Author Topic: Brushless DC motor as a alternator  (Read 10026 times)

Offline Pete49

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Re: Brushless DC motor as a alternator
« Reply #15 on: January 12, 2014, 01:44:52 AM »
my interpretation of the answers taking into account I'm nowhere near the level on electrics you all :Jester: are is:
blah blah blah blah blah blah blah blah blah smoke will escape blah blah blah etc.
But I have been following as it helps to expand what little mind I have left  :old: That's the good thing about this forum, we seem to cover all topics involved with model engineering :ThumbsUp:
Pete
I used to have a friend.....but the rope broke and he ran away :(

Offline airmodel

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Re: Brushless DC motor as a alternator
« Reply #16 on: January 12, 2014, 11:49:08 PM »
Ian S C

With that 60 watts I get 14 volts DC or AC because it is a resistance load. If the load has is inductive the power output is more complicated to work out. Also with that 60 watts I use a home made three phase trans former to step up the voltage to 240 volts. This load is also resistive but with the transformer it could be slightly less.

 Another factor is the multimeter I am using, measuring voltage with the higher frequency that the alternator is producing can lead to errors is the readings. A way to get around that is to compare two light globes, one run from mains frequency and the other from the alternator.  The light globe run from the alternator will always be slightly dimmer even though the meter reads 240 volts AC. The same comparison can be done with a 12 volt battery and using 12 volt globes.

Bezalel

I did have a go at putting 12DC on two of the output terminals. The motor does not lock up it moves to the next pole and stops. Because there are not enough turns on that pole the wire gets hot very quickly. It would be possible to have mechanical switches to make the motor run but would be very complicated. I can see why electronics is a much better choice for these to work.

Bill.

Offline Bezalel

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Re: Brushless DC motor as a alternator
« Reply #17 on: January 13, 2014, 04:55:15 AM »
Thanks Bill / Airmodel
I notice I omitted a few things in my post, not the least of which was my appreciation for you sharing your model with us.
I must admit I spent a few hours working my way though your youtube channel.
Thouroughly enjoyed all of it.
Lots of good tips and ideas hidden away in there, and lots not so hidden.
 
The other bit, you're quite right, I omitted mentioning the initial pole alignment which occurs if they aren't already aligned.
 
Switching mechanically, I think its ok to call such a mechanical switch a cummutator if it is part of, or attached to the rotor.
Just as Don describbed at then end of his Post. ( but I guess it wouldn't be a brushless motor then)
I don't know what you would call it if you used micro switches operated by cams.   :shrug:
 
A future project ???? any one??   :zap: 
 
Bez
Queensland - wet one day, humid the next

Offline Ian S C

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Re: Brushless DC motor as a alternator
« Reply #18 on: January 13, 2014, 12:47:58 PM »
Here is a shaded pole motor, converted into an alternator, with a claw type armature, with permanent magnet in it.  This has been seen before, but since then I managed to cut the shading turns, thereby improving the performance. Ian S C
« Last Edit: January 13, 2014, 12:51:16 PM by Ian S C »

Offline airmodel

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Re: Brushless DC motor as a alternator
« Reply #19 on: January 14, 2014, 01:56:20 AM »
Ian S C

I didn't think too many model makers were into making their own alternators so I was pleased to see your conversion. Any idea of output voltage, amps? I have never tried to put magnets into a ceiling fan motor. They would be good for models because they rotate so slow and would output a high voltage at a slow speed.

Offline airmodel

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Re: Brushless DC motor as a alternator
« Reply #20 on: January 14, 2014, 03:09:26 AM »
Just in case someone would like to experiment with brushless motors as alternators, I made a video about where to find them and how to dismantle the appliance to get the motor out.

Have a look at the video  http://youtu.be/RYCWY52yVVQ 

Bezalel

Did you see my video on how I machined all the parts for the air turbine/alternator?

Offline Ian S C

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Re: Brushless DC motor as a alternator
« Reply #21 on: January 14, 2014, 10:57:55 AM »
I fiddle around with motors/ generators/ alternators for my hot air engines, trying to get the maximum out put, with a minimum in put.
I ran this alternator with the Stuart S9, I think I got some thing like 80V, and used a 40W, 230V light bulb as a load, it glowed a bit more than just a glimmer, didn't measure it, but probably around 10W, S9 running on 30psi air, It might do better now with the shading loops cut.
Sorry it's a bit fuzzy, but here's the armature, it has two magnets from the back of a speaker.   
The original motor was 5W, 230V, 0.3A, 850rpm, 50Hz.  It is about 4" in diameter.
                                Ian S C
« Last Edit: January 14, 2014, 11:09:15 AM by Ian S C »

Offline Bezalel

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Re: Brushless DC motor as a alternator
« Reply #22 on: January 14, 2014, 11:26:57 AM »
Yep! Sure did.
 
There is only a handful of your vids I am yet to see.
 
It looks like there is a lot I can learn from your posts and build logs, I'm loking forward seeing more if you are happy to indulge us.
 
