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  • Originally posted by tom rickard View Post
    BMS is NOT expensive, my system cost less than $400AUD excluding the contactors (which are required regardless of top or bottom balancing).
    LOL. You do not call $400 plus support hardware expensive. Good luck convincing anyone.

    Tom it is real easy to know if you have drift, and even easier to fix if it should ever occur. Once you get down to 10% SOC all th evoltages are equal. If not you have had drift. I have never seen any drift in 6 months of operation. I also know of about 136 EV's made by Jack Rickard, all Bottom Balanced and in operation from recent to 4 years ago and no drift.

    If they do, we all have a very simple RC Hobby chargers to fix any battery problems. Most use a Powerlab 8. They will charge/discharge, balance, measure any characteristic you can name of battery of today and tomorrow. Rated at 1200 watts max. Just drive until you get near the bottom, then clip it on a cell, set to discharge to whatever voltage you want at any current you want within its limit. On a single cell can go to 30 amps charge or discharge. If you want to Top Balance it will do that with computer accuracy up to 8 cells.

    Attached Files
    MSEE, PE

    Comment


    • Originally posted by karrak View Post
      Oops, I have made a mistake, using the terminology that SK uses, Tesla use 'Passive Middle Balance'. All this means is that they keep the charging voltage of all the cells in the battery within a narrow range of each other for the whole charging cycle. Fully charging a lithium battery using this technique is equivalent to top balancing a battery.
      You are nucking Futs Simon. No EV manufacture goes anywhere near the Top or Bottom. They could not offer 8 and 10 year warranties doing that. Top Balance is for amateurs and novices. Chevy volt operates 80/20, Tesla and Nissan 90/10. Tesla's controller never turns off, which is why it cannot set for long periods without being plugged in. It use 1 Kwh per day doing nothing but monitoring batteries and shuffling power, heat, and cooling around Brick to Brick.
      MSEE, PE

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      • Originally posted by tom rickard View Post
        Why would bottom balance be any more valid than top balance for any other reason than to get a more accurate representation of 0%SOC (largely irrelevant in an off-grid system)
        BS. A solar system you do not design for 5 day reserve capacity, more like 2 to 3 days. I do not know what Utopia you live in, but the rest of us live in places with cloudy days and our batteries spend most of their life around 50%. Then we have to take vacation once in a while and cannot be there every day to take corrective action. I guess you guys down under never leave home or have a cloudy day?

        Very strange you and Karrak came here on to take part in this thread. You both came at the same time and only one or two threads. Very Interesting.

        Here is the bottom line. I don't care how you manage your batteries. Karrak already admitted he does nothing and has no BMS so i have no idea what he is squaking about. If you want to use Top Balance have it. I prefer to get the most out of my investment. What you do with your investment is your problem. But no commercial EV uses Top Balance.

        Neither of you can explain why you can buy 12, 24, and 48 volt LFP batteries right now today and no need for any BMS. If drift was a real problem they could not give you 2 to 5 year warranties. I know why you 2 do not want to acknowledge that. Right here is 13 of them sized from Motorcycle to RV House battery. NO BMS of any kind or Balance Boards. It is a FACT. They are Drop In replacements. Feed then no more than 14.2 volts and do not let them get below 10 volts.

        So stop the nonsense, you do not need BMS.
        MSEE, PE

        Comment


        • Originally posted by Sunking View Post
          I do not know what Utopia you live in, but the rest of us live in places with cloudy days and our batteries spend most of their life around 50%. Then we have to take vacation once in a while and cannot be there every day to take corrective action. I guess you guys down under never leave home or have a cloudy day?
          You have a Golf Cart charged on grid, how does this fit you or is this some general statement meant to be about solar users ??

          Comment


          • I mean a solar user having lithium batteries normally sizes their batteries for 2 or 3 days rather than 5 days like lead acid. It will be frequent you are in the lower 1/3 of the operating range of the batteries with a cloudy day or two. And if you are not there you need some fail safe protection from over discharge. All I am saying is you do not need a BMS to protect yourself form over charge and over discharge. Fine if you want to use one.

