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    Parallel Batteries with Ludi BBSHD

    I hav been testing parallel battery setups with my hub motor. Everything good and safe and stable. I get consistent more power for longer and a bit more torque.

    my question is this 2 40A BMS 52 V 19.2 AH BATTERIES

    would this mean I can setup controller to draw 80A without overwhelming the bms in each battery since it will draw 40 and 40 or will I still be limited to the per battery max bmsbut it’s still splits for example set controller for 40A max and it will use 20 and 20.

    also is this the same for wattage as both batteries ideal output ration is 200-2000watts. Would that mean that combined the draw can be up to 4000w.

    asking this questions I don’t want my ludi to ruin my batteries would like to setup settings on ludi well.

    thanks in advance

    #2
    Well it may seem like its working good, but theres a little war going on and there are no settings inside your bike controller that can stop it. When you plug 2 strait together, they imediately start charging each other up at very high current. And if one battery is further off from charge than the other battery, it will be extremely high current. And that wastes your charge and its hard on the batteries. After a bit of time, the war settles down and your batteries are warm or even hot. Thats the charge you had that was wasted. So you will get longer range with 2 batteries but not twice the range.

    AS for 80amps from the pair, yea its possible. But theres nothing stopping 50 amps out of one and 30 amps out of the other. Especially if you take off on a hard run right after plugging both batteries in. Its all up the internal resistance of the batteries. So as they age and the resistance changes, more problems will rise up of one pack being forced to work lots harder than the other pack while you have no idea a war is going on.

    So you really need a circuit gizzmo that allows 2 packs to be parallel. The only thing simple is this thing from Amazon.
    https://www.amazon.com/gp/product/B0...MIJXIQ5P&psc=1

    Its not perfect and also wastes some of your charge, but it keeps the 2 packs from fighting each other. But it still wont stop one pack from being forced to pump out more than its amp rating. But even this device is not good for more than 40 amps total. And its unkown how this gizzmo will reacted to being over amped. It may simply fail while the BMS might simply shut down temperarily.

    Comment


    • paxtana
      paxtana commented
      Editing a comment
      We have tested and found running parallel with significant imbalances does not cause a huge rush of current from one pack to the other even with voltage difference of a volt or two. Though to be fair we did not take things further extreme than that; likely the equalization would scale with the level of imbalance, but to what extent we do not know.

    #3
    I'm not an expert at his so check what I say . But it seems that you have created a 52V (which would be 14s battery) that is twice as large (so maybe 8- 10p). The individual cells have an Amp limit.
    18650 is usually 35A. But 21700 can go to 45A. So you have the same Voltage and Amps, but twice the Watt hours. It actually might make as much sense to just have a switch to go from one battery to the other to avoid the issues mentioned above. 2x36V batteries in series would get you 72V. But there are 72V 21700 batteries available. Higher Voltage at the same amps is easier on everything. But thermal limits can be exceeded that way also. The Ludi controller can probably handle that but the stock one won't.
    You said BBSHD, but then mentioned hub motor???
    If you put them in series then 104V x 40A= 4160W. That's getting into electric oven territory. So if you're trying to cook something.........
    But 60-72 Volts 21700 batteries makes more sense.
    A fully charged 52V=58Vx40A=2300W so that's where I think you're at. Up from 30Ax48V (54V)x30A=1620. And with almost 40Ah you can actually use it when needed.
    750W=1HP. So you've gone from 2HP to 3HP. A pretty good bump.
    Last edited by Retrorockit; 09-04-2022, 07:38 AM.

    Comment


      #4
      Have you read through the discussion on parallel packs?

      https://electricbike.com/forum/forum...d-li-ion-packs

      Comment


        #5
        Guys my setup has worked wonders. The performance increase by joining packs 2x 20ah is significant I use to be 1 pack at a time guy.
        stts Ebiker​—- you are right I monitor every run for this reason and suspect this will be an issue in some time but both parkas are brand new and together.

        my biggest dilemma is this the Ludi setting have a battery Amp limit. It goes up to 105A. The confusing part is the the wolf pack has a 50A bms yet the Luna press for the app and 52 wolf pack and fire wolf pack are much higher than that so it has me going in circles.

        im not sure what to put there because the mate does not have 50a for a wolf pack.
        Attached Files
        Last edited by Wamedrano; 09-04-2022, 11:14 PM.

        Comment


          #6
          When doing the parallel thing, The best way to deal with it is to charge them both at the same time from the same plug. Then they are both at the exact same voltage because they are hooked together. Then they wont have big currents running between then. They could each settle from their charge differently, so you keep them hooked together until you put them in your bike, so they cant settle to different voltages. That keeps the war between them from getting very big. For now. As for the BMS rating, Its not clear what will happen. These batteries can spike at hundreds of amps for very short time periods, with no danger to the batteries. No heat is generated for these short spikes. But its unknown how many of these spikes the BMS will tolerate. It depends on the BMS. So if each of your packs has a different BMS, Its unlikely that each will react the same as you demand amps that are twice the single pack limits. If one pack is not willing to supply all of its fair share, then you got no idea if the other pack will supply all the rest without that BMS doing something. Like its fuse blowing, or a current limit circuit shutting it off, or a thermal failure of the BMS drivers. And when something does happen to that battery to cut off its current, then ALL demand then goes back to the other pack that refused to do its fair share. And its BMS will then quickly cut off all its current, blow its fuse or blow up its drivers. Making both packs dead all the sudden. And possibly a rather violent death.

