Pure sine wave and small loads

JESSICA
JESSICA Solar Expert Posts: 289 ✭✭
in Advanced Solar Electric Technical Forum #1
Is this true?:


"A note about the use of most Pure Sine Wave inverters here.
Most of these inverters will not perform well at all with
light loading. Small loads tend to give problems. Either
a smaller watt size inverter is needed, or the use of a
Modified Sine inverter. Sensitive equipment does need the
pure sine inverter to protect the equipment, but a small
load demand can cause problems in the inverter. I had
made this mistake myself before a good study of the
problem. Now, I use MSW for smaller loading, and smaller
wattage PSW for smaller loading with sensitive equipment.
Also, I always figure that any inverter may not be expected
to perform satisfactorily beyond 30% less than the stated
continuous power. That 30% less figure is a good margin of
safety when calculating your expected watt requirements
versus the inverter power you buy. You will never get
overloaded this way..."

[I found this message here: http://www.fieldlines.com/story/2005/1/4/22723/01264 ]
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Comments

  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #2
    Re: Pure sine wave and small loads

    complete and 100% total BS ...

    While any inverter may not be as efficient at small loads, they most certainly have to function properly or all sorts of bad things ( instability's ) will occur

    All the Sine Wave inverters I have used anad tested can operate at low wattage just fine. My Xantrex XW6048, a 6kw inverter regularly handles 10 watt loads and my Outback GTFX3048 has worked without issue just powering walwarts.

    The link is to a thread of nontechnical people of which mod-sine unit is the best , I would say all of the posts are pure opinion and leave it at that.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #3
    Re: Pure sine wave and small loads

    *SNORT*

    Now I have to clean my my breakfast off my keyboard .

    "With a built in charger, you can use your inverter to charge your 12 volt batteries while you draw power from your inverter. Simply connect your inverter to a 12V dc battery, such as the one you would find in your car,"

    I perfer the shot put method of inverter testing. If I can throw it far enough to not mash my foot, that's good enough?

    I think there are too many Bozos there to trust them much.
    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 ,

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #4
    Re: Pure sine wave and small loads

    There is one point where small loads can "cause issues" with high end large TSW inverters. Besides the simple issue of an idling large 3kW capacity inverter (or one supplying only a few percent of its total capacity) being less efficient than a small 300 watt inverter supplying loads of a few watts...

    Some of the large inverters have a "search mode option" to save power when there is no load (look for a load before they turn on)... They wait until a minimum load (typically around 8 watts as default) before turning on--so small loads (like a single cell phone charger) may not be a large enough load to turn the inverter on.

    Either program a smaller "search wattage set point", or disable "search mode" to make it work with smaller AC loads. Of course, then you will manually need to turn the inverter on/off (to save power when AC power is not needed).

    -Bill

    ps: I think that the original post just may be poorly written... The poster was sort of conflating several issues together. The first about running an inverter with a small/light load should not be a problem. I believe the intent of the last point was that you should run the inverter at a maximum of 70% of the inverter's rated output to allow room for surges and to keep the inverter cooler. That is not a bad recommendation.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • boB
    boB Solar Expert Posts: 1,032 ✭✭✭✭
    #5
    Re: Pure sine wave and small loads

    Also, TSW inverters of the high power type tend to have idle (tare) losses in the 20s, 30s, or 40 more Watts, so if your load is like, 10 Watts, you may be wasting energy where a smaller or MSW inverter would not be as bad.

    As far as MSW being better for low loads, I don't see how that could be.

    One case in point is the Dewalt cordless drill chargers. If they haven't changed their design recently, they will break when plugged into a MSW inverter. TSW is required for things like that.


    boB
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #6
    Re: Pure sine wave and small loads

    For new users--expecting somebody to go out and find/download 6 different manuals from 6 different companies to ascertain what is common knowledge or not--I am not going to assume that somebody could not be bothered with looking for the information--especially somebody new to the whole off-grid power thing.

    That is why I ask what people want/need/expect their new system to do... Then one of us can direct them to a couple products that may meet their requirements and suggest that they download those couple of manuals to study.

    Sometimes, a combination of products (small true sine for small loads/electronics) and a large MSW for a well pump may end up meeting their needs better than one big expen$ive T$W inverter that requires another couple panel$ and batterie$ just to power the $tandby lo$$e$.

    Everyone here is pretty good about not jumping on newbie's/"dumb" questions... As we all know--the only "dumb" questions are the ones not asked.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    #7
    Re: Pure sine wave and small loads

    I've not had any "low load" problems with my OutBack FX2524T...

    Regards,
    Jim / crewzer
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #8
    Re: Pure sine wave and small loads

    the efficiency of most inverters is lower with smaller loads, but they operate just fine. they all (sine or modsine) draw a dc load in conjunction with the ac loads and also need that basic power to operate the inverter with no ac loads even present.
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  • n3qik
    n3qik Solar Expert Posts: 741 ✭✭
    #9
    Re: Pure sine wave and small loads
    BB. wrote: »
    Sometimes, a combination of products (small true sine for small loads/electronics) and a large MSW for a well pump may end up meeting their needs better than one big expen$ive T$W inverter that requires another couple panel$ and batterie$ just to power the $tandby lo$$e$.

