Announcement

Collapse
No announcement yet.

Paralleling BMS protected Li-ion packs.

Collapse
This is a sticky topic.
X
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    #61
    Well, I made it and it works. Not as convenient but I am charging through all four BMS's Still want opinions. Obviously I negate everything if the Batteries are paralleled through the discharge ports on the bike.

    Comment


      #62
      It all looks scary to me but then again anytime any batteries are paralleled I'm uncomfortable and the only way I'd even consider it is if the batteries were identical and purchased at the same time

      There are ways to run multiple dissimilar batteries but I wouldn't do it with out very smart management electronics

      Best is to obtain a single suitable battery

      I guess I'm not the right guy to comment

      Comment


        #63
        I had a motorcycle that had a reserve fuel valve and had a pickup truck with two fuel tanks that had a tank switch. Rather than add electronics to stabilize the discharge from multiple batteries it seems to me that a DPDT and maybe a center off switch in the pigtail between the batteries and the motor controller isolates each battery so dissimilar charges or even dissimilar batteries could be added. There would be minimal resistance loss, minor cost and something most people could build on their bench. The downside would be that you would need to switch manually.
        Would something like this work? https://www.amazon.com/Baomain-Unive...72668131&psc=1

        Comment


        • 73Eldo
          73Eldo commented
          Editing a comment
          That switch could be made to work but it looks fairly large and not even slightly water resistant. It looks like its really intended to be a reversing switch for a 3 phase AC industrial motor.which ironically is what most e bike motors are but we are controlling them quite differently.

        #64
        I just use connectors to switch between two batteries - inexpensive, reliable, quick, easy

        Click image for larger version  Name:	sw_2639.jpg Views:	0 Size:	227.7 KB ID:	128607

        Click image for larger version  Name:	sw_2641.jpg Views:	0 Size:	257.5 KB ID:	128608

        Comment


        • Growbur
          Growbur commented
          Editing a comment
          No resistance loss there. Very simple switch. Simple is good.

        • AZguy
          AZguy commented
          Editing a comment
          Since they're The "S" versions they manage the arcs too - I think that might be hard on a switch

        #65
        My post is to try and keep these like examples in one place on this forum as I originally had quite a few questions about running parallel that I couldn't find answers to. I run a BBHSD from Luna with a 52v Wolf battery. It's a country cruiser with a 52T Leckie ring up front and about 2,500 miles on the conversion. I usually charge to 80%. But, even at 100% I out-rode the Wolf battery a few times. Just when I'm most tired, it cuts out. So I built a second battery from used medical cells 52v but 5x14 instead of 4x14. (I've built packs before.) It has a 40 amp BMS wired in and it's output port is it's charge port. It is plugged directly into the second Wolf pack XT90 port. It splits the load with the Wolf pack and charges with the Wolf pack when the Wolf is charging through it's charge port. It's strapped into a trunk bag on the rear rack and I figure the two give me about 27 ah. I've never charged them together to 100%. I did that separately and then rode them individually and recharged to 80% before reconnecting. (I've only done it once as it's not quite been a year with the dual battery set up.) I'm not saying everyone should do this that wants to run a parallel setup. But I also think (as someone stated before) that many are over-thinking the issue bit. I don't like the idea of running individual packs and switching back and forth. Parallel packs reduce the load to 50% on each pack and I rarely discharge the pair below 40% (and don't charge past 80%) even on long rides. Should make for a long happy battery life not to mention the performance gains of little to no voltage sags when pulling hard on the packs.
        Last edited by Diggs Ut; 06-06-2021, 06:28 AM.

        Comment


          #66
          I'm of the notion that making a Li-ion battery from two batteries (paralleling them essentially is making one big battery from two) is a bad idea (at least not without proper electronics in between them), especially with dissimilar batteries and especially if it's to get higher current handling. There are very few competent engineers worth their salt that would say it's a good idea and if being a competent engineer that's worth their salt means over thinking things than so be it - engineers "over think" things as a matter of course to ensure it's been thunk enough Click image for larger version  Name:	i-VQKdnjW.gif Views:	0 Size:	316 Bytes ID:	129575

          I'm of the notion that if you want a larger battery for more current handling then ideally get/build a single larger battery - it's the ideal engineering approach and entirely practical with electric bikes... if there's a compelling reason to parallel batteries then provide the proper well-engineered electronics to manage that - also the proper engineering approach


          Can you get away using things that aren't well engineered or "under thought"? Of course - doesn't mean it's "optimal" or even safe... I probably wouldn't cross a high bridge with a heavy load that was designed by a guy that puts Li-ion batteries in parallel... just sayin'

          Comment


          • hoggdoc
            hoggdoc commented
            Editing a comment
            I think you are confusing the increase aH capacity running batteries in parallel with being able to provide more current (amps). To increase the current capacity the individual batteries have to be designed to output more current.

