Generators and Inverters in parallel

[Motofixxer]

OK so those handy little pure sine inverter generators can be parallel to run larger loads. OK great but maybe it's not quite enough so you tie in a pure sine wave DC to AC inverter cuz the in rush current of your compressor is too much for your generators. That would all work right. The parallel generators will match and add the inverter to the load capability right?

 

[checkthisout]

OK so those handy little inverter generators can be parallel to run larger loads. OK great but maybe it's not quite enough so you tie in a pure sine wave inverter cuz the in rush current of your compressor is too much for your generators. That would all work right. The parallel generators will match and add the inverter to the load capability right?

No, because you have no way to ensure the phase from your inverter matches the phase from the generator.

 

[ibedayank]

as far as I know only honda makes a model that you can hook 2 of them togather

 

[checkthisout]

as far as I know only honda makes a model that you can hook 2 of them togather

He's talking about linking an inverter (running off batteries) and a generator.

 

[manwithtools]

I think he is not talking about batteries and inverters.

Honda, Yamaha and a couple others make inverter technology generators that will operate in parallel. I think you can get them up to 2kw each, so 4kw with a pair of them. The best feature of these is very clean power that modern electronics seem to like. They are also very quiet and fuel efficient.

To answer the original posters question, no it would not be good idea to add a third generator to the mix. If you have high inrush loads I'd suggest you get a large generator with excess capacity to handle those instantaneous loads.

 

[rockwithjason]

OK so those handy little inverter generators can be parallel to run larger loads. OK great but maybe it's not quite enough so you tie in a pure sine wave inverter cuz the in rush current of your compressor is too much for your generators. That would all work right. The parallel generators will match and add the inverter to the load capability right?

only if the inverter is able to sync to the generator, otherwise you are setting up a fault in the circuit and possibly damaging equipment.

 

[theoldwizard1]

only if the inverter is able to sync to the generator, ...

I have always wondered how they got 2 inverter generators to sync ...

 

[Pwrgeek]

I've had as many as four Hondas in parallel. There is a specific procedure for starting them that causes the second (or third) to sync with those already running. I tried it with a pure sine inverter (actually a few different ones) and just destroyed the inverters.


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[wyliesdiesels]

OK so those handy little inverter generators can be parallel to run larger loads. OK great but maybe it's not quite enough so you tie in a pure sine wave inverter cuz the in rush current of your compressor is too much for your generators. That would all work right. The parallel generators will match and add the inverter to the load capability right?

What is the HP rating on the compressor?

U do know that motors have in-rush currents of 4x-8x FLC....

U would need a large generator to power that.

 

[ForceFed70]

Link the generators together yes - if they have that technology.

But adding a 3rd power source consisting of a standalone 12VDC to 120VAC inverter is not possible.

 

[theoldwizard1]

I've had as many as four Hondas in parallel. There is a specific procedure for starting them that causes the second (or third) to sync with those already running.

The second (third and fourth) generators must "sense" that there is voltage out there and use what is "on the line" as its reference instead of the internal reference.

I tried it with a pure sine inverter (actually a few different ones) and just destroyed the inverters.

Good to know ! I think that was the OP real question.


FYI : Some Yamaha generators use their starting battery for a temporray "boost"

From the Yamaha website

The Yamaha EF3000iSEB is one of the most technologically advanced inverter generators available. Get that extra “boost” of power to get your power tool or air conditioner started quickly and efficiently thanks to the EF3000iSEB generator from Yamaha. The “B” on EF3000iSEB means it features Yamaha Boost Technology®, which provides additional power when you need it. Perfect for the RV enthusiast, the EF3000iSEB is an ideal source of power for either a fifth wheel or travel trailer. The Boost Control Unit in the generator automatically senses when you need additional boost and uses power from the internal 12-volt battery to produce additional amperage. With the additional 10-second boost, the power is comparable to a conventional 3500-watt (peak) generator.

 

[Chilliwack Murray]

Unless the generators or inverters are designed to be connected together it is only a matter of time before something is damaged. Initially connecting them together requires them to be synchronized (sine waves aligned with each other), if they aren't you will usually have a large surge of current - essentially a short circuit until they come into synchronization.

