PWM Controller

[Capt-Cudellez]

Since February of this year I have been running with a home made PWM controller, after letting the magic smoke out of my rather expensive store bought phase angle controller.

Well it looks like this

I do have a design for a clear adhesive decal to go on the fascia, but the mistake I made was wiring the plug on. Once it was functional I forgot about making it look pretty.

Inside it looks a bit like this, its a bit of a jumble, but it all works.


The parts that make it work are..

a 40amp SSR http://www.sourcingmap.com/ssr40da-single-phase-heat-sink-ssr-solid-state-relay-40a-p-138807.html

A PWM control board http://www.ebay.co.uk/itm/DC-Motor-Speed-Control-HHO-PWM-12V-2A-20W-/140535132501?pt=LH_DefaultDomain_0&hash=item20b88bf155

And a power supply http://www.ebay.co.uk/itm/12V-2A-24W-Switch-Power-Supply-Driver-For-LED-Strip-New-Strip-light-Display-220V-/280757788009?pt=UK_Mobile_Phones_Communication_Radio_Parts_Accessories&hash=item415e77dd69

All of which came to about £20 delivered to my door. Some other bits and bobs from Maplin and RS components, like the fans and the LED were all that was needed to finish it.

The PWM board is for DC motors so cycles several thousand times per second, way too fast for the SSR. I swapped out one of the capacitors for a 2.2uF electrolytic cap, this brought the cycle down to around 1hz.
Fast switching is what really heats up these SSRs so 1hz seems to work well, it would probably work fine without the forced cooling, but this will extend its life and is a good idea.

This PWM card only has a maximum duty cycle of 92.5% meaning it is in the on mode for 92.5% of the time and off mode for 7.5% of the time. So I fitted a toggle switch to bypass the controller and have the SSR switched on 100% of the time, I use this for strripping and on warm up.

The LED flashes along with the duty cycle giving a good indication of how much juice its getting - click to see the video if that doesn't make sense.

[Almanac]

You have to get with the program and put a nice sticker on the front otherwise it just won't do

Nice job - where did you get the metal case. I had to put mine in a wooden box

Mine has an SSR mounted on a heat sink cooled by a 220V PC fan and the current to the element is regulated by a potentiometer and that's it - I've no idea what the other things you have do or are for and mine doesn't look as neat as yours.

You said "Inside it looks a bit like this, its a bit of a jumble"

That's not a proper jumble....this is jumble, in fact it's a bloody mess...
...but when the lid's closed nobody will notice.

AM

[Capt-Cudellez]

Mine has an SSR mounted on a heat sink cooled by a 220V PC fan and the current to the element is regulated by a potentiometer and that's it - I've no idea what the other things you have do or are for and mine doesn't look as neat as yours.

Its just a different type of SSR, the model I went with is turned either on or off when a small dc voltage is applied, just like a normal magnetic relay.
So you need a way of turning the control voltage on an off which is where the timer board is used.
Its just a simple board with a 555 timer chip, you could build one easily if you had the urge, its just that one is so cheap its hardly worth the issue of buying the bits, same with the power supply, I've built some before, but you can't buy the components (in 1's and 2's) for the cost of that unit, so why bother.

I bought the box from RS, it cost almost as much as the components, but I liked the look of it. I should have read the description better, as its made from plate mild steel, and is a bugger to drill out and do the cut outs for the switch.

I will do the vinyl decals on the Mk2 , its got an additional input for the pressure switch, so will cut the power and sound a buzzer if the still goes above 2psi and you'll need to push a reset button.
I've tested it out with a cork in the still mouth, and it works fine. Just need to look for a box to put it in.

[Capt-Cudellez]

Aiden, I realize I didn't explain the difference between the SSRs. I "think" yours manipulates the voltage, so when you're running at 50% its providing 120v and therefore half the Watts.

With mine, when I'm running its always providing 240V, but when I'm at 50% for each 1 second period it provides the full 240V for 0.5s, and no power for 0.5s providing half the Watts over the period.

2 ways of doing the same thing.

[Almanac]

That's why I needed Brian to tell me what to buy and how to assemble it 'cause I'm a bit thick when it comes to that sort of thing.

I'm not sure why but the technical side of electricity/electronics has always been something I just felt best left to those who like that stuff.

My talents lay elsewhere ....I do have talents...really

AM

[Capt-Cudellez]

FYI, the decal would have looked like this. I really should laser it onto the clear vinyl and finish the box off.