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Hobart GR-303 Welder-Gen Help


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  #1  
Old 01-24-2011, 05:03:22 PM
Jim Tremble Jim Tremble is offline
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Default Hobart GR-303 Welder-Gen Help

I didn't get any help on the welder site so I am posting to you generator guys.

My nephew was given a Hobart GR-303 Welder-Gen.
It will not produce DC or AC power. The brushes (3) are clean and not stuck. We cleaned the slip rings and still nothing. I found what appears to be 2 rectifiers wired to the brushes. After checking them, one of them appears to be bad as it reads open in both directions. What are these for (bridge rectifier) and where could I get new ones ? Could something else be used if I can not find exact replacements ?? A wiring diagram would really help.

These rectifiers have a stamped number. S-490 and another stamp--1K.

I am going to check resistance on the slip rings in the morning. Common to the center one and common to the outer one. I have found info on the slip ring that the inner one is the common. I will post the readings when I get back. Is this setup a dual generator ?? One DC, for welding, and the other AC ?? Trust me, I know very little about these.

Checked the slip rings, 22.8 ohms from common to center ring. 17.0 ohms from common to outer ring. Does this sound right OR ?? This was done with the brush pack removed.

I can post a photo of the brush holder and rectifiers if that would help.

Hobart GR-303
300 Amp
Volts 40
Specs 5404
Duty 100%
Serial #DW-69983
Gen Volts 115AC
KW 3

Any help is greatly appreciated,

Thanks, Jim
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  #2  
Old 01-24-2011, 06:58:33 PM
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BTPost BTPost is offline
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Talking Re: Hobart GR-303 Welder-Gen Help

Most likely the Bridge rectifiers are for the Field Windings. To make AC into DC to power the Field Windings. Where do the BIG Heavy Welding Cable connect to? Do the connect to the Slip Rings, or do they connect to Fixed Stator Windings? answer that and then you will know if you have a Rotating Field, OR a Rotating Stator. Then you can start looking for a replacement Rectifier Pack.
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Old 01-24-2011, 07:03:39 PM
Jim Tremble Jim Tremble is offline
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Default Re: Hobart GR-303 Welder-Gen Help

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Originally Posted by BTPost View Post
Most likely the Bridge rectifiers are for the Field Windings. To make AC into DC to power the Field Windings. Where do the BIG Heavy Welding Cable connect to? Do the connect to the Slip Rings, or do they connect to Fixed Stator Windings? answer that and then you will know if you have a Rotating Field, OR a Rotating Stator. Then you can start looking for a replacement Rectifier Pack.
Bruce

I will make a drawing of the wiring for the brush pack and rectifiers, showing the small and large wires. I don't know if there should be + & - on the rectifier as they are not marked.

I'll be back after a while, and Thanks

Jim

Last edited by Jim Tremble; 01-24-2011 at 07:44:34 PM.
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Old 01-24-2011, 07:54:12 PM
Jim Tremble Jim Tremble is offline
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Default Re: Hobart GR-303 Welder-Gen Help

Bruce

The large wires go back into the housing. Field windings ???? Nothing connects to the slip rings except the brushes. The mounting studs on the rectifiers are bolted to the frame of the gen. If need be, I can get the info on which way the rectifier is open and closed. (terminals as per drawing)

The local welding shop is trying to get me a diagram for this. Fingers crossed.

Thanks for the reply,

Jim
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Old 01-25-2011, 10:56:48 AM
Jim Rankin Jim Rankin is offline
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Default Re: Hobart GR-303 Welder-Gen Help

Most types of diodes will be something standard and are available from sources like Digikey, Mouser and others.

Usually there will be a rectifier symbol printed on the side (an arrow head pointing up away from the stud base or down into the stud base). On the other hand, from your drawing it may be that these are a type of "puck" which can be installed either way around instead of a stud base mount type. In that case, be careful to note the polarity of the bad one before you remove it.

I would also take ohm reading from each slipring to the shaft of the armature as well as the reading between the two on the right side of your drawing. I'm thinking the readings to "common" should be closer to the same between them and that may indicate shorted turns in the rotor. Normally there should be no connection (or very high resistance) to the shaft from any of the sliprings once the brushes are lifted off.

A very heavy rectifier most likely is to rectify the welding current instead of just driving the excitation.
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Old 01-25-2011, 03:45:36 PM
K D Redd K D Redd is offline
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Default Re: Hobart GR-303 Welder-Gen Help

If the drawing is accurate, they are showing selenium plate type diodes. These thing will go bad setting on a parts store shelf. This is why selenium has been in most cases replaces by silicon. I would bet replacing the diode will fix the welder.
I had some friends, now both sadly gone who had a lathe built in Germany. This thing had a 6 jaw chuck with I think a 3.75 inch hole through the spindle and about 14 feet between centers. It went down one day when a selenium bridge rectifier in the control cabinet. About a week later, after they had called all over the world, this was BWWW ( Before World Wide Web ) looking for a replacement of a selenium they called me to fix their lathe. Four silicon diodes later they had their lathe back in operation. These were good friend from my tractor pulling days. This was 25 years ago. The last I knew the Lathe was still working but I have lost track of the lathe. The brother both died of heart problem with the last one gone about 15 years ago.

Kent
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Old 01-25-2011, 04:33:26 PM
Jim Tremble Jim Tremble is offline
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Default Re: Hobart GR-303 Welder-Gen Help

OK, I posted some wrong info. The 3 heavey wires do not go back to the windings. The common brush wire goes to a control board. The center wire goes to a heavy resistor. And the third wire goes to the control board also.

Checked the slip rings to the rotor shaft. All were open and not shorted. #2&3 slip rings measures 40.0 ohms.

Waiting to hear from the welding shop.

And Kent, they look just like I drew them.

Jim
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Old 01-27-2011, 11:42:49 AM
Jim Tremble Jim Tremble is offline
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Default Re: Hobart GR-303 Welder-Gen Help

UPDATE------

The welder is welding, the generator is generating and we are smiling.

What a deal. I found a shop in Ohio and talked with the man about the problem. He said the 2 rectifiers were in fact surge suppressors. He told me to just remove them as they were not needed. Hobart put them in there to try to smooth out the surge if it happened.

Well, removed the parts and this thing runs quite well.

Not bad for a unit like this at no cost to us.

BTW, if anyone needs help on a Hobart welder, call-------

Mike
C&M Welding
419-584-0008

This guy knows everything about Hobart.

Thanks for the replies and help,

Jim

Last edited by Jim Tremble; 01-27-2011 at 11:53:35 AM.
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