    -Bill

    That describes my setup. A 600W TSW running at less than 100 watts (laptop and heater) and a 1000W MSW for the fridge.
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  • JESSICA
    JESSICA Solar Expert Posts: 289 ✭✭
    #10
    Re: Pure sine wave and small loads
    n3qik wrote: »
    That describes my setup. A 600W TSW running at less than 100 watts (laptop and heater) and a 1000W MSW for the fridge.

    N3qik:

    As I have learned in this Forum, the modified wave inverter may shorten the useful life of your fridge’s motor.
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  • boB
    boB Solar Expert Posts: 1,032 ✭✭✭✭
    #11
    Re: Pure sine wave and small loads
    JESSICA wrote: »
    N3qik:

    As I have learned in this Forum, the modified wave inverter may shorten the useful life of your fridge’s motor.

    True... Motors do like sine-waves best.

    boB
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  • n3qik
    n3qik Solar Expert Posts: 741 ✭✭
    #12
    Re: Pure sine wave and small loads
    boB wrote: »
    True... Motors do like sine-waves best.

    boB

    Yes, very true, but how can I justify a $1000.00 inverter for a $ 200.00 frig.
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  • System2
    System2 Posts: 6,290 admin
    #13
    Re: Pure sine wave and small loads

    complete nonsense..how do they make up this stuff??
    so much detail too -- wwhat a waste of people's time and energy!
    just another drop in the tsunami of BS out there..
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #14
    Re: Pure sine wave and small loads

    Welcome and Hi TedtheLed...

    I guess you are one and the same from CandlePowerForums?

    Take care and hope you enjoy it here too!
    -Bill "CPF BB"
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • boB
    boB Solar Expert Posts: 1,032 ✭✭✭✭
    #15
    Re: Pure sine wave and small loads
    n3qik wrote: »
    Yes, very true, but how can I justify a $1000.00 inverter for a $ 200.00 frig.

    $2000+ of spoiled food ??

    boB
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #16
    Re: Pure sine wave and small loads

    me thinks that is a bit high for the cost of the food in a fridge that would cost $200 that i suspect would be smaller in size, but none the less boB is right because even if it were only $500 in food and it happens twice with no power then there's the cost and the justification. thinking it will run ok on modsine and shorten the fridge life you better figure in the higher costs of fridges nowadays as good models aren't $400-$500 (circa 1985-1990) anymore as i've priced many well over $1000 and smaller ones are much higher too.
    however way you have it figured it will cost you in the end.
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  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    #17
    Re: Pure sine wave and small loads

    There's no reason in my view to spend $1000 or more on a new fridge. For example, here's a link to 54 variants -- some with ice makers -- of two basic Sears fridge models (20.6 cf and 21.7 cf) with top freezers. Energy Star consumption specs are 408 kWh/yr (1.12 kWh/day) and 422 kWh/yr (1.16 kWh/day) respectively, and prices range from $535 to $825. :cool:

    HTH,
    Jim / crewzer
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  • n3qik
    n3qik Solar Expert Posts: 741 ✭✭
    #18
    Re: Pure sine wave and small loads
    boB wrote: »
    $2000+ of spoiled food ??

    boB

    Need to clear some things up. I have a 4.4 Cu. Ft. like this:
    http://www.lowes.com/lowes/lkn?action=productDetail&productId=235882-47224-FRT045GM&lpage=none

    In it right now are 11 frozen waffles, 1/2 Gal of cool-aid, 1 qt. of OJ, 1 qt. of milk, so if it blewup/died it will cost me more in fuel to get the new one that the food is worth ( approx. $20.00 )

    Yes, I am single:D:D
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  • boB
    boB Solar Expert Posts: 1,032 ✭✭✭✭
    #19
    Re: Pure sine wave and small loads

    I said: $2000+ of spoiled food ??

    ********************************

    OK... Add some expensive medication and/or chemicals to be stored in that fridge and raise it to $5000 worth of contents.

    boB :D
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  • n3qik
    n3qik Solar Expert Posts: 741 ✭✭
    #20
    Re: Pure sine wave and small loads
    boB wrote: »
    I said: $2000+ of spoiled food ??

    ********************************

    OK... Add some expensive medication and/or chemicals to be stored in that fridge and raise it to $5000 worth of contents.

    boB :D

    That's ok, I remember something long ago about hiding jewels/money in the freezer section.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #21
    Re: Pure sine wave and small loads

    There is that congressman that stored $90,000 in his freezer.

    Hmmmm, maybe he would be very concerned if his freezer defrosted / food spoiled--the cash would get pretty rank. Maybe that was why the National Guard was there to help move "...a box about the size of a small refrigerator..." during Katrina.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • boB
    boB Solar Expert Posts: 1,032 ✭✭✭✭
    #22
    Re: Pure sine wave and small loads

    And don't forget Jeffery Dawmer...

    When asked if he had any lettuce, I think he said "Yes, I have a head in the refrigerator".

    boB :D
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #23
    Re: Pure sine wave and small loads

    didn't i see an infomercial about getting ahead with more cold cash?:roll::p
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