Author Topic: I’m toying with the idea of a car engine + generator for power backup  (Read 21560 times)

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Offline james_s

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Re: I’m toying with the idea of a car engine + generator for power backup
« Reply #75 on: December 08, 2021, 07:51:35 pm »
Well, motorcycles can go >140mph with an open chain drive, I haven't tried calculating the wheel RPM of a typical crotch rocket but it wouldn't be too hard to do. The horsepower of a bike is going to be more than any reasonable domestic load on a generator will be.
 

Offline brucehoult

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Re: I’m toying with the idea of a car engine + generator for power backup
« Reply #76 on: December 08, 2021, 09:42:02 pm »
Honda EU2000i inverter generator

It's also pretty inefficient with the fuel.

It is very efficient. Unlike a normal generator it can adjust the rotation speed depending on the load. This saves lots of fuel at lower loads.

All the Honda units run the engine slower at light loads. But the bigger ones make more electricity from less fuel.

It does make me wonder how they react to sudden increases in load. There may be a really serious voltage droop while they accelerate the engine, unlike something that is already at speed. Unless there's energy storage (battery, capacitor, independent flywheel) sufficient to cover the deficit for 1/4 (?) of a second.

The 2200 W unit uses 1.14 l/hour at rated load or 0.52 litres of fuel per kWh
The 7000 W unit uses 2.9 l/hour at rated load or 0.41 litres per kWh

The bigger unit is 27% more efficient.

More than that, if you run the 7000 W unit at 1/4 power  (1750 W) it will run for 18 hours instead of 6.5, for about 1.05 l/hour or about 0.6 litres per kWh, so you're not losing much at lighter loads (unless your lighter load is 500 W or something)


It's all pretty expensive electricity. At my current local prices for regular petrol the 7 kW unit is US$0.69/kWh. The 2200 W unit is $0.86/kWh.

That's not counting depreciation and maintenance.
 

Offline brucehoult

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Re: I’m toying with the idea of a car engine + generator for power backup
« Reply #77 on: December 08, 2021, 09:47:42 pm »
Here are some diesel generators. An 8 kW one using 2.4 l/hour at full load and 0.8 l/hour at 1/4 load. So that's less fuel consumption than the Honda petrol engines, and using much cheaper fuel too (at least here in NZ diesel is $1.62 vs 91 petrol at $2.42 right now)

I didn't check prices or noise levels. But 0.3 litres and US$0.33 per kWh is attractive vs 2x or 2.5x the fuel cost.

https://www.ablesales.com.au/blog/diesel-generator-fuel-consumption-chart-in-litres.html
 

Offline bdunham7

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Re: I’m toying with the idea of a car engine + generator for power backup
« Reply #78 on: December 08, 2021, 09:59:03 pm »
It does make me wonder how they react to sudden increases in load. There may be a really serious voltage droop while they accelerate the engine, unlike something that is already at speed. Unless there's energy storage (battery, capacitor, independent flywheel) sufficient to cover the deficit for 1/4 (?) of a second.

They sag.  My Generac version adjustable as to how far it spools down at low load.  If you have a desktop computer without a UPS, you need to not allow it to idle all the way down or you'll have a dropout.

Quote
The 2200 W unit uses 1.14 l/hour at rated load or 0.52 litres of fuel per kWh
The 7000 W unit uses 2.9 l/hour at rated load or 0.41 litres per kWh


The bigger unit is 27% more efficient.

You're using the wrong numbers, I think.  0.41L/kWh would be astonishingly efficient for a single-stage (no heat recovery) gasoline IC generator system. The nameplate rating is the surge rating, the rated load is somewhat less.  And while I would expect the larger unit to be more efficient, that doesn't make the small one "very inefficient".

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It's pretty expensive electricity. At my current local prices for regular petrol the 7 kW unit is US$0.69/kWh. The 2200 W unit is $0.86/kWh.

Expensive compared to what?  Using a generator implies that your normal utilities have gone offline.  As demonstrated recently in Texas, people will pay a lot more than $1/kWh if they need to in an emergency.
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Offline brucehoult

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Re: I’m toying with the idea of a car engine + generator for power backup
« Reply #79 on: December 08, 2021, 10:40:08 pm »
The 2200 W unit uses 1.14 l/hour at rated load or 0.52 litres of fuel per kWh
The 7000 W unit uses 2.9 l/hour at rated load or 0.41 litres per kWh


The bigger unit is 27% more efficient.

