No matter what you come up with, someone has probably already thought of it or done it. With that said, I don’t claim any of this as original thinking, but it all makes perfect sense to me. The following is written in a random way and will be added to and changed as time goes on.
Some DIY people don’t want anything to do with micro controllers. NOTE, if they are deployed properly, you have all the manual functionality remaining if they fail, you have little to lose and much to gain by building them into your design. Furthermore, some electronic stuff is junk, it casts a shadow on all electronic equipment when it fails. I know a guy who has replaced the controller for his gen set (motor home) twice already, that’s because it’s a junk design …. not because electronics is unreliable.
I start by assuming that there will be loads that are not economical to run off batteries, I also assume that the wind won’t always blow, and the sun will not always shine, or at least that the associated equipment will not always be on line to make it. I offer arc welding as an example of an occasional load that doesn’t make sense to run off batteries, but if one lives off grid, it’s nice to have. There will also be times when you have company and the demands exceed all rational design parameters, they’ll come just to see what living off grid is all about!
The main power source is the diesel generator, it is diesel for several reasons, one being the greater efficiency. The engine is water cooled providing a longer life, quieter running, and a noteworthy by product, hot water; which provides an effective means of storing otherwise wasted energy. The diesel used is simple to work on and has an advanced fuel and oil filter system that helps the engine live a longer and more trouble free life. Of course the controller has duties here as well, monitoring and alerting you to any abnormal conditions.
There are all types of diesels, the ones I’m interested in are heavy cast iron units with proven reliability and long lives. Their massive flywheels help provide a smooth constant speed. The stored energy within them allows a load to be added without the lights dimming like that of a hardware store generator. Many stationary diesels are designed to be repaired in the field, large access covers allow you to get at the guts of the machine in minutes if necessary. The down side, is the weight, some 6hp engines weigh 800 pounds! You won’t ship one of these via UPS.
Other important factors are loading, pre lubing, and running the engine within design parameters. Diesels don’t appreciate light loading long term, a controller can monitor for under loading and apply additional loads to assure the power plant is happy and running efficiently.
The study of Marine diesels could provide some clues to longevity. Some suggest that the light weight diesels being sold to the boat building industry do not last any longer than a gas engine. They claim that time kills these new diesels as rapidly as their gas counterparts. Their examples include boats of the same class needing overhauls at the same time interval regardless of hours. We can wonder just how dry an engine gets after it has set for 3 months and is started without a pre lube system? How much damage is done? How much moisture lays in the crank case? How much moisture is brought into the engine during the heating and cooling cycle of a 24 hour day? Have you ever seen a water tight light fixture half full of water? One small pin hole leak will allow moist air to be sucked in during the night and condensed inside the fixture when the sun hits it. Sooner or later, it is filled with water. I am certain that a power plant left outside where the sun can shine directly on it will experience some of this, and it is noteworthy that this moisture can become acidic. Dissimilar metals within the engine can create a current flow and damage important metallic surfaces within the engine. Where you place your Generator Set, and even the color you paint it can have some bearing on it’s operating life. any efforts to keep moisture out of fuel tanks and the crank case can pay big dividends.
I figure about 3kW continious will be enough to meet my needs when there is a lot of flywheel mass to help start loads. There are some small Diesels that really are efficient and long life. I once read about a big one cylinder diesel that made electricity for a small town. It was in service for SIXTY years with no bearing changes! The only reason they quit using it was power came to town and the Government subsidies made it way too attractive to ignore.
Some folks will say that we should be kinder to Mother Earth and not pollute the planet with a stinky diesel. My adopted reply…. “If Mr. Diesel were still alive, he might agree with you in part”. His engine was designed to burn vegetable oil; a renewable resource and a clean burning one at that. If you wish to run your stationary diesel on veggie oil, it could work fine. (There’s info all over the WEB on this subject)…but the trick is to heat the veggie oil before it enters the injector, here’s another place the controller comes to play, it could start the diesel on diesel fuel, and transfer to veggie when the temp is right. It can also transfer back to diesel and purge the lines of veggie before a shut down occurs. This is critical but easy to do with a controller.