            I use a BMS but nothing like you are thinking. I have no vampire boards. My BMS is Battery Monitor System, not Battery Management System. I mimic Middle Balance by using a Bottom Balance reference. I don't even need the monitor system. Like I said Willy I use to be in the Top Balance park. I got my Orion Jr long before I built the EV. By the time I built it I flipped to Bottom Balance and worked with a couple of guru's to reprogram my Orion to use as Middle Balance. I reall do not need it as the charger can handle the charge part, and motor controler can handle the LVD. The Orion is mostly a Gas Gauge, Motor RPM, Speedometer, and system monitor. It interfaces with the motor controller. The majority of Bottom Balance EV guys do not use anything. All they do is periodic voltage checks.

            When it gets right down to it. Lithium is not ready for Solar. Too expensive right now and using Chi-Com LFP cells is a huge gamble no one if they will hold up. So far their track record is HORRIBLE. To get the good stuff like A123, Enerdel, Panasonic is 4 to 6 times more than Chi-Com. Chi-Com is 2 to 3 times higher than top end Pb which is proven 5 year service. Nlo Chi-Com has made it that long yet. CALB has been around the longest since 2007 and on their 3rd generation released last year.
            MSEE, PE

            Comment


            • Is this you Sunkink?

              Typo that I can't seem to edit, I meant [B]Is this you Sunking[/B]

              http://www.diyelectriccar.com/forums...77&postcount=1

              Anyone know for sure if Tesla BMS is Passive or Active.

              I would think Active Mid Balance shuffling power from higher energy state Bricks to Lower state Bricks. At least I think that is what I have read before. I just don't see Tesla claiming to have the "Most Advance BMS in the World." Bleeding power off as lost waste heat is not advanced IMO. But then again Musk is full of himself.

              Anyone know or have links?
              Off-Grid LFP(LiFePO4) system since April 2013

              Comment


              • Originally posted by Sunking View Post
                I have done contract work for him, and was offered a position as Executive Engineer at his company 2 yyears ago before I moved to Panama.
                Good for you, I hired an Electronic Engineer to write our Quality Assurance manual, wouldn't hire him to design anything...

                Simon
                Off-Grid LFP(LiFePO4) system since April 2013

                Comment


                • Originally posted by Sunking View Post
                  You are nucking Futs Simon. No EV manufacture goes anywhere near the Top or Bottom. They could not offer 8 and 10 year warranties doing that. Top Balance is for amateurs and novices. Chevy volt operates 80/20, Tesla and Nissan 90/10. Tesla's controller never turns off, which is why it cannot set for long periods without being plugged in.
                  I didn't say they go near the top or bottom, I said, "Fully charging a lithium battery using this technique is equivalent to top balancing a battery.". Is it that you don't read or comprehend other peoples posts unless they agree with your viewpoint, or unless you think you can use it against them?

                  I try not to go near the top or bottom except to balance my pack which I do around once a year. If you were to balance your pack you would have to take it to the very bottom 0% SOC.

                  By the way, it is very hard if not impossible to middle balance SOC of an LFP battery using voltage between the SOC range 20%-80% due to the very flat charge profile with around 0.1 volts between an SOC of 20%-80%. This flat profile means that the battery voltage will be in balance without outside intervention unless the battery is badly out of balance.

                  It use 1 Kwh per day doing nothing but monitoring batteries and shuffling power, heat, and cooling around Brick to Brick.
                  Please give me evidence of Tesla shuffling power around.

                  Simon
                  Off-Grid LFP(LiFePO4) system since April 2013

                  Comment


                  • Originally posted by Sunking View Post
                    BS. A solar system you do not design for 5 day reserve capacity, more like 2 to 3 days. I do not know what Utopia you live in, but the rest of us live in places with cloudy days and our batteries spend most of their life around 50%.
                    SK, I haven't seen any evidence that you actually have an off-grid solar powered power system with an LFP battery. As I have stated before the average SOC of my battery is 71% and has about tree days of storage in it.

