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Post by sean on May 30, 2008 19:36:57 GMT 10
This is a question for those who know something about AC electricity, unlike myself...
I've bought a 12-30V 100VA 6 Amp Multitap transformer to power a hot-wire setup. Only problem is I don't know how to wire it up. Output is in AC, it has six "secondary" connectors, three on each side, the connectors are marked as follows:
15V 12V 0V 15V 12V 0V
These are the only output connectors. Would I be right in assuming that 0V is the ground? How would I wire this to get say 30V? My best guess would be to connect one end of the hotwire to 0V and the other to both 15V outputs. Does that sound right? I don't want to wire it up wrong and blow it up, cause it wasn't real cheap! This would be much easier if it was DC, I'm not really up to speed on AC electrics. Any help greatly appreciated!
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Post by Pij on May 30, 2008 19:54:17 GMT 10
Sounds confusing. Can you check the outlets with a multimeter?
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Post by sean on May 30, 2008 20:06:46 GMT 10
I could, but I have a fear of blowing something up! Not sure if it's OK to run a transformer like this with no load. Any thoughts?
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Post by Pij on May 30, 2008 20:14:48 GMT 10
There might be more experienced people on the forum, but my thoughts would be, it should be OK to test. Better wear your thick rubber boots just in case. You don't have any metal plates inserted do you?
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Post by ding on May 31, 2008 8:01:31 GMT 10
Hmmm.. I'm not sure. We found when cutting foam that you need to make precise adjustments and sometimes it's nice to be able to make them on the fly (while cutting). We used an electric light dimmer. We found it was a fine line between too hot and too cold. When it's too hot it goes too fast and if you hesitate it eats the foam. When too cold it tends to drag. Fortunately you usually get some time to sort out temps with a practice first.
We found it was a good idea to have a few drinks first too... as my best man told all at my wedding.. LOL.
I'll send this to a mate for an opinion and see what he says.
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wrx
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Post by wrx on May 31, 2008 14:32:44 GMT 10
We found it was a good idea to have a few drinks first too... as my best man told all at my wedding.. LOL. I'll send this to a mate for an opinion and see what he says. Yep - a few drinks definitely improved the results Is this just a bare transformer that also needs mains wiring? If your not really sure what your doing then buying an adjustable power supply may be cheap life insurance... Now that that is out of the way it sounds like this transformer has two isolated secondary windings. These can be connected in series for higher voltage or parallel for higher current. If the transformer is as follows: side A: 0V 12V 15V side B: 0V 12V 15V For series connction, if you connect A:15V to B:0V: measuring from A:0V to B:12V will give 15V + 12V = 27V measuring from A:0V to B:15V will give 15V + 15V = 30V Depending on the wire you use this may be way too much voltage unless you are using a very long piece of wire. May be ok with nichrome but not sure about stainless steel trace - haven't done this for quite a while.
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Post by sean on May 31, 2008 19:46:06 GMT 10
Thanks wrx, that is exactly what I was after! You got it right regarding the secondary windings. I wired the new transformer up this arvo and it works perfectly. I'm not completely new to this - I played around with hot wire cutting a couple of years ago using a 20V 1A DC supply hooked up to a dimmer switch. It all worked perfectly but not enough power to heat up the wire to an acceptable temp (the dimmer switch wasn't needed ) - under load it was only giving 12V. I even made a gravity powered cutting table to try to get a smooth cut but I never got it working well so put it aside. Thought I'd have another crack at it - I'm pretty sure the problems I was having were down to insufficient power - thus the more powerful supply. My bow is maybe 800mm - I'm not planning to use the full 30V unless it proves necessary - I've hooked this new transformer up to the dimmer switch to fine-tune the heat. I'll be using stainless steel fishing line wire (I think it's called lead wire, can't remember the correct name ). Also have some formica for making the templates. It certainly is very involved making a hot wire cutter that does a good job, fingers crossed it works OK this time around!
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Post by skyboyken on May 31, 2008 21:52:57 GMT 10
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Post by ding on May 31, 2008 21:54:31 GMT 10
You could also try a thinner wire.
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Post by thevon on May 31, 2008 22:21:44 GMT 10
Sean, we'll all be putting in orders soon!
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Post by sean on Jun 1, 2008 18:23:27 GMT 10
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Post by jirvin4505 on Jun 3, 2008 23:44:35 GMT 10
Hi Sean,
I've built a few foam cutter power supplies. The rcgroup link is good. My supplies have always been a transformer out of a discarded power amp (100 watts) driven by a light dimmer. Seems like you are already onto the correct track here.
The easiest cutting wire to get is hard stainless fishing trace from tackle shops- The most commonly used in my shed is 16thou. I like the Marlin brand - main thing is to get the hard wire not the soft for making trace wire.
You are welcome to visit my hanger (shed) if I can help in any way.
cheers jeff
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Post by felix on Jun 3, 2008 23:56:50 GMT 10
sean make sure you do a build post with pics! love to know where everything came from,construction and any tips you can pass on.
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Post by sean on Jun 4, 2008 9:39:57 GMT 10
Thanks Jeff! I'll have to take you up on that offer. I bought some 16 thou ss fishing line yesterday - but I think it's the soft kind, I didn't realise there were two kinds. Not to worry. Felix - if I get it working well I'll do a thread on it, but if it's hit and miss I'd rather not lead anyone astray....
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