Oh yes, this system has batteries too, the generator doesn’t roll 24×7, wind power and solar power are Plug In options.
Imagine having the time to watch every gauge, and listen to every noise in your power shed. That’s the controller’s job, and she’ll do it night and day with no pay and take appropriate action should anything go wrong.
The basic plan
If you’re going to deploy artificial intelligence, you need a way of communicating information and requests from one place to another. How about using a one wire bus between major appliances and the controller?, a relay would isolate the appliance from the AC bus. Lets use a Fridge as an example, the resistance across the appliance side of the relay would be interpreted as a (request to run). The controller would receive this request and make a decision based on a number of factors.
Is the generator currently running? When is it scheduled to run next? What is the float voltage of the batteries? Could the Inverter handle this appliance? Depending on the current conditions and the set of rules given to the controller, the mission is carried out. And example might be… The current loads are being handled by the inverter running off batteries, that load might be a few compact fluorescent lights and the 19 inch TV running off the satellite dish.
This time, the controller decides it’s worth running the generator, the controller prepares the diesel to start, it sets the compression release and engages the starter, once up to cranking speed, it dumps the compression release and monitors the set for a start. Once running, the starter is disengaged and the set is allowed to warm up at a reduced speed until it comes up to temp, (This is done to extend the life of the diesel and to cut down on emissions). Once the gen set has reached operating parameters, the controller sets the speed to 1800 RPMs and transfers all loads to the diesel except the satellite receiver. The controller pumps water, fills the cistern, recharges batteries, captures waste heat for domestic hot water as well as granting the fridge the RTR, (request to run). Once the controller thinks there’s nothing left to be gained by running the generator, it transfers the loads back to the inverter and shuts down the diesel.
If you wish to add solar or wind power, their outputs feed the batteries. The controller factors these sources of energy and may choose to run more loads off the inverter automatically.
This system is being assembled and tested now. The engine under test is a Chinese made German designed 195 diesel. There is a documented case of this engine running for 50,000 hours before being overhauled, there are other engines like some of the Listers that ran 100,000 hours before they need an overhaul. Adding good filters, making sure that the fuel is high quality, operating your diesel at the right temp, and carrying loads only when the temp is optimum, is a necessity if you are trying for longevity like this.
The controller is being designed around the ATMEL Mega8 processor, it’s loaded with built in goodies that will lower the parts count. Their are lots of electronic equipment designs out there that are missing components that protect the circuits from over voltage and current. Equipment often operates for years without it, but when you’re off grid, and you are depending on a controller to do a job, it should be well protected from the hostile world that it watches over. Inputs should be idiot proof, you should be able to hook up the battery and ground backwards without causing smoke.
One thing that is essential in any installation is a plan to handle fault current and lightning. Basically you want to create a path that routes the current away from, versus through you or your equipment. There are week long schools that address nothing but this subject. The one I attended was most interesting. One example of (interesting) is the inspection of grounding, bonding, and ground cable routing in communications centers. Inspectors often find serious errors that would have rendered the grounding plan far less effective or even dangerous. I have personally found a number of ground fault cables that pass through a short piece of metal conduit cast into a concrete wall. Few of us would suspect that this piece of conduit would be a problem, in reality, it acts as a choke and makes it difficult for the fault current in a lighting strike to pass through the conductor. This could cause the lightning to find a better path through your controller, or worse yet… you!
Picture yourself snowed in, it’s light an fluffy, and the trip to the main road via the snow mobile may not be possible for a few days. You have plenty of fire wood and there’s 100 gallons of fuel in the generator tank. You can stay here till spring if you have to, and be comfortable doing it…. “if nothing breaks you can’t fix”.
Then it happens, the snow load on the roof pushes on your chimney pipe and the last joint is pushed apart; your cabin fills with smoke. You think about the summer days you spent looking up and wondering if you should re do that sloppy installation up there before winter; now you get to mess with it at a far less desirable time.
