Mppt vs pwm

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  • westbranchwestbranch ✭✭✭✭ Solar Expert Posts: 5,149 ✭✭✭✭
    Re: Mppt vs pwm
    Photowhit wrote: »
    In a discussion of "MPPT vs PWM" if your leaving out that the last 10% of charging is the same, What some(I) would call "...nears full charge ..." ...

    And, as a group, we typically recommend not discharging more than 20%...

    It is important in the understanding of the advantages of MPPT charge controllers.
    ..... Not the overall advantage which this fact is very important in the comparison of MPPT vs PWM.
    ....

    You lost me Photowhit... I am assuming that you are saying that the last 10% of charging is NOT the same..
    BUT how can this be? The absorb and float V settings 'should' be the same regardless of type of CC, Absorb is fixed V, decreasing A and Float is a fixed lower V as well, with a lower and tapering Amps.
    I do not see any 'advantage MPPT' over PWM....??
     
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  • PhotowhitPhotowhit ✭✭✭✭ Solar Expert Posts: 5,007 ✭✭✭✭
    Re: Mppt vs pwm
    westbranch wrote: »
    You lost me Photowhit... I am assuming that you are saying that the last 10% of charging is NOT the same..
    BUT how can this be? The absorb and float V settings 'should' be the same regardless of type of CC, Absorb is fixed V, decreasing A and Float is a fixed lower V as well, with a lower and tapering Amps.
    I do not see any 'advantage MPPT' over PWM....??

    Sorry for editing this long after it was posted, I was resopnding to Neil who stated that with an MPPT "...nears full charge ..." there was still an advantage, I was pointing out that the last 10% of charging, there was NO advantage and that this was important in a comparison of MPPT vs PWM, the thread we are all writing in.

    I think Neil and I have a good understanding of this, it's just that I thought his statement was misleading in a thread of MPPT vs PWM. Neil makes things even clearer in a later post.
    .


    This was a response to Neil who had responded to me. May have gotten confusing. I reread it and so long as you read it as in a discussion of 'advantages' and not that it 'IS' and advantage, it reads the way I had intended.

    Since I'm posting yet again, let me say that MPPT has many advantages, not the least of which is running more panels in series, reducing wiring(size and quantity) and fusing. Higher voltage for longer runs, and of course the use with panels not designed for nominal battery ratings, which are being made in quantity and often offer the best price pre watt.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • nielniel ✭✭✭✭ Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Mppt vs pwm

    photowhit and westbranch,
    mppt is for bulk charging and not absorb or float charging. the absorb and float stages of charge are ones of regulating or holding back current and/or voltage and should be pretty much the same no matter the charge controller type. at this point not all of the power from pv is needed and some is held back. if one is only drawing down to 80% soc (20% dod) then mppt may not be worthwhile for you and odds are you've got quite a bit of solar charge power available to cover most of the needs of recovering the at most 20% of discharge over the course of the day. this is a case of one of the particulars that i mentioned could sway one's decision making. most do not have over sized battery banks with over sized pv arrays to afford just an 80% soc and do draw down on the batteries further. now if you didn't typo and meant 80% dod then the battery is mostly depleted and mppt is most likely very worthwhile in this case.

    calbiker,
    we have been waiting for you to back up your claims for you to show us how it is i am wrong (on more than one issue too i might add) and all you do is call me a liar in so many words while you give an arrogant tight lip to my inquiries as to how i am wrong. others have told you repeatedly to stop the attitude and now i'm telling you to put up or shut up. i do not mind being told somebody feels that i am wrong and they need to state their case why they think this as others here have done. sometimes it is a misunderstanding of what is being said, but you say nothing in defense of your claims for anybody to even properly address by clarifying why you believe anybody is wrong.

