StillSmart

Here are details of my home made power controller. It is a very simple circuit and should be easily constructed for around £35.00 by anyone who can use a soldering iron. It gives a variable power output and enables very fine control. Most parts should be available from a company such as Farnell.com or for the most part Maplins.

First a warning. It should be obvious that this unit operates on 230v AC mains power which if not treated with respect can be lethal. If you do not feel confident with this then look away now. On your own head be it.

Below is the circuit diagram with parts. There are only five active parts involved.




Firstly I recommend a medium sized aluminium box about half the size of an A4 sheet of paper as a minimum. You should drill some ventilation holes to allow a circulation of air through it and the triac Should be bolted to the back of this with some heat conductive grease as it can get fairly warm at higher outputs. For belt and braces an additional heat sink can be used. The potentiometer VR1 should be mounted on the front as this is the control for varying the output. The remaining parts can be soldered to a couple of solder tag strips mounted at a convenient place in the box and wired to the potentiometer with a couple of flying leads. Beware when connecting the Triac and Diac that these parts can be easily damaged with excess heat from soldering. 1/2 watt resistors and potentiometer will be more than adequate. The polarity of the Diac is of no consequence and if something does go bang the I suggest that this is the bit to look at first.

Be aware that the main power flow of the circuit is between the N and the L shown in the diagram, passing through the Triac. This wire should be of heavy enough gauge to cope with the power rating of the heater. Ensure that all wiring except the earth is well insulated from the case

The diagram shown is very basic. The inclusion of a plug and socket for the mains input with a fuse rated for your heaters power and a plug and socket for the heater outlet would make it easier to use. I also highly recommend the use of a mains contact breaker as an additional safety feature. I will leave the layout of the parts to you but I advise that you give it some thought when you have all the parts to hand. Have fun and enjoy.

I should add to the above that this controller works well with my 2Kw immersion heater and it could well handle a more powerful one but it will get hotter so a bigger heat sink should be considered. Overheating will damage the semi conductors.

Thanks for that Zocco.

I've no problems with the soldering, ex TV engineer, it's the designing of circuits that I can't do.

What I sometimes use for project cases is old PC power supplies. Good for variable power if using the type with built in power supply for the monitor as the in/out sockets are already there.

I dont do designing either. I found the basics for this by trawling the internet and found the circuit for a fan speed controller. I then upgraded the triac for the biggest I could find and it worked. As a schoolboy many years ago my hobby was electronics so I wasnt afraid to jump in with both feet. Its only money, what the heck.

It is great building your own stuff and I'm glad you posted it here to share with people. For myself I do like building up to a point but don't mind buying things in if it's cheaper from some big factory than I could build it myself. Brian's (YHB) use of a package that has everything but the pot built into one SSR package springs to mind in this case. I would probably go that way as it costs less and involves less wiring up. Still good to see what is going on inside though. Helps to understand things. Besides without a price breakdown it's possible that your solution is cheaper on just the electronic bits. It's often the extras like case and connectors, meters, switches etc that boost the cost.

Too true ant, the nickel and dime stuff sure adds up.

Thanks for the comments guys. There aren't too many extras. the case can be bought quite cheaply from Maplins as can most of the other stuff. Triac from Farnell so it is easy to do the costings. See their online catalogues. As for the mains switch Use a 13 Amp fused Spur with a built in neon. This part is optional anyway, you can just plug it in to a wall outlet. The output socket can be the faceplate of an ordinary 3 pin mains socket both items can be bolted to the front of the case. Many DIYers could have these lurking at the back of their shed. Failing that a friendly electrician could supply them second hand possibly FOC. and if the worst comes to the worst Try B&Q. In any case you will soon recoup the costs with the power saved.

Come on lads don't keep looking for excuses think of the satisfaction it is a hobby after all.

Might be worth having a look at futurlec .. thailand based electronics company that I have used quite a bit over the years .. if you don't mind the wait (upto 2 weeks) they have cracking prices on components ...

Not a huge selection in comparison to rs, etc but if it's there it's cheap lol

Iain

I copied YHB's Power Controller except for the volt meter...
viewtopic.php?f=15&t=1001
This is my one

It has a dial indicator on the potentiometer to indicate the power input level, an overkill heat sink attached to the solid state relay (never even gets warm) and a 240v PC cooling fan.

Very effective, never had a problem with it and it's simple enough for even me to understand how to put it together.

AM

Aidan,

I made this overlay for the dial on my controller to reflect Kilowatts. It compensates for the non linear output of the electronics.

I find that having an indication of heat on the dial makes adjustment much easier. With just numbers turning the dial down 20% does not turn down the temperature by 20%, but turning the dial from 1.2kw to 1.0kw does.

Now I have this I never use the meters (but I still think they look cool).

Here's my ugly little effort. Can't remember the maximum wattage but probably not enough for a t500. Besides, it'll go with the air still when I put it on ebay.

Those cases also hold a the smallest variac from Maplins.

A great use for variable power is reconditioning the capacitors of long unused equipment. ie. Kenwood Chef in the loft for 30 years, turn it on and 10 minutes later there's smoke. iirc, half an hour a day starting with very low power can stop that happening.