Generator and ac couple ideal

gww1 · December 2014

I have a gvfx3648 outback inverter and a box store generator. The grid tie inverters are not recomended for generator use though some get the inverter generators to work well with them. I have never tried my "cheep" generator to the inverter so it might be possible that the inverter charger would work with it. I have no other charger that will work on 48 volts.

Is it worth investigating trying to ac couple my cheep generator to the output of my inverter to try and acomplish the same thing. I know I could power my critical loads with just the generator but would this posibly put the excess back to the batteries. Is this even worth looking at or will the dirty power on output cause the same droping of the inverter as it would if hooked to the imput? IE holding voltage and meeting hrz requirements.

Is this a crazy ideal?
Thanks
gww

Cariboocoot · December 2014

Re: Generator and ac couple ideal

The main problem with using non-inverter-generators on grid-tie inverters is that the quality of the power fluctuates outside of acceptable parameters which causes the inverter to drop the gen. So you get "qualified power" and it connects, the load then shift the gen's RPM and so frequency and Voltage, the power is no longer acceptable, the inverter disconnects from the gen. Over and over. Pretty useless connection, eh?

But you can change parameters for what is qualified power on an Outback. Possibly (but not certainly) enough that it will accept the wandering power of a standard gen. Much depends on how well regulated the generator is and how heavy the loads are/their effect on the gen output.

You don't connect the gen to the GVFX AC OUT, btw, but to the AC IN. Make sure SELL is off too, as you don't want the inverter trying to back-feed the generator. You may also want to enable HBX mode.

I believe Blackcherry04 has done a lot of work in this area.

BB. · December 2014

Re: Generator and ac couple ideal

Don't do it (AC coupling or connecting both the genset and AC inverter outputs together)... You can damage either or both the inverter and/or the genset.

In the best of cases, if you connect the genset to the AC input of the hybrid inverter-charger (as would be done nomrally), the Grid Tied function will probably not work. The inverter "qualifies" the frequency and the voltage for ~5 minutes (+/- 0.5 Hz). Standard gensets usually cannot hold the frequency that accurately. Inverter-Gensets can hold the frequency that accurately, but feeding back energy from the hybrid inverter (if the excess solar energy has no place to go) will, at the very least, cause the genset AC Voltage to go out of regulation, and could cause damage too.

If you set up the Outback for generator support mode--That is the way to use it with an inverter-generator.

However, one question I have, is can the gvfx inverter family do generator support? Or is its frequency specification too tight for use with a standard genset? Hopefully somebody here has the answer.

-Bill

Cariboocoot · December 2014

Re: Generator and ac couple ideal

Bill;

GVFX is a hybrid grid-tie inverter and can do gen support (although "not supported" apparently because Outback wasn't satisfied with how well it worked).

You can put a gen on AC IN as I described. You don't put it on AC OUT.

BB. · December 2014

Re: Generator and ac couple ideal

Marc,

One question I had was the AC input's ability to sync to the genset. I thought it was set to a tight frequency tolerance (0.5 Hz) and non-inverter generators obviously cannot usually hold that tight of frequency tolerance.

I know they have a south American version that has much loser frequency tolerance, but I was not sure if the US version AC input frequency could be adjusted with a mate or not.

-Bill

gww1 · December 2014

Re: Generator and ac couple ideal

Thanks
I know mtdoc and Blackcherry have done gen support with my inverter. Both have vidios on utube. I know out back can be ac coupled with prue grid tie inverters. Outback sends the voltage and frequency to the pure gridtie inverter to activate it and then the pure gridtie inverter sends power back to the batteries through the ouback output.

I am grid tied and don't sell but don't really need the generator but I have one and would like to find a way to charge my battery with it. I don't need it so am reluctant to spend money on it. I also wan't to experment some day with wood gas but may destroy the generator doing so and don't want to spend alot and won't experment with wood gas till I can figure how to use the generator for charging.

I wanted to know the pitfalls and figure the biggest one is that the outback qualifies the pure grid tie but does not qualify a generator.

