Toroidal transformer vs induction coil (choke) confusion

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andybb

New Member
Please be gentle. I am a DIY'er who knows a little about a lot of things but I am not an electronics professional. I know diodes, resistors and capacitors and can solder. I am trying to modify an AC welder to a DC welder as per instructions in multiple youtube videos like this one here both done by EE's. One mentions the use of a toroid transformer but I am at a loss to understand how to integrate it into the system. I have one pictured below from an old audio amp. However, I also see that in a few of these vids they just wire a "choke" in line using 8g wire. Should I just strip off all of the wire from the toroid and wrap 8g wire around the bed and splice it in? Still not really sure what it's doing but that is probably a lot easier. I have a 200 amp rectifier and a 100K uf 50V cap. I also know I need to wire in a bleed resistor on the caps for safety even thought he doesn't mention that. The mod also calls for another 24V transformer to power the wire feed motor relay whose output is affected when using power from the main transformer but that I think is an easy mod.

I guess my question is, is the toroid doing the same thing as an induction coil I could make just using the bed inside the toroid and some 8g wire, and what size resistor should I get to bridge and discharge the cap so I don't accidentally stop my heart???

dknguyen

Well-Known Member
The core of a transformers and inductor can come in many different shapes. A toroid is just one of the many shapes, just like a cylinder is, or a square, or an shape that looks like an "El"

If that is a choke, and I'm not saying it is, then it is a differential choke (as opposed to a common-mode choke). A choke is basically an inductor optimized to be lossy at high frequencies (by virtue of selection of the core material) so it bleeds off the high frequency energy. It's an inductor made specifically to be inefficient at high frequencies so they are dissipated as heat.

Just to fill in the gaps, a differential choke is something similar but is a transformer instead and is current of two lines is passed each winding such that the magnetic fields cancel out inside the transformer so high frequencies that are common to both lines are suppressed.

A toroidal transformer (or any transformer really) can be rewound with just a single loop of wire to turn it into an inductor. or you can leave the toroidal transformer wound and connect the primary and secondary windings in series with each other in the appropriate direction so it becomes an inductor. Technically, you could also use a transformer with all but one winding open and then it would become an inductor as well. Of course if you do this it's an efficient use of wire and you have a bunch of open connections which could be at very high voltages. Whether or not it will act as a choke (to bleed off high frequency energy as I described above) is dependent on the core material used.

The sections bolded sections above might directly answer at least some of the question you asked.

Now, I don't know anything about welding, but I think that inductor so that the charge stored in the capacitor does not instantly discharge and short-circuit across the workpiece causing a short but brilliant flash. If I'm right, it's to regulate the current coming out of the capacitors in the crudest way. So in that sense, it's not really a choke in the sense that it's supposed to dissipate high frequency energy.

What size bleed resistor? Normally I would say at at least 1 megaohm. Possibly higher depending on how high a voltage your thing runs at and how low current it runs at. The higher the voltage or the lower the current, the higher the resistor you should use. HOWEVER, these types of values only ensure that the capacitors won't stay charged at lethal levels for a day or more after you've turned the thing off. They don't make the caps rapidly safe as much as they ensure that if someone touches it a day or a week later they get shocked to death. It can take minutes or more for the caps to discharge to safe levels with these values of bleed resistors.

With a welder where the cap terminals are clearly exposed to the outside and can be easily touched, it might be standard to go with much lower value bleed resistors so they discharge very rapidly after the machine is turned off to make it safe.

That resistor is 50ohm and there is discussion about why it is so low and beefy with regards to power handling. 50ohms would indeed discharge the caps extremely quickly so that the welding tips would not be hazardous shortly after the welder was turned off. The thread also has some theorizing that the resistor does double duty in that it allows a "relief" current path to across the capacitors when the current is interuppted since the inductor would cause a very high voltage kick if the current had no where to flow, damaging components.

Inductors store energy in their magnetic field and use it to smooth out changes in current. If you interrupt current flowing through an inductor, it will release that stored energy to try and keep that current going at similar levels (by producing a voltage, sometimes a very high voltage, that will push that current to smash through anything in the way in an effort to maintain it's present level).

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andybb

New Member
A million thanks for the response. I'll try and keep my uninformed questions to a minimum.

