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  1. #76
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    Re: Converting 90 amp AC welder to DC

    Quote Originally Posted by Pavinsteelman View Post
    Go to HF website look up SKU 98871 open up owners manuel PG -8 tell me what you find ???? John
    I find it funny that this guy refuses to believe the output of the welder is AC only because the manual, which has been translated from another language entirely and is probably very similar to the manual used for their actual mig welder, says it it DCEN. Even when the OP has personally tested the machine with a known fully functional and properly configured FLUKE meter which informed him that the machine does indeed push AC between its contact tip and the ground clamp. Unless something is horribly wrong with the meter and the labeling on the machine then I am pretty sure that it is indeed AC and that the MANUAL has a typo that has not been brought to the attention of those delegated to the task of writing said manuals for the harbor freight importer.

  2. #77
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    Re: Converting 90 amp AC welder to DC

    ME TOO,I got the manual and the welder plus I've checked it with a digital volt meter,with the meter on DC it reads O,with it on AC it reads 31V on high and 26V on low.That's AC volts..............
    Previous thread I said 8 gauge spade connectors,I meant quick connects or disconnects or some call them push-on and pull-off connectors
    Last edited by dugndeep; 05-20-2011 at 03:47 PM.
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  3. #78
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    Re: Converting 90 amp AC welder to DC

    Quote Originally Posted by ironmangq View Post
    I find it funny that this guy refuses to believe the output of the welder is AC only because the manual, which has been translated from another language entirely and is probably very similar to the manual used for their actual mig welder, says it it DCEN. Even when the OP has personally tested the machine with a known fully functional and properly configured FLUKE meter which informed him that the machine does indeed push AC between its contact tip and the ground clamp. Unless something is horribly wrong with the meter and the labeling on the machine then I am pretty sure that it is indeed AC and that the MANUAL has a typo that has not been brought to the attention of those delegated to the task of writing said manuals for the harbor freight importer.
    They used to have about 4 models of the 90a flux core welders,I think the manual thing is just some sort of screw up,because the models over lapped.

    If you use a meter on it and it's AC,and you open it up and it has no rectifiers it's AC.
    As to why someone would insist that they are all DC,despite all of this, I have no idea.

  4. #79
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    Re: Converting 90 amp AC welder to DC

    A friend brought by a female disconnect connector made for 10 gauge wire,it's made to slip over a 7/16" male disconnect terminal,it's huge.I would hate to see one made for 8 gauge wire,it would probably be 1/2" to 3/4" wide.The bridge rectifier's male disconnect terminal is just 1/4" wide,I might just use the 10 gauge wire I have to wire it all.By the time I remove some of the strands to make it fit inside of the terminals I'm defeating the purpose of using the 8 gauge wire.
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  5. #80
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    Re: Converting 90 amp AC welder to DC

    Since it's torch is live all the time,I'll try to use the 8 gauge for all connection except the capacitor.Maybe help with the heat situation.I'm ready to get this done and see what the results are lol I'm tired of thinking about it.Probably everybody else is too so I'm gonna let it rest until I get the rest of my parts.
    Maxus Pro-125 Mig
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  6. #81
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    Re: Converting 90 amp AC welder to DC

    You can cut the insulator off of those connectors and open them up so that an 8ga wire will fit in them, then just squeeze them back down and solder them, reinsulate with good shrink tube, Your connection will be better than from the factory and in my experience soldered connections hold up better and are less succeptible to corrosion and vibration

  7. #82
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    Re: Converting 90 amp AC welder to DC

    Thanks for the advice,never thought of that,I want to do everything right so I can get the best possible results.I might use a ring connector and a screw with a nut to attach the 8 awg wire to the rectifier,I just don't know if the quick connect terminal will be solid enough to get the best contact area.It's like they get loose over time and get real easy to push on and off.Plus I do want to solder wherever possible.I have been checking around the internet for them.They got them at Digi-key for 8 awg wire,you can buy different widths for different width blades that they slide over,you had to buy a box of 500,I just don't need that many lol
    Thanks for the advice,I will try that,I'm trial running everything,I want it to be right so if it don't work I'll know I done it right to begin with.

