What to do with an AC Electric Motor? (Car alternator + AC motor = lawnmower?)

[corrado33]

Work was throwing away some old hand dryers, and I asked if I could have them.  They have 1/8 HP ac electric motors in them.  I mean I'm not really interested in building stationary things that always need to be plugged in so...

I was thinking I could use a car alternator with the rectifier removed to power a couple of them to make a... oh I don't know... maybe a robotic lawnmower?  What kind of AC power do alternators produce?  If I had to guess, I'd say they're regulated to about 14VDC (or else they'd produce a ton more and melt the battery... right?)  Does that mean the DC is regulated or is the AC regulated then fed into the rectifier to convert it to DC?  I think most alternators are @ 50 amps, so that's 700 watts.  This is where I get lost.  I'd have no idea how to get 14VAC to 110 or 120.  If I could amplify it to 120VAC I would have @5.8 Amps at 100% efficiency.  I'd have enough power even at 50% efficiency.

I mean, I guess I could just keep it as-is, and use a DC to AC converter, but I think it'd be stupid to convert AC to DC just to convert it back to AC.  Besides, I'd need a large (note: expensive) DC to AC converter as the motor(s) are 1 amp each.  And, the rectifiers usually have wind blowing over them to keep them cool.  Not so much on a robotic lawnmower.  

I don't know, I'm just throwing out ideas here.

Could I simply extend the distance between the alternator and rectifier and tap into the AC power (however I'm going to do that), then have it go through the rectifier and charge a battery to power the electronics?  

You know, I'll probably end up never building this, but I still like to know the answers.  What can I say, I like knowledge.  Besides, the more I know the more things I think of and one of those things might actually be something I build.  

EDIT:  Found a thread about a similar topic from a while back started by ArcMan (or similar), but didn't deal with the AC portion of the alternator.  

EDIT2:  I know AC motors are generally used for applications where they stay at one speed, so I'd probably just run them at speed and gear them down to however fast I needed.  Maybe then I could use only one motor... but then I couldn't steer...

EDIT3:  Hmmmm, after some googling, I'm probably going to need a step up transformer.  Transformers are very simple, yet I'm guessing I shouldn't try to make one, cause messing with this stuff is probably bad for my health?   

[Soeren]

Hi,

Your 1/8 HP motors will probably take somewhere between 100W and 150W, depending on efficiency.
If you use a car alternator, it will be 3 phase and you'll need another motor to spin it, so it's really not worthwhile to go that route.

Some AC motors don't care if they're fed AC or DC (like a mains driven power drill), so you could check if it will run on DC.
However... Hawing a switcher to make the voltage needed will also make it potentially lethal, so I'd advice against it (and so will your laws on electricity if they're anything like in DK, where anything above 48V is considered high voltage).

Personally, I'd use the motors for something mains driven (automatic door, bed adjuster, TV lift etc.) and get some other motors for mobile apps. Any car junk yard have plenty of motors for pocket change - lots of different sizes to find as well: Wiper motors, automatic antenna motors, power window motors, power seat motors, fan motors and they're all 12V if you keep away from trucks.

[corrado33]

Hi,

I knew you'd drop by.  

Your 1/8 HP motors will probably take somewhere between 100W and 150W, depending on efficiency.

Makes sense.  So, forgive my ignorance, could I provide half the voltage and twice the amperage?  I'm SURE it matters how I get that power, but is there any leeway?  That'd be the same power...I know for DC motors sometimes they're rated at 6, 12, and 24 V.  I don't think I'd be that lucky though...  It'd not like I'd need this thing to run at full blast anyway.  I'm guessing it'd put more stress on the motor if I tried to run it at a voltage it wasn't designed for. 

If you use a car alternator, it will be 3 phase and you'll need another motor to spin it, so it's really not worthwhile to go that route.

I know, I was planning on keeping the lawnmower mostly gas driven, and run a belt off of the motor that powers the blade.  (I'd test this without the blade on of course  )  I haven't really thought this part out, but I was debating cannibalizing a FWD lawnmower that doesn't work in our hilly, muddy yard very well and just seeing how the drive mechanism was connected.  

Some AC motors don't care if they're fed AC or DC (like a mains driven power drill), so you could check if it will run on DC.

This one has no brushes...    That's the first thing I found when I googled.  From my quick glance at a couple of sites I believe you need brushes for a universal motor?

However... Hawing a switcher to make the voltage needed will also make it potentially lethal, so I'd advice against it (and so will your laws on electricity if they're anything like in DK, where anything above 48V is considered high voltage).

So you're saying for me (a definitely not certified electrician) mess with "high voltage" is illegal?  I did not know that.

