JK 200a vs Overkill 100a

[TheHappyNomads]

My battery modules have arrived and I am preparing to (trying to at least) get the rest of the initial components necessary for my 48v bank. I'll have a total of (4) 48v battery banks and understand that best practice would be to have a separate BMS for each one. I have been looking at getting a JK-BMS 2a 200a and an Overkill 100a but am not really sure what would be ideal?

I know Overkill has rave reviews from Will and it's the first BMS he suggests on his website but I have observed that people on the forum have very high praise for the JK's.

 

[curiouscarbon]

First question: is your need for amps satisfied by both of those? (100A vs 200A)
Using a 200A BMS at only up to 100A poses no problem as long as the cost is tolerable.

JK pros : active balancing, pretty good track record
JK cons : software/firmware seems a little immature (my opinion)

JBD pros : pretty good track record, maybe more DIY code available if that's your thing
JBD cons : only passive balancing, some models can't update firmware (it seems?)

I stumbled across JBD first, and went with that for my projects, and it's been reliable so far. I don't need active balancing right now, so it's ok.

Both can do bluetooth monitoring/settings from a mobile phone, so that's nice.

What sort of requirements do you have for the project? How many watts do you want to be able to discharge at the peak? Do you have any care or opinion about whether active balancing?

 

[Rednecktek]

JK Con: Stupid power button screaming rebooting hassle!

The thing to consider is really the load.

48v @ 200a = 9600w continuous draw
48v @ 100a = 4800w continuous draw

So a 6Kw inverter would require at least 2 batteries at 100a or a single 200a battery.

Personally I'm a JBD fan, but they don't make anything for 24v over 100a which nixes them for my projects.

 

[TheHappyNomads]

My plan is to use (2) LV6548s. I'm still trying to wrap my head around the load draw. Can you say a little more?

What's the difference between active and passive balancing?

 

[curiouscarbon]

Is 120V AC power the goal? (Parallel connecting the two inverters)
Listing off some of the appliances that need to be run will help estimate the load draw.

LV6548 says 6,500 Watts and 48 Volts.
Amperes = Watts / Volts
Watts = Volts * Amperes
(Referring to Ohm's Law)
so
6500 Watts / 48 Volts = 135 Ampere minimum, ignoring any loss from resistance in the wiring and connectors.
Around 15% loss can be assumed for the inverter itself. So around 135A/0.85efficiency = 155 Amps. (1-0.15 = 0.85) per inverter

If you wish to run Two (2) LV6548 devices, then the max load of 6.5kW * 2 might be around 155 A * 2 = 310 Amps @ 48V.

Four 48V batteries (in parallel) are mentioned for the plan, so this ~310 Ampere load would be hopefully spread evenly as ~77 A to each battery.
This would imply that a 100A BMS should suffice, assuming all four batteries are sharing the load somewhat evenly.

---

Active vs Passive balancing.

The battery is made up of cells. In order to get the most energy in/out of a battery, the cells need to be somewhat balanced.
If any one cell goes too high or low in voltage, the BMS will have to disconnect.
So, a balancer helps keep the cells paced at the same part of the lap to prevent "early" disconnect.

Passive balancers just "burn off" energy by heating up a resistor temporarily connected to the highest voltage cell.
Active balancers actually exchange energy between cells by taking energy from the highest and spreading it back out to slightly recharge other cells.

There's a slight efficiency win with active balancers, but with new cells there's usually little need for balancing at first.
As the cells age and go different ways, the balancing function becomes more valuable.

hope this helps, please ask more questions about anything that didn't make sense.

 

[Tomthumb62]

There's a slight efficiency win with active balancers, but with new cells there's usually little need for balancing at first.
As the cells age and go different ways, the balancing function becomes more valuable.

So with aging cells, is passive balancing “good enough” to keep cells relatively balanced or is it too slow/ineffective to keep up? Meaning, will the cells simply continue to get more out of balance, but just at slower rate due to passive balancing functions?

My understanding that active balancing is faster (as well as more efficient in terms of net energy) and so in theory could better keep up keeping aging cells to remain balanced. Am I misunderstanding this?

Thank you.

 

[curiouscarbon]

So with aging cells, is passive balancing “good enough” to keep cells relatively balanced or is it too slow/ineffective to keep up? Meaning, will the cells simply continue to get more out of balance, but just at slower rate due to passive balancing functions?

My understanding that active balancing is faster (as well as more efficient in terms of net energy) and so in theory could better keep up keeping aging cells to remain balanced. Am I misunderstanding this?

Thank you.

Neither type is intrinsically faster (more amps).

Look for the Ampere balance rating for either Active or Passive balancing device. Sometimes specified in milliamps.

For example, it is possible to have an active balancer (0.1 amp rate) that is slower than some other passive balancer (1.0 amp rate).

As cells change in internal resistance over time, eventually whatever amp balance speed can be overwhelmed.
Active balancers do seem to often have higher amp rating than a given passive balancer included in a BMS.

In this case, JBD passive balancing rate is like 0.1 amp? vs up to 2A with JK.
So in the long run, a JK BMS with 2A active balancer would probably be able to keep the cells coordinated for more time than a JBD BMS with 0.1A balancing.

 

[Bleedingblue]

I have 6 overkill BMS on a 16s 280AH packs and they cannot keep balancing in check. I only have 1 pack that is 280AH the rest have had significant reductions in capacity with one all the way down to 157AH.

 

[Tomthumb62]

I have 6 overkill BMS on a 16s 280AH packs and they cannot keep balancing in check. I only have 1 pack that is 280AH the rest have had significant reductions in capacity with one all the way down to 157AH.

??? Not sure I understand why you have 6 BMS on a 16s pack? Why not just 1 BMS? Seems like the BMS would be fighting each other.

 

[Rednecktek]

I really hope you have 6 packs you mean.

 

[Bleedingblue]

??? Not sure I understand why you have 6 BMS on a 16s pack? Why not just 1 BMS? Seems like the BMS would be fighting each other.

Because I have 96-280AH cells. That is 6 strings of 16s thus I need 6 BMS's.
That is why I used the plural of "packs" not a singular of "pack" in my post.
And then the rest of my post I'm talking about how I have just 1 pack that is 280AH and the others have had significant reductions in capacity with 1 down to 157AH.
So by reading my post I have more than 1 pack obviously and by saying I have 6 BMS it's very obvious I have 6 strings

 

[Tomthumb62]

Because I have 96-280AH cells. That is 6 strings of 16s thus I need 6 BMS's.
That is why I used the plural of "packs" not a singular of "pack" in my post.
And then the rest of my post I'm talking about how I have just 1 pack that is 280AH and the others have had significant reductions in capacity with 1 down to 157AH.
So by reading my post I have more than 1 pack obviously and by saying I have 6 BMS it's very obvious I have 6 strings

Ok, I getcha now. It wasn't obvious to me (and it seems to others) that you actually have 6 packs. I read it as the "just 1 pack" ones were apart from the 1 16s pack you had with 6 BMS (which was not 1 pack, but I thought it was because you said 16s and most people only make a single pack with 16s. By "packs" not "pack", I thought it was a typo, because your message didn't make sense to me. Sorry for the confusion. A picture worth a 1000 words sort of thing, lol.