Generator stability questions

lazzalazza Solar Expert Posts: 330 ✭✭✭
HI Forum

We've recencently been working with an "all-in-one" inverter-charger system that uses grid or generator current to charge the batteries as well as charging via solar.

When the voltage and frequency of the input from the generator/grid is stable, it works brilliantly. However, clients often have small Honda-type cheap generators that give varying voltage and what seems worse, unstable frequencies. With this instability the inverter´s charger system struggles to give the normal current that it's supposed to to the batteries.

My questions are:

- is it normal for these small generators to be so unstable-? If so, their compatibility with inverter/chargers is dubious.
- could it be that they need their AVR replacing?
- what causes the frequency variations and will replacing the AVR deal with that too??

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Generator stability questions

    It is normal for standard fixed RPM generators to be unstable in Voltage and frequency. The greater the load change in relation to the generator's capacity the more unstable it becomes.

    Most of the small Hondas (at least what we get around here) are inverter-generators which are extremely stable for both Voltage and frequency.

    It is also normal for any system expecting generator power input to recognize a wider range of V & f in order to function properly.

    So whether or not the generator(s) in question works properly depends on exactly which gen it is. The output can be tested to see if it meets manufacturer's specifications. If it does, there's nothing wrong with it; the application is unsuited.
  • westbranchwestbranch Solar Expert Posts: 5,142 ✭✭✭✭
    Re: Generator stability questions

    Lazza, I use a P3 Kill a Watt meter on my stuff to check out the Frequency, PF and Voltage. Have found the 1000w Honda Inverter gens I have to be ~ 123 V and dead steady loads (light) or not. The non inverter gen is set at about 125V so that when a ~ 10 amp load is applied it comes down to 60 Hz, but it too is quite stable under load, Jap Mitsubishi motor on it. The 3000w Honda hardly blips when applying same 10A load (Sliding miter saw)
     
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  • mike95490mike95490 Solar Expert Posts: 8,377 ✭✭✭✭✭
    Re: Generator stability questions

    What sort of "load" does your "all-in-one" inverter-charger system present to the generator? Is it a good power factor ? If a generator is not matched to the load, then poor results can be expected
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: Generator stability questions

    It takes two, both the generator and the Inverter to be able to work together. The Inverters charging control has to Ramp up the amperage to the Charger set limit, it cannot over shoot or go wide open and then cut it's self back. It has to be able to be set in small increments of no more that 1-2 amps. The ACin limits have to able to be set in 1 amp increments.

    Inverter generators take care of themselves unless you overload them. A small non inverter Generator's RPM usually correlates the voltage and hertz of the output. Example : 125 V is 62-63 HZ. Most inverters will not accept HZ this high, 120V is 60hz. Sometimes putting a dummy load on them will get them to qualify, then you can start to load them a little at a time and remove the dummy load. The Governor has to be responsive enough to keep the RPM steady.

    Over all the best Inverter / Charger is the Outbacks, they have a lot of flexibility built in the firmware. Brand X is 5,10,15,20,25,30 a small generator cannot adjust to those limits that fast.
  • lazzalazza Solar Expert Posts: 330 ✭✭✭
    Re: Generator stability questions

    THanks for the replies.

    All I know is that the frequency varies between 42Hz and 48Hz (50Hz system).. the frequency doesnt stay around any fixed point.. which to me harks of a problem with the generator.. but i could be wrong??
  • Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: Generator stability questions
    lazza wrote: »
    THanks for the replies.

    All I know is that the frequency varies between 42Hz and 48Hz (50Hz system).. the frequency doesnt stay around any fixed point.. which to me harks of a problem with the generator.. but i could be wrong??
    Sorry, I forgot your HZ would be different. There you need to raise the RPM by adjusting the Governor to give you a higher loaded output. put maybe a 5 amp load on it and see how it does as you adjust it. It's a trial and error. The other option is to use a stand alone charger with them, or buy a inverter generator.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Generator stability questions

    If the gen's frequency is only hitting a high of 48 then it is running too slow. Usually they want the gen loaded 25%-50% of capacity for speed/frequency/Voltage adjustment. The gen's specs should tell you what range it is meant to operate in. As I said before it depends on which generator. If its specs are too loose to be any good, you can't use it. If it does not operate within spec it's defective. You have to remove the variables to find the problem.
  • Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: Generator stability questions
    If the gen's frequency is only hitting a high of 48 then it is running too slow. Usually they want the gen loaded 25%-50% of capacity for speed/frequency/Voltage adjustment. The gen's specs should tell you what range it is meant to operate in. As I said before it depends on which generator. If its specs are too loose to be any good, you can't use it. If it does not operate within spec it's defective. You have to remove the variables to find the problem.
    This is true on the ( 25-50% loading ) but you also have to get into a range where it will qualify and at least establish some pass through and charger loading. I wasn't very clear about what I was saying.

    If your going to try a dummy load it needs to be variable. I have a old hot plate that I have used that has a variable rheostat on it, marked so you can repeat the loading. You have to set the governed speed and also the sensitivity. My best guess your not going to be successful. It's really hard to get the inverter to do pass through and charge at the same time with a small non inverter generator, but you might to get it to charge. Allowing multiple transfers on the Relays is not a good thing to do, as they wear out fast and fail.
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