Mod-Your-151 How-To Guide

[Galaxieman]

Sorry to hear about your explosion! Since your capacitor was rated at 85 volts, I suspect that you had a defective capacitor or incorrect wiring. The peak voltage that the capacitor can charge to in a 151 is no higher than 60 volts.

Originally Posted by erikg

I think the cap charge delay only happens the first time you use the welder after storing it, or if you pause long enough between welds for the charge to drain down completely, or if you ground out the tip between welds.

The capacitor time delay happens every time you weld. There is a charge delay when you pull the trigger and a discharge delay when you release the trigger. The capacitor is 'mostly' discharged every time you pull trigger (unless you are welding in very rapid succession).

The discharge time of the capicitor when not welding is fixed by the 'time-constant' of the circuit.

The discharge time-constant (in seconds) is determined by multiplying the capacitor value (in farads) by the bleed resistor value (in ohms). When not welding, the capacitor will discharge roughly 2/3 of its charge in one time constant. It will be 'totally' discharged in 5 time-constants. For practical purposes, in having enough charge to aid in welding, the capacitor is pretty much discharged in 1 or less time-constant.

In my modified 151:

'large capacitor' C = 100,000 uf (.1 farads)
'bleed resistor' R = 50 ohms

Time-constant = RxC = .1x50 = 5 seconds

So, in 5 seconds the capacitor is about 2/3 discharged. But, if I ground the tip it will spark (in decreasing amouts) for up to 25 seconds.

The full charge time of the capacitor, after pulling the trigger, is very rapid (only a couple of seconds) because the resistance of the main transformer is pretty low. It is this charge time that the time delay circuit, described above, compensates for.

[truckin23]

Originally Posted by Galaxieman

This HF 151 modification thread has been very quiet lately......

Finally...the wiring. The schematic, below, shows how the relay is connected to delay the start of wire feed. The relay is powered by the SWITCHED 230 volts that powers the PRIMARY of the MAIN welding transformer. Use one of the normally open relay contacts to interrupt (and delay) the power to the dc wire feed motor. There are other places that the power can be interrupted to the wire feed circuit, but breaking the ground feed worked best for my setup.

CAUTION: You will be splicing into 230 volt circuits...use care to make solid connections and insulate splices well....

Hi Galaxieman,

Was wondering if you could show me which wires I use for 230 power and how you spliced in and what gauge wire you used for both power and 12vdc motor and what termanals to use . I'm electrical and electronic illiterate. I did a picture with paint so you could tell me the numbers.

Thanks Bob

[Galaxieman]

truckin23 wrote”

“Was wondering if you could show me which wires I use for 230 power and how you spliced in and what gauge wire you used for both power and 12vdc motor and what termanals to use. I'm electrical and electronic illiterate. I did a picture with paint so you could tell me the numbers. “

Before I get to answering your questions we all need to be reminded of what ‘Mobes’ wrote in the first post of this long thread:

”When following this or any how-to, be sure to unplug your welder and keep safety in mind. Double check your own work. I'm not responsible if you or your wife, husband, brother, sister, cat, dog, etc get hurt. Without further adieu...”

Wire gages:

Both the 230 volt and dc motor wires carry less than about 1 amp. 16,18 or 20 gage will be OK. Good insulation on the 230 volt wires is important. For those connections I used a piece of old ac line cord that was rated for 230 volt use.

Terminals for wire-feed motor connections:

Referring to YOUR picture, above, with YOUR numbers...the normally open relay contact I used was between screws ‘4’ and ‘6’. (Note: These are NOT the same numbers as printed on the side of the time-delay relay). Polarity does not matter. Simply cut the ground wire to the wire feed motor and connect the normally open contact in series as shown in my schematic, above.

230 volt wires and connection method:

Refer to the picture below and my schematic above...

There are two 230 volt connections:

The first is directly to one side of the 230 volt output of the 151’s power switch. In your unmodified 151 there is a black wire from the power switch to the third pin on the white connector on the pc board. The pc board end of that wire can plainly be seen in my photograph as it enters the third pin up from the bottom of the white connector. Cut that wire and splice in a third wire for routing to the time-delay relay. On the left side of my photo you can see the splice which has been soldered, covered with heat-shrink tubing and secured with a black tie-wrap.