My terminology may be incorrect. Lets just call it a low tech inductor. It will go where I think I have it circled in the schematic. Is there any real advantage to figuring out how to wire the toroid windings in series vs just wrapping 8g wire around a core and calling it good? Like I said, I could just strip the windings off of the toroid. The other reason I'm reluctant to use the toroid is because the welder is using 8g wire which is much thicker than the gauge on the toroid. Seems counterintuitive to send 8 gauge into 18 gauge and back to 8 gauge again. Some of these mods don't even use the toroid/inductor so it's just icing on the cake.

Edit - I see you added info after your initial response. Thanks. Re: the resistor...If that's the case I can just as easily remember to ground the tip after I turn it off. Nobody uses it but me.

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dr pepper

Well-Known Member
In a weld set the choke 'smooths' the arc & produces a cleaner weld.
Often in cheap sets its ommitted altogther.
Really you should obtain an inductance value & design the choke to fit, your torroid will not be up to much, how much inductance do you want?
Commercial sets, at least good ones have 3 or 4 outputs from the choke brought out to seperate ground terminals so you can select how much choke you want.

dknguyen

Well-Known Member
The other reason I'm reluctant to use the toroid is because the welder is using 8g wire which is much thicker than the gauge on the toroid. Seems counterintuitive to send 8 gauge into 18 gauge and back to 8 gauge again.
I was describing general methods, not specific to your application. In yours I would definitely not take a low-effort lazy way out. Technically there would be little problem if the 18AWG wire could handle your current, but that would then mean your 8AWG is hugely oversized and a massive waste of space on the core so you're still better off taking it all off and rewining if with 18AWG if that was the case.

andybb

New Member
In a weld set the choke 'smooths' the arc & produces a cleaner weld.
Often in cheap sets its ommitted altogther.
Really you should obtain an inductance value & design the choke to fit, your torroid will not be up to much, how much inductance do you want?
Commercial sets, at least good ones have 3 or 4 outputs from the choke brought out to seperate ground terminals so you can select how much choke you want.
I'm a woodworker so other than a basic multimeter I'm not really set up to obtain an inductance value.

In yours I would definitely not take a low-effort lazy way out.
Not really sure what the low tech lazy way out is.The 18awg is just an estimate but it's just smaller wire as seen in the toroid picture. The current is no greater than 50 volts at the tip but it's 100 amps. As I recall from 100 years ago in college amps are the size of the hose and volts are the flow speed. (I may have that backwards). So wrapping the bare core with 8g as in the video (or smaller gauge to obtain more turns) would do more than nothing to help smooth the performance or should I just skip that step altogether?

MichaelaJoy

Active Member
He has a few mods going on. One is using a transformer to equalize the feed rate. The other is the output choke. (That's what the toroid is.)
The output choke will remove some of the AC "hum" (for lack of a better word) from the DC output.

The capacitors will take care of the rest.

He stacks two cores on top of one another and winds the #8 GA wire through the two cores.
The reason for this is to 'beef up' the inductance to give it better filtering.

At one point in the video, He says that he would have put more turns if he could.
What you can do is to pick a toroid that has a large enough hole in the center so that you can fit more windings.

Remember: There is a -LOT- of current, so heat is a big issue here.
Also, EPDM wire is not cheap, so I think he's using welding cable to wind the coil on the toroid.

Edit: Please be very careful with this. The fact that it's DC makes it very dangerous!

dknguyen: #18 ga might handle the current, but the heat would melt the insulation.
But I completely agree with you. Welders are very dangerous.

andybb: Voltage can be thought of as electrical pressure (Electro-Motive Force)
and current is the flow rate (how many electrons pass a point in a second)

1 Ampere = 6.242 × 10^18 electrons / second

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dr pepper

Well-Known Member
My mrs is a woodturner, I get plenty of sawdust on my projects.
I can help you design a choke if you know the inductance value.

andybb

New Member
You guys are awesome. Responding quicker than I can reply. Thanks.

MichaelaJoy - Yes, I figured out that the two transformers were separate applications and I think I can handle the mod through the relay so it powers the wire feed when the trigger is pulled. He doesn't go that far but someone else did in a different vid. Can I just strip the windings off of the old amp toroid I have and wrap it with copper out of household romex? Do I need to be concerned how many turns I can put on it.

dr pepper - How would I know/find/calculate the inductance factor? I'm doing this so I can shorten the bed of a cast iron wood lathe but I want to make a quality weld as welding cast iron is a skill in an of itself but should be an upgrade to the welder regardless. Plus, its a challenge.

