Author Topic: Accurate Tools Inverters  (Read 3472 times)

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ChrisOlson

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Accurate Tools Inverters
« on: September 20, 2010, 09:43:20 AM »
The Accurate Tools stackable inverters use the same type of internal circuitry as a cheap $29 400 watt Cobra inverter that you get at Walmart.  That is, if ground ever touches a leg (hot or neutral) the inverter is junk.  The seller of these inverters says you can't hook up the ground at all - he says you should drive a ground rod for the inverter and a separate ground rod for your appliances or loads.  This is not allowed under NEC.  So for any installation that has to meet code, which is all installations in the US, these inverters can only be used for one time ground fault protection.

If your appliance or load ever has a ground fault problem, instead of tripping the breaker like it does on any normal inverter, it burns these inverters out.  For 120 volt applications they provide no ground fault protection at ALL with appliances using two-prong plugs.  You're hanging on an ungrounded "hot" tool, and if you're standing in water or wet grass you'll get knocked on your butt because YOU become the path to ground.

On the 240 volt units, or on 120 volt applications with a three prong plug, and the inverter ground wired to a ground bus in the panel, the inverter will provide ground fault protection only one time.  It'll save your butt at the expense of a blown inverter.

Based on what I've found out after testing my 240 volt unit (now blown), I cannot recommend these inverters to anybody installing them in an off-grid or residential application.
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Volvo farmer

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Re: Accurate Tools Inverters
« Reply #1 on: September 20, 2010, 03:35:18 PM »
Quote from: ChrisOlson

If your appliance or load ever has a ground fault problem, instead of tripping the breaker like it does on any normal inverter, it burns these inverters out.  For 120 volt applications they provide no ground fault protection at ALL with appliances using two-prong plugs.  You're hanging on an ungrounded "hot" tool, and if you're standing in water or wet grass you'll get knocked on your butt because YOU become the path to ground.


I'm curious as to how this could happen. Let's say I have a 12V battery, (not grounded), hooked up to a crappy Accurate Tools inverter (also not grounded) hooked to my circular saw.

Now lets say a wire goes bare and hits the frame of my circular saw and I am standing in a puddle holding the saw.  How does the electricity get out of my body, into the ground and back to the inverter, if the inverter is not grounded?  I thought the hot was only hot in reference to the neutral, not to the ground itself in a small ungrounded system like this.

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rogeriko

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Re: Accurate Tools Inverters
« Reply #2 on: September 20, 2010, 06:02:11 PM »
I work with european 220 volt inverters and you are better of not grounding anything. You can actually hold the output live or neutral obviously only one at a time and not feel a thing because there is no ground return. Power companies use ground return because it means they would have to double up all the cabling in the country to make a return path to the generator. What an inverter does is make an isolation transformer  circuit like used in gardens etc so that you cannot get a shock. I know that any trained electricians will disagree immeadiately because it goes against their "training" but to get a shock off an inverter you have to contact BOTH output leads simultaneously.
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ChrisOlson

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Re: Accurate Tools Inverters
« Reply #3 on: September 20, 2010, 07:14:52 PM »
I know that any trained electricians will disagree immeadiately because it goes against their "training" but to get a shock off an inverter you have to contact BOTH output leads simultaneously.

Ground is reference for any circuit.

When the winding or wire inside Volvo Farmer's circular saw contacts the case both leads are connected, as well as the case.  You're hanging on to both leads thru the case.  The purpose of ground fault protection is for that current to flow from the grounded case back to ground instead of thru you.

The NEC in the US outlines very precise specifications for grounding of electrical services.  Using humans for ground rods is just simply not a good idea.
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frackers

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Re: Accurate Tools Inverters
« Reply #4 on: September 20, 2010, 08:53:20 PM »
Ground is reference for any circuit.

Nope - sorry, this is not correct.

The reference for a circuit can be anything - for example on my sealed Kilowatt power meter clone the 9 volts internal operating voltage that drives all the electronics is referenced to the live 240volt AC line.

Similarly, the 24vAC that drives my irrigation controller valves is referenced to +12vDC to allow the triacs to be driven by a phaseIII current source.

The main reason for using a ground reference to a mains supply is because one of the legs (neutral) is already grounded which provides the return path in the case of a fault to earth - this fault current can then be detected and the circuit tripped.

The whole ground reference propagates through the supply system. Mine is an 11KV 3 phase line going down the road with myself and a neighbour sharing a transformer. Delta in, star connected out with the neutral common to all 3 phases being bonded to ground. This is necessary because any of the 11KV 3 phases could have leakage to ground anywhere in the system which would allow capacitive coupling (and ohmic to a small extent) from the high voltage lines, through the transformer, and into my house.



