definitive foam cutter

[Den Moran]

AC,DC,TAKS,BATS,and CRATS - like most people there are two in there I have a vague idea about.

Does anyone have a wiring diagram, and/or a clear suggestion for powering a foam bow cutter please? I'm not an expert on wiring, as the above shows.I have a transformer that takes 240 volts AC down to 12v AC. I also possess a car battery (12volt), and a 'leisure' battery (12volt), plus some nichrome wire.Oh,and a 'dimmer' switch.I saw an interesting article by David Deadman using a battery charger and a dimmer switch,but no go here I'm afraid!

My problem is stringing it all together - my car battery charger( Halfords) doesn't seem to do much, and the dimmer switch I have is a mains one -does that matter.? Any help would be gratefully appreciated, but please mention AC or DC,my first stumbling block in terms of safety alone, probably!

If I succeed in making one, the description will be fulfilled - something simple to cut foam with - ME!

Den Moran,Abertawe

Edited By Den Moran on 06/06/2012 11:34:11

[Chris Bott - Moderator]

Hi Den.

There's two ways I'd approach this and I expect much better ways will be posted soon.

1. My LiPo battery charger, one of the iCharger range has a setting for foam cutting. So I'd try that first with a length of nichrome wire stretched in a bow.

2. Without that I might try a leisure battery through a brushed motor type speed controller, using a servo tester to control it. Again, because I have these things lying around. NOTE: a speed controller for a brushless motor won't do.

Have a google for iCharger, they are not too expensive.

Oh, PS - I haven't tried any of this myself...

Good luck and let us know what works.
Cheers
Chris

[Tim C]

If you have a soldering gun you can try this, I converted an old one and it works a treat

**LINK**

[Martin Harris - Moderator]

I use a selection of old laptop/printer/scanner power supplies - I've got anything from 12 - 30V with decent current ratings...one of the benefits of being a hoarder!

[Cyclicscooby]

Must admit, i've been looking too, and still haven't found anywhere that just says ' 12inches of 1mm wire needs x volts on a x amp psu'

I like the idea of an old ESC.. Got a 12v capable 40A spare for the boat, a 200w psu, and a servo tester.. !!

I've got the heating element from an old fan heater, which I presume is Nichrome..? But all the info i've found relates to SWG, and i'm lost..

 

IF, I find the info i'm after, i'll have a go, but as I got a bench, powered fret-saw for Xmas, i'll stick with that for now..

 

Luv

Chrisie.. xx

Edited By Cyclicscooby on 06/06/2012 14:07:54

[Tom Wright 2]

I have a dozen or so so mains transformers with secondary windings that produce 12V - 48V.The first thing is to ensure all cables, plugs and terminations on the mains supply side are SAFE .

Mains dimmers don't generally work with inductive loads eg transformer primaries,although recently some have become available that do .

A/C is the abbreviation for alternating current DC direct current in simplified terms batteries are DC .A transformer secondary will be a AC .

AC or DC will heat a cutting wire but ensure the voltage level is safe to handle 12V-24V is generally regarded as safe BUT if the source is capable of supplying large currents (AMPS) then severe skin burns and or fire is a risk, a car battery is capable causing both.

Tom.

[Jonnor]

If you don't want to shell out, or if you just want to cut a bit of foam, get a steel ruler, heat it up well and use that as a Flintstone age scalpel You'll need gloves to hold it, but it works!!!

[Chris Bott - Moderator]

Chrisie if you can monitor the current with something, say a wattmeter then you could just apply 12V to the whole length of the heater element, then bit by bit move one connection nearer to the other until you feel some warmth, that way you'll get some idea of the length of wire that 12V will heat. The current reading will save you over powering any of your wiring or indeed the ESC if that is in circuit.

Ohms law suggests that a 1KW mains heating element runs at around 4ish amps, but that would be far too hot. At 12V you'd need 1/20 of the length for the same current / temperature, longer on the same voltage will be less hot..

