phuffstatler

My Feedback: (20)

My old cutter supply (an old American Flyer train transformer) was giving up the ghost after many, many years of service, so I figured it was time for a new setup. Looked at the Tekoa, and while very nice (and a bit pricy at $135), I wanted something a bit cheaper, and more flexible than just those three settings, so I went on the search for an old article I had seen long ago. I found it at -

http://www.nsrca.org/technical/tip_t...wer_supply.htm


and Boy!, does it work like a champ! Spent an hour or so at Fry's this morning gathering parts, and put it together this afternoon... The only thing I I changed was the fact that the transformer I got already has a fuse mounted on it. Other than that, it looks pretty much how you see it on the web page.

Believe it or not, it worked right off the board. No fires or anything!

Took it out and promptly had foam dropping all over the floor.

I'm very pleased...... It DID cost me $85 in parts total, plus about 4 hours or so building time, but I'm very pleased!!!!


Did I say I was pleased???



Phil in Austin

BMatthews

Wow, I'm surprised it only needs a 2 amp transformer. I'd have thought 5 amp anyway. Does the transformer get a little warm in use? That may indicate that it's a trifle overstressed which wouldn't surprise me. If not then that's super.

Most transformers can get to where it's noticably quite warm to your skin without harm but if you can't hold your hand on it for a long time or it's quite uncomfortable to do so then I'd say it's TOO hot and you should find a higher rated current model.

phuffstatler

My Feedback: (20)

Nope, not a bit of it. I was a bit surprised at the low rating, too. The only thing that's gets really warm are the 10 watt resistors for the short bow setting, and that's only when it's in use. The triac warms up some, but it's heat-sinked. And that's out in my 105 degree garage... The transformer never really heats up. I'm running a 24VAC transformer with a 3A slo-blo in it, which is a bit different from the original spec. Works fine. I've got a 40" bow on it right now (old Wing Mfg. bow), and I've got the power turned all the way down, and it zips right on through the foam.

I'm cutting a new set of large cores tonight, so will have it on for an extended amount of time. Will be a good stress test. I'm also building up a new 60" bow, to see how that works and to do longer pieces (just cuz) and we'll see how much I have to turn that up....

Be good,
phil in austin

jw_j

show your full setup if you can, im wanting to make a foam cutter but i wouldnt be making the power supply ill leave that to someone who can solder, but the other stuff sounds like i might be able to make

scole

My Feedback: (5)

Cool!

phuffstatler

My Feedback: (20)

This was before I put nice labels on the front, but you can see the simplicity of it....

hayman

Can you use an instructional video on Vacuum Bagging to go along with that nice looking power supply?

Bill
http://www.paonline.com/hayman/video.htm

f4upilot

My Feedback: (1)

Here is the URL with the directions for building a foam cutting power supply that is super simple and works great. All the parts are readily available and it can be build for about $40 -$50 depending on the case that you put it in.

One very important thing is to use the continuously variable ceiling fan speed control as stated in the article. It is available for $9.99 at Lowes and it works like a champ. Don't even bother with the three position fan speed controls....you need to continuously variable one.

Also instead of using nichrome wire, you can use stainless steel fishing leader from Academy or Walmart 25 feet for $1.79..I think the wire diameter was something like 0.072 in.

I built the power supply and then built a band saw like affair to hold the wire with a spring to at one end to take up tension when you turn on the power....hot wire stretches a bit. At any rate, it works great. One note, when you turn the variable speed fan control on and it is connected to the stainless steel wire, turn the speed control completely clockwise for the lowest voltage output or the wire will start glowing red almost immediately because the ceiling fan control is set up so that when you come off the "OFF" position, it goes to the highest voltage setting and that causes a ceiling fan to go at the fastest speed...

By the way the instruction on building the foam cutter power supply are on the AMA web site...

http://www.modelaircraft.org/templates/ama/999_7.asp

phuffstatler

My Feedback: (20)

Yes, that one will work. However, you still have 110 volts out there at the work end! I've been popped more than once in my life, and I don't like it!

The one I built only passes 25 volts out to the wire, and I've grabbed it directly (the 'stupid' test) and it is very safe. The triac in the one I built is carrying the main load, instead of the potentiometer. The pot is being used to gate the triac. It costs a few dollars more in parts, but is still half the price of the Tekoa unit. You can also use a small bow on it, if you like.

As an added tidbit, make sure whomever builds this gets the heatsink on the triac properly!. I forgot to put the conductive plastic on it, and burned out the first triac at about the 2 hour mark. I put a new triac in, and got the heat sink on there better, and it's working fine... A small cooling fan would be nice in there, but have been unable to find a 25 volt one, and have been unwilling to build in a rectifier and other parts for a 12V dc one. I only think I need this because of the Texas heat in my garage(100-110 degrees) makes the unit work much harder. Cuts like a banshee though!!!!


phil in austin

f4upilot

My Feedback: (1)

Just to ensure that there is clarity around the circuit on the AMA site..

