I’m toying with the idea of a car engine + generator for power backup

[BrokenYugo]

I'd suggest hitting the auctions and finding a commercial skid mount or trailer 1800rpm diesel genset. It is difficult to beat a mature commercial product at it's own game.

[Jester]

I'd suggest hitting the auctions and finding a commercial skid mount or trailer 1800rpm diesel genset. It is difficult to beat a mature commercial product at it's own game.

Your probably right.

Are they as quiet as a car engine?

Takes some of the fun out of it.

[Ian.M]

What heating fuel do you have on site?  There's a considerable advantage in regularly 'turning over' the fuel supply so when you fire up the genset you are using fairly fresh fuel.

Natural gas, or propane would give a significant advantage to a gasoline engine.

Low sulfur heating oil is very close to being diesel fuel, and it may well be practical to run older mechanically injected diesel engines on it with minimal modification.  Mix in additives for lubricity and to improve the cetane rating in a day tank and you'll get very similar performance and reliability.  Its also worth noting that mechanically injected and governed marine diesels are effectively constant speed rated for constant power and can be expected to run continuously for days at a time as long as you stay on top of maintenance, so are ideal for conventional genset service.

Kerosene is more problematic, as little except vintage hot bulb and military multifuel engines can run on just kerosene without substantial modifications.

If you use solid fuel you are probably S.O.L as your only options would be a gasifier to run a gasoline engine, or a steam or sterling engine.

I'd suggest hitting the auctions and finding a commercial skid mount or trailer 1800rpm diesel genset. It is difficult to beat a mature commercial product at it's own game.

If you want to indulge your shadetree mechanic tendencies, rebuilding the engine of an old commercial/industrial 1800rpm  genset may be the way to go.  However if the generator head shows significant signs of distress, probably best not to bid!

[james_s]

Kerosene is more problematic, as little except vintage hot bulb and military multifuel engines can run on just kerosene without substantial modifications.

I have a Briggs & Stratton service manual from the early 70s that covers kerosene engines. Apparently they were available off the shelf at one time and there is a conversion procedure which IIRC mostly involves reducing the compression by installing two head gaskets and adding a small gasoline tank for starting. You start the engine on gas, let it warm up and then switch to kerosene. I doubt it is as efficient as an engine designed to burn kerosene though.

[AaronD]

Kerosene is more problematic, as little except vintage hot bulb and military multifuel engines can run on just kerosene without substantial modifications.

And aviation turbines.  Jet fuel is essentially kerosene, so that's where it all went. 

[Jester]

In all likelihood I would run this off regular gas (possibly propane if conversion was easy enough). I would keep the fuel tank empty and fill it when needed. Perhaps with a very small alternate tank 1L or so for periodic start-ups that I would run dry.

[David Hess]

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?

Propane is a great option if you can find the parts to convert the engine to run on it.  The tanks are not cheap, but sometimes you can find deals on 30 and 40 pound tanks.

[bdunham7]

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.

Well, this is EEVBlog not American Chopper, so an inverter seems more appropriate than things like welding up old differentials as a gear reduction system.  Actually I see that he has only a 7kW generator, so he could easily just use the Insight engine w/ IMA and charge a series of 10 or so SLA batteries, then use an inverter from there, leaving his existing generator aside.  That way the backup could be instantaneous and the engine start can be delayed.  The Insight also has a standard 12V starter as an auxiliary backup, so you wouldn't need to copy the full two-way power system of the original IMA design--you can just wire it up as a generator.  The result is just a big version of the small EU-series inverter generators.  Unfortunately I don't know enough about the specific details of the control systems to know how much of the car's electronics could be readily repurposed for a stationary generator.  The early models (which were all manual transmissions) did not have an electronic throttle AFAIK. 

Someone mentioned waste heat.  An efficiently operating Insight engine at idle or just above will struggle to keep itself warm in very cold weather, so there just isn't going to be a whole lot left over.  Probably the only viable source of waste heat would be some sort of exchanger on the exhaust--and you don't want to be heating your house that way.

[jpanhalt]

If  your concern is the shelf life of regular gasoline, you can use marine gasoline.  It is alcohol free, about 90 octane, and is a little more expensive than regular gasoline in Ohio  (USA), but it has great shelf life.  I have used it exclusively in my 2-cycle engines (e.g., string trimmers, leaf blower, other trimmer, and chainsaw) for the past 10 years.  It stores well and has not caused any corrosion in the carburetors of those engines.

