High Output Alternators - Any Advantage?

My '87 B2 with 123,000 miles seems to have a weak alternator and electrical system (battery is fine). When the revs go up a bit, the headlights get significantly brighter, and the window motors work faster etc. than when at idle.

I was looking at the 40W, 60W 100W and 140W alternators available through LMC Truck and wondering if installing a 100W alternator would kick-up my overall electrical system performance? I will be replacing my old radio/cassette unit with a new CD player in the next few weeks, but do NOT have a loud system, and no electrical extras. Also, if I installed a 100W alternator and a high voltage coil, might I expect any noticeable or measurable performance improvement? In either power or gas mileage?

Any insight appreciated. Thanks.

CraigK

CraigK said:

My '87 B2 with 123,000 miles seems to have a weak alternator and electrical system (battery is fine). When the revs go up a bit, the headlights get significantly brighter, and the window motors work faster etc. than when at idle.
I was looking at the 40W, 60W 100W and 140W alternators available through LMC Truck and wondering if installing a 100W alternator would kick-up my overall electrical system performance? I will be replacing my old radio/cassette unit with a new CD player in the next few weeks, but do NOT have a loud system, and no electrical extras. Also, if I installed a 100W alternator and a high voltage coil, might I expect any noticeable or measurable performance improvement? In either power or gas mileage?

Any insight appreciated. Thanks.

CraigK

Click to expand...

Some auto electric basics.

1. Alternators are rated by the maximum Amperage output they can produce at a given alternator RPM.

2. The alternator is intended to supply the entire electrical load once the engine is running.

3. Recharging the battery after starting the engine.

4. The battery is for:

A. starting the engine.

B. supplying current for devices when the engine is off (short term only).

C. keeping very low current devices going when the engine is off like the computer and clock.

D. when the engine is running, supplying very short term loads that exceed the alternators ability

until the regulator can adjust the output.

What you could be seeing may be the result of a weak aging battery and/or alternator system. The reason for the change in brightness is that the alternator can not supply enough current (Amps) at low RPM to support all the load requirement. It is even possible that it isn't putting out at all at low RPM, (there are other possible factors but I'm not covering them right now). When you increase the engine RPM the alternator is able to put out more current and the load requirement is satisfied.

Now to answer your question. The advantages of a high output alternator are:

1. higher out put at engine idle RPM

2. the ability to supply loads not originally in the truck design, (like the new audio stuff).

3. the ability to recharge your battery while also supporting the other electrical loads

4. general overall improvement in supplying a full 12V to the loads like:

engine, lights, and equipment in the truck.

As far as your headlights, I would suggest a headlight harness upgrade. The advantage is that full voltage is supplied directly to the head lights over heavier wire that the original design.

If you are going to change alternators, I'd go for a 3G which has much better output at low RPM than what came in your truck. If you go for a 3G then you will need to increase the size of wire from the alternator to the battery and start relay.

Both changes are common improvements on the original and very simple to do. You can buy the headlight harness already built and is pretty much a Plug and Play installation. The 3G upgrade takes a little thought ahead of time, but is still very simple.

Attached is a output chart for a, "PA Performance", 3G alternator and is typical of what you will find for any manufacturers 3G alternator.

Hope that helps.

Good luck,

>-

Seabronc

Thanks for the great information. Someone on another site suggested my problem (apparently common?) may be a burnt low speed diode in the alternator. A new 80W alternator is about $115 locally, and shouldn't require a wiring upgrade. (Last time I installed a remanufactered alternator, it lasted 102 days!) The 3G alternator is $200 and requires a $45 wire upgrade and shipping etc., but I doubt I need that for my stock B2. (I don't really need extra power, as my new CD player will be a simple in-dash replacement of the old unit - I do not have extra amplifiers, big booming speakers or special lighting.) Does this sound like a solution? Do you know if alternator internal rebuild parts are available?

Also, do you know if a high performance coil might improve performance or mileage? (Perhaps simply replacing my alternator with a unit with good diodes might help my mileage and cold idle issues?)

Thanks.

CraigK

If you want to rebuild your alternator, you can try http://www.alternatorparts.com/ford_alt_re...pgrade_kits.htm or http://www.autopartswarehouse.com/search/?...10371&Nty=1. I'm not sure if you have a 1G or 2G in your truck, if it has an external voltage regulator, it is a 1G. Do you have the ability to post a picture of your alternator?

Do you have a carbed or EFI engine?

I doubt that you would see much of a mileage improvement from just changing the ignition coil. It wouldn't hurt, but I doubt that you could prove it without some very stringent testing procedures and a dyno to test on.

>-

Seabronc

I'm pretty sure I have a 2G unit with the internal regulator as there is a unit bolted to the back that looks exactly like the internal voltage regulators for sale separately. The rebuild kits on the link you provided indicate 1- OEM rated Rectifier and 1- Regulator are included in the kits, but I am not sure these includes the required "diodes"??? My B2 is an '87 Eddie Bauer 4WD AT, single pulley, but I do not know either the amperage (65?) or understand the "position" selections. The alternator is mounted on the passenger side of the engine, at about 10 o'clock facing the vehicle.

CraigK

I'm not familiar with the BII configurations, but the clocking refers to where the connections are located 12 O'clock, 9 O'clock, 6 O'clock, or 3 O'clock. If you go to the second ling above, they have a live chat and should be able to answer your questions.

Good luck,

>-

I am not sure my comment would be of any practical value, however, if you do not have any major power draining accessories on your truck, anwer the question about what would cause the dimming and then brightening with high engine revs with a standard alternator.

Since I am working on my engine starting and electrical system, I have been looking at alternator and battery information. It seems the battery drain is an important factor even without major power-draining accessories.

If I was loading my truck with a couple of accessories, I would opt for a suitable alternator/battery combo, but personally, I am not, so I recently purchased a standard 80 amp new alternator, but the battery was the issue.

So, I thought about using an Optima or an Odyssey battery, but opted for a Motorcraft, instead. Reading about the Optima, the information and charts seemed to indicate that it counteracted the power drain more effectively than standard battery types.

I ran my Bronco II on an old, original, standard alternator for a long-time and had the same problem with the lights. The concomitant problem was overcharging and this was primarily isolated to the internal voltage regulator. Through the last five years the other bandage repairs I found that were needed were loose or junked-up wire connections around the engine starting/electrical components.