RC India

hey guys if any one has built a hot wire cutter can you please tell me which transformer or power source they used as i need it urgently going to buy tomorrow i have nichrome wire and everything else other than the power source please suggest

hi

what gauge is the nichrome wire ??? this is my setup,3rd post from last
http://www.rcindia.org/electric-planes/scratch-built-rc-traniner-plane-2-channel-build-log-!/

power supply will generally depend upon wire gauge (current) and length of the wire (voltage)
i think a 16 volt 2 amp transformer with a light dimmer should be more that enough for your work but if you are going to cut small stuff like under 20 inches length then 12 volts should be fine with a current of 1 amp

let me how it turns out and most important of all in a foam cutter is good wire tension n strong bow with these you can do beautiful cuts

best
sahil

Dear Sahil,
In my hot wire foam cutter I used a transformer salvaged from an old 600VA UPS lying  around doing nothing.
It is a 12 - 0 -12 volt Transformer but I used it as a 0 - 24 V transformer using the outer taps. On the transformer's primary  side I connected a 300 Watt Dimmer used as Fan controllers etc  in series in Live wire
of 220VAC supply.
My bow is 40" long and I used the smallest string of the four major strings of VEENA
The Temperature can be varied by the dimmer to suit different temps required for diff kinds of foams and my cutter makes perfect cuts in any kind of foam and any shape.

Rao

thanks to every one will buy a 16v 2amp one today so that i have enough power. also i will use the fan regulator so this will be the order.   plug socket - dimmer - to the transformer - nichrome.

actually i have a 15v 1 amp adapter lying around can i use it

hi pikle6

why don't you first try out the 15v/1amp adapter you have and see if works, if your are going to use lengths of 40 inches then you need more voltage may 30v/3amps transformer will do.

here is the minimum parts you need for the power supply

1. step down transformer rating 30volts@3 amps single tape ( i.e 0-30volts not 30-0-30v this type is called center taped transformer)  cost around 375/-
2. SPST or SPDT or ordinary switch with minimum 5 amp rating 230volts
3. fuse adapter plus one 3 amps fuse to be used at the seconder side of the transformer
4. one dimmer 300watt should be more that sufficient
5. good quality wire 3core type i.e neutral,live,earthing
6. 5 amp/10amp 230v 3 pin plug to long with the wire
7. some sort of wire connector or you can get an additional  2 pin plug and socket to use at the foam cutter side
8. other misc. items

this is all i can remember for now , will post a circuit diagram

sahil

circuit diagram

wow you have a killer set up,you should add a volt meter  :)

sahil

thanks for everything i actually tried the 15 v one with the guitar string what happens is it heats up in 2 secs it stops that the reading at start is 1 A and after 2 secs its 0A i dont know why i will try it with nichrome then buy the parts you suggested

Dear Sahil,
The Dimmer should be connected in the primary i.e, the 230 Volt side of the transformer.Not in the secondary as shown in your diagram
Rao.

http://members.fortunecity.co.uk/slmohr/rcinterest2.htm

here is one more example, similar to the one i have given but like rao says the dimmer in the primary side of the transformer

to rao

what difference does it make ?? as far as i remember all of these use triacs to control power right ??

thanks

sahil

http://members.fortunecity.co.uk/slmohr/rcinterest2A.htm

this is the controller i build for my self

Looks like it doesn't make any difference. Use it where you feel comfortable.

The dimmers usually use a RC with a pot network and a diac to vary the firing time. If you use it in secondary side, first of all the voltage needs to be high enough for the diac to trigger. The firing angle will also change because of the lower voltage. If it works for you, then great, but it won't work properly in most cases.

Also the other ckt you have built looks unnecessarily complicated. I don't see the need for a opto coupler and also so many power transistors. I have built one with a simple 555 PWM with a mosfet for the switching transistor. It is more efficient, I have a small heatsink on the mosfet and that was way more than enough for over 10A.

okay got it,the one build is nearly 7 years old, in my intermediate so......l kinda over built it  ;D

Ya, I totally forgot about the diac. Was thinking only of the zero crossing. It may work though depending on the voltage drop and RC values.

-Ismail

just a minute ago i tried with nichrome and the same 15v 1A adapter and guess what it works but the thing is that it doesnot have that much of heat,think of increasing the amp. actually it did have enough heat for the foam but for a bigger one i need bigger power will post video in 10 mins

hey guys for some reason youtube aint uploading the video will post it tomorrow early morning

I think it does make a difference Sahil. Fan regulators are designed to operate at 220 - 240 AC domestic power supply and it is natural that the components used are designed and rated to operate at that voltage levels.Also I doubt( IMHO) a regulator designed to operate at 230 Volts AC would operate at 12 - 24 Volts. I just don't know with out getting the specification of used components. Also fan regulators are designed for Inductive Load like a fan's windings and my reasoning is that the transformer primary is also inductive it makes sense  to use it on the primary side because if the regulator is used in the secondary side the load is the heating wire which is a resistive load. I may be right or I may be wrong. But when a simple Fan Regulator, Transformer and Music Wire can do the work why go for unnecessary complicated circuits.
Regards
Rao.

i was thinking of a light bulb dimmer not fan regulator and both have been answered, away i was just showing him an example of what i have been using that's it.

thanks
sahil

heres the video guys
wait ten minutes as it is being processed

http://www.youtube.com/watch?v=ZkGex3ocT04

hey guys its done now