Generator on LPG

[kitestrings]

Three years ago I bought a "parts" generator on ebay.  Aside from being setup for gas, we have this identical unit; Onan Commercial 4500, extended PTO .  I thought we might be able to use the starter, control board, rectifier, regulator, etc, and ours has got pretty high run-hours.  It didn't look like much.  It came out of a bucket truck and an oil leak blew hydraulic oil from tip to tip.


I played with it a bit, some minor ignition issue, spent o-ring in the carb, and soon had it running enough to know the engine had some life to give - hours were quite low - the carburetor needed some work.  Three years later I found a brand new LP carb, and the project took a turn:




Just got it going.  This thing now runs like a top.  And, we can drop it in place if/when we want to replace it or pull major repairs on our original unit:

[JW]

I have a nice 6kw diesel gen-set. I lost the documentation but have run it several times.  since its a diesel im happy with fuel economy. I actually ran my direct tv and picked up the signal just using the gen set. So its safe for electronics.

[kitestrings]

Is that Onan green?

I guess the ideal thing is a to have robust, reliable and quiet generator that you rarely need.  I've grown partial to LPG.  It starts well in cold temps and doesn't carbon up nearly as much... and you don't have handle fuel.  Gasoline is tricky now a days, because if it sits too long you can have some uninvited problems.

We originally set ours up so that we could use the same engine to split firewood.  I keep the hydraulic pump permanently mounts on the end, and then just swap spacers to couple to the pump motor.



This keeps the noise in the shed, and lets me listen to music while I spit.  It makes for a rather enjoyable fall day.

[ChrisOlson]

I guess the ideal thing is a to have robust, reliable and quiet generator that you rarely need.  I've grown partial to LPG.  It starts well in cold temps and doesn't carbon up nearly as much... and you don't have handle fuel.  Gasoline is tricky now a days, because if it sits too long you can have some uninvited problems.

We had a LPG generator and got rid of it. Way too inefficient and costly to run. The cost/kWh didn't make sense.

We got diesel but only use it for standby.

Our Honda EM4000SX is our main unit for peak load power to offset overload on the inverter. We have 100 gallon gas tank for it and refill it when it gets down to about 10-15 gallons left in it. I treat the gas with Stabil when it goes in the tank, have never had a problem with it. The tank gets refilled, on average, a little over once a year. It is wired into our XW-AGS for autostart by system demand.

Despite having around 1,000 gallons of gas thru it over the past 7 years it never fails to start on the first start sequence, even at 40 below zero when neither the diesel nor the LPG unit would start and run without significant pre-heat. It is in our generator room which is unheated, when it gets below zero in the winter time we have a 100 watt heat lamp that shines on the engine on the carb side. That's all it takes to get it to start reliably, which is 1/3 the power it would take to keep a diesel or LPG unit pre-heated to start on-demand, then go to full power output within 30 seconds to meet inverter overload. The gasoline generator can do it reliably, every single time.

To get our diesel started in the winter time for battery charging/load management I manually start the Honda and run it for an hour to warm it up to 70F in the generator room. Then start the diesel and let it idle for 10 minutes before bringing it online.

[kitestrings]

The fuel efficiency is lower as you say, but in our case, the generator sits for months - I haven't run ours this spring/summer at all, except to exercise it.  I do like not having to handle fuel.  Diesel I suppose long-term is better, but every time I change oil in my truck, I'm reminded how comparatively messy and expensive it is, and you do have cold-temp starting to consider.

I haven't had starting issues with LPG, but when it gets real cold I usually just pop on some heat in the shed half an hour or so before I fire up.  The thing I have had to watch is moisture at the air intake.  It is not just the cold, but the combination of cold and humidity.  We get these spells where it is warm wet/snow, then the temps drop 30-40 deg.  Under vacuum the air filter can ice up real quick.  I usually mount a shop light beside the intake and have it on it when the conditions warrant.

What is your diesel unit Chris?

