Electronic – Generating electricity by moving door handle to produce 3 Watts


I want to attach a generator to a door handle and have the output charge a battery. My system needs to provide about 3 Watts. A similar question was asked here and I referenced it to get an idea of what kind of force, torque, power, and energy are needed to turn the door handle. These values, however, were calculated without the generator attached to the door handle. My question is, how would attaching the generator to the door handle affect these values? I know that the generator will also require some torque to turn it. What I'm confused on is if I should just connect the generator directly to the door handle or use gear ratios to figure out some gear system? The gear system would be to increase the angular velocity of the generator based on the gear ratio and the angular velocity of the door handle. Generators that I have looked at usually have some rating where they say what voltage and current are produced based on the rpm, so I figured I could get these rpms with gears, but gear ratios also relate the two torques.

I know there is more than one question in here, but if you could help me with understanding any of this I would really appreciate this. Even if this isn't quite feasible, what would be the major constraints?

Best Answer

This battery should be able to
power a pic 24 continuously at 0.63 mW, should be able to
keep a fingerprint reader on continuously at 429 mW, and
keep a wifi module in standby mode continuously at 3.96 mW.
I am also considering attaching a dc motor to the deadbolt latch and driving it with an h-bridge. This would also be powered by the battery at 1 W, but this isn't continuous and would last for about 0.5s.

You say you want a continuous mean power output of
0.63 + 429 + 3.96 mW + 1W very occasionally
= 429mW + irrelevant.

In a day that's about 10 Watt.hours

So a user inputting 3 Watts continuously via a door handle would need to do so
10/3 = 3 + hours per day.
Or 30 W for 20 minutes - that's a significant exercise level.
Or 300 Watts for 2 minutes - most people could not do that.

ie you can easily see with such simple calculations that what you have asked for is unrealistic AND that you do not need most or the power you requested. It seems extremely unlikely that you need a continuously powered card reader or that it would need siuch a high poer level in standby mode.

Try again.
5 mW to 10 mW average should be enough.
Over 24 hours, 10 mW =~ 0.25 W.h
0.24 W for 1 hour
2.4 W for 6 minutes
24 W for 36 seconds.
If you can obtain that in 10 sessions it's 24W x 3.6 seconds x 10
Or 2.4W x 3.6 seconds x 100

The last figure sounds like what you might easily be able to obtain from opening a door without it bein too too obvious. In practice you'd want several times more to allowfor inefficiencies and practicalities.

Is 100 operations a day too many - that will depend on application.
But the above gives you a basis for a realistic calculation using assumptions that suit you.

Once you have refined the spec we can talk about power generation.

At 100% efficiency

Watt.seconds ~= kg_force x metres travelled x 10.

This could be derived from opening a door, pulling on a lever or eg standing on a step (that moves under applied weight to power an alternator).