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ChrisOlson

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Re: Accurate Tools Inverters
« Reply #5 on: September 20, 2010, 10:05:32 PM »
The whole ground reference propagates through the supply system.

Well, yes, you are correct, of course.

I guess my point was that NEC requires an AC source to be referenced to ground.  And the code specifies in detail how that is to be done.  In residential wiring, for measurement purposes, Earth serves as a (reasonably) constant potential reference against which other potentials can be measured.

So suggesting that grounding be not used at all, or worse yet, going by the recommendation of the seller of these Accurate Tools inverters and using multiple ground points to prevent burning out the inverter in the event of a ground fault, is bad.  It doesn't meet code.  If you live back in the woods, you see, with the woman and the kids, and the dogs and me - and you figure getting fried by your appliances is normal because that's what that durned electricity does - nobody probably cares.

But if you live around civilization in a home that probably has insurance on it, and maybe a mortgage - the National Electrical Code was developed to provide for your safety, and those in your home, when using electricity.

My gripe with these inverters is that if you wire the AC ground in the inverter to the AC panel grounds the way it should be done, and you have a ground fault, the inverter is junk.  If you bond the neutral to the ground at the service panel that the inverter is wired to (because there is no internal NG bond), the inverter is junk.

NEC Article 250 and all its subparts outline how electrical services, subpanels and equipment is to be grounded, and there is no way, shape or form that these inverters can be wired to meet NEC.
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Volvo farmer

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Re: Accurate Tools Inverters
« Reply #6 on: September 20, 2010, 10:48:16 PM »
Well, the NEC is one thing. Getting shocked by an ungrounded inverter is quite another.  If you want to hate on the inverter because it cannot be wired to NEC specifications, fine.  However I think you were misleading (probably unintentionally) in your first post about the real danger of getting shocked.

I believe that rogeriko is correct and that I can grab a hold of either lead on an ungrounded inverter like this and stand in a puddle of water in my bare feet without getting shocked.  My opinion is in direct opposition to your first post in this thread which says I will get knocked on my butt.

Do you still stand by your assertion?  I just worry that people will come and read this thread sometime in the future and get the wrong idea about how these inverters work if this isn't clarified and set straight.

Less bark, more wag.

ChrisOlson

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Re: Accurate Tools Inverters
« Reply #7 on: September 20, 2010, 11:07:39 PM »
I believe that rogeriko is correct and that I can grab a hold of either lead on an ungrounded inverter like this and stand in a puddle of water in my bare feet without getting shocked.  My opinion is in direct opposition to your first post in this thread which says I will get knocked on my butt.

I speak from experience here, not theory.  I have a Schumacher 2 kW 120 volt inverter in my farm service truck.  That inverter has built-in GFCI and the external ground on the inverter is wired to the vehicle frame, as per the instructions that came with it.

One day last fall I was using a 3/4" drill, hooked to that inverter, to run a winch on a 72 foot auger to raise it to the bin roof.  The cord on that drill had been bad for a long time with the outer jacket on the cord going into the handle gone and the black and white wires exposed.  While running that auger up one of the wires rubbed thru on a screw in the handle.  I was standing in wet grass at the time and the GFCI tripped on the inverter at the same instant I got layed right out on the ground feeling like somebody had hit me with a 10 lb maul.

The inverter ground insulated from earth by rubber tires on the truck.

So I would suggest that if you don't believe it, wire yourself up to the "hot" on an ungrounded inverter, flip it on, and let us know what happens.  Maybe have a witness standing by that can tell us what happened in case you don't make it.
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ChrisOlson

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Re: Accurate Tools Inverters
« Reply #8 on: September 20, 2010, 11:40:49 PM »
And I'll tell you about another incident that happened to me once.

About nine or ten years ago, when we had single phase utility power, I was loading corn into a semi from a bin.  The auger I was loading the truck with had a 10 hp single phase motor on it and was connected to the panel by a #8 Type SO cord.  The ground was wet and the cord was draped over the auger, had a dip in it where it was draped over one of the rungs on the ladder on the bin, and then on to the panel.

Where that dip was in the cord it was about 4" from the ground.

This was early in the morning about 5:00 AM and it was still dark outside.  Suddenly the night sky to the east was lit up by a huge fireball and then I heard the explosion.  A car had ran off the road on highway 25, 1/2 mile to the east and hit a power pole.  One or more of those high voltage lines evidently slapped the neutral.  The power surge blew our transformer right off the pole and it was dangling by the wires.  Where that #8 cord was drooped down to the ground it arced to ground burned that cord completely in two.

