"generator" from alternator and motor

[Tikvah]

I'm sure this has been covered before.  But I realized that when my engine is running, and my bus alternator is turning, I have plenty of power from my inverter and battery bank.  I've run my AC while driving and after a few hours of driving, my batteries were fully charged, and my AC and other loads have been consistent.

So, I got to thinking, If I had a small motor (gas/diesel) that only needed to turn an alternator, I'd have all the generator I need.

Thoughts?

[Lin]

And if you used an electric motor to turn the alternator, it could run for free!

Oh well, back to reality.  I would think that you could do what you suggest, although there certainly could be logistic issues to overcome. But I don't know why it would be better than having a store bought generator.

[Gary Hatt - Publisher BCM]

Yes, this all makes sense, but like Lin mentioned, you are basically creating a generator. 

If you have  300W alternator, how many HP gas engine would you need to rotate the armature at a relatively constant velocity for long periods of time and how much fuel would it consume?  One of the smallest generator is the Honda and puts out 1000W and runs very quite on very little fuel and is very quiet. How can you beat that?

Maybe you can find some way to disable 7 of the 8 cylinders on your engine and shut the fuel off to those cylinders and then you can burn diesel which you already have then you only have to change the oil in one engine, not two. :-)

[chessie4905]

Back when we had our ACF Brill, the previous owner had an approx 5 to 8 up engine hooked to an automobile alternator. He had a small panel with a volt and ammeter and a rheostat connected to the field? circuit. You started up the engine, then turned up the rheostat for desired output. Full up should would make that engine work. Used it with no issues as long as we had that coach. In those days, couldn't afford any better.

[Geoff]

Tikvah

A small engine running an alternator has been bounced around here in the past.  The consensus has been that it is not energy efficient.  

--Geoff

[bevans6]

For me, there is little difference between an engine running an alternator that supplies an inverter (your typical Honda/Yamaha inverter generator) and an engine running an alternator that runs an inverter a la carte.  I was going to use a small automotive gas engine and a pair of large 24 volt alternators, and my existing Magnum 4024 and existing battery bank.  The main difficulty was finding a way to govern the engine speed vs load.

Brian

[chessie4905]

If you are looking at doing something with a low investment, you could try one of the Harbor freight units. They are reasonable in price when on sale and will give a better idea of what ultimately works for your situation.

[Tikvah]

A typical generator consists of an engine that drives a "generator" that produces AC electricity.  that electricity goes to my battery charger, and converts the power to DC and charges my batteries.  A replacement generator head is expensive but the system works great.

Another solution, is that same engine, driving an "24v alternator" that directly charges the batteries.  Bus alternators are also expensive, but not as expensive as a generator head.

Engine speed isn't as critical, an alternator produces 24V regardless of speed, but produces more amperage with higher speed (of course using a typical voyage regulator).

Just seems really easy and affordable.

[bobofthenorth]

A typical generator consists of an engine that drives a "generator" that produces AC electricity.  that electricity goes to my battery charger, and converts the power to DC and charges my batteries.  A replacement generator head is expensive but the system works great.

Another solution, is that same engine, driving an "24v alternator" that directly charges the batteries.  Bus alternators are also expensive, but not as expensive as a generator head.

Engine speed isn't as critical, an alternator produces 24V regardless of speed, but produces more amperage with higher speed (of course using a typical voyage regulator).

Just seems really easy and affordable.

I don't know but I assume that's the principal that the little inverter gensets work on.  The challenge for a homebrew setup is doing it for the low cost that you can now purchase a store bought unit for.  I just picked up a 3100 watt Champion inverter genset with remote start, brand spanking new for a measly 1200 Canuck bux.  That's under $1000 in real dollars and did I mention, it has remote start?  Its also a clean professional looking unit that I can throw in the back of the truck or roll around the shop on its own wheels.  Its gonna be pretty hard to top that with a homebrew unit.  And I don't know about you but my homebrew units tend to end up looking like homebrew units.

[TomC]

Bottom line with generating electricity, you need a power source. That can be a Diesel engine, gasoline/propane engine, the sun, water power, nuclear power, etc that turns an alternator. Many of us have the big Delco 50DN direct drive alternators on our engines. 12V 300amps at 14.1 running volts or 4,230 watts. 24V 270amps at 28.2 running volts or 7,614 volts. Then run these through an inverter.
Whether it be a separate engine, or running from the big engine, you'll be burning fuel to create energy. You will burn less drawing the power from the big engine while driving, as compared to running your generator going down the road. Nothing is for free.
Good Luck, TomC

[Oonrahnjay]

...  And I don't know about you but my homebrew units tend to end up looking like homebrew units.

    Yes, there is that but (IMO), the bigger issue is control of the output power.  The newer Honda units (and their competition) are known for putting out power that more consistent, efficient, and "cleaner" than the power coming down the electric company grid in a lot of places.  Even a very good inverter (and very good = $$$), is limited to how good it can be by the quality of "juice" coming from the home-brew alternator.  Will it probably work OK?  Yes, probably. Will is be more likely to act up just when you need it to work right? Yes, probably.
    IMO again, paying $900 (real $$$, but who's gloating) for a unit with engineered power control is going to be the way to go in almost all instances.

[Geoff]

Those little inverter generators​ are great for tent camping, but I need 8kw for the bus.

--Geoff

[Dave5Cs]

Dave
Ah but there is something free. Wind power. How about some kind of turbin type fan that would work going down the road and it would turn a belt to your second 24 volt Alternator. Put it inside the side back doors to the engine compartment with an air scoop pushing the air through the fan. Have a regulator on it to adjust the output , done.... Just thinking outside the box!....
Dave5Cs

[Tikvah]

I believe myself to have lost my ability to communicate with writing. 

I only intended to speculate on the potential of a simple engine and bus alternator for a simple, cost effective solution as a generator.  I have no idea how much amperage my 24V alternator produces, but it's more than enough for all my needs.

Yes, I realize all engines use some kind of fuel.  But, while burning that fuel, would it make sense to simply power my eight golf-cart batteries instead of producing AC power?  The battery storage is already there.  The Inverter is already there.  Alternators are $200+

An engine???

A little 1000W Chinese generator for $1000 won't run my battery charger, much less an air conditioner.  So, let us not make comparisons there.  I would be happy with about 3OOO watts. 

Remember, I installed a mini-splits before mini-splits were cool (pun intended).  I've also done stupid stuff - not to be unearthed here.

Okay, so let us start over, is this another stupid idea, or might this be ranked with the genius of the mini-split?

[Tikvah]

Found it... This is not something totally new.  It can be done.  New question - how much hp to run a bus alternator at full load?  And, where can I get a quiet diesel engine?

https://www.youtube.com/watch?v=lzIf6ifjwN8