MPPT vs PWM controllers?

NScooknetNScooknet Solar Expert Posts: 30
Hello,
I've been reading so much about controllers that I"m starting to go numb, so I'm hoping that someone here can clarify for the the benifits of a MPPT charge controller vs a PWM type of controller.

I know they both have different ways of actually monitoring and charging the batteries, but which one is better in terms of power output and efficiency?

I keep seeing MPPT controllers advertised as having 10-30% more power output. Is this true?

Is it better to buy a 20A MPPT controller with 16A worth of solar panels (as the kits advertise) or is it better to buy a more hefty 60A PWM controller for the same price?

Thanks!
Chris :)
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Comments

  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: MPPT vs PWM controllers?

    Do a search on the NAWS home site for. Very good descriptions of how MPPT works.

    (I would provide the link, but I am on. Very slow connection!)
    the bottom line is that MPPT controllers do provide more harvest all other things being equal. The advantage is greater with lower battery states of charge, and colder panel temps. 10% might be reasonable, 30% is pretty optimistic IMHO.


    Tony
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: MPPT vs PWM controllers?

    The answer is the wonderfully non-committal "it depends". :p

    If you were able to equalize all the factors in two systems so that the only difference is the charge controller and there were no exceptional circumstances such as long wire runs or cold array temperatures you would be hard-pressed to notice the difference between the two, especially on a smaller system. Under such conditions the MPPT advantage would be tiny, and mostly a matter of very small variations in Vmp * Imp output it is capable of producing. The situation changes if you have a need for high Voltage array or have to compensate for odd panel Vmp or the panel temps are cold enough to produce greater than normal Voltages.

    As for the other question, the only reason to buy a 60 Amp charge controller is if you are going to need its capacity. Generally you don't want to run any piece of equipment at its maximum all the time, but "16 Amps" of PV isn't going to produce 16 Amps all the time so the 20 Amp controller would be fine. If you plan to expand, that's different.
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: MPPT vs PWM controllers?

    Here is what Tony was referencing:

    All About Charge Controllers
    Read this page about power tracking controllers

    The short answer is for smaller systems (around 200-400 watts maximum), a PWM controller is cheaper and may be somewhat more efficient (fewer switching devices inside).

    For larger arrays, (around 400-800 watts and larger), a MPPT may be more efficient and easier to install (you can use a higher voltage solar array Vmp-array and use smaller gauge wiring and/or send the PV Array to Charge controller power longer distances).

    In very cold weather (sub freezing), Vmp-array rises, and a MPPT charge controller can take advantage of that increase in voltage (Power=Volts*Amps == So if volts goes up, then power goes up). Again--the 10% to 30% range (30% is probably rare for most people).

    But, PWM controllers are 1/3rd (or less) the cost of a MPPT controller.

    More or less, layout your system needs first, then figure out what components you will need to complete the job. Picking the components first then designing the system generally is more difficult and can end up with higher costs and other issues.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • silvertopsilvertop Solar Expert Posts: 155 ✭✭✭✭✭
    Re: MPPT vs PWM controllers?

    I think it really depends on how large array you intend to have. Just as a ball park, when I was running a 12 volt system with my Xantrex XW mppt 150, I saw about what you mentioned 10% to 30% increase in production. If you're only going to have a couple hundred watts of panels, I would go with the pulse width modulation-something like a Xantrex C60. I have noticed that on small arrays, it takes a bit of sun to bring the XW's online (wake-up), whereas, at that same amount of sunlight, which I've verified, my Xantrex C series controllers were already online. Once the XW's wake up, all bets are off. I think if you're looking at 12 volt and coming close to 800 watts, I would consider an MPPT controller. Less than 400 watts; stick with the pulse width modulation. Just my opinion........
  • NScooknetNScooknet Solar Expert Posts: 30
    Re: MPPT vs PWM controllers?

    Thanks for all your replies. I appreciate it very much!

    I'm still chasing my tail a bit about my requirements, but have just one goal at the moment, to simply run a 120V above ground well pump in case of power outages.

    I plan on purchasing between 190 - 250W 12V solar panels to begin with, and have the ability to expand and run more things as I do so.