Your generator is no different; do it right and you’ll have less trouble. The more things you anticipate the better, but all of them will cost you time, money, or both to address up front. where do you draw the line when it comes to prepping a gen set for an isolated off grid setting? I think it’s a personal thing, but if you look at environments where reliability is a concern, you can get some ideas.
I think aircraft is a great place to pick up knowledge of how mechanical systems are made more reliable. In their world, they have scheduled inspections where potential problems can be found before they interfere with the operation of the aircraft. Safety wire is used everywhere, fasteners are literally wired in place. Parts that are ‘certified for service’ are used; you don’t find a piece of bailing wire tying the throttle cable to the carb; or at least you shouldn’t
I got an email from a good mechanic that just had a serious engine failure. I expect we’ll exchange a number of emails in an attempt to figure how we could have prevented the problem from becoming as large as it was. It appears that something in (or around) the valve train broke off and found it’s way to the sump. At this point we think it was sucked up through the inlet screen into the pump. Once this metallic piece entered the pump, it jammed the meshing gears and the drive tab sheared.
With no oil pressure, things went from bad to worse….
I think this is a good example of a typical problem. Had he taken some preventative steps, this could have been found before it did the serious damage. He knows it, we all know it…”There’s only so much time to deploy these things”.
Here’s a few ideas: Place a neo magnet in the pan where steel parts would cling before they could get to the inlet of the pump. Place a neo magnet in the oil return path of the rocker box to intercept and hold any loose steel pieces headed for the sump. Equip your diesel with an oil pressure switch and figure out how to shut down the set when the pressure goes away. This could be done with a solenoid, spring, and latch that would override the connection between the governor and fuel rack, and close the fuel rack when the oil pressure is not present.
Modify the sump where it is deep around the pump pickup, where the suction action wouldn’t suck up small metallic stuff in the sump. Make a bigger pickup, with a fine mesh screen.
It’s all easy stuff to do, but you have to do it before the need.
August 7, 2002 Putting more of your BTUs to work ????
For the last few weeks, I’ve been thinking of all this waste heat rolling out of the diesel, the cooling tank does a fine job of storing it. The heat exchanger I’m building for the exhaust will capture even more. In the winter, I could find a use for all of it. In the summer it would be nice to use this waste energy to heat a refrigerant and to provide cooling… maybe to run an ice box or freezer?
I started thinking about an air dryer we had at work. It would run on one side, absorb water in a canister until it was no longer effective and then switch to the second canister. The wet side (off line) would be heated driving out the water; when dry, the canisters would be switched and the process would go back and forth. I discussed the idea with my neighbor and friend who works at Boeing. Use two canisters with coils in them to charge with a refrigerant, then heat it via a coil with hot water from waste heat. We talked about Ammonia, ether, and a number of potential refrigerants that might be compatible with the temperatures I thought we’d have to work with. Ether might do real work at 180 degrees, especially if you have an abundance of cooler water to cool down the canister after charging it with waste heat?
Using a micro controller, a few thermistors, a couple valves, a condenser, and two canisters with coils, you could put some more of this wasted energy to work off grid! Come to think of it, you might just conduct the waste heat off the exhaust system to run the heat pump section in a typical RV Ammonia fridge! There’s no reason you couldn’t put some distance between the heat driven pump section and the fridge itself!
About 3 days after Brian and I talked, he rushed across the street with the latest copy of the “Boeing Frontiers” magazine. He had it folded back to page 35, an article titled “Hot idea to cool down”.
Here in the magazine is Craig Christy extracting the heat from a diesel exhaust and using it to potentially cool one of those refrigerated Vans without a compressor! DIYer ‘Bill Levitt’ sends a link to the article on line! http://www.boeing.com/news/frontiers/archive/2002/august/i_people1.html
People can curse diesels, but if you could capture 75 percent of the BTUs in diesel fuel and put them to work, you’d have something really significant!