12V batt charger/inverter/diesel

[Ronmar]

At 14.5V, I am guessing you are going to need close to around 120A to meet the inverters steady state 1500W output 1500W divided by 14.5V is 103.4A of current, +15%(15.5A) for inverter conversion losses equals 118.9A of DC input to the inverter to put out 1500W of AC...

Now in a perfect world, an alternator should maintain around that 14.5V(typical automotive regulated output 14.5V +/- 0.5V) regulated output right up to it's rated amp output, but RPM and temperature are factors...  I guess you need an alternator that reaches it's peak output just before your engine reaches it's HP limit.  Or you need a cutout/limiting circuit to match the alternators peak output to your available HP...  I have looked a little at alternator regulators, but havn't ever thought about a limiting circuit.  Perhaps something controlled by the fuel rack position that switches a field limiting resistor into circuit...

[cujet]

Next question! What about getting the size of the alternator and the RPM correct, so the engine is never overloaded, regardless of RPM?

Obviously, the alternators peak output decreases at lower RPM's. I suppose I should know what the specs are prior to setting up the pulley sizes. Do you guys think this is a valid way to manage the power?

It sure would be nice to slow down the engine when little power is needed. Obviously, the ideal situation is to have the engine speed match the load.

[JLMTECH]

Hi Cutet, Design your project is very interesting, we can "over engineer the h### out of it".
Could give us a few secondary performance parameters?
Engine life?
Fuel efficiency?
Inital cost?
Etc.?
Larry

[cujet]

Engine life? It's a Changfa clone. Low quality. I don't expect 4000 hours. However, I would like to use this to power a weekend cabin. So, maybe 300 hours/year. The thing is apart right now, because the Chinese bearings failed. I'm locating quality bearings for this thing. Plus, I'm balancing the crankshaft, as it had no counterweights.

Fuel efficiency? Dunno. What ever the little diesel burns. I have plenty of waste jet fuel, waste motor oil, used turbine engine oil, etc.

Cost? I seem to be able to source things cheaply. Plus, I don't mind spending a few dollars.

[JLMTECH]

Hi Cujet and Others,    

The main reason to have high efficiency for your system is because of limited Hp. Using a
smaller alternator will reduce over all efficiency. A "better" approach is to "gear down" the
alternator. I think a 150 amp alternator is the smallest for your system

My knowledge of alternators is limited so Others may have better ideas. Mobilbob suggests that
the feedback loop of a regulator in the alternator is of minimal power. Also the maximum feed
back voltage is limited. So "gear the alternator" so that the engine can spin the alternator at full
regulator feedback voltage. Then control the maximum alternator output by engine RPM.

My guess, based of comments of Others on this list, is a maximum output of about 1200 watts,
continuous, from your engine. Or about 80 to 100 amps at 14 volts. This matches the (as the
power curves suggest of alternators in general) highest efficiency range. The efficiency falls off
as output approaches rated output.

My version of this system has the alternator geared about 2:1. With the original alternator pulley,
I saw a lot of black smoke (gearing at about 4:1). I am using a polyvee belt off the engine
flywheel to drive the  power steering pulley on the alternator. At engine speed of 2000 rpm the
alternator is spinning about 4000 rpm. At maximum engine speed of 3000 rpm the alternator is
spinning about 6000 rpm.
      
Larry

[cujet]

Well, the alternator speed relationship is a simple way to control the engine load. I suppose it's the most simple.

I had considered a 24V system, but I'm now thinking 12V so I can tie it in to my car's battery too!