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Windynation P20L Li-Ion Charge Controller

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  • Windynation P20L Li-Ion Charge Controller

    I'm looking at putting together a small test setup with a 40ah GBS heavily influenced by PNJunction's generous online contributions.

    I have not seen mention of this charge controller, whose manual indicates an option for Li-Ion mode upon a selection and setting adjustable float charge (13.8V to 27.6V). I will be using as a 12V system and anticipate charging to 13.9 volts across the 4 cells.

    I have been trying to figure out if temperature compensation indicated in the manual and charge method are truly compatible, with this being indicated on Amazon to be two stage charging. Additionally, I'm unsure if float voltage needs to be lower than bulk setting (and absorb/equalize I guess) to treat the battery gently and to minimize cell voltage drift. Battery will be charged with two paralleled 100W 12v nominal PV panels for at total of around 12A, so modest charge rate if that makes a difference.

    On a side note, I plan to either use the load port of this controller with LVD at 12.8V (adjustable 10.7 to 21.4), or employ a Xantrex C35 with adjustable LVD for higher discharge rate capabilities.

    So I reached out to the manufacturer and got the following responses that weren't excessively helpful for me:

    "Is the temperature compensation disabled in Lithium Battery mode? No, it`s ok for all type of batteries.

    Is the float voltage applied continually in the lithium mode? Yes, you need to setup the float voltage and set the controller for lion battery.

    Can you explain how the charge cycle works in lithium mode? It`s a PWM controller, the charge mode is boost-equalizer-float."

    My impression is that temperature compensation is a CC electronics compensation and not a charge value compensation like would be expected for lead acid (I don't see that the CC has a temp probe input to use). The last answer seems like it might be three stages of charging, but I am not sure if boost=bulk and equalize=absorb.

    What say you on whether Is this a decent cost effective option for (bottom balance) PWM charging or a product whose "lithium mode" is not compatible with PNJunction style (conservative charge and discharge stop points, no BMS as I understand) Li-Ion care?

    Thanks much.

  • #2
    First to charge a lithium is very simple 1-stage Constant Current / Constant Voltae. 3-stage is useless for Lithium. 3-stage is for Pb batteries. You want to force the controller to behave as a 1-Stage Constant Current / Constant Voltage by setting Bulk = Absorb = Float. For the GBS battery without a BMS you can run up to 14 volts, I would use 13.8. With a BMS if you wish to charge to 100% is 14.4 volts. Stay between 13.8 and 14.

    Disable Temp Comp. All Temp Comp does is raise the voltage as the temp goes down. Great for Pb batteries, exactly opposite of what LFP batteries require. That tells you the controller is not made for Lithium and just marketers trying to make a bigger mouse trap. True Lithium chargers are 1 stage of CC/CV. Real simple and easy. Pb can use the complicated circuitry of 3-stages. 3-stages made for Pb has no use for lithium.

    Lastly LVD you can set as high as you want. 12 volts or 3.0 vpc is more than high enough. Danger zone starts at 11 volts, and death at 10 volts. At 12.8 you are eliminating the bottom 50% of your capacity in the battery. To access 80% of the capacity of the battery and stay away from the knees, the operating voltage on a 4S battery is 13.8 volts @ 90% Capacity, down to 12 volts @ 10 to 15% capacity. So that 40 AH battery you have if ran 12 to 13.8 is 32 AH usable. If you run 13.8 to 12.8 (12.8 is roughly 50% SOC left in the battery) is only 15 to 20 AH usable. You do not want to go above 90% SOC (roughly 13.8 to 13.95) or below 10% SOC (roughly 12 volts). Stay away from the ends (14.4 and 10 volts).

    [I]You have not asked or stated the most important question. How do you intend to balance the capacity of the cells initially? You cannot just take them out of the box, and put them into service. You have one very important step to perform before you do that. If you fail to do that, say goodbye to your new batteries and say hello to your new boat anchors. [/I]
    Last edited by Sunking; 04-14-2016, 06:53 PM.
    MSEE, PE

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    • #3
      Been away for awhile...

      adoublee -- Sunking rightly points out the issue of initial cell balance. Given your skill set (no offense, really!) what I recommend for so-called initial top-balance is using a so-called "single cell" charger for nominal 3.2v lifepo4 batteries. This charger will actually take each cell to about 3.65 to 3.75v. Get at least a 6 to 10ah single cell charger, since going too low will try to push the cell to 3.7v and never get there, damaging the cell - or if it does, spend too much time doing so!