    general forum,
    this thread has actually took a few people by surprise, i might add, as many here may have had misconceptions about mppt and pwm and what generally is the same or different between the 2 methods. maybe it's a good thing somebody had asked the very question of mppt vs pwm. the real difference bottom line is that mppt will take the power and transform it to allow extra current for bulk charging over just the max of the imp that the pwm is only capable of delivering. factors such as wire resistance and pv temps affect both mppt and pwm alike as these are losses not caused by the controller. how much of that power that is normally wasted that is recouped is a difference between mppt controllers along with the actual draw to operate the controllers for what good is getting say 50% of the wasted power back if the cc will use 95% of that to run itself? none the less that is still a gain mppt has over using pwm even if small at times due to old technology or whatever. costs of getting the added power recouped is the factor many must weigh when considering going mppt and is one reason smaller mppt controllers have come out to allow some smaller systems to not have to pay $500-$600. it's still more costly and costs still would be a factor.

    note that even if i word my arguments wrong for someone to comprehend that it doesn't change what is.
  • boBboB ✭✭✭✭ Solar Expert Posts: 965 ✭✭✭✭
    Re: Mppt vs pwm

    One comment regarding MPPT vs. PWM when in Absorb or Float constant voltage mode....

    Just because a charge controller is in the Absorb or Float stage and does not need ALL PV array power,
    it may very well need most of, or very close to full available power to keep that voltage constant.
    This is true especially when there are other DC loads than just the battery and when the charge
    cycle has just gone into Absorb or Float. Less so the farther into Absorb or Float cycle it
    has gone, given a constant external DC load across the battery.

    Being able to hold that voltage with these loads on the battery side will not be possible
    with PWM unless the PV is able to hold those loads up (along with the battery voltage)
    while connected directly to the battery. Only if the PV array can do this, directly connected,
    can a PWM controller be turned off periodically to keep the battery voltage from exceeding
    the set point voltage.

    If the system, running with just PWM on-off-on-off direct connection cannot do this, then
    MPPT has a much better chance if the temperature does not put the Max power point
    voltage too close to the battery voltage.... Otherwise, neither one is necessarily
    better than the other and the system has not been designed as good as it can be.

    boB
  • nielniel ✭✭✭✭ Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Mppt vs pwm

    i was going to mention the exception as the classic can up the voltage for float as i found out, but i didn't want to further confuse everybody here. my current undersized us64 pv does fall short of taking care of my 400+ah battery bank and until i solve my problem of getting the new pvs mounted to my wall then my primary charge source is from the magnum mms1012 charger. you guessed it for in the mean time i use the us64 as a float charger of sorts.
  • Jigme UrgyenJigme Urgyen Registered Users Posts: 13
    Re: Mppt vs pwm
    niel wrote: »
    do understand in general that i have nothing against pwm controllers and have had a few of them myself. also, understand that mppt does not create a power gain as i would better describe it as a power recovery from that which would've been normally lost just using a pwm style of cc. the controller is not creating anything, but rather is working with what it is presented with to be better utilized in charging the batteries through more current available from said power.

    as to how you describe mppt is not quite accurate as you make it sound as if it is an addon to a pwm controller and that's just not quite right. it is, at the risk of oversimplifying, a dc to dc converter that has provision to self adjust for the changing input conditions it's presented with during the bulk stage. now during absorb or float it may act more like a pwm.

    in operation the mppt wins hands down, but in the real world it may not always be cost effective for a small system as mppt costs quite a bit more than pwm. this cost aspect was not the aspect of the discussion i was addressing, however, it is worth considering. there are always factors that may sway one individual over another under the same general system setup. things like future expansion and long wire runs can be 2 of the influencing factors that i believe were mentioned already by bb, but often it will boil down to an individual's personal preferences and decision on what is good for them to go with.

    I appreciate your precision words. there is always a lot on offer in a thead about MPPT. it seems to get the heart of the PV matter.