If you get them all connected and running in sync, without a system to control loading of the engine (kw) and the excitation system (voltage) there is no way to ensure all units are producing their share of the required power. It is possible (likely) that one unit will be driven by the other(s) particularly when dealing with mechanical governors. This will cause the unit to fail in time, alternators are not designed to operate as motors. The greater the reverse power, the sooner it will fail.

Parallel control systems can be very complex (google isochronous load sharing) or as simple as equipment set up to 'droop' as load increases (engine speed and voltage drop as load increases) however for this system to work everything must be carefully adjusted and maintained. So if you want to run them this way, buy something designed to do this - whether inverter or generator.

 

[checkthisout]

.


FYI : Some Yamaha generators use their starting battery for a temporray "boost"

From the Yamaha website

This is the generator I have. It does exactly what they say it does. Nothing ever bogs down or goes dim when using it and things like fridges, washers, air conditioners etc start up.

 

[checkthisout]

Link the generators together yes - if they have that technology.

But adding a 3rd power source consisting of a standalone 12VDC to 120VAC inverter is not possible.

You can do it. You just link the output circuit drivers together in the inverters.

This requires some knowledge of electronics and of course you have to disassemble your inverter to do it.

The little inverter generators that can already by linked in parallel already have signal wire connections so you would only have to mess with your own inverter and not the expensive inverter inside the expensive inverter generator.

Heres a video that gives you an idea of what you have to do.

 

[nehog]

I have always wondered how they got 2 inverter generators to sync ...

Two generators are relatively easy to sync. (Notice I didn't say inverter generators, that is a different kettle of fish...)

You start both generators, measure the phase angle (which because both will not be running at exactly the same speed/frequency) and when they match you connect them together. Once connected together they will remain synced until one fails/stops.

My big diesel generator has a syncing feature using a couple of lights. When the lights go out, you tie 'em together. Not difficult at all. Not trivial to implement however!

 

[checkthisout]

Two generators are relatively easy to sync. (Notice I didn't say inverter generators, that is a different kettle of fish...)

You start both generators, measure the phase angle (which because both will not be running at exactly the same speed/frequency) and when they match you connect them together. Once connected together they will remain synced until one fails/stops.

My big diesel generator has a syncing feature using a couple of lights. When the lights go out, you tie 'em together. Not difficult at all. Not trivial to implement however!

Why would they stay matched?? That would mean they have to maintain perfect engine speeds.

 

[theoldwizard1]

Why would they stay matched?? That would mean they have to maintain perfect engine speeds.

Really BIG flywheel and running at much less than full load ! Still ... I would not do it !

 

[Chilliwack Murray]

Once generators are connected together they are magnetically coupled and it is very difficult for them to come out of sync unless the excitation system fails and they lose the magnetism on the rotor.

Without proper protection and controls however you cannot make the units produce the same amount of power and eventually one will begin to drive the other like a motor. This is particularly bad if one stops producing power (hp) due to an engine failure or loses oil pressure - the other unit(s) will continue to drive it until it disintegrates.

Inverters and generators that are meant to operate this way have a means to sense when they are in sync with each other OR they do not build voltage until they are all connected together. Once connected, as they build voltage at the same time and they will fall into sync. This is called dead field paralleling - crude but more or less reliable. Either of these still require the protection and control above.

 

[manwithtools]

This thread is full of things that can go bad, really, really bad. I think before you follow the advice of folks on youtube tying together UPS's and extrapolate that to inverter generators and other power sources you all need to buy some insurance from that mayhem guy...just saying....

BTW, please have someone video these escapades so others can learn from it later.

 

[HOTFR8]

as far as I know only honda makes a model that you can hook 2 of them togather

He's talking about linking an inverter (running off batteries) and a generator.

The way I read it he wants to connect two inverter generators.

The link to You Tube shows a couple of Yamaha set ups.

 

[manwithtools]

Yes, it's already been established he want's to connect two invertor generators and then some. It's simple to do two, the OP want's to do two inverter generators and one conventional generator. Read his complete post.

It's folly to try and do this. That's why I want video and receipts for all the destroyed equipment.

