I've got my 80A unit in. It stays put at 14.2V from 650rpm to 5000rpm.

I had to keep the smaller SAAB pulley, the larger MB one would not work with the 1000 or 1025mm belts I had. The adjusting bracket kept contacting the heater pipe casting on the waterpump.

I just re-used the stock MB field wire and ran two 10-gauge wires for the + output.

I did re-clock the back half 90* to get better clearance for the + wires.

Mabye some pics later.

If you change the pulley to a smaller size, you could get more out of the Alternator, but the bearing an brushes will wear faster. I guess you have to change the diodes as well. :-)

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1992 300SD, 290K miles.

Changing to a smaller pulley will require changing the belt length. This is relatively easy on a V-belt setup, however for cars with serpentine belts and automatic tensioners, it's much safer to retain the original pulley diameter. The smaller pulley will increase output at idle only, there will be no change in peak output, since the alternator reaches peak output by approx 2000rpm (that's engine rpm, btw.)

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Dave
Boise, ID
Check out my website photos, documents, and movies!

I plan to use one tank SVO/UVO . So I need an electric inline heater to start the car with warm oil, and something like this:
http://svopower.tripod.com/heater.jpg to keep the SVO/UVO hot.

That's the reason for wanting to upgrade the Alternator. Probably adding a second Battery as well.

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1992 300SD, 290K miles.

Ah yes, a WVO heater is a good reason to upgrade. You probably don't need the second battery though, the stock Group 49 should be plenty. Usually a second battery is only needed if you like to run an aftermarket stereo for long periods with the engine off. I would definitely pick up a 150A unit, and upgrade the cable (from alternator to battery, or alternator to terminal block if battery is not in the engine compartment) to at least 4ga, preferably 2ga.

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Dave
Boise, ID
Check out my website photos, documents, and movies!

When running my blower fan in the '81 240D, its speed changes at idle and at highway speed. I really don't need a high output alternator, but would like a little more juice. Anyone out there know what would make a good upgrade for just a little more power? What amount of increase could the stock wiring handle before the wires would need to be upgraded?

Thanks in advance.

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1981 240D, Auto Trans, 160k miles -- CRASHED!

The speed changes becuase the engine is not making much HP and the alternator is sucking it down.
This is an indication that the charging circuit has extra juice when the blower is off.

You are probably okay...a 65amp in a 240D would be just fine unless you had anything "non stock" to need the amperage.

The older alternators couldn't put out enough current at idle. The newer 'high' output ones, while puttout out more than you really need at peak output, also put out a LOT more at idle. And that's what you want. I think the stock unit in your car is 55A or 65A, so bumping up to something in the 80-110A range should be plenty. Try that AL129X mentioned in the subject line of this thread (way back on page 1.) I wouldn't go past 80A without upgrading the wiring, which is not hard at all really.

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Dave
Boise, ID
Check out my website photos, documents, and movies!

Electrical Questions for Dave...

"The older alternators couldn't put out enough current at idle." Yeah, but do you remember Generators at idle ? LOL

If a person put a higher output Alternator into their car.. and the regulator was working properly... AND they did NOT increase their LOAD .... would they need to upgrade the wiring or would the system only put out the amount needed to service the load ?

If they put the higher output alternator in and DID up the load... which wires EXACTLY would need enlarging ?

By " putting out more than you really need at peak output" did you mean " have the capability to put out " or that they really put it out ?
Or are you saying that the increase in fuel usage on the big ones depends on their capability as compared to the load ?

I am thinking that the 80 amp alternator on my 240 with the addition of a Spal Aux fan running all the time the AC is on would be a nice combo for summer stop and go traffic.....

You would need to upgrade the wiring if it did not provide sufficient capacity for the maximum rating of the alternator. You never know when the battery voltage might be low, due to extended cranking, or extended periods of sitting idle.

If you started the engine under such a condition you might smoke some wires.

With regard to "putting out more than you need", it's simply a situation where the alternator has a rating of more amps than the combined load of every consumer in the vehicle.

The alternator won't put out more than what can be consumed. But, the battery can be considered the largest consumer of them all, if it is in a discharged conditon (see above).

Your existing wires will probably be OK at 80 amps. Do you know the current wire size?

I do not know the wire size... if I know WHICH wires to upgrade I will do that automatically with the larger alternator... I believe in not taking chances on voltage drop or excess resistance due to wire size... wire is cheap and lasts a LONG TIME.... LOL

The alternator just puts out enough to cover the load (plus some current to keep the battery topped off). If your load is not more than stock, the stock wiring *should* be ok. However you may be getting some voltage drop, which is never a good thing. Most of the smaller alternators (approx 55-70A) had a pair of 10ga wires, which IMO is barely adequate for up to 80A. I'd prefer a single 6ga or 4ga, or a pair of 8ga, whatever is easiest to add on your particular car.

I personally don't like sitting at idle and having the headlights dim and blower fan slow down, then watch them brighten & speed up as I pull away from a stoplight. That's where the "high output" units are nice, they can usually maintain >14v at idle without breaking a sweat. This isn't really a problem unless you spend a LOT of time idling with high electric loads (even stock loads) if the load exceeds idle output current.

If you add any additional load (SPAL fans, WVO heaters, overwatt H3/H4 bulbs, thumpin' stereo, etc) then an alternator & wiring upgrade is pretty much mandatory. Just my $0.02...

Dave, EXACTLY which wires should be upgraded ?

Only the big wire(s) from the alternator B+ terminal to the battery (or junction block) need to be up-sized. The smaller field wire can be left alone. However, I removed the entire stock harness and created my own new harness, so I could later re-install the stock alternator and wires if desired.

Will Do !
How about pictures and schematic of your new harness...?
I also like the idea of backwards restorability if needed...
Thanks, Greg