ALTERNATOR VS. GENERATOR...DIFFERENCE?

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surfbug1
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ALTERNATOR VS. GENERATOR...DIFFERENCE?

Post by surfbug1 » Thu Sep 28, 2006 10:43 pm

Hi,

what is the difference between an alt and a gen>?



I am being told that the main dif are....


alternator pumps more current

and

alternator has built in voltage regulator

Is this it?

or is there more to it......

thanks


al

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Marc
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Post by Marc » Fri Sep 29, 2006 12:15 am

"Generators" make DC, and alternators make AC which is then rectified to a ripple-DC by internal semiconductor diodes. These diodes are susceptible to damage from improper jumper-cable use or if welding takes place on the car without disconnecting the alternator first.
The Type I generator is rated at 30A (there's a 38A unit used in Things and '69-'71 buses but it requires different sheetmetal, fan hub, and $$$ pulley so I wouldn't recommend it).
When VW first fitted alternators to bugs they had external regulators, but internally-regulated ones became the norm in '74 and that's the type sold today for conversion. They use the same hardware as generators except that a special pedestal is required, and it's highly recommended that you use the correct 11.3x912a belt rather than the 9.5x905LA which can slip and cause engine overheating when the alternator is working hard. Standard alternators are rated at around 55A, and you can get "heavy-duty" ones good for 75A (or more) for which the stock B+ wiring should be upgraded to 8GA.
Generators charge very little if at all at idle, while alternators cut in at a lower speed. Generators can be connected as motors to provide some cooling air if you don't have a fanbelt, not possible with an alternator.
The fan-end bearing in a generator is carried in a cast iron endplate, while in most alternators it rides in a bore in the aluminum housing. This can make alternators more susceptible to fan-imbalance problems - rather than just knocking out the replaceable bearing, the whole unit must be scrapped (or the end milled off to accept an iron plate like a generator). If you're running a stock carburetor, there could be interference problem between the accelerator pump linkage and the larger-diameter housing (factory alternator-equipped cars came with a carburetor that had a modified linkage to solve this).
Generators use brushes to pass the output current and they need periodic replacement. Alternators have brushes too, but they only have to handle the field current and typically last the life of the unit. Generators are prone to having commutator bars dislodge at extreme RPM, when that happens the brushes will wipe out in no time and it's not economically feasible to repair anymore. Replacement brush assemblies and internal regulators for alternators are seldom in-stock items at your F.L.A.P.S. (there are several different versions depending upon the alternator's origin, and most places would rather just sell you a new complete unit than try to stock the repair parts for all of them).
All in all, there are advantages/disadvantages to either. If you have a generator and it's getting the job done for you there's really no reason to change it, provided it never needs more than brushes or a new regulator. But if you're trying to decide which to start with, the alternator is probably the better choice.

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Post by allsierra123 » Fri Sep 29, 2006 12:37 am

well which would work better for running alot of lights?

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Marc
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Post by Marc » Fri Sep 29, 2006 10:20 am

The more loads on the system the greater the need for more charging output - the alternator wins hands down.

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Post by allsierra123 » Fri Sep 29, 2006 1:30 pm

that would be the major difference in my head.

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Post by surfbug1 » Fri Sep 29, 2006 11:14 pm

on an alternator....

D+

D-

DF


what is that ?


where does the voltage gauge go?

across the battery, or across something on the alternator.....or regulator....

thanks!


al

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Post by Marc » Fri Sep 29, 2006 11:51 pm

Externally-regulated alternators have those three terminals, where wires connect to corresponding terminals on the regulator. Internally-regulated alternators have just one push-on terminal for the warning light wire.
On either style, the big stud (B+) connects to the battery and loads.
There are several places up front where you can connect a voltmeter, there's no need to run a dedicated wire for it all the way back to the engine compartment. What's the year/model?
On a `71 Super w/12-fuse box, any of the first three fuses on the driver's side end of the fusebox are "hot" only when the key is on and could be used for a voltage-sensing point.

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Post by turboblue » Sat Sep 30, 2006 7:37 am

allsierra123 wrote:well which would work better for running alot of lights?
Alternator is always better IMHO.
If you want to figure your amperage load, take the wattage of all your lights and divide by the voltage (12) and that is you amperage load.
Plus the ignition system and anything else that is electrical.
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Post by rsb » Sat Mar 08, 2008 2:24 pm

They use the same hardware as generators except that a special pedestal is required... If you're running a stock carburetor, there could be interference problem between the accelerator pump linkage and the larger-diameter housing (factory alternator-equipped cars came with a carburetor that had a modified linkage to solve this).


As posted by Turbo Blue on a different thread of the same topic...

"12v generators and alternators are the same diameter where they sit on the stand. The difference is at the pulley side of the stand. It is offset to clear the alternators larger winding diameter near the pulley. You can use an generator on an alternator stand, but not an alternator on a generator stand.
6volt stands are smaller in diameter at the cradle.
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My story...

I had a shop swap out my generator with an alternator, and it would intermittently make an awful scraping noise for the full 3hr drive home. Got to looking at it, and the alternator wasn't seating in the stand properly, which allowed the fan to lean into the shroud, causing the scraping. I was able to figure out the gap between the stand and the alternator and shimmed it up with a couple sets of feeler gauges. No more scraping noise.

After I tore the motor part a few years later, I discovered the problem which Marc and Turboblue describe above.

Image alternator rubbing generator stand.

Image generator stand rubbing alternator

Image Alternator clearanced to fit generator stand.

Image The installing shop's clearancing of alternator for accelerator pump linkage

-Brian

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SparksLP
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Re: ALTERNATOR VS. GENERATOR...DIFFERENCE?

Post by SparksLP » Mon Apr 23, 2018 10:24 pm

Can anyone tell me the difference between the two types of stands, generator vs alternator? Is there a way to tell the difference by looking at it?

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Re: ALTERNATOR VS. GENERATOR...DIFFERENCE?

Post by Dale M. » Thu Apr 26, 2018 8:43 am

The lip on front of alternator stand (that locates alternator) is shorter than generator stand...

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Re: ALTERNATOR VS. GENERATOR...DIFFERENCE?

Post by Ol'fogasaurus » Thu Apr 26, 2018 9:21 am

... and the fuel pump is different as it of-set to clear the alt & stand. As I remember, the push rod required is different also.

Auto generators usually have a lower limit of ability (usually in the 30 AMP-ish range while the Alt can more than double that) but, as Dale said previously, the Alt is more sensitive to damage. Unlike VW, I always put some "protection" in the output line for an alt.

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Re: ALTERNATOR VS. GENERATOR...DIFFERENCE?

Post by SparksLP » Sat Apr 28, 2018 4:01 pm

Nice picture, that helps! Define "protection" for the output?

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Re: ALTERNATOR VS. GENERATOR...DIFFERENCE?

Post by madmike » Sat Jun 02, 2018 6:20 am

An Old guy told me with an Alternator: I won't need to drive to Indiana and back to charge the battery :lol: :lol: :lol:

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Re: ALTERNATOR VS. GENERATOR...DIFFERENCE?

Post by Ol'fogasaurus » Sat Jun 02, 2018 11:20 am

SparksLP wrote:
Sat Apr 28, 2018 4:01 pm
Nice picture, that helps! Define "protection" for the output?
Simply put, I add a circuit breaker (a fuse could be used) in line to the output lead from the ALT before it connects to anything; I match it to the output of the ALT. VW did not do this in the early VWs. It is there just for circuit protection so now the power lead goes forward protected.

Lee

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