[james_s]

Well, this is EEVBlog not American Chopper, so an inverter seems more appropriate than things like welding up old differentials as a gear reduction system.  Actually I see that he has only a 7kW generator, so he could easily just use the Insight engine w/ IMA and charge a series of 10 or so SLA batteries, then use an inverter from there, leaving his existing generator aside.  That way the backup could be instantaneous and the engine start can be delayed.  The Insight also has a standard 12V starter as an auxiliary backup, so you wouldn't need to copy the full two-way power system of the original IMA design--you can just wire it up as a generator.  The result is just a big version of the small EU-series inverter generators.  Unfortunately I don't know enough about the specific details of the control systems to know how much of the car's electronics could be readily repurposed for a stationary generator.  The early models (which were all manual transmissions) did not have an electronic throttle AFAIK. 

Well I think that building a reliable multi-kW inverter that can run off of a variable DC bus voltage from a permanent magnet alternator is a very advanced project. Going by the OP's post, it sounds like he has a small 3600 RPM generator head already and just wants to bolt it up to a quieter less stressed engine. It is much easier to just buy a proper backup generator with a liquid cooled engine than to build such an advanced thing from junk. If a person has the knowledge to build a project like that, they probably would not need to ask here how to do it.

One issue with trying to gear up a salvaged generator head is that many of the sort of generators that come attached to a small air cooled engine have only one bearing, the other end of the rotor fits over the engine shaft and relies on the bearing in the engine.

[Berni]

I wouldn't say fuel would be that big of a problem.

A diesel engine will not only run on Diesel but also on kerosine(jet aircraft will be needed) or cooking oil(people need to eat). While a gasoline engine can resonably easily be made to run on ethanol(industrialy important) or propane(heats peoples houses and runs stoves).

The whole idea is not that bad in my opinion. You can buy generators that connect onto the PTO output shaft of a tractor(Used for backup power or power out in the field). They do tend to be in the 10 to 40 kW range, so all you need is to couple one of those to a car engine and you are set. You can probably use the engines existing gearbox to get it spinning at the right speed (PTO shafts are not very high rpm). The generators have built in voltage regulation electronics but the Hz will likely be tied to the engine rpm (having a VFD on board is expensive so they will try to avoid it). The technical bit here might be the need to adjust the engine throttle according to load for a steady rpm.

But thing is car engines seam so quiet because you mostly hear them at/near idle throttle. When a car engine is producing >30kW it might still be pretty loud.

[CJay]

It occurs to me that a REx from something like a BMW i3 might be worth investigating if you have a wrecker's yard that takes EVs.

But if I were at significant risk of being cut off from electricity for an extended period of time I'd probably go for a mil surplus generator that runs on kerosene/diesel and have the ability to run my home heating on it as well.

[Ed.Kloonk]

Not disagreeing with the replies above.

But my own experience with a number of very old but well built alternators that I've got in the 5-10 kW range, 3 phase. These things I've had since the fuel crisis in the 70's. Still going strong. Sadly their original motors are not.

I suggest a stationary engine, at least 16 HP. I used 2 of these motors with my 7.5kw and 5kw. The five is a spare without a starting battery (pull start only) and has slightly different pulleys so it runs about 2800 rpm vs 3000 rpm.

The reason I would use the stationary motor off ebay before a car engine is what you get for the price. The stationary motor will have all the throttle control figured out so you can set and forget and the governor will regulate the throttle to the varying loads. An ordinary car motor's carburettor won't allow you to do that without serious modification.

The next problem is engine compression. The car motor will typically be higher and more difficult to crank.

Fuel tank. The stationary motor will have a fuel tank on top ready to go.

Engine speed. I don't believe it is a good idea to run normal car engines at one continuous speed for some reason. I don't know why. A mechanic told me once and I forgot the reason.

Output shaft. Will be standard 1"(25mm) and be very easy to change different pulleys for it if you want to tweak the run speed.

Fuel/choke levers above carby are easy to locate and use. (in the dark!)

I could go on. But I've got plenty of old motors laying around here but I've always opted for the new motors just because of the sheer ease and reliability. Run them at least every three months. 

Search ebay: 16HP stationary motor.

Sing out if you need help choosing pulley sizes, v-groove type, number of grooves, fan belt length etc.
 

[langwadt]

What heating fuel do you have on site?  There's a considerable advantage in regularly 'turning over' the fuel supply so when you fire up the genset you are using fairly fresh fuel.

Natural gas, or propane would give a significant advantage to a gasoline engine.