 

[MikeF2316]

Two generators are relatively easy to sync. (Notice I didn't say inverter generators, that is a different kettle of fish...)

You start both generators, measure the phase angle (which because both will not be running at exactly the same speed/frequency) and when they match you connect them together. Once connected together they will remain synced until one fails/stops.

My big diesel generator has a syncing feature using a couple of lights. When the lights go out, you tie 'em together. Not difficult at all. Not trivial to implement however!

Why would they stay matched?? That would mean they have to maintain perfect engine speeds.

We did this in when I was in university in one of my power courses. The key is the generators have to be synchronous machines. Once it's connected to the line it will act as a motor if it loses its source of rotational energy, assuming that what other power is there is adequate to power it. Think of how many of these generators are connected to the power grid. These connections are what makes those cool cascading power failures possible.

In that lab the machines were 50 hp 3 phase synchronous machines hooked to 50 hp DC machines. We used the DC machines to bring the synchronous machine up to line speed. You have a triple throw switch to connect all 3 phases at once, using a light board. The switch has a bulb across all 3 throws, so when the light is off, the voltage across the switch is 0 and you make the connection. One of the other groups in the lab thought you were supposed to close the switch when the bulbs were on full bright. The snap was the loudest I've ever heard and blue flash lit up the walls inside the lab - fortunately nothing was hurt but the switch. My back was turned, so I only saw the flash as it lit up the walls.

However this is not the principle use to sync inverter generators. Tying outputs together that are not designed for it will let the smoke out.

 

[Motofixxer]

OK to clarify. Yes 2 pure sine inverter generators and a DC pure sine wave inverter. From the research I have done says even the nonlabeled inverter generators can be parallel by just plugging a cord between them and running your load.You may be limited to the 15a breaker unless you connect to a 30a receptacle. Which you would then be limited to the max combined generator output.

The parallel cables just connect to the output side.

From what I gather the sync is in the electronics or something. So it got me thinking maybe the same works with the DC inverter too and it's in the pure sine wave electronics. The power grid is made up of thousands of power stations that all work together.

 

[checkthisout]

Once generators are connected together they are magnetically coupled and it is very difficult for them to come out of sync unless the excitation system fails and they lose the magnetism on the rotor.

Without proper protection and controls however you cannot make the units produce the same amount of power and eventually one will begin to drive the other like a motor. This is particularly bad if one stops producing power (hp) due to an engine failure or loses oil pressure - the other unit(s) will continue to drive it until it disintegrates.

Inverters and generators that are meant to operate this way have a means to sense when they are in sync with each other OR they do not build voltage until they are all connected together. Once connected, as they build voltage at the same time and they will fall into sync. This is called dead field paralleling - crude but more or less reliable. Either of these still require the protection and control above.

Well now that's just interesting as all hell.

So this can be done with 2 run-of-the-mill big box store generators???

 

[checkthisout]

The parallel cables just connect to the output side.

From what I gather the sync is in the electronics or something. So it got me thinking maybe the same works with the DC inverter too and it's in the pure sine wave electronics. The power grid is made up of thousands of power stations that all work together.

It's linking the output drivers in the inverters in the generators together. In other words it's linking up the signal that generates the Herz frequency between the two generators in the same fashion as the electronics geek links the two output drivers from the two off-the-shelf inverters in the video.

 

[nadogail]

I like the question, and I think I could do it at my house; but for most of us I don't think we have a practical solution.

I have 26 photovoltaic (Solar Electric Generation) panels on my roof. They feed a synchronized ABB grid tied inverter that is connected to the electric power grid. The inverter is synchronized to the power lines feeding my house.

When the sun shines brightly the panels make more electricity than I use and the surplus makes my meter run backwards.

When I use more than I make, my meter runs just like everybody else's.

The inverter will not make AC from the panel output if the electric power is out. This a safety feature.

My theory , yet to be confirmed, is that if the power grid should fail I could disconnect my home from the grid and then feed my house from my generator. The solar inverter would then be in parallel with my generator.

The inverter would then synchronize to the generator.

Because I do not own the panels or the inverter, I am not about to endanger my contract by experimentation.

