Thursday, September 4, 2014

Power Supply Convo...

I guess I'm not sure if I should keep posting these emails or not.. The questions seem to be common and I get them regularly. And I suppose not everyone reads the blog or news section, lol... BUT maybe it will help someone searching the web if the happen upon it. SO, here's another PS question.

We need to cut PU Foam having a density of 6 to 7 kg/ by using a straight
hot wire cutter.
As per suggestions, we have worked out to use  a  26 gauge NiCr wire of 2 feet length for a straight wire cutter using a power supply of 12 volt 2 amp.

I think you should anticipate at least 4 amps.. The 2 amp mark is really a minimum when it comes to cutting foam. Also, try to find a power supply that allows you to adjust the voltage.

When you start to cut foam, heat exchanges from the wire to your substrate (PUFoam). As the wire cools, it takes time to heat back up to a cutting temperature. In most cases what happens is your cutting speed slows dramatically, and most often will lead to wire breakage as people push harder to cut faster. 

With 3-4 amps you have a hotter wire, that can replenish heat faster, and cut faster without compromising your wire. Ideally the substrate (PUFoam) never actually touches the wire, it is the heat radiating around the wire (the kerf) that actually cuts the foam. 

Please let us know if we need output voltage as 12v DC or 12v AC.

AC versus DC, doesn’t matter. It is just important that you have enough current. Try to find a 24v4a variable power supply, and you should be all set!

Depending on where you’re at in the world, this power supply should suit all your needs and is rated for international use. 

Thanks for your guidance and are sure that will positively be of immense use to me.

I would like to tell you the exact use of hot wire foam cutter which I want to use for commercial
purposes to cut low density (ranging  from 6 to 7 kg/ PU Foam sheets of thickness varying from 2.5 mm to 6 mm stacked to a height of about 18 inches (i.e. say 100 sheets of 4.50 mm piled over one another) and cutting to smaller size sheets of size 8 X 18 inches from bigger sheets of size 32 x 72 inches.

So please suggest what type of nichrome wire and power supply would be required for a straight hot wire foam cutter so that large volumes of the above sheets can be cut.

It looks like you’re cutting wire will need to be 36” wide to make a comfortable cut. You always want to give a little extra cutting line to make it easier on yourself, but should be able to get everything to line up if you have a standard cutting jig or a stop-board. But I’m sure you can figure that out. 

Polyurethane foam is a little funny when it comes to cutting. Because it is an open cell foam, the little pockets of air between the foam matrix will actually suck up a little heat during your cut. Interestingly enough, the air acts like a little insulator during the cutting process and actually slows things down further.

At cutting lengths over 24” I tell people it is a good idea to go with 24 gauge nichrome wire. It is a little more stiff and is a little stronger than 26 gauge wire. Plus, the voltage/amperage requirements of 24 gauge is a little easier to deal with than 26 gauge nichrome wire. 

One draw back with nichrome wire at longer distances is that it may be hard to control the wire expansion and line “sag.” I’ve had some wavy cuts with larger cutters, but you can help prevent this by making the wire quite tight with a spring and use a higher temperature. A higher temperature helps less PU foam touch the wire during cutting, and the tight spring helps prevent line sag.

One other thought would be for you to use/try Rene Wire (link). Rene is sort of a “top of the line” cutting wire. It is highly resistant to breaking, won’t have as much line sag, and cuts well for both hobby and industrial purposes. For power supply calculations, 27 gauge Rene wire is similar to 28 gauge Nichrome wire.

If you want to make your own power supply, I would recommend the XFR3018E transformer from Jacobs-online. You’ll have to have a bit of electrical ability, and wire in a dimmer switch. I have a walk-through tutorial where I use a different transformer, but the images are essentially the same. 

Saturday, August 30, 2014


Just another question on AC or DC power supplies. Seems to be common.

when we say power supply requirement is 12 volt 2 amp .does this mean that we need a power supply to convert 230 volt ac supply to 12 volt dc or ac.

For Nichrome Wire, it doesn’t matter if it is AC or DC. You just want to make sure your power supply has enough power (wattage) to handle the circuit’s current (amperage). I usually tell people that 2 amp is kind of your minimum. If you can find a 4 amp power supply you’ll be able to have a wider range of wire temperatures. 

Also, remember that the voltage is constant and amperage is a function of your wires resistance. So depending on your circuit, and depending on your voltage setting, you may only require 2.5 amps to heat rather than the full power supply’s 4 amps… Just remember voltage is constant, amperage is variable based on wire/circuit resistance

Monday, August 25, 2014

Kanthal Wire

I am interested to know whether it is possible to use round Kanthal 0.32mm wire as opposed to Nichrome wire in a HWFC?

I don’t see why not? My experience is in Nichrome wire and a little in stainless steel. But when building a simple cutter, you only really need a resistance wire and the alloy shouldn’t really matter. 

I have used and recommend NiChrome because its electrical properties are known and easy to calculate. Most of the other alloys have resistance information but not necessarily amperage-to-heat tables. 

Using Ohms law, with a given wire’s resistance you should be able to calculate an amperage based on applied voltage. So you can see if your power supply has enough juice to handle the circuit. 