          So its Russian roulette to be running 2 big packs together like that for the purpose of getting twice the current. Its best to not demand on a continual basis more than each can put out alone. The more you demand over that, the more dangerous it becomes. And that's the way it is with batteries just hooked together. Packs are made with small batteries hooked in parallel. But the max pack current never goes beyond what each cell is able to put out. And the BMS is like the safety fuse. Your two packs have "fuses" that are too small for what you are doing. And its unknown what each cell is being demanded to do because we don't know the details of your pack build.

          Assuming 18650's, each cell being 2500mH. Then for that pack to run for an hour, it would be 8p pack to give 20 amps for an hour at 2.5 amps per cell. No sweat for the cells. Double the demand to 40 amps, and your pack would last 30 minutes with each cell dumping 5 amps. Still workable for each cell. Double it again to 80 amps and each cell is now forced to dump 10 amps each for 15 minutes before they are drained. These cells today can do it but they will have a shorter lifespan. But the BMS in the pack wont allow it. The further past 40 amps it goes the sooner the BMS will react. It could allow 50 amps for a short time. But we got no clue what the tolerance is.

          And what if its not an 8p pack. Then each cell has an easier or harder life. Totally unknown without the build details. The BMS was chosen to limit the maximum strain on the batteries. Its not a regulator circuit. They limit by totally cutting out. That's fine in a single pack situation because the BMS is in complete control. But with 2 in parallel, and neither BMS talking to the other, shit can hit the fan if one BMS decides its had enough. If there is a cell failure, then all the sudden the internal resistance on one pack is not the same as the other pack. So now you got one pack suddenly feeding the other pack balancing current, in addition to all the current demands its already pumping out.

          So its indeed russian roulette that's going on when demanding more that a single packs rating. I always look at parallel packs as range extenders. Especially if you have 2 small packs. But its dancing with the devil to run them like power amplifiers.

          As for the Luna software, leaving it at 105A is just very dangerous. Your packs may quit violently if your Luna demands 105 amps. 40A BMSs wont put up with it. And Im confused more about what you have because you said before that you had 40A BMS in your packs. I can only say to drop the current to around 40Amps because I don't cliff dive or fly wing suits. Both of those activities work. But it's not a recommended activity, Hah :)

          Last edited by stts; 09-05-2022, 01:52 AM.

          Comment


            #7
            One thing about the Volts vs. Amps question is wire sizes go up considerably with Amperage. In automotive systems 6 Volt requires larger cables than 12V, and buses with their rear engines, complex lighting, with climate control and safety interlocks for various devices go to 24V to reduce the weight and cost of their more complex electrical system. Even though this makes every single electrical part specialized and more expensive. So 72V @30A. would probably be a better solution than 52V. @ 40A. for the same power. You may have a controller rated for higher power but the windings in the motor are the same.
            At the power you have now how are your brakes, tires, driveline, and suspension working for you?

            Comment


              #8
              Guys we are getting technical and I appreciate it but it does not answer my question. The Ludi app has 3 preconfigured profiles for the Luna batteries. My concern is that wolf pack has a 50 amp bms but in the app the wolf pack profile has it at 70 amps. Am I missing something ? if you do not know how to use Ludi settings app probably not the question for you. I would never run 105 amps that would be ludicrous. And I have been running the 20ah ones for a while on my juiced bike always at the same voltage .

              Comment


                #9
                You want a non technical answer to a technical question. I got no clue what you think your missing. BMSs are known to be able to supply more than their advertised rating. So there you go. A 50 amp could pump out 70 Amps. But that doesn't mean this is what's going on. For highly specific technical details, You have to call Ludi customer support. They have V1 and V2 packs. They use medium and high energy cells. And the App pic you posted is clear as mud. There's 3 unselected pack choices and no clue what those settings are referring to. You start out talking twin 40 amps and then switch to 50amps. The app in your picture is 105 amps. Not 70 amps. So trying to figure what you want is like watching flies buzz around my head. Some BMSs will over current more than others. Some wont even last very long at their rated current. You have to ask them to tell you what setting for your App. And they probably wont tell you why. Or they might not tell you anything if you tell them you have 2 packs in parallel.

                Comment


                  #10
                  Okay SSTS thanks for your input but the app has three settings max is 105A but; when you select Wolfpack it marks it as 70A yet the battery tech spec is 50A bms. When doing parallel the batteries share the load so when pulling 40 amps they are pulling 20 and 20 amps each hence why voltage slag is very low when batteries in parallel. Example one battery in R mode will sag 6-7 volts While in parallel it only sags 1-2 volts max. So that’s why I assumed it would do but I mentioned 40a because I also have 20ah 40 a packa

                  Comment


                    #11
                    Well that makes it abit clearer. But my answer is still the same. Its possible that the 50amp BMS can put out burts of 70 amps. Hence why the Ludi is allowing you more Amp room. To know for sure means you would have to research the 50amp BMS in that pack. But they pot it in. So its not easy to discover what Luna put in that pack. And not easy to figure out exactly how much over current that BMS allows. Tech support would know, but they pot the whole pack in. That implys that they don't want people digging into their packs. So you can call them and quiz them a bunch for technical details, but its hard to say if you will get anywhere. So all you can do is ask why the 70amp wolf setting is right for the 50 amp BMS. Or if they seriously suggest you drop it lower. If they say 70 is fine, then that implys they have a robust BMS in there. If they say drop the setting way lower, then their BMS is not so much. :)

                    Comment


                      #12
                      Wamedrano you do not have to select one of the presets, you can adjust the max current to whatever you want. The presets are just a handy thing to use if you want to do so but selecting them is not inherently better than manually selecting what would work best for your situation.

                      With two in parallel you could probably set max in the app anywhere from 80-100A without tripping the bms. At that much current I would be more concerned about the chain snapping than a battery issue; I recommend a beefy 8s groupset from box components

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