The governor on my generator has been tested under load; from a 1% to 50% load change the frequency momentarily dropped only one half cycle. IMHO that is pretty good for a 13 horse Chonda (Chinese made Honda clone) spinning a 10 KW peak rated, HF alternator.

 

[Pwrgeek]

My theory , yet to be confirmed, is that if the power grid should fail I could disconnect my home from the grid and then feed my house from my generator. The solar inverter would then be in parallel with my generator.

The inverter would then synchronize to the generator.
.

This will work so long as your load is larger than the output of your solar system. As soon as your solar puts out more than your load things will go badly. If you are lucky your generator has reverse power protection on it and everything will shut down. If you aren't lucky then you'll destroy the motor on your generator. The odds of you hurting the inverter are very low. These grid tied inverters have to be tested to UL 1741 which is pretty stringent and results in a fairly robust product.


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[Pwrgeek]

By the way couple things

Paralleling on Honda (and all other inverter generators I'm aware of) is on the ac side of the inverter. The second generator to start senses the presence of voltage on its output and syncs to it. They then share load using a voltage droop control loop.

The easiest way to sync two traditional generators is as follows.

Have the two generators connected together by an open switch in parallel with a rehostat.

Turn the rehostat to maximum resistance

Start one generator
Apply some load to it (this will keep either generator from back feeding/motoring the other one)

Start the other generator

Slowly turn the rehostat resistance down until it gets to zero

Close the switch

All of the above is at your own risk. I have done it for various reasons many times but I have also left expensive equipment smoldering when one of the generators lost its fuel source. Sometimes you take risks when the need is there and you don't have other options.


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[Motofixxer]

So it seems like if the DC inverter had a load on it, then Generator 1 is started and syncs itself to inverter cycles, then Generator 2 is started and it syncs itself to DC inverter and Generator 2. Seems simple enough. It's really only the DC inverter that is the questionable issue here.

As I stated before it seems that from my research any of the small inverter generators can be paralled with multiple by simple running a cord between them. Even when they are not labeled as being parallel capable. Leading me to believe it's more in the electronics than if they are tied to the output drivers.

 

[nadogail]

This will work so long as your load is larger than the output of your solar system. As soon as your solar puts out more than your load things will go badly. If you are lucky your generator has reverse power protection on it and everything will shut down. If you aren't lucky then you'll destroy the motor on your generator. The odds of you hurting the inverter are very low. These grid tied inverters have to be tested to UL 1741 which is pretty stringent and results in a fairly robust product.


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Because my Harbor Freight alternator was built to a price, I will not attempt this possible risky experiment.

 

[Pwrgeek]

So it seems like if the DC inverter had a load on it, then Generator 1 is started and syncs itself to inverter cycles, then Generator 2 is started and it syncs itself to DC inverter and Generator 2. Seems simple enough. It's really only the DC inverter that is the questionable issue here.

As I stated before it seems that from my research any of the small inverter generators can be paralled with multiple by simple running a cord between them. Even when they are not labeled as being parallel capable. Leading me to believe it's more in the electronics than if they are tied to the output drivers.

As I said earlier I tried this with several different brands of pure sine inverters. It resulted in dead inverters. Youtube doesn't always tell the truth. All I can figure for why is that the inverters dont have an appropriate droop equation and are therefore not responding to the presence of the generator. Therefore the generator sees the inverter as a load and reverse drives it (what we would call motoring it if the inverter were a generator). This plays havoc on the output stage of the inverters and blows the output MOSFETS (what I found dead inside the ones I tried it with).

 

[manwithtools]

As I said earlier I tried this with several different brands of pure sine inverters. It resulted in dead inverters. Youtube doesn't always tell the truth. All I can figure for why is that the inverters dont have an appropriate droop equation and are therefore not responding to the presence of the generator. Therefore the generator sees the inverter as a load and reverse drives it (what we would call motoring it if the inverter were a generator). This plays havoc on the output stage of the inverters and blows the output MOSFETS (what I found dead inside the ones I tried it with).

Did you keep your receipts and take videos like I asked

 

[Pwrgeek]

Did it years ago. I ended up blowing about 3 grand worth of equipment. Luckily this was a project for work.


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