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Old 18-08-2014, 08:14   #31
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Re: Inverter Dying?

I followed the wire sizing recommendations in the installation manual. The wire size might be 1... I have to measure it.

BUT

It is impossible to fit a larger diameter wire into their connector!

I am also guessing at the length from memory it could be even 7'.

WHY IS THE 12 NEG corroded and not the 12V POS?
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Old 18-08-2014, 08:29   #32
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Re: Inverter Dying?

Is this a compression connector they supply with the unit? Maybe I am looking at the wrong manual. The manual on their web site shows a flat metal blade with a bolt through it. It sounds like you are describing a compression connector.

One other possibility for negative terminal corrosion is the voltage drop across the connection may be high enough to accelerate dissimilar metal corrosion. The voltage drop is one polarity on the plus terminal and opposite polarity on the minus terminal. You are using copper wire I presume?
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Old 18-08-2014, 08:38   #33
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Re: Inverter Dying?

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Originally Posted by Sandero View Post

WHY IS THE 12 NEG corroded and not the 12V POS?
Because that's where the bad connection was.
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Old 18-08-2014, 09:07   #34
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Re: Inverter Dying?

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Is this a compression connector they supply with the unit? Maybe I am looking at the wrong manual. The manual on their web site shows a flat metal blade with a bolt through it. It sounds like you are describing a compression connector.

One other possibility for negative terminal corrosion is the voltage drop across the connection may be high enough to accelerate dissimilar metal corrosion. The voltage drop is one polarity on the plus terminal and opposite polarity on the minus terminal. You are using copper wire I presume?
The unit which went down was purchased in 2005 and does NOT use ring connectors as the new model which replaced it does (I added ring connectors to attach to pos and neg for the new one) the old had "compression" fittings... strip the wire.. shove it in the hole and tighten the screw. The connector was isolated from the chassis with by a plastic block.

I am using marine grade tinned copper wire.
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Old 18-08-2014, 10:35   #35
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Re: Inverter Dying?

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The wire is not big enough. Use 0 gauge minimum size. Also, the wire is too long. For 13 foot total distance you should at least double the gauge of wire. But it would be better if you could find a way to shorten the run from inverter to batteries. Be sure you are counting the entire run length from inverter to battery.

I have seen this problem quite often. For some reason it's hard to believe that such large wire is required for inverters. But it is.
0awg is overkill if one is interested in a "right size" design. Ampacity on a 4awg wire with 90ºC rated insulation is around 94 amps or better, as long as the strand count is low. Resistance should be around .25 ohms per 1000 foot (again, making assumptions about the strand count). At 11.0V at the terminals, one is still under the threshold, although not appreciably so. A longer cable run, say greater than 10ft, starts to play with the ampacity limit when the inverter is at the 10.5V minimum threshold. Stepping up to 2awg leaves plenty of extra margin with the distances we are contemplating.
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Old 18-08-2014, 10:59   #36
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Re: Inverter Dying?

Folks, he said the inverter used to work fine but now it doesn't. That pretty well eliminates the wire being too small or too long doesn't it? Think about this.
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Old 18-08-2014, 11:27   #37
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Re: Inverter Dying?

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0awg is overkill if one is interested in a "right size" design. Ampacity on a 4awg wire with 90ºC rated insulation is around 94 amps or better, as long as the strand count is low. Resistance should be around .25 ohms per 1000 foot (again, making assumptions about the strand count). At 11.0V at the terminals, one is still under the threshold, although not appreciably so. A longer cable run, say greater than 10ft, starts to play with the ampacity limit when the inverter is at the 10.5V minimum threshold. Stepping up to 2awg leaves plenty of extra margin with the distances we are contemplating.
I would strongly urge you not to use ampacity tables for sizing inverter wiring. If the wire gets to 90 degrees C then it will damage the inverter. That's what happened to his first unit.

It sounds like Xantrex realized they had a design problem with the original one with compression terminals too small for the proper size wire. Now they are using a different terminal that allows proper lugs and wire sizes. That is the most logical reason they changed the design.
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Old 18-08-2014, 11:31   #38
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Re: Inverter Dying?

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Folks, he said the inverter used to work fine but now it doesn't. That pretty well eliminates the wire being too small or too long doesn't it? Think about this.
I read where he said the inverter had melted the negative terminal. That's why it stopped working. Sounds like too small wire and/or not enough compression on the terminal. But too small wire is my best guess. The wire got hot and caused the wire to expand. When it cooled it had less compression. Over time it cycled enough to burn up.
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Old 18-08-2014, 11:53   #39
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Re: Inverter Dying?

