using 2812 9c motor as a generator

[miuan]

Hi All! A relative wants to build a stationary 4-person bike with a hub motor that generates electricity for some home appliances like water kettle, bulbs, music player etc. He wants the output voltage and power to vary along with the pedal power input.

I want to keep it very simple, without any mains inverter or DC converters. A 2812 9C can output slightly over 100V if gear ratio is kept high enough, e.g. 53/11. Then what we need is a a controller with high enough voltage rating and regen enabled, or even a sturdy enough rectifier bridge with some HV caps could be enough. A couple 24V bulbs in series or a 110V water kettle / hair dryer could work just fine, maybe less power but still they'd work. Also, any switching supply would probably work too.

Am I on the right track here? Any input welcome. Especially what voltage and power I should expect. It is a fun project for kids/students, so don't take it dead serious please

 

[veloman]

Here's a simple wind turbine design. Do you have a spare junk bike to mount a spare DD rear hub into? And a spare controller to get the regen off the motor? Then you have a very easy wind turbine. See this video. Just plop your hub motor in. [youtube]n74E42yd4_c[/youtube]

 

[Hillhater]

You can only get out what you put in ( less efficiency losses)
I assume you realise that an average human will not be able to output even 200W for very long ?
So your 4 person bike ? will give you probably 600 ish watts output.
..That will take a while to boil a kettle !
(and by the time its boiled, there will be 4 people who need a long cold drink !)

And i hate to think how little power you would get from that wind generator !

 

[miuan]

Thanks but I wasn't asking about a wind generator.
Even 400W would be enough for a kettle, we don't need to boil the water in 2 minutes anyway. It's more or less a fun and educative project for the kids and can be used to recharge batteries that power basic appliances on off-grid places.
I was particularly looking for someone who was tried it, and what I could expect from that motor winding, since it could be used to directly power 110V appliances without an inverter.

 

[John in CR]

I believe a speed wind hubbie would be far better for your plan. The reason is the same as the difference in regen between speed wind and slow wind hubmotors. The proportionately high torque per amp of the slow wind when used as a motor works the same when you engage regen. ie it hits hard with the braking force. A speed wind has nice gentle regen for the same current to the battery over what feels like a broader rpm range.

I could be wrong and the results are identical with the same current limits and tuning with gearing, but I do think the speed wind will be easier to match with a comfortable cadence over a wider range. As an example, I've actually pedaled a couple hundred yards with regen engaged on a speed wind hubmotor, while with slower winds I couldn't even get started.

My regen recovery % has always been much higher with speed wind motors, which leads me to believe it's more efficient. That does seem to drop off at higher voltages, so I'm not sure about trying to achieve 100V out, because I think it will result in higher losses at lower rpms.

If heating water is something you expect to do frequently with the rig, then I'd include a bypass of all the electronics so that switch simply goes to a length of nichrome wire that shorts the phases. Then you eliminate all the losses in the electronics and directly heat the water. You can tune it to your liking with the length of nichrome wire used, and since the resistance of the motor windings is very very low compared to the length of nichrome the water heating can be very efficient, especially compared to going thru some conversion steps with electronics before going back to heat through a resistor.

I've seen several pedal rigs for making electricity, and unless you're a science teacher and can use it in class every year, I wouldn't go to much effort at all. That's because it will get discouraging in a hurry. To make electricity the way to go is to fly a turbine or get some solar panels. Pedaling a bike for transportation is great, because it requires so little power, but trying to generate useful electricity for more than a handful of watts to light some LEDs or to charge a cell phone or emergency radio could only be useful to a fat guy like me as a weight loss program. OTOH, there's real value in a quick and easy rig for pretty much a one time use as a lesson to demonstrate the limited output of a human for creating electricity. For useful electricity from humans you'd probably need some kind of rig like the machines in the Matrix used.

 

[kdog]

a motorbike PM alternator is a cheap alternative to a hub motor (unless you already have one). they also have robust 12v rectifiers that can rectify and regulate the output. you dont have use this though, then Vout is proportional to speed. the only thing is youll have to build a housing/mount. pick one up for cheap at a wreckers. they need to run at higher RPM than a hub motor so it might not be worth the hassle