Oct 30, 2012, 10:26 AM
Registered User
United States, MO, Fenton
Joined Jul 2012
13 Posts
Thanks all for helping me out here!!

Quote:
 Originally Posted by vtdiy Yes, it is an issue. The calculator said 1.9 amps if you used the suggested .011 diameter wire. You chose to ignore that and use much thicker wire (.023").
Unfortunately, I went with what was easy and cheap to find for me- 0.023" carbon steel MIG wire. Also, I was mistaken in thinking that a thinner wire is going to have LOWER resistance. So, with the same amount of voltage, it would draw more current (V=IR). Therefore, I went with a thicker wire with the notion that I will then reduce the current. Obviously, I had that all backwards.

Quote:
 Originally Posted by vtdiy I substituted your .023" mig wire in the calculator and it shows you drawing 6.6 amps, which is close to the LED dimmer's maximum rating of 8 amps Since the actual composition and resistance of the Harbor freight MIG wire you chose is unknown, it could exceed the max for the LED dimmer. Also as Flypaper said they may not work well, especially near their max output rating. I suspect that it would have worked well if you'd got some .011 stainless fishing leader, and your amp draw was around 1.9 amps as suggested in the calculator. Rather than nearly 7amps.
vidiy, is there way for me to do the reverse calculation (either in the Excel sheet you made or with a formula that I could calculate manually) where I could enter the thickness of the wire and calculate the length of wire needed to achieve a desired amperage? I think that with the wire I have, drawing 2-3 amp probably is enough to heat up the wire. If I do that, I could probably not need a dimmer switch, right?

Quote:
 Originally Posted by vtdiy Another problem -- your specs are confusing -- important to keep these straight. In the first part of your post you say .023" dia wire and 36" length. In the above quote from the last part of your post you say .033" wire and 38" length. Which is it?
The wire thickness is 0.023" diameter. The "0.033" was a typo.

The length of wire I used was somewhere in between 36-38". I used 36" in the calculation.

Thanks again for the help!!
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 Oct 30, 2012, 11:58 AM low tech high tech Southern Vermont Joined Feb 2007 3,029 Posts Single strand stainless fishing leader is what I use. It has double the resistance of steel wire, won't corrode or stretch or break as easily, and lasts longer It is just as easily available as Harbor freight mig wire -- here for instance: http://warehouse.haddrellspoint.com/...e-148293-1.htm free shipping there, too. On the other hand, you can use the hot wire calculator to determine bow length for your present wire without a dimmer switch by setting up the spreadsheet with your voltage (12), your available power supply amperage (20), your adjustment (100% for fixed power supply), your desired heat level (try 0.6), your wire resistivity (not sure for your wire --but try the steel value at 325). Then just try different desired cutting lengths in that box until the calculated wire thickness matches what you have on hand. Looks to me like 65 inches or so. Since a five and a half foot cutting bow looks impractically large, you could take say 30 inches of that wire and wind an air coil resistor out of it. To do that I would wind it around a broom stick or something similar, then remove the stick. Put that coil in series with your 36" bow and it should drop the current to somewhere around 3.3 amps, according to the hot wire calculator. In other words, make it act like a 66" long wire. Just divided into two lengths. Remember that the coil will get just as hot as your cutting wire, so mount it someplace (on an insulator of course) so it is sticking up in the air, but where nothing will likely touch it. Remember also however that only the electrically active part will get hot, so most air resistor coils terminate in wire legs attached to an insulator mechanically with electrical connection points above that so the legs don't get hot. If you use at least one alligator clip to connect to it, you can move the clip to different parts of the coil to get more heat. I would start out with the full coil length however -- which is the lowest heat setting. All this is predicated on the resistivity of your wire being 325 or so -- that's just an estimate, since only one person has reported data results for steel wire when I originally asked for them in developing the HW Calculator. Note also that mig wire is often thinly copper coated, which may effect the resistivity Therefore also, if you do decide to do this with your Harbor Freight MIG wire, please report your results here -- that will help in making the calculator more accurate. No guarantees on this working, and safety of your rig and any experiment is your responsibility. But that's how I would do it if that was the problem I wanted to solve that way. Which I don't. A router speed controller and old style automotive battery charger with stainless steel .011 single strand fishing leader is my choice of weaponry when it comes to melting foam. ps. and as always I recommend putting a fuse in line with any experimental hot bow -- automotive style is good, and say 5 amps. That would have protected your LED dimmer as well. Last edited by vtdiy; Oct 30, 2012 at 12:18 PM.
 Oct 30, 2012, 03:12 PM Registered User United States, MO, Fenton Joined Jul 2012 13 Posts Thanks for the info on stainless steel fishing leader. I will look into it. Your suggestion of making an air-coil was what I had in mind of doing in terms of increasing the length of wire without increasing the size of the bow. Although, it seems that steel leader would be the better way to go. I will see if I get back to the welding wire. The welding wire I got was supposed to be carbon steel welding wire. It is, however, copper colored. So, I guess that it is coated with copper. It stretched quite a bit, I have to say, when heated. Adding a fuse inline in between the power supply and the hot wire (now that my LED dimmer is blown) will be a good idea. By the way, I think that the part that blew in the LED dimmer is called the "triac". I guess that there is no way to resurrect my LED dimmer now, right? I do have great respect for electricity and I will be careful with it! Thanks!
Oct 30, 2012, 04:46 PM
low tech high tech
Southern Vermont
Joined Feb 2007
3,029 Posts
Quote:
 Originally Posted by f14tom The welding wire I got was supposed to be carbon steel welding wire. It is, however, copper colored. So, I guess that it is coated with copper. It stretched quite a bit, I have to say, when heated. By the way, I think that the part that blew in the LED dimmer is called the "triac". I guess that there is no way to resurrect my LED dimmer now, right?
The wire probably stretched more than usual because of the high wattage you put through it.

