[66strat]

Thanks for catching my error....I better get some better glasses or my welds will never work:jester:

I finally found this Cap on Ebay and was wondering if it looks like a keeper
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=190836507476

Alot of the others were out of stock with long lead times, and Miller4less looked like it wanted $75 for their cap..

 

[Galaxieman]

IMHO the 50V rating on that capacitor is too low. To be safe you need at least 60V.

 

[cell]

I picked up a MIG 170 a few days ago, and my capacitor is on order.

However, browsing further into the "Mod-Your-151" thread (http://weldingweb.com/showthread.php?t=33848), vandal968 took come open circuit voltage measurements to see what sort of voltages the cap would be exposed to:

http://weldingweb.com/showpost.php?p=356348&postcount=126

I'm finishing up this welder mod (thanks Blue!) and I'm taking some measurements so that I've got a true before & after comparison. I also plan on taking some before & after welding pictures.

Voltage measured at the rectifier:

Setting: --No Cap ---Cap --------Open Circuit voltage according to manual
Min 1 -----27.43v -----31.70v -----15.2v
Min 2 -----32.30v -----37.55v -----16.5v
Max 1 -----38.55v -----44.90v -----17.7v
Max 2 -----48.80v -----57.10v -----19.2v

Why does the owner's manual state that the open-circuit voltage is so much lower than it actually is? Is OCV something different than what I'm assuming it is?

Notice that the voltage on the top setting exceeds the capacitor's maximum rated voltage. I ran this by a friend of mine that is a working EE (30yrs working), here is his response.

"If, or should I say, when it fails, it might be very unpleasant. That cap holds 163 Joules which can cause some serious damage, i.e. blow up and cover you in shrapnel and acid ooze. In general you should keep a 10 - 20 % safety margin and therefore not exceed 40 - 45 V for this cap."

I notice that Digikey sells an 80v version of this cap for $30 instead of $20 for the 50v version. If I were doing this again, I would spend the extra 10 bucks for the peace of mind. I also would have worn safety glasses when powering up that big cap and taking my measurements.

My guess is that the cap is surviving because it only sees this over voltage at the highest setting and then, only during the time between when the trigger is pulled and when the arc is struck (since the actual voltage probably drops into the caps rated capacity during the weld).

Thoughts?
v

Having just ordered a 50v capacitor, I was now worried that rating was too low, and I should have ordered at least the 63v capacitor.

So I gave a shot at reproducing his results, but by using a 1uf 100v capacitor until my larger cap arrives (the voltage results should be comparable).

I ran a couple of trials. Procedure: pop loose the wire drive wheels so the wire won't feed, then hold down the trigger for 3 or 4 seconds, and take a voltage reading.

First, with just a 10k resistor connecting the output leads.

10k resistor

setting:  voltage:
MIN 1     22.4v
MIN 2     25.6v
MAX 1     29.6v
MAX 2     35.3v

Then with 1uf capacitor as well:

10k resistor, 1uf capacitor

setting:  voltage:
MIN 1     22.5v
MIN 2     25.7v
MAX 1     29.7v
MAX 2     35.3v

Then I swapped out the 10k resistor for a 100k:

100k resistor, 1uf capacitor

setting:  voltage:
MIN 1     22.6v
MIN 2     25.8v
MAX 1     29.9v
MAX 2     35.6v

I began to think "where are the huge voltages which vandal968 was reporting...?"

Finally, I performed the tests with just a capacitor and no resistor. The voltage table was roughly the same, but something which jumped out at me was that as I let off the trigger of the MIG gun, the voltage would swing way up and drift around for a while (there was no resistor to pull the cap back down to ground, so it was revealing any sort of spikes induced by the transformer as it shuts down?).

At the MIN 1 setting, the cap would float up to about 50v briefly after letting off the trigger, and at the MAX 2 setting it would float up to about 64v.

So perhaps what vandal968 was doing was just bumping the trigger, without a "bleed" resistor, and reported the post-trigger spike as the open circuit voltage?