There is a step down transformer that reduces 110 VAC to 24 VAC on the secondary terminals on the Foam Cutting Power Supply on the AMA Site. The secondary terminals are where you connect up the cord that goes to your foam cutting bow or tool that holds the resistance wire (nichrome or stainless steel) as mentioned in my note.

When measured at the secondary terminals of the transformer, the voltage is varied by turning the fan speed control between 12VAC and 23 VAC....

So the only place that you have 110 VAC is on the primary side of the transformer...since that is all encased in an enclosure, exposure to 110 VAC outside of the case is non-existent....

When ever working on any thing powered by 110VAC, good practices should be performed...the best on is keeping one hand in your pocket or behind your back, wearing good insulated soles on your shoes. and removing and jewelry on yor wrist or rings on your fingers....

f4upilot

My Feedback: (1)

When you compare the circuit that phuffstatler shares and the AMA circuit you will see they both make use of a step down transformer...110 VAC to 24 or 25 VAC...

So the real comparison is on the availability, expense, special insulators, etc of the parts downstream of the transformer...

phuffstatler you did a nice job of wiring your foam cutter power supply. What kinds of foam cutting tools have you hooked it up to?

phuffstatler

My Feedback: (20)

You're right, F4U, I didn't observe the circuit closely enough.... My fault!!!!

I've only used a couple of bows on it thus far.... a 40" bow and a 60" bow. The first one is an old Wing Mfg. bow, and the second one I made....

I'm in the process of making a short bow to mount on the bench in the form of a "scroll saw"/"band saw" setup, to do some free-form work, and some shorter rounded pieces.... The main problem with all of this is that foam cutting takes lots of shop space! I've run out of room, and would like to double my shop size... That won't be happening anytime soon....


phil in austin

P.S. Thanks again for pointing that out... My boo-boo.

Johng

My Feedback: (4)

Why not just put two small fans or blowers in series?

William Robison

My Feedback: (3)

All:

Here is my foam cutter power supply. It is also my trickle charger for the car, the power supply for home use of my field chargers, and my general bench-top power supply for radio work.

It's an old (VERY old) EICO model 1064 bench supply. It is selectable voltage (up to 12v) and current (up to 20A) that runs a 6" bow just as nicely as it does a 72" bow.

I got it at a Ham Fest, I have no idea how old it truly is. It was free. I did have to replace the fuse holder, so it might have cost me a buck and a quarter. Plus tax, of course.

Bill.

blue62

My Feedback: (3)

you can get a fan that runs on 110 at radio shack they also use them in microwaves i think.....maybe there is a donor around!!!


john

phuffstatler

My Feedback: (20)

Yeah, I had forgotten about potential donors floating around....


I just today picked up a set of cooling fans on clearance at CompUSA, I think I may just put in the gadgetry need to make them work... at $7.50 for two as a push-pull set, I couldn't pass it up.

Is that a Perfection I see there in your avatar, John?


phil in austin

blue62

My Feedback: (3)

nah itsa pt40 i been buildin/flyin c/l planes for yrs, but i am just startin r/c. gettin ready to scratch build a 4*40 but i am gonna kit bash it into an cessna agwagon cropduster! i am tryin to make it complete with a spraybar and everything!



john

Guardian

Hi phill could you draw me up a diagram on how to put this power supply together, and also would be intrested in know how to put a 24", 36",48", and 60" bows together, and what are the best meterials for doing this ?

Thanks,
Mike

phuffstatler

My Feedback: (20)

http://nsrca.org/technical/tip_trick...wer_supply.htm

is the source I used. Just print out all the pages that go with this, and work from that....


There are various sources all over the 'Net for bow design, but here's a couple of ideas that an get you thinking...

phuffstatler

My Feedback: (20)

yet another one

phuffstatler

My Feedback: (20)

If you're not wanting to build a bow setup, and would like to purchase something, www.tekoa.com is probably the best known for hobby setups. It'll set you back a few hundred to get started, but it works, and you can do it alone. Cutting by hand normally take two folks (one each end of the bow) to do it right. One of those neat gravity gadgets like Tekoa uses will let you do it alone. However, that design is not unique or patented, and some searching around again will yield several designs that are public domain, and work. I have my wife on the other end of the bow at my house, and she even takes orders reasonably well... MUCH more expensive, though....

Then, you get into the computerized foam cutters, which designs are public domain again, or can be bought at any level of assembly from a few hundred for the basic parts to over a $1000 for a good assembled cutter, to many tens of thousands for the big professional systems.

http://www.members.cox.net/ap1fuels/
is one...
http://www.members.cox.net/ap1fuels/prod05.htm
the first three links there will get you a ton of info of building your own....


Good luck!!!!!

phil in austin

Guardian

Thanks Phil for all the help and links, Now its time to finally cut those wing cores

Mike