L7 Drive, Combo battery-bms-controller

[MikelBikel]

Don't know what to make of this. Sounds like a smart switch mode power supply in reverse, where many individual batteries are pwm switched into higher dc voltage combinations as required to dc-dc convert it up? Claims to be simple but would've thought this means 1 power fets, etc, per cell and a cpu that can monitor & control all cells individually.
They claim to have a 250w product ready for production.

Home - L7 Drive

Powering your solutions. Driven by power of innovation, we bring that power to your solution. Keep your batteries alive for longer than before with our game-changing power electronics technology. Stay connected and control your system through an innovative cloud based system wherever you are...

l7drive.eu

Found on EvNerds website.
Cheers. Mikel

 

[Woosh]

what's wrong with these people? they keep dreaming of new ways to reinvent the wheel.

 

[Deus]

very interesting thanks for posting

 

[MikelBikel]

I was wondering if they were looking for beta testers, but as they're in Helsinki, Finland, I think they'd want people nearer home!

 

[Woosh]

the guy who designed that system is an idiot.
he wants to step up a DC voltage of a 3.6V battery to a 36V to drive a 36V motor, wasting easily 10%-20% of the battery energy in the process to replace a BMS which burns less than 0.5% when the motor is working under the same condition.

 

[MikelBikel]

do you mean one can work out what the total losses are by multiplying the loss per FET by the number of cells to arrive at 10-20%? I.e. 6, 9, 12 vs 50 or more?

 

[Woosh]

although it's theoretically possible to have a single stage DC-DC boost converter from 3V-4V to 30V-40V but I have not seen one starting from as low as 3V-4V Lithium battery. All the converters for solar panels have the same common characteristics: higher input voltage = higher yield. Each stage will introduce a loss about 7%-15%, increasing with the step up factor.
If he uses 4 stages, he'll be lucky to get 60% yield.

TI has published a plot on the efficiency of their boost converters on page 7 if you are interested in the subject.
http://www.ti.com/lit/ds/symlink/tps61175.pdf

 

[Woosh]

there is a simulator here if you want to explore this concept of replacing BMS and controller in one step up design, he'll need a minimum of 2 stages.
https://webench.ti.com/power-designer/

 

[MikelBikel]

Its all beyond my pay grade, but the idea of just switching in extra cells intrigued me. One vid shows a mock up of a kick scooter and they were removing & adding individual cells while it was running! So I wondered if it was some kind of matrix switching rather than just into series.

 

[Woosh]

switching cells is not a clever plan either. Lithium ion cells are mechanical devices, Lithium ions move from one electrode to the other, like a lung. Switching them on/off with high instant demand does not do them much good. Just think of a door being kicked open or closed 1000 times an hour. How long before the hinges fall apart? The main thing is, what do they try to save? the efficiency of a BMS + controller? you have 4 FETs in parallel in the BMS in series with 2 FETs in the controller per phase to do the switching. If you replace them with an array of 1 switch each, you'll end up with connecting in series about 5-10 stages, about 7 * 0.75 = 5.25 times more on resistance on average.

 

[MikelBikel]

Yes

switching cells is not a clever plan either. Lithium ion cells are mechanical devices, Lithium ions move from one electrode to the other, like a lung. Switching them on/off with high instant demand does not do them much good. Just think of a door being kicked open or closed 1000 times an hour. How long before the hinges fall apart?...

Yes, it seems hard on a chemical battery to be shunting it on/off like that (as i, hopefully humbly, opined in the post about Wisper 806 speed limit 'surging' issue). And i expect the variation of phases turning on/off is smoothed by the ouput capacitors charging/discharging.

 

[sjpt]

Glancing at the patent it appears the 'novelty' is connection of several (4) DC converters in parallel, with intelligent control of them. As far as I can see he isn't claiming any novelty in each converter that would get over the efficiency issues Woosh mentions. He even mentions 3.2 Volts to 100 Volts for car applications.

An important feature of the system is that the output voltage of the converters (input to the motors) is varied according to need, under the theory that a given motor will generate lower power more efficiently at a lower voltage than the voltage needed for full power.

WIPO - Search International and National Patent Collections

patentscope.wipo.int

US Patent Application for METHOD AND DEVICE FOR AN ELECTRIC MOTOR DRIVE Patent Application (Application #20140049196 issued February 20, 2014) - Justia Patents Search

Method and device for an electric-motor drive, particularly in connection with electric vehicles, in which a system consisting of rechargeable batteries produces operating current for the electric motor/electric motors moving the vehicle. An essential part of the method and device is that one...

patents.justia.com

 

[MikelBikel]

Thx all, for the info. Not such a big plus for electric bikes then, at least not for me. I get out on the highway and its full on until i get to the other end, fingers crossed . Oh, forgot hills, drat :-(.
Cars, buses, vans, in a city however, different story, though gears could help instead? Like a mid-drive bike or a Xiongda 2sp auto.. for those dratted hills.
Better to concentrate on the balancing & cell swapping aspects, using old cells, got a bad one, no problem, its taken out of cct and swapped out later. But maybe the expense of the complexity outweighs the saving on recycled cells?

 

[vfr400]

It seems to be a system that takes power from any arrangement of cells in parallel to drive a motor directly with three phase power. I reckon efficiency could be quite good because a lot of conventional losses are eliminated, though some new ones are brought in.

The main advantage would be ease of battery construction and better reliability because you wouldn't have to worry about balancing or weak cells.

What's missing is how to control it. Presumably, you would have the part of a controller that controls and regulates the power driving it. Basically, it's equivalent to the mosfets, switching transistors and capacitors in a normal controller.

I like this concept. If it's as efficient as conventional systems, I think it will go far.

 

[Woosh]

If it's as efficient as conventional systems,

it is not.
it's is a boost converter. If you read the claims of the patent that sjpt posted, the system consists of (eg 4) DC-DC boost converters whose outputs are arranged such that they overlap one another, smoothing out gaps in their duty cycles. As the patent holder puts it, the system saves space and money on 'expensive output capacitors'.
Now, if you read the specs of all the high current boost converter chips, they operate from 220kHz to 2.2MHz. Therefore, if the objective is to send the output to a motor whose 3 phases run at about 10KHz-20KHz, there is absolutely no reason to 'fill in the gaps', the output of the boost converter runs already at 20-200 times the frequency of the motor phases.
The guy tries to sell ice to eskimos.