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I’m toying with the idea of a car engine + generator for power backup
Posted by Jester on 06 Dec, 2021 18:27 -
Our power here is pretty reliable, that being said if it goes down during the winter, not so pleasant that happened a few years ago during a nasty ice storm, no power for about 2-3 days, I’m glad we had a conventional fireplace.
I’m pretty comfortable with auto engines as one of my hobbies is auto racing so I have assembled and disassembled plenty of engines etc.
I have a cheap 7kW generator (Neighbour gave it to me in broken state and I fixed it), however the thing is really loud when under load. Honda makes some really quiet small generators and some sort of quiet mid size generators, but they are fairly expensive and not really quiet.
My thought of the day is to pickup a used small engine from a wrecked econo-box car perhaps 1.5 litre and mate it to a suitable generator something about 20-30kW (will depend on what is available used and cheap). I will need some sort of gear box to increase speed to generator perhaps 2:1 or 2.5:1 would allow the engine to run at about 1500 rpm. Will need to make some sort of speed control to keep the generator at 3600 rpm as load changes.
If I re-use the original exhaust and plumb it up say 8’ and away from the house I would think that it would be near in-audible from the house. I would mount this contraption in the smallest metal shed I can find on craigslist and about 100’ from the house.
Wacky idea or fun project what do you think?
Keep in mind I’m retired and enjoy pet projects.
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Here in Amish counties, that is quite commonly done. Many people believe Amish won't use electricity as it is evil or something. That is not so. The prohibition is against using electrical power from public power lines. Many of their industries generate electricity on site. As one example, they are well known for work with canvas materials for tents/boat covers/etc. Sewing machines don't run on diesel or horses. Those enterprises generate on site. Woodworking is another example.
I don't have access to any of those plans, but it is certainly not a crazy idea. An old 4-cylinder, air-cooled VW engine might be simple. Meeting pollution restrictions might be a problem. Small diesels (Kubota, Yanmar, others) are another possibility, but will likely be more expensive than a used automotive engine. Riding mower engines (e.g., Kohler 25 HP) do not have a very good record for longevity. -
Our power here is pretty reliable, that being said if it goes down during the winter, not so pleasant that happened a few years ago during a nasty ice storm, no power for about 2-3 days, I’m glad we had a conventional fireplace.
I’m pretty comfortable with auto engines as one of my hobbies is auto racing so I have assembled and disassembled plenty of engines etc.
I have a cheap 7kW generator (Neighbour gave it to me in broken state and I fixed it), however the thing is really loud when under load. Honda makes some really quiet small generators and some sort of quiet mid size generators, but they are fairly expensive and not really quiet.
My thought of the day is to pickup a used small engine from a wrecked econo-box car perhaps 1.5 litre and mate it to a suitable generator something about 20-30kW (will depend on what is available used and cheap). I will need some sort of gear box to increase speed to generator perhaps 2:1 or 2.5:1 would allow the engine to run at about 1500 rpm. Will need to make some sort of speed control to keep the generator at 3600 rpm as load changes.
If I re-use the original exhaust and plumb it up say 8’ and away from the house I would think that it would be near in-audible from the house. I would mount this contraption in the smallest metal shed I can find on craigslist and about 100’ from the house.
Wacky idea or fun project what do you think?
Keep in mind I’m retired and enjoy pet projects.
A few observations:
1. For 2.5 gears you would need at least a 2.5, but most likely a 3 multiple for engine power. So for 30kW you would need an engine 3 X desired kW in order to run said generator. Also, those small engines do not develop power at 1500 RPM. but more like at around the 3600 RPM that you will require. You possibly could get a diesel that can do this.
2. Placing this generator so far from the house would mean large gage wire in order to carry 30kW 100' to house. This , along with the switch and protection equipment, would be expensive.
3. The ICE engine will be all but eliminated for most uses in the next 20 years, so that is a consideration as far as fuel cost and availability. Have you considered a battery based power wall, such as the one Tesla offers?