                    Then we have to take vacation once in a while and cannot be there every day to take corrective action. I guess you guys down under never leave home or have a cloudy day?
                    This is exactly the reason we have a BMS, to take care of the system when we are away or not monitoring it. In my case, I can look at my battery state and query or reprogram my Solar Controller or my Battery Monitor (https://github.com/simat/BatteryMonitor) anywhere via the Internet. At some point I might get my Battery Monitor to send me an email if something is going wrong.

                    Here is the bottom line. I don't care how you manage your batteries. Karrak already admitted he does nothing and has no BMS so i have no idea what he is squaking about. If you want to use Top Balance have it. I prefer to get the most out of my investment. What you do with your investment is your problem.
                    Wrong again. My first BMS was me and a modified Cellog8, which with all the other bits and pieces would have cost me less than $50. The Cellog8 generates an alarm if any cell voltage gets out of the range of 3.6 volts to 2.8 volts, I will act on the alarm. A few days after I installed my battery this simple setup saved my battery. Still use the Cellog 8, but now have my Battery Monitor. The Cellog 8 will be retired when I get around to putting alarms on my Battery Monitor. Another part of a BMS, balancing is done manually by me. Am looking at doing it automatically using my Battery Monitor.

                    But no commercial EV uses Top Balance.
                    Evidence please, you have been wrong on so many things so why not this.

                    12, 24, and 48 volt LFP batteries right now today and no need for any BMS. If drift was a real problem they could not give you 2 to 5 year warranties.
                    It is probably a matter of economics, not so much reason to put a BMS which might cost up to several hundred dollars on a battery worth less than $1,000. Now for batteries costing several thousand on even tens of thousands of dollars it is a different story.

                    I am not looking at 2-5 years. I am hoping than by putting as little stress on my LFP battery while storing enough energy to make it financially viable that I will get around ten years use out of the battery. Time will tell...

                    Simon
                    Last edited by karrak; 05-24-2015, 02:31 AM. Reason: Added Economic reason
                    Off-Grid LFP(LiFePO4) system since April 2013

                    Comment


                    • Originally posted by karrak View Post
                      Good for you, I hired an Electronic Engineer to write our Quality Assurance manual, wouldn't hire him to design anything...

                      Simon
                      I knew it, [B]you are a manufacture[/B]. [B][COLOR=#ff0000]Busted[/COLOR][/B]. Explains it all. You do not want anyone to know you do not need a BMS. Would be bad for biz.
                      MSEE, PE

                      Comment


                      • I'm not a manufacturer, i'm a DIY off-grid customer who is trying to make information available so people reading forums like this can make an informed choice.

                        My BMS was $400AUD INCLUDING hardware and software to use a PC to monitor / reprogram cell shunts.. There was no further cost other than contactors for HVD and LVD.

                        Sunking, you keep banging on about how expensive this is, yet you then turn around and say you use a powerlab 8 to recalibrate your bottom-balanced cells.

                        So now not only do you have to deplete your cells to 10%SOC (so you have to monitor the last part of your load while you wait for your cells to reach this point), then you use a powerlab 8 which I just checked on ebay and it averages $350AUD.

                        Who's the crazy one! Now all of a sudden my BMS is less expensive than your bottom balancing system that also requires a cell-monitoring system, and a unit to activate a contactor for HVD (assuming you use your inverter for LVD and have no redundancy)

                        So for less cost, my system will keep the cells at the same voltage where they spend the majority of their life, it has a backup HVD and LVD, and can be connected to a laptop to log or monitor the cell temp / voltage / bypass current, as well as pack voltage and current.

                        Anyone reading this thread that is in the process of setting up an off-grid system can make their own decisions. Either system will work, take your pick based on the info available.

                        With regard to your drop in replacement batteries, I only personally know of one manufacturer making these (lifetech lithium), and they do contain a BMS, I looked at the link you provided, how do you know these batteries don't have inbuilt BMS ?

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                        • Interesting thread. I'll put in my 5 cents since I actually have an off-grid lithium system.

                          My battery is 35kW big and consists of 70 modules from the batteries of wrecked Leafs. Each Leaf battery holds 48 modules which each has 4 cells connected 2S2P. I have connected those 7S10P, for a 14S battery with 662Ah capacity. Total cost for the modules was approx. $3750 which I consider a good deal.