[Cyclicscooby]

Posted by Chris Bott - Moderator on 06/06/2012 15:10:59:

Chrisie if you can monitor the current with something, say a wattmeter then you could just apply 12V to the whole length of the heater element, then bit by bit move one connection nearer to the other until you feel some warmth, that way you'll get some idea of the length of wire that 12V will heat. The current reading will save you over powering any of your wiring or indeed the ESC if that is in circuit.

Now that's a damn fine idea Chris.. I've got a wattmeter too..

As soon as the bench is clear, i'll give that a go...

Luv

Chrisie.. xx

[Den Moran]

Thanks everyone - I haven't a clue what a brushed thingamebob is, and I still get a reluctance with your answersto mention AC/DC. I do understand that 12volt AC is ok to use,as long as the connections are safe.

Since I posted I have linked an ordinary 12volt DC car battery to a guitar string,and crocodile clipped it - it worked a treat over approx 30" of cutting length. I need to be able to contol the heat,though.I know I can do it by lengthening/shortening the cut, but really want a little easier control than that for various jobs. Once again,thanks a lot,everyone. Den

[Ben B]

I do like the idea of using a brushed ESC. However I've always used homebrewed ones of a dimmer switch stuck on the primary of a transformer (usually from car battery chargers where the regulator has gone south). Always worked for me (although I realise the issue with induction etc etc, just not been a problem so far).

the only issue with using a brushed ESC is that some of them have a max input voltage of 10 NiMH cells (IE 12v) whereas for a long bow you might need more than that (depending on how thick your nichrome is).

[Den Moran]

This what I'm trying to get to. Is the dimmer switch an ordinary mains one -AC? What on earth is a primary,and why cannot I use my halfords charger, stuck it together but nothing happening.does the dimmer go before or after the charger? does a good car batt charger work i.e. one presumably with a regulator? Still looking for that elusive simplicity,thanks again,Den

[Ben B]

If you're not sure about primaries and secondaries it might not be a good idea mucking around with the inards of mains equipment.

Yes, I used an ordinary mains dimmer, I ripped the regulator out of the charger (it had broken), wired the dimmer in series into the primary coils and put the output via a bridge rectifier and then through the dc ameter on the front of the box and out to the charger croc clips.

I was happy doing all this myself but then I'm stupid. I had a broken charger and I wanted a hot wire cutter supply. If I was doing it again I wouldn't do it

[FunnyFlyer]

Link to Nichrome wire site.

Gives some specs on resistivity and temperatures - might be useful.

[Paul C.]

Manny moons ago i was into cutting wing cores and used a cutter sold by Ripmax, have not seen any recent adverts for this type of product. Problems i encountered was that the wire would drag in the middle of the core if the temperature ws too low and would melt the foam if too high, right pain in the neck. My mate came up with a rariiable resistance device, i think it was called a reostat or simmilar (electrics is not my thing) but this was usefull because the foam was not consistant and temperature needed to be set for each session. On a health and saferty point i was told that the fumes from white foam was bad for you but the fumes from blue foam was down right nasty. this was all about 16 years ago so it has all probably been banned by now. Best of luck!

[Shaunie]

It is possible to use a lamp dimmer on the primary (mains side) of a transformer for this application. Because of the way a transformer works when there is a resistive load at its output it behaves as a resistive load at its input but at a different impedance. As a result the dimmer doesn't mind this. Do not switch off the heater at the low voltage side, switch it off at the mains side.

As always take care with mains voltages, if you don't know the proper way you are probably not competent, seek advice from someone who is!

There are many low voltage supplies available at very reasonable prices intended for driving LiPo chargers which would do the job very effectively and avoid working with mains directly.

The foam cutter I built many years ago used 0.8mm stainless steel MIG welding wire very effectively. Pop down to your local welders and ask nicely!

[Andy Green]

This is the spec you are after. This item though is very expensive.

Andy

[SDF]

If your using a 12v battery as a power source a simple temperature control can be made using the spring from an old roller blind. Connect one side of the battery to the salvaged spring and the other side to the cutting bow. Then connect the remaining end of the bow partway along the spring using a crocodile clip. The closer to the battery end of the spring you move the croc clip the hotter the wire in the bow will get.