Aside from that, I did find a website that has some reference data ( here ).  Whenever people ask about novel wire or applications, I always encourage them to give it a try knowing that you can always fall back on nichrome if you need to!

Thank for the quick reply. I have done a lot of research in constructing a HWFC's, and of all the websites and YT videos no one seems to have tried Kanthal. So being a bit of an experimenter, I have ordered some Kanthal from a supplier on eBay.
 Also I would like to use a 12v 6a supply apapter and regulate the dc output (as opposed to regulating  the ac input) with a high amperage dimmer switch that I also saw on eBay.... similar to eBay item number  191295309081 
Thanks for the the info from your website, it has been most useful.
Perhaps I will make a video of the HWFC I build and post it on YT.
Yes, I will let you know the outcome of using Kanthal when I finish constructing my HWFC.

All that sounds great, I don’t have any additional input just some thoughts.  

In general, you never really want to dim the primary side (AC input) of a transformer. Especially if it is an AC-to-DC power supply. It can have unreliable but also potentially adverse effects on the electrical set up. Even with your AC step down transformers (AC-AC) you want to dim the secondary windings (output side) of the power supply. 

As for that DC dimmer, that is cheap! I’ll have to save that information. I had a user email me some information on a DC dimmer, but they were hard to find. I don’t know why I never thought of a LED strip dimmer…! Thanks for the information. 

I think your set up is going to work well. Having the 6a output on your power supply should be more than enough to amperage to power almost any circuit. You’ll just have to watch out for your circuit’s overall resistance though, as the 12v might not be enough pressure gradient to push current though high resistance circuits. But as always, give it a crack and see if it works!

I read your email with great interest - thanks for sending it.
I received the Kanthal wire yesterday. I got the 0.32mm 28 AWG Kanthal A1 gauge wire.
From this website:
It states that Kanthal A1 for 28 AWG is 0.439 ohms per inch. Now, if I construct a HWFC with about a 24 inch length of wire this should give a resistance of 10.536 ohms (24in x 0.439 ohms). Which if I use a 12v supply the wire should draw (presumably) a maximum of 1.14 Amps (12v ÷ 10.536 ohms) and also presumably the wire should be glowing. Please let me know if my calculations are incorrect or I've overlooked somthing. :)

I am still waiting for the dimmer switch and adaptor, hopefully these should arrive soon then I can start construction.
I'll let you know what happens...... success or failure!! :D

All your calculations look correct to me, I’m just not sure about the amperage-to-heat ratio. In the world of NiChrome 1.14 amps really isn’t that much at all. But, if a low amperage like 1.14 can heat up Kanthal enough to glow… it will be a great low amperage alternative to NiChrome. Now you’ve peaked my interest, lol, let me know how it goes.

Thursday, June 12, 2014

DIY Power Supply

Hey All -

Every few weeks or so, I'll get an email asking about the DIY power supply video and information I provide on my website (here).

When Jacobs-Online originally sold their step down transformers, they only had a single input on the primary windings. A few months back (maybe a year), they changed the primary windings to allow for both 120 and 220v input. Thus making the power supplies rated for international use.

My video only has a walk through for the old style transformer, but the website has all the diagrams necessary to wire the transformer into either 120v input or 220v input.

I am currently in the process of updating my video to account for this change, which will also include all the new diagrams I have posted on the DIY diagram page.

I hope this clarifies any questions, although I have a feeling I'll still receive emails until I get the video done... :P

Saturday, April 19, 2014

Cold wire...

I recently purchased a Mastech Hy30005D power supply for a Hotwire foam cutter. This unit is working well for lighter 27 gauge wire.  However, I need to use heavier 20 gauge wire for detailed shapes, and this unit seems to be under powered for the task. Could you please guide me in a selection?  Funds are by no means unlimited, but a need a reliable unit that can provide ample heat to cut at a good pace.,

Just for reference, I'm sure this is the unit you purchased? Link

This unit has a max output of 5amps, which is going to be the source of your problems. 

Let's quick reference the nichrome data chart found on my website - Link

As you'll note, for 20 gauge NiChrome wire, 5 amps will generate just shy of 600°F. But for 27 gauge wire, 5 amps will generate just shy of 1800°F!

The thing that I've found is wire temperature and cutting speed are related, but often two different things… 

Most styrofoam products will melt at around 400-600°F, so theoretically a 600°F cutting line should suffice for cutting purposes. But remember, heat has to LEAVE your wire, and enter the sytrofoam to melt and cut the substrate. So your wire has to heat BACK UP in order to cut the next section of foam. Often what people will notice is when the wire FIRST touches the styrofoam it will cut REALLY well, then it will slow down as you get more into the cut.  This is because the heat has left your wire, and the wire is having a hard time heating back up to match your cutting speed. 

The fix is that you need to send more current through your wire. You need to have a hotter over-all wire, to increase your cutting speed. The heating-cooling-heating process will find a happy medium, you just have to find out what that is…

For 20 gauge nichrome, 5 amps will work.. albeit a little slow. For some people, considering the cost, a little slower cut might be acceptable if you have a working product as a trade off.  

