Hotwire power supply. Will this be good?

Hi all,

I want to mess with XPS.

this is about the best variable supply for its price around where I live.

anybody see any issues with it for cutting rockers?


CS-It looks like enough watts to do the job, and interesting that it has meters. What gauge nichrome are you going to use?-J

I’m not sure. I know a variac does work. I got mine for a little over a hundred. The model you linked has a protection for short circuits. A hot wire is like a short. Just a thought

It has decent voltage and amperage ranges.  But what concerns me is that the amperage appears to vary directly with voltage.  This could significantly affect wire temperature.

You need to decide what gauge and length of nichrome wire you will use.

I would use the amp voltage curve that is provided at your link.  And see if the voltage and amp combinations would work with the gauge and length of wire you plan to use.

You want a wire temp in the 600 F range plus/minus 100 F.

Play with the calculator at this link to see what voltage, amp and wire gauge/length combinations will be needed to get the correct cutting temperature:

There are a lot of good information links about hotwire cutters found at that website also.

search function on is at the upper right hand side of the page…see that google search thing? Go there.

…funny stuff really…Go with EverySurfer…he builds surfboards…the other guy is good at research…but lacking on building…never posts photos…hates me…Ha,ha ha.

So Stoneburner? You seem to know all things…why only links and not comments about the stuff you are building? Why not photos of surfboard projects. Or skateboard projects?

I would love to see your hot wire set up Mr Stoneburner. Please post photos so the rest of us can learn from you. Thank you

My shadow stalker has returned.

Define and enumerate “all things.”

Words and numbers replaced pictures as effective means of communication centuries ago.

Explain to the OP what is important in a power supply for heating a cutting wire – amperage, volts, resistance.  Explain a short, heat generating resistance and amperage draw.  Is there a difference?

It is unfortunate that you have an aversion to knowledge, education and written technology transfer.

Have you ever met met me?  Do you know who I am?  Document what you say about me DingRay.

Are you capable of staying on topic?

Can you stay on topic

Can you stay on topic and provide actionable information


My first hotwire was rigged with an off-the-shelf battery charger…the nichrome was .9mm (?) from memory…worked extremely well , but a bit slow…suggests higher amperage battery charger or smaller gauge nichrome wire needed , I suppose…but it was very effective ,without investing a bucket of cash…(and you could still use it to charge up your car battery)

For 65 cm lenght 0.5mm diam nickel chrome wire, 100VA (100 Watts DC) is enough. Here you have P=UxI=24x6=144W. Alim is a tensil (U in Volt) generator, intensity (I in Ampere), depend of resistance of electric consumer, if it have near no resistance, intensity is infinit (U=RI²), alim is in shortcut. With a resistive wire no risk of short cut.

Stingray, I have read every thread on Sway’s. I got to them via that Google search thing. Whilst I can grasp the basic principals of volts/amps vs wire length and thickness, I am completely unschooled in electrics.

I am also located in Australia, and a lot of the practical and affordable otr sources are simply un available to me ie variacs. Well, as far as that Google search thing is concerned anyway.

Many of the build diagrams also deal with 110vac and I understand transformers may need to be either wired in serial/parallel depending on the wall voltage. As far as fucking around with mains power goes, i may be dumb, but I’m not fucking stupid!

These are my reasons for asking others to give their opinion on the power supply I’m interested in. Hard as it may be for someone of your genius and hubris to understand, most people come here to learn or ask questions. Some, god bless 'em to share. Not to condescendingly dismiss queries as laziness or stupidity. Certainly not to launch into a troll attack on another poster.

Either play nicely with the other kids or fuck off. Either choice would be a positive one. … To everyone else that has taken the time to post, thank you! I’ve got a bit of 28 gauge (.315) Nichrome to try for starters. I may be able to find different gauges with a bit of scrounging.

I’ll try to get a variac secondhand, but they’re pretty rare here and I may just buy this posted unit instead.

Cheers guys!

Hey Clamsmasher,
I tried to get a variac at first , but I live on a small island, and I had a hard time finding one at a reasonable price. Also alot of the offers on eBay don’t ship to Hawaii.