The second 230 volt connection is from the OUTPUT of the ‘contactor relay’. On the pc board there is a black cubed shaped object (see photo). That is the ‘contactor relay’, which activates when you pull the torch trigger. There are two wires plugged into the contactor relay. They are right next to each other and both are black. You want the wire on the RIGHT. This is a very fat wire with slip on insulation. The wire is aluminum and it routes directly to the main welding transformer primary. This wire is not easy to connect to because you cannot cut and solder the aluminum wire. The 151’s connection to the contactor relay is made using a female connector that has been crimped to the aluminum wire. You need to splice an additional wire onto that female connector to route the contactors output 230 volts to your time-delay relay. The way I did it was: unplug that wire from the contactor relay....slide back the black insulation exposing the female connector....carefully remove all of the outer plastic insulation from the female connector...solder an additional wire to the female connector shell near the crimp (not to the aluminum wire) without disturbing the crimp to the aluminum wire.....cover with heat shrink tubing....plug female connector back onto the contactor relay....secure with tie wraps.

The two 230 volt wires just added are then connected to the time-delay relay. Referring to YOUR picture, above, with YOUR numbers, connect them to screws ‘7’ and ‘8’.(Note: These are NOT the same numbers as printed on the side of the time-delay relay). Polarity does not matter.

[truckin23]

Mike,
Thanks you explained it perfectly to a complete simpleton like myself. I appreciate you taking the time and the pics to do this .Your modification is so neat and clean I hope mine comes out that good I'll post when completed still waiting on a different capacitor.

Bob

[truckin23]

Hi Galaxieman,

Mike, 2 more quick questions 1st what did you mount the hose clamp to to hold the big cap and 2nd did you drill holes in the rectifier to hold the big cap buss bar or did you use the existing holes that are slightly off center. My cap came in the mail yesterday I'm ready to get this off the ground lol.

Thanks Bob

[Galaxieman]

"1st what did you mount the hose clamp to to hold the big cap"?

I actually fabricated a small bracket out of some scrap metal and screwed it to 'this side' of the wall that has the wire reel on the 'other side' (behind the capacitor). It was just a simple 'hook' that allowed me to pass the hose clamp through it.

"2nd did you drill holes in the rectifier to hold the big cap buss bar or did you use the existing holes that are slightly off center."?

No, I did not drill the aluminum rectifier heatsinks. I just bolted my buss bars to the existing empty holes. When fabricating the buss bars I allowed for the 'slightly off center' alignment. You need to be carefull here that the buss bars do not touch the diodes that are mounted very near the empty holes. Also, be sure to get the capacitor polarity correct! I measured the polarity with a volt-meter and 'Sharpied' a large '+' mark on the correct aluminum heatsink. You can see that plus mark in one of my photos...

[truckin23]

Galaxieman ,

Mike thanks for all your help heres a youtube video of part of the install



Bob

[Galaxieman]

Bob,

Your capacitor install looks great. I mounted it without removing the rear panel. Very tight! But, if I had to do it again, I would remove the panel.

Let us know how it works when you get all the mods done....

[truckin23]

Originally Posted by Galaxieman

I recently purchased a Harbor Freight 151 (97503) with intent to modify per the great ideas in this thread. I have been using it as is ‘out of the box’ and I thought I would give my impressions BEFORE making any changes.

My welding ‘expertise’ .... you surely could call me a ‘hobby welder’. Been welding for about 20 years. Mostly it has been ‘stick’ welding with a very old Lincoln Weld-N-Power (6013 rods). I found that the DC on that welder gave pretty good results with 1/8 in. to 1/4 in. thick steel and I got pretty good with it. Most welding was done at 90 to 100 amps DC. That Weld-N-Power died about 10 years ago and I replaced it with a Lincoln 225 (tombstone) AC only stick welder. It works OK, but I surely missed the ease of DC. I have used a friends Miller ‘Cadillac’ MIG welder a few times...nice! My main complaint about stick welding was my ability to weld thinner material well and have the control afforded by MIG welders. Getting the arc going in a controlled manner always seemed to be a problem.

My initial 151 impressions:

All welding, so far, has been with the the .030 in. flux-core wire that came with the 151. (Before use I did change the line cord to 20 feet of 12-3 wire and moved the heavy duty ground clamp and wire over from my (retired?) Lincoln 225 tombstone.)