Low sulfur heating oil is very close to being diesel fuel, and it may well be practical to run older mechanically injected diesel engines on it with minimal modification.  Mix in additives for lubricity and to improve the cetane rating in a day tank and you'll get very similar performance and reliability.  Its also worth noting that mechanically injected and governed marine diesels are effectively constant speed rated for constant power and can be expected to run continuously for days at a time as long as you stay on top of maintenance, so are ideal for conventional genset service.

Kerosene is more problematic, as little except vintage hot bulb and military multifuel engines can run on just kerosene without substantial modifications.

I thought airports and military ran everything diesel on  Jet-A1 which is basically kerosine

[Gyro]

In all likelihood I would run this off regular gas (possibly propane if conversion was easy enough). I would keep the fuel tank empty and fill it when needed. Perhaps with a very small alternate tank 1L or so for periodic start-ups that I would run dry.

LPG conversions used to be quite common for cars over here, particularly on fleet vehicles. They had a gas cylinder fitted in the boot (trunk). Look in the right place and you can probably find all the required kit off the shelf, probably with changeover switching too.


EDIT: I don't know if you get any similar hits on ebay in Canada... https://www.ebay.co.uk/sch/6030/i.html?_nkw=lpg+conversion&LH_TitleDe&_odkw=lpg+conversion+kit&_osacat=131090&sc=0

[Jester]

In all likelihood I would run this off regular gas (possibly propane if conversion was easy enough). I would keep the fuel tank empty and fill it when needed. Perhaps with a very small alternate tank 1L or so for periodic start-ups that I would run dry.

LPG conversions used to be quite common for cars over here, particularly on fleet vehicles. They had a gas cylinder fitted in the boot (trunk). Look in the right place and you can probably find all the required kit off the shelf, probably with changeover switching too.


EDIT: I don't know if you get any similar hits on ebay in Canada... https://www.ebay.co.uk/sch/6030/i.html?_nkw=lpg+conversion&LH_TitleDe&_odkw=lpg+conversion+kit&_osacat=131090&sc=0

At one point a lot of taxis were using propane, I’m not sure if that is still going on. If the conversion is straightforward seems like a good idea, when we had the really BIG power outage in 2003 getting gas was a problem, propane was generally available because they didn’t need electricity to pump. Lots of BBQing during that outage.

I’m completely comfortable fabricating, welding etc. I have every thing I need; lathes, milling machine etc.
For speed control small uC and possibly a stepper or servo to drive the throttle.

I like the suggestions for either pulleys and belts or chain and sprocket, that will make tweaks to fine tune the ratio easy and Princess Auto stocks a great selection of both (10 minutes away).

[Berni]

I thought airports and military ran everything diesel on  Jet-A1 which is basically kerosine

Yep kerosine has pretty similar properties to diesel. The older diesel engines run at lower compressions with less tight tolerance fuel handling components. So almost anything that lubricates, burns well and doesn't eat the seals will run fine in it. Old tractors run great on heating oil (tho its illegal because it means less tax dollars for uncle sam)

The new engines are more problematic because the fuel runs trough a more advanced fuel system with fine tolerances and jets. They easily clog with dirt, they are picky about viscosity and lubrication...etc. So you probably don't want to feed heating oil, cooking oil. kerosine..etc into one of these new fanged electronic injection common rail engines. And even if it works mechanically then the electronics being pedantic about modern strict emissions control might get upset with it.

LPG conversions are also pretty common. My previous car was converted to run on it. The spare tire is replaced with a cylindrical tank and an extra filling hole is added under the gas flap. The fuel injector signals are tapped into by a box of electronics that switch the signal over to separate gas injector valves in the intake manifold. The problem however is that LPG has a low boiling point, so the electronics keep running it on gasoline mode until the engine block is no longer cold. So i assume starting it in a cold winter night might not work on pure LPG.

[David Hess]

Propane in a gasoline engine has advantages.  It does not mix with the oil, so the oil lasts longer and the engine wears less, and the exhaust is not nearly as noxious, which is why propane powered forklifts are allowed indoors.

Propane in a gasoline engine also results in about 20% less power, but this would only matter in an engine properly sized for the application using gasoline.  Converted backup generators have to be power derated.

Old tractors run great on heating oil (tho its illegal because it means less tax dollars for uncle sam)

In the US, fuel used for farm equipment which is not driven on public roads is not generally taxed.  Farmers either buy untaxed fuel or apply to the taxing agencies for a refund.

Where I am in Missouri, propane costs significantly less if purchased for a motor vehicle.