You're using the wrong numbers, I think.  0.41L/kWh would be astonishingly efficient for a single-stage (no heat recovery) gasoline IC generator system. The nameplate rating is the surge rating, the rated load is somewhat less.  And while I would expect the larger unit to be more efficient, that doesn't make the small one "very inefficient".

As long as Honda is using comparable numbers for both units the comparison should be valid.

Quote
Quote
It's pretty expensive electricity. At my current local prices for regular petrol the 7 kW unit is US$0.69/kWh. The 2200 W unit is $0.86/kWh.

Expensive compared to what?  Using a generator implies that your normal utilities have gone offline.  As demonstrated recently in Texas, people will pay a lot more than $1/kWh if they need to in an emergency.

My use-case for a generator would be to supplement solar to charge batteries in bad weather, as an alternative to being connected to grid power for the bad weather days.

Here in NZ, even in a town you're charged about US$1.25/day just to be connected to the grid, before you even use any electricity.

I'm considering the equations to go live somewhere that would require $30k or $100k or more to get connected to the grid in the first place. Solar plus (occasional use) generator for computers, lighting, fridge and bottled gas for cooking and heating (maybe wood fire too) seems completely doable these days. AC is optional in northern NZ, though nice. But it's something you only need on days with an excess of solar anyway, so that's probably fine.

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Offline Gyro

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Re: I’m toying with the idea of a car engine + generator for power backup
« Reply #80 on: December 08, 2021, 11:05:24 pm »
Just a thought about the discussions on multiple tensioned belts or chains for coupling. These will impose a significant radial load on either the crankshaft end or the transmission output shaft, depending on configuration. There is of course a timing belt / chain and auxiliary belt at the front of the engine, but nowhere near the radial load of a power takeoff. These don't normally see any radial load, maybe intermittent axial load on in the case of a manual transmission, but otherwise they are just splined connections.

It might not be an issue, but is probably worth consideration.
Best Regards, Chris
 

Offline bdunham7

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Re: I’m toying with the idea of a car engine + generator for power backup
« Reply #81 on: December 08, 2021, 11:21:40 pm »
It might not be an issue, but is probably worth consideration.

It's a huge issue.  There are, or at least were, industrial engines designed for this purpose with huge roller bearings and extra-stout crankshaft stubs, but absent those design features a radial load is not good for long term operation and may even snap a crankshaft quite quickly unless you used a coupling shaft driving a pulley with its own very robust bearings.  Most designs using belts for power transfer are crude, low-volume machines that just weren't worth the effort to engineer a proper powertrain.  There are exceptions as belts do protect from extreme shock loading for things like concrete saws and stump grinders.  Even there, though, belts are less common these days.

Belt driven generator setups are not unknown, but to connect them directly with belts you do need a generator assembly that is designed for the purpose, just like the engine.  I've never seen a chain drive and suspect that it would be challenging to make that quiet and reliable.

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Offline Gyro

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Re: I’m toying with the idea of a car engine + generator for power backup
« Reply #82 on: December 08, 2021, 11:36:36 pm »
It's a huge issue.

Yes, I should probably have added 'in a limited life application, using a small percentage of the engine's maximum output torque'. The best solution would be to put the pulleys on a dual bearing supported sub axle and either couple using the existing splines (if loose enough accurately aligned) or a flexible coupling.
« Last Edit: December 08, 2021, 11:42:45 pm by Gyro »
Best Regards, Chris
 

Offline JesterTopic starter

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Re: I’m toying with the idea of a car engine + generator for power backup
« Reply #83 on: December 08, 2021, 11:59:55 pm »
I though about the radial loading, I would support the shaft with bearings on either end, that should take care of that., I doubt it would snap the crankshaft, but it would likely do a number on the rear bearing and seal.

I was in my car today and made a point of listening to how loud it was at say 1500, 1800 3600 RPM, pretty darn quiet at 1500-1800 RPM even while accelerating, not a completely fair comparison though as my daily driver is a 3.0 litre V6.

