Inverter Dying?

[sparrowhawk1]

Please watch "important inverter safety warning." By ranadacnam7321. On YouTube

[irwin37]

Xantrex Pro Series inverters are 1000 and 1800 watt output. They are modified sine wave inverters.

Sorry my mistake should have been Pro Sign 1000 and 1800 watt which are both pure sine wave output.

Also there are cheep inverters out there that are transformerless, no isolation, these are not supposed to be sold in the states but who knows?

Because an inverters 120 ac output is isolated by a high frequency transformer a digital meter may indicate an ac voltage between one one of the ac legs and a battery cable but there should be no current flow. Connecting the neg battery lead, boat ground, and the ac ground together will eliminate this voltage reading. Most inverters do this when you ground the case to your engine block / boat ground which is also the neg side of the battery.

[Auspicious]

Originally Posted by Coops

If you "experts' cannot agree, what chance does an imbecile like me have of knowing what is believable? Eeeny meeny miny mo?

Nope. We're up to three (at least) EEs and a (at least) marine engineer who have affirmed that transmitterdan is mistaken.

I am tempted to pack up this thread in a convenient fashion and ship it off to contacts at Mastervolt and Magnum, to a Columbia University EE professor, and a Webb Institute EE professor. The challenge will be getting them to stop laughing about AC coming out of a battery.

Originally Posted by transmitterdan

When the voltage is maximum the current is also maximum and the instantaneous power at that moment is twice the average power.

Unless I don't remember correctly, the RMS amplitude of a pure sine wave is 0.7 (1/SQRT(2)) of the peak value.

One of the reasons RMS measures are so useful is because they are more meaningful.

Originally Posted by Wikipedia

For alternating current electric power, the universal practice is to specify RMS values of a sinusoidal waveform. One property of root mean square voltages and currents is that they produce the same heating effect as DC in a given resistance.

Ohm's Law continues to apply.

Originally Posted by Ex-Calif

For the scientists...

I enjoy a learned conversation. Often I learn something. However tossing theory back and forth is not useful.

Let's be really clear here - scientists have theories. Engineers work with demonstrated facts. The strength of the last bridge you drove over is based on fact, not theory. The distribution of electricity to your house and dock are based on fact, not theory. The operation of your VHF radio is based on fact, not theory.

Facts, theory, and opinion should not be confused.

Originally Posted by Ex-Calif

How about we look at the attached white paper covering a Texas Instruments full sine wave inverter with battery charger.

Excellent.

Lets walk through the document at a high level.

Start with the block diagram in figure 2. The four MOSFETs (Q1 - Q4) provide the switching that flips the feed back and forth across the inputs to the transformer. They are controlled by the leftmost IC. The switchers generate AC from the DC provided by the battery BP1. I suspect that if you look at the actual circuit diagram for a product (the block is for a reference design) you'll see additional filtering to clean up the output waveform with particular attention to harmonics which would otherwise make the waveform quite dirty and anything but a pure sine wave. Pulse width modulation (PWM) is going to need filtering that will likely show up at both the inputs and outputs of the step-up transformer. A high Q transformer will provide filtering in and of itself.

Note this reference design is clearly for an grid-tied residential inverter, thus the mains bypass. Some marine inverters and many combination inverter-chargers have similar circuits.

Note this statement on page 5:

Here H-bridge circuit converts battery DC voltage {N.B. DC!} into AC using high frequency PWM (6 kHz to 20 KHz) thus feeding the 50 Hz transformer which Boost it to 120V/220V AC. {N.B. switching is at a high frequency but the pulse width modulation (the frequency at which the pulses change width) is at the desired output frequency of 50 Hz, 60 Hz, or for some aircraft 400 Hz.} The output of transformer contains a capacitor which filters it to make clean 50Hz AC. (Details of Switching can be found in the sections to come).

So what does this mean so far? For a 60 Hz output the controller turns a pair of MOSFETs on and off really fast for a little over 8 milliseconds (ms). This generates what will be after filtering half a sine wave. For the next time period of a little over 8 ms the other two MOSFETS will be turned on and off really fast to generate the other half of the sine wave. The only difference between the two pairs is the leads of the transformer that are fed. Current is always drawn from the battery in the same direction. There simply is no AC component. The next few pages actually demonstrate the function of the switching circuitry.