From a power supply, I think you would want to have the ability to increase your amperage to 7-8 amps, just so you can play around with your final cutting speed. Here are a few options
30v10a - Link - $94
30v10a - Link - $170
18v10a - Link - $140

Another option would be to select a variac, which is an AC transformer… higher voltage, so be cautious during use
130v20a - Link - $109
130v30a - Link - $134

For the money, I'd select the $94 unit from circuit specialists. It has both a higher voltage (good for small wire) and a higher amperage (good for large wire). 

Friday, April 18, 2014

Tattoo Power Supply Freak Out

I am building a hotwire table. I'm using my tattoo power supply as a source. It's output is fine (3-15-V Dc).Even the clip cord reads the same . When I connect it to the table my voltage goes crazy! So the problem has to be in my table components. Is a "stove" Bolt necessary? Or will any bolt do?

Any bolt will do fine, but I agree the problem is not necessarily with your power supply.

So… let's see if I can keep this simple. 

Any time a power supply is placed under an electrical load (your cutter) you will see a small voltage drop at any attached reader. This is a normal result of electrical resistance, current output, etc. 

But your problem is MOST likely related to the maximum output amperage/wattage of your power supply. If the numbers are going all crazy once you hook up your supply, then I'd wager a guess you're "clipping" out the power supply as an over current protection. Or, if there is no OCP, then it could just be feeding back, overloading your power supply and it's shorting out. 

Here is a document I have on OCP - Link

While you mentioned your power supply is 3-15v DC, that is not the most important part. You need to determine the maximum safe output amperage and/or the max output wattage. THAT is what tells you the capacity of your power supply. In MOST circumstances tattoo power supplies max out around 2.0 - 2.5 amps, but usually 2.0. Some are only 1.5 amps. The issue is that most hot wire foam cutters, depending on what wire gauge you use, require about 2.5-3.5 amps to heat effectively.

Relating all this back to your cutter.

Your cutter has a defined resistance, and when an electrical pressure (voltage) is placed on that circuit (cutter) it will generate a current (amperage). If your resistance is too low, and your voltage is too high, it will allow too much current to flow; and that flowing current may be higher than what your power supply can handle. 

Your solution is to use a smaller gauge nichrome wire (which has a higher resistance) or include a resistor in your circuit. I have a tutorial video on making your own resistor out of aluminum wire. 

Check out my Electrical Calculations Videos ( link ) which should be a really good walk through from beginning to end.

Monday, April 14, 2014

Large length CNC cutter

Another email, a user in Malaysia is trying to build a CNC foam cutter. Needed help on a 10 foot cutter… This message starts out already broken up, and with my replies.

I'm in orange.


I live in Malaysia, and our current here is about 240V, i believe.

Yes, you're right, but not to split hairs :) You're Voltage is ~220-240v, the Current will be depend on your circuit. 

I am trying to make a mini hot wire cnc cutter for my small production area, to cut our 8ft x 4ft x 2ft block of 16kg per piece foam. The machine I intend to build is about 10 ft x 5 ft x 4 ft, actual cutting is about the block size. One block at a time, I will need to cut them. I went to your site and saw this, you recommend a gauge 26 straight wire from Jacobs.

Yes, in general I recommend 26 gauge for straight wire cutting. But 26 gauge isn't necessarily the best choice at lengths greater than 2-3 feet. It is a higher resistance wire, and a lot of the times you then need a higher voltage in order to power it. 

A lot of CNC and Wing cutters have recommended going with a stainless steel wire OR using 27 gauge Rene wire. Jacobs just started carrying 27 gauge Rene wire and Terminal Tackle has stainless steel leader wire. 

You may find that Rene wire or stainless steel wire allows for a higher tensile strength and allows you to keep your wire tight while cutting. The 26 gauge wire may bow during cutting and/or may snap if you place too high of a pressure while cutting at those lengths. 

, and with the calculator, I used, it seems to say, at about 5 ft across, using a gauge 26 hot wire at 600F temp, I will need a 28Volts & 2.1Amps.

However, sometimes, if I change the direction of the plane to 10 ft cuts, it will require 56Volts & 2.1Amps.

I am running two setups on one machine, in that case, do I use 2 different power supplies with variable voltages & variable amps? or do I just go with something that can cope with two of them, since I only use either one setup at any given time.

Definitely go with one power supply that can cope with both circuits. The last thing you want to do is switch between power supplies half way in. 

Your calculations are very accurate, and you did a great job. But the ONE thing that most people don't take into account is cutting speed. And that has just as much to do with wire temperature as anything else. 

Technically 600°F is enough heat to melt and cut foam, but as that heat transfers from the wire to the foam your wire is cooled. Then your wire has to heat back up. This is a continuous and ongoing process as you cut foam, and often you will find a "steady state" where heat is leaving your wire and the wire is heating back up. 

As a rough gauge, I like no less than 4 amps pulling through a LONG wire at any given time. While it is a hotter cutting temperature to start out, the total wire temperature will actually decrease once you start cutting. So if you start out calculated and start cutting at 600°F and it cools to 400°F, that is a lot slower cutting than if you start out at 1000°F and it cools to 800°F. Also, at a higher current (4-5 amps) the wire will replenish heat quicker, which means there will be less of a temperature drop than at lower currents. Of course, all theoretical temperature drops, but it illustrates the point. 

also, you said something about adding a 20% on top of this numbers, so I should getting something like 33.6Volts & 2.52Amps for the 1st setup (5ft)? and 67.2Volts & 2.52Amps for the 2nd setup (10ft)?

