BMS capacity in parallel connection.

[Pawel1976]

"What happen if I set my controller at 40Amps for example and forget to turn one battery ON?
Knowing, that my battery pack BMS is 30Amps. Does it mean the controller or BMS will shut the system? Because of overcurrent?"

It's already been established that there is no overcurrent protection from the BMS, unless you have a short circuit. It will not stop you from running at 40A, if the cells in the single battery are capable of that. It could overheat and melt. That will stop you,

It should also be emphasized that you're not allowed to forget things when you run batteries in parallel. Forget to turn on one battery, Ride 20 miles, Better not turn the other battery back on. because the voltages re no longer equal. That's why I like battery blenders. CHalo points out their limits, but humans have worse limits,

What kind of bike are you riding that needs to pull 40A anyway. I have to assume it's a pre-built commercial scooter?

No escooter, It's a bike. Yes, I build it. It is similar to MATE, PVY, ENGWE engine Pro etc. or other 20x4 inch fat tire ebikes.
Yes I use 40Amps blender

 

[Pawel1976]

"What happen if I set my controller at 40Amps for example and forget to turn one battery ON?
Knowing, that my battery pack BMS is 30Amps. Does it mean the controller or BMS will shut the system? Because of overcurrent?"

It's already been established that there is no overcurrent protection from the BMS, unless you have a short circuit. It will not stop you from running at 40A, if the cells in the single battery are capable of that. It could overheat and melt. That will stop you,

It should also be emphasized that you're not allowed to forget things when you run batteries in parallel. Forget to turn on one battery, Ride 20 miles, Better not turn the other battery back on. because the voltages re no longer equal. That's why I like battery blenders. CHalo points out their limits, but humans have worse limits,

What kind of bike are you riding that needs to pull 40A anyway. I have to assume it's a pre-built commercial scooter?

No, I'm not going to go crazy holding the throttle all the time. I'm pedaling most of the time, but it's good to have it in your head, you have the power and you can use it if you need it.

 

[Pawel1976]

"What happen if I set my controller at 40Amps for example and forget to turn one battery ON?
Knowing, that my battery pack BMS is 30Amps. Does it mean the controller or BMS will shut the system? Because of overcurrent?"

It's already been established that there is no overcurrent protection from the BMS, unless you have a short circuit. It will not stop you from running at 40A, if the cells in the single battery are capable of that. It could overheat and melt. That will stop you,

It should also be emphasized that you're not allowed to forget things when you run batteries in parallel. Forget to turn on one battery, Ride 20 miles, Better not turn the other battery back on. because the voltages re no longer equal. That's why I like battery blenders. CHalo points out their limits, but humans have worse limits,

What kind of bike are you riding that needs to pull 40A anyway. I have to assume it's a pre-built commercial scooter?

Ok, You don't even know how much I appreciate your advice. Thanks so much. Im going to keep it at 25 or 28Amps, then, when I change the batteries for 52V I get full enjoyment then.

 

[lnanek]

Every BMS I've ever had, had a max current it cuts out at that forces me to turn the pack off and on to reset again. I've even run into the case chalo mentioned where I had a battery with 20A max discharge rated BMS and a battery with 40A max discharge rated BMS plugged into a battery blender, had my controller set to draw 30A max, and the BMS on the weaker battery tripped the first time the blender switched to using it as the stronger battery depleted. That battery was then useless the entire trip until I stopped to turn it off and on again and reprogrammed my controller not to draw over 20A.

 

[Pawel1976]

Every BMS I've ever had, had a max current it cuts out at that forces me to turn the pack off and on to reset again. I've even run into the case chalo mentioned where I had a battery with 20A max discharge rated BMS and a battery with 40A max discharge rated BMS plugged into a battery blender, had my controller set to draw 30A max, and the BMS on the weaker battery tripped the first time the blender switched to using it as the stronger battery depleted. That battery was then useless the entire trip until I stopped to turn it off and on again and reprogrammed my controller not to draw over 20A.

Yes, exactly whst happened to me twice. I run 2x48V, 30Amps BMS each battery, in parallel via blender. Set my controller for 35Amps and during the ride with a throttle more than pedalling... In one moment on the middle of the road everything went down, all power off. The controller was extremely hot, but after few hours, everything hss been reset and was working again. So, I didn't change anything. I wanted see, if the same happens again and YES, it happened again, all power off. Now, I did set my controller for 25Amps and second day riding everything looks good.
Going to change my batteries for 52V with better and bigger BMS. Then, I will use my motor and controller fully.

 

[wturber]

Ok, so the answer should be NO!!!
NOooo, you can not, its not safe, set it under 30Amps. Period.
Simple as that. Thanks

Unfortunately, the world isn't as "binary" as so many people want it to be. You were given a nice, nuanced explanation but seem either unable or unwilling to assimilate it.