Hope this helps... -
Probably use an old differential unit, with the spider gears welded together to make a locker, as the gearbox. That way you run the engine at around 22oo RPM, where most small engines, like the 1.4l VW engines, are reasonably fuel efficient, and low noise, but pretty far along the torque curve. 3600RPM and straight in to the alternator, probably a 2 pole version with that speed, and you will pretty much match peak torque and power of the engine easily. Not going to be the best fuel economy wise, but you will have the most power output from the alternator, and it will still last a long time in use.
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I would consider a 1.0L engine from an early Honda Insight, with the (IMA) Integrated Motor Assist still attached. That motor will run quite efficiently at 3600RPM, but if you are particularly clever you can use slower speeds and the IMA to generate lower levels of power when demand is low, then spin it up to use the main generator for full loads.
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I don't see why not.
Thinking about the gear-up from 1500 (engine) to 3600 (generator), I wonder how tall of an overdrive you can get in an automotive transmission? I'm guessing it's not that much. Or maybe you could manage to turn a transmission around so that 1st gear has the engine practically idling, and what used to be overdrive has it close to redline for the same generator speed?
Or maybe you could just do a single-stage fixed-speed arrangement by sourcing your own two pulleys and a belt. That'd be a lot easier! And it would disconnect the shaft requirements from each other as well. And the mounting requirements.
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For a governor, the cost and complexity depend on how tightly you want to control it. A single-purpose lawnmower engine might simply have a vane in the airflow of the mechanical cooling fan, which acts against a spring to control the throttle. You probably want something better than that! The John Deere 140 that my family had for a LONG time (Kohler 14hp single-cylinder) had flyweights on the camshaft, that acted against a spring. The other end of that spring went to the operator's throttle control.
I'd thought for a while about making a DIY cruise control for my '97 Jeep (Inline 6 with a manual 5-speed) out of the assumed-good actuator from a failed aftermarket cruise control (possibly bad assumption, never tried it) and the tachometer. Never actually did it, but one of my potential uses, allowed by using the tach instead of the speedo, was to be a stationary electric generator as well. (disconnect the rear driveshaft and hook it up to the generator; then use 4-wheel-drive, which would now be front-only, to drive with that arrangement)
Just letting my mind run with that for a while, got me the idea to use an ammeter and/or torque sensor as a feedforward component. (put load cells in either the engine mounts or the generator mounts, to be that torque sensor) The idea being that the rotating mass takes a while to change speed, but that doesn't help at all with long-term trends. So if I can tune it so that the average throttle is well matched to the immediate load, and make that work in real-time, then the actual control loop simply does an offset around that average in response to speed. Should allow for tighter control that way. Probably would have used an 8-bit PIC or AVR running all custom code, to actually do it.
Caveat:
The "immediate load" feedforward component is essentially positive feedback. Too much of that, and the system becomes unstable, especially if the AC load has a net-positive impedance. (it'll just run up to redline or down to idle, and stay there) The speed control loop provides negative feedback, so if that's "stronger", then it can still be okay overall. Several things to tune here, all of which lead to runaway or oscillation if the combination isn't good, so you have to watch very carefully and simulate it in your head, to know what to adjust and how.
Once you get it all right though, it can be amazing! Switching a massive load on and off results in only a volume change from the exhaust, and not a speed change at all...
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I had also thought about the engine speed itself. My 4th gear, in a 5-speed, is 1:1, so I do have an overdrive. That would allow me to run the engine a little bit slower for a 1:1 tailshaft-to-generator connection at 3600rpm, but with a redline of 5k, that speed is also inside of the normal operating range for this engine. (my experience with highway entrance ramps tells me that it's about in the middle of the "power band"
) So...does it actually hurt anything to let it sit at 3600 all day with varying load??? 
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There are ways to muffle the sound from generators ranging from simple plywood sheets to sound absorbing materials placed at strategic angles. Sound comes from both intake and exhaust, so muffler on exhaust may not be enough. Construct a sound deadening box for generator or car engine of your choice if you have dedicated space for it.
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What would be really cool / (uhm hot actually) is if that engine can supply your house radiators as well. I guess in the US they most often pump hot air around but what is common in Canada?