    The thing is, I am torn between buying a high power (up to 160W or more) PWM controller in case I do expand, and buying a kit that already comes with a MPPT controller that is just enough to handle the solar panels it comes with. In that scenario, I'd have to upgrade my controller to handle more power if I buy more panels.

    If I buy a higher powered controller, I have less money to buy panels with, so I'll have lower wattage panels for awhile, but I can at least expand later.

    I plan on having probably no more than 500W eventually, so when I need more power after that, I plan on a major upgrade, but that may not be for a long time, it's all about money, so right now, I just have to get what I can afford.

    So, knowing that, maybe I "should" splurge for the higher watt PWM controller??

    Thanks again!
    Chris :)
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: MPPT vs PWM controllers?

    There are very few "12 volt" (Vmp~17.5-18.5 volt) solar panels in the 150 watt range these days (Evergreen was one manufacturer--but they are gone now). So, you may have to end up with a MPPT controller anyway to properly (and efficiently) match your solar array to your specific application.

    Lay out your power, hours of runtime per day, distances, etc. first. Then start breaking it down into components.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • NScooknetNScooknet Solar Expert Posts: 30
    Re: MPPT vs PWM controllers?
    BB. wrote: »
    There are very few "12 volt" (Vmp~17.5-18.5 volt) solar panels in the 150 watt range these days (Evergreen was one manufacturer--but they are gone now). So, you may have to end up with a MPPT controller anyway to properly (and efficiently) match your solar array to your specific application.

    Lay out your power, hours of runtime per day, distances, etc. first. Then start breaking it down into components.

    -Bill

    I thought that you could add as many additional panels later using MC4 parallel connectors to connect all the solar panels as the amperage of the controller would allow?

    One kit that has a PWM controller has 2X 95W solar panels and is expandable to 5 x 95W solar panels, but the other kit that comes with an MPPT controller has 3x 95W Solar Panel + 20A MPPT charge controller, but says nothing about being able to expand it.

    If they are all the same make and model panels, are you able to add more one by one as budget allows?

    I'm confused

    :(
  • shiftshift Solar Expert Posts: 48
    Re: MPPT vs PWM controllers?

    I actually had a good chat with a solar installer today and asked about mppt and his advise was don't bother until you have 600watts or greater in your array. Anything under and the gain is minimal compared to the added price for a mppt controller.
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: MPPT vs PWM controllers?

    I probably misunderstood your "190 - 250W 12V solar panels" statement. I though you were talking about purchasing "single" 190-250 watt panels, not 3*95 watt panels.

    In any case, you can add panels in parallel (Imp adds). With MPPT controllers, you can add panels in series (Vmp adds--but to the limit of the specific controller).

    In the end, it can be difficult to "expand" a solar PV system... Solar panels "come and go"--You might not find the same Vmp/Imp 95 watt solar panels next time. Also, what was efficient for a smaller system and PWM controller--may be better with a MPPT controller as the system gets larger.

    Also, as you increase your system size, you run into battery bank voltage/amperage issues. As the power (and charging) requirements go up--higher voltage battery banks (and sometimes MPPT controllers) make better sense.

    The easiest way for us to proceed--Give us an idea of your "starter system" and your "end system" specifications (peak Watt/WH loads per day, any special needs like 12 VDC for RV/Radios, etc.).

    There are so many variables, it is easier to start with hard numbers then see where that leads us. Otherwise, there is just lots of confusing hand waving.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: MPPT vs PWM controllers?
    NScooknet wrote: »
    I thought that you could add as many additional panels later using MC4 parallel connectors to connect all the solar panels as the amperage of the controller would allow?

    those parallel adapters are good for combing 2 pvs and no more. paralleling more would require a combiner box and fuses for every pv or strings of pvs being combined.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: MPPT vs PWM controllers?
    NScooknet wrote: »
    I thought that you could add as many additional panels later using MC4 parallel connectors to connect all the solar panels as the amperage of the controller would allow?

    One kit that has a PWM controller has 2X 95W solar panels and is expandable to 5 x 95W solar panels, but the other kit that comes with an MPPT controller has 3x 95W Solar Panel + 20A MPPT charge controller, but says nothing about being able to expand it.

    If they are all the same make and model panels, are you able to add more one by one as budget allows?