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I read where he said the inverter had melted the negative terminal. That's why it stopped working. Sounds like too small wire and/or not enough compression on the terminal. But too small wire is my best guess. The wire got hot and caused the wire to expand. When it cooled it had less compression. Over time it cycled enough to burn up.
I doubt it. If that was the case both terminals would have melted. The inverter wouldn't have worked properly with cables that were too small. There would have been a voltage drop from day one.

Perhaps the connection got damp and corroded or wasn't properly crimped in the first place. Perhaps the nut wasn't tight enough.
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Old 18-08-2014, 12:22   #40
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Re: Inverter Dying?

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I doubt it. If that was the case both terminals would have melted. The inverter wouldn't have worked properly with cables that were too small. There would have been a voltage drop from day one.

Perhaps the connection got damp and corroded or wasn't properly crimped in the first place. Perhaps the nut wasn't tight enough.
Eventually both would have failed but one got hotter than the other and it failed first. I see this sort of thing all the time in high current applications. It takes a fractional difference like you mentioned such as slightly less force for one of these compression connections to thermally run away. These things are notorious too for using flat blade or cross-head screw driver terminals that don't lend themselves to good tightening techniques. Good compression terminals use a hex key.

It's not the wire voltage drop that caused the problem. The overheated connection itself became a very high voltage drop over time to the point that it caused the low voltage shutdown of the inverter to activate. A good thing too because without that feature it could have easily become a fire.
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Old 18-08-2014, 12:35   #41
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Re: Inverter Dying?

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The unit which went down was purchased in 2005 and does NOT use ring connectors as the new model which replaced it does (I added ring connectors to attach to pos and neg for the new one) the old had "compression" fittings... strip the wire.. shove it in the hole and tighten the screw. The connector was isolated from the chassis with by a plastic block.

I am using marine grade tinned copper wire.
The new terminal type sounds much better. If you used the closed end lugs and a hydraulic crimper as it appears in the terminations in the photo then probably you are ok. Just keep checking the bolted connections at both ends of the wires to make sure they stay tight. Once a month is not too often to check this. Boats, especially with diesels, have lots of vibration transferred to the hull. It's amazing how something can become loose in a short time. Also, make sure the lock washer is installed properly (next to the nut with flat washer beneath the lock). Be sure the flat washer did not get bent when the bolt was tightened.
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Old 18-08-2014, 12:56   #42
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Re: Inverter Dying?

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I would strongly urge you not to use ampacity tables for sizing inverter wiring. If the wire gets to 90 degrees C then it will damage the inverter. That's what happened to his first unit.

It sounds like Xantrex realized they had a design problem with the original one with compression terminals too small for the proper size wire. Now they are using a different terminal that allows proper lugs and wire sizes. That is the most logical reason they changed the design.
At the risk of sounding flippant I don't think reverse engineering all end devices in order to determine wire sizing is a workable solution. Yes, I concede to you that Xantrex might have had a design flaw in their previous product (although I have no detailed knowledge of their unit).
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Old 18-08-2014, 13:09   #43
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Re: Inverter Dying?

The unit worked perfectly for 9 years and only recently went south. The corrosion could have been progressing... perhaps must have been progressing. Why the neg and the pos was perfect is the mystery to me.

The connection is not in a place which can be inspected. Xantrax DID change the connection from compression to lugs which seems sensible. The wire was appropriately sized based on their recommendations.
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Old 18-08-2014, 14:18   #44
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Re: Inverter Dying?

Dan--good posts.

The negative terminal failed because it was the weak link; the connection had higher resistance due perhaps to being a bit loose or dirty. Arcing occurred, further exacerbating the problem. Low voltage resulted.
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Old 18-08-2014, 15:06   #45
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Re: Inverter Dying?

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At the risk of sounding flippant I don't think reverse engineering all end devices in order to determine wire sizing is a workable solution. Yes, I concede to you that Xantrex might have had a design flaw in their previous product (although I have no detailed knowledge of their unit).

The installation manual of the current day unit could be made more clear. What they are trying to say is that at nominal rated load they want 1% voltage drop. Clearly it takes a big wire to get that at 100A. Whether that is reverse engineering or not I'm not sure.

I have found many times the proper size wire can't fit the terminals or fit through a hole meant for the wire which is frustrating. But it's not a solution to just say "Oh well, that's the biggest wire I can fit." Sometimes you have to get creative like using big wire for 95% of the run and then switch to smaller wire close to the inverter. In this case Xantrex is trying to make it easier to do the job right which seems like a good idea.
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