We can walk through the circuit diagrams if anyone really wants to. I'm willing to set up a Google Hangout video chat for anyone that is that interested.

The MOSFET switcher takes the place of the old relays in electromechanical inverters (the buzzy ones). Those were marginally reliable and getting any kind of decent waveform out of them was practically impossible.

Bored yet? *grin*

Originally Posted by Ex-Calif

There is no magic DC that is AC. There are two steps. Amplify the low voltage DC to high voltage DC and then convert the high voltage DC to AC. I am not an electrical engineer but that's how I read it.

You got pretty close. DC to AC happens first (the switchers) and then voltage transformation. Ah - I see you got that later. We usually talk about the voltage increase as a "step-up" vice "amplify." In a step-up the voltage increases and the current is reduced so power remains the same (neglecting efficiency). In amplification power is increased; that function is usually found in audio and radio applications.

Originally Posted by Ex-Calif

I would love to hear the discussion about how the scientists think this thing works.

I'll be happy to bring in some scientists, but the engineers are the ones all on the same side here. *grin*

Originally Posted by Ex-Calif

I am still wondering how battery alternating current comes into play.

I doesn't. It is based on not understanding what is being measured and what the numbers mean. You have to understand your tools.

The MOSFET switcher draws current from the batteries by switching on and off very quickly. The DC from the battery is switched on and off very quickly. A clamp-on AC meter assumes it is measuring a sinusoidal wave form. Since it isn't (it is measuring a bunch of variable width square waves) it gives misleading readings.

Originally Posted by transmitterdan

The Fourier series describing the battery current contains a zero frequency term (DC) and several harmonics of the AC output frequency.

No. It has a zero frequency term (DC) that has a varying amplitude. Your clamp-on AC meter responds to the changing electromagnetic field and displays a number but that number doesn't mean what you appear to think it means. If you really want to see what's happening you need a spectrum analyzer and an oscilloscope.

Originally Posted by transmitterdan

What I don't understand is why it is important to anyone to try to prove I am wrong about it.

Because misinformation is bad for people that are struggling to understand concepts they haven't had to deal with before.

Originally Posted by transmitterdan

The reason it is important is that this explains and should reinforce why we should not scrimp on the inverter battery wires.

I agree with your motivation. Your incorrect techno-speak confuses the issue, dilutes your message, and diminishes the credibility of all your posts on any subject.

[sparrowhawk1]

Auspicious. I've read all your posts on this thread. Some really great information. I wish you would comment on the last video I posted a link to. well I don't know how to post a link on my smartphone but you know what I mean. And one of the biggest problems with the Internet is misinformation Thanks for fighting it

[Auspicious]

Originally Posted by sparrowhawk1

Auspicious. I've read all your posts on this thread. Some really great information. I wish you would comment on the last video I posted a link to. well I don't know how to post a link on my smartphone but you know what I mean. And one of the biggest problems with the Internet is misinformation Thanks for fighting it

I sat down and watched the video you suggested and noted Irwin37's post before I responded. I think he is spot on.

The video relates to an inverter concept I haven't seen in years. It may be more common in grid-tie applications. I don't know.

The most important thing in the video is the recommendation to use a transfer switch if you have an inverter fed emergency bus in your house. As Irwin37 notes, the transformer separates the DC negative from the safety ground in a household application.

On boats, power distribution is different. The neutral-to-ground connection on shore power happens at the distribution system for the dock. For shore power you should not be connecting neutral to ground on board. When not connected to shore power and while using a generator or inverter that connection should be made.

If the electrical system on board is properly designed (read up on "single-point ground") and you treat DC, AC, and RF grounds separately up to the single-point ground I don't understand the issue the YouTube presenter is concerned about. Ground is ground and properly tying the AC neutral to it is a proper safety element of establishing the reference level.

You have to have a voltage differential to have safety hazard. That's why birds can sit on high voltage lines and not get electrocuted.

What that means to you is that power source switching on your boat (shore - inverter - generator) should include switching for isolated ground and neutral on board (shore) and connected ground and neutral on board (inverter and generator). If you have a combination inverter-charger make sure it does the switching internally. If you have separate units and you can charge batteries off shore power while running the inverter internally (as some do with US 60 Hz boats on EU 50 Hz docks) you must have isolation between the shore power AC and the boat side AC.

