200 kW Wireless EV Charging? Momentum Dynamics Says So
Originally published on EV Obsession.
The wireless electric vehicle charging technology company Momentum Dynamics will deliver a 200 kilowatt (kW) wireless (inductive) charging system for the municipal bus market by the end of the year, going by recent comments made by company reps.
The company’s CEO, Andrew Daga, recently commented that 2015 saw the company deliver 25 kilowatt (kW) and 50 kW charging systems to “strategic partners in the automotive industry” — and that the expansion to a 200 kW system offering was an expected and “natural” progression. There are reportedly higher-powered systems in development now as well, according to Daga.
A recent press release provides more: “Daga said the company is planning to deliver two wireless charging systems to municipal agencies this year in Maryland and Washington state. Wireless chargers use resonant magnetic induction to transfer power without the use of cables. They include the transmitter on the ground and a power receiver mounted to the underside of the vehicle. Despite an air gap of up to 12”, the efficiency of inductive charging is equivalent to plug-in charging.”
Green Car Congress adds: “In March, Oak Ridge National Laboratory (ORNL) reported the successful demonstration of a 20 kW wireless charging system with 90% efficiency. The researchers are already looking ahead to their next target of 50-kilowatt wireless charging, which would match the power levels of commercially available plug-in quick chargers. Standards for wireless charging — eg, SAE J2954 — are still under development.”
Note that I previously wrote about this company in August 2015: “Wireless EV Charging As Fast & Efficient As A Tesla Supercharger?” And Jo Borras wrote about it back in 2013: “Momentum Dynamics Adds Volt Brainpower To Wireless Charging Team.”
It should be remembered here that efficiency losses for wireless charging systems are still pretty high. While it may make sense from the perspective of convenience in some (or many?) situations, I do have to wonder if the technology will ever end up possessing a significant market share.
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A great option for my future Model 3, if priced right.
I assume the the 90% is from plate to plate in the system not into final battery, which would be dependent on each car’s charge system. So the statement “Despite an air gap of up to 12”, the efficiency of inductive charging is equivalent to plug-in charging.”” is misleading at best. I don’t think that even a large power chord loses 10% over the 10ft from device to car.
I think there is a spot for wireless charging in the market, but saying it is as efficient as a wire is not true.
The efficiency is measured from power source to load. That means NOT from disk to disk. The disk to disk efficiency is better than 99%. Once again, the losses do not occur largely in the conductor cable of plug-in chargers but rather in the power conversion electronics. The magnetic energy of wireless chargers is not lost to space; energy not captured by the receiving disk recirculates. It is completely incorrect to say that the losses happen only in the cable conductors of plug-in chargers. They have power electronics as well, and that is where the losses occur.
Thanks for jumping in here, Andrew.
I’m trying to understand the system loss. If we start “at the circuit breaker” and go hard wire to the EV AC/DC converter we expect essentially no loss (if the wire is adequately sized).
Correct?
With the Momentum Dynamics system what percentage of the original electricity gets to the EV converter?
Bob, yes, from the circuit breaker (“source”) to the power electronics cabinet (your “AC/DC converter”) there is very little loss, although this depends somewhat on the distance between the circuit breaker and the AC/DC conversion electronics. Even when properly sized, there are I^2R losses in any conductor. But these are not major and let’s say a fraction of 1%.
Next the AC power that feeds into the converter has to be converted to DC (rectified) and then switched to 20 kHz (like a switch mode power supply), filtered, and resonated. (The same thing happens in a an EV motor controller.) Each of these stages generate heat, which is the expression of energy lost. Next comes the primary inductor, which experiences essentially I^2R losses again (like cable would). The inductor generates a magnetic field, which is intercepted by the secondary inductor across an air gap. What confuses people is that this magnetic field does not fly off into space. The portion of the magnetic flux that does not get intercepted by the secondary inductor returns to the primary. Just like the flux lines of a grade school bar magnet experiment; the lines emanates from one pole and curves around to go to the opposite pole. In doing so, there is essentially no loss.
The block diagram of a plug-in charger in many respects looks the same way. For a J-1772 Level 2 charger, the “charger” is really built into the vehicle but most people never see it or know about it — the charger is not the thing on your garage wall, or the kiosk at the office parking lot. That thing is really just a wire and a control circuit and a contact switch. All the power conversion occurs on the vehicle — but people don’t know about this or experience it, and they think there are no losses in the cable that leads to the car.
