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V-0-V Generator?

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One can of cause open up the alternator and find and common the two 0V legs on the V-O-V winding (provided they are not connected directly on the alternator's casing internally).

Not sure if it will be accessible without loosening some winding.

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Hey All

I have a Ryobi RG-2000i inverter generator that I wired into the db, it was working well to keep the lights on, internet up and the beers cold but then I noticed that my LED motion sensor light was dimly lit even when it wasn't activated so I did some tests and found live between neutral and earth. I immediately shut everything down, sat in the dark mumbling to myself about the state of the country 😂 A quick google search later and I found this whole story of V-0-V generators and safely wiring them to a db.

I would like to modify the generator so that it is no longer V-0-V but at this stage being an inverter type, I don't know if it's even possible. Everything is compact, with only a small access panel so I don't see any exposed alternator contacts like the picture floating around shows. If needs be I'll strip the whole thing down to pieces but I'm not looking forward to that.

There is however an exposed an earth busbar on the side of the motor. My thinking is that one of them may be the centre tap? Disconnect it, insulate the ring terminal, wire a neutral from the inverter output to the earth busbar and done, or is that a bit too optimistic?

I just need to find the centre tap. From left to right 1, 2, 3, 4.

1. Unknown earth, heat shielded, disappears under the motor - possible candidate for centre tap?

2. Wired to the ignition coil. You can stay.

3. Unknown earth, disappears into a plastic box - possible candidate for centre tap?

4. Yellow/Green, wired the the inverter chassis, gnd terminal, plug gnd, and plug plate. You can stay.

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Am I on the right track here?

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Ok, so it turns out I was completely off the mark. The schematic is from another ryobi inverter generator that looks to be very similar internally. If I am correct in my assumption that a "centre tap" would be where the green arrow is. Then the generator doesn't appear to be centre tapped according to the schematic, I also confirmed this by meter readings of 5.5Ω across the windings, but infinity between any winding and earth. So I should rather be looking at the inverter. I believe this is called a floating neutral on the inverter? Now to figure out if the neutral can be bound to earth without letting the magic smoke out...

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5 minutes ago, DrewZA said:

Ok, so it turns out I was completely off the mark. The schematic is from another ryobi inverter generator that looks to be very similar internally. If I am correct in my assumption that a "centre tap" would be where the green arrow is. Then the generator doesn't appear to be centre tapped according to the schematic, I also confirmed this by meter readings of 5.5Ω across the windings, but infinity between any winding and earth. So I should rather be looking at the inverter. I believe this is called a floating neutral on the inverter? Now to figure out if the neutral can be bound to earth without letting the magic smoke out...

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With an inverter generator, the "generator" part is actually an alternator - so there is no concept of center-tapped. It is the same as having an inverter connected to a battery, except in this case the battery is the alternator. You need to apply the same rules as for an inverter that you connect to the DB.

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Thanks @P1000. So in order for this to work properly I'm going to have to bond the neutral and earth on the output, but reading up and I'm seeing mentions that split phase inverters might not like having the Neutral and Earth bonded. I'm assuming this inverter is split phase, because I'm getting 120V N-E and 120V L-E.

I found this suggestion to test it before making a hard connection so going to give this a try.

"You might try with a resistance making a connection between Neutral and Earth, for example with an incandescent light bulb. If you measure no current, and if the voltage difference between Neutral and Earth disappears, then I assume you can connect Neutral to Earth without provoking a short circuit."

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6 minutes ago, DrewZA said:

I found this suggestion to test it before making a hard connection so going to give this a try.

"You might try with a resistance making a connection between Neutral and Earth, for example with an incandescent light bulb. If you measure no current, and if the voltage difference between Neutral and Earth disappears, then I assume you can connect Neutral to Earth without provoking a short circuit."

Yup. Measuring 120V on each of the legs does not mean it is split phase, it is most likely just the output filter causing that measurement.

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I tested with a 40w light bulb and the voltage across N-E dropped to around 15V, I proceeded to make a hard connection and it's looking good. N-E=0V L-E=230V L-N=230V.

Just a question regarding grounding. Am I correct in thinking that with the neutral/ground bond in place, if the generator were not connected to a ground spike, there would be potential between the chassis of the generator and terra firma, essentially making the ground points on the generator "live"?

 

 

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Well, here is an idea. Wire a 230V incandescent lamp, or something around that wattage, between neutral and earth. If the lamp actually glows dimly, and you can measure 115V across it, then you have V-0-V setup and you can't bond it. If the lamp fails to glow and you read zero volts across it, then the floating you see is a result of a filter or something else that creates a voltage divider.

Basically, the trick is to bond neutral and earth through something with a bit of resistance, that can also dissipate the power should there be any. That way, if it is indeed a V-0-V setup, you're not shorting out half of it.

Edit: Oh wait... I see it's already been suggested above 🙂

 

Edited by plonkster

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3 minutes ago, DrewZA said:

Just a question regarding grounding. Am I correct in thinking that with the neutral/ground bond in place, if the generator were not connected to a ground spike, there would be potential between the chassis of the generator and terra firma, essentially making the ground points on the generator "live"?

You should tie the earth of the generator to the earth of the rest of your installation. That will essentially tie the earth of the generator to the earth spike on your property (if you have TN-C-S) or to the earth at the transformer (if you have TN-S).

So if you do this, then no, the generator itself will not have a different potential to earth.

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2 minutes ago, plonkster said:

You should tie the earth of the generator to the earth of the rest of your installation. That will essentially tie the earth of the generator to the earth spike on your property (if you have TN-C-S) or to the earth at the transformer (if you have TN-S).

So if you do this, then no, the generator itself will not have a different potential to earth.

Perfect, thank you!

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Yes, you can make things work, but I don't like this at all.

