Lithium ion (18650) battery packs

[Gizmo10001]

Having built 3 x 20A 24v (7s 18650) battery packs, each with its own BMS. My question is would there be any problems with parallel connecting them with charging/ discharging having separate 3 bms. Having done some research cannot find a yes or no answer. Also as an afterthought I intended to add some bigger 7s batteries would that be detrimental to the setup.

Many thanks in advance to any help given,

Dave UK.

 

[Bbbbrass]

As long as BMS doesn’t freak out, no problem at all.

 

[Goboatingnow]

If you parallel charge and discharge only one bms is needed

 

[MattiFin]

As long as BMS doesn’t freak out, no problem at all.

I'd say separate BMS:ses is even the preferred method. Gives some redundancy and limits the energy in single cell internal short.
Tesla for example uses fusible links for each parallel cell so that one failing cell is not fed by dozens of cells connected parallel to it.

 

[Gizmo10001]

So if I just parallel the bms with fuses on each bank that would be safest option because removing already installed bms's would be a pain.
Also have acquired a lot of brand new 18650 2.6A/hr batteries do I have to make bank same size or can I upgrade a bit?.

Thanks all very much for the assistance, it gratefully received.
Dave