    I'm confused

    :(

    Don't buy solar power kits. They tend to be a bunch of stuff put together to make profit for the seller, rather than what you need. Buying one large panel instead of two small ones will save you a lot of money as they are cheaper per Watt: http://www.solar-electric.com/hiposopa.html

    It is difficult to say if you will be able to add more of the same panels in future, as panel specs change. The Kyocera 135 has been in production a long time, but Sharp recently discontinued the 175's I bought five years ago. Mixing different panels can be done if you pay attention to the specifications. Try to stay with panels design for battery systems: they will have a Vmp of either 17.5 +/- (a "12 Volt" panel) or 35 +/- (a "24 Volt" panel). Many panels are design to work with GT systems where the actual Vmp isn't critical because they put many in a string to get the 250 to 500 Volt array. They will have Vmp' like "26.6" or "30.5" - too far off to be useful for battery-based systems without an MPPT controller - and a lot of headache.

    The bad new is that well pumps are notoriously high power users. Big start-up surge from the motor having to wind up against water pressure and pretty hefty power consumption thereafter. The exact numbers will depend on the actual installation of course.
  • WindsunWindsun Solar Expert Posts: 1,164 ✭✭
    Re: MPPT vs PWM controllers?
    shift wrote: »
    I actually had a good chat with a solar installer today and asked about mppt and his advise was don't bother until you have 600watts or greater in your array. Anything under and the gain is minimal compared to the added price for a mppt controller.

    Your installer may not be totally clued in to all the advantages of MPPT, and not sure where he came up with that 600 watt figure, as that would depend on the situation. If you have limited space, such as on an RV or boat, MPPT might be the only way to get more output.

    One of the big advantages of MPPT is that it allows you to series panels for higher voltage, which equals smaller wire and less loss, especially for longer runs. Series is nearly always a lot cheaper to install than parallel, as you need a lot less wiring and cabling.
  • NScooknetNScooknet Solar Expert Posts: 30
    Re: MPPT vs PWM controllers?
    Windsun wrote: »
    Your installer may not be totally clued in to all the advantages of MPPT, and not sure where he came up with that 600 watt figure, as that would depend on the situation. If you have limited space, such as on an RV or boat, MPPT might be the only way to get more output.

    One of the big advantages of MPPT is that it allows you to series panels for higher voltage, which equals smaller wire and less loss, especially for longer runs. Series is nearly always a lot cheaper to install than parallel, as you need a lot less wiring and cabling.

    I don't have an installer, "I" am the installer....lol.

    So far I'm getting alot of mixed responses about MPPT controllers. Some here said to get them, some said it's a waste of money.

    I'm still confused.

    Seems like there is no hard and fast rule, just opinions.

    I've seen the same kit from a few different suppliers now, some on ebay, some in the US, and some in Canada, they are basically the panels, usually two 190-240W panels for 12V, and they come with a cheap Chinese PWM controller, which I don't like. I recognize the maker of those controllers, and I had one, a different model, but the same manufacturer, and after a year of use with only two 15W panels, it croaked. So yeah, I know what you mean about cheap stuff put together.

    I only considered the kit to guarantee compatibility, but I think I know enough now to pick and choose separate controllers.

    I've now realized that one of the controllers I was looking at that has a connection for solar, and one for wind, is a diversion controller, and not a PWM like I thought. It's advertised as a 440W controller, but I'm not sure about that. I just liked the idea of having a solar controller that if need be in the future I could just add a turbine to with a few extra components. But I won't get into that now, that's a whole other conversation, I was just thinking about future expansion.

    It's tough when you just don't have the bucks for a big system, do yu invest in high quality higher power gear bit by bit, then one day have it all to finally put together into a system, or do you do what I'm trying to, build a system that is scalable, and by scalable, I mean under 800W total if I ever even built it up that big.

    I know what you mean about well pumps, I'm not sure if the solar can run one unless i have a crapload of batteries. I did invest in a 3000W generator that "says" it can run a well pump, but I haven't tried it yet.

    Chris :)
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: MPPT vs PWM controllers?

    The 440W dump controller is probably the 440 Amp Dump Controller, here are a couple posts (and video) about that controller.

    At 440 amps--That controller would be dripping red hot copper if operated at its rated output for any length of time.

