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Forum Index : Windmills : Brushless PM e-motorcycle motor?
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rothko Newbie  Joined: 27/02/2009 Location: NetherlandsPosts: 8 |
Hi, chaps. I was wondering if these electric motorbike hub motors might not be just the ticket for a set of 8 or 9 foot PVC blades? Might need some thing to reduce to power take-off at lower wind speeds. Duty-cycle switching? Performance data here: clicky! Any thoughts? Go easy as it's my first post and stuff. |
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GWatPE Senior Member  Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
The graphs are for use as a motor. There appears to be approx 200W of fixed loss in the unit at the lower power levels and this increases in a fairly linear fashion to 300W at max power levels. What contributed to this power would need to be known, before consideration as suitability for a windmill. Gordon. become more energy aware |
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| rothko Newbie Joined: 27/02/2009 Location: NetherlandsPosts: 8 |
Okay. Excuse me if this question makes me seem a bit thick - why does the source of the fixed loss matter? I'm sure I could ask the guys who make them to up-spec the magnets and the wire a bit if that's a problem. |
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| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
If all of the losses are iron related, then it will affect windmill performance. If all the losses are in bearings and seals, then there is possibility of improving these aspects. I suspect iron losses will be major contributor. For a comparison, my AxFx alternator requires < 1W to achieve rotation. This motor would require 200W, based on the data provided. Blade designs would probably pose a challenge. Gordon. become more energy aware |
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| rothko Newbie Joined: 27/02/2009 Location: NetherlandsPosts: 8 |
Ah. So potentially the entire magnetic circuit might need redoing. That might well put the tin lid on it. They make a rather smaller one too, intended as a helper motor for pushbikes. It has fixed losses of only about 30 watts at low loads, so maybe my attention might be better focused there, then... it's a fair amount cheaper, too. Seems to lose a disproportionate amount of power at higher speeds, though - might that be a heating issue that could be alleviated with thicker wire? [url]http://www.goldenmotor.com/hubmotors/hubmotor-36V_450W.pdf[/url], if you're interested. |
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| rothko Newbie Joined: 27/02/2009 Location: NetherlandsPosts: 8 |
While I'm up here exposing my ignorance, what are the drawbacks of duty-cycle switching as a means of reducing load at low speeds? Besides the obvious switching losses/circuit driving. |
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| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Duty cycle switching is used in DC-DC converters. The analogue and digital Boost maximisers I have use this principle. The capacitor arrangements offer similar benefits without complex signal measurements and control algorithms. There are many options and many schools of thought. If you are into modulators and micro computers, then you may attempt windmill MPPT. I have spent many years now in this difficult area of research. I have now settled with the capacitor arrangements I have presented elsewhere, that were sparked from discrepencies in testing from early work by Dennis [FandPwithPVC] and Bryan [bryan1]. There is a certain satisfaction from making something yourself. Some purpose built machines may be retrofitted to another purpose, but usually best results are from purpose built. Windmills have the knack of highlighting problems in the powerhead design when a retrofitted unit is used. Gordon. become more energy aware |
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| Feral Newbie Joined: 03/12/2006 Location: AustraliaPosts: 39 |
Would this be the item being commented on. Its 250 W at 36 V with dimentions of 160mm dia and magnets 40 only at 40x10x3. 
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5119 |
I have one of those hub motors. Mine has 46 magnets, 52 stator poles, and the stator is about 200mm diameter. Its rated at 300 watts. There is no cogging, and its easy to spin by hand. I've been meaning to put together a test jig to see how it performs. The weak link in these motors is the wires that lead in through the axle hole. The stator itself uses multible strands of .8mm wire, giving a bundle diameter of about 3mm. This is then connected to 1mm wire to feed out the axle  . I think with 3mm lead in wires these motors could pump out much more than the rated 300 watts.
To use as a windmill alternator, I would mount the rectifier onto the stator, then connect the -ve output to the axle shaft, and feed a single 3 or 4mm +ve wire through the axle hole. I dont think the axle itself is up to the job as a windmill without some strengthing. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Hi Gizmo, these hub motors would make good alternators with a new hollow stub type, axle and new bearing housings. They have been around for a good many years. I first saw one in 1990. They were pretty rudimentary then, but presumably now are more refined. The one I saw only had ferrite magnets. This unit presumably has Neo type magnets. If the units are easy to spin by hand, then the efficiency figs quoted in the data above must relate to switching losses etc, and not necessarily just iron losses. Gordon. become more energy aware |
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| rothko Newbie Joined: 27/02/2009 Location: NetherlandsPosts: 8 |
Cheers, guys. So the points I should be looking at are mainly the axle and the bearings, and fitting a more serious wire into the back of it. I'll give the chap who has them a call at some point and take the plunge. Thanks for the assistance, lads! |
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