    Also in a lot of cases, if your going with an off the shelf system or a more integrated approach, you cannot choose to have MPPT, you just get it and that's all there is to it. think outback, SMA etc.
  • calbikercalbiker ✭✭✭✭ Banned Posts: 50 ✭✭✭✭
    Re: Mppt vs pwm
    niel wrote: »

    we have been waiting for you to back up your claims for you to show us how it is i am wrong (on more than one issue too i might add) and all you do is call me a liar in so many words while you give an arrogant tight lip to my inquiries as to how i am wrong. others have told you repeatedly to stop the attitude and now i'm telling you to put up or shut up. i do not mind being told somebody feels that i am wrong and they need to state their case why they think this as others here have done. sometimes it is a misunderstanding of what is being said, but you say nothing in defense of your claims for anybody to even properly address by clarifying why you believe anybody is wrong.

    You need to tone it down a bit buddy. Me, calling you liar??? I can say you guys are also arrogant. It's a two way street. Where's the proof that BS significantly under performs other mppt CC? Talk is cheap.

    Why don't you list the issues you need "clarity" on and I'll see what I can do. But YOU need to be civil.

    For those wanting to know what's wrong with the battery FAQ:

    The charge rate of 13% is poorly written. Is it meant for PV systems or also for battery chargers? Is it a max rate, or what? I know of one moderator that uses 13% as absolute max for any type of charging system. That is wrong. The Prosine2.0 manual states generic flooded batteries can handle 30% (including Trojan). I wouldn't charge at that rate, but that's besides the point. See Appendix C.

    http://www.xantrex.com/documents/Inverter-Chargers/PROsine-2/PROsine_2.0_User%27s_Manual%28445-0089-01-01_rev-C%29.pdf

    Cal
  • icarusicarus ✭✭✭✭ Solar Expert Posts: 5,304 ✭✭✭✭
    Re: Mppt vs pwm

    Ah,, Cal,

    If you want to be respected around here, (and not get booted) you should show some respect! If you have a differing opinion on any subject, Greg, back that up with some research and back up your claim with cogent thought! As it tried to say earlier, there are some very sharp people here including among others (one who has posted on this very thread) are senior design engineers with major solar manufacturers. (I will leave it to them to ID themselves if they wish!).

    So keep it civil, or take it elsewhere! If you have a beef with one of us MODs take it up via PM rather than being nasty on the public boards. We have a very clean, very organized forum, that is far and away one of the best forums that I have been involved with, and indeed the est on alternative energy.

    Icarus

    As for the Blue Sky out performing the Rogue,, as I have stated in this thread, I have a BS and a Rogue wired side by side with an AB switch and a Trimetric so I can very quickly switch between controllers in nearly identical conditions. I say nearly instantaneously because the Rogue goes into a sleep cycle after being shut off, and it take about a minute to come back on. The BS comes back much faster. That said, the Rogue on a nearly identical condition out performs the BS. As I also mentioned earlier, I am away from home on a job right now, and won't be. Qck for a while so it annoy give you a side by side of today,, but I will if I ever get home for long enough to get my feet on the ground.

    T
  • CariboocootCariboocoot ✭✭ Banned Posts: 17,615 ✭✭
    Re: Mppt vs pwm

    No one has ever said it is not possible to charge at higher than 13% of capacity.

    Quoting the referenced document (which states a maximum current of 30%):

    "Different battery manufacturers suggest different battery charging algorithms. The
    following information has been provided to Xantrex by the associated battery
    manufacturer. This list is provided as a reference only. It is highly recommended
    that you confirm the actual charging algorithm with your battery manufacturer.
    "


    So nothing new there and nothing that contradicts the Battery FAQ's which says (and I have quoted this before for the benefit of those who don't or won't understand what is written):

    "Most flooded batteries should be charged at no more than the "C/8" rate for any sustained period."


    No place in the document does it say you absolutely can not exceed 13% or that it is the maximum. The repeated reference on this forum is that 5%-13% is the recommended rate, and obviously that recommendation takes into account many factors including the economic viability of having to buy enough panels (this is a solar forum) to achieve the charge rate. Everyone, including newbies, has been able to understand this as stated. Until now, it seems.
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