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.
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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 commentComment
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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=1Comment
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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
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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
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
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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
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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
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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
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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
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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 -
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. -
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...
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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.
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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
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I have seen these around.Originally posted by Diggs Ut View PostTo 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
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 plugsComment
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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
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Would this be a suitable diode to isolate battery packs?
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
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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)
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waste of timeLast edited by stts; 03-24-2023, 03:24 PM.Comment
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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 ;-}
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