    I had to go and try it,I think it will work,just got to make sure you get it full of solder.Now just put some heat shrink on it and it is good to go.
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    Last edited by dugndeep; 05-21-2011 at 11:03 PM.
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  8. #83
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    Re: Converting 90 amp AC welder to DC

    I did find some of these at Lowes,copper crimp connectors which I'm going to solder up to hold my final connection wires.
    Whoever wrote the specs up for lowes don't know nothing about wire sizes,they got maximum wire size for these is 14 awg and minimum wire size is 8 awg lol
    I do wish I had ordered a bigger cap now,been looking at the specs for some of the older mig welders,for like a 125 amp welder,they used a 91,000uf cap.One 70 amp welder had a 71,000uf cap.I just figure the older welder's had less circuitry than today's welders and mainly just used a bigger uf cap to get the smoothing they wanted.They do have a 100,000uf that is not too much more just a whole lot bigger can.
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    Last edited by dugndeep; 05-22-2011 at 08:49 AM.
    Maxus Pro-125 Mig
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  9. #84
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    Re: Converting 90 amp AC welder to DC

    I found this one company in China and all they make is bridge rectifier's for welders.They make all kinds of different amp models.Here's the one I was looking at,could probably fit it in this welder somewhere.This is the 100 amp bridge rectifier.It cost less than $10.I would rather go with something like this than the one I ordered.It's just 5 1/2" X 3 7/8" X 1 1/2".It about the same size as the one I ordered except it is about 1 1/2" longer.Which longer wouldn't matter.Minimum order is just 10,000 pieces and a shipping container to get them over here shouldn't be too expensive if you could afford the 10,000 pieces lol
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    Last edited by dugndeep; 05-22-2011 at 01:13 PM.
    Maxus Pro-125 Mig
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  10. #85
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    Re: Converting 90 amp AC welder to DC

    The wires coming off of my transformer are aluminum,so I'll have to crimp this connection to get the AC to the bridge rectifier.I hate crimping plus there's not alot of room to get it right.I got the side panel off now trying to figure out how I'm going to mount this stuff,only thing I have figured out,it's going to be tight.
    Maxus Pro-125 Mig
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  11. #86
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    Re: Converting 90 amp AC welder to DC

    I don't much like crimping either. You could use a nut and bolt.
    Solder a ring terminal onto the end of the wire you wish to connect to the alum wire, then bend the alum wire into an eye, and use a bolt to clamp the alum wire to the ring. Maybe it would be a good idea to put a spot of grease on the connection to minimize any possible galvanic corrosion problems.
    "Great spirits have always encountered violent oppostion from mediocre minds." -- Albert Einstein

  12. #87
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    Re: Converting 90 amp AC welder to DC

    I was wondering about that dissimilar metals thing too,I'm trying to get everything figured out before it's time to actually do it.Might use your idea with the ring and bolt then heat shrink it all up.
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  13. #88
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    Re: Converting 90 amp AC welder to DC

    They do make a paste for use on aluminum wire connections, I cant remember what it is but Im sure someone on here knows about it

  14. #89
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    Re: Converting 90 amp AC welder to DC

    It is 6 awg solid aluminum wire to be connected to 8 awg copper strand,here's what I have found and you do need to use an anti-oxidant for the aluminum side.It has a barrier in the middle so they can't touch.I read somewhere on the internet that you can solder aluminum to copper but I don't know about that.
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  15. #90
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    Re: Converting 90 amp AC welder to DC

    My capacitor shipped out this morning,now just have to wait on bridge rectifier from Hong Kong.I was just wondering,does the capacitor get real hot when the welder is on?The reason I ask is about placement in the welder,is it going to need alot of air too?
    Last edited by dugndeep; 05-23-2011 at 02:29 PM.
    Maxus Pro-125 Mig
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  16. #91
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    Re: Converting 90 amp AC welder to DC

    The capacitor shouldn't get noticeably warm..

  17. #92
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    Re: Converting 90 amp AC welder to DC

    Here's where I'm going to mount the rectifier,the air from the fan bounces off the transformer & goes up & over it.Should get alot of air.
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  18. #93
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    Re: Converting 90 amp AC welder to DC

    I would use the anti-oxidizing paste on any connection where aluminum will contact a different type of metal. If those lugs are aluminum use it on the copper wire side, if steel use it on the aluminum side

  19. #94
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    Re: Converting 90 amp AC welder to DC

    If you have some idle time in the shop, or want/need to make a portable welder, you could use one or two car batteries. Connect the battery positive to the work, and the negative to a wire going to the gun, and then don't connect the work clamp from the welder. The welder will still power the feed motor but the battery/ies will provide the welding current. If you want it to be portable, you will need to connect the battery to the feed motor w/o the main transformer acting as a DC load on the battery... which it will be a significant one. Probably connect after the rectifier that the motor power goes thru.