You see enough of these things with electricity and you learn to never take anything for granted when working around it.
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Edit:
I was going to mention that wasn't the only damage.  Every appliance in our house and shop that was plugged in was burned out.  The neutral bus in the main panel in our house was burned completely off - arced to L2 in the panel.  And get this - the 5 hp motor that was driving the horizontal bin auger that comes out under the aeration floor was also running at the time, plugged into the same panel that the 10 hp motor was plugged into.  That 5 hp motor, other than having the cord burned off where it went thru the wire clamp into the junction box on the motor, survived the ordeal unscathed.

The 10 hp motor was instantly fried.  I tried to take it apart later and couldn't turn the shaft with a pipe wrench.  I unbolted the endcaps and couldn't even get the rotor out of it.

We turned the whole works into our insurance company, and they had to pay for it.  They tried to go after the guy who hit the power pole, but it was his fifth DWI and he didn't even have insurance.

Anyway, to make a long story short - anybody that tries to tell me that running ungrounded inverters is the thing to do is a little more adventurous than I am.
« Last Edit: September 21, 2010, 12:35:45 AM by ChrisOlson »

rogeriko

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Re: Accurate Tools Inverters
« Reply #9 on: September 21, 2010, 03:09:26 AM »
chrisolson

you were standing on wet grass means wet tires means electrical circuit to ground. tires have wire inside if they are worn they are not insulation.  electricity needs a circuit to flow around it needs 2 connections.  I regularly work on ungrounded inverters 220v and really you can touch one wire and not feel a thing just like birds sitting on 11kv lines= no circuit.
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Re: Accurate Tools Inverters
« Reply #10 on: September 21, 2010, 03:34:40 AM »
Wires are grounded to keep them from floating to voltages sufficient to cause damage to things, arcing over or punching through insulation, etc.

If you float an inverter's output (or the secondary of a transformer), in the absence of leakage or an internal connection between the output and some part of the output or a separate ground connection, the output voltage relative to ground will be established by the stray capacitance of the two sides of the line and the internal circuitry to something that is grounded.  Typically this will result in something close to "center tap grounded", with a high series impedance which is still low enough that you can get at least a nasty shock and possibly a killing one.

rossw

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Re: Accurate Tools Inverters
« Reply #11 on: September 21, 2010, 03:44:38 AM »
chrisolson

you were standing on wet grass means wet tires means electrical circuit to ground. tires have wire inside if they are worn they are not insulation.  electricity needs a circuit to flow around it needs 2 connections.  I regularly work on ungrounded inverters 220v and really you can touch one wire and not feel a thing just like birds sitting on 11kv lines= no circuit.

I agree with you on principle, but disagree on one important and often unmentioned consideration.

With AC circuits, and especially where there is a relatively long cable run involved, there may be a substantial capacitive coupling. More than enough to get a very unpleasant boot from. If the conductors are close to ground (or grounded stuff like metal ladders, metal roof, tanks, metal conduit etc) then that coupling is increased, so you get a boot from even fairly short runs, or an even bigger boot from moderate runs.

Volvo farmer

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Re: Accurate Tools Inverters
« Reply #12 on: September 21, 2010, 06:04:08 AM »
Interesting! I believe I learned something here.


So do I understand this correctly? .... It might be possible for me to set up an experiment where I purposely minimized any stray capacitance and do my bare feet and puddle of water thing without getting shocked. However, in the real world, with commonly used extension cords and such, this "capacitive coupling" can actually pass enough current to the ground to cause a person who gets hold of one of the inverter output leads to get shocked?

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ghurd

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Re: Accurate Tools Inverters
« Reply #13 on: September 21, 2010, 08:45:09 AM »
It is a cheap chinese inverter intended for use in cars.
They can not be compared to grid power on very many levels.

The ground is a moot point.  Pull the outlet and look at what is connected to the outlet ground terminal.  Nothing?
There is no neutral.  One power terminal is roughly +70V while the other is roughly -70V, then they swap values, and that is referenced to the battery negative.
Grounding the battery negative pretty much makes a dead short to either inverter power terminal, if they should ever meet.

Accurate Tools is pretty much a fly-by-night company.  As such I expect the manual is about nonexistent.
Might read the manual for a Vector VEC049 or VEC051.  They have info regarding grounding these cheap chinese type inverters, mostly they say what NOT to do.
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ChrisOlson

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Re: Accurate Tools Inverters
« Reply #14 on: September 21, 2010, 08:58:41 AM »
you were standing on wet grass means wet tires means electrical circuit to ground. tires have wire inside if they are worn they are not insulation.  electricity needs a circuit to flow around it needs 2 connections.  I regularly work on ungrounded inverters 220v and really you can touch one wire and not feel a thing just like birds sitting on 11kv lines= no circuit.