    Regarding PWM and MPPT controllers--If cost is important (and it usually is), the trade off is buying a cheaper PWM controller plus an extra 100-200 watts of solar panel vs a "better" MPPT controller but you cannot afford as many watts of solar power.

    In the end, you should probably do two designs--One with PWM and a second with MPPT and see which does a better job for your needs.

    MPPT otherwise, are great for longer distances between the Solar Array and the charge controller. You can use smaller cable (save money) and have longer distances (put panels in sun, park RV in shade, etc.).

    Also, since MPPT controllers are newer and more expensive, the usually have more bells and whistles (Logging, Internet connection, aux controls, computer interface, etc.). Which may or may not be of interest to you.

    Another advantage for MPPT--Allows you to use larger (and less expensive) solar panels (>150 watts, Vmp is usually not 17.5 volts or so) for your battery charging.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: MPPT vs PWM controllers?

    A couple of things that need to be pointed out:

    Each charge source, regardless of type, needs its own controller. You can not hook up a wind or hydro turbine to the same controller you have solar panels on. Likewise you should not connect two different PV arrays (which would be two with different aspects to the sun) to one controller or two turbines to one controller.

    It is nearly impossible to "grow"" a system. Unless you can plan every step of expansion in advance and be sure the components will be available in future (panels go out of manufacture as they are replaced by better units) you will end up starting over at some point. There is also the problem of increased power capacity necessitating increased system Voltage. Install a 12 Volt system now and down the road when you need more Watt hours or higher peak Watts or 240 VAC - you're stuck.

    As for running the pump, if you know what the pump is and how long it will run you can figure out roughly what sort of capacity you need. For AC induction motors, true sine wave is a must - which lets out all the cheap, high Watt MSW inverters. Oh it might work with one of those, but it will draw more power, run hotter, and give up sooner.

    My system cost $8,000 in 2008, put in myself. It runs a 1/3 HP water pump easily (most pumps are 1/2 HP, and they go up from there). It also runs the refrigerator and everything else. These days I could put together a somewhat better system for slightly less money (in the U.S.). The main trouble is, just to start the pump (or 'frige) you need a hefty inverter and enough battery capacity to handle the surge. After that it's easy to run almost anything else off it.
  • NScooknetNScooknet Solar Expert Posts: 30
    Re: MPPT vs PWM controllers?
    BB. wrote: »
    The 440W dump controller is probably the 440 Amp Dump Controller, here are a couple posts (and video) about that controller.

    At 440 amps--That controller would be dripping red hot copper if operated at its rated output for any length of time.

    Regarding PWM and MPPT controllers--If cost is important (and it usually is), the trade off is buying a cheaper PWM controller plus an extra 100-200 watts of solar panel vs a "better" MPPT controller but you cannot afford as many watts of solar power.

    In the end, you should probably do two designs--One with PWM and a second with MPPT and see which does a better job for your needs.

    MPPT otherwise, are great for longer distances between the Solar Array and the charge controller. You can use smaller cable (save money) and have longer distances (put panels in sun, park RV in shade, etc.).

    Also, since MPPT controllers are newer and more expensive, the usually have more bells and whistles (Logging, Internet connection, aux controls, computer interface, etc.). Which may or may not be of interest to you.

    Another advantage for MPPT--Allows you to use larger (and less expensive) solar panels (>150 watts, Vmp is usually not 17.5 volts or so) for your battery charging.

    -Bill

    That controller in the video is "the same only different" to the one I've been looking at on ebay. I'm not going to mention the manufacturer or ebay info for fear of being reprimanded again...lol.

    It looks like there are at least two companies making the same controller with the same guts, only with slightly different features. The one i saw had current and voltage meters, and did not have that big industrial ugly button on the front panel, but everything else looked identical.

    The info for that controller shows a schematic with 2 inputs, one for wind, and one for solar, and 3 hookup scenarios, one with solar alone, one with wind alone with the load attached, and one with both connected to their own dedicated terminals at the same time, stating you can run wind and solar simultaneously. False advertising??

    I have a 3000W Eliminator (Canadian Tire) brand modified sine wave inverter that I purchased recently, and a 1000W pure sine inverter from the same brand.