I ended up using the 12v line from a computer power supply. And basically made something similar to what you are looking at. To answer your question, that power supply should be fine.
When I did the calculations, I didn’t need more than around 2 amps. So you should be fine. The big question is, how much does it cost?

Another option is use a led power supply and dimmer switch rated at a sufficient amperage. What I mean by this is, the led lights normally used in homes use a 12V DC power supply, to dim them they use a special dimmer. If you can find this significantly cheaper than the power supply use that. Also as mentioned by Kayu, if you have a battery charger that is 6/12 volts and rated for a high enough current, you can put a led dimmer switch after the charger to vary the current. If you have a computer power supply, you can use a led dimmer switch after that also.
The nice thing about using the hotwire is that it doesn’t need a fancy power supply.

Whatever you do, go to the Jacobs website and fart around with their calculator. Put in 28 gauge wire. Then vary the wire length. Take note of the voltage and current needed as you vary the wire length. This will give you an idea of the max voltage and current you will need. You mentioned you want to cut out rocker, if that is the case you might need a little more than 12 volts. I used my 12v power supply and was able to heat up a 22inch piece of comparable wire, and cut through three glue lines. But that is pushing it. If you want to heat up a longer piece of wire, the power supply you are looking at would be nice because it has up to 24volts. Also it is nice to be able to vary the voltage/current so you can use different lengths of wire.

The reason they gave the varying voltage current chart just means as you change the voltage the maximum current available changes. The actual current will depend on the voltage setting, and the wire length/type used.
Feel free to pm me any questions.


Just another thought for your choice of power supply. For my 30 inch bow, my voltage setting is around 24 volts a.c. using Inconel wire. That temperature cuts smooth and quick. It looks like that is around your units max output. That’s going to be a problem if you ever want a longer bow. Greg Loehr has a video where his wire is around 8 feet for cutting stringers. And if Stoneburner was right about your units amperage and voltage working inversely, then the wattage (the real measure of power) might remain constant.

For me, I’d mail order a Variac. No matter where you live, if you can mail order a bride from the Phillipines, you can mail order a Variac. Otherwise get yourself a wire saw and manually cut it. Cheap, and it just takes longer.

Google wire saw to see what I mean.

Aircraft Spruce Co. has listed a set up recommended by Rutan Aircraft Factory. Cheap and simple. A houshold doorbell transformer about 15$ Home Depot and a household 110V light dimmer switch about 5$ Home Depot. Stainless steel cutting wire is sold by Aircraft Spruce in two sizes. I’ve used both sizes, preferre the smaller. My wire bows are about 30" wide for cutting full size and another about 18" for small cuts. Works perfect. The wiring diagram in Aircraft Spruce is incorrect but easy to figure out. I havn’t been able to find stainless wire at handier local stores.

I tried the light dimmer switch. Maybe with a high quality dimmer. But the ones they sell today is a no-go. They go from 0 to an instant voltage that is too high. 0 to instant flash, melted wire, and my EPS WAS ON FIRE! Could have been tragic.

The voltage and amperage do not vary inversely on the unit CS is considering.  The probem may be that he can not vary voltage while maintaining a constant amperage.  This means each setting will require a different length and/or gauge of wire to achieve the desired temperature (i.e. each setting has a different wattage output – look at the chart he linked to).

The amperage needed to heat the wire to 600 F is specific for each guage of wire and the same regaldless of its length.  As wire length increases, more voltage is required to drive the needed amperage through the wire.  He will need to match wire gauge and length to voltage-amperage output combinations available from that power unit.  His 28 guage wire is a bit thin and could break easily if he tries to cut to quickly or gets the wire too hot.

A light dimmer switch can be used to adjust cutting wire temperature with a transformer as long as the dimmer switch is placed in the input (115 v ac) line before it reaches the transformer.  If I interpret the principles for the following design correctly (links below), this will vary transformer voltage output while maintaining constant amperage output:

It is true that the dimmer switch must be pushed up to at least 50% power first in order to engage the full range of its variable ouput.  After doing that, you can vary from zero to maximum output.