I don't know.  I know the tires on that truck were brand new Firestone Transforce AT's - not worn out.  The truck was sitting in the gravel driveway between the bins, not in the grass,  The only connection between me and that inverter was the cord, and it is a two wire with a polarized plug.

If you want to play bird sitting on the highline wire that's fine with me.  But I'll tell you this - you don't fly like a bird and sooner or later you're going to end up like squirrel running along wire and coming into contact with pole.  After you get laid out on the ground once, wondering if you're dead or not, you won't do it again.
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ChrisOlson

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Re: Accurate Tools Inverters
« Reply #15 on: September 21, 2010, 09:30:29 AM »
The ground is a moot point.  Pull the outlet and look at what is connected to the outlet ground terminal.  Nothing?
There is no neutral.  One power terminal is roughly +70V while the other is roughly -70V, then they swap values, and that is referenced to the battery negative.
Grounding the battery negative pretty much makes a dead short to either inverter power terminal, if they should ever meet.

What ghurd said.  Dale (fabricator) has had two of these inverters fry, running his well pump.  I was using mine to drive a 240 volt water heater element for my dump load on my system.  I cannot afford to have one fry and subsequently fry my batteries.  After talking to fab about this I decided to test mine two nights ago by hooking it up to a single phase motor that I know has an internal problem because it trips the breaker all the time.  Instantly fried that inverter.  And that told me all I needed to know.  It's not a real inverter - it's cheap unit built the same internally as a $29 Cobra inverter that you plug into your cigarette lighter plug in your car.  It's not suitable for off-grid power in a residence.
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Jon Miller

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Re: Accurate Tools Inverters
« Reply #16 on: January 17, 2011, 06:31:36 PM »
What ghurd said.  Dale (fabricator) has had two of these inverters fry, running his well pump.  I was using mine to drive a 240 volt water heater element for my dump load on my system.  I cannot afford to have one fry and subsequently fry my batteries.  After talking to fab about this I decided to test mine two nights ago by hooking it up to a single phase motor that I know has an internal problem because it trips the breaker all the time.  Instantly fried that inverter.  And that told me all I needed to know.  It's not a real inverter - it's cheap unit built the same internally as a $29 Cobra inverter that you plug into your cigarette lighter plug in your car.  It's not suitable for off-grid power in a residence.
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Agreed.

Its the wrong place to be saving money, keep these invertes for a 120 watt car inverter not a 2.5kW inverter to run a house.  It hurts when you get hit by mains and there is no way I am tuching any more bare wires to prove a point so please less talk about it.

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ChrisOlson

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Re: Accurate Tools Inverters
« Reply #17 on: January 17, 2011, 07:00:40 PM »
Its the wrong place to be saving money, keep these invertes for a 120 watt car inverter not a 2.5kW inverter to run a house.  It hurts when you get hit by mains and there is no way I am tuching any more bare wires to prove a point so please less talk about it.

Well, I should probably mention that the dealer was nice enough to replace my burned out inverter with a warning that you cannot hook the ground to the neutral at any point in the system.

But I can't use that in my house.  So I sold the replacement inverter to a fellow who's using it in a mobile application, for which it was designed in the first place.  It's been working fine for him, the last time I talked to him about it.
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Re: Accurate Tools Inverters
« Reply #18 on: January 18, 2011, 03:50:58 AM »
I tried to connect one of these to the house mains a about a year ago As soon as i plugged it in in buzzed loudly. experimenting with it I found that if i  connected either side of it to ground with the other side not connected to anything it buzzed. connecting an amp meter between either side and ground i got 4 to 5 amps and about 70 volts. These connections were only for a few seconds.  I asked a few electricians about this they said that it couldn't happen as there was know return path. After I posted  the problem here the good people here explained what was happening.
I wouldn't want to get myself in this path.

Several years ago I was installing satellite dishes and received some nasty shocks touching the coax shielding and ground. It measured 70 v. shortly after this the co changed to 3 prong plugs.
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oztules

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Re: Accurate Tools Inverters
« Reply #19 on: January 18, 2011, 04:52:43 PM »
"Several years ago I was installing satellite dishes and received some nasty shocks touching the coax shielding and ground. It measured 70 v. shortly after this the co changed to 3 prong plugs."