The triac could be replaced, but someone with more component knowledge than I have would have to recommend a part number.
Oct 31, 2012, 02:24 AM
Registered User
New Zealand, Canterbury, Rolleston
Joined Oct 2011
1,432 Posts
Quote:
 Originally Posted by f14tom By the way, I think that the part that blew in the LED dimmer is called the "triac". I guess that there is no way to resurrect my LED dimmer now, right?
A Triac switches ON when told to. It can not be switched OFF.

To switch it off you remove the power supply which is why it is used with an AC supply. The point on the AC curve that it is switched on will be how much power, is transmitted. So, if you switch the triac on halfway through its cycle on the plus and minus parts of the wave form, you will be getting half power.

A triac rather than an SCR is used as it will switch ON on positive and negative cycles. You'd need 2 SCRs to do the same job and a bit more circuitry to do the same job.

When I say AC (alternating current) I'm talking about the voltage level being a sine wave and as it passes through zero that is (or near) the point that a triac or SCR will switch off. There is actually a minimum current that a triac or SCR will stay on at, different for differently rated devices.

The cycle rate is 60 Hz in USA and some other parts of the world, 50 Hz in Britain and the colonies.

If you blew up your LED controller it sounds like you supplied it with DC (direct current).
 Oct 31, 2012, 08:17 AM low tech high tech Southern Vermont Joined Feb 2007 3,029 Posts Not sure what that all has to do with getting him a replacement part number. The LED controller is a DC powered device, btw.
Oct 31, 2012, 06:42 PM
Registered User
New Zealand, Canterbury, Rolleston
Joined Oct 2011
1,432 Posts
Quote:
 Originally Posted by vtdiy Not sure what that all has to do with getting him a replacement part number. The LED controller is a DC powered device, btw.
There should be a number on the triac.

If the triac is in a DC controller there there has to be a chopping circuit to change it to AC or at least chopped DC.

What is the blown device's number?
 Oct 31, 2012, 07:11 PM low tech high tech Southern Vermont Joined Feb 2007 3,029 Posts Here's a pic from post #72 above so you can see what we're taking about. Maybe F14tom will be back shorty and give you a part number.
Oct 31, 2012, 07:25 PM
low tech high tech
Southern Vermont
Joined Feb 2007
3,029 Posts
In case it helps, here's a contrast enhanced enlargement of the chip in question from the photo above.

# Images

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 Nov 01, 2012, 04:13 AM Registered User New Zealand, Canterbury, Rolleston Joined Oct 2011 1,432 Posts I tried MB60 but couldn't come up with anything sensible. I presume that it is an "M"? The second number (E184-2) is usually something like a batch number, usually, but...???
Nov 01, 2012, 08:47 PM
Registered User
United States, MO, Fenton
Joined Jul 2012
13 Posts
Thanks so much for trying!!

Thank you, vidiy and Mac50L, for trying to solve the issue of the "triac". I am sure if the blown component is really a triac. I saw a picture of a triac on some other posts and thought that it looked just like it.

The LED dimmer is not that expensive (~ \$4.97). It would end up much cheaper to get one than trying to repair it myself.

I am going to follow vidiy's advice in getting stainless steel leader wire and put a 5 amp car fuse in between my power supply and the dimmer. Hopefully, I will be able to report some success.

At the meantime, any suggestions are more than welcome!

Thanks, guys!

Quote:
 Originally Posted by Mac50L I tried MB60 but couldn't come up with anything sensible. I presume that it is an "M"? The second number (E184-2) is usually something like a batch number, usually, but...???
Nov 02, 2012, 05:28 AM
Registered User
New Zealand, Canterbury, Rolleston
Joined Oct 2011
1,432 Posts
Quote:
 Originally Posted by f14tom I am sure if the blown component is really a triac. I saw a picture of a triac on some other posts and thought that it looked just like it.
The problem is any power semiconductor looks like that. A pair of diodes, a transistor, MosFet, etc. As the unit is for DC use I'd be most surprised if it is a triac. Far more likely to be a power transistor or MosFet. The centre leg of the device is internally connected to the heatshink metal on the back so if the centre leg has been cut off as it looks, the metal back is soldered to the PC board. The metal often/usually extends out the other side from the legs and has a mounting hole in it. They are often screwed to a larger heatsink with a mica or silicon rubber washer electrically insulating the semiconductor from the heatsink.
Last edited by Mac50L; Nov 02, 2012 at 05:35 AM.
 Nov 02, 2012, 07:04 PM Registered User Houston, Texas Joined May 2007 428 Posts Wanted to include some of my experiences. I have found that K&S 0.015 wire (usually the smallest diameter available) makes a decent cutting wire. Don't know what the resistivity is. I always used it with a Lionell train transformer and it cut well with a 30" bow set on 10 mph. Recently I read where board member chambo88 took a plastic dustpan purchased at a supermarket and cut out most of the flat pan part and strung the wire where the scooping edge used to be then used it for a hand-held bow. Built in handle, neat!
 Nov 19, 2012, 11:59 AM Registered User Imlay City, MI Joined Dec 2006 96 Posts I recently bought one of the PC server power supplies for my chargers and was wondering if I could just get a rheostat (or use one of my chargers) and use this as a PS for a hot wire cutter? Any thoughts or suggestions? Thanks, Steve Last edited by icsteve; Nov 19, 2012 at 01:03 PM. Reason: Added text
 Nov 19, 2012, 12:08 PM Registered User USA, MO, Ozark Joined Nov 2006 1,583 Posts OOPs on the controler :-( However I thought I would toss out there that SS fishing leader and U control wire are the same thing. Some of us still have that stuf around ;-)

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