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Old 02-19-2021, 12:19 AM
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JidoukaSS JidoukaSS is offline
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Default Miller XMT 350 MPA with automatic voltage drop compensation

Proper parts, prints, and demo for this project should be done soon. I'm just going to start this thread to give me motivation to get it done.

My dad had a job to do a lot of welding on a CAT articulating hauler so he bought the remote suitcase feeder for the Miller XMT 350 MPA. Initially we only got 12 inches of weld before the suitcase failed caused by a bad internal connection plug. Which will happen when you fill the plugs with silicone grease FFS. After cleaning the pins and putting on some Deoxit, we were back in business. He started welding and it was very inconsistent, so the voltage and wire speed were adjusted with no improvement. After taking a look at it, I figured it might have something to do with voltage drop. The remote unit was connected with a 50 or 75ft cable(100-150ft loop) and the measured voltage drop was around 2-4v. When the voltage setting was increased, the wire speed was also, inevitably causing the same problem.


The XMT is a switch mode welder so I figured it must already have a voltage output compensation loop. Looking at the prints, sure enough the output terminals are tapped with a connection to the front panel circuit board. So, like a linear power supply with sense terminals, which should be connected to the farthest load point, so too should the welder if we want to use settings we're used to. A quick test with a piece of wire connected to the positive sense tap and remote positive buss bar improved the voltage delivery to the unit. If the voltage setting was set to 24v, then the XMT will output what is required to meet 24v as measured from the suitcase buss bar, automatically putting out 26v.

This demonstrated proof of concept, so to make it easier, I added a Local / Remote Sense rotary selection switch to the front panel of the XMT. Local mode would be factory, and remote for suitcase. Ultimately, all you have to do is tie into the Sense feedback connection as can be seen on prints with the Black and White wires connected to #40 Negative/#39 Positive. Connect the rotary switch common to the White(+) wire to Front Panel Connector. Then connect #39 XMT Positive Lug to Local Selector Position and Remote Wire to Remote Selector Position. I also added LED indicators; Local Mode Green, Remote Mode Blue. I've been trying to get
a single piece vinyl sticker made, but I can't figure out why they can't get the scaling right. Picture shown is to test to see it covers up the LED bleed through.
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Last edited by JidoukaSS; 02-19-2021 at 12:30 AM.
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  #2  
Old 02-19-2021, 12:22 AM
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JidoukaSS JidoukaSS is offline
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Remote unit pictures. Voltage tapped at buss bar with 1 amp fuse. I didn't have a proper inline fuse holder at the time so there's just 1/4" QD connectors for fuse.
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Last edited by JidoukaSS; 02-19-2021 at 12:28 AM.
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Old 02-19-2021, 08:56 AM
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greywynd greywynd is offline
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Interesting. We have several XMT 350’s at work, we use them for the bore welders, as well as with various wire feeders. I can’t say I, or others have encountered rhis sort of issue, though we don’t have the feeders that far away from the power source. Our suitcase feeders are voltage sensing, so I wonder if they would compensate for the drop as well?


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Old 02-22-2021, 12:15 AM
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Link to test video, 100ft and 150ft local/remote V-sense results.



https://www.youtube.com/watch?v=dwuSENNMuCU
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