    The 3000W inverter states it will easily handle the inductive kick of a well pump, and gives a chart of how long it will run depending on the battery aH's.

    It shows a chart of items that can be run by an inverter, and shows it as either 2 or 3 "stars" for either a pure sine, or modified sine wave inverter.

    It shows the well pump as a "2" star for the modified inverter, and "ideally" a 3 star for pure sine to run a well pump.

    If it said it wouldn't run a well pump, i surely wouldn't have bought the darn thing!

    I can deal with things not being "ideal", but not working is another thing all together. The more I look at it, the more useless a modified sine wave inverter really is. Guess it will do in a pinch.

    I actually just got through "making" cables to connect the 3000W inverter to my battery bank. I only have 2 marine deep cycle batteries which will soon be replaced by proper deep cycle AGM batteries.

    I bought 2 sets of 6 gauge wire jumper cables, and chopped them up into 4 pieces each, so I have four 3.5 foot lengths of cable that consist of four 6 gauge wires bundled together in parallel to handle the current.

    There are 2 positive and 2 negative terminals on the back of the battery, and from each one of those 4 terminals are those four 6 gauge wires each going to the battery.
    I'm guessing that's enough to handle anything the inverter will draw from my batteries? Maybe overkill??

    So regarding expanding my system later on, are you saying that if I buy solar panels now, say two 120W panels, and then later on, plan to add more panels of "similar" specs, that it cant' be done? Are you saying all panels added MUST be exactly alike?

    I've currently got two 15W 12V panels, can I connect them in parallel with the new panels I buy, or do I have to disconnect them and run only the new higher power panels??

    Thanks!
    Chris :)
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: MPPT vs PWM controllers?

    Still have the receipt for the CT Eliminator inverter? Take it back.
    I actually tested most of their MSW inverters a few years back. I found the Wattage ratings to be "optimistic".

    Here's another thing: 3000 Watts on 12 VDC is 250 Amps. That is a lot of current. Your pump will probably not demand that much, but it is reasonable to assume it will tax the limits of a 12 VDC supply. 6 AWG, btw, is really only good for about 40 Amps maximum. That's 480 Watts on 12 VDC, and probably less than the water pump will use. If you are going to use this inverter, go for the biggest wire you can physically connect and keep the lengths to a minimum. You'd be amazed at the amount of power loss to the inverter from too small cables. Paralleling wires is not a good idea either; resistance goes high in one (for whatever reason) and the other is left to carry the overload. If you do this, put a 50 Amp fuse on each positive line. The dual power inlets on inverters like this is something I'm famous for ranting against. ;)

    As far as adding panels is concerned, probably your best bet is the Kyocera 135W. They've been around a while and as such are likely to continue in production. They're a pretty good deal in terms of $ per Watt and are small enough to be shipped and handled easily.

    When matching up dissimilar panels, the rule of thumb is to keep Vmp within 5% to 10% for parallel connections and Imp within 5% to 10% for any serial connections. If there is a significant difference in current potential, fusing the smaller panel according to its Isc rating is a good safety step. More than two (identical) parallel connections and you have to fuse each string (one or more panels in series) in case something goes wrong. That way the remaining good panels can't pump dangerous amounts of current into a shorted one, causing a fire.

    Regarding controllers with dual inputs that claim you can put both solar and wind on them ... Either they've got almost the equivalent of two controllers in there, or they are lying. The MPP for the two input devices will almost never be the same. Of course you can do it if you don't mind throwing away significant amounts of power from one or the other source.
  • VicVic Solar Expert Posts: 3,112 ✭✭✭✭
    Re: MPPT vs PWM controllers?

    And NSc,
    ]
    Not to pile on too much. In addition to all of the above good comments, there is some caution needed in using Jumper Cable as general wiring. Jumper cables are normally SAE guage wire, which has somewhat smaller Cross-Sectional Area -- there is less copper in it than one would find with AWG cables. It is even possible that some manufacturers (perhaps from some other country) might have cut a few extra percent from the copper content of the cable.

