Looking For Advice On MIG welder DIY upgrades (capacitor bank, inductor, etc)

[Daedalus]

Hey Guys,

First of all, these forums are amazing, I've learned most of how to do all the stuff I discuss below just from trawling these posts for the last week!

Ok, here goes:

I have two welders at this point:
A Hobart Handler 125 EZ MIG welder and old an old Stinger 3 Airco 230amp stick welder which I just rebuilt (cleaned all the dust and grease out to stop it overheating, put in a superior ventilation system with air-filters, and re-placed the cable contacts).

I have two batches of electrolytic capacitors that I've scavenged and plan to build into large capacitor banks to help stabilize/smooth the arc on my MIG. I have four 6500uf 50VDC computer grade capacitors, and fifteen 7300uf 75VDC computer grade capacitors making a total capacitance of 135,500uf if I built them into a single bank

question 1: is it a bad idea to build a bank for my MIG from dissimilar capacitors? If this is the case, should I just build one that's all fifteen of the 7300uf capacitors = 109500uf total?

question 2: How much overkill is it to have that large a capacitor bank in a MIG welder that only supplies 125 amps? Could this damage the electronic components of the main board? could it fry the diodes (they have small caps to protect them from the normal surges). Or is there no such thing as too large a capacitor bank? Does it matter where I place the bank in the circuit? should I place it before the gun? Should I place it on the ground clamp side?

question 3: should I attempt to convert the CC power source of the stick welder into a CV power source to be used with the wire-feed mechanism in my Handler 125 MIG welder? Would the capacitor bank I have make this possible or is this just a pipe dream? I've built a large 300amp full bridge rectifier out of twelve 100amp/600v diodes (To convert the AC current from my stick welder into DC current). Since the stick welder is already a constant current (CC) power source (as opposed to the constant voltage source (CV) of the MIG welder),with a fair amount of inductance created by the transformer itself, is it unnecessary to install an additional inductor to help smooth the rectified DC output current (which is what most MIG welders have)?

NOTE: the Hobart Handler 125 has its own (standard factory installed) inductor coil to help smooth the rectified DC load, but no capacitor bank.

Finally, how much of a performance increase can I expect to see by adding this capacitor bank to my MIG welder?.

any advice/warnings/encouragement would be greatly appreciated.

[awright]

Yeah. I have some advice. Don't do it. At least not until you study welder electronic design more thoroughly.

I'm an enthusiastic do-it-yourselfer and electronic hobbyist (with no formal training in electronics) and I like the idea of do-it-yourself equipment performance enhancement, but you are messing with a large amount of energy and must know what you are doing to avoid damaging yourself or your equipment. The nature of some of your questions gives me concern that your enthusiasm may exceed your knowledge base at this point. I appreciate that you are asking the questions before proceeding with the mods you have in mind. However, unless you are essentially copying circuitry in existing commercial products or successful projects by other experimenters (not a bad idea at all), I'm not sure the expertise to design your proposed mods is available here. (Is there anybody out there that I haven't insulted yet?)

I realize that I may be misunderstanding your intentions, but here are my observations on what I think you are proposing:

"Does it matter where I place the bank in the circuit?" YES, absolutely! I get the impression that you are considering placing the capacitor bank on the output of your welder and just before your gun. This would bypass the current control elements in your welder, leaving only the resistance and inductance of the welding wire, welding cable, and work to limit the peak current during discharge of the capacitor bank.

Your full capacitor bank can store up to (CV^2)/2, or (0.1355*50*50)/2 = 170 Joules. (You can't exceed the voltage rating of the lowest rated capacitor in your bank.) The bank of 75 volt caps, if charged to 75 volts would hold 307 joules. 307 Joules is not a huge amount of energy, but released in a few microseconds with nothing to limit the current except the stray resistance and inductance of the cable/wire/work loop, it would probably at least cause an embarrassing flash at the instant of contact of the wire with the work and might blast a small crater in the work and vaporize the wire. By vaporize, I do not mean deposit the filler metal in your weld puddle. I mean fill the atmosphere near your work with metal vapor.

Whether your idea of adding a capacitor bank to your welder could be beneficial or not would depend upon the circuitry of the welder. My initial thought is that it would not, but for all I know, it may be a common practice.

One thing to bear in mind is that placing too large a capacitor bank on the output of a rectifier bridge can cause failure of the rectifiers because the charge required to recharge the capacitors can be concentrated into short periods near the peak of the voltage waveform rather than over a longer portion of the charging cycle. This results in shorter, higher current pulses through the rectifiers than the system was designed for. I have no idea how to analyze this without research, and it may not be a problem at all with your proposed setup.

"question 1: is it a bad idea to build a bank for my MIG from dissimilar capacitors?" No, as long as you never exceed the voltage of the lowest rated cap.

How would you place the cap bank on the ground clamp side?

If your stick welder uses loose coupling between the primary and the secondary of the transformer as the current control method, I don't think you can convert it to CV. The transformer is probably designed for much higher output voltage than you want. If it uses active control circuitry, you might be able to make such a conversion but you would have to get into the guts of the controls.

Using multiple diodes in parallel does not necessarily give you the sum of the current ratings of all the diodes. Welder manufacturers do it for economy sometimes but they presumably grade the diode batch into groups with matching forward voltage drop. In the absence of that grading or low value ballast resistors in series with each diode, one diode can hog current from the paralleled ones and fail due to excessive current.

