Hi chad, welcome.
Your calculation is wrong.
Rigol DP832 with channels 1 and 2 in series to output 64 volts.
The max I can put out via the Rigol is 3.2 x 2 or 6.4 amps at 64 volts.
When you series your Rigol, you don't get more Amps, only the voltage doubles.
You can get 30V x 3A = 90W power per channel, so 180W in total.
There is no "curve" charging in the RIDEN firmware, but you can (should) set "Max Power".
From the manual:
"Limits output power to set value.
- Protects the primary power supply if not capable of providing full power to the RD60xx.
Manufacturer recommended setting:
No higher than 95% of the rated power for the Primary Power Supply."
So for 180W power IN, set the Riden to 171W power OUT. This can be delivered to your batteries.
This is the best case but buck efficiency might be worse than 95% when regulating 64V down to 24V.
A fully charged LiFePO4 cell is 3.6V so 8 in series are 28.8V.
This is the V out you have to set your RIDEN to.
BTW, you can parallel your Rigol channels to get 32V 6.4A out. It is more complicated, you need to make sure that one output doesn't feed back to the other, but you might get better buck efficiency on the RIDEN side. It doesn't change the power calculations though.
I don't know much about LiFePO4 but Li-Ion must be charged CC-CV (Constant Current then Constant Voltage).
With the above values, current limit your Riden to 171W / 28.8V = 5.93A.
As you charge, the voltage will slowly increase - keeping the current at 5.93A - until it reaches the preset 28.8V value.
At this point the charging will change to Constant Voltage and the current will start to decrease.
With such a large battery pack I would stop at around 300-400mA.
Using this method you only reach peak 171W output power at the end of the CC phase, when the voltage reaches 28.8V and the current is at max.
Before this point the voltage is lower, after this point the current is lower so both Input and Output power will be lower. (not much)
I know this is not the possible fastest way, but it doesn't require someone sitting there the whole time manually tweaking values with the tongue at the right angle.
However, I think you are on the wrong way charging like this. I don't recommend it. Here is why.
You have a 280ah pack.
Charging at a constant 6A will take 46.6 hours, not counting losses and the short CV phase at the end.
Thats 2 days!
Meanwhile you are running the Rigol at 32V 3.2A output, which is 114% of its rated power.
I am almost 99.9% sure
the manufacturer didn't design that equipment to survive such load on the long run.
In other words, you'll F up your primary PS. Which seems to be a pretty nice unit.
If you are lucky, only 1 channel will die and when you get it fixed the other one will die in a few days or weeks.
So if you are rich and money doesn't count, buy a proper charger for your pack.
One would think a nice charger that speaks 7 languages can be had for 2-3 hundred bucks.
If you are not rich, save your Rigol and buy (or build) an economy charger that was designed to do this job.
In any case, with a dedicated charger you can charge this pack in 6-10 hours, max a day.