Inverter Dying?

[Sandero]

Originally Posted by transmitterdan

Sandero,

I see this all the time. It takes a tiny difference for heat to build up and run away. Please don't be too surprised by what happened to you. It happens very often the way you described.

Good luck with your new installation. But don't be too surprised if the same thing happens again.

Different connectors... perhaps that will make a difference. It did last for 10 yrs before frying.

[mitiempo]

Originally Posted by Sandero

It's difficult to accept that the neg connection and pos connection were done differently and that one failed and the other remained perfect.

Both wire probably warmed up. The negative just got a bit hotter - slightly less torque on the nut holding the lug on, a bit of dirt between the mating surfaces, a crimp not quite as good as those on the positive cable, or moisture present on the connections. As posted the results you found are common.

All the more reason to use heavier wire than recommended. There is no downside to heavier cabling except for the few extra dollars it costs. Inverters probably last longer with heavier cables.

[transmitterdan]

I had time to run some numbers for those whose eyes have not yet glazed over. If the average (i.e. DC) battery current is 100A for a given inverter then assuming an ideal battery with no voltage sag the peak current is pi/2 times which is approximately 160A. The RMS (i.e. effective heating) current is pi/sqrt(8) times which is approximately 111A RMS. The heat generated is RMS current squared thus about 23% more than what one would expect from pure 100A DC.

The voltage drop will be at least 60% more than the simple DC math indicates. This is another good reason for using the recommended wire size or bigger.

[rwidman]

Originally Posted by transmitterdan

Before everyone starts foaming at the mouth about this please understand I am not looking for a fight nor to teach AC/DC circuits.

That's probably a good thing. You may know something but you're not doing a very good job of trying to explain it.

Again, you can't get alternating current out of a battery. And the DC current drawn by the inverter won't be more than what the manufacturer specifies so the manufacturer's installation instructions can be followed. There's certainly no harm in using larger capacity cables than required except for the cost and the difficulty installing them.

If you're trying to say that the inverter draws a high current followed by no current followed by a high current, etc. That's true in a sense but it's the average current over time that would cause the ampacity requirement..

[sparrowhawk1]

Anyone care to explain why both of the slots on the outlet to my west marine inverter are the same size. Meaning a two prong" safety"plug can go in with the neutral (larger) on the left or on the right. Answer because both are hot

[socaldmax]

Originally Posted by transmitterdan

No, it's not pulsating DC I am referring too (although cheap inverters do that too). It is the real 60 (or 50) Hz current waveform that flows from the battery. If you could see it, it would look like a sine wave except every other half cycle would be inverted. I'm not at a place where I can draw a picture easily but I will try to when I can.

I see.


So batteries sold in the US are 60 hertz and the ones in Europe are 50 hertz? Is there a way to tell if you're getting a 50 or 60 hertz battery in the store without an AC ammeter?

[transmitterdan]

Originally Posted by rwidman

That's probably a good thing. You may know something but you're not doing a very good job of trying to explain it.



Again, you can't get alternating current out of a battery. And the DC current drawn by the inverter won't be more than what the manufacturer specifies so the manufacturer's installation instructions can be followed. There's certainly no harm in using larger capacity cables than required except for the cost and the difficulty installing them.



If you're trying to say that the inverter draws a high current followed by no current followed by a high current, etc. That's true in a sense but it's the average current over time that would cause the ampacity requirement..

The current demand from the battery has both DC and AC components as you correctly stated above. The peak battery current demand can and does greatly exceed the published DC value. I would just ask you to measure it sometime and then we discuss why it must be so.

Ampacity is an RMS number because heating is due to RMS current which is not the same as mean or DC current. Inverters draw higher RMS current than DC current. That is because of the AC current component. The AC component does not contribute to the DC but it does cause heating. In an ideal world it causes 23% more heating and even more in the real world.

Voltage sag is caused by impedance (resistance+reactance) times instantaneous current. When the current demand is at the 160% peak of DC the voltage sag is much greater than the published DC value would indicate.

Ignoring RMS heating current and peak voltage sag is why many inverter installations do not last or perform as expected. When the inverter manual recommends wire size for 1% DC voltage drop they are not kidding.

[transmitterdan]

Originally Posted by socaldmax

I see.





So batteries sold in the US are 60 hertz and the ones in Europe are 50 hertz? Is there a way to tell if you're getting a 50 or 60 hertz battery in the store without an AC ammeter?

That's just silly and not what I said at all. The frequency is determined by the inverter. I didn't think I needed to say that because it is so obvious.

[transmitterdan]

Originally Posted by sparrowhawk1

Anyone care to explain why both of the slots on the outlet to my west marine inverter are the same size. Meaning a two prong" safety"plug can go in with the neutral (larger) on the left or on the right. Answer because both are hot

I am not sure which model inverter you have. The reason could be as you state that black and white are each 60 volts making the total 120V. But I don't believe that comports with ABYC requirements. It could also be that the ground terminal is not connected to the white neutral circuit. That might make it seem as if neutral is hot but in reality it isn't.

If you have the model # or a link to the inverter user manual maybe I can figure out what they have done.

[sparrowhawk1]

Transmitterdan. You will take the time to look up my inverter which is nice. but you won't take the time (a few minutes) to watch a video where they explain why cheap inverters put half of the power on the neutral side? There's probably dozens of videos of people explaining it on YouTube. I don't claim to be anything near an electrician but this is something I'm sure of and it makes total sense

[transmitterdan]

Then I am not sure what you want to learn from us.

I have no access to You Tube at this time.

[Ex-Calif]

Originally Posted by transmitterdan

Then I am not sure what you want to learn from us.

I have no access to You Tube at this time.

This is surreal.

What I'd like to learn is how my battery is producing AC current and if it is why do I need an inverter?

[sparrowhawk1]

I learn a lot on this forum,that's why when I have some knowledge I like to share it. Why both slots on my cheap inverter are large was a rhetorical question. How can u not have utube if you're talking to me?

[colemj]

Originally Posted by sparrowhawk1

How can u not have utube if you're talking to me?

There are many parts of the world where utube is either blocked or takes up so much bandwidth that trying to watch it is like watching paint dry - one frame at a time. We are almost constantly in those parts of the world where this is true. Google searches and chat forums are not even in that ballpark, so there is a gulf of difference between them.

Mark

[StuM]

Maybe I'm dumb, but I thought that the "alternating" in AC meant that the direction of current flow alternated, otherwise it would be called VC (variable current).

If the current is alternating, half the time you would be charging the battery instead of discharging it. Hey - perpetual motion!