'Unite' geared DC motors as pedal generators

[Gotwind Ben]

These are geared 24v, 250w motors with a sprocket pitch the same as bicycle chains - Chinese in origin.
Designed as bicycle driving motors. expensive in the U.K, but available in the U.S. I believe, under the Currie brand?
I would bet they would make a nice pedal generator, with a 3:1 drive i.e. a pedaled chainwheel of 52 teeth to that 16 tooth chain driven gear.



Certainly there are 4 poles of Neo magnets inside, brushed also, I doubt anyone could wear those out on a pedal machine.

hi ben,

these little motors do ok for an off the shelf item. we do have to overdrive them quite a bit to get over the low volt/rpm and high resistance though.

here is what it might look like mounted to a pedal machine.



it's all good fun!

full details here.
http://picasaweb.google.com/davidamesof ... atorBuild#

cheers, dave

I've been looking at these motors but with having gearing I'd just assumed that it was a standard motor with no magnets. You can get one of those all in for about £60 :shock: Are they possible VAWT material?
What rpm of the sprocket does it hit 12v?

[Gotwind Ben]

Available from China unfortunatly Shawn.
Some useful data on this eBay listing also.
http://cgi.ebay.co.uk/24V-250Watt-Elect ... 2a02e5177b

That's a lot of engineering for the money! I've found one for £55 all in.
See why I think a wind turbine should be £150 off the shelf :mrgreen: :mrgreen:

So would this be about right? its top revs are 2750 so if you divide that by the gearing ratio it will make its TOP power at 2750/7.18= 383rpm of the sprocket. :?

[Gotwind Ben]

Correct Shawn.
A reasonably fit human being can pedal at around 100 rpm, the bike chainwheel to sprocket (52:16) will give you that extra 3.25:1 ratio.

The low price is due to mass production of such units, in China obviously.
You can buy a 300w turbine for £230
We just can't compete with small scale wind turbines, hence the Samrey Wren is £500
A shame really, but thats the truth of it.

hi guys,

everyones math sounds reasonable. however these little motors failed math class (hard to believe being asian and all).

driven at it's rated rpm (2750) it will generate 19 vdc and export 200ma (3 watts) into a 12 volt battery.

to generate 250 watts into a 12v bank it needs to spin 7,060 rpm :shock:

cheers, dave

edit: re-reading this post, i see that the 3 watts should be more like 40 watts oops! sorry :oops:
system volts ~14 leaves 5 for power /1.7ohms=2.9x14=~41 watts

[Gotwind Ben]

Maybe the 36v version is the way to go?

Dave,
That "to generate 250 watts into a 12v bank it needs to spin 7,060 rpm" thing.
Is that calculated or actual output?
G-

hi glen,

thanks for calling me on that one, good eyes there. that is a calculated output based on actual outputs measured at much lower rpms. my guess is that we would NEVER see 250 watts from that motor at any speed. bet we would top out at 100 watts or so with a 12 volt nominal set up and then start going down from there until it burnt itself up.

the volts per rev on these things is only 0.7volt per 100 rpms. (measured value) and the restance internal while running as a generator is 1.7ohms. (the calculated value based on actual readings)

i have had the same little motor, but the 450 watt version running at those speeds though and have seen 280 watts at ~7,300 rpm (speed of armature)for short intervals. (measured values)

the 36 volt version does only slightly better at 0.9volt per 100 rpms (measured value).

these are fun little motors and are fine as motors but the low volt per rev when used as a generator is the real killer here unless we can over drive the darn things...which we can with a pedal machine and gearing easily, but not so easy with any kind of wind application.

it's all good clean fun :)

kind regards, dave