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valhalla360's avatar
valhalla360
Navigator
Oct 29, 2014

Grid Tie Inverters with Generator

The reason most people go to a second generator (or a larger generator) is because of the startup amps needed to get the Air/Con compressor turning. Once it's turning a 2000-2400watt generator will usually be able to handle the continous load.

One option I've looked at in the past are inverters that can match the hz of the generator and give it the boost to get the compressor turning. The problem is these inverters are about as expensive as a second generator.

I recently came across grid tied inverters. They are intended for household solar arrays, so that they can feed into the AC system. I assume this means they match the hz.

The interesting thing is they are much more reasonably priced (maybe 1/4 of what the high end units I've looked at before).

Could you connect them to a battery bank rather than a solar array and tie that into your AC system? I don't see why it would care where it gets the DC from (assuming it meets the voltage range).

The only problem I see is I believe these are designed to take as much DC as is available and translate it to AC. If you hook it up to your battery will it just run at full power until it kills the battery (or worse will it pull 1000amps and burn the unit out)? If so, is there a simple way to address this (maybe a manual switch you turn on just before you turn on the air/con and then a small battery charger, you turn on to keep the batteries up while still remaining in the generaters total output capability.

I'm guessing there is a fatal flaw or everyone would be replacing thier inverters with grid tied units.

Thoughts?

9 Replies

  • valhalla360's avatar
    valhalla360
    Navigator
    Oct 30, 2014
    I was aware of the victron and similar units but with the prices, they just don't make sense for this purpose.

    http://www.amazon.com/iMeshbean%C2%AE-Inverter-Accept-10-8v-30-Seller/dp/B009B57L1Q/ref=sr_1_4?ie=UTF8&qid=1414685614&sr=8-4&keywords=grid+tie+inverter

    Dakota: See link above for an example but found many.

    Westend: The one in the link at least claims to start down to 10.8V.

    Mexicowander: The honda/yamaha generators put out pretty clean power, so I would expect it should be able to match the frequency if it can do it for normal grid power.

    Chris Bryant: In my example, there would be a source of power (the battery bank). The problem appears to be that it wouldn't just draw power as needed but it would pull power continously as fast as it can.

    Thanks for the feedback. I figured it was too good to be true (500-1000watt inverter for $200-300)
  • pianotuna's avatar
    pianotuna
    Nomad III
    Oct 30, 2014
    Hi

    BFL13 found a 2000 watt hybrid inverter for $700.00 That would do the trick.

    I'm loving the Magnum I purchased.
  • KD4UPL's avatar
    KD4UPL
    Explorer
    Oct 30, 2014
    I install grid tied solar systems for a living. I don't know of any grid tie inverters that have a DC input that will accept 12v. Some of the microinverters will take DC in the 20 to 30 volt range but they are only 250 watt inverters. Most inverters require DC at 200 volts or more.
    A grid tie inverter only does one thing: make as much power as it can and push it into the grid. If you connect an inverter as you propose and feed it a high enough DC voltage, and if your generator is stable enough in frequency for it to sync then it just might come on and start feeding AC into your gen. It will feed as much as it can draw from the battery and raise the AC voltage as high as necessary (up to the UL limit) in order to push the AC into your system. Your generator will not like this one bit. Your battery bank won't like it either.
    There are really a whole host of reasons why this won't work. Instead of typing out all the technical details just skip this plan.
    There are inverters that have a feature called "generator support". These are battery based inverters that can sync to a generator and provide power. Yes, they are expensive. I think Magnum and Victron both offer this feature in a 12v DC model inverter. Xantrex and Outback make them too but only in 24v and 48v configurations. An inverter like this is what you need to allow your small gen. to start an AC unit.
  • Chris_Bryant's avatar
    Chris_Bryant
    Explorer II
    Oct 29, 2014
    The trouble with grid tie is they will not work stand alone- they must have power in to operate.
    Many new inverters will do a boost, or generator support.
  • time2roll's avatar
    time2roll
    Nomad
    Oct 29, 2014
    No typically you cannot use a battery to drive a grid tie inverter.
    Also the grid tie is designed to produce continuously and may drop out if your grid does not absorb all the energy produced.

    I recommend a Victron Multiplus inverter that is designed to combine battery power with generator or utility power.
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Oct 29, 2014
    You need to do a lot of technical investigating and verification before this should be decided as being feasible. What is the tolerance of the grid tie inverter to frequency, for example. And line voltage? There are a lot of savvy inverter manufacturers out there and if a simple grid tie type unit would resolve the issue you wish to address, I fear it would have been done a long time ago.
  • Golden_HVAC's avatar
    Golden_HVAC
    Explorer
    Oct 29, 2014
    Hi,

    I tend to agree with some of your thinking. If the grid tie inverter sees 1,000 amps at 12 volts available, it is designed to put all that power into the grid as quickly as it's 5,000 watt rating can transfer it. This can backfeed the generator, and probably melt it. . .

    Grid tie inverters such as Xantex can match the incoming Hz, and just add 'enough' power to overcome the power coming in, so that you do not exceed your maximum input rating. So I have a remote control on my 1997 Trace M1512 inverter control panel. I can set inlet from 5-30 amps in 5 amp steps. It will lower the charge rate to a point where incoming power + charge amps will not exceed the inlet rating. So if I am using the A/C and set the inverter to a 20 amp shore power, it will sense the 14 amps being used by the A/C and not charge at a rate to exceed 20 amps total. Yet the M1512 is modified sine inverter, so it will not contribute to the loads the way you described.

    The SW2512 inverter can contribute to the loads, they way you described. If set for say a 15 amp shore power, it will charge the batteries when it can, and if you exceed the 15 amp load, the inverter will contribute to the line amperage, and prevent the 15 amp breaker from tripping, even if you have a 20 - 25 amp load running.

    You might be able to find a used SW2512 inverter. It might not be as expensive as a second generator. You might need a 440 amp hour battery bank - 4 batteries to run it that way.

    Fred.
  • westend's avatar
    westend
    Explorer
    Oct 29, 2014
    I think most of the larger grid tie inverters have fairly high minimum DC voltage set point. It might require reconfiguring a typical RV battery bank. Then again, technological changes with grid tie devices are happening quickly. In a few years Siri should be able to handle the programming. :B

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