          • AZguy
            AZguy commented
            Editing a comment
            I don't think I'm confused at all

            If the only thing someone is looking for is range than there's far less compelling reasons to parallel instead of a switchover or at least some or'ing electronics. Granted if everything is perfect the batteries can share the load and only have to run at ~half output which should give a bit more life but if you aren't stressing them in the first place (they are properly sized) it's not likely to make a heck of a lot of difference and IMO still much better off to start off with a single larger battery

            If the goal is to increase output capability then it's not just a little better to go with a properly sized battery in the first place

          • Diggs Ut
            Diggs Ut commented
            Editing a comment
            hoggdoc when paralleling two packs of the same both the Ah and the current carrying capabilities double.

          #67
          I think if you had a pretty well matched set and both had the 2 wire BMSs (not a separate charge port) you would be alright without anything in between them because the BMSs should be able to at least do their jobs. Having them not very well or at all matched just seems like its hard on everything and I don't think the BMS in the Wolf can do much if you are possibly charging it though the discharge port. Big boom probably not but is it really the best use of resources? If they are pretty well matched and balanced then ya you should be splitting the load but not matched I don't think you will have an even split.

          I'm no expert on these sort of packs. Most of my series parallel experience comes from things like golf carts and diesel equipment that often uses more than one battery. In all that stuff if there is one that isn't a good match either because of age or that its just different the rest seem to suffer too. If you do decide to toss used stuff together your best results come when you load test all your options and put the closest matches together. You also should periodically load test them just to make sure they are all staying close.

          Comment


          • AZguy
            AZguy commented
            Editing a comment
            I agree it's much better if packs are identical and new, hopefully with cells from the same lot. But it's still a compromise from an engineering perspective and better to go with a properly sized/constructed battery

            Golf carts and the like are typically lead-acid and the individual batteries going into the "composite" battery are 1P - entirely different animals than what we're using here... they can/do explode (from hydrogen release) but that potential is generally much smaller and the electrolytes while highly corrosive aren't flammable

          #68
          Well, with the price of 56/70 cell packs being what it is, they are not exactly disposable that I can just throw a pack away and build or buy a 126 cell pack to replace it so adding to what I already own makes the most sense. I am a mechanical engineer (in another life) and me and my electrical engineering friends see no issues with a parallel setup as I am running as long as 100% charging is not being used and the BMSs are not balancing. (Sure, they'd like to see a fuse or two thrown in also, but....) (I see calfee20 earlier in this thread is doing the same with parallel uneven packs.) Pack voltage needs to be the same but uneven Ah packs can be used with no issues also. Again - I'm just saying this is what I've done to add to the knowledge in this thread. Everyone needs to make their own decisions......

          Comment


          • AZguy
            AZguy commented
            Editing a comment
            Why throw it away? Use it for shorter rides and save weight. Two batteries or double sized batteries are heavy (my 14s8p weighs a bit shy of 7kg!). Once you parallel a couple of batteries best to leave them that way and not try and use them independently if you are planning on continuing to use them in a parallel arrangement

          • Diggs Ut
            Diggs Ut commented
            Editing a comment
            My style is a country cruiser so the weight isn't really an issue. Some of my "short" 15-20 mile rides have spontaneously turned into some of my epic 50-60 mile wanderings because I do carry 27ah on board. I've developed a different attitude riding with that much battery. No range anxiety at all and I like to travel far and see new things.

            They do stay tied together all year except for a peak charge once in a great while as I mentioned to let the BMSs level the packs.

          • AZguy
            AZguy commented
            Editing a comment
            With two batteries I'm carrying close to the same but frankly usable Ah is closer to 22Ah which is close to what I get out of the single 8s beast

            Even thrashing it's far more than I can use but it sure is nice to not have that range anxiety

            I do ride off-road a fair bit and I remove my monster lock (prolly as heavy as one of my 4p batteries) and just run the lightweight downtube battery (13.5Ah/52V) and the bike is very noticeably much lighter than the in town configuration with two or the beast. In the desert I'm usually carrying at least 2.5kg of water though - more when it's hotter. The 13.5/52 is plenty of battery for that kind of riding too which wears me out more quickly. There are times when I've carried another on the back rack just to deal with the potential range anxiety but it's always been overkill...

          #69
          I got lucky and inherited a 14s8p pack. If I'm looking for range I still vastly prefer running two small 4p packs with the connectors to switch between them over carrying that beast. With two it's all about having a reserve/backup since only once or twice have I needed to switch over to the second battery and admittedly on those occasions I was running the packs hard (5-10A) and going on very long rides (>50mi) compared to how I normally run. I'm typically only pulling between 2.5-7A so not usually pushing anything and most rides are 30-40mi on the high side and many more 20-30mi. When I run the 8p it's when I'm pulling 10-15A for long periods and it's great for that but I just do that so infrequently that monster battery just sits - I think I've only done two-three cycles on it.

