DIY Inverter Generator for home CHP

[veggie]

Ponderings on DIY CHP inverter generators....

I would like to introduce another form of inverter generator (IG) in contrast to the smaller fully integrated units sold by Honda, Yamaha, etc...
It is my understanding that the small mainstream commercial IG's are basically a DC alternator producing wild AC which is fed into circuitry which converts first to DC and then through and inverter circuit to make sine wave AC.
Additional load sensing circuits are used to match engine RPM to the demand load thereby allowing throttle control for optimum fuel economy.

While pondering the best method of pulling electrical power from a small CHP unit, I wondered how one could get the benefits of an inverter generator but in a larger 2kw or 3kw system. In the following video I demonstrated that a inverter type system can be built from readily available components.
That being a heavy duty automotive type alternator (LEESE), a battery (to act as a voltage clamp for the alternator voltage regulator), and a standard 12 volt/AC inverter.

https://www.youtube.com/watch?v=UR57Hh611r0

In this demo I am only driving an .8KW system but the components worked very well together.

The alternator is capable of producing 2kw of power and I do have a 5kw (8kw peak) inverter to couple to it in future.
So I do have the components to produce a robust 2kw inverter generator which would allow my small Kubota diesel to speed up or down according to load while maintaining a perfect 60hz output.
What is missing in my test system is the ability to sense load and alter engine/alternator speed accordingly.

I suppose it could be as simple as a current sensor connected to an Arduino microcontroller which drives a throttle servo.
What might be a little tricky is the algorithm which controls the throttle reaction time in relation to the change in loads.
Maybe a PID algorithm linking throttle position to the amperage load reading ?

In any case, I will continue to explore this method of generating power because is opens up the door to having a system which can be adaptive to loads and produce power as gently or aggressively as needed without intervention.

At the risk of rambling   I will now stop ...

cheers,
veggie

[veggie]

.... Another benefit just occurred to me.
Because the primary power is 12v (or 24v) DC being first fed into a battery, the possibility exists to bring additional generators on line at any time by simply connecting more alternators.(provide the downstream wire is sized accordingly).
No synchronization necessary.
Just day dreaming hear....but it would be so cool to have additional units automatically fire up in high load situations.
When not needed they shut down and the primary unit spools down to a lower rpm and sips fuel until larger loads arrive. 

veggie

[dkeav]

I've had a similar theory based on some of the newer switching locomtive units which make use of 3 small (say 8.3L cummins or the likes) engine/gen units where the primary unit (which can be any of the 3, round robin even) would run all the time during a duty cycle, the second engine/set would start as load demands and shuts down if load falls blow threshold for a moderate period of time.  The third unit kicks in as load requires, but is also more aggressivley disabled as the load lowers.  The idea being that most of the time only 1 engine is running, some of the time 2 and only occasionally all 3.  Built moldularly, the units should be interchanagble, where any of the group can serve any role and be swapped out or disabled in the controller as needed for maintenenace.

https://www.youtube.com/watch?v=PqwHB6jX7vM
http://www.northeastdiesel.org/pdf/low-emissions-switcher-012206.pdf

So in a CHP system we might design a basic system that eploys multiple units of gensets, maybe even identical or mix match.  Say you have 3 vanguard natural gas converted engines coupled to 2.5kw or so output alternator, feeding into a bank.  A controller could monitor the status and track the hours/usage of the modules to keep them even or mark one as disabled for service or the likes.  Monitoring the battery bank, you can start 1 unit as needed, if the draw keeps increasing add a second or all three.  The inverter portion is getting the power out of the battery bank instead of directly.

This would have a higher cost of build, though you could be using smaller engines and cheaper alternator sources.  The benefit would be in the managment of the modules maintenance windows.  While your total capacity for generation could say be 7.5kw of charging into your bank, 900 hours of generation would not be 900 hours of operation on a cheap gas engine.  It would ideally be ~300 on 3 engines.

[glort]

Rambling thoughts in response.....

Engine speed does not make a significant Difference to Fuel Consumption on diesels. I have found the consumption is far more load rated. If the engine is doing say 2000 RPM with a 2 Kw Load or 1500 Rpm with the same load. the fuel consumption is the same to the accuracy I can measure it.  Noise would be different and I'm not convinced wear is all that different either at lower revs for the same load. I believe that if the engine is in it;s peak torque band under load the wear will be minimized.
The point here being that running the engine at an RPM that will sustain the higher load may not make a worthwhile difference to justify the expense, and complication of having a load sensing system, especially if the thing is an intermittent use.

If the use is intermittant, what about a very simple remotely controled Hi/ low switch that just activates a solenoid? You can buy radio remote switches very cheap of ebay these days so you may not even have to hardwire the thing back to the house or where ever. If you are going to put a higher load on you just flick the engine to high before you switch on the load and all good.

As far as load sensing, Could this be done with belt tension?  Perhaps an idler with a spring holding tension with a switch. When the load increases the belt pulls tighter increasing the tension that sends a signal for the genny to go high.  Load backs off, tension drops, genny goes low.  Now once the thing throttles up I don't know if the tension will back off again causing the motor to go up and down but perhaps this could be tuned with the spring tension on the idler or it may give you an idea for something more practical. 

Another way of doing this may be with the throttle position sensor off a car only the thing senses the idler position and through a controller ramps the throttle accordingly.  Maybe the Idler  can have a lever which runs back to the throttle and acts directly just like the governor?


I take it you are wanting to run this stand alone but if not, what about a grid feed setup?   You can see on this vid I set up an induction motor to run as a generator and rectified the power back to DC then fed it into a solar inverter.

