# No BMS needed - what do we make of this?



## Benjaminpalma (Oct 25, 2017)

https://l7drive.eu/home/

Also, not clear if they're selling whole system or just a controller.

Thoughts?


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## brian_ (Feb 7, 2017)

They're clearly offering (whether they have actually ever built and sold one or not) an integrated controller and charger. I don't see any indication of packaged systems or matched motors being offered.

Their approach does avoid some potential battery issues, but is explicitly based (according to their Technology page) on the idea that it is better to boost the voltage of a single cell (so, 3 to 4 volts) to the motor's requirement than to cut the voltage of a series set (typically 360 V or more in current automotive practice) to the motor's requirement.

The result is that the cables from the battery to the controller will carry four thousand amps at full power and 3.7 V nominal cell voltage in the case of a 15 kW application (the upper end of their stated power range). This sounds like a marginally workable plan for an e-bike, as long as you don't mind wiring that makes automotive booster cables look small.


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## Benjaminpalma (Oct 25, 2017)

So... you could just use four such cables to carry, say, 60kw? Sounds like a fair deal if we’re getting rid of the BMS...?

How do you even increase voltage per their website?

Are they onto something?


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## brian_ (Feb 7, 2017)

Benjaminpalma said:


> How do you even increase voltage per their website?
> 
> Are they onto something?


DC-DC converters, stepping voltage up or down as desired, are readily available. Toyota even puts a step up stage in their hybrid controllers, to match the lower-voltage battery pack to the higher-voltage motor... and has been doing it for two decades.


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## Benjaminpalma (Oct 25, 2017)

This looks like the patent: https://worldwide.espacenet.com/pub...locale=en_EP&CC=WO&NR=2019081814A1&KC=A1&ND=5. Still not much wiser as to how it works in layperson’s terms of whether it’s a good or practical concept.


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## brian_ (Feb 7, 2017)

Benjaminpalma said:


> This looks like the patent: https://worldwide.espacenet.com/pub...locale=en_EP&CC=WO&NR=2019081814A1&KC=A1&ND=5. Still not much wiser as to how it works in layperson’s terms of whether it’s a good or practical concept.


It says that a bunch of DC-to-DC converters in parallel, timed so that their switching glitches are staggered, can handle a lot of current with smooth output.

Well, yeah.  What has happened with patents over the last few decades is that most of the traditional requirements for patentability have been abandoned, so that now as long as the "invention" isn't identical to something previous, and the application meets all of the documentation requirements including acknowledging relevant prior patents, any stupid rambling can get a patent. It no longer needs to be "obvious on the claim date to a person skilled in the art or science to which it pertains" (the Canadian version of the typical non-obviousness requirement); it doesn't even need to work or to be useful, although this one will work and would be useful for a very high-current application.

In this case, it take 26 pages to say almost nothing. I think it is deliberately verbose, to make it look there is some content, although some of this is the usual practice of trying to cover every possible variation.


So the step-up DC-DC is straightforward. This leaves the question of whether massively stepping up the output of a parallel-only battery pack, thus allowing the use of only parallel cell connections, has any net value. I don't know... maybe, but I'm pretty sure that it makes no sense at an automotive scale.


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## Benjaminpalma (Oct 25, 2017)

Thanks for your thoughts. Useless for AC motors then...


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## brian_ (Feb 7, 2017)

Benjaminpalma said:


> Useless for AC motors then...


Not quite. The patent is about their voltage booster, and the booster's output is DC, but it's really just taking the place of a direct battery output. That DC output would then supply a normal inverter/controller to suit whatever motor is chosen.

Judging from their website, their target is light vehicles (scooters) with "brushless DC" motors... which of course are AC motors. With no products or ideas for lithium cells, controllers, or motors, their only specific technology is the DC-to-DC converter to boost the voltage of a battery running at single-cell voltage to a level which is useful to run a motor.


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## Hollie Maea (Dec 9, 2009)

brian_ said:


> I'm pretty sure that it makes no sense at an automotive scale.


Ah, come now...to power a Nissan Leaf at nominal SOC it would take a mere 25 thousand Amps...


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## brian_ (Feb 7, 2017)

Hollie Maea said:


> Ah, come now...to power a Nissan Leaf at nominal SOC it would take a mere 25 thousand Amps...


No problem!


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