... Lots of spatter but probably less than when stick welding. The spatter is on your work, surroundings and also quite a bit of spatter gets up into the torch tip.
... Lots of smoke (need a fan to create a slight breeze and a breathing mask).
... Very hard or impossible to actually see the weld puddle. Thus, it is hard to see if you are actually welding on the joint or ‘next’ to the joint...
... Starts an arc easier than stick but still stumbles a little almost every time.
... Loading the wire roll and tensioning properly is not easy. I learned some of the tricks from sites referenced on this thread. I am pretty good at it now but you cannot be in a hurry. Always remember to remove the brass tip on the torch when feeding wire. I remove the wire roll and put it in a plastic bag between uses. It is very humid down here in South Florida and I have seen a roll of wire completely rusted on my friend’s Miller. That rusted wire would not weld.
...Welding 1/8 in. steel tubing on the MAX-2 setting got results similar to stick welding. With stick welding, if I could not see the joint I could always stay on course by ‘feeling’ the joint as I moved the stick back and forth along the bead. With the 151 flux-core wire it was just harder to weld ‘where’ I wanted. Another note: As I moved along a bead I could easily see the end of the wire where the arc starts. That point always seemed to oscillate up and down about 1/16 to 1/18 inch about once per second as I moved along the weld. I don’t think it had anything to do with the wire feed. Maybe varying power output from the welder? Or, is this normal for a wire feed welder?
... Welding 5/8 in. re-bar. Welded ‘OK’ on MAX-2 but did not seem to penetrate very well. Could break weld with heavy hammer blow.
... Welding .075 (14 gage) thick steel plate. Welded OK but had to use ‘stich’ method rather than running a bead. Wanted to burn through when running a bead.
... Welding .025 (about 3 gage) very thin square steel tubing...was surprised that I could very effectively ‘stitch’ weld this tubing. Although, the duration of the ‘stich’ was hard to control because of the varying time it took to start a stable arc.

All in all, I would say that the 151 is a pretty good buy for its price. I could do my ‘hobby’ welding, just fine, with an unmodified 151 and the 151 would be easier and more versatile (but less penetrating) than a stick welder.

Well....I have received all of my modification parts so it’s time to void my warranty.......

Mke ,

One last question I see in this photo you have 2 small caps ( what size are they?) did you install them I know one goes between the feed motor where does the other one go or eliminate them when you did the small bridge train .

Thanks for all your help Bob

[Galaxieman]

Bob wrote:

"One last question I see in this photo you have 2 small caps ( what size are they?) did you install them I know one goes between the feed motor where does the other one go or eliminate them when you did the small bridge train."


Good catch Bob....

When I incorporated the 'small bridge train' solution to tame wire speed, I did not need or use the small capacitors.

I finally settled on six small bridges in the train. It worked OK with four but even better with six.

[truckin23]

Thanks Mike ,

For answering my question so fast , so 6 it is now is that 6 including the isolation bridge or 6 and 1 for the isolation bridge.

Thanks again Bob

[Galaxieman]

Six, including the isolation bridge...An isolation bridge followed by 5 bridges used for their diode drops...If all you have is four...it will work like that, just leave room on the board in case you want to add more later...

[SQ is the SQUAD]

someone should make a youtube video of the process of this mod. i really want to do it to my 171 i am just not comfortable reading electronic diagrams.

if anyone who has done this is close to the Boston Ma area and is willing to help id appreciate it.

[SQ is the SQUAD]

thanks Galaxieman. i am ordering my parts now from digikey. i am going to try your train mod

[truckin23]

Originally Posted by SQ is the SQUAD

someone should make a youtube video of the process of this mod. i really want to do it to my 171 i am just not comfortable reading electronic diagrams.

if anyone who has done this is close to the Boston Ma area and is willing to help id appreciate it.

you and me both I'll try and take pics of what i'm doing I'm just a little slow getting it done as I drive a big rig for a living and put 2870 to 3510 miles in a week so just a bit tired when I get home

Bob

[Galaxieman]

Looks good to me Bob....

[SQ is the SQUAD]

Thanks bob, i really needed that, i ordered the 6 fro digikey, ill find the board locally at radioshack

[truckin23]

I decided to do something different with the fan ran down tonight to Fry's Electronics stores and picked up a fan grill and I had some thin gauge sheet aluminum I'm using for the back trim piece . I think Galaxieman's
unit turn out nice with that . Also got the diode's soldered up and shrink wraped and mounted . Hope I can find time to get more done tomorrow .

[truckin23]

All I got done today was to remount the fan I think it turned out all right rest of the day was honey do list .
Thanks Galaxieman for all the great ideas and help .

Bob

[Dave1941]

Looking good Bob. Hang in there and you'll get er done. Putting time in on our toys, goes a lot smoother when the honey do list is taken care of first.

