attaching a generator to a system??

bartbenbartben Registered Users Posts: 2
I have a small off grid island cottage that uses a small solar power system for lights etc. I am wanting to permanently attach a gas generator to the system so that in the cold and dark days of winter i can fire it up and top off my batteries. I am pretty much a newb but i DO understand a bit about the system, and am wondering what advice you folks might have for me. I believe i need to instal a "shunt" to prevent the electricity being feed to the system by the generator from backfeeding to the panels. Am i correct? What sort of shunt do i need? where do i get one? etc etc. As i said, the system is pretty small at this point About 90 watts of panels, and four 6v t-105's wired to give me a 12v output.

thanks in advance.

m

Comments

  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: attaching a generator to a system??

    You need an AC battery charger with 12V output. Some inverters already have this feature built in, what is the make and model of your inverter?
    Usually you don't need anything to prevent backfeeding your solar panels in a "normal" system. Do you have a charge controller between your solar panels and batteries?
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: attaching a generator to a system??
    bartben wrote: »
    I believe i need to instal a "shunt" to prevent the electricity being feed to the system by the generator from backfeeding to the panels. Am i correct?

    Welcome to the forum,

    A shunt has nothing to do with preventing backfeeding. If your panels have a charge controller between them and the battery, the charge controller will prevent any backfeeding from the generator or any other charging source.

    As StephenDV wrote, you also need to buy a battery charger to take the generator output and regulate it for the battery.
    bartben wrote: »
    I am wanting to permanently attach a gas generator to the system so that in the cold and dark days of winter i can fire it up and top off my batteries.

    Bad idea. You don't want to top up your batteries with a generator... you want to bulk them up in the morning (with the generator) and then let the solar panels take over to top up the batteries. During the absorb stage of charging the current into the battery tapers off. If you run your multi-kilowatt generator through the absorb stage, you will be running that generator to supply a few hundred watts (or less) for hours.

    Tell us more about your system, your generator, and what battery charger you are thinking of. It is helpful to make a signature with your system components.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • mike95490mike95490 Solar Expert Posts: 8,377 ✭✭✭✭✭
    Re: attaching a generator to a system??

    In the dark days of winter, any charge, is a good charge.

    So you need a generator, and a ordinary battery charger, of a decent size, to make it worth burning the gasoline.

    If you have a 100Ah 12V battery, you generally don't want more than 15 amps of charger for each 100 a of battery. But, if
    you watch the charging close, you could go a little more than 15% of capacity ( 15 C ) . Pay attention to the Power Factor (PF) of the charger, that will increase the size of the generator needed, if your PF is poor.

    Clip the charger on, fire up the generator, and watch it charge. Before you depart, BULK the batteries up, so they don't sulfate while waiting for enough sun to complete the charge.
    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: attaching a generator to a system??
    mike95490 wrote: »
    Pay attention to the Power Factor (PF) of the charger, that will increase the size of the generator needed, if your PF is poor.
    You know this to be a fact ?? Tell me how it works and what how would you prove it is true ??
  • NorthGuyNorthGuy Solar Expert Posts: 1,925 ✭✭
    Re: attaching a generator to a system??
    Tell me how it works and what how would you prove it is true ??

    W = pf*V*I (W = power, V = voltage, I = current)

    Assuming W and V are the same, lower pf means higher I. Say, if pf = 0.6, I is 1/0.6 = 1.67 times higher than if pf was 1. The heat produced in the windings is proportional to I2, so if pf = 0.6, it will produce (1.67)2 = 2.78 times more heat. I would guess windings should be thick enough to take this if W is within specs and pf is not too bad. But if winding wire is undersized, it may overheat, short or something of that sort.
  • Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: attaching a generator to a system??
    NorthGuy wrote: »
    W = pf*V*I (W = power, V = voltage, I = current)

    Assuming W and V are the same, lower pf means higher I. Say, if pf = 0.6, I is 1/0.6 = 1.67 times higher than if pf was 1. The heat produced in the windings is proportional to I2, so if pf = 0.6, it will produce (1.67)2 = 2.78 times more heat. I would guess windings should be thick enough to take this if W is within specs and pf is not too bad. But if winding wire is undersized, it may overheat, short or something of that sort.
    I hear you, thats the theory of putting it in the specifications. What does the that mean about the Input vs the output of the charger and the load on the generator ??

    Would this be a good 60 Amp charger @ 12 Volt ??

