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NEED HELP: have 480W of solar, trying to buy LiFePO4 and charge controller

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  • NEED HELP: have 480W of solar, trying to buy LiFePO4 and charge controller

    I have 480W of solar (4x120W) and am thinking of getting 2 of these 100Ah LiFePO4 batteries. This is for a 2016 RAM Promaster with a stock 180A alternator that I'd also like to tie into but don't know how yet...

    I found a 40A MPPT charge controller that claims to work with LiFePO4 in addition to gel, sealed, and open types.

    Is this possible? What am I missing?

    I believe the batteries each need a BMS but the ad for the batteries mentions BMS. The seller of the charge controller said the 200Ah LiFePO4 bank could only handle up to 200W - how is that possible if the batteries are rated at ~80A charge/discharge and the charge controller is only 40A at 480W?


  • #2
    I do not know if you can use those batteries (even with their own BMS) to be charged from a CC for solar panels.

    Also at that price I would be cautious into believing that 40Amp CC is really a MPPT.

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    • #3
      Those were my thoughts, too.

      We want to go Lithium for a lot of reasons (weight, size, charge time) but the only thing that's simple are the way overpriced kits, like $3k for 200Ah lithium setup. Trying to put something together to save money, but don't want to waste money buying the wrong thing or fake/inferior products.

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      • #4
        Originally posted by sdbuck View Post
        Those were my thoughts, too.

        We want to go Lithium for a lot of reasons (weight, size, charge time) but the only thing that's simple are the way overpriced kits, like $3k for 200Ah lithium setup. Trying to put something together to save money, but don't want to waste money buying the wrong thing or fake/inferior products.
        Well Lithium batteries come in all sorts of chemistry and charging requirements. Some work with PV others do not.

        IMO I would not trust what they say about that CC working with Li since I also don't believe it is really an MPPT CC.

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        • #5
          My Tracer 30A MPPT (3215?) was only $170 and it's a legit MPPT controller, albeit 30A and not 40A. This one appears legit as MPPT given the size and heat sinks...just don't know if it's safe for LiFePO4 and why the seller says 200W MAX for solar given a 200Ah LI battery bank

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          • #6
            Originally posted by sdbuck View Post
            My Tracer 30A MPPT (3215?) was only $170 and it's a legit MPPT controller, albeit 30A and not 40A. This one appears legit as MPPT given the size and heat sinks...just don't know if it's safe for LiFePO4 and why the seller says 200W MAX for solar given a 200Ah LI battery bank
            It is hard to say. Maybe someone else that has hands on experience with that CC will make a statement.

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            • #7
              I'm also fairly confident that those 100Ah 12v LiFePO4 batteries for $472 are too good to be true. Like, maybe they have a really low charge rate or require $700 worth of additional battery management? This is all Greek to me, but there must be a reason they're 2-3x cheaper than most 100Ah batteries aside from the mere fact that they take 6-9 weeks to ship from China.
              Last edited by sdbuck; 10-17-2016, 03:51 PM.

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              • #8
                STOP!

                These are "E-Bike" batteries, usually hand-crafted and slapped together with some kapton-tape and heatshrink. It is far different from the quality you want, and actually need since you have no knowledge to judge them with.

                Controller? Just because they "say" they can charge lifepo4 in addition to all the rest of the lead-acid chemistries, have they even taken the time to DISable temperature-compensation for LFP if it has any at all?

                Time for more homework. Don't just throw money at a LiFeP04 project, or you'll throw it down the drain. An LFP system is engineered. You can't wing it.

                Because the price for admission is so high with LFP, you can easily step into a wallet-wasting hole of unproven and ultimately unsafe products if you go the cheap route.

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                • #9
                  Do not do something STUPID. Trust us you would be very stupid to use those batteries. Lithium is not ready for solar yet. They are just to expensive and do not have the cycle life of Lead Acid.

                  So two of those batteries will cost you $1200, and if you are extremely luck will last 2 years if that long. The equivalent Lead Acid battery would be 300 AH, cost $500 to $600 and last 3 to 5 years.

                  Lithium batteries have to be justified. At this time power tools, EV's of any kind like e-bikes, lap tops, tablets, and cell phones can justify the expense because Energy Density is most important in those applications.

                  For solar stationary energy storage lithium is a poor choice and would require a special application like being stupid enough to use a 2000 watt Invert with a 12 volt 200 AH battery where discharge rates exceed Lead Acid capability. Even then if that were the case one would use an AGM battery wghich again is a Lead Acid Battery.

                  Using Lithium is also a liability. Take a look at Samsung stock price. Might be a good time to buy while the price is so far down. Question is can they survive the lithium fires. It is going to cost them billion$.

                  Having said all that. Any good quality MPPT controler can charge a Lithium Battery just fine. It just needs to be able to be forced into a Float Type Charger with only one voltage setting of 14.2 to 14.4 volts. Lithium is easier to charge than lead acid. On the other hand lithium is a lot more dangerous. They can catch fire without any warning in your pocket while flying on a airplane when turned off or on.
                  Last edited by Sunking; 10-18-2016, 01:32 PM.
                  MSEE, PE

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