So then I went back and tried it again with the 100k and 10k bleed resistors, and I noticed that I could also see the high voltage spike after letting off the trigger, but only much more briefly (the bleed resistor is constantly draining it back to ground, so the spike is only briefly visible).

I'm guessing that this post-trigger spike is a relatively small amount of energy, which means we should be able to take care of this by adding a "Transil" (Transient-voltage-suppression diode) (see http://en.wikipedia.org/wiki/Transient-voltage-suppression_diode ) to "clamp" the voltage below 50v.

If we choose a value of, say, 47v (like this one http://www.digikey.com/product-detail/en/1.5KE47A/497-11382-1-ND/2674532?enterprise=44 ) then when we let off the trigger and the welder sends out a high voltage spike, as soon as that spike reaches 47 volts, the transil will open up and short that spike to ground, which will ensure that the capacitor never sees anything over 47 volts.

For $0.94, it's worth investigating.

I've got a transil on order and I'll hook my oscilloscope and try to get some nice data for a follow-up post when my parts arrive.

But I'm guessing that the end result of this is going to be that the spike is small enough that most people with a 50v cap can probably just not worry about it.

 

[Bluewelders]

Do you have the negative of the capacitor hooked to the positive terminal,in the photo ?

 

[cell]

Blue: yes, I did. Boy was that loud . After having experienced a tiny cap letting go, I became interested in the transil idea.

 

[Bluewelders]

Usually the surge rating for a 50v electrolytic will be about 63v.
A larger capacitor wouldn't allow the inductive kick to go as high as your small capacitor allowed.
Also the highest OCV is just when the welder is not arcing.

 

[cell]

So I tried the mod, and got some strange results. I must be doing it wrong.

First, I thought I'd try a little simplification of the wiring: put the cap in the wire-spool section of the welder, and just connect the cap to where the output leads connect.

(that's strange, the IMG tags don't seem to be working, the above just shows up as a link instead of showing the image itself... and I don't see the image button in the reply composer. Am I not allowed to post images to this thread?)

So I thought that would be a neat little variation which would allow someone to perform this hack without actually having to take the welder apart.

Well, my results indicate this version of the hack somehow makes the welder's performance WAY worse, not better.

No matter what settings I tried, I could barely get enough heat out of the welder (even on MAX 2, with wire speed all the way up) (this was with 0.023 wire and CO2 gas), and it created so much spatter that I had to stop and clean out the MIG gun about every two inches of weld. The arc was terrible inconsistent. This was the worst welding I have ever experienced. The picture speaks for itself:

After spending about half an hour in frustration, I decided to disconnect the capacitor, just to see how much worse it could get. I unscrewed the positive lead to the cap.

...and all of a sudden it became a very well behaved welder. I had no problems running a bead, and the arc was very smooth and WAY hotter. In fact, the first thing I noticed was that it was so much brighter that I had to stop and turn my hood darker (I had to turn it down to number 9 shade with the cap in-circuit, because I could barely see what I was doing, and after removing the cap, had to turn it up to a number 11 shade in order to not be blinded).

(this photo is of some scrap steel from TechShop, so not all of the welds are mine)

So... I must be doing something wrong, but I don't understand what. This is a constant voltage power supply, so adding more capacitance anywhere along the output path should help things out... right?

 

[cell]

Oh, it looks like there's an inductor on the ground lead:

It looks like everyone else put their capacitor before the inductor, and I put mine after. That must be the problem.

I had assumed the smaller "transformer" which was stacked on top of the larger transformer was controlled by the MIN/MAX or 1/2 switches. Perhaps it isn't a transformer, and is instead a giant choke (inductor).

 

[Bluewelders]

The small transformer is a choke,it makes the arc easier to maintain and does a few other things besides.
The inductor/choke needs to isolate the arcing voltage from the capacitor.

 

[California]

IMG tags don't seem to be working, the above just shows up as a link instead of showing the image itself... Am I not allowed to post images to this thread?)

Apparently linking to images hosted elsewhere isn't allowed on WW. I've had this experience too.

