Linked-roller Regen Quick Charging with 2 EVs

[FalconFour]

So, this idea started bashing its way through my head last night... couldn't help but try to get it down in the forum and bounce some ideas around here.

A Leaf can regenerate charge using the motor controller at exactly the same rate it's also capable of plugging into a super-expensive CHAdeMO quick-charge unit. They both top out at 30kW. And, given the degeneration of my car's regeneration capability P), it seems to be just as tightly regulated for battery safety, if not more so. The only thing limiting this from being used for charging the car is that it's kinda clumsy and unsafe to drag one car behind another.

So, in the course of trying to piece together the puzzle of the regen "throttling", I thought of the idea of putting two Leafs together, facing the same direction, on a "linked dynamo" platform - just with a long set of free-spinning rollers from one car to the other. Both would be on, should start the sequence in neutral. One would enter Drive and begin turning the other car's wheels, the other would enter Eco mode Drive and slow the rollers down. The one in Drive would then slowly accelerate, and the one that's in Eco would start regen'ing to about half its capability - about 15kW - around 25 MPH. Since regen is speed-dependent (all at the throttle level, though - only limited by programming, so...), the "charger" car could probably go faster than that and get up to 20 or 25kW, within judgement of the rig's safety.

The end result would be a great test platform for regen and battery behavior, as well as an amazing low-cost solution to offer quick-charging in an area like Fresno without any quick-chargers to be found anywhere (and no business interest, it seems, in doing so). It would just take one fully charged car, and one of any other model EV with regen that needs charging. One charges the other, then goes back to charge its own battery at good-ole' L2. It'd put a ding on both odometers, of course, but given that 15kW is the motor power typically needed to go 60MPH and this system would be going more to the tune of half that... it'd probably only consume 1/2 the miles of capacity regained by charging. And there would be no air-resistance losses for regen - I'd estimate it somewhere in the 70-80% efficiency ball-park. A fully charged Leaf could probably charge another Leaf from VLBW to 80% just like a quick-charger. Alternatively, heck... a gas-guzzler could probably run at its peak efficiency while regenning an EV using this rig.

My big question is... how could (and, sure... "should") it be built? I can't imagine this kind of platform being useful in any other vehicle usage other than for an EV. I was envisioning a platform with two large metal pipes supported by a large number of ball bearings in a low-profile frame. The pipes could be removed from the frame for easier carrying and storage, though I don't know of any good way to unlink the two "bays" to make the pipes shorter. I'd probably need to link two shorter pipes together using a threaded connector, threaded in the direction of power flow, to get the right length pipe.

Much as I'd love to build it, I just have the mechanical knowledge and the concept, but no experience fabricating things. I know the base needs to be damn strong, the rollers and pipe perfectly smooth and level, and the cars would need to be restrained while running. And the rollers would need to be able to be locked (probably with a lock pin) to allow the cars to mount and dismount the rig. But I don't even know where to begin on the base... :?

 

[GetOffYourGas]

Interesting idea. A friend and I have discussed a similar "fast charger", but instead of using a second car, you could just use a 30-40kW motor to drive the "treadmill". The beauty of this idea is that you could quick charge any car with significant regen (e.g. a Volt). I would never want to build one, but it's fun to dream.

 

[essaunders]

interesting approach to the electrical isolation that Phil keeps reminding is necessary for a proper DC charge... Of course, I do wonder about the weight and bulk of the chains needed to keep the cars safely chained down. Might be easier to get a proper CHADEMO...

 

[Yogi62]

You might want to look at how mobile and in floor engine dynos are constructed. When we use these to check engine tuning in race cars (with 110 HP motors, so not that big), we strap down the car with eight 5,000# straps.

 

[FalconFour]

Weight wouldn't be an issue with proper design of the base and supporting bearings... dynamos do it all day and all night with smog test rigs. The chain shouldn't have to be too big, either... the car already has lots of weight keeping it between the two rollers (which is why they'd need to be locked to get the car in and out of it). The powered car would have an inclination to pull forward, and the receiving car would want to pull backward, both at similar force. I think the base could be made short enough to not even bottom-out either one of the cars if it accidentally rolls all the way over it. I think taking a page from a smog-check dynamo's safety and operations would ensure similar safety for this rig. Definitely nothing on the scale of the costs associated with installing a proper QC station... but of course, at the same time, definitely not intended to act as a full-time station either. Heck, the downtime between uses would be at least 4 hours to recharge the car at L2.