Yo Clam!  For my 28" hotwire I used a IBM laptop charger. 16v and it’ll give 4.5A!!! Works a treat and was free (as work has IBM laptops). 28SWG as calculated off Jacobs. Rigged up a rheostat out off another 22" off 28SWG wire to give a voltage balance for 6" and 12" hotwire too…also works great…all made from scrape.  Used a variable lead acid charger but it didnt have enough beans.

Hey Everysurfer, what type of dimmer switch, and what voltage did you hook it up to?
The regular ones for 120VAC are completely different then an LED dimmer switch. The 120 VAC dimmer varies resistance. The dimmer switch for 12v led lights, switches the power on and off really fast to vary the current. It is the same concept behind a switching power supply. So it should be hooked to 12VDC output. Led lights need constant voltage power, and they are ‘dimmed’ by being turned on and off real quick to give the illusion that they are dimmed.

I was an electrician for a bit, and have seen people get pretty fucked up from messing with electricity. If you don’t know what you are doing please don’t mess around. Here is a link detailing a qualified, experienced electrician that made a simple mistake and paid dearly for it. He lived, many people don’t.
At the output of a 120V variac, you can have up to 120VAC on the wire. That is not good. I am not here to upset the status quo, the variac works for you guys, that’s nice. From a safety perspective it is a horrible idea. Low voltage dc is much safer, especially since you have uninsulated wires exposed. If you live outside the US and have 240VAC that is even worse. That voltage is pretty deadly because it holds you there and you can’t move. I was talking to some of the local electrical contractors at a meeting about the old days of no face protection and working on live circuits, and they mentioned that will get you fired if caught. Point being you guys have made it this far without injury, that doesn’t make it smart.

Not to speak for stoneburner but he was making the helpful comment to look at the voltage current chart. That is different than then a simple power rating as seen on a transformer. In particular at each voltage the available power is different. Look on the chart 24x6=144 which doesn’t equal 12x15=180. Those are both points on the curve. Anyways once again if it is for a good price, and as everysurfer said you are not planning on using a piece of 28 gauge longer then 20-24 inches it should work.

Also as mentioned on the other link and by gtfd, you can use a step down transformer, and regular dimmer switch as another option. I would go with the safest then cheapest option, as heating a wire is not rocker science:).

Just saw your comment stoneburner.
The deal with the dimmer switches is there are two types.
1)resistive based, this is what stoneburner is mentioning

  1. low voltage 12vdc led dimmer

I built a power supply that could handle high current, so I could use a lot of different wire gauges. At the end of the day the wire I bought works perfect and haven’t needed the high current. i.e., martymo’s idea makes a lot of sense also. Cheap and safe is good.

Yes I was referring to a 115-120v ac dimmer switch which is commonly recommended for use with a doorbell transformer.  The dimmer switch is for 115-120v ac power, not low voltage dc power.

This is why I Iike the low voltage, variable output power supply design at Jacobs – link in my last post.  I would love to find a good buy on 10a 30v lab power supply – still watching Craigs list and for auctions.

Amen brother.

This is was what put me on my initial information quest.  I wanted to use the new unused 6/12 v car battery charger I had sitting on a shelf in my closet.  After 2 mos., with little information available at Sways or elsewhere online, I finally compiled the info I found in a blog for use by others on a similar information quest:


The dimmer switch i flamed on was the simple rotary switch me like fish linked to. It acted like it went from zero volts to fifty volts in an instant. From stone cold to flash of molten wire and burning EPS. To me it just isn’t worth the time playing around. Different wire guages and lengths, foam densities, and voltage levels from the Utility company. You can get a small Variac for the price of a long board blank.

Already had a new 6/12v 2/6a battery charger I bought for a motorcycle I sold years ago.

Good enough for now.

Bought a 12v 10a LED transformer for 20 bucks on eBay, might try to use it for the Jacobs design just for fun.

Also have 12v 8a or 10a computer power supply I got for free to play with also.