 :cheers:
 
Bez
Queensland - wet one day, humid the next

Offline airmodel

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Re: Brushless DC motor as a alternator
« Reply #23 on: January 14, 2014, 11:21:51 PM »
Ian S C

Thank you for the photo. I used the same idea with a 35 amp car alternator using microwave oven magnets. It only put out 6 amps. I am not sure why it gave such a terrible output. Maybe the magnets were not powerful enough?

Bezalel

I am glad that you enjoy my models and workshop tinkering. You seem to know a lot about electricity, is that your full time job?

Offline Bezalel

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Re: Brushless DC motor as a alternator
« Reply #24 on: January 15, 2014, 07:35:24 AM »
Yes, normally  high power electro magnetic transmission
 
Queensland - wet one day, humid the next

Offline Ian S C

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Re: Brushless DC motor as a alternator
« Reply #25 on: January 15, 2014, 11:39:51 AM »
Bezalel, you might call electricity a hobby/interest, I'v been playing around with it for over 50 years.  I started as an aircraft engineer, first in the RNZAF, then for a short time with the New Zealand Cessna agents, on becoming redundant there, I went nursing(quite often got the job of fixing anything broken, other than human as well).    Ian S C

Offline dieselpilot

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Re: Brushless DC motor as a alternator
« Reply #26 on: January 15, 2014, 02:24:17 PM »
I used the same idea with a 35 amp car alternator using microwave oven magnets. It only put out 6 amps. I am not sure why it gave such a terrible output. Maybe the magnets were not powerful enough?

First, you have to have enough mechanical power to generate the electrical output you're trying to achieve. Then the voltage and current output will be dependent on the characteristics of the motor/generator. Matching the generator to the engine and load is important for efficiency. Depending the type of electrical load it also must be controlled in order to achieve the most output from the engine. None of the details are really important unless you're trying to be efficient, but then you'd probably would just buy a generator off the shelf. Any text about motors discussing motor characteristics would give the required information.

Greg

Offline Rustkolector

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Re: Brushless DC motor as a alternator
« Reply #27 on: January 17, 2014, 05:39:12 AM »
I'm glad to see a generator topic here. I build slow speed early 1900 vintage model IC engines and finding capable alternator designs in the 300-600 RPM range has been difficult. I finally built one of my own for a 4 cylinder IC engine I built a few years ago. I used an 18 pole, 100 watt 120v ceiling fan motor stator. I got the idea from the windmill guys. The first rotor used 18 magnets aligned with the rotor poles. The cogging torque was so great I couldn't get it to turn without a wrench on the shaft. I tried skewing the magnets and that eventually allowed fairly light starting torque. The cogging is quite mild, but the cogging still causes a humming noise when it runs. The stator is 6" diameter (152 mm for you metric guys) and I fashioned it after a Westinghouse alternator I had seen. The stator was a two phase design. The original voltage output was 240v at about 650 RPM. Way too high! I split the phases into two separate 100 watt coils and got a more respectable 120v at 600 RPM. I now use one coil for AC lighting demonstration load and the other coil is connected through a multi voltage DC converter to drive a computer cooling fan for the engine. I run the engine with 3 or 4 7 watt light bulbs at 100-110v which puts a light running load on the engine. The alternator and engine have demonstrated 90 watts at about 750 RPM. It struggled at that load but did carry it with a little more throttle left. I don't normally torture my models like that but, the temptation was just too great. I have no idea of efficiency and don't really care. I wanted useful accessory for my engine to drive and now I am hooked on alternators and generators.

The second electric plant I built was smaller engine and in the absence of finding a suitable motor to cobble up, I used a PM Research Inc. 12 vdc 10 watt generator kit. I requires very high speed and gets rather noisy. I had to exchange the generator bushings for ball bearings as they didn't like the belt load. The generator drives a few 2 watt lights through and external voltage regulator which makes for a much steadier light.

I am still looking for a 4" dia short stack 12-18 pole stator for an engine I have just started building. I would like a more modest 30-50v output in the 400-600 RPM range. The only thing I see so far are motorcycle alternator stators which I would have to spin inside a outer magnet ring. Any suggestions on something this size would be appreciated.

I hope to see more posts and ideas on model engine driven alternators and generators. Here are links to a couple video's of my engine electric plants mentioned above. 



Jeff

Offline Roger B

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Re: Brushless DC motor as a alternator
« Reply #28 on: January 17, 2014, 09:34:45 AM »
Very nice looking engines Jeff  :ThumbsUp:  :ThumbsUp:

I also used a small permenant magnet motor as a generator for my first engine. It powered four 6V 0.5A bike headlamp bulbs.
Best regards

Roger

Offline Ian S C

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Re: Brushless DC motor as a alternator
« Reply #29 on: January 17, 2014, 11:39:08 AM »
I was test running an alternator I have rigged up, driven by a 3hp Kawasaki industrial engine, so I got the little alternator(see above), put a belt on the 30 mm pulley, to the pulley on the Kawasaki running at 3000rpm, this worked out at 7500rpm at the alternator, this came up as 320 volts no load, the motor then ran out of fuel, experiment ended.
For a low speed(ready built) alternator, a hub type dynamo for a bike, I'v got a Sturmy Archer hub dyno that I prepared for use as a wind turbine power unit, about 12V at 200rpm.        Ian S C