This is not hard but it is important.

[transmitterdan]

Originally Posted by Auspicious

Nope. We're up to three (at least) EEs and a (at least) marine engineer who have affirmed that transmitterdan is mistaken.

I am tempted to pack up this thread in a convenient fashion and ship it off to contacts at Mastervolt and Magnum, to a Columbia University EE professor, and a Webb Institute EE professor. The challenge will be getting them to stop laughing about AC coming out of a battery.



Unless I don't remember correctly, the RMS amplitude of a pure sine wave is 0.7 (1/SQRT(2)) of the peak value.

One of the reasons RMS measures are so useful is because they are more meaningful.

You are right that RMS is the important number because that is what heats the wire.

I like your idea of asking others about this. Here are a couple of test question for the EEs:

You have a 12VDC light at your nav station. It draws 2A from the battery and is too bright. You decide to make a simple switching circuit to turn the light on and off 50 times per second with a 50% duty cycle.The lamp is now not as bright and it uses less AH so you are happy.

For the purposes of this test assume the switch used has zero resistance.

Easy question #1: What should a DC ammeter show as the DC current drawn by the light bulb?

Little harder question #2: What should an RMS AC ammeter show as the current drawn by the light bulb? Hint: The answer is not zero. If you put a good true RMS AC clamp-on ammeter on the wire to the bulb it will in fact give the correct answer to this question.

Why is the answer to #2 not zero? My answer is there is an AC term in the Forurier series of the current that the DC measurement correctly ignores.

Extra Credit: Using the answers to #1 and #2 what is the true RMS current drawn by the light bulb? Hint: It is not the sum of #1 and #2.

PS: Sorry I didn't respond earlier. My laptop on the boat died. Just got back to civilization. I'm thinking it might be a good idea to not get another laptop for the boat for a while .

[transmitterdan]

Originally Posted by Auspicious

We can walk through the circuit diagrams if anyone really wants to. I'm willing to set up a Google Hangout video chat for anyone that is that interested.
:
:
I'll be happy to bring in some scientists, but the engineers are the ones all on the same side here. *grin*

I'll be happy to participate. I promise not to call anyone names or try to impugn their integrity or intelligence. In engineering problems with numeric answers there is usually only one correct answer and it is usually easy to find out if it is correct or not.

Opinions are another matter altogether.

[rwidman]

Originally Posted by transmitterdan

........... You have a 12VDC light at your nav station. It draws 2A from the battery and is too bright. You decide to make a simple switching circuit to turn the light on and off 50 times per second with a 50% duty cycle.The lamp is now not as bright and it uses less AH so you are happy...............

Well I'm not an engineer, only a technician, so my decision would be to replace the bulb with one with a smaller wattage rating.

What do you think of that solution?

[transmitterdan]

Originally Posted by transmitterdan

You are right that RMS is the important number because that is what heats the wire.



I like your idea of asking others about this. Here are a couple of test question for the EEs:



You have a 12VDC light at your nav station. It draws 2A from the battery and is too bright. You decide to make a simple switching circuit to turn the light on and off 50 times per second with a 50% duty cycle.The lamp is now not as bright and it uses less AH so you are happy.



For the purposes of this test assume the switch used has zero resistance.



Easy question #1: What should a DC ammeter show as the DC current drawn by the light bulb?



Little harder question #2: What should an RMS AC ammeter show as the current drawn by the light bulb? Hint: The answer is not zero. If you put a good true RMS AC clamp-on ammeter on the wire to the bulb it will in fact give the correct answer to this question.



Why is the answer to #2 not zero? My answer is there is an AC term in the Forurier series of the current that the DC measurement correctly ignores.



Extra Credit: Using the answers to #1 and #2 what is the true RMS current drawn by the light bulb? Hint: It is not the sum of #1 and #2.



PS: Sorry I didn't respond earlier. My laptop on the boat died. Just got back to civilization. I'm thinking it might be a good idea to not get another laptop for the boat for a while .

My apologies, this is degenerate case. Change the bulb current to 4A instead of 2A. Also, ignore that the bulb resistance might change a little.

