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Witch Toroidal Transformer (Hotwire Foam Cutter)

PostPosted: Thu Nov 15, 2012 6:43 am
by Artful Owl
Hi all I am in the process of building a hotwire foam cutter. I have two Toroidal transformers and I don't know what one to use. One is 50V 3.0A and the other is
55V 1.45A. Witch one will be powerful enough to power a welding wire at 1800mm long? I'm using a light dimmer switch to control the heat. Not to sure of the resistance of the welding wire. One more thing at what Volts/Amps dose electricity become dangeris or deadly?

Re: Witch Toroidal Transformer (Hotwire Foam Cutter)

PostPosted: Thu Nov 15, 2012 6:44 am
by Artful Owl
Hi all

Another question. Can a Toroidal transformer be wired in parallel? I have 240/120V in and 55V(1.45A) out. There are two of these secondary outputs. How can I wire them to get 55V(2.9A)

Re: Witch Toroidal Transformer (Hotwire Foam Cutter)

PostPosted: Wed Nov 21, 2012 6:04 am
by ergocentric
Artful Owl wrote:Hi all

Another question. Can a Toroidal transformer be wired in parallel? I have 240/120V in and 55V(1.45A) out. There are two of these secondary outputs. How can I wire them to get 55V(2.9A)


Quick answer: yes

Long answer: must be same phase and number of turns and wire gauge, MUST be

seriously, if you don't have a tech to check your work you can kill yourself or someone else, even with 55 Volts

Re: Witch Toroidal Transformer (Hotwire Foam Cutter)

PostPosted: Thu Nov 22, 2012 5:18 pm
by AltechMYOB
Artful Owl wrote:Hi all I am in the process of building a hotwire foam cutter. I have two Toroidal transformers and I don't know what one to use. One is 50V 3.0A and the other is
55V 1.45A. Witch one will be powerful enough to power a welding wire at 1800mm long? I'm using a light dimmer switch to control the heat. Not to sure of the resistance of the welding wire. One more thing at what Volts/Amps dose electricity become dangeris or deadly?


Hi... re if your transformers are powerful enough, sorry I don't know... I've never been into it however it shouldn't be to hard to track down on the net.

re "Volts/Amps dose electricity become dangeris" is a complex question.

A few milliamps thru your heart I've read can kill you. That's (say) 0.002 amps, a very small amount. It's a complex question that requires a lot of definition in order to reply with any meaningful answer. E.G. AC or DC? What is the potential? How are you standing? What are you wearing? What is the humidity? What are all the voltages present and do they have a common point of reference? etc etc. It's a bit like asking 'how long are all the pieces of string in the world'?

For me if there is a lot of current potential ie. say a car/truck battery (100s of amps can flow) I'm 'very awake' at just 12 volts! Just a few amps at 12v I'm more mindful of destroying whatever I'm working on than my own safety. I've endured by accident some very powerful electric shocks... but then I don't have a heart condition and I was young. The next person could have been killed by 1/100th of the power that hit me.

About the only thing that all will agree is be VERY CAREFUL around mains... regardless of where you live. :)

Re: Witch Toroidal Transformer (Hotwire Foam Cutter)

PostPosted: Thu Nov 22, 2012 5:38 pm
by BillGriffiths100

Re: Witch Toroidal Transformer (Hotwire Foam Cutter)

PostPosted: Fri Nov 23, 2012 10:02 am
by stickycheee
ergocentric wrote:
Artful Owl wrote:Hi all

Another question. Can a Toroidal transformer be wired in parallel? I have 240/120V in and 55V(1.45A) out. There are two of these secondary outputs. How can I wire them to get 55V(2.9A)


Quick answer: yes

Long answer: must be same phase and number of turns and wire gauge, MUST be

seriously, if you don't have a tech to check your work you can kill yourself or someone else, even with 55 Volts


Is ergocentric talking about two parallel transformers? From the scant details that sounds like a center-tapped transformer. Wire those together you just short the transformer, it'll just get hot and your wire wont ( I must be a terrible apprentice because I'm not super confident about this).

Is it powerful enough? You really need to get yourself a meter (a cheap one is like $5). When I did some hot-wire work a meter of my nichrome wire was about 3ohms. My transformer had a tap that seemed about 9V. So 9/3= 3A which seemed ok-ish but cut very slowly. 24v was much quicker.
In your case i=v/r=55/3 = about 19amps way too high. So you need to choose a wire that makes sense for you.
If you want to protect your transformer; wire in a slow-blow glass cartridge 1.45A fuse on ELV side.
If you're worried about shocks from the ELV side you an use an isolation transformer, then you an safely touch active parts- just don't touch active and neutral.
An rcd won't protect you.