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Ideas for wireless shoe heater

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LAN_403

Mates

Fri Jan 01 2010, 11:37PM

Registered Member #1025 Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566

Hi guys,
I do a lot of winter biking (downhill in the snow on a good mounting bike is much better than skiing and snowboarding) and Iâ€™d like to discuss a problem which all the winter bikers have and which might have some solution.

The problem is that no matter how good is your cloth your feet will always suffer from cold. This has physiological reason and more or warmer socks cannot solve the problem. So I came with an idea which would be some kind of electric heater placed inside the shoe as part of the inner sole. However, there is problem how to connect the heater with a power source. Iâ€™d like to avoid cables if possible and came with this idea:

You all probably know the stupid little mobile phones accessories (stickers and small toys) working as a small antenna stealing some of the RF energy and giving some diode flashes. What if the whole inner sole would be designed as a big dipole antenna collecting RF energy from a source which would be placed close to the shoe? (e.g. fixed on the leg - maximum distance 20cm) Any chance for energy transfer which would be practical in such setup? Remember there is no need for large amount of watts going into the shoe. It is well insulated so I think even 1W of heat could be enough. Is this realistic project?

...

Sat Jan 02 2010, 12:12AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

That seems entirely reasonable, if you have a pair of shoes that have a integral steel stiffening plate (or add some steel plate of your own) you could just set it near an induction heater with a pancake coil (like the inductive stoves).

haxor5354

Sat Jan 02 2010, 02:18AM

Registered Member #2063 Joined: Sat Apr 04 2009, 03:16PM
Location: Toronto
Posts: 352

... wrote ...

That seems entirely reasonable, if you have a pair of shoes that have a integral steel stiffening plate (or add some steel plate of your own) you could just set it near an induction heater with a pancake coil (like the inductive stoves).

then drive the coil with a minature ZVS driver

radiotech

Sat Jan 02 2010, 02:50AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

there are ways to generate the energy while the bike moves. Hack a toothbrush charger for a way to move it to your foot. A nice translator is a shake chargeable flaslhight.

wylie

Sat Jan 02 2010, 11:24PM

Registered Member #882 Joined: Sat Jul 07 2007, 04:32AM
Location:
Posts: 103

How about those shoes that lock into the pedals? Could just conduct power from a battery mounted on the bike into your shoe. Not sure about how to setup the return path to the battery without an example pedal/shoe combination in front of me though.

Wouldn't it'd be simpler and more efficient than any RF heating/power-xfer schemes?

Turkey9

Sun Jan 03 2010, 01:18AM

Registered Member #1451 Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661

Put a small rf transmitter in the pedal with an antenna in your shoe connected to the heating element. Then tune it to resonance! Similar to those wireless cell phone chargers that are coming out on the market.

Avalanche

Sun Jan 03 2010, 12:42PM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

am I the only one thinking this would be nearly impossible? Any induction heating of your 'foot' would also heat the pedal...? I also think you'd need a lot more than 1 watt, maybe 25 watts - not including losses!

I think realistically you'd need to use a wired system, similar to heated grips for motorbikes. Run it from a frame mounted battery, a similar arrangement that those old halogen bike lights used.

Myke

Sun Jan 03 2010, 04:51PM

Registered Member #540 Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969

No, you aren't the only one. I was also thinking that you would need a lot of power to heat up the plate and also that induction heating would be pretty inefficient. There are a lot more losses compared to just some heating element because of the loose coupling and such.
You would be better off going with a resistive element.

The wireless phone chargers aren't working with enough power to heat up a plate noticeably. They are working with just enough power to charge a little li-ion battery.

Steve Conner

Sun Jan 03 2010, 05:51PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Maplin's heated insoles

work off three AA batteries that probably strap to your ankle. If that isn't high tech enough, you could use lithium-ion.

Do we have any hard data on how many watts of heat human feet give off?

kell

Mon Jan 04 2010, 12:41AM

Registered Member #142 Joined: Sat Feb 11 2006, 01:19PM
Location:
Posts: 102

I thought the 25 watt figure somebody threw out was way too high. Imagine putting a 25 watt bulb inside your sock -- it would burn you.
According to this site

the entire human body only puts out about 95 watts of infrared heat.
Surely a very small fraction of that would keep your feet warm, unless you have wet socks sucking away the heat. One of the tricks used by bike messengers (I speak from experience as a former NYC messenger) in winter is to put plastic bags over your socks, inside your shoes. Your shoes will get wet but not your socks. Keeping your socks dry and inputting just a few watts by way of a DRY electric insole (inside the plastic bag) might do the trick.

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