I also tried to find HP vs. RPM graphs for 1.5l engines, no shortage for “hopped up” engines, I did not find a graph for a totally stock Toyota or Honda, but I’m guessing it will make plenty of power at 1500RPM to comfortably power the house. I’m really not concerned with consumer reliability vs. industrial, if people put 400km+ on these engines without a rebuild I’m guessing running for a few days at 1500RPM will be nothing.
 

Online langwadt

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Re: I’m toying with the idea of a car engine + generator for power backup
« Reply #84 on: December 09, 2021, 12:12:11 am »
I though about the radial loading, I would support the shaft with bearings on either end, that should take care of that., I doubt it would snap the crankshaft, but it would likely do a number on the rear bearing and seal.

I was in my car today and made a point of listening to how loud it was at say 1500, 1800 3600 RPM, pretty darn quiet at 1500-1800 RPM even while accelerating, not a completely fair comparison though as my daily driver is a 3.0 litre V6.

I also tried to find HP vs. RPM graphs for 1.5l engines, no shortage for “hopped up” engines, I did not find a graph for a totally stock Toyota or Honda, but I’m guessing it will make plenty of power at 1500RPM to comfortably power the house. I’m really not concerned with consumer reliability vs. industrial, if people put 400km+ on these engines without a rebuild I’m guessing running for a few days at 1500RPM will be nothing.

it adds up quickly, say a 5000km oil change interval, guessing an average speed of 50km/h, that's only 100hours

 

Offline james_s

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Re: I’m toying with the idea of a car engine + generator for power backup
« Reply #85 on: December 09, 2021, 12:17:57 am »
All the Honda units run the engine slower at light loads. But the bigger ones make more electricity from less fuel.

It does make me wonder how they react to sudden increases in load. There may be a really serious voltage droop while they accelerate the engine, unlike something that is already at speed. Unless there's energy storage (battery, capacitor, independent flywheel) sufficient to cover the deficit for 1/4 (?) of a second.

The 2200 W unit uses 1.14 l/hour at rated load or 0.52 litres of fuel per kWh
The 7000 W unit uses 2.9 l/hour at rated load or 0.41 litres per kWh

The bigger unit is 27% more efficient.

More than that, if you run the 7000 W unit at 1/4 power  (1750 W) it will run for 18 hours instead of 6.5, for about 1.05 l/hour or about 0.6 litres per kWh, so you're not losing much at lighter loads (unless your lighter load is 500 W or something)


It's all pretty expensive electricity. At my current local prices for regular petrol the 7 kW unit is US$0.69/kWh. The 2200 W unit is $0.86/kWh.

That's not counting depreciation and maintenance.

I have a Honda EU2000i, like the rest in the series it has an "Eco-throttle" switch on the front and if you turn this on it throttles down under light load which results in a substantial fuel savings and equally important to me, a large reduction in noise. The downside is that yes it does take a moment for the engine to respond to an increase in load, it will cause the lights to dim briefly when something like the refrigerator or furnace blower starts up but since I have UPS's on everything that matters this is not an issue for me. Honda says to turn off eco throttle when using large loads but I generally don't bother since that requires going outside. Even at full throttle these things are so much quieter than a conventional generator that I'd never even consider owning a conventional non-inverter type anymore.

Yes if you run it at full load a conventional generator is going to be more fuel efficient, however in the real world in a domestic setting a generator is going to spend more than 90% of the time operating at probably 1/4 load or less. My house typically "idles" at around 250-500 watts depending on the time of day and what I'm doing so during a power outage the little Honda spends most of its time just puttering at or near idle. When my heat comes on, or the refrigerator, or some other large load it spools up and then whenever that shuts off it returns to idle. It's absolutely brilliant, I can run it all day long on a gallon of gas. A comparably sized conventional generator will consume several times that while emitting a deafening roar the entire time.

Yes, it is expensive electricity relative to utility power, but during a power outage when utility power is not an option it's really nice to have a backup source. When considering the fuel efficiency, don't forget to look at the big picture and consider the average load you're going to be drawing. A 7kW generator is going to burn a lot more fuel delivering 400 watts than a 2kW generator will, even when it's an inverter generator that can throttle down, it's still a much larger displacement engine. Many people get hung up on needing to run everything in their house at once and size a generator accordingly. I look at it from an emergency standpoint and don't mind doing some manual power management to get by with a much smaller generator, I have gas heat, hot water and cooking so I find a 2kW inverter generator to be perfectly capable of running my entire house. I can't use my microwave oven but so what, at least I'm not using candles to see and freezing my butt off like back in the day.
 