I read some one who mentioned them wanting to do this in passing and thought it sounded interesting. Thanks for you responces, sounds like I spinning my wheels.
Thanks
gww

Cariboocoot · December 2014

Re: Generator and ac couple ideal

The input frequency range for the North American '60 Hz' GVFX is 55 to 65 Hz. I just checked.

gww1 · December 2014

Re: Generator and ac couple ideal

bill
The manual say the adjustments don't work on the gridtie outback. Thus the reason people use inverter gens.
gww

BB. · December 2014

Re: Generator and ac couple ideal

You really do not want to Grid Tie back to a genset--They have no place to put the "excess power" (if solar power > load, then excess energy has to feed back to genset). This works well on the utility grid because the other utility loads can "sink" this excess power.

A genset cannot and I would usually expect the genset to go out of AC regulation (voltage/frequency) and drop the GT qualification.

If you use Generator Support--The Outback will use all of the AC power of the genset (up to a programmed limit) to support the loads and recharge the battery bank. And if the generator cannot supply more power, then the Outback will take power from the battery bank to support the "extra" AC load current.

That is really what you want to happen anyway. There is no reason to AC couple or setup for Grid Tied feedback to the genset.

If the Outback will sync from 55 to 65 Hz with the genset and do generator support--Then that is great. I know that people are doing it--But maybe it was Outback "disavowing" the generator support function that has me confused. It sounded like only the South American version of the Outback would work with a genset and do "generator support" (at least on paper).

-Bill

Cariboocoot · December 2014

Re: Generator and ac couple ideal

Yes; do not AC couple a gen to the AC OUT.

If you want to use the gen when the utility is down install a transfer switch on the AC IN side.

gww1 · December 2014

Re: Generator and ac couple ideal

Ok, Thanks guys.
gww

gww1 · December 2014

Re: Generator and ac couple ideal

bill
I would make one point.

Those who ac couple with outback and gridtie inverters but have no grid, have to worry about overcharging the battery. The incoming solar to the battery is usually shut off first due to battery voltage. The danger is not being able to stop the pure gridtie from producing too much and most use divertion load or have some way to get the pure grid tie to not except the imput ac from the outback.

I only know this from reading not from experiance.

This is why I tought it might work altough would have to be monitored contantly.

I don't mind not trying it due to danger of damage. It just hit me that it might be a way not to have to buy a battery charger.

Thanks for you help
I believe you
gww

BB. · December 2014

Re: Generator and ac couple ideal

gww,

Maybe I am confused... I thought you asked to connect a genset to the output of the Outback inverter (traditional definition of AC coupling).

A typical genset is not designed to sync with other AC power sources... So, just connecting an Off Grid inverter output to a genset output can produce lots of smoke and tears (damaged hardware costs).

A GT Inverter is designed to "follow" the AC voltage. And if you connect a GT inverter to an off grid inverter output (should be a TSW type inverter), the GT inverter will sync with the Off Grid inverter's output and either help with the AC loads, or even is capable of feeding power backwards through the OG Inverter and recharge the battery bank. Of course, then you need either the OG inverter to control the battery bank's State of Charge (typical method is to shift the frequency outside of +/- 0.5 Hz and "knock" the GT inverter off line--Although SMA does have the capability to vary the frequency and the GT inverter will cut back on output current--feedback loop).

Another way is to measure battery voltage and use a relay on the output of the GT inverter... When the battery is full, turn off the GT Inverter's output. Can work OK too.

With a Hybrid inverter--Things are more complex. Generally the Hybrid Inverter has an AC input where you would connect the genset or grid. The hybrid inverter's output should not have a genset directly connected there. However, you could connect a GT inverter to the Hybrid inverter's output (depending on lots of mfg. specific design specs that we have no idea about) and you can run your system that way.

There are, of course, gensets designed to sync with the grid (hospitals and such use these). And even some of the inverter generators (Honday+Yamaha) have gensets that can be paralleled AC output for additional load support... But I do not KNOW how they sync and if this would be a good idea to connect to the output of a Off Grid AC inverter.

So, for safety sake, I would never connect a Honda eu2000i to the output of an off grid TSW inverter unless I was perfectly OK with 1) assuming that there is a real risk of several thousand dollars of hardware (including possible smoke and fire) and 2) had the instrumentation and loads that I could actually measure what was happening (to see if it worked and was stable).

I cannot say it will not work--People disprove predictions all the time by doing something new and different. The whole idea of GT inverters connected to OG Inverters sounds crazy to even try--But even with my limited knowledge of how the inverters function, I can see how it can work, and work pretty well. Within limits.

-Bill

Cariboocoot · December 2014

Re: Generator and ac couple ideal

How about "never connect any generator to the AC output of any inverter"?

