Foam Cutter Power Supply Problems

[Shezer]

Today I got my foam cutting power supply built and running. I went by the plans at http://www.utahflyers.org/index.php?option=com_content&task=view&id=37&Itemid=33

The only problem I'm having is the dimmer switch doesn't seem to change the temp of the bow. Actually I don't have a way to measure the actual temp but, I'm reading 12.8 volts (it's a 12v tansformer) at the bow and that doesn't change with the posisition of the dimmer switch. Should it change?

I'm heading out tomorow to pick up some foam. Can't wait!

Thanks for any help.

Shezer

After thought: Whith power running the bow really hums and vibrates a bit. Is that normal?

[paulo810]

Mine is based on the same design.

The humming is good. That tells you the juice is flowing. I have never measured the voltage of mine.

Look around and get some FREE foam to practice on. Packing foam is pretty easy to come by.

Try cutting at different dimmer settings. Look at the width of the cut and ease of pushing the foam. You will quickly learn what dimmer setting to use for different foams.

If you have it set up correctly and are using a lightbulb, does the bulb brightness change as you adjust the dimmer?

[Shezer]

Diddn't even think of trying a light lol I'll try it out.

Thanks.

[paulo810]

You need something putting a load on the circuit ( light bulb).

[Shezer]

So, without the load the dimmer doesn't work?

[paulo810]

Here is exactly how mine is set up. It does not get any easier.

I only use it in the garage which has it's own fuse box, so that is my safety circuit breaker instead of a fuse built in. In 2 years I have never tripped a breaker.

[Shezer]

Mine has the GFI oulet for a fuse.

[paulo810]

I used to use the light bulb as a visual voltage guage. Now I just have marks on the dimmer to set the voltage but the bulb is still there so I know if the power is on to the hot wire.

Hot wire design has a cult following here and I expect soon they will discover your thread and overwhelm you with design variations and safety warnings.

Here's a link you might want to read about how dimmer switches work.

http://home.howstuffworks.com/dimmer-switch1.htm

Above all, be safe. ( see, there you go already! )

[Shezer]

That would explain the constant 12v reading. Foam is in the truck. See what happens later today :)

Thanks for the help.

[Shezer]

Hooked up a light and no go on the dimmer. Cuts the 2" blue foam pretty good though. I'll have to try another dimmer switch.

[paulo810]

It will cut it "perfectly" once you get your dimmer functioning properly. Also, different foams cut best at different heats.

Good luck with it and have fun.

[Shezer]

New dimmer switch did the trick! Now to get to cutting!

[Dan Baldwin]

New dimmer switch did the trick! Now to get to cutting!

What dimmer did you end up using that worked. I've heard that some (perhaps most) dimmers don't work with transformers.

Dan

[jim_ag3y]

A lot of dimmers actually cut the 60 Hz sine wave into something that resembles a spike of voltage, that cuts away some of the waveform. Unfortunately, that sharp spike will cause the transformer to react in a non linear fashion, so setting the dimmer to 50% will not necessarily, in fact more than likely will not, cause the voltage on the secondary side of the transformer to drop down to the expected 50% of full voltage.

A better device to get rather than a dimmer, would be an "auto-transformer" that actually maintains the 60 Hz waveform, while dropping the voltage down in a linear fashion. This device could be hooked up on the primary side of the transformer, and the result would be a very easily adjustable output voltage on the bow side of the circuit.

Look at Mouser electronics, or some other electronics device sources, and you should be sure to find auto-transformers!


There are dimmers made for controlling florescent lamps. These might maintain a more symmetrical waveform and give a more predictable output. I haven't actually observed the waveform of a florescent dimmer, but I am making an educated guess that this would be the case. Someone can correct me if I am wrong.

Good luck Jim S.

[XJet]

I've been using a dimmer for years with no problems at all.

[Ron W3FJW]

A better device to get rather than a dimmer, would be an "auto-transformer" that actually maintains the 60 Hz waveform, while dropping the voltage down in a linear fashion.

But the auto-transformer is a gold plated $100 solution compared to a $5 dimmer which works just as good for the purpose at hand. We're not talking lab standards here as far as voltage waveform is concerned..

[AndyKunz]

I just use a model train transformer.

Andy