OT-Automobile alternator rotation direction

I'm thinking that all else left alone, it probably doesn't matter which way the shaft of an automobile alternator is rotated since the machine
produces ac which is then rectified to create a polarized dc output.
Am I right about that?
The question came up just now when eldest son and I were kibitzing about this week's "Car Talk" puzzler:
http://www.cartalk.com/content/puzzler/transcripts/200918/index.html
Thanks guys,
Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

The only issue should be the cooling fan. If it spins the wrong way, it won't cool anything.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I built an inboard boat. Chev 283. The alternator hung off one side too far, interfering with the sidewalls of the compartment, so I made a new bracket and turned the alternator around, facing the engine and closer to centerline. The angled-blade fan I replaced with a straight-blade fan (blades directly radiating from shaft) from the junkyard, some cars had them and it doesn't matter which way they turn. That alternator ran for hundreds of hours before I sold the boat. The brushes in all the alternators I've had apart point straight at the shaft and they don't care about rotation unless they're badly worn and the holder has let them cock and wear at an angle. The output will be the same in either direction.
If the battery is totally dead the alternator won't pick it up. Its rotor won't hold enough magnetism to generate enough voltage to overcome the diode drops, especially if there's any load present, as there always is. Leaned this the hard way, towing a dead truck to try to start it. Engine turned merrily but would not fire. Had to jump it. Generators, on the other hand, have field pole shoes that will carry enough flux to bootstrap the system. No diodes there.
In about 1977 I bought, for $27.95, a black box that, once wired into my pickup, would generate 110VDC for series-wound power tools and the like. Before I put it in I took it apart to see what I had paid $28 for. It was: One plastic box; one 110VAC household duplex outlet; one DPDT toggle switch, one neon lamp assembly (NE-2H, IIRC), and one resistor of something like 33K. Total cost in those days of about $4. The outlet was wired through one pole of the DPDT switch to the alternator output. The other throw of the same pole went to the battery +. The other pole of that switch simply switched the alternator's field between the regulator and the battery +. The neon assembly, with its suitable resistor to make it fire at 110V, was across the duplex outlet's terminals. So with the switch "off, everything worked normally. With it "on," the field got full battery voltage and the alternator's output, freed of the battery via the switch, generated increasing voltage as the throttle was opened until the light lit up and you wnt to work for ten of 15 minutes, then switched back to normal for a minute or so to recharge the battery. The diodes in the alternator took this for as long as I had the truck. My only peeve with it was being hosed so badly for a handful of cheap parts. No magic in that box at all. Disappointing. $28 in 1978 was worth something. I could rent an airplane for an hour for not much more than that.
Dan
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

The wear on the slip ring brushes may be different.
And I agree with your thinking as to the Puzzler.
--
A host is a host from coast to snipped-for-privacy@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

My drill is reversible, so it doesn't really matter anyway...
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Joe Pfeiffer wrote:

And all my 120 volt drills turn only CW. (That tells ya how olde they (and I) am. <G>
Son just pinged me to say that if you ran the alternator belt over the alternator pulley and then over the drill chuck you could point the drill in the appropriate direction. That may be the answer the Car Talk guys are looking for, as it's not likely there'd be enough room under the hood to connect the drill through a socket directly to the alternator shaft nut.
But, you could always unmount the alternator and.......
Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
writes:

I may be splitting hairs here, doesn't the battery have to have a little bit of charge in order for the alsternator to be excited enought to generate?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Maybe. But often the soft iron contains enough flux to self-excite. And a ""dead"" battery isn't usually. Turn off the headlights, wait 10 minutes, and you'll likely get several volts out...
--
A host is a host from coast to snipped-for-privacy@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

You don't have enough power to turn the engine over (and will refer to the battery as "dead") a long, long time before the juice is too low to run the alternator.
The part of the problem I'm wondering about is getting the belt back on, and tight enough to turn the alternator, with the engine running. Or else you better live pretty close..
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Never happen.... Charge battery; replace belt, and hope it will start. If not, yank belt, and charge 3x as long, try again.
I've tried to think up a belt-unloading scheme using the extra-virgin olive oil, to no success....
I might UNPLUG the alternator while cranking; to remove that load from the system...
--
A host is a host from coast to snipped-for-privacy@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
David Lesher wrote:

What load? The alternator isn't producing enough voltage while cranking, to have usable output. The voltage has to equal or exceed the battery voltage before it supplies any current.
--
You can't have a sense of humor, if you have no sense!

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

And the battery voltage at this point is ..? At some point the curves cross. But when?
Unplugging the field makes the load nil. Once the engine is going, plug it back in. It will go to full field excitation, and provide as much current as it can at idle.... and engine load.
--
A host is a host from coast to snipped-for-privacy@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
David Lesher wrote:

Whatever you want to believe is fine by me. I hope you don't miss that hand too much.
--
You can't have a sense of humor, if you have no sense!

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Tue, 5 May 2009 06:06:59 +0000 (UTC), the infamous David Lesher

Uh, Joe, with a charged battery, you can stop and start the engine at will. There is no need to play around moving fan blades. Hmm, I hope you're not a TEACHER at nmsu... <heh heh heh>

Oh, no. Charge battery, start engine, stop engine, replace belt, start engine, drive home. Otherwise, charge longer and repeat above.
Oh, and tell that idiot who left his lights on to put the _fuse_ back in so his warning buzzer actually warns him next time, eh? ;)

That might have been a spoof item to take your mind off the real fix.

Huh? If you did that, it wouldn't be charging the battery.
-- The scientific theory I like best is that the rings of Saturn are composed entirely of lost airline luggage. --Mark Russell
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I wasn't anticipating standing there with the drill long enough to fully charge the battery, just long enough to get the engine to turn over. Yeah, leaving it there long enough to really charge would do it...
I am a professor; you'd need to ask my students whether I'm a teacher :)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

You want to charge only long enough to start the engine once. Your drill will likely be junk, your hand burnt, and your arm sore by then.
--
A host is a host from coast to snipped-for-privacy@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Assuming a fair sized drill, 1/2 hp = 373 watts. 13.6v nominal charging 373/13.6 = 27A No figuring conversion efficiency at each level.
Yup, that drill is going to be a bit warm and the arm sore. Maybe the olive oil is to lube the bushings in the cheap walmart drill you are using. ;)
Wes
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Tue, 05 May 2009 18:03:49 -0400, the infamous Wes

Nah, it's likely for the massage of your arms when you're done with all this funky apeshit stuff.
Either that or as a, um, lube to amuse yourself while you wait for the battery to charge. <beeg steeky grinne>
-- The scientific theory I like best is that the rings of Saturn are composed entirely of lost airline luggage. --Mark Russell
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Too many conversion and mechanical losses in spinning the 18V drill to spin the alternator to turn it back into 12V DC. You will start out with 2.5 AH in the drill battery and if you're lucky get 1 AH into the car batery.
Plus, you would have to leave the car ignition key on to excite the alternator, and all the power you transfer would get sucked up by the car ECU and other stuff that would be turned on at the same time. Even the dome light could make the difference betwen Go and No Go.
You would be MUCH better off wiring one 18V drill battery straight to the car battery, and let the car battery take a surface charge. Then hook up a second drill battery and try starting the engine with the two batteries in parallel.
And as to the rotation question - the only difference is the fan, and the set the brushes take. Corvairs turn their alternators "backwards" from the usual, so they require a reverse fan or they don't live long.
--<< Bruce >>--
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

It's a 120V drill, and you've got a generator to run it.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.