Some houses here have boilers and circulating hot water, however the majority have natural gas forced air. I only need a few amps to run the furnace (more during spin up of the fan). -
Here in Amish counties, that is quite commonly done. Many people believe Amish won't use electricity as it is evil or something. That is not so. The prohibition is against using electrical power from public power lines. Many of their industries generate electricity on site. As one example, they are well known for work with canvas materials for tents/boat covers/etc. Sewing machines don't run on diesel or horses. Those enterprises generate on site. Woodworking is another example.
I don't have access to any of those plans, but it is certainly not a crazy idea. An old 4-cylinder, air-cooled VW engine might be simple. Meeting pollution restrictions might be a problem. Small diesels (Kubota, Yanmar, others) are another possibility, but will likely be more expensive than a used automotive engine. Riding mower engines (e.g., Kohler 25 HP) do not have a very good record for longevity.
Agree on the reliability aspect, I can probably get a used Toyota engine with 250k that will be 10x more reliable than any typical small engine, and something like a 1.2 - 1.5 litre should make plenty of power even at say 1500 rpm. Probably be better on fuel as well. I’m okay with water cooled, I will just grab the radiator at the same time.
Water cooled should be quieter.
Regarding your comment about the Amish, I totally get it, when I was in high school I had a summer job at a place that made electronic farm control equipment for a similar group as the Amish, these guys were no fools I think they were way more automated than the typical farm of their time. -
I would consider a 1.0L engine from an early Honda Insight, with the (IMA) Integrated Motor Assist still attached. That motor will run quite efficiently at 3600RPM, but if you are particularly clever you can use slower speeds and the IMA to generate lower levels of power when demand is low, then spin it up to use the main generator for full loads.
I will need to read up on that engine, 1l seems ideal -
There are ways to muffle the sound from generators ranging from simple plywood sheets to sound absorbing materials placed at strategic angles. Sound comes from both intake and exhaust, so muffler on exhaust may not be enough. Construct a sound deadening box for generator or car engine of your choice if you have dedicated space for it.
I have watched a few videos (with sound meters) of this, it helps, however the results are not that great, especially if the goal is to have it car idling quiet. -
Our power here is pretty reliable, that being said if it goes down during the winter, not so pleasant that happened a few years ago during a nasty ice storm, no power for about 2-3 days, I’m glad we had a conventional fireplace.
I had that experience during the 2007 North American Ice Storm. I burned a month's worth of wood in one week to keep from freezing. Since then I bought a backup generator, which I have used yearly since, and backup propane and kerosene heating.QuoteMy thought of the day is to pickup a used small engine from a wrecked econo-box car perhaps 1.5 litre and mate it to a suitable generator something about 20-30kW (will depend on what is available used and cheap). I will need some sort of gear box to increase speed to generator perhaps 2:1 or 2.5:1 would allow the engine to run at about 1500 rpm. Will need to make some sort of speed control to keep the generator at 3600 rpm as load changes.
For simplicity, I would consider using pulleys and belts instead of a geared transmission.
They are less common, but a 4-pole generator head would allow engine operation at 1800 RPM. They are more common with backup diesel generators.
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ICE will not be going away any time soon, they will be around in some capacity until after all of us here are dead and gone. A battery is completely unsuitable for occasional emergency needs, the cost is HUGE compared to a generator and it will deteriorate just sitting there waiting for something to do. Gasoline is a less than ideal fuel for emergency use though as it goes bad fairly quickly. Do you have natural gas service at your house? Converting a car engine to run on natural gas or propane is fairly easy and both are much better fuels for this application.
For a 7kW generator you will only need about 15HP so while a car engine may not produce much power at 1500 RPM it doesn't need to. Most car engines will be rated for >100HP and you only need a small fraction of that. I would look for the smallest, simplest engine I could find, more than 2 valves per cylinder is fairly pointless for low RPM low power use, and stuff like variable valve timing and other fancy features will be useless. Remove the fuel injection and replace it with a demand regulator metering propane or natural gas into the intake manifold. For the ignition you might look at the ignition system from an older car or a standalone aftermarket system, you want simple. For a conventional generator you will also need to devise a governor to keep the frequency relatively constant regardless of demand. Typically this is a centrifugal mechanism acting against a spring but an electronic solution with a servo operating the throttle body may be more flexible and possibly easier to implement.
