Non-Contact Battery Charging and Comms

Are there any parts out there that provide for non-contact power and communications for electronic devices?

I'm working on a product that'll consume low power (around 200mW), but that would benefit greatly if it could be mated to a computer via some super-low-range non-contact power source. The model of what I'm thinking of is an inductive loop that transmits using some means (FSK?) and receives by sensing variations in the load of the loop.

There's a standard out there (Qi) that covers the power part, but I'm not finding anything that covers the power and talking back and forth.

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Tim Wescott 
Wescott Design Services 
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Tim Wescott
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Oops -- comms can be pretty slow: 100k-baud would be nice, but 10k would be acceptable.

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Tim Wescott 
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Tim Wescott

That's a bit much for modulating the power transfer signal directly. Since it most likely has to pass EMC I'd look into data transfer on an ISM band. Not necessarily 13.56MHz because that could be plastered in some heavy industry area and the band is kind of narrow anyhow. 27.12MHz is better, or just use 2.45GHz since there's lots of chips available.

For non-contact power it is customary to stay below 150kHz in order to dodge some EMC regulation bullets. How much distance must be allowed vertically and laterally? Electric toothbrushes often use ferrite rod cores. I'd also stay away from 60kHz and 120kHz, to avoid complaints about atomic clocks suddenly quitting or disturbing home automation systems.

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Regards, Joerg 

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Joerg

Vertical and lateral distance is negotiable at the moment. The customer was thinking of having something that plugs into the side of the unit (I think he's seen those tooth brushes).

It doesn't seem to be a problem that has bazzilions of pre-packaged solutions out there, which does take one aback.

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Tim Wescott 
Wescott Design Services 
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Tim Wescott

"Plugs into the side" is good news, meaning the distance and offset is well controllable. You'll also have to ask them about any efficiency rules they must fulfill, EPA and whatnot. I remember when I was happily roaring into a switcher design and casually asked the client whether there'd be any power factor requirement. "Oh, darn, yes!" ... whew.

The power transfer doesn't have any canned solutions, there is not enough market and the requirements are too widely scattered. Plus most of the stuff is cut-throat cost-sensitive so any ICs would not stand a chance anyhow. It's generally all done in discretes.

If it has to be low loss think in the direction of resonant power transfer when designing it. Resonance is your friend with wireless power transfer. Unfortunately it's usually only practical to have one side (power source side) resonant.

On the data side you should be able to use standard stuff unless it absolutely must be transferred via the same set of coils. On a resonant transfer scheme that could get you deep into an analog hellhole. But those can be fun, like a mountain biker seeing a scary downhill section :-)

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Regards, Joerg 

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Joerg

Goofy idea: Wad of white LEDs on the PC, solar cell on the portable device. Modulate the LEDs from 90% to 100% with the data; pick up the varying solar cell output on the portable device to get the data back.

Plus you get "free" extra battery charging if the user leaves the portable device in a sunny spot.

Probably needs too much surface area on the portable device, and I don't know what the bandwidth of your average solar cell (photodiode) is.

Matt Roberds

Reply to
mroberds

If it 'plugs in', what advantage is there to contact-free transfer?

RL

Reply to
legg

We should discuss. I've designed 200 W and 2kW WPT systems. If your client has the expected volume in Production, we could knock their socks off.

If you're after 'prepackaged' solution, also contact me.

The 'worst' was 1.25W transferred over 4 inches with incredible design restrictions for the sizes of the source AND receiver.

Most important question is 'what is the size of the receiver?'

Reply to
RobertMacy

Tim,

few months ago i was consulted for a design of a docking station where i plan to use silvertel modules. AFAIK Qi specs did not assume that data transmitted are for other purpose than power management. Besides i dont understand "inductive loop that transmits using some means (FSK?) and receives by sensing variations in the load of the loop" What does that mean ?

Better to use BLE modules for data trans ...