          Everyone's riding styles are different and attitudes towards "engineering" different for sure - bike building is about individualism towards the approach, risks, costs, etc. - we're all "amateur engineers" to a point

          For me the two packs with switching between the two covers 99% of my riding super well with the peace of knowing that I don't have to try and manage a parallel effort, that I can mix 48v and 52V or different age batteries with zero concern and that I can save weight for ~80% of my rides by only carrying one. I like that having two gives me that added benefit of not only improved reliability over a parallel arrangement but also if one does go bad for whatever reason I have the second as backup. Once I had a minor battery failure at the connector where it goes into the mount and I just scratched my head, switched over to the "reserve" and dealt with it back at the shop.

          I have that monster 14s8p if I'm feeling frisky and IMO is just light-years more preferable to a parallel setup. I may end up getting one of those V2 controllers one of these days and it would be great for that - far more appropriate than a parallel.

          If someone's continuous draw is typically well under half the rated output of the battery and the primary reason to carry two is range then I see a simple switch-over setup being far more preferable to a parallel setup. It's a different discussion if it's about getting higher currents but still there's just no way a parallel arrangement is better than a large battery designed for those currents.

          Click image for larger version

Name:	ricky.gif
Views:	518
Size:	1.3 KB
ID:	129639

          Comment


          • AZguy
            AZguy commented
            Editing a comment
            Originally posted by Fred
            ....I have learned that while the combined batteries may be able to deliver 140Km +, my ass cannot.
            +1!!!

            I've done 100km and that's past what my old bones can handle

          • 73Eldo
            73Eldo commented
            Editing a comment
            Ya my ass and grip strength range is greater than a 12ah Wolf but not by much. When I only had the 12ah battery I thought that was my limit but after I got the 13.9 and a 20 something I found out ass is the limiting factor. Ah really stands for Ass Hours?

          • calfee20
            calfee20 commented
            Editing a comment
            Just letting you know I am going to use that. " Ah really stands for Ass Hours!"

          #70
          To add to the knowledge of this thread there is a device distributed by Bolten Ebikes that allows any battery packs of the same voltage to be used in parallel. They can even have significantly different charge levels. He provides the details here -




          ...and there is also this
          Last edited by Diggs Ut; 10-13-2021, 05:05 AM.

          Comment


            #71
            Originally posted by Diggs Ut View Post
            To add to the knowledge of this thread there is a device distributed by Bolten Ebikes that allows any battery packs of the same voltage to be used in parallel. They can even have significantly different charge levels. He provides the details here -




            ...and there is also this
            I have seen these around.
            If one were to guess, what is inside these units that demand such a high price? especially the DATEx2? I have been searching for a DIY solution and the closest I can find is to use schottky diodes, as mentioned earlier in this thread.

            There is also this unit from Victron Energy.

            I think at this point I will just keep it simple and get some XT90-S plugs
            Guarantee continuous DC power to mission-critical equipment with Argo Diode Battery Combiners. Find a Victron Energy dealer near you.

            Comment


            • AZguy
              AZguy commented
              Editing a comment
              The problem with schottkeys, even really large ones is they will drop a lot of voltage, likely even more than the large Si diodes... so you end up losing a voltage right off the bat that just turns into plenty of heat instead of motion

              These are what they call MOSFET "ideal" diodes or or'ing diodes which use MOSFET's in place of the diodes to get a lot less drop... it's not magic for sure and the sharing concept still only really works with like batteries at similar charge... if one is much less than the other the greater one will be handling nearly all the load until it gets down where the other one is and if one has a higher ESR (internal internal resistance) then it won't provide as much current even once they reach a "balance"

              It's not like it's a bunch of super expensive parts but they aren't free and by the time you make it into a product it will really depend on how many you sell to offset all the up front costs which aren't free by any streatch

            • slugn
              slugn commented
              Editing a comment
              Thanks very much for the info! For now I will stick with the XT90-s plugs until I am more educated on the subject.

            • AZguy
              AZguy commented
              Editing a comment
              There is a real economy and simplicity to just using the XT90S's

            #72
            Would this be a suitable diode to isolate battery packs?

            https://www.mouser.com/ProductDetail...N5APAW0w%3D%3D

            It's for a peak 1750w build, I'd like it to be compatible with 52v batteries for future proofing, and also that can handle 35 amps per battery as a just in case scenario. At 150v and 40 amps per leg this is overkill, but the next best option a step down is 30 amps per leg and the only benefit is maybe .1v less voltage loss so I don't see the benefit. This one also has extremely low reverse current to prevent batteries charging each other.