I found the same problem with the satellite decoders etc..... and your TV,cd player, dvd player........ it suprised me to find that any 2 pin consumer device would have a roughly 120v charge on any rca plug, aerial plug, chassis and real ground. (240v ac in Australia)

This got me a bit surprised. It was low current high voltage..... enough to make you jump a little on a sloping tin roof.... not good.

It seems to come about because of the modern use of PWM power supplies in these consumer goods.

Part of the input filtering in the rotten things, is to have 2 very small uf value capacitors series  connected from ac rail to ac  rail.

The center point is then connected to chassis ground....... If you open any computer power supply you will find these caps (usually blue) and the circuit board will be grounded to the power supply box.... which will be earthed as the computer is generally with the 3 pin plugs, and so has a proper ground..... so it works fine.

But in a your decoder/dvd/tv etc box with no earth with a 2 pin plug, the chassis is tied to the shield of the plugs, AND the center point of those darned caps.

How this could be allowed to happen is beyond me..... but is common practice...... go check your decoder. If it has 2 pin plug, it will probably have 1/2 mains to actual ground on any shield/chassis plug etc...... unbelievable but true.


I just don't see how this is allowed.


As an example Here is a typical dvd player power supply board. Notice the two blue caps at the bottom left. The yellow ones are across the mains for filtering... but look at the blue ones


You can see where they attatch to the legs of the filter caps.......


Now we can see then directly connected to the ground of the LV side of things..... guess what voltage this puts between chassis ground and the real ground of the house?


So I can't for the life of me see why they ship these dvd players etc with NO earth pin, if they deliberatly kill the isolation of the AC side to the DC side.... the rca plugs are effectively live via the caps..... go figure???

What am I missing here. ....... it is not fun getting a HV zap when your up on a sloping roof.

This is a typical arrangement




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« Last Edit: January 18, 2011, 05:17:24 PM by oztules »
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wooferhound

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Re: Accurate Tools Inverters
« Reply #20 on: January 18, 2011, 06:16:04 PM »
Those blue discs look like Varisters to me, for surge protection.

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Re: Accurate Tools Inverters
« Reply #21 on: January 18, 2011, 08:18:26 PM »
Hmm putting surge to chassis would be more unlikely..... but no, you can see from the board silk screen, they are C17 and C18 (C19 is the filter cap)
The black RT1 (temperature dependent resistor) is what your input surge is using to soften start up surge, and there are no  MOV on this board.

The blue C17 and C19 are marked as 471  (470pf or .47n) @ 1000v and measure the same on a cap meter.



I had a better view but the file was too large by 1.8k.... so thats it.

So Woofer, I don't know what to say. .471n is a small cap, but with 240v 50hz.... it does tickle a bit more than you would think.

..... and no I don't have software in this box to resize, the forum should do it for you.... just another reason to dislike this software..... grrrr



........oztules
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CompuTutor

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Re: Accurate Tools Inverters
« Reply #22 on: February 07, 2011, 02:03:21 AM »
First, if anywone has a blown Accurate-Tools inverter they feel like parting with,
I am seeking one to do a full rework on one as a project, thanks.



Everyone here seems very intellegent about paths and ground references.
But everyone seems to expect inverters to be common neutral devices or they are bad.

When we look at our push-pull outputs on our stereo's, we don't get all riled up when the negative speaker lead swings above and below the ground reference chosen for It's design as much as the positive speaker lead does.

We accept this as the only practical way to produce that much output efficiently. The negative speaker lead may be at -60V, while the positive speaker lead would inversly be at +60V same time. This of course yields the 120V swing needed to meet the desired overall output.

Just think of a standard full wave bridge rectifier layout, and replace the diodes with output transitors and you get the picture.

Same is true in the car, the days of single-ended amplifier output stereos that have the car chassis as reference for the speakers is just a dusty memory now as another example.

None of this is news, I'm sure you all know this, but most inverters are no more than this exact push-pull quasi-bridge style of four seperate output sections. Two of them pulling one output lead to either the positive or negative power bus's available from the switch-mode  power supply section of the inverter, the other do doing the same for the other output lead.

The only difference is we see the standard duplex outlet on those two output leads instead of a matched pair of outputs like on the stereo's speaker jacks have and we EXPECT it to be something else automaticly...

And, as many have also noted here,
of course there is no connection to the ground pin of that duplex outlet, that would be product-suicide

The solution for some is to actually ground the "Neutral" lead as defined, and float the battery's negative lead instead. In all systems there are always references to a common of some form, and others that must be treated with respect. Choosing where to define the common/neutral/ground/earth reference here is what seems to be overlooked on dry land.

And yes Chris, this is in no way NEC approvable, nor is any of the zillion marine vessals out there wired this way either though...