In fact I've tried to link to a photo I posted here previously - nope. The image contained in a prior WW post can't be displayed in a new WW post by linking to the url of the prior image even when it is your own image. This is different from other VB-based sites that I am familiar with that usually allow displaying a photo from anywhere.

 

[Elmar66]

Finally got mine wired up, just waiting for a tank of mig gas so I can test it out. I didn't like how tight the area you guys were putting yours was so I relocated mine on the wire feed side and used a stock hole in the bottom with a longer screw. I also got allen head bolts for the capacitor so I didn't have to deal with fitting a screw driver there. Check it out.

Being I am pretty new at this and just getting back into welding with the 170. I find some of the pictures confusing and lacking detail. Does anyone have a more precise schematic of where everything goes regarding the capacitor and resistor? I hope to do this soon.

 

[Bluewelders]

http://weldingweb.com/showpost.php?p=989321&postcount=32
I mounted the capacitor in the lower right of the picture.
I put two 10ga wires on the capacitor and marked the positive one with red paint.
The wires hook from the capacitor to the rectifier plates.
The resistor is across the same rectifier plates that the capacitor hooks to.

 

[SimSamurai]

Hi guys, this is my first post in these here parts! I just got one of these CE MIG-170's on sale at HF for $169. I was on the fence about it for awhile but eventually decided I will never use it enough to warrant the cost of a new Millermatic 180. I would definitely like to mod this after a few trial runs (and maybe after the 1 year warranty I got is expired) but I want to ask a few things first. Will this capacitor and toggle mod apply to both flux core and MIG with gas? I would like to make this into a true MIG at some point or do these mods negate that ability?

Secondly, and before I start putting carts before horses, I need to upgrade my service panel for this unit. I know you need 240v power and the actual wall plug on the cord is 3 wire 50 amp. Is that wired as positive-neutral-ground or double hots and single ground? (I assume 2 hots thus 240, correct?) Secondly, I saw that it says 20-amp capacity on the cardboard box but does this mean you can use two standard single pole 20-amp breakers or a single (paired) double pole 20-amp? - Regardless, the manual is absurdly vague and I'm a little confused because the welder's cord itself has the huge 50-amp plug so does this automatically mean I must also pair that up with an equally heavy duty 50-amp service with double pole breaker? I was hoping to just use ~ 25 feet of 10/2 wire to fashion an extension cord and for the receptacle use a smaller 30-amp twist lock 3 wire female plug wired to a 30-amp double pole breaker (both of which I already have on hand). With the 10/2 wire extension cord one end would be a 50-amp female plug (to match the existing welder cord) and the other end would be a 30-amp 3 prong male twist lock plug to mate up to the wall's twist lock 30-amp female receptacle. I specifically want to use the twist lock style because I'm not too hip on ever having to disconnect the other types of flat plugs with nothing to grab onto save for right round where the connection actually is. I've been zapped with both 120v and 240v before and neither are fun. A longer twist lock plug at least gives you much more of a safer body to grab onto, and the twist lock helps from ever being disconnected. To get these in 50-amp style is ridiculously expensive. Anyway, for all of those who own this model please weigh in with what you did. Much thanks guys.

 

[victor_pv]

Hi,

I just got the same model a couple of weeks ago and added the capacitor the other day. Let me answer with what I know.

Hi guys, this is my first post in these here parts! I just got one of these CE MIG-170's on sale at HF for $169. I was on the fence about it for awhile but eventually decided I will never use it enough to warrant the cost of a new Millermatic 180. I would definitely like to mod this after a few trial runs (and maybe after the 1 year warranty I got is expired) but I want to ask a few things first. Will this capacitor and toggle mod apply to both flux core and MIG with gas? I would like to make this into a true MIG at some point or do these mods negate that ability? 

The capacitor mod do not prevent you from using gas, and would benefit both flux and gas welding. It stabilizes the arc, and in fact most welders from known brands like Esab or Lincoln have a capacitor bank except for vary basic models.
Some of the mods for the 151 do not apply to the 170 as the feeder control board is different, so you don't need to change anything related to the feeder after adding the capacitor. Regarding the warranty, you can add the capacitor without making any hole or cutting any of the original cables, so if it fails and you want to return it, you can remove the capacitor.