[transmitterdan]

That's fine but when an inverter engineer has to use a similar trick he can't use that option.

[transmitterdan]

Originally Posted by sparrowhawk1

Auspicious. I've read all your posts on this thread. Some really great information. I wish you would comment on the last video I posted a link to. well I don't know how to post a link on my smartphone but you know what I mean. And one of the biggest problems with the Internet is misinformation Thanks for fighting it

Look at this manual from Xantrex web site.

http://xantrex.com/documents/Power-I...007_rev-_).pdf

Figure 1 on page 2 shows one way you can have problems with connecting inverters to house wiring with a "death cord" (one with male plugs on both ends). The inverter has 2 "independent" outputs that are 60V each but 180 degreees out of phase relative to "ground" which is also battery minus. Since a US home has neutral and ground shorted together somewhere near the meter there is now a short circuit between the neutral phase of the inverter and battery minus. Either the inverter shuts down due to the overload or something will probably burn up. There is a big warning in the manual on page 10 about this.

If you were to measure the voltage between the inverter neutral and battery minus you would find 60V AC. This is not an error as the voltage across these terminals really exists. But between inverter ground and battery minus there should be zero volts.

[transmitterdan]

Originally Posted by Auspicious

Unless I don't remember correctly, the RMS amplitude of a pure sine wave is 0.7 (1/SQRT(2)) of the peak value.

One of the reasons RMS measures are so useful is because they are more meaningful.

Ohm's Law continues to apply.

RMS is a useful concept because we can compute power with Ohm's Law which works both in theory and practice. It is especially elegant when dealing with time varying waveforms that are not a single frequency. One does have to be careful with RMS because it involves a nonlinear computation so superposition is often not applicable.

Originally Posted by Auspicious

Pulse width modulation (PWM) is going to need filtering that will likely show up at both the inputs and outputs of the step-up transformer. A high Q transformer will provide filtering in and of itself.

The transformer has some leakage inductance which when combined with the 1uF capacitor (C24) at the secondary forms a 2 pole low pass filter that removes most of the PWM switching frequency harmonics. There is no filter before the primary.

Originally Posted by Auspicious

It is based on not understanding what is being measured and what the numbers mean. You have to understand your tools.

The MOSFET switcher draws current from the batteries by switching on and off very quickly. The DC from the battery is switched on and off very quickly. A clamp-on AC meter assumes it is measuring a sinusoidal wave form. Since it isn't (it is measuring a bunch of variable width square waves) it gives misleading readings.

Scientists and engineers have been relying on these "misleading readings" for decades. Electrical circuit theory (including Ohm's Law) and circuit simulators such as Spice match these "misleading readings".

Fluke make high quality true RMS clamp-on meters as do other test equipment manufacturers. They will be disappointed to learn here on the internet that they are selling expensive equipment that provides misleading results to those poor unsuspecting "scientists" who don't understand their tools.

Originally Posted by Auspicious

No. It has a zero frequency term (DC) that has a varying amplitude. Your clamp-on AC meter responds to the changing electromagnetic field and displays a number but that number doesn't mean what you appear to think it means. If you really want to see what's happening you need a spectrum analyzer and an oscilloscope.

You mean the scope with the "AC/DC" switch on the front? If you switch an oscilloscope to the "AC" coupling position what you see is exactly what it says. They don't call it the "ripple" position or the "misleading" position or the "varying DC position" or anything else. It's the AC position for the simple reason that's what it shows.

There are a bunch of definitions of AC and DC floating around. The first one we learned in K-12 is simplistic and misleading. Even Wikipedia can't agree so we aren't likely to resolve it here. But in electrical engineering we have to be able to calculate performance and verify same by measurement. So we define DC as the mean of the signal (voltage or current) over the interval of interest and our test equipment matches that definition. AC is what you get if you subtract out the DC term which the superposition principle says we can do.

All the other definitions can't be used mathematically so I don't use them. If you want to ridicule me then I am ok with that since Hewlett and Packard agree with me. They printed it on the front of hundreds of thousands of scopes and multi-meters. As do Fluke, Rohde & Schwarz, Tektronix and a host of other respected vendors.

Originally Posted by Auspicious

Because misinformation is bad for people that are struggling to understand concepts they haven't had to deal with before.