[truckin23]

Thanks Dave someday I hope between long hours on the road and chores not much time left in a day can't wait for those 7 day weekends lol

Bob

[truckin23]

Ok before I fire this bad boy up I just want to double check to see if I have the wiring right .
I have some questions did I wire the bridge isolation and step down diode correctly and
I think I wired the time delay correct . The next thing will be to take it for a spin as soon as
I get the nod it's right . Thanks to everyone who has contributed to this mod .

[Galaxieman]

Bob,

NO....those connections you have in RED are wrong! DO NOT fire up!

I will explain where they connect.

Please wait for my next post....

Galaxieman

[Galaxieman]

Bob,

As I mentioned, above, your markups of my ‘bridge train’ schematic are incorrect. Do not wire it that way....

With over 500 posts on the subject of modifying the HF 151 mig welder, there is certainly room for confusion. The mods have evolved over the years, additions have been made. Before I made the mods I read through ALL of the posts. Some of it was off topic, or contradictory. There is no place where there is a comprehensive tell all (and after this post that will still be the case!).

In this post I will attempt ONLY to explain how and where the ‘isolation bridge’ or ‘bridge train’ gets connected into the 151.

In all electrical matters, schematic diagrams are the defining documents. Anyone who attempts these mods should be able to at least read and understand the area the schematic changing in their 151. The 151 is wired with mostly black wires so careful matching and sorting of wires with appropriate schematics is required. As you sort wires, carefully mark them with labels. Don’t cut or rewire anything until you are sure you have the correct wires and that the mods will match the appropriate schematic. And, as they say, ‘the only stupid question is the one we don’t ask’....

To understand connection of the ‘isolation bridge’ or ‘bridge train’ part of the mod we will start with the original unmodified schematic for the 151. I received this schematic in .pdf format directly from HF technical support:
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I have highlighted two connections in the schematic, above, that we are interested in:

1. Colored Blue ‘6’ - This wire connects from pin 6 of the pcb to a common point (the positive output side of the main bridge and (+) torch feed) AND to one side of the torch switch. In my 151 the wire from the torch switch was blue (yours may vary). The connections highlighted in blue on the schematic must be DISCONNECTED from the ‘the positive output side of the main bridge and (+) torch feed’ when doing the bridge mod.

2. Colored Red ‘10’ - This wire connects from pin 10 of the pcb to a common point (the negative output side of the main bridge and (-) torch feed) AND the negative side of the dc wire feed motor. The connections highlighted in red on the schematic must be DISCONNECTED from the ‘the negative output side of the main bridge and (-) torch feed’ when doing the bridge mod.

The next schematic was supplied by ‘Bluewelders’. This schematic shows mods to the 151 including the ‘big capacitor’, bleed resistor, isolation bridge and capacitor across the wire feed motor:
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On Bluewelders schematic I have again highlighted two connections of interest:

1. Colored Blue ‘6’ – This wire connects to pin 6 of the pcb AND to one side of the torch switch AND to the positive (+) output of the added ‘isolation bridge’. Note that this connection no longer connects to the positive output of the main bridge and (+) torch feed.

2. Colored Red ‘10’ – This wire connects to pin 10 of the pcb AND to the negative side of the dc wire feed motor AND to the negative output of the added ‘isolation bridge’. Note that this connection no longer connects to the negative output of the main bridge and (-) torch feed.

The next step is to change the Bluewelders’ isolation bridge method of ‘taming wire feed’ to the bridge train method. To do this, the little square in Bluewelder’s schematic labeled ‘Bridge Rectifier’ is directly replaced with this ‘bridge train’:
-----

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The bridge train circuit has the same four connections as the isolation bridge in Bluewelders’ schematic and thus can be thought of as simply replacing that isolation bridge in his schematic. The two ac connections on the left connect to the output of the main transformer as in Bluewelder’s schematic. Then:

1. Output colored blue (6, torch blue) - is connected to pin 6 of the pcb AND to one side of the torch switch as in Bluewelders' schematic.

2. Output colored red (10, motor-) - is connected to pin 10 of the pcb AND to the negative side of the dc wire feed motor as in Bluewelders' schematic.

When using the 'bridge train', the capacitor is NOT added across the wire feed motor.

[truckin23]

Thanks Galaxieman ,

Thats why I didn't plug it in I wasn't sure and thought something didn't look right I'm printing out the diagrams as I type when I'm done swicthing the wires I'll report back to make sure I didn't screw something else up before i fire it up I sure appreciate all the help Mike .