These can be used as safely referenced to (earth) ground (like in the marine industry) as long as you respect that BOTH of the inverters output leads swing both above and below the "Other" reference all to commonly referred to, the battery's negative lead...

Put a darned duplex outlet on it, and people forget it is just a push-pull amplifier that also operates into the saturation region of the output transistor's operating curve. No different.

Frackers indicated it best, that what is chosen as earth reference in power systems may not be what you expect, and for both good and practical reasons.

As long as your battery bank can float electrically, and your charger is isolated as in solar cells, or decoupled by a transformer in the case of chargers, then your fine. And yes, that means that the battery's negative lead to the inverter becomes referenced to one half of the inverter's rated output voltage like so many here have measured on their meters and posted about.

I also assume that people here doing wind power are making their equipment using double-insulated practices to prevent electrolysis to exposed common metal components, so they are viable to float too.

But if you are hell-bent to be safe, you can use a floating ground switch-mode charger from the marine industry and keep your solar and wind tied to ground too...

Putting a large 8D marine deep cycle battery in with a floating ground charger is just old hat in the marine world,
yet on land people strive so strong to seek a fully grounded system. Something has to give, or you have to shell out for inverters that don't save money by tying the supply rails to the output rails.

And for the record, inverters DO NOT have to have their input stages tied to any reference AT ALL in the output stages. Ask any toroid power transformer... But it is true most lesser manufacturers (Like the Sun/ATSIU/AccurateTools units) save a few bucks and a few components by doing this.

The microprocessor controlled aspect of this ATSIU unit is (AccurateTools is most likely a reseller with an authorized label to put over the real label I suspect...) the only reason I have any interest in it. With a little rework to break the primary from the secondary sections from referencing each other causing this NEC deal-breaking issue, and a phase reversal option to run a second bank out of phase to feed standard poly-phase breaker panels properly, and they may be worth a penny or so...

I hope I can land one of these burned out units, two of the people here have had their's replaced already, so I'm calling the eBay guy tomorrow to ask what he does with the dead ducks.

You will see a full dissection and review here when I get one,
as this is the Accurate Tools inverter review thread.

I'l probaby get flamed for the concept of floating the battery bank instead, but remember this post if you ever work on a marine installation please.
« Last Edit: February 07, 2011, 03:28:19 AM by CompuTutor »

CompuTutor

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Re: Accurate Tools Inverters
« Reply #23 on: February 07, 2011, 02:23:07 AM »
Hmm putting surge to chassis would be more unlikely.....
The blue C17 and C19 are marked as 471  (470pf or .47n) @ 1000v and measure the same on a cap meter.

You have that right, what is not apparant from the markings is these are made to be poor-man's spark gaps, and capacitors, both in one.

That very low value relates to the decoupling of RF frequencies to chassis, and shunting across polesthe RF  picked up by wire acting as an antenna.
 
Metal Oxide Varistors (MOV's for others) are often used for their abrupt non-linear resistance change following protective devices like fuses, fusistors, fusible links, and narrowed (expendable trace) printed circuit traces intended to be sacrificial in nature.

But they cost more than cheap caps made with sacrificial dialectric material that can serve double-duty as a spark gap to clamp incoming power line transient spikes. Hence the blue indicator color, probably due to industry getting used to blue MOV's I would hazard a guess...
« Last Edit: February 07, 2011, 03:38:26 AM by CompuTutor »

CompuTutor

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Re: Accurate Tools Inverters
« Reply #24 on: February 07, 2011, 03:31:49 AM »
my sealed Kilowatt power meter clone the 9 volts internal operating voltage that drives all the electronics is referenced to the live 240volt AC line


I've done several modifications on the original kill-a-watt units, like remote RF-read, etc.
what is the brand of the clone you've found please ?

Maybe a model number or something I can Google down perhaps ?

Thanks

CompuTutor

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Re: Accurate Tools Inverters
« Reply #25 on: February 07, 2011, 03:40:27 AM »
Are there those here that have more than one of these networked ?
Does the second one actually stay powered own until needed ?

Any other info (other than they are junk) would be welcome.

joestue

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Re: Accurate Tools Inverters
« Reply #26 on: February 07, 2011, 07:47:59 PM »
Hmm putting surge to chassis would be more unlikely.....
The blue C17 and C19 are marked as 471  (470pf or .47n) @ 1000v and measure the same on a cap meter.

You have that right, what is not apparant from the markings is these are made to be poor-man's spark gaps, and capacitors, both in one.

That very low value relates to the decoupling of RF frequencies to chassis, and shunting across polesthe RF  picked up by wire acting as an antenna.
 