As for using an electric motor to power it, that would take a pretty fair bit of equipment and installation, as well as the huge amount of utility work, to get the 20 or 30kW power another EV could provide. The big advantage of using a mechanical energy-transfer interconnect like this is that you can get the mechanical energy from anything else willing to provide it - even a gas engine. And you don't need to take out a second mortgage on the property to bring in the wiring from the power company. :lol:

There's a hackerspace here that I'm going to bring the idea up with... they've got all kinds of big equipment and plenty of fabrication geeks there. My next big challenge would be trying to find the funding to build this stuff with. My signature line below explains that hurdle. And, maths. Thinking of something to the tune of 3 bearings per section on each of the 2 pipes, 4 sections per car, so a total of 48 ball bearings across the whole thing which support the pipes and the weight/force of the cars. The frame design itself is still just not coming together on a piece-by-piece basis, though... just one block I can't yet figure out how to split into buildable pieces. :?

 

[planet4ever]

I'd estimate it somewhere in the 70-80% efficiency ball-park.

You're going through two water-cooled motors and two water-cooled inverters plus two efficiency losses in chemical/electrical conversion, and probably a sizeable amount of friction in bearings and tires to hold those two bucking horses down, not to mention two gear trains under strain. I suspect that 70-80% is highly optimistic.

Ray

 

[palmermd]

what could possibly go wrong?

http://www.youtube.com/watch?v=oKFGr_mkQaA" onclick="window.open(this.href);return false;

 

[FalconFour]

what could possibly go wrong?

http://www.youtube.com/watch?v=oKFGr_mkQaA" onclick="window.open(this.href);return false;

Yeah, at full torque, insane speeds, high up off the ground, and supported by a flimsy strap!

Emphasis on low (<60MPH) running speed, low potential kinetic forces (no huge engine and flywheel to stop in a split second if something goes horribly wrong!), and a well-regulated startup sequence are key! Haha. I hope you don't think this whole thing is nearly as dangerous as these guys. :lol:

That's also why I hope to design this thing with relatively inexpensive parts - strong metal, low profile to reduce the forces needing distribution, and few points of failure. I'm starting to get an idea of the base design, too. Essentially, it'll have the profile of a long speed bump. That way, if a car jumps it (almost certainly the supply car, as the receiving car would stop immediately anyway), it'll just roll over it and stop it when the rear wheels bump into it. Believe me, I have no delusions of bulletproof safety here - lots of safeguards need to be built in, and operated only by competent drivers, unlike those in the video. :lol:

As for efficiency, you'd be surprised - the heat produced by the motor and controller is rather low when in that 25-40% capacity range. Even after hot-rodding all around town, the coolant, even on a warm day, is still just lukewarm. Given the amount of energy taken from the battery during that time, it seems rather efficient at what it does. Air-cooling would just be a death sentence for motors and controllers of this size, so water cooling isn't because there's a lot of heat - but just because it's an efficient way to design it. Sure, 80% is optimistic, but I rather think 70% is on the low end.

But that's why I want to build this thing! So many estimated statistics that really need hard evidence to prove, and a direct link between two cars that know exactly how much energy they're consuming and producing would be an amazing scientific tool, at the very least. It might only live a short run to decide that it isn't suitable as a charging solution, but then we'd at least have hard data to prove it. Or, best case... prove that it can be done efficiently!

 

[evphreak]

Not sure if this has been posted...if you don't speak Scandahoovian, there are English subtitles.

http://www.youtube.com/watch?v=5Sujv90PLLY" onclick="window.open(this.href);return false;

 

[GetOffYourGas]

Not sure if this has been posted...if you don't speak Scandahoovian, there are English subtitles.

http://www.youtube.com/watch?v=5Sujv90PLLY" onclick="window.open(this.href);return false;

That's one leaf owner who can no longer say he's 100% gas-free!