How much power does it take to turn an alternator
 

This gives you an idea of how much:
Mopar Engines - Power Vs. Luxury - Mopar Muscle Magazine
(found originally by t vargo)
The hot rod article says 3 to 4.5hp depending on how fast you spin the very small 60 amp alternator they used. Its reasonable to assume the far larger 200 amp AD244 I am going to use will take even more engine power to free spin.

Going to run a test that might answer this question. A small scale test before a larger build.
For the test engine I have my brand new 5.5hp Honda horizontal shaft engine I bought to make a portable air compressor out of.
The alternator will be an AD244 with the voltage regulator replaced with a big rheostat.
The idea is to take the engine, run it at various no load speeds to see how long a set amount of gas runs for. Then put the alternator with no load on the engine and see how long it takes to burn through the same amount of gas.
We will assume 0.5lb/hr per horsepower.
Then redo some of the tests with a load. Double check some to ensure consistency.
The main objective is to calculate horsepower to turn the alternator at max output for that engine with various pulley sizes (2.6'' on the alternator and 4 and 5 inch on the engine), that should give me about a 1 to 1.5 ratio and 1 to 2 ratio. The max power tests will likely need to do the loaded test first and then run the engine that speed with the alternator running no load after. Max power tests should be run at about 5,000 alternator RPM and about 6,800 alternator RPMs.
Then later on scale it up to see what it would take to run this alternator full field output at target speed, some where around 6,000 or 7,000 RPM.

Twenty years ago I maintained a small fleet of ambulances for our city of 7000 people. One thing that I noticed was the belt tension and belt life on a single 200 amp Leese-Neville alternator. I had to replace the single 1/2" drive belt with an OEM belt every other oil change to have a reliable ambulance.
You only loose one belt on an ambulance before you step up your game!
The situation got much better when the manufacturer went to twin 125 amp alternators with a 6 rib belt.

I am going to use industrial sized half inch belts and I still don't think the belts will last a real long time with what I have planned for them.
For testing I believe I will be using an automotive 1/2 inch belt.

This spells it out pretty clearly.
Note this is a 24v alternator.
http://ecomodder.com/forum/attachmen...1&d=1469680926

When I am driving, if at a steady load acceleration with a somewhat depleted battery I switch on my alternator I can feel the load engage. It shudders the car in that same subtle way you sometimes feel DFCO or an air conditioning compressor engage.

Wait, why are you testing this? You can find alternator efficiency charts everywhere. 60A load * 14V / 50% efficiency = 2.25hp, that would be a pretty typical load I think.

Calculating the amp draw power is easy. I am more interested in the now load power draw since we will assume a fairly typical ecomodder car will use very little power.
Seems everyone that makes these charts focuses on how much brake horsepower these use when making big power. We don't need big power.

A chart like this?
http://ecomodder.com/forum/attachmen...1&d=1470048377

So I took a heavy duty pickup and SUV alternator and hooked it up to a 5hp Honda GX200 engine.
One thing I found was that energizing the exciter field even with no output load put nice little load on the engine. I was not expecting that.

http://ecomodder.com/forum/attachmen...1&d=1471620551

Eddy current and iron hysteresis losses.

Alternator laminations are usually on the thicker side for cost savings, so they have higher losses.

I am trying to find a second cheap DR44G alternator.
I had the compressor go out on one of my air compressors so I have an electric motor with mounting plate that will be free for a while.

Any updates or data for this project?

I just picked up my second DR44G alternator those past Saturday and I have not messed with my air compressor with the bad compressor head unit.

I finely got to building my test stand and putting an alternator on it.
The alternator is a modern 150 amp output ACdelco DR44G, also the AD244 is almost the same. So it's not a small alternator.
Turning the alternator at an unrealistically slow speed of about 3,600rpm only took between 100 and 120 watts for the alternator plus belt..
A little less than what I expected.
Next I had a 4 inch pulley to put on the motor. The larger pulley should spin it up to 5,760rpm.
A bit more plausible for a usable speed but no where near cruise RPM. It only used between 120 and 140 watts to turn the alternator plus belt.
A minimum cruise speed is going to be at least 7,500rpm.
Edit: no field current. Just free spinning.