What you have to do is count the total accumulation of losses all along the way from the circuit breaker to the battery on the vehicle (i.e., the load). In this way, it is accurate to say that plug-in chargers and wireless chargers experience approximately the same losses.
I do appreciate all the detail but what I was trying to do is to get a very easy to understand answer for those who want simple. Let’s try this one…
If you start with 50 kWh at the circuit breaker –
1) how many kWh end up in the car’s battery using a cable?
2) how many kWh end up in the car’s battery using the Momentum Dynamics system?
You don’t start at the circuit breaker with kilowatt-hours (kWh, energy), you start with kilowatts (power). But if you start at the circuit breaker with 50 kilowatts with a plug in charger, you’ll probably deliver 45.5 kilowatts to the battery. And if you start with 50 kilowatts at the circuit breaker with a wireless charger, you’ll deliver 45.5 kilowatts to the battery.
The amount of energy delivered depends on how long you charge for, but the answer will be the same in both cases.
OK, “start” was a bad word choice. I should have used “pull”.
But thanks for the answer. What you are saying, if I read it correctly, is that the MD system is lossless.
Given that is the case then the question becomes which would be cheaper to install and maintain, wireless or robotic/snake chargers.
No Bob, it’s not lossless, 45.5 kW is less than 50 kW. We lost 9% in both types of chargers. No energy conversion is lossless. Every electrical device you use loses energy in doing its work.
The acquisition cost of wireless will also be comparable to plug in too. The maintenance cost, however, will be less precisely because there are no cables or mechanical plugs.
I doubt we will ever see a robotic arm charger for cars. That still seems like an April Fools joke to me. Doable but unaffordable – and talk about maintenance costs…
Sorry, Andrew. I’m just not being precise enough for you.
There is (according to you) no extra loss when using a MD wireless system vs. a charging cable.
Wireless or robotic cable. The market will decide. We’ll have to wait to see product go on sale and prices posted.
Compare this wireless 200KW… to 250KW – 600KW of current bus charging technology.
http://www.greencarcongress.co…
http://cleantechnica.com/2015/…
http://www.plugincars.com/elec…
Ask how much does the wireless system cost.. And you’ll find it’s much cheaper to do conductive charging, at much higher power levels, and much more efficient too.
Where is the value of wireless? Other than the “Cool” factor of being what many people associate with “futuristic”.
Value of wireless? At least a couple.
1) Convenience. Just park and forget it. Even a 10% loss for a 13,000 mile, 12c/kWh driver would cost less than 15 cents a day. Lots of people would be willing to pay that if they didn’t have to deal with plugging and it might get some into EVs quicker.
2) Public charging “safety”. No charge cables for jerks to unplug or steal. Bury them under the pavement and you don’t clutter up the sidewalk.
View the links I’ve posted. I am talking about comparing to automated systems that are equally convenient, just as safe (safer really), can’t be jerked out or stolen.
Clutter is the only value you’ve mentioned. It is easier to prettify a wireless system than a robotic one.
But really, a robot snake arm would merely look like an enclosed cylinder when stashed away.
First one led nowhere. Second led to a page full of assorted articles on stuff like climate change and Audi and India. Didn’t bother with the third.
I agree that a robotic cable is another option. It would come down to cost (including maintenance). Moving stuff is usually more expensive.
I’m still waiting for an efficiency number that I understand.
With anonymous driving a reality, smart street charging also can become a reality. I can not find the (link) but parked cars over night move them selves to charge then return back to your driveway for your morning commute. And then there is charging when your sitting waiting for the light to turn green. I think it will go main stream.
The one question that I had when starting this article wasn’t answered. What will this do to reduce passenger car charge times to 80% charge?
I can’t wait for this technology to become commercially available. Electric cars have full torque at 0 rpm and they would be much simpler to maintain without oil, gas, and radiator fluid to worry about. Also native torque vectoring would be available on all models not just luxury models.
Andrew – I enjoyed your patience with folks and your keen awareness of the fundamentals which is sadly lost in the digital world of today.