There may be one combination out there somewhere that would work, but 99.44% of the time it will be asking for trouble.

The inverters that are designed to work with AC coupling such as the Sunny Island or XW skew their output frequency to throw any AC coupled GTI's offline. You can't do that with a generator.

Regulating generator coupling on the AC input is done much differently; by adjusting the charging of the batteries rather than messing with the AC as the load on that will not be a problem to gen or inverter.

gww1 · December 2014

Re: Generator and ac couple ideal

Again, I believe you.
Thanks
gww

gww1 · December 2014

Re: Generator and ac couple ideal

Bill and coot
I am with you guys, I just want to show that I don't dream this stuff up.

back up generator

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Re: 48 volt battery bank charging

by klundquist on Mon Dec 22, 2014 9:21 am

Please do not try to AC couple a generator to the OutBack Inverter AC output. I think Billi understands that this is not possible but just wanted to confirm in case anyone is confused.

The DC generator is certainly a nice option if you always want inverter quality AC. On the down side, it may be hard to EQ your battery bank unless the generator has special settings for a high voltage charge. In general DC gens are not designed to fully charge batteries that are designed for off grid/cycle use. If your system design requires heavy generator use for part of the year the batteries may fail prematurely from operating at partial state of charge for extended periods. The other down side of the DC generator is cost. This is a niche market and you can expect to pay quite a bit more for a DC generator at the same power rating as an AC generator.

Splitting out the sensitive loads into a dedicated circuit isn't a bad idea. The circuit should have a dedicated hot, neutral, and ground so that it is completely isolated from the rest of the main house wiring. Since you haven't built the house yet this is a option that is worth further research.

As a 3rd option you may want to consider looking at an Inverter based generator. In the last few years several companies are now offering AC generators that put out inverter quality power. The cost is higher than a standard AC generator but may be a bit less than a DC option.

Connecting the Furnace to an online UPS could be a 4th option. An online UPS uses double conversion to ensure the load always has quality power. The AC power is turned into DC, then turned back into AC to run the load. Online UPS's are expensive but I wanted to mention it partially because Ferretman thinks the lack of double conversion technology is a design flaw in the Radian. The Radian is an inverter charger, not an online UPS. It has one path for power to switch from DC to AC or AC to DC. As such it cannot charge and invert at the same time. Adding a second path so the inverter can charge and invert at the same time would be nice, however it would price the Radian out of the market that it was designed for.

-Kurt
klundquistOutBack Guru Posts: 246Joined: Tue May 31, 2011 7:23 amLocation: Arlington, WA

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Re: 48 volt battery bank charging

by ELYNN4 on Mon Dec 22, 2014 9:45 am

Thanks to everone for the thoughtful responses. My power system will be in a dedicated building that will be temperature controlled (we are in Alaska). The elevation is only 500 feet, so the generator will not have to be derated.

Another work-around that others are doing is to run dedicated circuits to the sensitive loads which are powered down when the generator runs and then powered back up when the generator switches off.

I would be interested in hearing about DC generators that folks are happy with.

Thanks - Happy Holidays

Elwood
ELYNN4Junior Member Posts: 2Joined: Thu Dec 18, 2014 3:58 pm

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Re: 48 volt battery bank charging

by billi on Mon Dec 22, 2014 4:42 pm

Please do not try to AC couple a generator to the OutBack Inverter AC output. I think Billi understands that this is not possible but just wanted to confirm in case anyone is confused.

Hi klundquist ,... no i meant it in kind of a realistic way , to get an engine and an alternator and a Grid tie inverter and AC couple on the Island side

I know of the shelf AC diesel or Gas Generaroters are not designed for AC-coupling , but windturbines and hydroturbines are ! so why should an other design of engine powered Generators not work ?

I thought one can AC couple to Outback inverters ??

http://www.solarpanelstore.com/solar-po ... nfo.1.html

OutBack FLEXcoupled AC Coupling Solution

ELYnn4 , do you need heat as well ? Fischer Panda DC generators have a good name and as far as i know easy to be converted to extract heat

http://fischerpanda.com/marinegen/dc-generators
As far as i remember , there is a US company called amplepower for DC generators

Like coot said in another post, "You see alot on the internet and some might work for awhile till it burns down your house." Disclaimer, Yea thats probly not your exact wording but what it said to me.
Cheers
gww

Generator and ac couple ideal

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