I agree with you. Just because a concept hasn't been simply explained doesn't make the complicated explanation wrong.

Here is a summary of what I "know" based on theory which can be easily verified by direct measurements with readily available test equipment. The peak current, RMS current and DC current demand of an inverter are the result of complex issues and there is no way to state the values for every inverter without measuring. For one reason, the installation itself affects these values. It is possible to measure them with ordinary test equipment (at least RMS AC and DC is easy, peaks can be measured with a special current transformer and oscilloscope most people won't have at hand). Depending on the target cost allocated and the cleverness of the design engineer, the inverter draws AC components of battery current (aka ripple current). Some inverters draw a peak current 50-60% higher than the DC. This has implications in the selection of battery size as well as voltage drop across the wires. The true RMS battery current can be higher than the DC current by as much as 12% due to the AC component (aka ripple). This can cause a 25% higher temperature rise of the wires and connections than DC calculations would indicate. I grant this isn't a huge difference, but it means you should err toward the next larger wire and not the next smaller wire.

Originally Posted by Auspicious

I agree with your motivation. Your incorrect techno-speak confuses the issue, dilutes your message, and diminishes the credibility of all your posts on any subject.

Really? I will let others decide if I am correct. In this case I think the credibility of all of us is diminished which is unfortunate.

This is what I hope others will takeaway from this "debate" as I am sure there is little disagreement on these points:

Follow the manufacturers installation instructions. Use the recommended wire size and type. If in doubt go one size bigger and never go one size smaller. If you can't use the recommended wire size for any reason abort the installation. Your crew will appreciate you not burning up the boat. Use the fuse size and type recommended. Keep the battery wires as short as possible. Keep the plus and minus wires as close together as possible. Use proper lugs and crimpers (not the hammer pounding type). Make the bolted connections tight and check them regularly to make sure they stay that way. Cover all the positive connections to avoid accidental shorts that can start fires and cause injury. Install a smoke detector in the compartment above the inverter and also one in each living space.

And most important, if you don't have any experience with high current DC wiring, let a professional do the installation. The extremely high currents from batteries in a mulit-kilowatt inverter installation can easily cause serious injury and fires. Just because it's only 12VDC does not make it foolproof.

[sparrowhawk1]

Yay finally someone else that understands that some inverters have the neutral hot. And yes if the case on the inverter is grounded and you hook it up to a house that has the ground and neutral connected it will go poof. If the case is not grounded you have the chance of being that ground. My boat has the ground. and neutral connected at the main breaker I guess this is not standard. It's a Colombia and have a hard time believing that they would wire boats incorrectly. And yes this breaker should blow.....PS. I've known the dual male plug extension cord as a suicide cord but death chord sounds better because you might kill someone besides yourself. PSS. Many of our people are off grid dirt dwellers.

[mitiempo]

Originally Posted by sparrowhawk1

Yay finally someone else that understands that some inverters have the neutral hot. And yes if the case on the inverter is grounded and you hook it up to a house that has the ground and neutral connected it will go poof. If the case is not grounded you have the chance of being that ground. My boat has the ground. and neutral connected at the main breaker I guess this is not standard. It's a Colombia and have a hard time believing that they would wire boats incorrectly. And yes this breaker should blow.....PS. I've known the dual male plug extension cord as a suicide cord but death chord sounds better because you might kill someone besides yourself

If your ground and neutral are connected on the boat it is dangerous. It is also not likely that Columbia wired it this way. I would hire a qualified marine electrician to inspect your wiring - from this evidence your wiring may have other issues as well.

I have not ever seen a marine quality inverter that has a "hot neutral". AC voltage measurement between hot and neutral should be 120 volts, as should the measurement between hot and ground be 120 volts. There should be no appreciable voltage between neutral and ground outputs of an inverter - nor any other AC source.

[sparrowhawk1]

It's connected together through a breaker. I describe it in a previous post. My main is three Breakers controlled by one switch. And it does not look like the breaker panel has been modified in any way. Edit: and just curious why is it mandatory for houses to connect the ground and the neutral where electricity enters the home but on boats it's dangerous. And please do not read wrong connotation into my texting. Edit 2. I've listed 3 videos and if you do a little internet search you will find that some(many?) CHEAP inverters put half of the sine wave on the neutral wire