Yea, you never want to run a power supply at 100% capacity. You should aim for 80%. You CAN run it at 100%, but that may decrease the life span of your power supply. At 80%, it doesn't have to work as hard. 

If you're interested in building your own variable voltage power supply, Jacobs does have some transformers that would work really well. Here is the link. Scroll to the bottom, I'd recommend the XFR-3018e. It would have a wide range of voltages and currents for you to work with. 

Otherwise you  might want to consider finding an "AC Step Down Transformer" also known as a "Variac". Those are usually nice units, and good for the price. But not too many are rated for 220V input. They're out there, just have to find them. THis is one unit from Mastech (link)

I hope that answers your questions, and feel free to write back. I'd be happy to help. Also, I just put up a new link from They are from Canada and specialize in large scale CNC cutters. You can try to get a hold of them and see what help they can provide too. 


You wrote "As a rough gauge, I like no less than 4 amps pulling through a LONG wire at any given time. While it is a hotter cutting temperature to start out, the total wire temperature will actually decrease once you start cutting. So if you start out calculated and start cutting at 600°F and it cools to 400°F, that is a lot slower cutting than if you start out at 1000°F and it cools to 800°F. Also, at a higher current (4-5 amps) the wire will replenish heat quicker, which means there will be less of a temperature drop than at lower currents. Of course, all theoretical temperature drops, but it illustrates the point."

so, at 56V, 2.1A on a 10ft gauge 26 Nichrome wire. you said that it would be better to start out cutting around 1000F, which means both the V and A are now increased to 86V & 3.2A.
what I am confused is, do I just UP the Amps, or i still use the calculator for both Volts and Amps INCREASE, as you said maintained no less than 4Amps?

This is a tricky one to explain, but once you understand it, it will make sense. 

When you are controlling a power supply, typically you can only ever control "voltage" you can not directly control amperage. Your amperage is a function of the applied voltage and circuit resistance…

However, when you're heating a wire, Amperage (and/or wattage) is what correlates to heat and temperature. 

So when I say I like about 4 amps, thats just a rough gauge based on a desired temperature and cutting speed; I was also only using 1000°F as a generalization as well. In order to obtain 4 amps, the voltage will vary depending on if you're using 26 gauge or if its 16 gauge. 

You calculated correctly, to hit ~1000°F with 10 feet of NiCr 26 gauge, you'll need around 85v and 3.2 amps. 

But again, at such long lengths, you might want to consider stainless steel wire or rene wire. 

when using bent shapes, i need to go for around gauge 16 ya?

Yea, that would be about right. Shouldn't need anything thicker. 14 gauge at most.

In that case, is there any place, you recommend to get 0~20Amps, 0~100Volts variable power supply? @ 220~240V input?

MastechPowerSupply has this one - link

It is called a "variac" or step down AC transformer. Much like what is available on jacobs online, but this one is an all-in-one model. You just have to attach your supply lines to the front and then over to your cutting equipment.

The one tricky thing is that this power supply has a built in voltmeter, not an ammeter. Which.. you're going to care about amperage, not voltage… but functionally won't matter.

Regarding the cutting speed, i saw many online uses 22inches/sec cutting speed?

not sure if this is too fast, this is the first time, I'm on this subject, so it will depends if I can figure out everything and do something that speed.
but just for information, do you think 22"/sec is ok cutting speed, given that I heat it up to 1000F to begin with.

Honestly I've never heard of 22"/s cutting speed. That is damn fast… are you sure that is the speed?

the power supply you said, is XFR3018E.
and the one I saw is XFR3024E.

I am a little confused because, it said:
is for  very large wire gauges of moderate length or very long lengths of medium gauges -- up to 87 inches of 14 gauge or 125 inches of 18 gauge."


"XFR3024E is for very long medium gauge wire -- up to 102 inches of 16 gauge or 139 inches of 20 gauge."

shouldn't XFR3024E be more suitable for my applications since, we also need to bend wires of gauge 16 sometimes to make bowls or domes?

just need some explanation of what's the differences and how I should be picking my Power Supply.

Now that I take a second look, I'm not sure either will work. If you go 10 feet with your 26 gauge, you're going to need 86v which neither supply can provide. So…. I think going with the variac from mastech would be best. 

Also, only occasionally that we will use more than 1 hot wire for cutting, so, normally its fine, on a 1-to-1 circuit.
on that special occasion when we do use 1-to-2 or more, would you recommend parallel or serial circuit to use?

Well… the easiest thing you can do is run them in series. That would only then change the voltage requirement of your circuit. 

If you place them in parallel, you will change both amperage and voltage. Which… sometimes can be used to your benefit if you want to play around with different types of wire… But parallel circuits just take a bit more calculations. 

If you check out my Circuit Theory page, I go in depth with series and parallel circuits, and what properties change. 

But again… series is just easier as long as your power supply has enough voltage (which that mastech will).


Nothing to be sorry about. It's all good. I learnt a lot from you and I deeply appreciate your help.
My pleasure, always glad to help!