Secondly, and before I start putting carts before horses, I need to upgrade my service panel for this unit. I know you need 240v power and the actual wall plug on the cord is 3 wire 50 amp. Is that wired as positive-neutral-ground or double hots and single ground? (I assume 2 hots thus 240, correct?) Secondly, I saw that it says 20-amp capacity on the cardboard box but does this mean you can use two standard single pole 20-amp breakers or a single (paired) double pole 20-amp? - Regardless, the manual is absurdly vague and I'm a little confused because the welder's cord itself has the huge 50-amp plug so does this automatically mean I must also pair that up with an equally heavy duty 50-amp service with double pole breaker? I was hoping to just use ~ 25 feet of 10/2 wire to fashion an extension cord and for the receptacle use a smaller 30-amp twist lock 3 wire female plug wired to a 30-amp double pole breaker (both of which I already have on hand). With the 10/2 wire extension cord one end would be a 50-amp female plug (to match the existing welder cord) and the other end would be a 30-amp 3 prong male twist lock plug to mate up to the wall's twist lock 30-amp female receptacle. I specifically want to use the twist lock style because I'm not too hip on ever having to disconnect the other types of flat plugs with nothing to grab onto save for right round where the connection actually is. I've been zapped with both 120v and 240v before and neither are fun. A longer twist lock plug at least gives you much more of a safer body to grab onto, and the twist lock helps from ever being disconnected. To get these in 50-amp style is ridiculously expensive. Anyway, for all of those who own this model please weigh in with what you did. Much thanks guys.

The plug for this unit has 2 hots and a ground, no neutral. About the breaker you need to use a dual pole breaker. Never use 2 single poles breakers for a device that uses 2 poles for safety reasons. Imagine one breaker trips, you think because of that that you can safely open the thing and touch wires, but the other breaker has not tripped and you touch the wrong wire and get electrified... With a dual pole breaker you know the electricity is completely cut to the device when it trips. I don't remember if the manual talks about the minimum ampacity of the breaker, please check it out. I would use at least a 30Amps one as this welder was rated for 20amp if I remember right, and a 20amp breaker may trip during start. In my case I had to add a 240 outlet in the garage, so instead of installing a smaller one and then having to upgrade if I want to plug something bigger, I installed a 50amp breaker, 50amp outlet, and 50amp nm wire (I think it was a 6/2, but not sure, I just checked which one I needed when buying it). You should be fine with anything 30amp or bigger. Just make sure your breaker is not bigger than the ampacity of the wire and the outlet.
About using an extension, the manual for some reason don't recommend it. I don't see why not as long as you use the right extension. The manual quotes the longest run you should use for 8/2 and 10/2 when replacing the power cord, just use the same limits for any extension (you would have to add both the included cord+the extension to make sure you are not over their stated limit).

One more thing, I installed my capacitor using 10gauge wire as I read somewhere in this boards. That is not a good idea, my wire heats up after a few minutes welding. Use 8gauge or thicker to be safe. I am planning on replacing it soon.
I used a 100.000uf 80V capacitor and while I could run beads at a slow speed in 16gauge steel at min1 before, now with the capacitor it mostly burns thru the steel unless I move really fast. I am just learning to weld, so I may have to adapt to this huge power increase, but the change is result is impressive.
By the way I have bought 2 x 33.000uf capacitors in Ebay, and will use those instead as soon as they arrive. I checked their datasheets and one concern is the max ripple current the capacitor can take. The one I was using can take 17amps, while a bank of the 2 I'm getting can take more than 30amps between the two of them in parallel. That means that the capacitors will heat up much less and last longer.
I noticed some Esab welders use a bank of 6 or 7 capacitors, with only 10.000uf and I have read on some technical documents they do that because it is normally too much amperage for a single capacitor.
The one from digikey in the first post in this thread is rated to 30amps if I remember right.
If you get a different capacitor, check the max ripple current it is rated for. Get the one with the maximum one you can find, or build a bank of smaller capacity ones if adding their max amps gives you a higher number.

