[NSRCA-discussion] Foam cutter power supply

Fri May 22 05:59:21 AKDT 2009

Yes, this sounds like an even better setup.

Ed

From: wgalligan at att.net
To: nsrca-discussion at lists.nsrca.org
Date: Fri, 22 May 2009 08:35:36 -0500
Subject: Re: [NSRCA-discussion] Foam cutter power supply

One thing I used to use back in the days was a toy train transformer.  The kind that had a variable speed slide.  Worked quite well as you could adjust it for any thickness of wire.  We used piano wire too and it worked well also.  

Wayne Galligan

----- Original Message ----- 
From: Ed Alt 
To: General pattern discussion 
Sent: Thursday, May 21, 2009 10:58 PM
Subject: Re: [NSRCA-discussion] Foam cutter power supply

Matt:
That might work, although I don't know if you would be getting much out of the light bulb at the current levels that would heat a nichrome wire.  It might be easier to just start with one turned up about half way (the fine tune dimmer) and the course control turned all the way down, then gradually turn up the course control dimmer until the wire is hot enough to melt some foam.  Mark that setting, then try the fine adjust to see if it gives the needed span of control.  If not, bump the course control up a little and repeat the initial calibration.  Never tried it myself, but that ought to work.  Another way is to get a step down transformer and place that on the output of just one dimmer control.  The secondary winding is then at a lower and safer voltage and you can do the fine tuning with just one control. I have a setup that works this way that I have used for small stuff, but it could be done with larger setups too.

Ed

----- Original Message ----- 

From: rcmaster199 at aol.com 
To: nsrca-discussion at lists.nsrca.org 
Sent: Thursday, May 21, 2009 11:22 PM
Subject: Re: [NSRCA-discussion] Foam cutter power supply

Hmmm.

It may work really well if the light (low watts) was in series with the NiCr wire. He might get a visual cue as to where to turn the dimmer

What do you think Eddie?

Matt

-----Original Message-----
From: Ed Alt <ed_alt at hotmail.com>
To: General pattern discussion <nsrca-discussion at lists.nsrca.org>
Sent: Thu, 21 May 2009 5:40 am
Subject: Re: [NSRCA-discussion] Foam cutter power supply

Paul:
The way a light dimmer works is to chop a variable percentage of the AC voltage waveform off, so the brighter the light is, the more full and complete the 60 hz sine wave is that represents the voltage applied to the load (the bulb). As you reduce the output, it chops off more and more of the output.  It has to work this way, otherwise the dimmer would be the size of a toaster oven to have enough mass and surface area to dissipate the heat that would build up in it if all it did was to drop a portion of the voltage across it.  In other words, it is either all the way off for a period of time (no power dissipated in it at that time), or all the way on like it was a piece of copper wire (no appreciable power disspated at that time).  Anyway, what you are apparently reading is the what the meter still "thinks" is the RMS (root mean square) voltage of the sine wave.  It probably is reducing the meter reading somewhat, but not nearly as much as you might expect.

The reason this works for heating the nichrome wire at the right temperature is for the same reason the light bulb would get dimmer.  You are changing the average power delivered to the resistive load (the nichrome wire), so even though there are still some high voltage peaks, the average power is managed effectively.  I hope this helps.

Ed

----- Original Message ----- 
From: Paul LaChance 
To: NSRCA Mailing List 
Sent: Thursday, May 21, 2009 4:25 AM
Subject: [NSRCA-discussion] Foam cutter power supply

Hi all,

I was told about a way to make a power supply for a foam cutter using 2 dimmer switches.  I was also told to measure the final voltage to get an approximate starting point of 15 volts.  I am not getting a voltage change with the dimmers.  I have tested to see that there is a difference by using a drill to see that it is reducing the speed.  Does anyone know how I can measure to get a starting point or is it going to be trial and error?  

Thanks in advance,

Paul

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