      Do not stray from the "nominal 3.2v lifepo4 single cell charger". There are other single-cell charger for non lfp chemistries, such as the nominal 3.7v type, which will actually take them to 4.2v !! NOoooooo.

      Places such as batteryspace sells single-cell chargers, just stay in the 3.2v nominal lifepo4 aisle please. Use this upon receipt of the GBS battery, and pay attention to your clip polarities as you charge each cell individually.

      Now that your cells are charged as equally as they can be let's talk normal operations ....

      Your 200w panel total are fine. However, again due to skill set, stick to a simple pwm controller for now, that can have the temperature compensation turned off, or set to zero. You'll have to actually read the manual for a prospect online to make sure you can do this. The cheapo Renogy controller that came with my folding panels allowed for disabling temp comp with a "zero" setting. Thing is, disabling temp-comp, or customizing it, is not usually a feature mentioned in the marketing for something designed for lead-acid - you have to read the manual to make sure you can do this.

      Now, to regulate the voltage of the controller, either choose the "canned" GEL setting, and make sure that is actually no more than about 14.1v. Again, the manual should be specific about this. Or, if the controller allows, do a custom absorb of no more than 14v, with 13.8v being the ideal. Yes, eventually, your system will go into float mode, usually at about 13.6v, but since you are already charged, there will be no current flowing in float - only an application of float voltage, which at this level is not harmful to LFP, since a real full charge can only be reached by a setting of 13.8v.

      Ideally, if you can disable float, then by all means do so, but if you can't, you can more or less ignore it at 13.6v or less with these lead-acid specific make-do's.

      Like any normal system, attach the battery first to the controller, and THEN the panels to the controller. This keeps the brains of the controller from trying to save you from what it thinks is a zero-voltage battery if you do it backwards. In some controllers, that might immediately put you into float as a safety measure. Not what you want.

      Rethink using the "load" terminals for anything other than dinky dinky loads, like led lighting. Real loads get attached to the battery terminals.

      The point I'm trying to make is that *I* am successful into shoe-horning lead-acid specific products to work with LFP, but you must make sure that you know what the specifications are when you do a shoe-horn like this. If you don't, you'll be buying new shoes pretty rapidly.

      Invest in an LVD. The simplest is a Powerwerx ITS-12 if you don't envision pulling more than 30A from the battery. Once again, this device is meant for lead-acid, but it has a provision for setting the LVD abnormally high for lead acid, which *if you know what you are doing*, can be shoe-horned into service with LFP. It runs 150ma in operation, and when the LVD trips, about 5ma. This means you can rest easy for a little while if you forget, but still, 5ma can add up to dead LFP if you use this thing totally remote and out of reach.

      See what I'm getting at here? It can be done, but one must be careful when dealing with gear not specifically designed for LFP.

      Oh, for AC recharge, the yellow-black Samlex SEC 12-15ul charger, * dip switches set for gel*, which is about 14.1v max, would be ok.

      Every once in a blue moon, you may want to hit those cells up individually again with your single-cell charger just to be on the safe side. You may want to invest in individual cell-voltage monitors, (provided the monitor is NOT run from the cells themselves!), or at least a decent voltmeter you can trust - the cheapest being a Fluke 11x series.
      Last edited by PNjunction; 04-15-2016, 05:41 AM.

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      • #4
        Thanks for both your replies Sunking and PNjunction.

        PNjunction - I understand shoe-horning lead-acid specific products if the are appropriately adjustable. In this case, I'm asking about a product that claims to actually be designed for charging lithium ion (LFP or other not specified). It also has a Li-ion mode selection and fully adjustable charge and LVD disconnect voltage settings down to 13.8V for charging (I may not use the LVD). I didn't see that the low cost Renogy PWM controllers have any direct voltage adjustability beyond lead-acid type selection - and the Renogy manuals do not specifically indicate and ability to disable the temperature compensation that I see after (I did read those manuals). I know that this is Windynation Li-ion claim is at least somewhat more developed than just a marketing claim, as the product has a lithium ion setting programmed in. I have read every word of the manual to try and get a reading on what they are acutally doing with this setting, which is why I posted the reply they provided. If it helps the manual might end up linked here if I can get this form figured out.

        I understand that nothing happens if float is a lower voltage than what the battery is charged to, but with the Windynation I'm concerned the voltage stays at the battery voltage full charge setting - even after the battery has "cooled". The Li-ion setting on that controller has me set the float value - not the boost or equalize values.