Metal Oxide Varistors (MOV's for others) are often used for their abrupt non-linear resistance change following protective devices like fuses, fusistors, fusible links, and narrowed (expendable trace) printed circuit traces intended to be sacrificial in nature.

But they cost more than cheap caps made with sacrificial dialectric material that can serve double-duty as a spark gap to clamp incoming power line transient spikes. Hence the blue indicator color, probably due to industry getting used to blue MOV's I would hazard a guess...


nope... none of the above.

those are 'Y' caps
they are specifically designed to never fail shorted, as this would be a shock hazard.
although they are typically rated to 660v or 1000v, it will take at least 2.5 times that to puch through the layers, and even then it will happen slowly.
those high density caps across the line are 'X' caps, they are cheaper and much higher density than the y caps.
most of them are still self healing, and they can still take about 2 times rated voltage momentarily.

you can remove the y caps or replace them with 4.7 or 10nf caps if its a shock hazard, at the risk of emi leaking into other stuff.
EDIT: 60hz across a .47 nf cap is like 5 megaohms.. you sure it wasn't something else?

good luck with breaking the typically dc linked feed back loop of those cheap inverters.
one reason they tie the dc-dc converter's grounds together is to save $1 on the feed back loop compensation required for an optical isolator.
« Last Edit: February 07, 2011, 07:53:10 PM by joestue »
My wife says I'm not just a different colored rubik's cube, i am a rubik's knot in a cage.

CompuTutor

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Re: Accurate Tools Inverters
« Reply #27 on: February 08, 2011, 03:13:40 AM »
Wow, absolutely correct, I downloaded that pic to my desktop
to enlarge it and see those markings clearer.

Thanks for catching that one.

oztules

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Re: Accurate Tools Inverters
« Reply #28 on: February 08, 2011, 03:40:05 AM »
"EDIT: 60hz across a .47 nf cap is like 5 megaohms.. you sure it wasn't something else?"

I'm reasonably sure.......

Now think about this, a 2 dvd players, a video player, a free to air satellite box, a paid to air satellite box,  the TV and that was on 1 power point/block....all chassis connected together via rca connectors and aerial connectors.... and all above ground

They all run in phase and add to each others capacitance.. so  about 3n to each rail...  also 240vac rms..(340vac peak). not 110v.

It is still a  high impedance but measured out to about 1.2ma.   A bench test reveals roughly the same  results with a 3n3 cap on @340vAC peak (240vac rms)
 mains plug into ac ma meter.
In hot humid conditions (moist skin), on a steep iron roof........... this gets your attention when you grab the LNB coupling and the aerial frame at the same time.


Thinking about it, the neutral rail is earth anyway, so when you grab the aerial, I short out the neutral rail cap/s with me, and I then see the 340v peak  through the active connected  capacitor... my impedance in this case will be quite low (sweat and fear of heights perhaps)......




..............oztules
edit fixed up typing
« Last Edit: February 08, 2011, 03:57:13 AM by oztules »
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Madscientist267

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Re: Accurate Tools Inverters
« Reply #29 on: February 08, 2011, 05:43:42 PM »
CT -

Quote
probaby get flamed for the concept of floating the battery bank instead

Naa, but you have to keep in mind that a 120/0/120 system isn't 'compatible' with a 60/0/60 system, intrinsically.

You've got your work cut out for you if you're going to make these things NEC 'approvable'.

And even if you free up the pseudo-ground so that you can tie 'neutral' to it, what about the other phase? Are you going to drive two of them out-of-phase/in-tandem for 120/0/120 operation with a true ground?

Don't get me wrong, I'm not exactly knocking the concepts, but it seems like a lot of work for little return... ?

And why do you need a fried one? You just have to 'fix' it to prove you're not crazy anyway. These things are going for like 100 bucks on ebay based on a link I saw somewhere around here not long ago. If you're convinced it's a relatively easy task, scoop up a couple of 'em and tie them together.

One thing is for sure, you come up with a cheap and easy solution to convert them over to a groundable set capable of being wired as 2 phase 120/0/120 to the main breaker of a distribution panel, you'll get the attention of a whole lot of individuals on here, no doubt.

Steve
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How much magic smoke it contains does !

CompuTutor

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Re: Accurate Tools Inverters
« Reply #30 on: February 09, 2011, 05:54:26 AM »
Quote
probaby get flamed for the concept of floating the battery bank instead

Naa, but you have to keep in mind that a 120/0/120 system isn't 'compatible' with a 60/0/60 system, intrinsically.

the 60-0-60 was just what it looks like if you choose the negative battery lead as the metered reference,
they are still 0-120 units if you loose that reference point and use the neutral out instead,
so henceforth when driven with a phase reversal interface box they are capable of being 120-0-120 networked.