 

[desertscout]

Depending on what year your house was built, depends on how its wired. My house is wired hot-hot-neutral...there are no grounds in my house they use the neutral for that.

 

[California]

was that the pre-1950 standard?

 

[victor_pv]

Depending on what year your house was built, depends on how its wired. My house is wired hot-hot-neutral...there are no grounds in my house they use the neutral for that.

Are you sure your neutral is not connected to ground in the main panel?

I am not sure what was done in the 50s in a specific area, but normally the neutral is grounded at the utility transformer, and is grounded again at the main service panel of your home.
From that point, many old houses do not run a separate grounding wire inside the house (that was the case in my previous home, built in 1959, probably had some updates after that time, and still had no separate grounding wire after the main panel).

In that case according to the NEC, you need to have a ground for any new circuit that you add to an existing panel. If you don't have a separate ground arriving to the panel in which you will connect the new circuit, you must add a ground to that panel first, and then run that ground to your new circuit.

was that the pre-1950 standard?

If your only have 1 panel that is both the main service disconnect and has all the breakers, then that one should have the neutral and the grounding wire bonded in it. In that case you can connect the grounding wire for a new circuit to the grounded bus.
To say it another way, in the very first panel that functions as a main service disconnect the grounded wires (neutral) and the grounding wires (the green grounds) can all go to the same bus bar.

I would advice checking the code and checking with an electrician or your city inspector to make sure you do it right. The inspectors can give pretty good advice on how to resolve a particular situation as they get to see every case and every solution people apply.

If you look at the user manual for the MIG 170, available in the harbor freight web, page 30 shows the electrical circuit and you can see the third conductor is used for ground. Personally I would not connect that to a neutral wire as the neutral can become electrified in some rare circumstances, and then the hole metal box that makes the exterior of the welder would be electrified, and you touching it could close a circuit to ground and get electrocuted. The main reason for having a separate ground nowadays is to protect from that kind of scenario.

If you are not sure what do you have in your house, find where your service disconnect is. That should be the first panel after the utility lines, and will have some big amps dual pole breaker (125Amp, 200amps, whatever your service is). That is the main service disconnect, and that one should have a grounding wire going to a rod or the cold water pipes. Now that panel may have all the circuit breakers in it (a few 15 amps, 20amps, 30amps, etc). Or it may be just for the main service disconnect, and then go to another panel inside your house with the circuit breakers. The first panel must be grounded, with neutral and grounding bond together. The second panel if any, may not have a separate ground if it is too old.

If you tell me in more detail what do you have I can try telling you what the NEC calls for in that case.

 

[California]

My 1910-ish farmhouse was apparently wired in the 1930's after the mains finally reached it. The wiring seems to conform to a 1950's edition of a Richter book that described how to do it. I'm sure there's never been a building inspector on the property. No green ground wire except on circuits added later.

There is a ground rod at the main panel and another 75 ft away at a 100 amp sub panel in the barn that was installed much later by amateurs. This second ground seems to be important for working out there safely, say welding on wet ground, but I've wondered if it is the reason why some plumbing rusts out (galvanic action) sooner than it should. Any comments on this corrosion?

 

[desertscout]

There is a ground rod outside of the panel that has a wire that goes to the neutral bus bar in the box. There are 3 wires coming into my panel...hot-hot-neutral, no ground. The house was built in 1986.

 

[victor_pv]

There is a ground rod outside of the panel that has a wire that goes to the neutral bus bar in the box. There are 3 wires coming into my panel...hot-hot-neutral, no ground. The house was built in 1986.

You can take a ground cable from that bus bar for any circuit. You can not join the neutral wire with the grounding wire anywhere else down the line, but only at the main panel, so what you have there is correct.
From that you can run ground to outlets or to any subpanel. Just make sure where ever you bring the ground wire that doesn't join the neutral.