Making use of the waste heat is definitely worthwhile. Forced air heating is the norm almost everywhere in North America but that doesn't preclude setting up an auxiliary heat source using a fancoil or radiator. Another option is a water to water heat exchanger to heat your hot water tank. -
There are ways to muffle the sound from generators ranging from simple plywood sheets to sound absorbing materials placed at strategic angles. Sound comes from both intake and exhaust, so muffler on exhaust may not be enough. Construct a sound deadening box for generator or car engine of your choice if you have dedicated space for it.
There's no way you'll ever get one anywhere near as quiet as a typical car engine. Not only does sound come from the intake and exhaust, but there is a lot of mechanical noise from small air cooled engines. There is no water jacket in the block or head, it is just thin aluminum, everything is thin and light, they are not particularly well balanced, and a conventional generator screams along at 3600 RPM regardless of load so it's going to be noisy no matter what you do.
Personally I got a Honda EU2000i inverter generator a few years ago and it's a lovely little machine. Despite the fact that it is also a small air cooled engine they have done a remarkable job of making it quiet, and since engine speed is decoupled from the frequency of the generated power, it spends most of its time near idle. It's quiet enough that I can let it run all night long without disturbing my neighbors. With it sitting out in front of my garage I can't hear it at all inside the house. -
Our power here is pretty reliable, that being said if it goes down during the winter, not so pleasant that happened a few years ago during a nasty ice storm, no power for about 2-3 days, I’m glad we had a conventional fireplace.
I had that experience during the 2007 North American Ice Storm. I burned a month's worth of wood in one week to keep from freezing. Since then I bought a backup generator, which I have used yearly since, and backup propane and kerosene heating.QuoteMy thought of the day is to pickup a used small engine from a wrecked econo-box car perhaps 1.5 litre and mate it to a suitable generator something about 20-30kW (will depend on what is available used and cheap). I will need some sort of gear box to increase speed to generator perhaps 2:1 or 2.5:1 would allow the engine to run at about 1500 rpm. Will need to make some sort of speed control to keep the generator at 3600 rpm as load changes.
For simplicity, I would consider using pulleys and belts instead of a geared transmission.
They are less common, but a 4-pole generator head would allow engine operation at 1800 RPM. They are more common with backup diesel generators.
Another great idea 4 pole generator
The belt and pulleys suggestion is also a great idea, makes things much simpler, need to figure out belt requirements, probably need one of those double or triple wide pulleys for 25 ish HP? -
I would consider a 1.0L engine from an early Honda Insight, with the (IMA) Integrated Motor Assist still attached. That motor will run quite efficiently at 3600RPM, but if you are particularly clever you can use slower speeds and the IMA to generate lower levels of power when demand is low, then spin it up to use the main generator for full loads.
That's going to require an inverter, which is going to make the whole project vastly more complex. Inverter generators are pretty much exactly what that is, a 3 phase permanent magnet generator attached directly to an engine. The resulting AC is rectified and feeds the DC bus of an inverter that produces clean 60Hz AC regardless of engine speed. -
Another great idea 4 pole generator
The belt and pulleys suggestion is also a great idea, makes things much simpler, need to figure out belt requirements, probably need one of those double or triple wide pulleys for 25 ish HP?
4 pole generators are definitely nice, but they're hard to find. If you want to go that route you could look for one of the old Kohler light plants, I saw one for sale a few years ago for a few hundred bucks, they were mostly made in the 1950s I think, nice machines.
Rather than V-belts which are fairly inefficient you could look at toothed belts. The sort that are used to drive superchargers on drag racers can transmit many horsepower, I'm sure there must be a wide range of sizes available in that style. Another option is a chain drive, I would think a motorcycle/ATV shop would be a good place to look for that sort of thing. -
There are ways to muffle the sound from generators ranging from simple plywood sheets to sound absorbing materials placed at strategic angles. Sound comes from both intake and exhaust, so muffler on exhaust may not be enough. Construct a sound deadening box for generator or car engine of your choice if you have dedicated space for it.
