OT-Automobile alternator rotation direction

The last descriprion, where the output from the alternator of the vehicle AND the pos of the battery are disconnected, and the output of thew (115vAC) generator is connected to the battery POST and the alternator output TERMINAL addresses all the issues.

By "permanent" connection I meant unswitched and simply removeing either the alternator output OR the battery positive and connecting the genset would have subjected those devices to possibly harmfull voltage conditions.

Reply to
clare
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The "official answer" from the Car Talk boys is:

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But I do have trouble buying it, there just can't be very many vehicles around with enough physical space in front of the alternator pulley to cram a typical 120 volt electric drill into.

But maybe I don't know where the "chock" is on a drill.

Jeff

Reply to
jeff_wisnia

On May 4, 3:09 pm, Cydrome Leader wrote:

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 c*ck 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

Reply to
Dan_Thomas_nospam

Click and Clack are idiots anyway.

Reply to
clare

I can't agree with that statement, Claire.

They are merely playing to the level of their current radio audience, and their show has remained on the air for over 30 years now.

Both of them graduated of my alma mater a few years after I did and in

1999 that school (MIT) honored them by having them as that years's commencement speakers.

I've met them both a few times in a non-radio show setting and they sure didn't sound like idiots to me.

And I still get a chuckle if I'm in Harvard Square, Cambridge and see "Dewey Cheetham and Howe" on that office window>

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Reply to
jeff_wisnia

Clare, not Claire - and if they are not idiots they are playng to the lowest common denominator. Their show is more humour than mechanics the few times I've had the opportunity/inclination to tune in. Mebee I just hit them on their off days.

Reply to
clare

You can't cheat a honest ham.

Reply to
Michael A. Terrell

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