I Want To Buy A PWM

[SilverZero]

I just got through mangling my attempt at building a PWM based on a common design around here, for my new electric kettle project. I don't have the skills or the equipment to solder up my own PWM board, so I'm hoping somebody can point me to a ready-made model. I really have no use for PID as I'm only controlling the boil in my main kettle, although if a PID will allow me to control the element (5500w) the same as a simple PWM I'd consider that.

Can anybody help me? I did what I could, but it's a limitation of my skills and my soldering gun. I'm going to burn out the 555 before I get a good connection every time, I just know it.

 

[matho]

just search for these http://www.fotek.com.tw/Ecenter1.asp?class1_sn=4&class2_sn=18 on ebay. They switch on each half cycle for a length of time determined by the variable resistor.

 

[SilverZero]

Interesting, this is different from the regular SSR I already have. Do I just connect a pot across the DC input side? What's the cycle frequency? I wasn't aware they made SSRs like this.

 

[Ravenshead]

That SSR (40 Amp) plus a PID from Auber (SYL 2363 is a good model) in manual mode will do what you're looking for. Manual mode lets you control the duty cycle a percentage of on time, i.e. 100% means always on, 50% means equal time on and off, etc. Be sure to mount a heat sink on the SSR though.

 

[SilverZero]

I think this is a newer type of SSR that has a control circuit built in. I thought they were just on/off but after reading a few other threads it seems there are adjustable SSRs that just need a variable input voltage via a power supply and a pot.

I understand how a PWM works, I tried to build one for the SSR (non- adjustable) that I already have (which I did mount to a heat sink even though it's a 40A model which some say isn't necessary) and I'm pretty well convinced I won't be able to do it myself. This seems like a way around all that. A PID is overkill because I'm just controlling a boil, but if the cost was reasonably similar I'd do it just to have the option to use it for temp control in the future.

 

[matho]

Interesting, this is different from the regular SSR I already have. Do I just connect a pot across the DC input side? What's the cycle frequency? I wasn't aware they made SSRs like this.

yeah they are phase control and yes you just connect the resistor across the 2 terminals that the dc input is connected to on normal SSR. I can't get on ebay at the moment but I wouldn't expect them to cost that much. They chop the waveform so they can produce a bit of noise but for switching a resistive heating element it won't produce that much.

cheers steve

 

[SilverZero]

Very cool, sounds like just what I want. I see there are discussions about these not being switched at zero-crossings but I don't know that I really care about that. In just checked Ebay, they can be had from China for $10-$12 or so, maybe not great quality but probably as good as my $5 SSR at the moment.

Thanks!