Personally, I'd use the motors for something mains driven (automatic door, bed adjuster, TV lift etc.) and get some other motors for mobile apps. Any car junk yard have plenty of motors for pocket change - lots of different sizes to find as well: Wiper motors, automatic antenna motors, power window motors, power seat motors, fan motors and they're all 12V if you keep away from trucks.

I've always though of this route.  Windshield wiper motors are usually pretty easy to get to, the rest, not so much.  I've just never taken the time to go to a junk yard and pull them out.  

Thanks for the insight!

[Soeren]

Hi,

[...] could I provide half the voltage and twice the amperage?  I'm SURE it matters how I get that power, but is there any leeway?  That'd be the same power...

As Ohms Law states... If you give it half the voltage, it will take half the current and hence burn 1/4 the power.

I know, I was planning on keeping the lawnmower mostly gas driven, and run a belt off of the motor that powers the blade.  (I'd test this without the blade on of course  )  I haven't really thought this part out, but I was debating cannibalizing a FWD lawnmower that doesn't work in our hilly, muddy yard very well and just seeing how the drive mechanism was connected.  

Sounds like something you have to be careful about, but if you're up to it (mechanically speaking), the gas engine could be used alone, with electromagnetic clutches to engage/disengage the drive to each side separately.

So you're saying for me (a definitely not certified electrician) mess with "high voltage" is illegal?  I did not know that.

I don't know what your laws are on electrical stuff and perhaps it only applies to house wiring and this may have relaxed a bit like in DK, where it has been legal for about 10 years or so, to change your own wall switches etc. if you know what you're doing.
Whatever the law states, worry more on how to stay alive

As a side note, never work on high voltage stuff when sick, tired, drunk or otherwise limited in your reactions and thinking. Back in the seventies I was working on a large audio amplifier and I needed to check the secondary side of the mains transformer (around 48VAC) and didn't see a voltmeter within reach, so did what you do with eg. a 9V battery to check for power 
I was really tired and not thinking straight, but I sure wake up then... And had trouble speaking coherently for a week or so - but today I consider myself lucky.

I've always though of this route.  Windshield wiper motors are usually pretty easy to get to, the rest, not so much.  I've just never taken the time to go to a junk yard and pull them out.  

Power window motors are easy to get to, when you have torn out the inside door cover. And while you're at it, there may be central locking motors with a short length of linear movement (or it can be used like a regular motor) as well.

[corrado33]

Sounds like something you have to be careful about, but if you're up to it (mechanically speaking), the gas engine could be used alone, with electromagnetic clutches to engage/disengage the drive to each side separately.

I originally though (something like) that, but the lawnmower... drive isn't powerful enough to push itself up the hill.  (I live on a pretty steep hill, if my yard was flat it'd be easy  ) Or, the mechanism powering the drive slips (cause I doubt it'd be a direct drive, as that'd probably be dangerous).  I bet it's just a belt and it slips when it faces too much resistance.  Also I can stop the wheels without the motor stopping.  So, if I tighten up the belt (if it is one), it'd have a bit more torque.  Or even maybe make it a chain drive?  How dangerous would that be?   

The clutches would be the interesting part.  First off, after a quick google they're not the cheapest things in the world...  But it's largely dependent on size and torque.  Well, would I REALLY need 2 clutches if I still kept the original belt in place?  If the "on-off" mechanism still worked for the drive, I could just turn it off to stop, turn it on to start one wheel, and use one clutch to stop the other wheel to turn... but then I could only turn one way...  That'd be a crazy lawnmower to watch!  Swiveling around like a mad machine.

And now I'm just rambling. 

[Soeren]

Hi,

I originally though (something like) that, but the lawnmower... drive isn't powerful enough to push itself up the hill.  (I live on a pretty steep hill, if my yard was flat it'd be easy  )

So, you think adding losses will somehow give it more power? 

Or, the mechanism powering the drive slips (cause I doubt it'd be a direct drive, as that'd probably be dangerous).  I bet it's just a belt and it slips when it faces too much resistance.  Also I can stop the wheels without the motor stopping.  So, if I tighten up the belt (if it is one), it'd have a bit more torque.  Or even maybe make it a chain drive?  How dangerous would that be?   

It's probably a (centrifugal?) clutch, but I'm not that much into lawnmowers (I rate mowing about as exciting as watching paint dry ). If it takes off when you speed up the motor, it probably is.

Perhaps you can find a workshop manual for it and see if you can tighten things up, without loosing the ability to stop with the motor running.

The clutches would be the interesting part.  First off, after a quick google they're not the cheapest things in the world... 

Sure, but you can find them as surplus at much lower rates as new ones.

Well, would I REALLY need 2 clutches if I still kept the original belt in place?  If the "on-off" mechanism still worked for the drive, I could just turn it off to stop, turn it on to start one wheel, and use one clutch to stop the other wheel to turn... but then I could only turn one way...  That'd be a crazy lawnmower to watch!  Swiveling around like a mad machine.