    Ah! In your case, once you're done with the DC mod, you can simply and exactly connect the battery/ies directly across the smoothing capacitor and you have a portable, cordless welder. The rectifier will keep the battery/ies from being shorted by the transformer, and at that point in the circuit, it is perfect for powering the feed motor.

    It's a whole lot cheaper than a readywelder, a big blue, big red, or big gray.

    An interesting thing to note here is that for wire feeders that connect to a constant current source (such as a stick welding machine), they are stated as being voltage sensing wire feeders. The HF fcaw machine works that way. The motor is powered by the same output as the welding is, so the motor will slow down when the wire contacts the work. With constant voltage, it should not matter either way; using the welder output to provide constant voltage to the motor, or running the motor off of the battery/ies.
    "Great spirits have always encountered violent oppostion from mediocre minds." -- Albert Einstein

  20. #95
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    Re: Converting 90 amp AC welder to DC

    The feed motor control boards on the Harbor Freight welders are an SCR type.
    They won't work off of pure DC,like a car battery.

  21. #96
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    Re: Converting 90 amp AC welder to DC

    Gah!!!

    Confirmed. It is a BT151 SCR. Yikes.
    Sorry for the bum steer

    Bluewelders; thank you for correcting me.

    Using it purely on battery would require a more complex motor speed control circuit.
    "Great spirits have always encountered violent oppostion from mediocre minds." -- Albert Einstein

  22. #97
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    Re: Converting 90 amp AC welder to DC

    It's a good circuit for what it does,just not for that.

  23. #98
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    Re: Converting 90 amp AC welder to DC

    I am about ready to try this,just need the bridge rectifier.I haven't got news about it,whether they've received payment or shipped or what,waiting patiently I guess you could say,just not patiently lol
    On that joint compound,it says to use it on copper too to help with conductivity,it has zinc particles in it.It says to work it in to the strands before you put the connector on.Crimp connection that is.
    Here's what I got in it so far:
    welder-ebay= $48.00
    capacitor-I prepaid so it was free shipping=$16.64 prepaid as in a money order
    joint compound-got it at lowes= $ 3.18
    Ideal 2-pak aluminum connectors= $ 6.32
    bridge rectifier-haven't received yet= $10.77
    wire-already had= $ 0.00
    connectors-already had= $ 0.00
    Total so far= $84.91
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    Last edited by dugndeep; 05-25-2011 at 04:03 PM.
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  24. #99
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    Re: Converting 90 amp AC welder to DC

    I finally got confirmation on the bridge rectifier,it is at the warehouse being picked and packed and should be here in 12 business days.Kinda had me worried about sending a money order to Hong Kong,but it made it to where it needed to go I reckon. I wasn't about to send credit card info to some place in Hong Kong so I sent a US postal money order.I didn't know if this kind of bridge rectifier would work so I went to some of the manufacturer's websites just to see what they recommend these for,mainly for generators,inverters but one manufacturer did say arc welders.So I feel better that it will work just don't know how long it will last.I do hope they package it securely so it makes it here in one piece.
    Last edited by dugndeep; 05-26-2011 at 01:54 PM.
    Maxus Pro-125 Mig
    Chicago Electric 90 amp DC flux-core
    Lincoln Electric AC 225 tombstone
    O/A torch
    M/O mini-torch
    10 acres of flatland
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  25. #100
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    Re: Converting 90 amp AC welder to DC

    Here's the one the manufacturer's use for inverter welders.The place where I ordered mine from had one just like it for $27,if anybody else is going to try this and don't mind spending a few more dollars than this would be the one to get.It could be mounted to a heatsink with some thermal paste and would stay cooler than the other one.
    I was wondering about the live torch but an inverter stick welder is live all the time too until it is shorted to the work piece so should be the same difference.
    The manufacturer's are saying these things don't need alot of air to stay cool so I reckon we'll see about that.I got an Extech infrared thermometer so I can keep a running tab on the heat with start-up.
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