Like I said, most of these youtube mods don't go the extra step of the inductor so anything I do will be better than nothing, or just skip that step.

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MichaelaJoy

Active Member
andybb: Are there any numbers on the toroid that you're planning to use? That might allow one of us to grab a spec sheet
and use the dimensions to figure out the inductance of the toroid. Otherwise, you'd need to take a caliper and measure the dimensions.

If the gauge of the romex is #8, and the insulation is rated for the temperature, then yes.
If you're not sure, then go with the #8 gauge welders' cable that he is using. For one thing, that insulation should be rated for 150C (Well above boiling water)

So, the size of the inner hole will determine how many turns you can get on that.

andybb

New Member
I think household romex is 12-2 to 14-2 AWG? Would I strip it out or just wrap it in the insulation and solder the ends into one and mate it with the 8AWG in the welder? Need to make a phone call re specs. It is out of a Velodyne subwoofer amp and made by a company named Toroid in MD. Was surprised to see they were still around when I Googled them as the amp is from 1989. No specs, just says it was manuf. for Velodyne Acoustics and Transformer #4449-B P/N 51-151. Gonna call them to see if they still have specs. Service manual and schematics attached but I don't see specs on the toroid. I'm on PST but it's after 5 in MD so will call tomorrow.

Now I'm reading up on inductance. Again, thank you all for your help and patience.

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shortbus=

Well-Known Member
If your doing this with the same welder in the Youtube video, I think you will be dissatisfied when your done, just my oppinion as a welder. The reason I say that is even after putting a DC converions on it you still don't have a Mig welder. Those flux core welders are a modified stick welder. They don't have the correct type of transformer design to be a Mig.

A Mig is a generally a CV constant voltage welder, but that flux core welder is a CC constant current machine. That's one thing the guy in the video dosen't address. He is correct that it will cut down the splatter when using the flux core wire, but it won't weld as a Mig any better.

andybb

New Member
If your doing this with the same welder in the Youtube video, I think you will be dissatisfied when your done, just my oppinion as a welder. The reason I say that is even after putting a DC converions on it you still don't have a Mig welder. Those flux core welders are a modified stick welder. They don't have the correct type of transformer design to be a Mig.

A Mig is a generally a CV constant voltage welder, but that flux core welder is a CC constant current machine. That's one thing the guy in the video dosen't address. He is correct that it will cut down the splatter when using the flux core wire, but it won't weld as a Mig any better.
Totally understand. But I only weld a few times a year and they rarely need to be pretty. I know it isn't using gas so it's not a true MIG but everybody who has done the mod says the performance is greatly enhanced with a deeper hotter bead. It's a Harbor Freight welder that was on sale a few years ago for $89 and serves the purposes of a hack welder like me. But it's an AC welder so spending$50 on parts to make it a DC welder is a lot cheaper than buying one. The cap was $30 and the rectifier was$15 plus wires and connectors. Plus, I enjoy the challenge in addition to the challenge of welding cast iron and pre and post heating and packing in sand to cool.

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andybb

New Member
I emailed the manufacturer and hopefully they will respond. Here is what appears to be the transformer section from the service manual. Does this help at all.

dr pepper

Well-Known Member
Go ahead and build a set if you like.
However if your welding cast you'd be better hiring a professional weld set.
In your position I'd probably aquire a big old microwave transformer, gut it and get as much 16mm2 cable on it as I could, you might get 100 microhenries or so.
You can use nickel rods for welding cast, but I've had more success with dissimilar metals rods, I've welded steel to cast with these.
Another issue with cast is cracking, you need to get the parts as hot as you can, weld them, then bury the thing in sand to make it cool as slow as you can. And bolt a splint to the job so it doesnt move.
Further up you mentioned wire feed, are you thinking mig?, unless you have some real fancy mig wire mig isnt the process for you, stick is the process to use for iron.

