Light control ideas needed

[Lateralg]

I'm refining my M2 enclosure to include four PAR 16 Halogen lamps for experiment in heating large models to avoiding lifting and delamination.

Each of the four will be <= 60 watts. I need individual dimming control of each. I could accomplish this with four dimmer switches, and a couple of 4" boxes, but this is pretty clunky and takes a lot of space.

I'm looking for a more elegant solution, one that's consistent with the class of the M2.

Any suggestions?

[Dale Reed]

I assume you don't need to control dimming from the Rambo via G-codes or such, that a box with four slide-pots would hit the spot nicely.

A number of lamp dimmer circuits are shown at https://www.google.com/search?q=TRIAC+l ... d=0CEkQsAQ --- on that page, on my 1920-wide monitor, the first and last images in the second row show the same circuit with the same component values. This was a popular circuit back in the 70s -- my brother and I both made them.

Basically, you need some triacs (on heat sinks), 50k slide pots, 0.068 uF higher-voltage capacitors, 15k 1/2W resistors, NE-2 lamps (I like this version because I can never find the diacs), a cord with plug, and sockets to plug the lamps into. Mouser has 25A 600V triacs for just over a buck ($1.15 USD in Qty=1) apiece ( http://www.mouser.com/ProductDetail/STM ... FinhmSo%3d )

Even better, you should be able to print a nice little enclosure for your quad dimmer with your M2

Dale

[Lateralg]

Thanks Dale.

Are your rows 5 across?

[Dale Reed]

More like 7. On my phone, they are the eighth and fifteenth images. Both have component values shown, and use the same circuit and same component values.

Dale

[Lateralg]

Dale,

I need help in selecting the right parts. I spent an hour @ Radio Shack yesterday & came away with only a PCB.
Today I spent >hour on Mouser & got nothing but a headache. I found the Triac you recommend, but had a problem identifying the correct other parts.
I'm also uncertain about the proper connections of the three legs of the Triac. (Closer look at Mouser description answers this) ... I think.

Please don't under-estimate my ignorance. I'm a good ME, but awful EE.
But I'm capable at soldering.

[ednisley]

Please don't under-estimate my ignorance.

At the risk of coming across as a nanny, be careful: 120 VAC will reach out, take you by the hand, throw you across the room, and stop your heart stone cold dead.

The main problem: you can't debug a line-voltage circuit by casually probing with multimeters and oscilloscopes as you do with low-voltage DC circuitry. You need, at least, an isolation transformer, the willingness to wear rubber-soled shoes, and the determination to keep one hand in your hip pocket. If you inadvertently bridge the circuit with two parts of your body, the current passes through your heart and then you die; the absolute best way to do that is running the current through your arms and across your chest.

That makes it really tough to figure out why some random circuit element doesn't do what you think it should.

I've been bringing up a homebrew sewing machine controller and, despite all my fussiness, recently had a near miss:

http://softsolder.com/2014/10/31/hallow ... the-loose/

That's why the controller case has an interlock cutoff, a grounded steel enclosure, and a line fuse, plus the usual GFI on the branch circuit. That simply means I must make at least two mistakes at the same time to kill myself; alas, that's entirely possible.

If this is your first experience with line voltage gear, spraying money on the problem to make it go away might be a Very Good Idea. Skip the construction & debugging, line up a pair of dual dimmers with four outlets in a quad deep outlet box, screw down the cover, and be done with it:

http://www.homedepot.com/p/Lutron-Skyla ... /100028486

It may be butt-ugly, but you'll (almost certainly) live to tell the tale...

[Dale Reed]

Lateralg,

I did a little poking around on Mouser and came up with these:

0.068 microFarad 300 Volt capacitors (need 8) : http://www.mouser.com/ProductDetail/Kem ... zAEFe3Q%3d

NE-2 neon lamps (need 4) : http://www.mouser.com/ProductDetail/Chi ... SZM1TUs%3d

15 kOhm 1/2 watt resistors (need 4) : http://www.mouser.com/ProductDetail/Vis ... fgbfDgE%3d

50 kOhm slide potentiometer (ned 4) : http://www.mouser.com/ProductDetail/Bou ... KCCq42o%3d

Panel-mount AC receptacles (need 4) : http://www.mouser.com/ProductDetail/Qua ... 09k8iE4%3d

I've tried to pick parts of suitable quality, available in stock with Quantity 1 pricing and reasonably inexpensive / good value for the money. I'm sure someone with more time to search could do a little bit better. The capacitors are 300V units -- for the price, it doesn't help to skimp on specs here. Quantities shown are minimum required for the project. I'd get several extras and build ONE circuit to test before embarking on building the four-banger.

I envision a box with the four receptacles on the back, an incoming power cord, also in the back, and the four slide protruding out the top. Perhaps add a master power switch on the top or the front.

With the size of the box needed for the outlets on the back and the slides on top, you can probably just stand the triacs up on your PC board with a heatsink bolted to each, just standing there inside the box. With the current capability of each triac being more than the whole box will ever handle, I can't imagine them getting too hot.

Be very careful as you build and test this -- the parts will in many (most) cases have exposed line voltage -- notably the heat sinks on the triacs!
Hope this helps!
Dale

[Lateralg]

Thanks Dale, Thanks Ed.

I really wanted to build this project. One reason is that I don't know how to do it.
I could probably pull it off. But I'm going with the decision process I tell my kids & grandkids. Think beyond the probability of failure, particularly if it's extremely low. Consider the consequences if the rare event occurs.

Tomorrow I'm off to Home Depot.

[Dale Reed]

Lateralg,

Totally agree with Ed, and with your decision to hit the home center. I have the curly hair to show how many times I've been "bit" by 120 VAC. That Included my first Heathkit, a 5-tube AM table radio. NO isolation from line to speak of --- the "infamous" 5-tube circuit uses a set of tubes (50C5, 35W4, and some 12A*7s) whose filament voltages add up to about 120 (and which all have the same filament current). The filaments are wired in series, right across the line, no transformer. A circuit like that would never make it through UL / CSA these days.

I've been building kits and homebrew circuits since I was about 10 years old, so I've grown totally foreign to the concept that most folks don't really know electricity all all.

Anyway, if somebody DOES decide to do the old 60's / 70's light dimmer circuit, there's your parts list!

Right on, Ed. Thanks for keeping us safe!

[jdacal]

I only broke the rule about keeping one hand in your pocket or behind you once. That's all it took. This was about 40 years ago... was working on a hot chassis TV and was crouched down on a carpeted floor. I didn't realize there was an intake vent cut into the carpet behind me for the heating system of the house. Lost my balance and reached back to catch myself with my right hand and still had my other hand on the hot chassis. My right hand landed on the vent which is obviously grounded and the rest was a lot of sparklies in my brain. Luckily it didn't last long, as I was falling over my hand came off the hot chassis.