Battery pack "carburetor," or middle man MCU for auxilliary boost pack?

[Tussenbroek]

Hello fellow completely sane, rational, non-obsessives - nice to see I'm clearly amongst a kind similar to myself as such because I've never let a known limitation with an easy fix become a focal point of numerous thought experiments and, well, psychiatrist call it "punding," but I call it a bonafide pathway to free education in engineering, soo.. who's wrong about their involuntary institutionalization now, huh?..

/facetous

So, analogous to how engines would have intricate blocks that would draw in and mix a specific ratio of fuel and air before being pressurized for combustion, would there not be some variety of relatively simple solution to "blend" two separate streams of power in order to make it a draw a predetermined degree of load from each one respectively? I'm talkin' like, a couple of lines of an arduino program, couple of nice chonky relays, maybe an isolated variable potentiometer that could gradually phase in an amount power to be cut off the top of a primary battery pack's power output and redirect the draw/load onto a small (mAH-wise), but reactive (max discharge-wise) booster pack to get around a braggadocios motor control MCU and a BMS that just isn't sure of its own power.

It seems like on paper it would be a relatively simple concept, and of course I know just buying a KT controller with a greater degree of power input management (ie a current draw limit) would be an exceptionally easy solution that wouldn't even cost all that much money and would probably take me maybe just one afternoon to get everything all rewired and ready to go - but I want to do it the hard way because such a thing just seems like an interesting challenge that would also bring me closer to just straight-up designing a whole-over motor control unit from scratch, but I wouldn't have to get bogged down into the tangible, rather uninteresting things, like having to learn how the MCU generates a proper UART signal in order to feed in a continuous stream of commands to an LCD controller, which when then, painstaking have to be instructed on what each and everything means, how to display it, what color Hannah Montana's tampons were in the 15th episode of this weeks Seinfeld reboot taking on John Stamos from that time he danced live for Friends, like, I just really don't want to know that shit - or at least right now.. but maybe one day.. but in the meantime

Any ideas you guys just feel like spitballin' if you have some spare time and maybe an interest in such a thing yourself - this very likely will be going nowhere, and I've figured out a few janky rework ways into to quell the problem, but goddamn, just how amazing it would be to open up that full throttle to the 1600 watts that I paid for all without having to worry about pushing it all just a little too hard and immediately tripping my BMS/shutting down the battery pack until it feels its been adequately disconnected and reconnected again.

Thanks so much!

 

[jonescg]

The battery is a bit like a water-based fire extinguisher. It's capacity is it's volume. The flow rate depends on the pressure (voltage) and the impedance (the nozzle). Your BMS is like a pre-nozzle, and the speed controller is the main nozzle. If you buy a second fire extinguisher, but force it to go through one or both of these nozzles, you're no better off. The only solution for more crazy spray (power) is to un-bottle the controller. So you can always try modding the shunt by adding some more conductor so it delivers a bit more power. Or buy a new controller. And/or buy a new BMS. The elegant solution usually means higher rated equipment.

 

[Chalo]

Unless you use voltage conversion (which is rather wasteful), the ratio between discharge rates of two batteries in parallel will be whatever makes them sag to the same voltage under load at whatever state of charge they're in. Any system that allows them to be connected directly to the same load in parallel will have that quality.

If you connect each of them to a buck or boost converter, then the power delivery capabilities of the converters will govern the discharge rates and ratio.

If you use a discharge controller (e.g. battery blender) to switch the packs separately but not parallel, you can control the energy split, but not the discharge rates.

If you use a microcontroller based solution, the way I can think of to get the kind of control you describe would be to have a boost converter on one pack (set to output higher than the fully charged voltage of the other pack), followed by a PWM regulator under the control of the Arduino or whatever. The other pack would have diode isolation. The brain box could use closed loop control to dictate the "on" time fraction for PWM, thereby controlling the power split between the boosted pack and the diode isolated pack, up to 100% for either one. This approach might be electrically noisy enough to confound the motor controller, unless the output to load is filtered with a capacitor or a choke.