And now I'm just rambling. 

You could make it run a spiral track of course, but if your lawn is square...

Seriously, you should be able to make do with only one side turning, if you plan the track it will follow and remember... 270° left equals 90° right.

[blackbeard]

stick one in your bathroom. it'll be so kick ass!

[corrado33]

It's probably a (centrifugal?) clutch, but I'm not that much into lawnmowers (I rate mowing about as exciting as watching paint dry ). If it takes off when you speed up the motor, it probably is.

Perhaps you can find a workshop manual for it and see if you can tighten things up, without loosing the ability to stop with the motor running.

I don't think it's a centrifugal clutch.  The motor stays at the same RPM all the time.  I honestly think it's a pulley moving back and forth when you pull the handle.  I'll check it out.  

You could make it run a spiral track of course, but if your lawn is square...

Seriously, you should be able to make do with only one side turning, if you plan the track it will follow and remember... 270° left equals 90° right.

See I really wanted to be able to make it do a couple different tracks.  Since I have a bunch of mud in my yard if I always go the same way I get big ruts in it.  Then the wheels get stuck in the ruts and lower the blade which hits the raised mud between the ruts and goes dull and stall.  It's annoying.  Sure I could make it a spiral track, but it'd be a lot easier to program if it could turn both ways.  

It's been raining here constantly for the past couple weeks, so whenever I get a chance to look at it I will.  


This is my lovely picture of my yard.  It's about a half acre.  (Still have the side and back yards too.)  Green arrows indicate really steep hill and the black things are trees and the island.  I think it might be a bit hard to do with one way turning.  I mean, it'd be possible, but it'd look really stupid doin it.  

I usually cut it side to side just cause it's annoying walking up and down the hill (and I've been known to slip and let the lawnmower go and since the thing to shut it off by itself gets stuck it just kinda keeps going till I run it down) 

[Soeren]

Hi,

I don't think it's a centrifugal clutch.  The motor stays at the same RPM all the time.  I honestly think it's a pulley moving back and forth when you pull the handle.  I'll check it out.  

Nah, if it's handle controlled it isn't. Centrifugal clutches engage when you rev up  and v.v.

See I really wanted to be able to make it do a couple different tracks.  Since I have a bunch of mud in my yard if I always go the same way I get big ruts in it.  Then the wheels get stuck in the ruts and lower the blade which hits the raised mud between the ruts and goes dull and stall.

What, no LASER controlled cutting height? 

Sure I could make it a spiral track, but it'd be a lot easier to program if it could turn both ways.  

Yeah, I merely argued that it could be done... Not that it should.

This is my lovely picture of my yard.  

And here I thought you'd discovered a very early Dali 

I usually cut it side to side just cause it's annoying walking up and down the hill (and I've been known to slip and let the lawnmower go and since the thing to shut it off by itself gets stuck it just kinda keeps going till I run it down) 

I wonder if you know Flymo and their range of hovering Mowers? In case you don't, they'll never dig in, as they... Hover over the grass and you can push (or pull) them with one finger for that reason - after my old man bought one of those, me and my siblings almost fought for the right to mow (quite different from our pre-Flymo days).

If I ever take on the task of making an autonomous mower, this will be my preferred base - and then I'd probably drive it like a swamp raft (with a huge fan).

I have seen the guys that mows the drainage trenches that we have alongside some of our country roads, using Flymos and handle them by tying a rope to the handle and then valk slowly at the top of a trench, with the mowers up/down and side to side controlled by the rope - light work to mow a hill that way.

[corrado33]

Hi,

Nah, if it's handle controlled it isn't. Centrifugal clutches engage when you rev up  and v.v.

Like a car with an auto. 

I wonder if you know Flymo and their range of hovering Mowers? In case you don't, they'll never dig in, as they... Hover over the grass and you can push (or pull) them with one finger for that reason - after my old man bought one of those, me and my siblings almost fought for the right to mow (quite different from our pre-Flymo days).

If I ever take on the task of making an autonomous mower, this will be my preferred base - and then I'd probably drive it like a swamp raft (with a huge fan).

Hmmmm, I always wanted to build a hovercraft...  They're surprisingly simple.  But wouldn't the wind blow the grass out of the way?  So the blades would be IN the base (I'm not up on my hovercraft lingo).  A while ago I researched them and found out there are a couple ways to build hovercrafts.  Interesting things.   

[Soeren]

Hi,

[...] But wouldn't the wind blow the grass out of the way?

The air stream for hovering is kept near the outside, escaping along the perimeter of the "housing".
The blade is like in a gas driven wheeled mower, but with a shape generating suction (or rather air circulation), to suck the grass up towards the blade (like a propellor would).