mains."

I can't argue with that either

"As far as the 220:110 dimmer theory you are right, but in my mind I was more worried about the current differences."

virtually the only difference between different (cheap) power rated dimmers is the current rating of the triac.
(sometimes a lower voltage rated triac is used for 110 Vac dimmers than for 230 Vac dimmers,
but the few cents saving is more often than not sacrificed to give a 'universal' production model)

The eBay 4000W dimmers have performed really well for me
(using 240 Vac devices with 240 Vac supply)
they have a small preset potentiometer to set minimum power,
you can just add a resistor or (preset) potentiometer in series with the main potentiometer to set a limit for maximum power.

derk19 - 8-7-2019 at 03:55

Thanks very much for the help, I have to study electricity a bit more I notice.

wg48temp9 - 8-7-2019 at 05:12

Quote: Originally posted by Sulaiman

"Very few appliances will think to filter power from the mains."

.

Actually if they are designing for Europe and probably many other places they have to meet RFI susceptibility and emission specifications. So most recent (at least the last ten years) electrical equipment have mains filtering and other measures to reduce RFI problems.

They even jitter the clocks (some clocks are in the GHz range) on most micros to spread the bandwidth of the RFI out to reduce its amplitude at a given frequency. There are also static discharge specs that must be met.