A V0V generator is a portable generator that is supposed to be used for double insulated handtools without earth leakage protection.

It is considered safer because only half voltage is available to shock you in an earth fault and its considered a temporary risk.

What you consider Neutral isn't neutral, but rather Live number 2.

So you get things working, what's the problem?

In standard house wiring the convention is that the neutral wire is at ground potential and we switch the live wire, using a V0V supply will mean all appliances are live even if switched off at the wall.

People are used to an appliance that is switched off being dead.

The MCB's in your DB box that should trip before that fire starts are all on the live wiring. Now a neutral to earth fault will pump away.

Your earth leakage protection may work or may not, depending on a few things.

There are no legal circumstances that a V0V generator can be hooked up to a fixed installation, with good reason.

You need a proper standby generator.

 

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1 hour ago, phil.g00 said:

Yes, you can make things work, but I don't like this at all.

A V0V generator is a portable generator that is supposed to be used for double insulated handtools without earth leakage protection.

It is considered safer because only half voltage is available to shock you in an earth fault and its considered a temporary risk.

What you consider Neutral isn't neutral, but rather Live number 2.

So you get things working, what's the problem?

In standard house wiring the convention is that the neutral wire is at ground potential and we switch the live wire, using a V0V supply will mean all appliances are live even if switched off at the wall.

People are used to an appliance that is switched off being dead.

The MCB's in your DB box that should trip before that fire starts are all on the live wiring. Now a neutral to earth fault will pump away.

Your earth leakage protection may work or may not, depending on a few things.

There are no legal circumstances that a V0V generator can be hooked up to a fixed installation, with good reason.

You need a proper standby generator.

 

With the neutral bonded to earth at the inverter output, it is no longer V-0-V...

N-E=0V
L-E=230V
L-N=230V

Please advise how it will differ from a standby genny @phil.g00?

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13 hours ago, phil.g00 said:

Yes, you can make things work, but I don't like this at all.

A V0V generator is a portable generator that is supposed to be used for double insulated handtools without earth leakage protection.

 

I do not think that he has a V0V generator.

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14 hours ago, DrewZA said:

With the neutral bonded to earth at the inverter output, it is no longer V-0-V...

N-E=0V
L-E=230V
L-N=230V

Please advise how it will differ from a standby genny @phil.g00?

If you can physically move the centre tap earth to the  to the neutral leg, it is no longer a V0V generator.

But bonded means bonded, a hard-wired direct connection. That is what a standby generator has.

What you seem to be doing is taking a V0V generator with a floating earth and giving it a high resistance earth reference through a light bulb.

Then you are going substitute this neutral for the incoming properly earthed grid neutral.

Nevermind, that a bulb can blow and that's a bad idea.

This will limit the available earth fault current, so your MCB's wont trip for an earth fault, and it is doubtful that your earth leakage will work.

So the difference between this set up and a standby generator, is you could burn your house down and shock people.

 

 

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9 minutes ago, phil.g00 said:

If you can physically move the centre tap earth to the  to the neutral leg, it is no longer a V0V generator.

But bonded means bonded, a hard-wired direct connection. That is what a standby generator has.

What you seem to be doing is taking a V0V generator with a floating earth and giving it a high resistance earth reference through a light bulb.

Then you are going substitute this neutral for the incoming properly earthed grid neutral.

Nevermind, that a bulb can blow and that's a bad idea.

This will limit the available earth fault current, so your MCB's wont trip for an earth fault, and it is doubtful that your earth leakage will work.

So the difference between this set up and a standby generator, is you could burn your house down and shock people.

 

 

I am confused? That is not what he is doing. He has an inverter generator, he is not moving the center tap, there is none. He just used the bulb for testing, and bonded neutral to earth after testing - direct connection. I believe it only seemed to be a V0V generator due to the output filter, a floating ground and the measurements he took.

Edited by P1000

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9 minutes ago, phil.g00 said:

What you seem to be doing is taking a V0V generator with a floating earth and giving it a high resistance earth reference through a light bulb.

I don't think the generator in question is V-0-V. I think it was unbonded, but it had some kind of filter on it that causes the voltage to settle in the usual manner about halfway on either side.

The lamp was a way to test. If it was an actual V-0-V generator, it would be able to push significant current on one of the "115V legs" and the lamp should light up dimly. Instead the voltage pulled right down, indicating that it is not a V-0-V generator.

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Is easy enough to find out.

But, we have to be clear about where the measurements are taken.

I doubt it is floating by design, V0V is a safety precaution of itself, when used properly.

Under no load:

L to the gen chassis = what voltage?

N to the gen chassis = what voltage?

Gen chassis to main system earth = what voltage?

 

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20 minutes ago, phil.g00 said:

Is easy enough to find out.

But, we have to be clear about where the measurements are taken.

I doubt it is floating by design, V0V is a safety precaution of itself, when used properly.

Under no load:

L to the gen chassis = what voltage?

N to the gen chassis = what voltage?

Gen chassis to main system earth = what voltage?

 

He has already taken those measurements and others. It is not V0V. It is an inverter generator.

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33 minutes ago, P1000 said:

It is an inverter generator

True, but you do get V-0-V inverters too, and I believe many inverter-generators are V-0-V. The Honda suitcase ones for example, they are V-0-V, right?

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See this for example. They got the Generac brand specifically because it allows the right kind of bonding. From 9:00 onwards if you're in a hurry. Of course this is an American video, so TN bonding bonds the middle, but the basic principle is still there, you can make the bond as required.

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8 minutes ago, plonkster said:

True, but you do get V-0-V inverters too, and I believe many inverter-generators are V-0-V. The Honda suitcase ones for example, they are V-0-V, right?

Fair enough, but we tested that. I did not know V-0-V inverter-generators are common, since it adds a little complexity.

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