4
\$\begingroup\$

I have read many posts on this site and everyone seems very competent, so here I am... very new to this. I'm trying to learn how to convert a motor into a generator. I'm just getting a bit overwhelmed with details and specs. Sorry I'm just a carpenter that likes to mess with stuff...

I'm trying to basically build a diy generator, nothing big, mostly conceptual. I won't waste your time with my failed attempts and research. Could anyone just give me a rundown on the type of motor (bush less induction perminate magnet). Where to commonly find one (fans drills microwaves)and how to regulate the power if nessary.

If I can even run a simple led or maybe a constant 5v to charge a USB device that would be fun.

I know this has been posted before but again I'm just a hobby guy getting confused. And tips or rule of thumbs or advice or links is much appreciated. Thank you all for your help.

Update: I just found a washing machine motor if that works. Researching how to convert it. Stupid question how can I tell if I need ac or dc, sorry I work with wood... Thank you for responding I am researching your advice

\$\endgroup\$
  • 1
    \$\begingroup\$ Can you say a lot more about what exactly you are trying to power? \$\endgroup\$ – Harper - Reinstate Monica Jun 21 '19 at 21:36
  • 1
    \$\begingroup\$ A photo of the washing machine motor would help greatly. ALL "plug me in" WM motors run on AC mains BUT some can be used as alternators. If it is flat and relatively thin and mounts on the bottom of the main drum shaft directly it is probably the "good" type. If it is more "usual motor aspect ratio" and drives via a belt it is probably not a good choice. \$\endgroup\$ – Russell McMahon Jun 22 '19 at 6:45
  • \$\begingroup\$ Basically, the only type of motors which are going to work well or easily as generators are motors which contain permanent magnets. This would be either brushless DC (BLDC) motors or plain old DC motors. Fancy front loading washing machines may have BLDC motors in them. Like Russel said, a picture may help. \$\endgroup\$ – mkeith Jun 22 '19 at 7:05
  • \$\begingroup\$ USB stuff is all DC. If it plugs into your wall outlet then it's AC (though many things convert that to DC at some point). AC is typically only used directly to run motors, lights, etc. \$\endgroup\$ – hekete Jun 22 '19 at 7:53
  • \$\begingroup\$ @hekete True re AC stuff BUT potentially misleading. eg the Fisher & Paykel "smart drive" washing machine motor is a 400W or so brushless DC motor crying out to be picked up for free from the roadsides of half the western world and taken home to be used as a superb alternator. \$\endgroup\$ – Russell McMahon Jun 22 '19 at 9:58
3
\$\begingroup\$

How to convert a motor into a generator?

Easy motors

If it's a permanent magnet motor, it's easy. Spin the motor, use the power, profit.

Brushed permanent magnet DC motors. Often found in toys, and old-style cordless drills and screwdrivers. These will produce DC. The gearing is often reasonable to simply spin an electric screwdriver via the chuck with your turbine.

If you buy a BLDC (brushless DC motor) these produce AC, which you can just 3-phase rectify from the output. These produce a (to me) stupendous amount of power per volume, as they use very strong magnets. This is what I'd use for a DIY windmill or turbine.

Mains synchronous motors like microwave turntable produce single phase AC, but at flea-power level, maybe worth a play.

Hard motors

If there are no magnets in it, it's hard. Spin the motor, provide excitation voltage, or specific starting and running conditions, waste of time if you're not already a motor/electronic engineer.

Induction motors - fans, washing machines
Wound motors - mains electric drills, food mixers, car starter motor

\$\endgroup\$
1
\$\begingroup\$

The easiest generators are made from permanent magnet motors. These motors are typically stiff and coggy when unpowered. They also are magnetic, unlike induction motors and universal motors which spin freely.

There are basically 3 types of permanent magnet motors.

  1. synchronous motors - these motors require AC for operation and when used as generators produce AC when the shaft is rotated, they have only 2 power terminals

  2. brush motors - these motors require DC for operation and when used as generators pruduce DC when the shaft is turned.

  3. electronically commutated motors - these motors have an electronic circuit that controls them, the circuit will need to be bypassed to use them as generators. when used as generators they produce AC.

For an easy first success, the platter motor in most microwave ovens is a synchronous motor with a gearbox. When the shaft is turned by hand, an AC voltage will be produced. It can be directly connected to AC LED lamps of suitable voltage so that turning the shaft by hand produces light.

For a second project, perhaps a pulley or power drill spinning a DC brush motor (found in ink-jet printers, tape players, many toys) powering individual LEDs.

\$\endgroup\$
1
\$\begingroup\$

To light an LED, look for "ultra simple generator" made of cardboard and wire. And magnets.

All of the little bitty DC motors are also DC generators. But to create a few volts, you'd have to figure out how to spin them fast. Or, just buy a little DC motor which already has a gearbox. Turn the shaft slow with pliers, and the motor spins fast, as a generator. Search: DC gearmotors, on hobby surplus sites like allelectronics.com, sciplus.com, surplussales.com

Also search: toy crank generator

\$\endgroup\$
1
\$\begingroup\$

As people have been saying pretty much any electric motor is also a generator. The type of current it produces is generally the same as the type used to drive it (other than 'brush-less DC' motors which are actually AC).

That leaves you with two problems. How do you turn the motor and how do you do something with the current it produces.

Given you want to make a 'generator', that probably means either turning it by hand or using some sort of combustion. Turning it by hand is the most simple, either using a gear box or maybe a flywheel and just getting it turning really fast.

Now you have your mechanical power being converted into electrical. It's not going to be great for using directly though, since the output is probably fluctuating quite a bit if you're turning it by hand. You need something to regulate the voltage. Voltage regulation and conversion is done all the time, so there are lots of options. First you need to measure what voltages you are producing and also figure out if it's AC or DC.

With that knowledge you can choose the appropriate electronics to regulate your output into something you can use. A buck/boost regulator is probably going to be your best bet and it's possible to get them fully assembled on a 3 pin package. That makes them as easy to use a linear regulator, just more expensive (but they are better). If it's producing AC you will of course have to convert that to DC first, but this can be as simple as putting a diode on the outputs.

In summery:

  • Get pretty much any motor and come up with a way to spin it.
  • Measure the out put of the motor while spinning it.
  • Use the measurements to get a buck/boost regulator with those values and the ouput you want (5V in the case of USB)
  • Profit from your 'free' power!

From that point you could start looking at adding storage in the form of capacitors or even charging up a lead-acid battery. And of course there is a lot you can do with at the input end. Add a model car/plane petrol motor to turn it, etc.

\$\endgroup\$
  • \$\begingroup\$ Induction motors are difficult to use as generators. At least for a hobbyist who is trying to get DC power. \$\endgroup\$ – mkeith Jun 22 '19 at 7:06
  • \$\begingroup\$ I'm just thinking of the likely places you would salvage a motor from and finding an induction motor seemed unlikely. \$\endgroup\$ – hekete Jun 22 '19 at 7:43
  • \$\begingroup\$ Old clothes dryers have induction motors in them. So do a lot of low-cost top-loading washing machines. \$\endgroup\$ – mkeith Jun 22 '19 at 14:47
0
\$\begingroup\$

To keep things as simple as possible, check

  • which speed your mechanical power source has
  • which power your mechanical power source has
  • which voltage your generator should deliver

Select a permanent magnet brushed DC motor with the matching characteristics in motor mode. If the speed from your mechanical power source is way off, you need a gearbox.

Select a 5V DC buck-boost regulator with a roughly 3V…10V input range and the matching power rating.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.