    AC CURRENT (Typ.) 12A/115VAC
    INRUSH CURRENT (Typ.) 25A/115VAC
    POWER FACTOR (Typ.) 0.98/115VAC at full load
    EFFICIENCY (Typ.) 85%
    .
  • NorthGuyNorthGuy Solar Expert Posts: 1,925 ✭✭
    Re: attaching a generator to a system??
    What does the that mean about the Input vs the output of the charger and the load on the generator ??

    It can increase transmission/winding losses, which theoretically should decrese overall efficiency. However, since losses are in the generator, this should not affect charger efficiency. I suspect the pf-corrected charger will be less efficient than a regular one. I cannot judge the relative significance of these factors. I guess it depends on the specific charger and specific generator.
    POWER FACTOR (Typ.) 0.98/115VAC at full load
    EFFICIENCY (Typ.) 85%

    For comparison, my XW6048 has pf of 96-97% (in fact better than this, because it also includes little bit of the loads) and efficiency of 88-89% at 80% load.

    IMHO, power factor shouldn't have any significant influence on the load as seen by the motor, however I know nothing about motors.
  • bartbenbartben Registered Users Posts: 2
    Re: attaching a generator to a system??

    WOW! so many replies!! thank you so much folks. It would behove me to respond to each bit of advice individually, but i dont think i could keep up. Some more info about my system...I have two 45 watt panels facing due south (my cottage is in N. central Ontario (CAN) in the peterborough area. i DO have a charge controller, unfortunately, its a fairly crappy blue sun force 30 amp unit (http://www.homedepot.ca/product/30-amp-charge-controller/986483). I have four 6 volt trojan t-105s (225 ah) wired in series creating a 12 v output. i DO have a small inverter, again a fairly crappy unit (http://www.canadiantire.ca/AST/browse/4/Auto/SolarPortablePower/Inverters/PRDOVR~0111866P/MotoMaster+1500W+Mobile+Power+Outlet+and+Inverter.jsp?locale=en) which i use very infrequently. The charger i have is a Genius g7200 (http://www.geniuschargers.com/G7200/specs) which i've had pretty good luck with. Lastly, i have a Champion 4000 w generator (http://www.canadiantire.ca/AST/browse/6/Tools/ShopEquipment/Generators/PRD~0550317P/Champion+4000W+Gas+Generator%2C+Camo.jsp?locale=en). just about all of this equipment was inherited when i purchased the cottage last year and im just starting to get to work on the system. Im hoping to upgrade much of the equipment in the spring and will likely tap into all of your vast wealth of knowledge when the time comes.

    Thanks again for all your help.

    m
  • mike95490mike95490 Solar Expert Posts: 8,377 ✭✭✭✭✭
    Re: attaching a generator to a system??
    bartben wrote: »
    ... The charger i have is a Genius g7200 (http://www.geniuschargers.com/G7200/specs) which i've had pretty good luck with.
    Lastly, i have a Champion 4000 w generator...

    Running a 2A battery charger (about 60 AC watts ?) off of a 4,000 watt generator, is .... uh..... expensive.
    four 6v t-105's wired to give me a 12v output.
    So I think the generic expression is: you have a
    12V, 400ah battery bank. That battery could easily take 40A of charge current, wind sun has a Iota 45A charger
    http://www.solar-electric.com/dls-45.html for not too bad of a price - it will pay for itself in the reduction of generator
    run time. 45A @ 15V = 700w, add in conversion losses, call it 1Kw, still hardly any load for that large 4Kw generator.
    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 ,

  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: attaching a generator to a system??
    bartben wrote: »
    I'm hoping to upgrade much of the equipment in the spring and will likely tap into all of your vast wealth of knowledge when the time comes.
    Don't spend another cent without getting some free advice here. As Mike95490 pointed out, your system is a bit unbalanced. You need to buy a battery charger as soon as possible because you will ruin your batteries if you don't get them fully charged, and I don't think you can get them charged with the system you have now. If you do buy a battery charger now, make sure it will still serve your needs after you upgrade in the spring.
    mike95490 wrote: »
    Running a 2A battery charger (about 60 AC watts ?) off of a 4,000 watt generator, is .... uh..... expensive.
    <snip>
    That battery could easily take 40A of charge current, wind sun has a Iota 45A charger
    http://www.solar-electric.com/dls-45.html for not too bad of a price - it will pay for itself in the reduction of generator
    run time. 45A @ 15V = 700w, add in conversion losses, call it 1Kw, still hardly any load for that large 4Kw generator.

    bartben,
    Many folks with small solar power systems have a large generator. They use it for occasional large loads that their solar power system can't handle. It is often not cost effective to super-size your solar power system just so that it can handle an occasional large load.

    Many of these same folks soon discover how expensive it is to use their large generator for battery charging, and then they go and buy a second, smaller generator for battery charging.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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