I am considering a dual transformer to perform the required output, but it would seem too wasteful of resources, which I should instead go for the Mastech you talked about.
Yea, your goal should always be one power supply to handle all circuits. It's not ALWAYS possible, but usually is. It cuts down on supplies, and upstart cost. 

14ga. Wires might be too much for me, so I go ahead with the 16ga. Wires and that should help me with keeping voltage down a little while still keeping the contours of what I need. Normal for dome or bowl shape items only.
Other long shapes will use the Rene 27ga. Wires to run CNC with.
Remember that your electrical requirements are opposite for small and large wires. 

Large gauge (16ga) requires less voltage and more amperage.
Small gauge (26ga) requires more voltage and less amperage. 

So when you're setting your dial on your power supply, always start out at zero and then turn it up until your wire has reached a desirable temperature and cutting speed. 

Speed wise, let me check, might be wrong with 22"/sec. Yes, i am wrong indeed, it should be max 55"/min. NOT per sec. Sorry about the confusion and thanks for the reminder.
Okay that sounds better…!  22"/second is DAMN FAST, but a 55"/min max is a bit better. That is about 1" per second which is a desirable cutting speed and temperature.

So confirming the wires, I will need output of max voltage about 100V & max amp about 13A for use with 16ga. (These are with 20% safety buffer)
Um… sorry, what length of 16 gauge are you using? I lost that in the emails somewhere…

But if you're applying 100v to 16 gauge and want 13a max, then you're wire has to be 30 feet long… I doubt you'd be using a wire that long?

So with the Mastech, I no longer need to buy the dimmer, fuse holder, slow blow fuse, and on/off toggle switch?
Or I still need them, slightly confused, because this is still just a variac transformer?  What's else am I missing?
No, you won't need any of that. It is a completely contained unit. All in one. I'm not 100% sure if it has a fuse or not.. probably does… but either way you probably won't need it. 

I decided to go with the new MasTECH for this one:

input 220V
output 0~250V , 0~20Amps
USD $168

I think will be best for all my applications, if one day, I decided to do something larger, I can still work on them without over killing my power unit.

Yea that is a really nice variac. It has a high amperage, and is nice for you that it has a 220v input. 

Most variacs are strong and withstand a lot of work. I think you'll be happy with that unit for quite some time.

there's only red and black at the front of the unit, it says IN/OUT, so where do the 3rd ground wire connects to from my outlet?
still looking at your serial connections.

These units only have an in and out, they're wired differently than the jacobs-online transformers. These units are essentially fool proof. 

The IN is what comes from your wall, and the OUT is what goes to your cutter. 

On the front of the unit, there is a little brass tab with the universal symbol for "ground".

This is where you'll want to attach the ground from your wall AND the ground from your cutter. BOth can touch there. If it doesn't fit, there is a screw on the other side that you can attach a wire too as well.. Or just make a jumper with a wire nut. 

still very grateful for all the help I am receiving.

I made a little mistake about the 16ga. wires.
only need about 30V & 11.2A to make it happen, even for the 10ft contours @ 800F.

That makes more sense :)  And yea, you wouldn't need much voltage at all to achieve that amperage and temperature. I bet you'll be happy with the dial set around 30-45 volts.

for the 27ga. rene wires, it takes about 70V & 2.6A to make it work, and yes its the max 10ft straight line @ 800F.

Yup, that too looks like a good estimate :)

the MASTECH 5K will do more than enough for all my applications and at a very reasonable price.
thanks for recommending MASTECH to me, it solved all my doubts and problems.

Your welcome. I have really taken a liking to the step down transformers and variacs. They're great for MANY applications and very reasonably priced. When you switch over to the DC world, there is more expense in all the internal components. Functionally, there is no difference between AC and DC circuits when cutting foam.. so go cheap and strong. 

as for you saying measuring the temperature, I saw that you use a Volt and Ampere meter to measure the desired output from the transformer.
But how do you actually measure the temperature?

WELLLL often you can't measure temperature. 

I usually only ever measure output amperage, and then reference the nichrome data chart (link) to see where my wire is. It's not the most effective means.. but it is one solution. I've tried an infrared gun before, but I'm not sure it's entirely accurate with such a fine wire. 

As far as I understand that these transformers are we can only adjust the VOLTage on it?
so if voltage increases what happens to the amperage?

Voltage directly correlates to amperage, as a function of your circuit's resistance. (Larger gauge, less resistance; smaller gauge, more resistance.)

Think of the voltage dial as a kitchen sink faucet handle. If you open the water faucet, it lets out more water because it is allowing more water pressure to escape your pipes.  If you turn up the voltage, it lets out more current flow because more electrical pressure is escaping the power supply. Voltage is your pressure, amperage is your flow.  Does that make sense?

So, in a sense, when you turn up the voltage it too will turn up the amperage. It's just that different amounts of amperage/current will flow depending on your circuits resistance. 

That's why with large gauge wire, there is less resistance, so it is easier for current to flow. Meaning, it requires less electrical pressure (less voltage) to allow the current to flow.

Where as with a small gauge wire, there is more resistance, so it is harder for current to flow. Meaning, it requires more electrical pressure (more voltage) to allow the current to flow. 