    SSssoooo, many crimp lugs that are sized for AWG, will be too large when crimped with the correct AWG crimping tool, causing loo little clamping force twix the wire and a lug (if you used crimp lugs). You might want to do a pull test on any crimps that you might have made. Perhaps you have used some screw type compression lug, and it might not be an issue. Also, when there are high current demands on, or charging of your batts, you might want to gingerly test the junction between the batt cables and any lug that you have added. Temp rise equates to loss, or worse.

    Good Luck with the new system, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: MPPT vs PWM controllers?

    Adding solar panels later becomes another "it depends" type of answer.

    More or less, if you add panels in parallel, the Vmp between the two strings should match within ~10% or less.

    Adding panels in series, they again should match Imp to within 10% or less.

    I cannot predict if your panels will be available in a couple years--Although, people who have gone through this ended up with a choice of the identical panels or getting was is currently in high production and 1/2 the price (or even less).

    It is a real toss of the dice.

    Regarding MSW or TSW inverters... For a well pump, if it is not operating at maximum power, you might be OK with an MSW inverter. Very roughly, the motor losses go up another 20% of rated power (i.e., a 600 watt motor my draw 720 watts to pump the same amount of water on a MSW inverter).

    For short run times, in well pumps with lots of water cooling running at less than maximum horse power, may not impact the overall life of the pump.

    The smaller stuff (computer power supplies, battery chargers, cell chargers, small electronics with wall mount transformers, etc.) tend to be less tolerant of MSW inverters. But you can get a smaller TSW inverter to run those loads very nicely, without paying huge amounts of money for a large TSW inverter.

    Here are a couple Inverter FAQs:

    All About Inverters
    Choosing an inverter for water pumping

    Many times, for true off-grid solar power, there are various options such as soft start and variable speed controllers (VFD--Variable Frequency Drives that connect to three wire and 3 phase motors). This can be all in one units or get a three wire or three phase pump motor with an external VFD.

    If you are going to look at high power... Very roughly, under 1,200 watts can be 12 volt battery bank. Under 2,400 watts a 24 volt battery bank. And over 2,400 watts, look at a 48 volt battery bank.

    For example, looking at a 12 volt 3kW inverter:
    • 3,000 watts * 1/0.85 inv eff * 1/10.5 cutoff voltage * 1.25 safety factor = 420 amp branch circuit and breaker minimum

    At 12 volts, suppling that amount of current with less than 1 volt drop is very expensive (lots of copper wire, expensive switches/breakers/fuses, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • NScooknetNScooknet Solar Expert Posts: 30
    Re: MPPT vs PWM controllers?
    Vic wrote: »
    And NSc,
    ]
    Not to pile on too much. In addition to all of the above good comments, there is some caution needed in using Jumper Cable as general wiring. Jumper cables are normally SAE guage wire, which has somewhat smaller Cross-Sectional Area -- there is less copper in it than one would find with AWG cables. It is even possible that some manufacturers (perhaps from some other country) might have cut a few extra percent from the copper content of the cable.

    SSssoooo, many crimp lugs that are sized for AWG, will be too large when crimped with the correct AWG crimping tool, causing loo little clamping force twix the wire and a lug (if you used crimp lugs). You might want to do a pull test on any crimps that you might have made. Perhaps you have used some screw type compression lug, and it might not be an issue. Also, when there are high current demands on, or charging of your batts, you might want to gingerly test the junction between the batt cables and any lug that you have added. Temp rise equates to loss, or worse.

    Good Luck with the new system, Vic

    Actually, the 4 wires were too large to fit in any lugs available from the store, so I made my own. I used a 1.5" section of copper tubing, fit it over the end of the 4 wires that were twisted together, and hammered it flat, and then soldered them thoroughly with a torch and verified that the solder flowed nicely and filled up the flattened tubing, and wicked into then 4 wires. Then I drilled a hole in the flattened copper tubing and voila.

    I was told previously by a guy who installs solar that adding 4 wires in parallel was ok as it was too expensive to buy a 1 conductor wire, and hard to find. Apparently, I'd have to go to a local welding shop to find them. I thought for sure i did that right at least, little did I know....lol.

    So what gauge wire would you recommend to ensure a safe connection between a 3000W inverter and the battery bank?

    Also, is the 1000W Eliminator pure sine wave inverter at least good to run small stuff, or is it also junk like the 3000 watt modified one?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: MPPT vs PWM controllers?