Have fun, but be careful.

awright

[Daedalus]

thanks for the well informed reply, I'm not insulted at all...your concerns are totally valid. I do in fact have little to no idea what I'm doing. You response was exactly the type I was looking for. I'm going to do some more research before I try it and fry all of the internal comments of my welder/body.

edit: Onwards and upwards! I found someone who has the same type of welder that I do and has used a much smaller capacitor bank than I was planning, so I'll start there...

thanks again

[cnywelder]

Yeah. I have some advice. Don't do it. At least not until you study welder electronic design more thoroughly.

I'm an enthusiastic do-it-yourselfer and electronic hobbyist (with no formal training in electronics).....

As someone with formal training in electronics, I just want to jump in and say that your comments are right on the money.

Big capacitor banks can present a number of problems, including but not limited to:
-Charging the bank appropriately
-Discharging the bank appropriately
-Ensuring that you have the right capacitors for the job

If you try this, I urge to to consider safety first at all times. You are working with a lot of stored energy.

If you must, I suggest starting by obtaining a full schematic for the circuit you will be modifying and reverse engineering it to the put that you understand the reasoning for the component values and ratings that are already present in the circuit.

For example, there may be a network inside the welder designed to discharge the cap bank when you turn off the power. (It is a good safety practice when designing equipment to include circuits like this.) When you increase the size of the cap bank, this circuit would need to dissiapate more energy and might very likely fail. A failure of this circuit might very well go undetected until you have an unexpected accidental discharge.

Let us know how it works out.

[yellow]

If you take a look at the Hobart site you can find the schematics of yours and larger Mig welders that do include the cap. Its a fairly common practice for people to add a cap to the HF Mig 151 (and other models) with no adverse affects. Several members on here have added their own cap banks. I just completed this on my own. I took a few pictures that are posted in the HF forum when I did this. I do not see why the HH125 would not benefit the same way.

Please take my advice with a grain of salt. Without some sort of discharge circuit for the cap I do not know how things will react but several people have done this successfully with no problems at all. It is one my my concerns as well.

[awright]

Yellow, did you place your cap directlyacross the welding leads at the machine output? How much capacitance? What voltage rating? Was there a noticeable improvement in performance?

awright

[Daedalus]

Hey guys, so after looking at some of the other Hobart models that include capacitors, I've installed a 26000MFD bank, and It works great. The increased penetration of the welds is amazing! and the improvement in general weld quality and appearance is fantastic, it's amazing to me that something as simple as an electrolytic capacitor could make such a difference. I also put an appropriate bleed resistor across the cap bank. I decided that I wanted the whole bank to be drained five seconds after I release the trigger and so purchased a high wattage 35ohm resistor which works great. the Miller capacitors use a 50 ohm 20 watt I think. I need to add a relay though to flip it on when I release the trigger...

The OCV jumped over 10v on every setting. the lowest was originally 19v now its 30, the highest was originally about 29v and now its around 43v. the machine seems to be able to handle it all fairly well, except that the now the wire feed motor is very loud, and feeding wire very quickly. It's great for laying a thick bead down, but I'm concerned that the added strain may burn it out fairly soon.

I may try to regulate the voltage across the motor.

I put the capacitor bank into the circuit the same way it's shown in the Hobart models with capacitors factory installed (across the negative side between the transformer and the inductor, and then across positive side after the rectifier assembly.

[awright]

can you post a schematic showing how you placed the capacitors?

awright

[Daedalus]

http://www.hobartwelders.com/om/0900/o925b_hob.pdf

look at pg. 33 you'll see the capacitor "C1" it's across the + and - leads on the negative side, you'll not eit goes between the transformer and the inductor the positive side just needs to be after the rectifier bridge.

[cnywelder]

Just a quick thought...(no warranty for this idea)
Adding the cap has incrased the OCV probably by a factor of 1.414.

You could try adding a second rectifier (with smaller diodes) just for the PC board connection, connected like the existing rectifier.

This would reduce the voltage seen by the control board (since the new rectifier would supply a lower average voltage without the capacitor) and thus may adjust the performance of the wire feed. (I think your wire feed may be voltage sensitive.)

Or maybe it will cause some other problem, like I said, no warranty.

[Czob]

I have a Clarke 130EN, the US (the US version, 110v, WE6523). Would putting in a capacitor on the transformer output help the welder? Or is one already there? And can anyone tell me if my machine has the wire speed auto adjust for the amp. Setting? Was told the ones from Europe do? Thanks for any help.

[Vladymere]

Czob,

I also have a Clarke 130EN. I do not know what you mean by "the wire speed auto adjust for the amp. Setting".

I purchased my Clarke 130EN used and the first time I went to use it I found that my wire feed circuit was bad. Wire speed was at constant maximum output. Unable to find a schematic for the control PCB I ended up tracing out the circuits and identifying the failed components so that I could repair the PCB rather than buy a replacement for $70.

I will attach a scan of the schematic I drew for the control PCB and a scan of the schematic for the welder also.

There is no capacitor in the Clarke 130EN but I think that it would benefit it.

Vlad

[Czob]

Was told, that some Clarke mig welders automatically adjusts the wire speed as you increase or decrease the amps setting??????