[james_s]

Yep kerosine has pretty similar properties to diesel. The older diesel engines run at lower compressions with less tight tolerance fuel handling components. So almost anything that lubricates, burns well and doesn't eat the seals will run fine in it. Old tractors run great on heating oil (tho its illegal because it means less tax dollars for uncle sam)

At one point for a couple of years a British acquaintance of mine was running his diesel van on vegetable oil he was buying at Costco, for a period of time it was more economical than buying diesel at a fuel station. It was an old mechanically injected engine and apparently it ran just fine on it.

[james_s]

Propane in a gasoline engine has advantages.  It does not mix with the oil, so the oil lasts longer and the engine wears less, and the exhaust is not nearly as noxious, which is why propane powered forklifts are allowed indoors.

Propane in a gasoline engine also results in about 20% less power, but this would only matter in an engine properly sized for the application using gasoline.  Converted backup generators have to be power derated.

Old tractors run great on heating oil (tho its illegal because it means less tax dollars for uncle sam)

In the US, fuel used for farm equipment which is not driven on public roads is not generally taxed.  Farmers either buy untaxed fuel or apply to the taxing agencies for a refund.

Where I am in Missouri, propane costs significantly less if purchased for a motor vehicle.

Propane conversion is very easy to do though, all you need is a demand regulator. You can even retain the existing gasoline injection system to make it duel fuel. The propane just gets fed into the intake manifold after the throttle body.

There's a co-op not too far from here that sells untaxed agricultural diesel, IIRC it's dyed red to prevent it from being used in road vehicles. It will work of course, but if they catch you doing it you can get in trouble.

[David Hess]

Propane conversion is very easy to do though, all you need is a demand regulator. You can even retain the existing gasoline injection system to make it duel fuel. The propane just gets fed into the intake manifold after the throttle body.

I have seen the kits but I am never sure if they will fit on my less common 3 kilowatt backup generator.

There's a co-op not too far from here that sells untaxed agricultural diesel, IIRC it's dyed red to prevent it from being used in road vehicles. It will work of course, but if they catch you doing it you can get in trouble.

I have heard about them running checks on RVs and pickups at motor race events.

[Berni]

There's a co-op not too far from here that sells untaxed agricultural diesel, IIRC it's dyed red to prevent it from being used in road vehicles. It will work of course, but if they catch you doing it you can get in trouble.

Over here due to zoning you will almost always need to use a road to get your tractor from the farm to the field, so it is a road vehicle that needs to be registered and road worthy. Farmers have to buy diesel just like everyone else, but they do get a bunch of subsidies back on a lot of stuff instead.

Heating oil is colored red here to make it easy to tell apart, and you do get in trouble if you are found having it in the tank of your vehicle. It's not just diesel with a die, the stuff is less pure and is generally only a good idea to put into old simple diesel engines. Seen plenty of 50 year old tractors that ran on only heating oil and they still run. Yet since a generator is not a vehicle its perfectly legal to run on cheep heating oil here.

The massive diesel engines in ships also tend to run on so called fuel oil (same stuff). Those use extra tricks too such as switching the engine mapping once out in sea where they escape strict emissions standards. So they crank up the compression to get more efficiency out of the same amount of fuel while making lots more NOX

[langwadt]

Propane in a gasoline engine has advantages.  It does not mix with the oil, so the oil lasts longer and the engine wears less, and the exhaust is not nearly as noxious, which is why propane powered forklifts are allowed indoors.

Propane in a gasoline engine also results in about 20% less power, but this would only matter in an engine properly sized for the application using gasoline.  Converted backup generators have to be power derated.

why is that? I don't see why an engine properly tuned for propane shouldn't make just as much power as on gasoline

[John B]

why is that? I don't see why an engine properly tuned for propane shouldn't make just as much power as on gasoline

Propane has a lower energy density compared to petrol, combined with the fact that propane has a slightly higher stoichiometric air-fuel ratio compared to petrol. Only way to increase the power would be to increase the mass of air (ie forced induction).

Not a problem at all in this application though.

[bdunham7]

why is that? I don't see why an engine properly tuned for propane shouldn't make just as much power as on gasoline

80% is actually optimistic for many engines because of more complex factors, but the simple analysis is that for two otherwise equivalent engines, the propane both displaces more air and produces less energy per equivalent mass of air due to the C/H ratio and enthalpy of the shorter alkane.  The assumption is that the two 'equivalent' engines are pumping the same volume of charge gas, whether that be air with a small fraction of evaporated gasoline or air with a larger fraction (volume) of propane.