Offline james_s

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Re: I’m toying with the idea of a car engine + generator for power backup
« Reply #86 on: December 09, 2021, 12:21:00 am »
it adds up quickly, say a 5000km oil change interval, guessing an average speed of 50km/h, that's only 100hours

100 hours is a lot of power outages. I've put 33 hours on my generator in the ~3 years I've owned it. I change the oil once a year regardless of the hours. Unless you're living off grid and using the generator full time this is not going to be an issue. If you are, it might be worth considering an external oil tank as is used with dry sump engines.
 

Offline james_s

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Re: I’m toying with the idea of a car engine + generator for power backup
« Reply #87 on: December 09, 2021, 12:23:01 am »
Just a thought about the discussions on multiple tensioned belts or chains for coupling. These will impose a significant radial load on either the crankshaft end or the transmission output shaft, depending on configuration. There is of course a timing belt / chain and auxiliary belt at the front of the engine, but nowhere near the radial load of a power takeoff. These don't normally see any radial load, maybe intermittent axial load on in the case of a manual transmission, but otherwise they are just splined connections.

It might not be an issue, but is probably worth consideration.

The superchargers on drag racers are belt driven, and they draw tens of horsepower at least. Running an engine at full load that would be a big issue, but he's talking about maybe 15-20 horsepower from an engine that is probably rated to produce 150 or so.
 

Online langwadt

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Re: I’m toying with the idea of a car engine + generator for power backup
« Reply #88 on: December 09, 2021, 12:33:09 am »
it adds up quickly, say a 5000km oil change interval, guessing an average speed of 50km/h, that's only 100hours

100 hours is a lot of power outages. I've put 33 hours on my generator in the ~3 years I've owned it. I change the oil once a year regardless of the hours. Unless you're living off grid and using the generator full time this is not going to be an issue. If you are, it might be worth considering an external oil tank as is used with dry sump engines.

I think I remember one power out in the last 20 years and it lasted for a few hours
 

Offline james_s

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Re: I’m toying with the idea of a car engine + generator for power backup
« Reply #89 on: December 09, 2021, 12:35:21 am »
I think I remember one power out in the last 20 years and it lasted for a few hours

Well, some places have much more reliable power than others. I suspect you pay quite a bit more for that reliable power than the $0.10/kWh I pay for mine, so I don't mind it going out for a few hours a year when storms knock down trees.
 

Online langwadt

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Re: I’m toying with the idea of a car engine + generator for power backup
« Reply #90 on: December 09, 2021, 12:45:32 am »
I think I remember one power out in the last 20 years and it lasted for a few hours

Well, some places have much more reliable power than others. I suspect you pay quite a bit more for that reliable power than the $0.10/kWh I pay for mine, so I don't mind it going out for a few hours a year when storms knock down trees.

price of the electricity about the same, but price I pay close to triple that because of taxes
 

Offline JesterTopic starter

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Re: I’m toying with the idea of a car engine + generator for power backup
« Reply #91 on: December 09, 2021, 12:58:57 am »
Just a thought about the discussions on multiple tensioned belts or chains for coupling. These will impose a significant radial load on either the crankshaft end or the transmission output shaft, depending on configuration. There is of course a timing belt / chain and auxiliary belt at the front of the engine, but nowhere near the radial load of a power takeoff. These don't normally see any radial load, maybe intermittent axial load on in the case of a manual transmission, but otherwise they are just splined connections.

It might not be an issue, but is probably worth consideration.

The superchargers on drag racers are belt driven, and they draw tens of horsepower at least. Running an engine at full load that would be a big issue, but he's talking about maybe 15-20 horsepower from an engine that is probably rated to produce 150 or so.