    I have to take issue with a couple of things Bill said (yes we do sometimes disagree).

    For one, a well pump "not operating at maximum power" is off. They generally have to start against a column of water and then work their way up to full pressure. Unlike, say, a saw motor than starts against no load and varies depending on how thick/tough the wood is.

    For another, not all well pumps are submerged. Shallow well pumps have no aide of water cooling. If the OP has said what sort of pump he has I've already forgotten. Shows how good my mind is. :blush:

    From my experience, the contention that electronics need true sine and big motors can be run on MSW is exactly the opposite of reality. Most "sensitive" electronics have really good power supplies capable of cleaning up pretty poor power sources, whereas AC induction motors have only their windings and perhaps a capacitor to help them along. They really do not like MSW. It "looks like" low Voltage to them, and they behave accordingly. Sometimes that means they don't work at all, sometimes it means they struggle and die, sometimes it means they can cope.

    Sometimes when you're looking at least-cost options for pumping water the answer is a different pump, not $10,000 worth of solar power. And sometimes the answer is a good generator. :D
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: MPPT vs PWM controllers?
    NScooknet wrote: »
    I was told previously by a guy who installs solar that adding 4 wires in parallel was ok as it was too expensive to buy a 1 conductor wire, and hard to find. Apparently, I'd have to go to a local welding shop to find them. I thought for sure i did that right at least, little did I know....lol.

    So what gauge wire would you recommend to ensure a safe connection between a 3000W inverter and the battery bank?

    Also, is the 1000W Eliminator pure sine wave inverter at least good to run small stuff, or is it also junk like the 3000 watt modified one?

    Actually to run 3kW off 12 Volts (which is a bad idea) you'd need 4/0 wire (aka "0000") and you'd probably have to get it from a welding supply or specialty electrical supply as you won't find it in Home Depot or Canadian Tyre. Let me introduce you to our host's wiring department, just so you can get an idea what you're looking for:
    http://www.solar-electric.com/electrical.html
    The big wires: http://www.solar-electric.com/bainca.html

    I've never put a scope on CT's "pure sine" inverters but imagine they are good enough to power light-duty loads like lights and electronics.

    If we knew how much power you actually need to supply maybe we could recommend a more suitable inverter, like one of the Exeltech units. Generally, for 12 Volt systems you don't want to go over 2kW and you don't want to need to supply that continuously. Most of the time my big inverter only needs to supply <500 Watts, but when everything kicks on at once - the difference shows.
  • mike95490mike95490 Solar Expert Posts: 9,361 ✭✭✭✭✭
    Re: MPPT vs PWM controllers?

    Well pump here, and depending on the size of your pump, and what you are aksing it to do, I have doubts a 12V system will be reliable for anything more than a 1/2 hp pump. My 1/2 hp pump, shows a 1,000w draw on the inverter control panel, and things like Power Factor, battery internal resistance, and wire resistance, will all add up to make things unhappy.

    MPPT - you only gain it's wattage conversion efficency while it is in BULK mode, once the controller eases off when switching to Absorb, all the ones I know of, revert to PWM mode for absorb and float.
    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 ,

  • john pjohn p Solar Expert Posts: 814 ✭✭✭
    Re: MPPT vs PWM controllers?

    MPPT - you only gain it's wattage conversion efficency while it is in BULK mode, once the controller eases off when switching to Absorb, all the ones I know of, revert to PWM mode for absorb and float.
    Mike that is the very point that I find is hardest to get across to everyone.And its the very reason you dont get 50% and above gains from them as most people claim.On another similar site a well know poster talked about |the mysteries of MPPTversus PWM" He never ever mentions that fact only give figures to show theory gains.
    You are also correct with "all the ones I know of, revert to PWM mode for absorb and float
    Ot of dozens I regularly test have never found one not to be like that.
    At the cost of panels now is more cost effective to buy another panel or get higher output ones. If system is below 600w.

    I think inverters above 1000w on 12v is just making things hard for yourself .1000 to 3000 =24v above 3000w =48v or above
  • NScooknetNScooknet Solar Expert Posts: 30
    Re: MPPT vs PWM controllers?

    Oh, BTW, since we are talking about inverters, I was wondering if there is a problem with having both the 1000W pure sine inverter and the 3000W modified inverter connected to the same battery bank at the same time.