KeepItSimpleStupid

Well-Known Member
andybb Using the @ symbol in front of a handle "tags" posts. e.g in post #20, instead of MichaelaJoy - Yes, I figured out that... use MichaelaJoy - Yes, I figured out that... Y The name becomes a link and the person gets notified. I did for you in this post.

You will also get "hints" when typing. so, e.g. Type "@MichaelaJoy". I disabled tags to show that,

shortbus=

Like the good DR. said this , even with the conversion, will never get good results on cast iron. If you only need to weld a few times a year that $50 would have been better spent on paying some one to do the job. Some one that will get a good result for you. I've been doing this kind of stuff since my early teens and just turned 71, so have a little bit of experience behind what I'm telling you. andybb New Member KeepItSimpleStupid Thank you. Not sure if I did it correctly but I tried. If you only need to weld a few times a year that$50 would have been better spent on paying some one to do the job. Some one that will get a good result for you.
True, but that takes all of the fun and learning out of it! Inductors and toroids and chokes, oh my! This lathe doesn't have to be welded. A well fitted block under the tailstock will be fine and functional on this old thing. I could easily buy a new lathe and welder but where's the fun and challenge in that?

I really appreciate the help so I don't want to impose on/bore you guys with non-EE stuff but actually, I started this before I decided to weld the cast iron just in an attempt to upgrade my welder and because i like to tinker, so they are really 2 different projects. Like I said, I'm a woodworker who has to weld stuff once in a while so if I can come out of this having gained knowledge about something new, have some fun and gain an upgraded welder, mission accomplished. Once I shorten the bed I can easily and effectively put a block under the tail end to support it and move on if the cast weld screws the pooch. I saw all of the info about trying to weld cast iron and pre/post heating and sand packing to cool and thought, "cool, that'll be fun to try". I'll use the cutoffs to practice the weld. If it sucks I'll just fashion a block to support the cut off end and be happy. As I think I mentioned I paid $25 for the lathe at a salvage yard, refurbished it and added a free treadmill motor and its variable speed control and a digital rpm meter for$12 from ebay.

When I made this steel tool rest the welds were mediocre at best and there was splatter everywhere and this mod is supposed to create better, hotter, deeper welds and significantly cut down on the splatter.

dknguyen, dr pepper , shortbus= , MichaelaJoy ,
Sorry if that was TMI. Anyway, I had an email in my box this morning from the manufacturer with the specs on the toroid. Not sure if this helps. I'm wondering if I should...`
1. Use the toroid? (still worried about connecting 8AWG to the much smaller wires on the toroid)
2. Just wind heavy wire around the stripped down core? How much? Inductance? Neither of those guys seemed to pay particular attention to the size or extent of the windings.
3. Just skip the transformer portion all together?

The welder is supposed to have somewhere around 24 volts at the tip from what I got from the mod videos.

If any of you guys need woodworking advice feel free to head over to our version of your site http://lumberjocks.com/

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shortbus=

Well-Known Member
1. Use the toroid? (still worried about connecting 8AWG to the much smaller wires on the toroid)
2. Just wind heavy wire around the stripped down core? How much? Inductance? Neither of those guys seemed to pay particular attention to the size or extent of the windings.
To my simple mind, I don't think you should hook up to the existing wires of the toroid. The video shows him having 2 bare toroid "forms" and winding a new one over them. I've even seen some chokes wound on a plastic core a so called 'air core'.

andybb

New Member
To my simple mind, I don't think you should hook up to the existing wires of the toroid. The video shows him having 2 bare toroid "forms" and winding a new one over them. I've even seen some chokes wound on a plastic core a so called 'air core'.
I'll try and find it but there was another vid where a guy who is an EE snatched a toroid out of a power amp. That's where that idea came from but again even my rudimentary knowledge tells me running 8AWG into an 18AWG coil is a bad idea and is above my pay grade.

I'm thinking that I'll just strip the toroid down to the core and wrap it with as many turns as I can fit of insulated 8AWG and call it a day. It seems like all the inductor is doing is helping to further smooth the charge. It seems like something is better than nothing and that more wraps is better but that putting as many wraps around a coil of the same gauge wire as the welder is what I need to do. One quote was "From what I can tell, the higher the inductance on the coil the better, but the limiting factor is space. The coil needs to be able to carry the full output current of the welder, which means the cable with which its wound needs to be the same gauge as your leads or thicker. "

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