It IS the flowing of electricity that generates your wire heat. And that generation of heat is also in part related to wire resistance. If a wire has more resistance, it is easier to generate heat. Meaning it requires less current flow. If there is less wire resistance, it is harder to generate heat. Meaning it requires more current to flow. 

So they're all related….!

what i am saying is, for the 16ga. wires, we need higher AMP and lower VOLT, so, obviously I can't just go with the lower VOLT on the MASTECH as this will also correspond to the lower AMP?

I believe I answered this above… but here's my personal theory…

When you are doing calculations manually, it is only to ever help estimate your electrical requirements. Your calculations are supposed to show you which is the BEST power supply to purchase for your application. 

BUT… When you get the cutters assembled, and the power supply hooked up. There is always a difference in circuit resistance than what you calculated… THe connectors, the additional wires, the other metal, everything adds to the resistance of your circuit.. even if it's just a little bit. 

So, now that you've selected a very good power supply, my recommendation is this.

Hook everything up, with your power supply turned off and starting at "zero". Your calculations will get you to the ballpark of where you need your voltage setting. But essentially you're starting off at zero, and slowly turning up the dial until your wire is cutting at the speed you desire….

When you are actually cutting in real life, just start at zero… turn up till its cutting.. and away you go. The theoretical calculations become much less important when it comes time to test the whole thing out.. :)

there's another question I kept forgetting, but I don't see any serial or parallel wiring that you have in your transformer page?

Yea, with the mastech there aren't going to be any serial or parallel wirings. There is an input (from the wall) and an output (to your cutter). Basically, the input is your primary windings, and the output is your secondary windings.

The difference is, you're buying a complete package with the Mastech. Everything is all in one, and it's all wired appropriately.

When you buy a naked transformer (like on jacobs online), you have to be accountable for wiring in series or parallel, and adding dimmer switches, and mounting brackets… etc etc…

So with that Mastech, it is a complete solution. All you'll need for quite some time… 

I am buying that MASTECH 5K as we speak, will hope to see a good manual on how I can properly use it.
There should be a manual, lol… I can't imagine there won't be. But again, input(wall) and output(cutter). You will need to make sure you wire the input appropriately (positive and negative terminals), but the output doesn't matter. 

I hope that all makes sense!!

Tuesday, March 4, 2014

Meters, Power Supply and Wire

Just a back'n'forth with a user via email. I'm in orange. This is a really common series of questions I get from people making their own cutters and power supplies. Hope it helps someone out there.

Could I wire in a digital AC voltmeter to output connectors, where cutter plugs into, to see what voltage I'm adjusted to with dimmer?

Yea, you can do that.

If memory serves me correctly… A voltmeter assesses the voltage differential across two points (positive & negative terminals). Therefore essentially being placed in parallel with your circuit. Where as an ammeter assess the flow of electricity through the circuit, needing to be placed in series with your circuit. 

The voltmeter should come with instructions for installation, as it might not work if you switch the leads (negative to positive, instead of positive to negative). 

I made the same power supply as you with the XFR-1006E.

Okay, I think you mentioned that previously and I forgot :) 

I purchased the 16 gage wire from Jacobs. Didn't see then u recommended the 20 for rigid cutter like I made. I created one with an adjustable are to use as a straight cutter or rigid, depending on wire. It can adjust from 2 inches up to like 20 inches. Have u used the 16 gage wire with ur same custom power supply? I don't wanna hurt my supply if I don't use right wire to voltage ratio.

Remind me, did you set up your power supply so that you can interchange between 12v/8.3a and 6v/16.7a? If so, then you shouldn't have a problem using the XFR1006e with 16ga.

This diagram shows the acceptable wire gauges and length with the XFR1006e. Just a REALLY rough gauge.. Using the 6 volt setting, and 16 gauge wire, you need to range between about 5" - 25" of workable wire. 

I looked at Jacobs calculator and it's confusing. Depending what I solve for, it's different I seems. I set temp to 600, gage to 16, choose button to solve for volts and adjusted length for wire. What do you think the min and max of wire I can safely use without burning up transformer. I'm using the same custom power supply as shown on ur site using the XFR-1006E transformer.

Check out the Electrical Power page. I have a tutorial video on how to use Jacob's calculator. 

Here's what I would do
Set the button to solve for "Temperature"
Move the slide to your wire length, let's say 5"
Set the Gauge to 16

Now here's what you're going to look at.
As you slide the voltage to the right, you should see the temperature, amperage and wattage change. You'll want to pay attention to the amperage and temperature.

You know that your power supply when set to the 6v setting, can max out at 16.7a. Typically I recommend not exceeding 90% of your power supply's total. But let's just say 16amps. 

Moving the voltage slide, you'll see you can not exceed 1.7-1.8 volts before over drawing your power supply. 

Next, move the "length" slide to the right, lets choose 10". Slide the voltage, and now you can increase to about 3.4-3.5v before over powering your power supply (~16 amps)

Since you're using a dimmer switch, 100% on is 6 volts.. so 3 volts is half way on… 

Does all that make sense?  It was a long winded explanation that you can certainly use 16g a with that power supply, it just has to be on the 6v setting. You'll also have to make sure you use AT LEAST 5" of wire, but 10" is probably easier to adjust your power supply with.

