Anyone with any thoughts?
Few things.......
Highly doubt the engine would be doing 20 Hp at 1000 rpm. It's a lot lower than you think. I have seen engines being Dynoed and at Idle even high power engines, petrol and diesel might be doing 6-12 Hp. Other thing is, if you are going to be just driving some alts, gear the things right up with BIG pulleys.
This will accomplish 2 things:
First, it will increase the load which is a good thing. 2nd, it will spin the alt in a more efficient range. 1000 Rpm is idle and the output from the alt will be less than half capacity. Large output alts are no so much designed for their max output but rather to get the amps at Idle up where a lot of smaller alts would be at the upper end of their curve.
The thing about diesels working hard is largely outdated internet Myth. If one looks at industrial engines, they are tuned to the job they are purposed for. These days it's electronic but it can also be done on mechanical engines just by winding the fuel down.
Industrial engines are purposefully de tuned for economy and moreso, Longevity.
The DIY'ers are all talking about working the engines hard, The industrial users are putting in oversize engines so they are NOT working hard and they get the longest life possible.
If you are using car alts as standard, the alternators are efficient enough but the charging control is poor. If you can get an alt like a Lecce Nevile and an EXTERNAL controller ( few different ones available and are not expensive) you can pretty much set the alt to whatever output you want. 12, 24, 36 or 48V. Just dial it up.
You will also get multi stage charging and efficiency as good as anything else at a much cheaper price.
Using the alts with the OEM built in charging, I calculate about a 60% inefficiency. IE, 1Kw of power out takes about 1.6Kw of motive power. Most of my 6 Hp Diesels from the lister to the China Diesels and Lombardini will be working hard with 2x 80A, 12V alts. I don't think they would drive 3 alts to full power without being overloaded and smoking badly which is not what you want.
I am looking at setting up my 5 Cyl 3.0L OM 617 Merc engine to a large 240V Generator and running some smaller 12/24V alts off the thing as well. Even a 20Kw 3 phase 240V alt will still be under loading this engine which is fine as I can just wind back the fuel screw so there is no excess fueling at all. As I will be running Veg oil, I will also be running water injection. I have been doing this a LONG time now and as usual, the internet fears and myths don't come near reality.
I would not run a diesel on any fuel without water injection. It solves so many problems and keeps diesel running at top performance as well as adding a fraction of power..... which on my Veg fueled truck is always fun no matter how well it's dialed up. Add 50% Methanol......Wheeee!
As far as keeping the alts cool, Pffft! Another internet myth conjured up by those with a lot of imagination but no experience.
Running a car alt in a stationary application, IE, not in an engine bay that can easily excede 100oC, the things are cruising and never breaking a sweat. Sure, they will get hot but the fact the cooling air is probably at least 80oc cooler makes a huge difference.
Like the difference between running a semi trailer up a mountain in the dessert and in the snow. Still going to be working and getting warm but totally different environments and effects on the machinery.
If you are supplying the same power from the alts as the inverter is pulling, the load on the battery is nil.
I have done this with 6Ah battery's driving 2Kw inverter and had no problems. IF the loaded voltage coming from the alts is at a decent voltage for the battery, it won't be loaded. If it pulls down hard, then the battery will "float" at that loaded voltage. IF one is pulling less than the alts output, the alts should level their voltage out at the proper battery float voltage.
I used 2x 80A Mitsubishi enclosed alternators which I have used extensively. I have found them to be virtually indestructible. I have run them direct to the inverter for many hours with NO battery's at all which folklore says will kill them. I have done the same with Bosch Alts and also had no problems.
Because I get the alts for nothing, I have TRIED to break them and so far failed. They are not anywhere near as fragile as people always seem to make out.
I have an interest in engine generated power and a lot of the feeling is use the heat and take the power as a bonus.
If you are using bought fuel, this can be important. If you are using Veg / alternative fuel, Maybe not so much.
Exhaust is supposed to be a significant amount of heat but many feel recovery from exhaust is not worth the time and effort. Myself, I think there is not much to making a tube in tube type HE, even if it were to direct the exhaust through an old gas water heater with the burner removed for pre heating.
Again, depends on what efficiency you are motivated to recover.