HBV

Reply to
Habib Bouaziz-Viallet

a. No soiling up of contacts b. No corrosion c. No safety reg infringements d. Resistance to harsh cleaning agents e. Can be simply hosed off f. Much less field failures g. Cosmetic (same color everywhere) .....

And so on.

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Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

You can modulate the data onto the power path and use the same magnetic link. But north of 10kbaud that gets dicey. Because if you have to spectrally go above 150kHz the conducted emissions cert can become tricky. Well, at least if it all has to be cheap.

Even below 150kHz it's not easy, one can quickly disturb home automation systems using PLC and als atomic clocks. For example, if stuff spills into the 60kHz WWVB or 77.5kHz DCF in Europe.

[...]
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Regards, Joerg 

http://www.analogconsultants.com/
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Joerg

Oh i see, same process than 125KHZ RFID tags. I'm not very comfortable with that and i think modulate the magnetic field (AM or FM) to transmit data (10Kbds) along with power seems to be difficult (but not impossible) with power = 0.2W.

DCF77 should not disturb to much in between two near field solenoids, well .. not sure of that at all ! just a conjecture.

Good luck, Habib.

PS : Project very interesting especially on protocol specifications between two TAGS.

Reply to
Habib Bouaziz-Viallet

You can modulate the data onto the power path and use the same magnetic link. But north of 10kbaud that gets dicey. Because if you have to spectrally go above 150kHz the conducted emissions cert can become tricky. Well, at least if it all has to be cheap.

Even below 150kHz it's not easy, one can quickly disturb home automation systems using PLC and als atomic clocks. For example, if stuff spills into the 60kHz WWVB or 77.5kHz DCF in Europe.

[...]
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Regards, Joerg 

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Reply to
Harry D

You wrote:

"WPT involves hi Q power transfer, so how do you FSK at 10K BAUD with a

150KHz carrier that has a Q=100 and not break Carson's Rule??"

(transferred because stuff under the sigline gets muted in most readers)

The only Carson that counts here in the west is this guy :-)

formatting link

You need to use your own carrier, feed the signal into the power path and equalize the heck out of it. Modulating is possible as well but the arriving amplitudes are very small. A Q of 100 does not mean that signals at a few kHz from the carrier will be zero, just very muffled. It would have to be muscled through. That is not an elegant solution though. And it's difficult, that is what I meant with "analog hellhole".

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Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

Joerg said it as well as I could.

It's to be used on shipboard. It probably won't be immersed in salt water in its daily life, but it needs to resist being splashed with it on a regular basis.

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Tim Wescott 
Control system and signal processing consulting 
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Tim Wescott

There is a standard out there that's getting adopted for smart phones and other similar sized bits of kit. It's the "Qi" standard that I mentioned. But making a compliant device would, I think, cost a lot more than it would be worth to the customer.

The customer suggested communicating over the power connection. I think it's probably not a good idea, however much fun it may be to try.

When I hit things like this I often have to discipline myself not to go there -- it's tempting to do things the fun way, forgetting that it's on the customer's dime and may not be the most cost effective way to proceed.

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Tim Wescott 
Control system and signal processing consulting 
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Tim Wescott

Way inefficient, but it just sparked the idea of using optical comms, which may well work -- I'll have to try it on for speed.

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Tim Wescott 
Wescott Design Services 
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Tim Wescott

Must be an interesting computer packaging exercise, in that case.

RL

Reply to
legg

It probably depends how onerous the standard and licensing is. Also, if you need fast datacom I believe that's not covered and then you have a custom situation at hand anyways. Might not be worth to bother with a standard then because nothing they'd ever wanted to plug in would be compatible with your data solution.

Yeah, I am sometimes tempted as well. But if there is any other method, such as a 2nd coil and core for data, that's way easier. Just keep in mind radio cert rules if you go ISM. In many jurisdictions that is considered "intentional radiator" and then the EMC test takes longer and costs more.

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Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

IR can transmit through certain kinds of plastic, meaning you could still have a hermetic seal.

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Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

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