I would interpret his answer to be: Yes, it would probably work. But there are enough variables in play that it might not. But see, that's not binary.

The concept of "safe" itself isn't binary either. Nothing is absolutely safe. Things are merely relatively more or less safe.

 

[Dui ni shuo de dui]

You said " So, to answer your original question, you should set your controller to limit the current at any number of your choice as long as it is below 60Amps."
What happen if I set my controller at 40Amps for example and forget to turn one battery ON?
Knowing, that my battery pack BMS is 30Amps. Does it mean the controller or BMS will shut the system? Because of overcurrent?

It means that the BMS will be likely to shut off the power when you will try to accelerate, yes.

I recommend that you keep both batteries always connected together and always ON or OFF at the same time.
You need to understand that both batteries should be in perfect balance all the time. Otherwise that might lead into big problems: lets say you have one battery that is fully charged and the other is discharged and you try to connect them together: the discharged battery will pump as much current as it can from the charged battery until they reach equilibrium. In which case it will trigger either one of the BMS from overcurrent. It is also possible that it might damage the BMS while connecting, so you should always keep that in mind, which is why its just better to never disconnect them from each other.

 

[Dui ni shuo de dui]

It's already been established that there is no overcurrent protection from the BMS, unless you have a short circuit. It will not stop you from running at 40A, if the cells in the single battery are capable of that. It could overheat and melt. That will stop you,

Established by whom?
Two people including myself already corrected you on this point.
Every BMS has overcurrent protection. Again, that is the main purpose of the BMS.
A BMS that offers no overcurrent protection is called a fuse.

 

[Pawel1976]

It means that the BMS will be likely to shut off the power when you will try to accelerate, yes.

I recommend that you keep both batteries always connected together and always ON or OFF at the same time.
You need to understand that both batteries should be in perfect balance all the time. Otherwise that might lead into big problems: lets say you have one battery that is fully charged and the other is discharged and you try to connect them together: the discharged battery will pump as much current as it can from the charged battery until they reach equilibrium. In which case it will trigger either one of the BMS from overcurrent. It is also possible that it might damage the BMS while connecting, so you should always keep that in mind, which is why its just better to never disconnect them from each other.

thanks I will do exactly as you said

 

[lnanek]

Maybe he's just used to working with separate/split port BMS instead of common port BMS. Common port, both the charger socket and controller leads connect to the same pads on the BMS. Therefore that negative pad has MOSFETs chained facing both directions to protect the pack from both charging and discharging too much.

Separate port BMS has different pads for the charger socket vs. controller. So the charger negative pad only has FETs one direction to protect from over charging and the controller negative pad only has FETs to protect from over discharging. Therefore regenerative braking and any second battery paralleled in to the controller bypasses any protection that BMS has for charging. This is why some people claim you should "parallel" batteries by plugging one into the charge socket of the other instead of connecting both batteries to the controller.

That or he's saying plugging in a discharged battery to a charged battery will burn things up so fast the BMS doesn't have time to save anything. Could technically be true if it is designed to just trip after a few seconds instead of immediately or the FETs overload and fail closed. They do have a certain breakdown voltage, I think.

 

[wturber]

It means that the BMS will be likely to shut off the power when you will try to accelerate, yes.

I recommend that you keep both batteries always connected together and always ON or OFF at the same time.
You need to understand that both batteries should be in perfect balance all the time. Otherwise that might lead into big problems: lets say you have one battery that is fully charged and the other is discharged and you try to connect them together: the discharged battery will pump as much current as it can from the charged battery until they reach equilibrium. In which case it will trigger either one of the BMS from overcurrent. It is also possible that it might damage the BMS while connecting, so you should always keep that in mind, which is why its just better to never disconnect them from each other.

Yes. I ran 8 "hoverboard" batteries (10s 2P) in parallel for five or six years now configured in two banks of four. They were always charged with all 8 connected and always run with all 8 connected. I only disconnected a bank or pack when I would occasionally do a spot check. I was pleased at how they all stayed charged/discharged at the same voltage for so many years. It was nice to have the capability of eliminating a bank or pack in case of a failure. But none ever did so I never had to run with any disconnected.

 

[Dui ni shuo de dui]

Yes. I ran 8 "hoverboard" batteries (10s 2P) in parallel for five or six years now configured in two banks of four. They were always charged with all 8 connected and always run with all 8 connected. I only disconnected a bank or pack when I would occasionally do a spot check. I was pleased at how they all stayed charged/discharged at the same voltage for so many years. It was nice to have the capability of eliminating a bank or pack in case of a failure. But none ever did so I never had to run with any disconnected.

Yeah, it's not forbidden to disconnect one from time to time of course, but better make sure both are always fully charged when connecting them together. That's the easiest way to make sure they are very close to balanced