[video]https://www.youtube.com/watch?v=HUE1RQRAXlg[/video]

The beauty of this setup was it allowed me to use all 3 phases from the motor and like your alternator/ Inverter setup ( which I have done many times myself) it's pretty much RPM independent. You could set up to produce whatever power you wanted and if you weren't using it all and didn't have one of those biased smartarse meters that lets the power company win every way, you could wind yourself some credit on your electricity meter.

As for staging Multi alternators, Piece of cake..... except if you want it full auto.  If you were happy to kick them in manually then all you would have to do depending on the alt setup you had would be to kist in the field wires. Some alts will self excite without that though but not if you ground them.
I am wondering though what the difference is between having 1 alt working and 2 freewheeling as it were and having all 3 working even if it is at low load. The Field amps would be more with 3 running but that's not a lot of current.
The other thing would be to use a magnetic clutch off a car air conditioner so the alt would freewheel that way and could be switched in as needed so you didn't have the parasitic drag of the fans and the rotor spinning.

Hope this inspires some ideas.

[Jens]

You guys are approaching this from the wrong angle. You would be better served if you look at thinngs with two seperate systems in mind. Power generation and power consumption.
The following is based on a STATIONARY system and it also assumes that the prime product required is power and not heat!

The basis for this system is my sailboat power setup.

You start with a Lithium battery pack. You the set up a basic charge monitoring system, load and charge disconnect systems and a simple battery management system. These items are all off the shelf and relatively inexpensive except for the disconnect relays. You then add your engine of choice with a standard automotive alternator.

All the necessary control of this system is in the battery charge monitoring system but of course you could get fancy if so desired.
The idea is that any time your battery reaches a set state of charge, let's say as a random point 40%, the battery charge monitoring system closes a relay that is used to signal an 'engine start' command. When the batter state of charge is at let's say 90 %, the relay opens up and the engine shuts down. (you don't want to go to 100% but that's another story).
As far as the load is concerned, you hook up a standard Canadian Tire on sale el cheapo modified sinewave inverter and possibly a second true sinewave inverter for critical stuff.
This system can be easily scaled if need be buit multiple engines will probably require an arduino or similar controller.
The engine is set to optimal rpm and optimal load by the charge controller that is controlling the alternator.
The battery system is sized based on load requirements but the key is the Lithium battery setup because you can pretty much dump any amount of current into them or pull out any amount of current. There is no real charge profile where you have to look after float or anything and can only partially load the engine.
You can easily expand this to whole house power by choosing components accordingly!
In operation, you draw power from the batteries via your inverters. When you reach 40% (or whatever) power left in the batteries, the monitoring system fires up the engine and it will run at optimal load and optimal rpm until the batteries are up to 90% (or whatever) charge at which time the monitoring system will signal the engine to shut down.

Very simple, very modular. Your engine and charger needs to be able to generate sufficient power in 24 hrs to cover all your usage in 24 hrs but it doesn't care (within limits) how much power you are pulling at any one point. The engine only runs when needed and for as long as needed so you could theoretically run a very high power alternator and run the engine for short runs or you could go lower power and run the engine for many hours to charge up the batteries. You could run multiple engines and a manual switch for which engine is running - ie engine one is being serviced so you switch to engine two. Running both engines together is easily done if needed, either via manual control or automatic load control.

Running a 12V system limits the total power (I can run about 3 kw on my boat system) but by going to 24 or 48V systems the power could be scaled as needed.

I use a Victrin BMV-700 as the charge controller and I believe a 'House Power' battery management system that prevents over or under voltage on individual battery cells. The BMV-700 controls the charging of my 700 Ah lithium battery system and it is set to start charging at about 50% and turn off charging at 90%. It does not control motor starting. Whenever I have my motor running it will charge if charge level has reached 50% and will turn charging off at 90% state of charge in the batteries.

Hope this might provide some suitable ideas to folks .....

[veggie]

Jens,

What you explained is exactly what I have in mind. Although you described the system in a much better way than I did.

So, where does a guy get 700aH worth of Lithium batteries ?
(I assume you mean LiPo, Lithium Polymer?... or are there different types of lithium bats?)
Are there some sizes/configurations that are more cost effective for making large banks ? (other than buying one from Tesla    )

Veggie

[dkeav]

Maybe trying to source a couple packs from hybrids at junkyard?

[mike90045]

There are MANY types of Lithium based batteries
  http://batteryuniversity.com/learn/article/types_of_lithium_ion

Only the LFP (Lithium Iron Phosphate(LiFePO4))  is regarded as suitable for low attention for a home battery bank.   It's not the densest, or the highest performing,  but among the most resistant to self ignition.  Still easy to ruin with one overcharge or deep discharge.

[Jens]

So, where does a guy get 700aH worth of Lithium batteries ?
Veggie

http://www.balqon.com/store-2/#!/Yttrium-LiFePO4-700-Ahr-Battery/p/11906026

Mine are anolder version without Yitrium (haven't got a clue what that stuff does)
At the time the Canadian Dollar was still around 90 cents US, they were listed at $700 per cell and I got them for a bit less than that. They were sold as new but I suspect they were old stock and possibly installed before. I did do a capacity test and they are close to rated capacity.
Having said that, I believe you need to be aware that purchasing from Balqon is a bit of a risk based on other peoples experiences. I had no issues though. I took the risk because it was by far the best price out there.
You need 4 cells to make up a 12V pack.

[Jens]

Maybe trying to source a couple packs from hybrids at junkyard?

You REALLY need to know what you are doing if you are going to do that. A lot of times the cells are not standard voltages, the chemistry might be more volatile in order to bring up capacity and as far as I know these packs use very sophisticated battery management systems.

[glort]

You need 4 cells to make up a 12V pack.

I was looking at the price of the packs and thinking that's pretty good for the capacity.  Then I looked for the Voltage and thought "Oh ohhh".
I'm sure the price per is good but Multiplied x4, that's a fair chunk of change!