I haven't got the resistance reading yet. Been trying to think how to calc it. If I knew ohm of circuit, how would I manually calc for max voltage if I don't know any other variables?

If you attach a multimeter and give me the resistance reading, in addition to what gauge nichrome you used, I'll send you a range of working voltages. 

Ohms Law states
Voltage = Amperage * Resistance

Amperage is essentially an equivalent of Temperature when using NiChrome wire. 

Select a temperature, find it's corresponding amperage, and multiply it times your circuit resistance.

Here is a PDF found on the website with relevant NiChrome Data

Ok, but I still want to learn how to calculate 

Using 16G = 8.7amps @ 600 deg

Do I take my length of cutter and divide it by 12 and then multiply that by my meter reading to get R?

Then multiply that R by 8.7 amps to get max V?

Short answer, yes!

Long answer...

Your meter reading IS the circuit resistance. You don't have to worry about measuring and dividing anything. Any math related to resistance calculation is only ever theoretical resistances. But if you have a multimeter, set to read resistance (ohms) then there you have it. Total circuit resistance.

Take that reading (my guess is it will be less than 1 ohm) and multiply by 8.7 to yield your power supply voltage setting to reach 8.7amps. Using the 6v power supply setting, your MAX output amps using the XFR1006E is ~16a. So if you want to find your MAX volts, just take the resistance reading and multiply by 16. 

In my experience, your calculated voltages/amperages/resistances are always a little different than what is seen in person. So just be prepared for about a 10% difference. Not that it will matter for cutting, but just incase you get really specific and want your readings to match your calculations. 

Used 15 inches of 16Gage and measured 0.50 ohms

Voltage = Amperage * Resistance

V = 8.7amps  * 0.5ohms
V = ~4.4v

V = 12amps * 0.5ohms
V = 6v


If you used the calculator and only ever looked at theoretical values… 15" of 16 gauge nichrome is only 0.32 ohms. But with all the other metal components, you picked up a little resistance and totaled out at 0.5 ohms. At this point, the only thing that matters is the 0.5 ohms, and no longer the theoretical 0.32 ohms of your 15" NiChrome wire. 

From here on out, using that exact set up and knowing that you have 0.5 ohms… whatever amperage you want to achieve, just half the voltage. Want 2 amps? Set 1 volt. Want 8 amps? Set 4 volts. So on and so forth.

It all changes if I use shorter or longer wire though, right?


whatever your measured resistance is (based on length of wire) you can plug it into ohms law.

Volts = Amps * Resistance

Amps = Volts / Resistance

Both equations work for whatever you may be doing

Ok. Think I can do it now. Only other question was I see with the chart is the 600 deg with 26 gage was 8.7amps. The 800 deg shows 10.9 amps. How did u get 12amps for the 800 deg you sent me?

This is that fudge factor I was talking about. You're starting to get too literal between theoretical, calculated and actual temperatures. 

Technically 12 amps, with 16 gauge wire, is theoretically 880°F. That temperature is provided by the jacobs calculator. 

But again, in my experience, that which is calculated is different than what is seen on your bench.  Not to mention, as the foam sucks heat away from your wire, the wire will cool and often slow cutting. So it's a fine balance between wire heat, wire transfer, wire recovery (getting hot) and foam cutting speed. 

The calculations are merely so you select a power supply strong enough to supply your circuit. Then get everything on your bench, and turn up the dial until it cuts foam.

I see. Are ammeters accurate? Could you attatch it over one wire to make sure you never overdraw Amps that could harm transformer? Do you test it before / input or after / output on transformer?

Yea you should be able to add in an Ammeter. I think the AC ammeters are expensive though. 

You would want to attach it to one of your "secondary wires" which are the after/output side of the transformer. You can make it easy though, and simply attach the ammeter to the terminals where your foam cutters plug into the power supply. That way you always get an accurate reading, regardless of which power supply circuit you have activated.

Saturday, March 1, 2014

Large Multicutter Design

Another fairly common question, large multi cutter design

I'm planning to build a prototype for a large foam block multi-wire slicer.
1. I will need 5-8 wires
2. The length of the NiChr are going to be 8-9 feet in length
3. I will be cutting different densities of foam, 1lb to 3lb
4. I will be using 220V power

What do yo recommend in this situation?

With a cutter that large, there are going to be a few difficulties.
1. Power Supply
2. Wire Tension

1. Power Supply

The size and power of your power supply will solely depend upon the wire you choose and the overall resistance of your circuit. Over those lengths, I'm not sure that NiChrome wire is going to be your best option. You may want to consider stainless steel wire.

The biggest factor with resistance and necessary amperage to heat your wire, is how you lay out your design. If you go with stainless steel wire, chances are you're going to want to set up your wires in circuit series, rather than parallel. But if you use NiChrome wire, you'll probably want to use a combination of series and parallel to achieve the best combination of voltage and amperage requirements. 

This is discussed in further detail on the website, and should help explain that recommendation a bit more.

Don't even both trying to find a DC power supply. For something like this an AC Step Down Transformer is going to be your cheapest option for overall output power. If you're using 220v power, I'd assume you're not in the US? If so, I do not have a ton of international options for power supplies. But feel free to scan through my power supply section for some US suppliers that can ship to you.

