Circuit for controlling heater power

[ikorman]

Hi there

I want make power controller that will control how much output power heater is generating (btw. I need this to control milk heating process for cheese making ;-)). I have seen some schematics for lightning systems DXM512 (controlling duty cycle with zero crossing), but could not find something that could work up to 2000W of power. Also I'm concern about problems and disturbances that such devices could cause in my home on other electrical devices.

I would appreciate any advices and links to some schematics (I'm good at cheese making and micro controller coding, but I s**k at pure electronics :lol

Best regards,
Ivan

 

[FvM]

In contrast to lighting systems that are using phase angle control, heater power can be better controlled by a pwm with a few seconds cycle. This mode of operation also reduces interferences and is required by EMC regulations.

 

[KJ6EAD]

Here's an inexpensive product: Autonics TC3YT Temperature Controller - instrumart.com or did you need a project?

 

[dick_freebird]

If you can tolerate some temperature "ripple", a bang-bang
controller with LASCR or photocoupled TRIACS might do.
I doubt you need linear closed loop control, this hysteretic
scheme might do the job if +/- a couple of degrees is OK.

Is it necessary that all the power run through one switch?
If so then you need something like a 20A TRIAC / relay /
whatever for some safety margin on 220V power, or a
40-50A on 110V. But if you have strip heaters plastered
around a big can you could separate them and run more,
lower current switches perhaps, with common control.

There are lots of cheap temperature controllers on eBay
that could run relays or the opto inputs of isolated TRIACs.

 

[ikorman]

Here's an inexpensive product: Autonics TC3YT Temperature Controller - instrumart.com or did you need a project?

If you can tolerate some temperature "ripple", a bang-bang
controller with LASCR or photocoupled TRIACS might do.
I doubt you need linear closed loop control, this hysteretic
scheme might do the job if +/- a couple of degrees is OK.

Is it necessary that all the power run through one switch?
If so then you need something like a 20A TRIAC / relay /
whatever for some safety margin on 220V power, or a
40-50A on 110V. But if you have strip heaters plastered
around a big can you could separate them and run more,
lower current switches perhaps, with common control.

There are lots of cheap temperature controllers on eBay
that could run relays or the opto inputs of isolated TRIACs.

I see that I did not explain my problem well . Let assume that I have 2000W heater. It will heat 1 galon in 5 minutes (just for example), but I need to heat up that quantity in lets say 1 hour. Therefore I need to regulate the power that this heater will produce - I had something in mind like PWM. This is what I'm aiming for.

 

[KJ6EAD]

There are plenty of temperature controllers that will ramp to setpoint as you want for $200 or less. Take a look at Omega or Watlow for some ideas. I don't think you'll save much by building your own.

 

[Enlightenment]

Use a Solid State Relay (SSR). You will have to mount them on a monster heat sink or piece of metal and maybe blow a fan across them to cool them when controlling 2000 Watt.

**broken link removed**
Solid state relay - Wikipedia, the free encyclopedia

These things are optically isolated, so you can easily control them from a microcontroller. If you are running with a microcontroller, I would add a temperature sensor mounted on the heat sink close to the SSR to monitor it and prevent it from getting too hot.

 

[ikorman]

Use a Solid State Relay (SSR). You will have to mount them on a monster heat sink or piece of metal and maybe blow a fan across them to cool them when controlling 2000 Watt.

**broken link removed**
Solid state relay - Wikipedia, the free encyclopedia

These things are optically isolated, so you can easily control them from a microcontroller. If you are running with a microcontroller, I would add a temperature sensor mounted on the heat sink close to the SSR to monitor it and prevent it from getting too hot.

That would be great! Can SSR be used to used to keep heater turned on for only one period (1/50 sec)? In another words can they be used for fast switching (e.g. PWM)?

Thx.
Ivan

 

[Enlightenment]

There are 2 types of SSR's: Random and Zero-Crossing.
- Random allows you to turn it on at any random time. This is the type that lighting dimmer packs use. You will need a big choke to help filter out the switching noise.
- Zero-Crossing only allows you to turn it on at the next AC Zero-Crossing. You don't have switching noise in this one because you aren't turning it on in the middle of an AC cycle.

I have not used the zero-crossing type. I assume the zero-crossing type would allow you to turn it on/off at each cycle as you desire. Download the datasheets and determine if it will.

 

[betwixt]

You are correct Enlightenment. The zero crossing types are the same a their non-zero crossing parts but they have an inhibit on the gate circuit so they can only be turned on at the AC crossing point. It stops them being used in phase control applications but for low speed (one or more complete AC cycles) PWM or 'bang-bang' applications they work fine. I always use zero-crossing in my AC power applications, it makes the filtering Soooo much simpler.

Brian.