        For LVD I will probably use Scheider/Xantrex P series with adjustable drop out voltage, if not just using the Windynation load port should loads stay dinky.

        I'll consider the AC chargers and initialization you recommend as I know you have thought through this. I was planning to balance them on the discharged end of the curve with loads across cells where 1) voltage changes occur more rapidly than in the useful energy horizontal portion of the curve and 2) voltage change more pronounced earlier in approach of full discharge than it is in the fully charged range of the charge curve (curve doesn't go vertical until well beyond 100%). You seem to be recommending top balance. In normal operation I see that it should be easier to respond to voltage at the upper end of the SOC without cutting out excessive amounts of useful energy, but negative impact of a full charge is not as great as impact of a full discharge should I balance around more reliable discharge protection.

        Sunking - Interesting that you are saying 12.8V on the low side is going to cut out 50% of the useful capacity. I had been trying to extrapolate the curves for something more like a .25C discharge. Trying to cut out in the more horizontal portion of the knee seems to place a greater sensitivity on the discharge rate in this regard than cutting off in the more vertical portion of the curve. With that, my thought was that staying on the more horizontal side of the knee might give the LVD a more accurate and timely response than if the voltage starts dropping more rapidly. I also it will allow more sloppiness on the balance over time which I know most will suggest should be checked regularly. I want to be conservative with extra protection of battery that is not babysat. 12.4V or 12.5V might get me there as well but I don't think I'd want to go lower than that, but might consider 12.7 or lower once I know my exact load and discharge rate.

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        • #5
          If the charger just has an Li-ion setting, and does not specify either LiFePO4 or other, you MUST look at the voltage setting itself to see which of the two families of Li mentioned by PN it actually supports.
          SunnyBoy 3000 US, 18 BP Solar 175B panels.

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          • #6
            Originally posted by inetdog View Post
            If the charger just has an Li-ion setting, and does not specify either LiFePO4 or other, you MUST look at the voltage setting itself to see which of the two families of Li mentioned by PN it actually supports.
            No worries, the controller voltage is adjustable, down to 13.8V which should be just low enough for conservative LFP charging.

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            • #7
              Heh, it all depends on how much you are into shoe-horning like I am ..

              Originally posted by adoublee View Post
              I didn't see that the low cost Renogy PWM controllers have any direct voltage adjustability beyond lead-acid type selection - and the Renogy manuals do not specifically indicate and ability to disable the temperature compensation that I see after (I did read those manuals).
              That's ok. With my unit that came with the folding panels, the user can choose canned-presets, or do a custom setting. While there isn't a specific temp-comp disabling setting, the same is achieved by being allowed to change the typical 3mv / C offset to your specifics. Which for LFP would be zero!

              Still, we're dealing with toy controllers. Let's move up the scale....

              The Xantrex C35 can be nicely shoehorned, with quite a bit of quality backing it up. (I use the C12 myself at times).

              Here's how: If you do not use the optional temp-sensors, then no temperature compensation will be used. Check!

              The ability to fine-tune your voltage settings, instead of using canned presets is a big plus. Since this is solar, I'd set it conservatively to 14.0v. You can really set if finely by using a Fluke or other trusted voltmeter, and the test-points on the board instead of the silk-screen settings for the settings.

              Because these controllers are 3-stage controllers designed for lead acid, some work by way of measuring the absorb current before dropping to float, and some will do it on a timer-basis.

              The C35 utilizes a timer in absorb, so even at a conservative 14.0v, you may never achieve a good charge when it times out in an hour or two, depending on your depth of discharge, solar conditions etc, so you compensate by setting the float value to say 13.8v for your conservative charge in case you forget and leave this thing in the sun for a few days.

              Of course, if you are really hurting with the Xantrex's timeout, even the workaround of a 13.8v float could be raised (say to 14.0 just like absorb!) to fool the overall system into doing a big absorb at the same voltage until the sun goes down.

              See how you gotta' be careful when shoe-horning?

              Truthfully, most so-called "li-ion" settings from inexpensive manufacturers are just making that claim and are just lead-acid in disguise.

              Fortunately, you are smarter than that, and see the need for knowing what is right, and what may be a marketing claim, or glossy specs.

              For example: The latest NOCO vehicular chargers have a "Lithium" setting. It is nothing more than a 2-stage charger set for 14.2v. Nothing lithium-specific about it, other than a sane specification for LFP 12v batteries.
              Last edited by PNjunction; 04-18-2016, 10:28 PM.

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