Re blower belt…..
I read the other day that a top fuel engine produces 400HP at idle, not sure how much of that is going to the blower, but I’m sure it’s plenty when the engine is making 11,000 HP at 9500RPM,
 

Offline bdunham7

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Re: I’m toying with the idea of a car engine + generator for power backup
« Reply #92 on: December 09, 2021, 01:02:54 am »
The superchargers on drag racers are belt driven, and they draw tens of horsepower at least. Running an engine at full load that would be a big issue, but he's talking about maybe 15-20 horsepower from an engine that is probably rated to produce 150 or so.

Depending on what class of drag racing the blower can take a lot more horsepower than that, but those engines also have massive 4340 forged crankshafts with a very limited lifetime.  I used to know someone that raced in the methanol class (not nitro) and was on a budget so he would try and salvage the crankshafts and other parts that were discarded by the nitro guys.  He would bring me a batch of cranks and probably a third of them were scrapped because the front of the crank was bent from the blower belt load. 

I realize we're talking about lower power settings (at lower RPMs as well--so torque may still be moderately high) but a typical small 4-banger with a nodular iron crank is not likely to last long with the side loading that come from even 20 HP.  They just aren't designed for it.  The crankshafts can't take the rotational flex loading and the bearings aren't designed for any side load at all.  An industrial engine designed for v-belt drive at say 45HP @ 3000RPM would have a 1-3/4" or so forged steel crankshaft stub and huge tapered roller bearings that weigh 5 lbs (as big as the axle bearings on a 1-ton truck) on each end of the crank.  This is an order of magnitude stronger than a typical econo-4-banger.  I don't know how you would even attach a pulley to the back of a small car engine in a way that wouldn't disintegrate in short order.  Perhaps replace the flywheel with a huge machined multi-groove pulley?

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« Last Edit: December 09, 2021, 01:27:17 am by bdunham7 »
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Online langwadt

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Re: I’m toying with the idea of a car engine + generator for power backup
« Reply #93 on: December 09, 2021, 01:37:45 am »
Just a thought about the discussions on multiple tensioned belts or chains for coupling. These will impose a significant radial load on either the crankshaft end or the transmission output shaft, depending on configuration. There is of course a timing belt / chain and auxiliary belt at the front of the engine, but nowhere near the radial load of a power takeoff. These don't normally see any radial load, maybe intermittent axial load on in the case of a manual transmission, but otherwise they are just splined connections.

It might not be an issue, but is probably worth consideration.

The superchargers on drag racers are belt driven, and they draw tens of horsepower at least. Running an engine at full load that would be a big issue, but he's talking about maybe 15-20 horsepower from an engine that is probably rated to produce 150 or so.

Re blower belt…..
I read the other day that a top fuel engine produces 400HP at idle, not sure how much of that is going to the blower, but I’m sure it’s plenty when the engine is making 11,000 HP at 9500RPM,


I think a blower can take something like 20% of the engine output, but a topfuel engine also get rebuild every ~900 revolution, probably less than half run in anger
 

Offline james_s

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Re: I’m toying with the idea of a car engine + generator for power backup
« Reply #94 on: December 09, 2021, 02:00:51 am »
price of the electricity about the same, but price I pay close to triple that because of taxes

Those taxes probably pay for things like putting power lines underground and trimming trees and such. I live in a heavily forested and mountainous region, there are lots of trees and lots of hills, the soil is mostly glacial till that is full of rocks. It rains a lot and when the wind blows it knocks trees down or causes them to lose branches. A lot of the power lines between towns are overhead and in the winter some power outages are just a fact of life. They have been noticeably more common in the last couple of years and I don't know why for sure but I suspect Covid has resulted in less preventative maintenance like tree pruning. In the cities most wiring is underground and outages are very rare, in more rural areas most wiring is overhead and outages are a lot more common. I much prefer living in a more rural area and will take the occasional power outage as a cost of living here. At least it isn't like some countries where outages happen all the time.
 

Offline brucehoult

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Re: I’m toying with the idea of a car engine + generator for power backup
« Reply #95 on: December 09, 2021, 02:01:23 am »
Yes if you run it at full load a conventional generator is going to be more fuel efficient, however in the real world in a domestic setting a generator is going to spend more than 90% of the time operating at probably 1/4 load or less. My house typically "idles" at around 250-500 watts depending on the time of day and what I'm doing so during a power outage the little Honda spends most of its time just puttering at or near idle.

