Converting Brushless Motor To A Generator - RC Groups
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Jul 09, 2016, 04:54 PM
BabyBootLegger
sunworksco's Avatar
Discussion

Converting Brushless Motor To A Generator


I am wanting to convert a brushless motor to a generator.
Not sure how to do the wiring and how to place the diodes for that.
Also if it's better to use an inrunner or an outrunner motor.
I do know that I want a quiet motor and the most efficient motor, that will not overheat.
I also need a motor shaft that is 1/4" and around 1" length.
All advice is very much welcome.
Thanks!
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Jul 09, 2016, 05:17 PM
BabyBootLegger
sunworksco's Avatar
Is this motor a good choice?
I like the extra shaft support.
Jul 09, 2016, 05:31 PM
Registered User
sunworksco
A brushless motor will create a 3 phase alternating current. Is this what you want?
It will require some electronics to covert it to DC.
Whether the extra shaft support is important will depend on how it is to be driven.
Jul 09, 2016, 05:46 PM
BabyBootLegger
sunworksco's Avatar
Quote:
Originally Posted by Quorneng
sunworksco
A brushless motor will create a 3 phase alternating current. Is this what you want?
It will require some electronics to covert it to DC.
Whether the extra shaft support is important will depend on how it is to be driven.
Thanks!
I want to use brushless.
Full scale turbines use 3-phase.
I have a few brushless motors, outrunner and inrunners.
I want to charge li-po batteries.
Need to figure out how to charge and properly disconnect, without destroying battery pack.
Jul 09, 2016, 05:46 PM
Registered User
vollrathd's Avatar
Quote:
Originally Posted by sunworksco
I am wanting to convert a brushless motor to a generator.
Not sure how to do the wiring and how to place the diodes for that.
Also if it's better to use an inrunner or an outrunner motor.
I do know that I want a quiet motor and the most efficient motor, that will not overheat.
I also need a motor shaft that is 1/4" and around 1" length.
All advice is very much welcome.
Thanks!
Any of our brushless motors can work as an alternator. Problem is, they require high RPM to get a reasonable voltage output.

We are talking at some 10,000 RPM or so.

What kind of voltage, current, Watts output are you after?
Jul 09, 2016, 07:33 PM
BabyBootLegger
sunworksco's Avatar
I want to charge a cell phone, blue tooth speakers, laptop, small stuff.
It may be spun up to 500rpm.
How about a 400kv motor?
Jul 09, 2016, 07:34 PM
BabyBootLegger
sunworksco's Avatar
Is there a more specific motor to use, like a brushed motor?
I wanted to stay away from the brush maintainance.
Jul 09, 2016, 07:36 PM
BabyBootLegger
sunworksco's Avatar
It will charge a battery pack, then the devices will charge from that...
Jul 09, 2016, 08:00 PM
Registered User
vollrathd's Avatar
Quote:
Originally Posted by sunworksco
I want to charge a cell phone, blue tooth speakers, laptop, small stuff.
It may be spun up to 500rpm.
How about a 400kv motor?
Won't work at 500 RPM.

As a rough guide, the motor KV is calculated as KV = RPM/Volts

Translated, Volts = RPM/KV
Using your numbers:

Volts = 500 RPM/440 KV = 1.3 Volts AC three phase.
Using a three phase Shottkey diode bridge, that will result in only about 3/4 Volt DC at 500 RPM. Using standard silicon diode rectifiers will result in little or no DC output due to their much higher voltage drop.

At 5000 RPM, you will get around 10 Volts DC.

Are you trying to get DC power to charge batteries in an isolated area with no AC power available? If you were to calculate the equivalent KV rating of a typical automotive alternator, that would be something like 5 or 10 KV.
Jul 09, 2016, 08:34 PM
BabyBootLegger
sunworksco's Avatar
Yes. It will be used for off-grid backpacking trips, man in the wilderness kind of existence.
Jul 09, 2016, 08:39 PM
BabyBootLegger
sunworksco's Avatar
Is a brushed motor better suited for a generator?
Jul 09, 2016, 08:59 PM
Registered User
vollrathd's Avatar
Quote:
Originally Posted by sunworksco
Is a brushed motor better suited for a generator?
A brushed type motor would be better suited, since no three phase bridge rectifier is required.

But, charging cell phones laptops and similar would require something like a 12 Volt DC supply. Again, you will have the issue of high RPM required to turn the brush type motor. That may not be available with something like a wind turbine or similar type of energy source.

Have you considered solar cells? Harbor Freight has an assortment of them. They might do the job, but won't work in a wooded area.
Jul 09, 2016, 09:04 PM
BabyBootLegger
sunworksco's Avatar
I'm using a small wind turbine. Three semi-flexible blades, each blade size around 48" X 12".
No solar. To much weight to carry. It will be used at high elevation. Where there is an abundance of wind power.
Last edited by sunworksco; Jul 09, 2016 at 09:09 PM.
Jul 10, 2016, 09:24 PM
Registered User
Quote:
Originally Posted by sunworksco
I'm using a small wind turbine. Three semi-flexible blades, each blade size around 48" X 12".
No solar. To much weight to carry. It will be used at high elevation. Where there is an abundance of wind power.
Only way this will work with RC equipment is if you gear it some where between 10:1 and 20:1 then use a motor with Kv in the range 300-700. You will then need a battery for smoothing (mostly because very few electronics will charge reliably from the variable output of a wind generator and may well just stall the turbine because they will attempt to charge at full rate) and associated regulation and charge control.

I am pretty sure that these things are commercially available, might be the easiest option.
Jul 10, 2016, 09:33 PM
BabyBootLegger
sunworksco's Avatar
Thanks!
Aluminum gears with a belt drive sounds doable.