What would be the second master on the second (out of) phase L2 would be set to slave instead,
and the "Turn on" signal mimicked to that first unit of th second phase to keep it on.

Again, this seems plausable, but it truely depands on how the master is communicating with It's slaves,
but I have also read on the sites I found these on they can be stacked up to ten, so wow.

At one a month, on the second month you have a basic 2500 watt starter kit,
and each sucessive pair of months and additional 2500 watts to the whole deal.

What I dare ask is wrong with that? in twenty months you would have amassed a dual phase 25KW network,
and if each unit is tied through It's own breaker to the panel buss, one unit can fail safely
without taking out the others or leaving you 100% down and in the dark.


You've got your work cut out for you if you're going to make these things NEC 'approvable'.

Not my intention, but the end product when modified would sure be a whole lot safer,
and nearer to what those rules require for a safe installation for sure, right ?


And even if you free up the pseudo-ground so that you can tie 'neutral' to it, what about the other phase?
Are you going to drive two of them out-of-phase/in-tandem for 120/0/120 operation with a true ground?

Plainly put, yes
They already have most of the required implementation in place is my belief, but I won't know until I tear one down.
They have the ability for one unit be master, and use both that master's clock and phase as reference.
And if what I read is (somewhere) correct, the ability to keep the additional units powered down until needed.

an external interface box at the first master would be able to reference the clock and It's phase
to be phase-reversed for the second bank to use, but again, I need to see what is in place first.


Don't get me wrong, I'm not exactly knocking the concepts, but it seems like a lot of work for little return... ?

Maybe I'm just being to optimistic on this concept, who knows...


And why do you need a fried one? You just have to 'fix' it to prove you're not crazy anyway.

Heheh, it wouldn't be the first time a thought like that was the starting point concerning me,
but what is just as amusing to me is the face after I have done what was thought improbable.
I want a blown one to track down the amount of damage sustained, and because it would be free.
Minus my paying for the shipping to me that is of course...


These things are going for like 100 bucks on ebay based on a link I saw somewhere around here not long ago.

The reserve for the eBay guy is currently between $200 And $239.99, I haven't watched them enough to pin the exact figure down yet. If you come across that link for $100 bucks sir, I'll buy one a month until I have all four needed for a test bed !


If you're convinced it's a relatively easy task, scoop up a couple of 'em and tie them together.

One thing is for sure, you come up with a cheap and easy solution to convert them over to a groundable set capable of being wired as 2 phase 120/0/120 to the main breaker of a distribution panel, you'll get the attention of a whole lot of individuals on here, no doubt.

I'm 51, and I can say with clarity that nothing is as easy as it seems, especially electronics rework.

I will share all at every step, but this is just a retired tech's project for me to do, no more.

Thanks for your questions, I hope I answer more when I get my hands on one of these.
This week is kind of in and out mostly, I hope to have a few (full) days home next week
to havel Mr eBay return a call about getting one or more blown units from him.

CompuTutor

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Re: Accurate Tools Inverters
« Reply #31 on: February 09, 2011, 08:07:24 AM »
I did find one for about $100 here:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=220650523562

Even though it is just under 1/2 the price, it is only 1/10 the output wattage (250 Watts).

A plus is that they sense existing phase and frequency, so they are grid-tie applicable,
and they are a pure-sinewave output style of unit.

They are also selectable for 110 and 220 use,
have a wide voltage range for each of the three offereings (12V=10.8V~30V,  24V=14V~28V, 48V=22V~60V).
and sync to a much lower frequency than most brands which is good if you are augmenting a generator
that tends to dip greatly in RPM due to sudden heavy loads (46Hz~65Hz).

Ooops, I sound that factory shill someone accused me of being again, lol...

Of the two in China making these (Sun/ATSIU), these are the Sun ones:

http://www.chinesegrid.com/Solar-Grid-Tie-Inverter/sun-250g_SUN-250G433.html

I've been concentrating on the eBay seller "dmssgs",
but there are another three sellers: "chargerangel", "chargerdeal", and "gear_fantasy" ("Green Life Green Future")

Did you mean these by chance ?
« Last Edit: February 09, 2011, 08:49:21 AM by CompuTutor »

ghurd

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Re: Accurate Tools Inverters
« Reply #32 on: February 09, 2011, 09:59:27 AM »
"I did find one for..."
Completely different animal.
It would be comparing apples to porcupines.

Some of your assumptions based on the data they provide are erroneous.
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