My house also uses around 500 W on average most of the year, 800 W in winter (added dehumidifier load).

Quote
Many people get hung up on needing to run everything in their house at once and size a generator accordingly. I look at it from an emergency standpoint and don't mind doing some manual power management to get by with a much smaller generator

For me it's not a matter of running everything at once. I'd just like to be able to run anything by itself. 2000 W isn't even enough for a kettle, hairdryer, vacuum cleaner, microwave *individually*.

That's if powering things directly from the generator.

If/when I go off grid the generator will be for charging the batteries, so peak loads don't matter, but neither does an econo mode on the generator -- I'd just want to charge the batteries using as little fuel as possible, and ideally as little time as possible. It should ideally be a fairly rare event, when there's bad weather for several days in a row.

Quote
I have gas heat, hot water and cooking so I find a 2kW inverter generator to be perfectly capable of running my entire house.

Gas for the high powered things certainly helps a lot.

No doubt there are very good uses for a $1300 2200 W light weight generator and it would be handy to have one around.
 

Offline Circlotron

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Re: I’m toying with the idea of a car engine + generator for power backup
« Reply #96 on: December 09, 2021, 04:26:55 am »
I don't know how you would even attach a pulley to the back of a small car engine in a way that wouldn't disintegrate in short order.  Perhaps replace the flywheel with a huge machined multi-groove pulley?
I'd say leave the flywheel and clutch in place and attach the bell housing as well. Get a manual trans input shaft and put it in it's normal place in the spigot bush and make something to hold a bearing in the bell housing. Then put a pulley or sprocket on the shaft but mount it close to the bell housing end of the shaft either inside or outside but close to the bearing so the engine bearing is not stressed so much.
 

Online Ed.Kloonk

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Re: I’m toying with the idea of a car engine + generator for power backup
« Reply #97 on: December 09, 2021, 04:40:38 am »
Oh yeah. Leave the flywheel.
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Offline JesterTopic starter

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Re: I’m toying with the idea of a car engine + generator for power backup
« Reply #98 on: December 09, 2021, 09:21:50 am »
Hopefully I will be able to find a stick car with a flywheel instead of auto with a flex plate. Making a plate for a suitable bearing where the transaxle was should be easy enough on the mill. A RWD configuration with the old style bellhousing would be simpler yet. I have to say these new engines although efficient are really ugly and complicated compared to engines of the 60’s, my hot rod engine had one vacuum hose, and the original K-code 289 engine had no vacuum hoses.
« Last Edit: December 09, 2021, 09:25:28 am by Jester »
 

Offline Berni

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Re: I’m toying with the idea of a car engine + generator for power backup
« Reply #99 on: December 09, 2021, 10:01:16 am »
I though about the radial loading, I would support the shaft with bearings on either end, that should take care of that., I doubt it would snap the crankshaft, but it would likely do a number on the rear bearing and seal.

I was in my car today and made a point of listening to how loud it was at say 1500, 1800 3600 RPM, pretty darn quiet at 1500-1800 RPM even while accelerating, not a completely fair comparison though as my daily driver is a 3.0 litre V6.

I also tried to find HP vs. RPM graphs for 1.5l engines, no shortage for “hopped up” engines, I did not find a graph for a totally stock Toyota or Honda, but I’m guessing it will make plenty of power at 1500RPM to comfortably power the house. I’m really not concerned with consumer reliability vs. industrial, if people put 400km+ on these engines without a rebuild I’m guessing running for a few days at 1500RPM will be nothing.

it adds up quickly, say a 5000km oil change interval, guessing an average speed of 50km/h, that's only 100hours

Well on my modern Volvo the service intervals are 25 000km. This is about how much i drive in a year, so it gets a yearly oil change. Most of this time is spent going 130km/h on a highway. Googling around it seams to take about 40 HP to maintain this speed in an average car. So on the typical commute to work it is continually producing 40 HP for about 30 minutes. This ads up to about 240 hours of running at 40 HP between oil changes.

So it looks like a typical car engine should be able to produce about 30kW for 10 days straight without service. In the process it would burn about 1500 liters of fuel(or about 1000$ to 4000$ worth of fuel depending on where you live). Tho 30kW is a lot of power so a house probably won't use nearly that much 24/7
 


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