Paralleling BMS protected Li-ion packs.

[AZguy]

There is a real economy and simplicity to just using the XT90S's

[slugn]

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]

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]

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

[Diggs Ut]

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

[calfee20]

Just letting you know I am going to use that. " Ah really stands for Ass Hours!"

[AZguy]

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...

[Diggs Ut]

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.

[73Eldo]

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?

[AZguy]

....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

[Fred]

A very rational approach IMHO. I have tried both and simplicity wins out. I currently have a 16Ah 48V pack as my main pack and an auxiliary 13Ah pack with the intention of taking it along if I'm going on a long trip. In practice I have found that with 80Km + range with the 16Ah pack, I seldom take along the auxiliary pack. I have learned that while the combined batteries may be able to deliver 140Km +, my ass cannot.

[AZguy]

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.

[AZguy]

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]

hoggdoc when paralleling two packs of the same both the Ah and the current carrying capabilities double.

[Diggs Ut]

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......