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Consider an inductive charging system like Magne Charge - it has a rather huge "coupler" coil off the vehicle and a corresponding slot on the vehicle and the coils in the "coupler" and in the slot are aligned perfectly parallel and brought close to each other. So it looks like a good old transformer.

Yet there's a huge box in each Magne Charge system (a wall-mounted unit) that most likely generates higher frequency current. Btw this box seems to be accountable for huge energy losses.

What's the need for that frequency increase? A good old transformer will run at the same frequency as mains - 50 or 60 Hz depending on the region - and have pretty good efficiency. Why would this slightly altered transformer setup need higher frequency?

Community
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sharptooth
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    Good old transformers weight hundreds of grams (more than your cellphone) and require both winding to be on a common ferromagnetic core to be efficient. – Dmitry Grigoryev Oct 29 '15 at 11:35

3 Answers3

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It all boils down to efficency.

As the frequency a transformer runs at increases, the transformer can be physically smaller.

To Plagiarize Quote Wikipedia:

The EMF of a transformer at a given flux density increases with frequency. By operating at higher frequencies, transformers can be physically more compact because a given core is able to transfer more power without reaching saturation and fewer turns are needed to achieve the same impedance.

Consider the size required for a 50/60 Hz transformer capable of 6.6 - 50 KW (the power rating range of the Magne-Charge systems).

Connor Wolf
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  • So basically the efficiency aspect optimized for here is the coupler/slot size, isn't it? – sharptooth Jan 16 '12 at 10:07
  • Well, you have two different concerns - Coupler size/weight, and efficiency, with an inverse relationship. You have to pick somewhere along the rance of possibilities. I can't put my self in the system designer's shoes, but I would imagine accessibility was pretty high on the importance scale. After all, granny has to be able to lift the charge paddle to charge her shiny new electric car, doesn't she? – Connor Wolf Jan 16 '12 at 10:17
  • I see. Could the same work with a mains-frequency transformer if the "coupler" was wall-mounted and the vehicle had a side-mounted counterpart for the coupler and was parked perfectly close to the wall-mount coupler? – sharptooth Jan 16 '12 at 12:05
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    @sharptooth - Kind of. The tolerances are tiny. You need essentially no air-gap, or you lose efficiency in a hurry. I don't have hard numbers (It's kind of a nebulous design, too), but a gap of even 1 mm would ruin things. Really, you should think of it as needing physical contact. It's basically a circuit, just like any other, just magnetic, rather then electrical. – Connor Wolf Jan 16 '12 at 12:28
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The frequency also affects safety too. The higher the frequency, the less likely the system will interact with biological objects when in operation. This is very important.

Uche Ohajuru
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    Microwaves have very high frequency, they are also known to [interact](https://en.wikipedia.org/wiki/Microwave_burn) with biological objects rather intensively. – Dmitry Grigoryev Oct 29 '15 at 11:39
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The high frequencies create a high voltage i.e. e=4.44n(phie)(f); so by increasing f we may increase the EMF which is helpful in induction in the second coil.

PeterJ
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