Double BMS - double charging speed possible?

Some one with greater technical understanding will, hopefully explain this better. But from my small understanding I think you would effectively be creating two new batteries each of them having the same environment and amount of discharge so each BMS would need to charge to the same rate that the cells require. Additionally if you only had one charge point your charge available would be split between the two batteries and would, therefore, be halved.

I might be wrong and hope some one with more knowledge will educate both of us.

 

It wouldn't be half the time it would mean both batteries would be charging at the same rate that the BMS would allow.How fast the battery charges depends on temperature and other factors. All the cells would be in the same environment.
You would also need two chargers so then you would have two batteries. Then you would need two connectors. BMS means Battery Management System. That's mainly the software that controls the electronics. In fact as, I think about it, they could easily design a BMS that controls two batteries.
I'm sure a car could be designed with two batteries and I suspect that the trucks will have multiple batteries. The batteries can be connected in series and a charger/management system designed to do this. I suspect there would be some inefficiencies creeping in.

I'm still speaking largely uninformed.

 

The BMS doesn't limit charging rate arbitrarily, it's there to protect the cells. Each of the 298 cells can take a charge in amps roughly same as the "Ah" rating, which is 60.

60A x 3.7V = 222 watts. 298 cells/pack x 222 watts = 66,156 watts/pack or about 66 kW. It doesn't matter how many BMS there are.

Mostly charging speed limits are all about how effectively waste heat can be removed, about 1% of the charge rate. Tesla do this by having liquid cooled bands wrapped part way around each cylindrical cell. The bands are like a wide flat extruded bar with channels inside for coolant, bent into an "S" shape, one bend for each cell.

Then they bake the whole lot into a thermally-conductive foam slab, Betty Crocker style.

In the Kona, Hyundai stack a number of large flat cells together and provide cooling surface only at the underside face below the lowest cell. The heat from the top cell has to conduct through all the others to get out. No doubt the Ioniq 5's cooling is more effective, as it would have to be.

 

Thanks KiwiMe! trying to work through my own confusion up there. Hope it's helped duende.

 

If you were to split the battery into two parallel units, you could hypothetically charge at twice the current. TLR; you're going the wrong way.

As KiwiME points out, the battery itself sets the amps. The general rule is battery charge/discharge rates are based on the battery capacity. A rate of "1C" means you are charging/discharging at a rate that will fully charge/deplete the cell in 1 hour. So a 60 amp-hour cell would have a "C" rating of 60 amps.

Cells connected in series must have the same current, so two 6o-amp-hour cells in series would still have a "C" rating of 60 amps. However the voltage would be double, so you'd get double the power. (Power = Voltage x Current)

Charging two cells in parallel would allow for 120 amps, because each of the two 60-amp-hour cells is charging at 60 amps. However this doubling of current comes at the cost of half the voltage, so you still get double the power.

So there's no actual advantage to splitting the battery like this... unless your power supply is limited either by current or voltage. Most (all?) DCFCs are limited by current, e.g. CCS spec maxes out at 350 amps, but can (and must) vary the voltage over a wide range. This is why we're starting to see vehicles with 800-volt class packs (The Kona's is 356 volts nominal, putting it into the 400-volt class). Twice the voltage means twice the power without increasing amps, and that's good because amps is what causes losses and heating. Instead of splitting the pack into two parallel sub-packs, you want to reconfigure it into longer series strings for higher voltage.

FYI this is exactly what Hummer EV's pack does; Two 400-volt packs get internally rewired into a single 800-volt pack for faster charging. An ideal 800 volts at 350 amps is 280KW, and the Hummer is said to charge at a peak of 250KW.

I guess you could say less is more?

 

Thanks Genevamech. I was hoping some experts would join in.