I am curious to know how much the alternator runs under 'normal' driving conditions. Normal being lets say driving around town, 30-40 mph.

Wondering a few things:
1. What is the output of the stock alternator ('04 QC 4.7L)?
2. I am aware that the output may change depending on RPM's, at what RPM does the alternator start 'working' (i think its somewhere around 1000)?
3. How much HP is the alternator requiring when active?

 

nothing?

 

Some quick facts to get you started:

The output of the alternator is not controlled by rpm. How much current it puts out (and how much power it consumes) in MAINLY controlled by the strength of the "field" that flows through the rotor inside the alternator.

In the old days the strength of this field was controlled by the 'voltage regulator'.

Today, Dodge has built the 'voltage regulator' inside the PCM computer, so it is not a seperate part....this also means that if you screw up your alternator circuit somehow...you can also 'fry' your expensive PCM computer.

But RPM does play a part. It is common today for alternators to have pulley sets that run them slower than in the past. Today, most factory alternator pulleys don't turn them fast enough at idle to be able to produce 100% of rated current, and the engine needs to be in the 1500-2000 rpm range before before 100% field strength will create 100% rated output current. Most Dodge truck alternators are either rated 95 amps or 134 amps. Some of the 4.7/5.7 Durangos are rated 160 amps.

You can figure out a 'good guess' as to how much horsepower your alternator is pulling from the engine by measuring the current, voltage and guessing the efficiency of your belts and alternator.

Volts times Amps = Watts
There is 746 Watts in 1 horsepower

When your alternator is putting out 90 amps at 14.0 volts it is
90 x 14 = 1260 Watts
1260 watts divided by 746 watts/HP = 1.7 electrical Horsepower

However your engine has to produce a bit more than this due to friction.

The belt driving the alternator probably 'eats up' 5-10% of the horsepower due to friction.

No alternator is 100% efficient either,
and also 'eats up' another 15-20%

So to get 1.7 electrical horsepower
a good guess is that you waste another 30% or so.

The engine shaft has to drive at about:

1.7 divided by 0.7 = 2.4 HORSEPOWER

It is not much, is it, compared to 230 hp?

Learn more:

click the 'understanding alternators' link at

http://www.autoshop101.com/autoshop16.html


Historical note here:
James Watt was a lathe and mill operator in the machine shop of Edinborough University in Scotland. When a college professor brought him a steam engine to do work on, Watt figured out how to make the steam engine MUCH more efficient and went into buisiness for himself making improved steam engines. Watt taught himself. He understood what torque was. He learned that rpm could be 'geared down' to create more torque. He realized that as a steam engine speed up in RPM the torque would begin to fall off. He was the first to realize that there was a point where climbing RPM and falling Torque created a 'Best Compromise' spot. He called this 'compromise' spot THE POINT OF MAXIMUM POWER because it is the rpm spot you can run an engine at and get the most torque out of the output shaft of a transmission attached to the engine. Watt later invented the term 'Horsepower' to explain this to his customers, but even today 99% of people don't know that HORSEPOWER tells them about how much TORQUE they can get out of their transmission.
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an old post that might also be of interest
---
https://dodgeforum.com/upfiles/3988/...AAA715D02F.jpg

I had seen where others had the question about where to get a high output
alternator for their HEMI Rams. After a little digging and some help from Bill
Marine Chrysler in Springfield, Ohio, I found a 160 Amp unit that SHOULD bolt
up to our trucks. The p/n is for a HEMI Durango, but it SHOULD interchange.
Now for the bad news.....the 136 Amp unit can be had online for $112.80 USD.
The 160 Amp unit is $293.60 USD!! The p/n for the 160 Amp unit is 56028697AA.
The website I got the prices from was
www.newdodgeparts.com
FWIW, the list on the 160 Amp unit was $375.00 USD
and the difference in wattage between the two
was 345.6 Watts (V*A=W, using 14.4 Volts) Hope this helps.

makeitmopar.com has it for $275.25.

Item Number MSRP Core Price Price
56028697AA $367.00 $0.00 $275.25
Alternator
ALTERNATOR, Durango, 160 Amp, 5.7L 2004 - 2006

 

That helps a lot thank you. Im going to have to read it again though lol