Inductive coupling charger?

Batteries, Chargers, and Battery Management Systems.
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Drunkskunk   100 GW

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Inductive coupling charger?

Post by Drunkskunk » Jun 23 2012 11:53am

One of the biggest problems for some people is remembering to plug in their bike after a ride. I want to build an Ebike for my father, but he isn't the type to care much about technology, and wouldn't remember to rechage his bike.

So it hit me that the ideal way to charge his bike is with an inductive charger. Something that could work like a floor mat. Park the bike on it, and it takes care of the rest.

Normaly efficancy is important to me, but when it comes to something like this, I don't care how inefficent it is, just that it works with no real fire risk. A Park-it-and-forget-it sort of thing.

On a bicycle, i would put the inductor on the kickstand foot, so it was close to the mat when parked. But I'm thinking this needs to be a trike for my dad, and the inductor on the bike will need to clear any curb, squirl, or speedbump he rides over, so it will be 6 to 8 inches above the mat.

Its not a plan yet, its just an idea. Anyone got thoughts, comments, or ideas for this?
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Jeremy Harris   10 GW

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Re: Inductive coupling charger?

Post by Jeremy Harris » Jun 23 2012 12:05pm

It's a really neat idea - my electric toothbrush uses the same system and it gets away from contacts, keeps things easily waterproofed, and, as you say, makes things pretty foolproof (as long as there's some pretty reliable on-board safety controls against over-charging etc).

The big problem is that to work the gap between the two coils needs to be really small. I played around with my old toothbrush unit, took it apart and found that there was virtually no current at all until the thing was fully home on the charger. I doubt you'd get good enough alignment on a mat or pad to get it to work well enough.

If you could design some sort of parking stand, such that a probe on the bike automatically went in to a socket on the stand, then I think you could get such a system to work pretty well. All you need is a couple of coils, one that would fit inside the other. You'd need something to ensure that the coil on the household supply side was OK when the coil in the probe was removed, you don't want that drawing loads of current and cooking when the bikes "unplugged".
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Drunkskunk   100 GW

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Re: Inductive coupling charger?

Post by Drunkskunk » Jun 23 2012 1:48pm

A stand would be an excilent idea. I'd use a 3-4in disk mounted to the front fork that slid beside a simular disk on the bike stand. Having the stand auto-power down the bike would also be good.

But I'd never get my dad to use it. I'd be lucky to get him to park on a mat. He'd always have some excuse. It was hot. he was tired. the kid's bikes were in the way. He had to get the icecream put away before it melted. And the bike wouldn't get charged, and the bike would be forgotten.

I may be off on a fruitless idea here, bit if it worked, it would simplify things.


Searching around, I've found refrences to Resonance inductive coupling, which is suppose to be more efficent. I've also seen vidieo like this:



5 watts isn't much, but if I could get 50 watts to the bike, I could make this work reasonably well. even at 20% efficancy, I'd call it a success.

I also remember working with Tesla coils back in collage. Aside from making sparks, they could be used to trasmit power over a wide gap fairly effectivly.
Last edited by Drunkskunk on Jun 24 2012 11:37am, edited 1 time in total.
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CamLight   10 kW

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Re: Inductive coupling charger?

Post by CamLight » Jun 23 2012 4:46pm

Drunkskunk wrote:So it hit me that the ideal way to charge his bike is with an inductive charger. Something that could work like a floor mat. Park the bike on it, and it takes care of the rest.
They've done some cool work on inductive charging for EV's and that works at distances of many inches (if not a lot more). The bigger systems are crazy expensive though. Texas Instruments has a great chip set (bqTesla) for wireless charging but their reference design is limited to 5W to comply with the Qi standard for charging (soon to be 10W, IIRC). There might be some info floating around on increasing that power limit. The chip set is great though for ensuring that the charger isn't beaming out all that energy until the device being charged is nearby and "replies" to queries that the charger sends out.

It can certainly be done but the cost will be high. And paying for 250W of electricity for a 50W charge will add to that too. :mrgreen:

[Edit] As an inexpensive alternative, perhaps have a mat with an embedded switch that the trike gets parked on? When that happens, the switch would actuate a flashing light or buzzer on/near the charger or charger cable to remind your father to plug in the charger. Some variation of this would be pretty easy to build, inexpensive, reliable, and much more efficient. Though not nearly as cool. :mrgreen:

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Drunkskunk   100 GW

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Re: Inductive coupling charger?

Post by Drunkskunk » Jun 24 2012 11:36am

CamLight wrote:
[Edit] As an inexpensive alternative, perhaps have a mat with an embedded switch that the trike gets parked on? When that happens, the switch would actuate a flashing light or buzzer on/near the charger or charger cable to remind your father to plug in the charger. Some variation of this would be pretty easy to build, inexpensive, reliable, and much more efficient. Though not nearly as cool. :mrgreen:
Interesting info on the chip. I'll look into it. 50w out of 250w is acceptable to me. I could refine it and make it more efficent later. I also see this as usefull for people with mobility scooters or wheelchairs. park on a mat, charge up. For some people, getting the cord in the plug is a huge chalange. wireless charging would be one more step to their personal freedom.

Lights and buzzer is a good idea. But my dad would take out the bulb, duct tape over the buzzer, plug the charger in backwards, and then blame me for all the smoke. The only workable plan for this is if he needs no interaction with the bike other than riding it.
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