BMS on two separate Limitless 15AH?

[Cardboardcat15]

Quick question here for lithium guys. I'm currently running a limitless 15ah as my secondary batt. I'm looking to grab a second one (space is an issue, hence the need for the 15ah specifically.) 

 

Do I need to run a BMS between the two? The one I currently have has been used for maybe 2 weeks now.  From what I understand, they are internally balanced, but I don't know if I need to run an external balancer between the two, or If I can just toss it in without one. 

 

[SnowDrifter]

A BMS isn't like an isolator - you don't run it between things

It's a comprehensive system that controls things like cell balance, error checking, low / high voltage protection, low / high temps and can do some temperature control like fans if you have that stuff hooked up.

I can't speak to what limitless uses inside their batts, if anything. But IF they have their own BMS internally, then you'd charge them to similar voltages and wire in parallel as conventional. If they don't then I wouldn't touch the things period.

[Cardboardcat15]

On 7/13/2020 at 10:52 AM, SnowDrifter said:

A BMS isn't like an isolator - you don't run it between things

It's a comprehensive system that controls things like cell balance, error checking, low / high voltage protection, low / high temps and can do some temperature control like fans if you have that stuff hooked up.

I can't speak to what limitless uses inside their batts, if anything. But IF they have their own BMS internally, then you'd charge them to similar voltages and wire in parallel as conventional. If they don't then I wouldn't touch the things period.

Thanks for the reply snow! I actually just got a response from the limitless guys and confirmed they do have an internal balancer, but not a full BMS. 

 

I do have temp sensors and fans on the current 15ah im running now, but i don't really have a way to check internal cell voltage or discrepancies between the cells. I'm wanting to run another 15ah due to weight concerns, but am still unsure about it.

[bmwking]

22 hours ago, Cardboardcat15 said:

Thanks for the reply snow! I actually just got a response from the limitless guys and confirmed they do have an internal balancer, but not a full BMS. 

 

I do have temp sensors and fans on the current 15ah im running now, but i don't really have a way to check internal cell voltage or discrepancies between the cells. I'm wanting to run another 15ah due to weight concerns, but am still unsure about it.

if they have an internal balancer, i wouldnt worry about discrepancies between cells.  that's literally what it's there for.  if you have one fail, limitless will take care of you.  dont crack it open unless you're sure you don't want customer support for it ever again.

 

whatever the voltage reads at the terminals is what you should go by.

 

you can freely connect both 15ah banks in parallel the same you would any other battery, there are plenty of examples out there on google n youtube of guys running multiple lithium banks

[bmwking]

and if memory serves correctly, limitless uses LTO cells in their batteries.  you may be able to make your own for cheaper.  i believe a 15ah bank is only 4 ying long cells wired in 4s

[slowfkncar]

The balancing circuit is only for cells in series, same health and chemistry in parallel is perfectly fine.

[SnowDrifter]

9 hours ago, bmwking said:

if they have an internal balancer, i wouldnt worry about discrepancies between cells.  that's literally what it's there for.  if you have one fail, limitless will take care of you.  dont crack it open unless you're sure you don't want customer support for it ever again.

 

whatever the voltage reads at the terminals is what you should go by.

 

you can freely connect both 15ah banks in parallel the same you would any other battery, there are plenty of examples out there on google n youtube of guys running multiple lithium banks

This is accurate

Just make sure there within a fraction of a volt of eachother before you connect them or you might have some sparks. 0.2-0.3 should be fine. But don't hook one up that's at 12.2v to one that's sitting at 14.2 or you'll be sad