generating DC

thank you they are very interesting. but I was looking to utilize a small magnet motor as a generator running backwards, if that is possible. I have not been able to find a small generator or alternator

thanks again kenn

Try dismantling a battery-operated toy and use the motor in that!

Any permanent-magnet DC motor will do what is asked. The only question is the sizing of it to match the intended load.

Have you tryied to disassemble a small old battery powered toy to remove its electric motor and use as a generator? Or maybe you could try to purchase one in an electronic/electric hardware store. They´re small, inexpensive, and may work fine as you are talking about just LEDs.

this is somethink that might work. i will see how much dc can be generated

Its been a heckuva long time since i had a soldering iron in my hand, but don't we get AC out of a generator?

To make it DC, we need a rectifier?

Rectifier = loss of much power?

Any IEEE's out there? This metallurgist will stop with these semantic questions.

milo

I got nuthin tuh do wit IEEE, but you are indeed correct. AC out out of a generator. Need a couple of schottky diodes or a rectifier to convert to DC.

Check out this link for a simple genny Kenn LINK ...it is simple, but you will need something bigger than a hamster to get it turning

That doesn't sound crazy. I thought you are Craziest OZZIE?

milo

Ah'd-uh-thunked u-duh looked at Wiki, first, and got "Properly-Semantic" about it...

From the page: "Through a series of accidental discoveries, the dynamo became the source of many later inventions, including the DC electric motor, the AC alternator, the AC synchronous motor, and the rotary converter." and "Without a commutator, the dynamo is an example of an alternator, which is a synchronous singly-fed generator. With an electromechanical commutator, the dynamo is a classical direct current (DC) generator."

Point being: most lay-persons associate generators with DC and alternators with AC ... as in your auto's alternator, which uses diodes to convert to DC...

Jus' Keepin' y'on yer toes...

meant to add ~ all (my) old VW Beetles and Ghia ('70) had true generators ... with the distinctive commutator quite visible ... everything else I've owned had an alternator.

"Yes", I'm aware lotsa older farm tractors had true generators too {as did numerous other older vehicles, I am sure. Just don't have any 1st hand "absolutes" to cite as certain examples...} Maybe someone else has a clear-cut tabulation...?

"but don't we get AC out of a generator?"

I don't think so! In my experience, a generator has brushes (remember 6V cars?). The brushes do the rectifying, so they put out DC (pulsating, but the current flow is always in the same direction). Alternators either have slip rings (electromagnetic armature) or no sliding contacts (permanent magnet armature). They do require diodes to convert the AC to DC.

It is true that many people talk about Gensets (implying generators), but strictly speaking, those devices don't usually use generators, but alternators.

Those permanent Magnet DC motors that use brushes will always act as generators when power is applied to spin the shaft. Obviously some are much more efficient than others. Brushless DC motors will NOT work as generators.

I stand somewhat corrected.

When I was a lad, generators were the term.

WHen I built a Battery eliminator to power my Heathkit CB' and other projects, It had a stepdown transformer and a Rectifier. AC (wall electricity in my daughter's parlance came from generators fired by coal. They didn't call them Alternating plants- they called them Generating plants.) Sigh, Layman's vocabulary.

After reviewing http://www.tpub.com/neets/book5/17.htm

I understand the linguistic/semantic issue better now. I say generators, You say alternators.

I admit I'm an old fart.

The real embarrassment is that my father was a motor inspector at the mill and he was always changing brushes and pulling armatures and the like. He helped me build a couple of motors using tin can scraps, wooden spools, a couple of spikes and a s***load of wire.

My Grandad woulda said "magneto?"

Mea culpa.

milo

lol...my age is indeed showing. "Pulsating" DC indeed is the term.

Hello Milo, Et.al.,

Regarding the AC vs DC issue, "automobiles manufactured prior to the late 1950's had generators providing DC power for the simple electronics available "way back then." Changing the brushes, often was generally considered basic maintenance. A rebuild generally required turning the area of the armature where the carbon brushes made contact as was necessary with these kinds of electronics, this along with replacing the bushings found at either end of the shaft. Way back then, if the bushings were determined to have worn so much that the wiring on the armature had made contact and was shorted out, a total overhaul would include rewinding this part.

