Devilbiss GB5000-2 generator rectifier wiring question

dwbdaveMay 20, 2013

Melted the bridge rectifier inside my Devilbiss gb5000-2 generator after plugging in a miswired extension cord during our last power outage. The photo above shows two white lead wires leaving the stator windings. One of these white wires is jacketed inside blue painted insulation, the other white wire is inside an unpainted white jacket. I believe these should be the positive and negative wires to the bridge rectifier, the other two wires leaving the stator are yellow and should connect to the AC (~) terminals on the bridge rectifier. I have ordered an identical replacement bridge rectifier (Devilbiss part GS0767, generic part number 512 GBPC1204), but I need to know the polarity of the two white wires in order to connect it correctly. Devilbiss diagrams for this generator do not even show the rectifier, just the 4 wires leaving the back of the disassembled parts. Anyone out there who can at least take a snapshot of your GB5000 or similar generator with the wires installed? This bridge rectifier or one similar is installed on many Porter Cable, DeWalt, Devilbiss, and other generators. Devilbiss seems to have abandoned their generators, and have obsoleted many of the parts for them as well.
Moved this from the tool shed forum after getting no response. Since then, I called the closest authorized repair center (it's over an hour away) and their tech person couldn't even find a reference to any type of rectifier being used on a Devilbiss generator. I should mention that the head went bad around ten years ago, Devilbiss paid to have it replaced with a different head even though it was out of warranty because this was a common failure in this model. So, I'm not sure if the rectifier was part of the original setup as sold in 1998.

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What outputs did this generator have originally? Voltage and amperage of those outputs? Post photos of the receptacles and the output panel on the unit if possible.

    Bookmark   June 1, 2013 at 3:12PM
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Here's a shot of the wiring diagram. It is a 5000 watt generator with both 120v and 240v outlets. No output panel, just the endcap of the generator with circuit breakers and two double receptacles. I will follow this post with an diagram of the parts.
This repair project took a back seat after I couldn't get definite answers on this problem. I ordered a Wen 3500w generator to replace this one, Mon Power's lack of maintenance on power line right of ways has forced me to go ahead and get another backup generator. Power outages have been more frequent in the last couple of years and I don't see the situation getting better.

    Bookmark   June 2, 2013 at 1:31PM
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It's not very clear, but this diagram is included to show how Devilbiss ignored the bridge rectifier in their parts diagram. The four wires at the left of #38 that leave the generator housing and end without connecting to anything... those are the yellow and white wires in my photo. The bridge rectifier is shown in some other diagrams of Devilbiss generators, but the stator wires connecting to it are ignored. I've never had this generator apart except for the end cap, but I believe that the stator assembly is two separate windings, one of which is an "exciter" winding with the four wires that connect to the bridge rectifier.

    Bookmark   June 2, 2013 at 1:58PM
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Never have seen one of this model and must confess that I have never needed to repair any portable generator.
The absence of a DC output makes one wonder what purpose the rectifier would serve. If there was such a DC output and both voltage and amperage was known, it would not be difficult to find a bridge rectifier that would electrically substitute for the original. If a DC output was included, it would most likely be 12 volt nominal. About 14.4 volts DC is needed for proper charging of the typical 12 volt vehicle storage battery.
Perhaps this little discussion will draw in the participation of one who knows more about the subject.

    Bookmark   June 2, 2013 at 3:06PM
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The purpose of the bridge rectifier is to convert some of the AC current to DC and feed it back to the main field coils in a brushless generator or alternator. This process eliminates the need for brushes and slip rings. Don't know much about generators either, I thought this was some new advance in portable backup generators back in '98 when I bought this one. Maybe it has backfired on companies who made them, mine had to be replaced a few years after I bought it, and even though there wasn't an official recall, you only had to call Devilbiss and mention that you saw where they had problems with this model, and they paid to replace the heads. The WEN 3500 I ordered has brushes, WEN has a procedure for the owner to service the brushes. Since my original post, I ordered two from Mouser Electronics for $10 shipped, thought I'd try to connect them myself, and shorted at least one diode on each bridge. The output voltage at the receptacles dropped from 117.5 volts with no load to 40 volts (the motor strained when this happened) whenever I tried to operate with the bridge rectifier connected. Without the rectifier connected, it returns to a steady 117.5 volts, but I doubt that it can supply much amperage. I'm not going further unless I can find out exactly how a rectifier should be wired. I suspect that when the original rectifier burned out, the stator's exciter wiring may have shorted.
I probably will give up on the Devilbiss, it's a shame because it probably has under 100 hours on it and I ran synthetic and changed it religiously over the years. Still, it is a noisy B&S 10hp motor that isn't set up for any other application.

This post was edited by dwbdave on Sun, Jun 2, 13 at 23:28

    Bookmark   June 2, 2013 at 9:31PM
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"The absence of a DC output makes one wonder what purpose the rectifier would serve. "

You need to set up the static magnetic field fr an alternator to operate.

An alternator takes the AC output of the stator.
A generator takes the output off the rotor.

The problem is that the slip rings in a generator carny the full output current, while in an alternator they only need to carry a small fraction to set up the magnetic field that is then rotated to produce the output on the stator coils.

    Bookmark   June 3, 2013 at 10:33AM
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