    Of course I realize that it would obviously be an issue if I had them both turned on at once and together they were attempting to draw a load heavier than the batteries could accommodate, but what I'm asking is that if they were both connected at the same time, or even turned on at the same time, providing they are not drawing excessive current, would there be any issues?
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: MPPT vs PWM controllers?

    More or less, if you draw too much surge current, the inverters will fault/shut down (maybe for a short period of time, or until they are reset).

    For a "good quality inverter", the supported surge power is about 2x rated output. 3,000 watt inverter should support is 6,000 watts surge (probably not happening with a 12 volt inverter--because):

    ->6,000 watts * 1/0.85 eff * 1/10.5 volts = 672 Amps @ 12 volts

    For a flooded cell battery bank the maximum recommended surge current is around C/2.5:

    ->672 amps * 2.5 surge capacity = 1,680 AH @ 12 volt battery bank (to reliably support 6,000 watt surge current on 12 volt battery bank)

    So--working backwards, what AH rated battery bank (20 Hour Rating) are you looking at? Flooded Cell or AGM (AGM can supply a lot more surge current--However, the wiring is still pretty large for such a small battery bank--Only useful if you are looking at UPS type applications where you can draw the battery flat in 15 minutes--or something similar).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • NScooknetNScooknet Solar Expert Posts: 30
    Re: MPPT vs PWM controllers?
    BB. wrote: »
    More or less, if you draw too much surge current, the inverters will fault/shut down (maybe for a short period of time, or until they are reset).

    For a "good quality inverter", the supported surge power is about 2x rated output. 3,000 watt inverter should support is 6,000 watts surge (probably not happing with a 12 volt inverter--because):

    ->6,000 watts * 1/0.85 eff * 1/10.5 volts = 672 Amps @ 12 volts

    For a flooded cell battery bank the maximum recommended surge current is around C/2.5:

    ->672 amps * 2.5 surge capacity = 1,680 AH @ 12 volt battery bank (to reliably support 6,000 watt surge current on 12 volt battery bank)

    So--working backwards, what AH rated battery bank (20 Hour Rating) are you looking at? Flooded Cell or AGM (AGM can supply a lot more surge current--However, the wiring is still pretty large for such a small battery bank--Only useful if you are looking at UPS type applications where you can draw the battery flat in 15 minutes--or something similar).

    -Bill

    I just wanted to ensure there was not some weird feedback from one inverter input to the other somehow.

    As I've learned, it's what you don't even know that you don't even know...lol.
  • SolaRevolutionSolaRevolution Solar Expert Posts: 407 ✭✭✭✭✭✭
    Re: MPPT vs PWM controllers?
    mike90045 wrote: »
    MPPT - you only gain it's wattage conversion efficency while it is in BULK mode, once the controller eases off when switching to Absorb, all the ones I know of, revert to PWM mode for absorb and float.

    Well... Bulk is when you need efficiency most.

    Why would you care if your PV charging system is as efficient as possible when you are not using it? In any system, when your PV controllers are regulating battery charging, your system efficiency factor is abysmal. If your batteries are low because you have been using power, every little bit afforded by efficiency is precious.

    Another consideration is the economy of scale for charge controller and module choices. More PV modules means higher charge controller output amperage design considerations. Depending on the scale of your system, trading more expensive but more efficient MPPT charge controllers for additional PV modules, may require a greater number of less expensive charge controllers and additional balance-of-system equipment costs.
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: MPPT vs PWM controllers?
    mike90045 wrote: »
    MPPT - you only gain it's wattage conversion efficency while it is in BULK mode, once the controller eases off when switching to Absorb, all the ones I know of, revert to PWM mode for absorb and float.

    Now that is interesting. What happens if the controller is in float and you then suddenly switch on a large load? Would the controller be using it's MPPT algorithms while supplying the load?
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: MPPT vs PWM controllers?

    Yes, it should go into MPPT mode to maintain Float Voltage.

    But--I would suggest that units should be tested to ensure they will operate in MPPT mode when in absorb and float. Would not be the first time a hardware/software engineer missed the obvious.

    -Bill "been there, done that" B. :blush:
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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