            Comment


            • AZguy
              AZguy commented
              Editing a comment
              Not really

              A quick look at the numbers in the datasheet and:

              15A through 1 diode you will be dumping somewhere around 10-15W (figure 1 in data), 30A closer to at least 25W and dropping voltage at least 0.5V @15A (figure 7) and approaching a full volt at 30A

              It will get hot, hot, hot and the heat is just wasted battery power - at 30A the temperature will depend on the heat sink (without one will just fry, they don't even specify the thermal impedance to ambient)

            #73
            Now this is a great thread. The world has circuits for everything to be done in every way. And the world has the Chinese that, until recently, have nothing better to do than build every circuit idea they can steal and sell it back to us. Im such a shameful criminal buying their stolen stuff like that. Hah. Anyways, here is a circuit that takes care of all the head aches of all the things we figured could go wrong. It basically keeps both batteries seperate, but keeps the power flowing till both batteries are spent. This is the circuit I want.



            Im just wondering if all this stuff is inside that Shunt Box thingy people posted about previously. Has anybody opened the Gizzmo to see whats inside? I see them costing $35 on AliExpress and they are good for 40 amps. Seems like it would have these Mosfets devices and all the goodies to control them.

            The thing is, to just hook 2 batteries in parrallel, you get the 2 wasting their energy charging each other. And this circuit prevents that. So you can add a fresh battery next to the half used one and they both get used with no waste at all. So its all brainless and you dont have to keep track of anything. You can even use a boost circuit to crank 36v hoverboard packs to 48v and then plug into this circuit. So both packs are used fully as if you have two 48v packs. Or even use 24v packs, if there any of those out there. American circuits are crazy expensive, but the chinese make them for pennies on the dollar. I remember the car stereo world was so much fun. Getting preamps, amps and boosters and they all hooked together so easy. Now they got compatibility modules that cost as much or more than the head units you want to power up. I cant even run my factory radio in my identical spare car that came with no radio. It says the vin number doesnt match. Hah.

            Comment


            • stts
              stts commented
              Editing a comment
              Well when I saw that circuit I figured everybody would go nuts over it, with all the worries of how batteries can be put together. I been thinking about it more and its not cheap to DIY entire circuits. Especially with the cheap prices the chinese charge for these things. So Ill end up doing something with this. Its just too sweet of an idea. And since BMSs are selling like hot cakes for cheap, Im thinking I could use those cheap for parts. One mos cost as much as some of those BMSs that are full of Nmos's. I may even just tap into a BMS as it is to use its battery cut off circuit. They all cut off the Negative with overcurent and undercharge. I could hyjack the gate drivers and put a small breadboard on top with the right side of that circuit suitably modified to handle higher voltages. That takes a bunch of work and expense out of actually working this out. But right this minute, ALIexpress wont even sell anything to me, so I got that problem to get worked out first. I looked at a bunch of other China websites but Ali seems to be the king of the electronics side. I may have to take a chance and start sending them wire transfers. Market places stateside are just too expensive these days.

            • AZguy
              AZguy commented
              Editing a comment
              Yeah I gave up on Ali - they wanted my passport and seemed like everything short of an anal probe

              I do a lot of small circuits but have all the tools and usually can quickly identify the limitations of what should be attempted at the small scale - I don't mind spending some time/money on these "hobby" electronics but I have limited time for it

              Whatever you choose to do good luck.. if looking for advice I've got plenty of background with this type of stuff... do it just about every day ;-}

            • stts
              stts commented
              Editing a comment
              Yea, Im having nothing but bad luck getting stuff right now. I just got an email that Battery hookup cancelled my battery order. It seems they had less than advertised. Just peachy. Oh well, I got plenty of machining on my bike parts to keep my busy for the time being. Next is angle aluminum to make a box on a hinge. 6 inch by 4 inch and 1/2 inch thick. Ill mount it to the center bolt on the handle bar. 8 inches wide should hold the computer, switches, temperture display, and whatever else I can cram in there with a rubber cushion. I can close and lock it to keep it dry and people out of it. So a vandal cant beat my controls to pieces. Seems people have been tossing the green rental scooters into the river. So we got haters around here. No point in giving easy access to the whizz bang stuff on my bike.

            #74
            I found the circuit thats in those shunt box thingies. Its an Nmos switching out the ground. But only on one battery. The other is running thru the schottky. Not very ideal. But it does go to show that either power or ground is a snap to be switching out. I wont be buying into this circuit for $40. The schottky is wasting the battery. Ill be looking more for a diode free solution. Like in that awesome circuit above. Who knows. Maybe Ill just build it up eventually. An Nmos version. They are way cheaper at the higher currents.

            Click image for larger version

Name:	51-IscVXwoL._AC_SL1000_.jpg
Views:	50
Size:	91.8 KB
ID:	154306

            Comment

            Working...
            X