That's with field current right? That's higher than I would've hoped :( It would be worse if that was just the bearings and belt, although if I understood correctly, your belt is less efficient than the common 6 rib belts on modern cars.

One thing to keep in mind is that the field current is adjusted downwards as the rpms go up, and your gasoline engine's efficiency is going up with increased load. Still, it's useful to see ballpark numbers.

Seems like the 0.5mm laminations on car alternators rob a fairly good amount of power. A cheapo Turnigy Rotomax 120mm only takes 200W to spin at 10000rpm despite its neodymium permanent magnets, and still not so great 0.2mm laminations, which reduce the eddy current losses by 83%.

I just performed a test on my passat (2011 1.8T), I was unable to attach to the cable directly connected to the alternator, but I was able to get the cable exiting the battery (so the power consumption of the car).

I must admit the test most probably did not work properly beacuse of the clamp type voltmeter that I used. But the car was drawing about 2A, when revved up 2.5A when all of th edevices inside (stereo, seat heaters, heater blower, rear window defrosting) the current went to 6A. That does not seem right as that makes about 85W, the seat heaters alone should be consuming that much.

I know from my alternator welder, energizing the field with no output puts a pretty good load on my 5hp OHV briggs and Stratton engine.
The steel core laminates on this alternator are more like 1mm thick.
With my welding alternator making around 2.2kw it takes everything the 5hp motor can muster

The DR44G alternator is rated to peak at 170amps. I bought an after market 250 amp stator.
When welding it makes around 24 to 29 volts at up to 90 amps. When not welding it makes up to 80v when there is no current flowing.

That means your efficiency is extremely poor, as most of the energy is lost to resistance in the stator. If you can, you should rewire it to produce less voltage but have lower resistance. Any idea if it's delta or wye wound?

The AD244 and DR44G alternator stator are delta wound.
This is normal for constant current welding machines.
Almost all 3 phase to DC welding alternators are delta.
I need it to produce up to 30 welding volts and at least 50 volts open current to help start the welding arc. The way it's making up to 80 volts is perfect.
The resistance is already very low in the stator. The reason for the voltage drop is welding creates a short circuit.
If I was tig welding the arc voltage would be even lower, between 11 and 16 volts.

Oh wait, does the generator slow down significantly when you start welding? I was thinking it was producing 80V, and then the generator would maintain the same rpm meaning you were dumping more than the rated current through the alternator stator, which is bad.

If that's the case I can see why people use alternator-welders, that is quite elegant. Mechanically producing higher voltage to start.

It doesn't slow down a lot, less than 500rpm on an alternator that is spinning at up to 7,500rpm unloaded.
At lower welding amps it doesn't slow down much if any.

My bad I got my stator mixed up. My old 10 and 12si alternators have very thick laminates. The newer AD244 and DR44G have very thin laminate plates.

Any testing done with stator current? But no electrical load?

The counter question to this is how much Solar-Power or Cell-Size is needed to replace or augment this loss [in mechanical efficiency - due to cost cutting at the Alternator factory].

Personally I have a few small Solar Panels that I could easily junk out my cars with.

The question is really how much fuel am I wasting by not charging the battery with those small Solar Panels ?

There is some data on this in the mods pages. %5 if i remember correctly.

Depending on your driving habbits you may need a bigger battery and or biggish solar panels or charging at home.

It also depends vastly on your car. The consumption can be as low as 6 amps gor a purely mechanical setup to over a hundred amps with all the bells and whistles running simultaneously.

I ran a 100Ah panel on my 1.6 for a couple of years. The factory alternator did a good job of keeping the battery full. On a sunny day the panel would be in float mode within a say ten minutes (100% city and 100% EOC). While my best tank was recorded with the panel, the overall gains aren't measurable against back ground noise. The main reason to do it is you have the convenience of not having to recharge your battery regularly.

Now if you have a smart alt and stop start, the gains are in the order of 0.5l/100km. I'm putting 360Wh on two of my cars (on with a smart alt - one will get an alt delete), I expect to see measurable gains.

Yes energizing the armature with no load does load the alternator. But I don't know how much.
My little 5hp Honda powered alternator welder notices when I build up volts on the stator with not stator current load.