I have spent two fairly annoying evenings trawling the forums trying not to post another question on hotwiring.
The answer from you guys (and gals?) seems to be “By a bloody variac!”. However I live in UK and they do not exist. We have the much less snappily named “variable power supplies”. What I can not find from all the posts is what voltage AND current I need for my 8 foot long 25 guage Nichrome wire.
I have had no problems with the 100 or so blanks I have made with my 12V - 120amp DC output car charger but I have yet to spit a blank for a stringer using hot wire which i now want to do - the current set up is not hot enough . I have found one used variac on e-bay here which has a voltage range up to 230Volts ac. This will surely kill me if i connect to hot wire and manage to touch it wont it?
Take an ohm meter and determine the resistance per given length.
The variable transformer shown should do the trick.
If the resistance is to high for the length of wire you’re working with 12V will not be enough and higher voltage will be your only answer. You have a 12V charger, how about two batteries in series?
To adjust the temperature change the length of wire the lead is connected to. Shorter = hotter, longer = cooler. Keep your wire as short as possible and you’ll require the least amount of voltage and use the smallest amount of current.
But its a variable voltage transformer. It may go up to 240, but if you look at the pic of the dial, it starts at 0.
You can just dial it in to the voltage necessary to run your long hotwire. It needs to be more than 12, so start there and progress up. Mark it off when you find the right spot. Don’t move it up too fast or you’ll break your wire. I’m betting it won’t be much higher than 20v, if that. But just go up slowly.
Good advice. My last build I tried the trick of using outside surfaces The 8 foot block i cut my blank from must have bowed sides as I simply couldn’t pull the ends together so had to rely on polyurethane glue to expand and fill the gap. Thanks for your help, much appreciated.
I did realise that the Variac I could buy has a dial from zero up, just didn’t like the idea of it being turned up by accident and then frying me. However will probably just buy it and have a go. last night I tried a hobby welder which got the wire hotter but still not enough to cut 8 foot. Many thanks.
MDS' idea is a good one as long as the sides are true and no chunks are knocked out of the block. I use a table saw to split blanks after our long hot wire bow bit the dust. It's a bit of a mess maker, but it does a good, true vertical cut.
Back to your question about how much output to put on your variac, just hook the wires to each end of the nichrome, turn the variac (slowly) until the wire glows red, then back it off just enough so that it doesn't glow anymore.
CHEERS SURF THIS. gOOD ANSWER. iF I AM WORRIED ONE OF MY KIDS COULD WONDER IN AND CRANK IT UP I CAN ALWAYS PUT SOME KIND OF LIMITER ON THE DIAL SO IT CAN’T GO ABOVE THE MAX I NEED. THANKS FOR YOUR ADVICE. JEMSKI
buy a pack of inline fuses that match your typical auto fuse holder and styles and put it inline with your cutter. You can either measure the resistance as stated for you wire based on the strand count and diameter, or watch the fuse pop when you crank it too high for the wire’s resistance. I say you should know and understand the actual voltage and current, but many do not care as long as it cuts foam.
The variac unit has a variable output based on a percentage of total output. Mine is 140 volts so, the dial setting of 50=70 volts. I have a 10’ table set up to split my blanks, makes it easy to do multi stringered lonboard blanks and offsets. I use the same variac unit mounted on my table to also attach to my hotwire bow for cutting out foiled blanks. Settings I use are 25-30% for hotwire bow, 50% for 10’ stringer hotwire. Hope the photos help you get the info you need. The variac is way more versatile than a battery charger which is where I started too. Tom S.
O my god...you're so worried about bascally nothing. Get the variac, plug it in and slice away. You have a slew of problems besides is my house going to burn down, or what if the kids crawl in under the door and touch my knob. 1) keep the kids out. 2) the wire will fry before anything goes bad "kaBoom" wrong.
You problems to watch out for:
1) wire breaks too hot. You don't pull it out fast enough. Wire is now melted EPS mess, and you cant get it out of blank.
2) Wire breaks too cold. Too much pressure. Now you have to start a recut and you blank has wobbles, and hard crusty EPS goop in it.
3) Wire is not tight (like you have seen above) wire bends. You get nice curve in stringer either long ways or short way.
Any variable electricity source will work fine. Some guys use model train transformers. I have even in a pinch just plugged the two wires into the wall socket.....you have about 10 seconds before the wire frys (depending on the wire gauge) or the house wiring frys....Or hopefully you just flip a breaker. You know that's why we have fuses in our homes, to keep idiots like me from burning the place down.
So make sure your on a 15 amp circut and plug that bi-och in. Start cutting. Then post up that board so we can all see it. Maybe you could call it the Phoenix.........you know, from the ashes etc.
Tomas and Resinhead, You Rock. This is the info I needed - cheers guys i am about become the proud owner of a Variac like I knew i’d end up being. Brilliant this swaylocks site - so good all you experts giving me the knowledge you’ve got the hard way.
Ddiolch 'ch verty lawer (welsh for - thanks a bunch)