2. Wire Tension

For lengths over 24" I typically recommend using 24 gauge NiChrome wire. But if you're looking at 8-9 feet, you're going to need something quite strong that will respond to both the pressure of cutting as well as the linear applied wire tension. I still think stainless steel wire is going to be your best option, but I do not have an idea of wire size. Good news is stainless steel wire is cheap, so buy a few rolls and see what gauge wire works best for your design. Keeping in mind that wire gauge and length have a bearing on circuit resistance, and require amperage to heat. You're going to want to find the smallest gauge wire, that can hold up to cutting pressure. Probably 24-18 gauge.

Next, I'd recommend designing your cutter so that at one end you have a rigid extension spring and at the other end some type of winding device. Even if that winding device is just an eye bolt you turn to increase wire tension. Keep in mind that as a wire is heated it will expand, and with expansion comes a saggy wire. If you're cutting a grid out of large foam billets, the last thing you want is wavy lines. I suppose it all depends on your application, but you're going to want wire tension. I have actually seen a design were someone used a FULLY threaded pipe, from end to end. And all they had to do was twist the entire pipe, and it increased resistance on all the wires. It was basically a huge, large diameter machine screw at that point. Simplistic design, just requires you to know someone who can thread pipe. 

I’m thinking of using the Transformer from MastechPowerSupply.

Volteq 5KW Transformer Variac 5000VA 0-250V 220V Input, with maximum current output of 20amps (@250V)
or do think I can get away with….
Volteq 2KW Transformer Variac 2000VA 0-250V 220V Input, with maximum current output of 8amps (@250V)

Not just because I'm American.. but I'd have to say "bigger is better." When it comes to non hobby large scale cutters, especially unique set ups, you do NOT want to be 100% ready to go and have an inadequate power supply.  With the 5kW unit, you have the same voltage regulation on the dial but have 2.5 times the power. Using the 5kW model, you'll have the best power supply, just in case you need to wire in series on the fly...

Just remember… Greater than 45 dry volts will penetrate human skin. If you're moving 5kW across something like that… there is a pretty high risk of shock. Just be incredibly careful. 

I’m also thinking of having them wired is Parallel setup, just so I can hook them up on two shafts, and have adjustability on the thickness of the slices, just by moving the Springs up and down along the shafts.

I love the idea, and would love to see it in action. Send some pictures when you get it set up. 

Just remember your electrical properties when placing a circuit in parallel. An easy way to think of it is like this….

Placing four wire in series, is like making one wire four times as long

Placing four wires in parallel is like making one wire four times as thick

When you have a long wire or wires placed in series, the resistance dramatically increases, the voltage required to heat dramatically increases, but the amperage pretty much stays the same. 

When you have a larger gauge wire or have wires placed in parallel, the resistance dramatically decreases, the required voltage decreases but the necessary amperage to heat the wires dramatically increases. 

I hope that wasn't confusing. 

Long story short… depending on how this pans out, you may end up needing a combination of series and parallel to find the right combination of circuit resistance, voltage and amperage. You may even consider having switches to "activate" a cutting line. You'll want something rated at 20amp max, which is usually a house circuit switch.

The majority of the time, I’ll be using one wire, but I want to make sure that I can do 5-7 wires without any issues.
With the Transformers I have listed above, what do you think there limits are as far as the number of 8-foot wires they can handle?  We’ve been using two sizes of wire, 0.010” and 0.014”, in 8-foot lengths for many of our cuts, usually lettering and shapes, so we need smaller wire gauge.  Do you think that Stainless Steel is better to use that NiChrome?… with the wire gauges we are using, 30 AWG and 27 AWG, which one would be best for heat and length? Right now we have it automated to cut at around 45in/min on 1 lb density foam.

Well… There are a few ways to answer. 

For lengths greater than 2-3' I typically tell people to shy away from NiChrome. Its a good wire, don't get me wrong. But often the resistance is too high at those lengths. Where as, for a small cutter <2' I exclusively recommend NiCHrome wire and NOT stainless steel because NiCr's resistance is higher and makes power supply selection easier. So both are good options, it just depends on your application. 

BUT… JUST started to carry 27 gauge Rene wire…. I think you might like this… Rene wire is considered a super alloy, and virtually indestructible. It is an "up and comer" in the foam cutting world, and a lot of guys use it to cut large (8') foam wings. You might like it a lot, I know Gary Jacobs really likes it. Personally, I am looking into using it for my combination foam cutter as a good straight wire cutter. 

27 gauge Rene wire has similar electrical properties to 28 gauge NiChrome wire, so you can use that reference for calculations. As you would imagine, high wire resistance will be counteracted when placed in parallel. 

Just for kicks, lets see what we can do with a little math. 

A single 8' length of rene (34ohms) would take about 150 volts to heat to 1800° and only draw about 4.5 amps from your power supply.  If you put six 8' lengths of rene wire in parallel (5.667 ohms), my guess would be it's similar to 20 gauge based on length and resistance. Here's the difference… you'd  require about 80 volts to heat to 1800° but drawing close to 15 amps from the power supply.