                          Picture of the battery bank: 2015-04-25 23.39.41.jpg

                          I use a Orion Jr. BMS which is set to start balancing at 3.900V if the difference is more than 10mV. This seems to work very well. I charge to 4.07V per cell and discharge to 3.40V per cell max. This means I use approx. 25kWh of the 35kWh the battery can deliver, this should vastly prolong the life of the modules.

                          Inverters are twin Outback VFX3048E's, a single Outback FM80 charge controller connected to 8 Sunpower 327W panels and an Outback FN-DC to monitor the energy of the pack (triple shunts, works better than the CAN-BUS output from the BMS). A Mate2 displays the info and there's a Victron Orion 360W DC-DC to supply the 12V devices from the 53V battery bank without going through the inverters (which are turned off when we're not at the cabin the system is installed in).

                          2015-06-18 16.04.22.jpg

                          Wrecked EVs should be plentiful in the future, I think the best deals for off-grid systems will be cells/modules from these and not brand new ones.

                          Comment


                          • Originally posted by jkirkebo View Post
                            Interesting thread. I'll put in my 5 cents since I actually have an off-grid lithium system.

                            My battery is 35kW big and consists of 70 modules from the batteries of wrecked Leafs. Each Leaf battery holds 48 modules which each has 4 cells connected 2S2P. I have connected those 7S10P, for a 14S battery with 662Ah capacity. Total cost for the modules was approx. $3750 which I consider a good deal.

                            Wrecked EVs should be plentiful in the future, I think the best deals for off-grid systems will be cells/modules from these and not brand new ones.
                            Interesting is one word for it...

                            Sounds like a great system, I am envious, it cost me around $4,000 for 10kW of new LFP batteries.

                            Wrecked EVs might be plentiful in the future in a progressive country like Norway but here in Australia I think not...

                            I think you are right, that for those people with enough technical knowledge to understand how to put together a safe system using these batteries that this is a good way to go.

                            I look forward to seeing future posts on how your system is going and how long the battery lasts for.

                            Simon
                            Off-Grid LFP(LiFePO4) system since April 2013

                            Comment


                            • Originally posted by karrak View Post
                              Wrecked EVs might be plentiful in the future in a progressive country like Norway but here in Australia I think not...
                              [FONT=Comic Sans MS]Carcasses of EVs burned by Luddites then?[/FONT]
                              SunnyBoy 3000 US, 18 BP Solar 175B panels.

                              Comment


                              • Lock up your Nissan Leafs from THEFT

                                Originally posted by jkirkebo View Post
                                Wrecked EVs should be plentiful in the future, I think the best deals for off-grid systems will be cells/modules from these and not brand new ones.
                                Interesting concept but no thanks. What nearly every serious forum that deals with batteries stresses is the importance of getting them from *reputable* dealers or authorized sources, be they AA rechargeables, FLA's, AGM's, to the latest lithiums. Wrecks or not, they are NOT SAFE when gotten from irreputable unauthorized sources. Nissan doesn't sell them to the public.

                                Aside from the ability to diy it for a one-off project for the true battery geek (and I am one!), all this really promotes is aside from salvage-yard non-authorized resellers, is the large temptation for outright THEFT. Why wait for a wreck? Leaf owners - better lock up your cars. Seriously advanced diy'ers will move beyond wrecks and eye your pristine cells...

                                There is a reason that we don't use hundreds of laptop-like cells - even if new- and simplify with large capacity lifepo4 prismatic cells instead again from authorized dealers who are reputable. There are many. Those that cheap out and go gray market pay the price both figuratively, and literally.

                                I know WB9K over at endless-sphere would probably agree about getting cells from *authorized* sources. Those that don't again pay the price for gray market, counterfeit, and unsafe cells. Your system is pretty much like a large e-bike. If you can manage that, then great, but I would never recommend this as a normal practice.

                                I know I will NEVER be PM'ing you to find out how and where to get wrecked cells. I recommend nobody else do either.

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