It was common place for service station mechanics, "a group often found hanging out under the local shade tree" to replace brushes, and attempt to true up the area of the shaft where the brushes made contact, and if a press was available, even replace the bushings, if the shaft was not too badly damaged. Beyond that we swapped the part out for either a new or reconditioned one.

Alternators for cars came around in the late 50"s, and as has been mentioned else where, produced AC power, converted to DC power thru the addition of directional diodes to the internal circuitry.

Therefore, the use of a perm mag motor will require the addition of these little critters added to the circuitry. Either that of find a very small brush motor, but that will not be an easy task, as the creation of the PMM made possible the elimination of brushes and generators.

" And as for the VW generator, mine had pulleys on each end, and I have a combination starter/generator laying around some where!" that was salvaged from an old lawn tractor, I think".

TMF

Small PM DC motors come in all sizes, shapes, voltages, and RPM ratings. You should be able to find one that, when used as a generator, can power a few LED's

I suggest an old discarded (battery operated) power tool. Disassemble and remove the PM DC motor inside.

Radio Shack stocks one or two small permanent magnet motors that can act as generators when spun by something else. They've have plenty of power to light a few LEDs.

Cell phones have even smaller PM motors in them for the vibrate function. The too, can be used to generate dc.

Hobby shops have all sorts of PM motors, some quite powerful, and all the brushed ones can act as generators without modification.

If you are looking for minimal size, you could get a very tiny DC motor and hook it up to a "joule thief" (look it up on Instructables or google if you don't know what it is) to get enough power to light up a few (or many) LEDs. If you wanted, you could include a super-capacitor to provide some energy storage as well.

GA!

It does depend a bit on the energy source. If the source has relatively high RPMs (eg. a small motor spun by a small wheel running on a bicycle tire), the small brushed DC motor would be easier to turn. If it is to be hand cranked or has other low RPM source, the stepper is definitely the way to go.

To the OP: small stepper motors are easily available from discarded floppy drives, printers, scanners, etc.

Kenn is this a demo project or are you trying to do real work as a practical solution which implies energy efficiencies. For a demo don't worry about the AC versus DC aspect. If you run the diodes from an AC source th eLED will pulse as the polarity changes. the frequency is a function of RPM.

More to the point. LED are notorious for being voltage senitive. Too little and they will not light up too much and they burn out. The effective range is very restricted compared to a filament type bulb.

So if you are trying to get steady LED light out of a rotating device, more regulation is involved. If you are trying to set up a demonstration have a look at the hand cranked flash lights. All the dollar stores sell them and so do the big box stores but at a higher price. I have several with clear cases so you can see what is inside.

As a practical device it may be a waste of your time. But still fun to do.

thanks for the help I'm familiar with some of what you say

I am working on a project in my shop that could have a number of possibilities

kenn

Kenn,

Add this to the list.

I have a bicycle lighting set that uses this type of sidewall permanent magnet dynamo to run a headlight and tail light.

It puts out ac. You would need something to spin it at the optimum speed and some circuitry for limiting the voltage, rectifying, regulating and operating LEDs.

Here are some general characteristic curves for the lights.

You can see how the cycling speed (RPM) and load determine the output voltage.

Jon

A small hobby motor will work. You don't need DC to power LEDs. The LED only conducts in one direction. If you place two in a parallel circuit and alternate their polarity, one will be burning while the other is off. I tried this years ago. I spun the motor by hand and the LED lit up. There is a pulsating light but if the RMPs are high enough, you won't notice. The lower the voltage that the LED will burn at the better maybe. You may need a zener to shunt excess voltage to keep from burning up the LED if your RPMs get too high though. I don't know what you are using to turn the motor and whether or not the speed will be regulated. This is a very interesting project though.

(for transparency i need to disclose that this is benbenben. i am only able to log in and comment as a guest and still do not know why..

[pb].) ### it is interesting to note that there are indeed DC Generator that producDC current natively, being: .

.....DC current without the use of commutators . ......relatively steady, substantially non-pulsating DC current . ....... DC current without the use of rectifiers nor diodes .

a homopolar generator produces DC current and although the typical configuration embodies brushes, no commutators are used...contact is continuous. typically low voltage high mperage non pulsing DC

Please supply web links/infos for such DC generators.

That will generate AC and you need to rectify and filter to make DC.