There's no way you'll ever get one anywhere near as quiet as a typical car engine. Not only does sound come from the intake and exhaust, but there is a lot of mechanical noise from small air cooled engines. There is no water jacket in the block or head, it is just thin aluminum, everything is thin and light, they are not particularly well balanced, and a conventional generator screams along at 3600 RPM regardless of load so it's going to be noisy no matter what you do.
Personally I got a Honda EU2000i inverter generator a few years ago and it's a lovely little machine. Despite the fact that it is also a small air cooled engine they have done a remarkable job of making it quiet, and since engine speed is decoupled from the frequency of the generated power, it spends most of its time near idle. It's quiet enough that I can let it run all night long without disturbing my neighbors. With it sitting out in front of my garage I can't hear it at all inside the house.
Your right on about all of this, Honda did some serious engineering on the sound side to achieve this with an air cooled engine. The inverter aspect surely helps. As soon as you start stepping up to the larger generators (even the Honda’s), they are not nearly as quiet as the EU2000i series. -
Weigh up the pro and cons of your fuel source. While a diesel engine would be more efficient, in practical terms it will only ever run on diesel without major, expensive and probably excessively difficult modification.
A regular port injection (important!) petrol can be tuned to run on a variety of fuel sources including ethanol and combustable gases relatively easily.
Also, have you looked into electronic regulation of the output voltage? I think you will be disappointed if you rely on purely mechanical means (trying to maintain the RPM through a gearbox). Remember any variation/pulsation of torque through the engine rotation will translate to voltage fluctuation. You'd be looking at a very heavy flywheel to negate this.
I've always wondered how feasible, or efficient it would be to build something more like an inverter generator. Use the motor to produce DC through rectifying a 3 phase generator, then buy a beefy off the shelf 48V low frequency inverter. You'd need some kind of control loop to change the engine RPM in response to electric loads.
I figured this approach would only be worth it if you acquired a number of the large components, like the engine, for free. -
Gasoline is a less than ideal fuel for emergency use though as it goes bad fairly quickly.
Yeah, regular gasoline has very short shelf life as it is made to be as cheap as possible (2-4 weeks, maybe up to 3 months in some cases - due to evaporation, chemical spoiling, water ingestion, ethanol content, layer separation). This is all very bad for small petrol engines (fuel lines, rubber seals, carburetors gum up and metals rot from inside). Car engines can deal it with it better due to bigger lines and fuel injection.
If petrol generator is intended to be used only in emergencies, regular fuel may be spoiled from sitting. One solution (although not the most economical) is to store more expensive alkalyte fuel (synthetic petrol fuel mix, stable for 2-4 years). There are few manufacturers of it. -
get decent muffler and build box lined with rockwool?
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Conventional generators regulate the output voltage by regulating the field. They do still rely on regulating engine speed ot maintain the frequency, although it is normally not a problem if that varies a few percent depending on load and other factors.
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Gasoline is a less than ideal fuel for emergency use though as it goes bad fairly quickly.
Yeah, regular gasoline has very short shelf life as it is made to be as cheap as possible (2-4 weeks, maybe up to 3 months in some cases - due to evaporation, chemical spoiling, water ingestion, ethanol content, layer separation). This is all very bad for small petrol engines (fuel lines, rubber seals, carburetors gum up and metals rot from inside). Car engines can deal it with it better due to bigger lines and fuel injection.
If petrol generator is intended to be used only in emergencies, regular fuel may be spoiled from sitting. One solution (although not the most economical) is to store more expensive alkalyte fuel (synthetic petrol fuel mix, stable for 2-4 years). There are few manufacturers of it.
propane tanks?
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Perhaps I’m suffering from generator jealousy syndrome, my neighbor a few doors down has a really big generator powered by natural gas. This thing looks appropriate to power a small hospital or police station etc (about the size of full sized van. Every once in a while the power goes off and thing automatically starts up.
LOL -
@Jester @post #10
Re: Amish communities
Absolutely right. No fools, but you always get what you pay for. No more, no less. Love them.