[waross]

An engine needs fuel to keep itself running.
There is a lot of heat rejected from the radiator and exhaust.
You have to burn fuel to produce that heat.
A loaded diesel gen-set will produce about 13 Kilo Watt Hours per gallon of standard diesel fuel.
As the load drops the ratio of load to losses drops and the efficiency drops.
We had to run our home on a small diesel set (6 KW) for a couple of months.
During the night it had to be kept on line for two reasons.
1. Power had to be available for the freezer, refrigerator, furnace and sewage pump out.
Most of the night the set ran unloaded.
2. Did I mention that the ambient was -20F to -30F.
Power had to be available for the fan in the natural gas furnace, and with no other power, if the set was left cold all night there would be no starting in the morning.
By far the most fuel consumption was during unloaded hours.
If your set is for occasional standby this may not be important.
If the set will be used frequently, fuel consumption becomes more important.
Another issue with low loading is wet stacking.
Modern diesel engines use the combustion pressure, ported to the back of the compression ring to help seal the rings.
At low load, there may not be enough combustion pressure to properly seal the rings and oil pumping or wet stacking may result.
The next step is the possibility of flaming globs of oil being expelled from the exhaust.
The other result is loss of lubricating oil.
Worst case, A new set, was started and left running with very little load a few days after I installed it.
In a few hours it pumped out all of the lube oil and shut down on low oil pressure.

Avoid a diesel set that is much oversized.
In cold weather, a radiator shutter or baffle to reduce the heat rejected from the radiator will improve fuel economy.

[MattM]

I thought diesels self lubricate at low rpm's.

[SparWeb]

Welcome to Fieldlines, waross!

[ChrisOlson]

The fuel efficiency is lower as you say, but in our case, the generator sits for months - I haven't run ours this spring/summer at all, except to exercise it.  I do like not having to handle fuel.  Diesel I suppose long-term is better, but every time I change oil in my truck, I'm reminded how comparatively messy and expensive it is, and you do have cold-temp starting to consider.

What is your diesel unit Chris?

kitestrings, we now have a Cummins QD 10000. We have been pretty happy with this unit. It ran for 6 weeks continuous after the tornado here that took out all of our infrastructure, including our solar panels. Having the diesel during that time was very good. There was no gas stations open, could not get gasoline or LPG for 4 weeks. The natural gas infrastructure was also out due to lack of power for pumping stations.

The diesel fuel was available for construction and logging equipment that spent a month clearing roads, removing trees from buildings, and rebuilding utility power lines. Our QD 10000 burned about 14 gallons per day, running 44 days straight. We have a 500 gallon tank for it, the Cenex truck came and refilled it twice during the tornado cleanup.

Also had to pay cash for the fuel when delivered. The banks were not open. Only one bank has a standby generator and it was a natural gas unit (Generac). So no credit cards or bank cards worked during that time either, and the internet services were also down for a month.

Some people who have gas portable generators were driving 40 miles to get gas for them, and long lines at the gas pumps to fill up cans and cars. Many people who's homes survived the tornado ended up losing everything in their freezers and fridges.

[Bruce S]

ChrisO;
Late to the party on this one, but good to read that you're okay.
Cheers
Bruce S

[aka47]

On generators

I am currently looking around for a cheap marinised engine to use as a genset prime mover. The cooling circuit then can heat up other stuff I want heated and save me generating electricity to do it. Marinised engines also usually have an exhaust manifold/water tank fitted.

I have always been a bit non plussed about the whole generating electricity to heat stuff whist throwing away the heat (that is is always around twice the energy of the electricity produced)

For an off grid application combined heat and power has to be the way to go.

Air cooled gen sets are a touch more challenging when it comes to using the hot air.

[Bruce S]

One of the long time posters on here did a tri-gen. It'll take me a bit to look through the old posts to remember his login name, but perhaps someone else can find it quicker.
There were also posts about people using air-cooled engines with copper wrapped around the cylinder and head to effectively cool the engine while heating up water/antifreeze.

Hope this helps

Bruce S

[tanner0441]

Hi

Many years ago here in the UK there were some houses built that had a device called a TOTEM Total Energy Management Sytem.  It was a generator running on natural gas, it supplied all the electrical power required by the house the cooling water and heat scavenged from the ehaust was used for domestic hot water and heating.

I don't know how the system performed but after the fan fare to anounce it the whole thing faded into obscurity and was never heard of again.

I have a 2Kw suitcase inverter generator with intelegent throttle for my camper and a 2.5Kw as a stand by unit after living in an area where everytime the wind went above 20MPH the power went off. One christmas after a big storm nearly two weeks. During thst time the Utility company were using me to boil their kettles for their hut they used for breaks, which I thought was a good thing as they kept me supplied in fuel, in fact a very good deal I had several 5 gallon containers of the stuff sitting in the corner of my workshop.

Brian

[tanner0441]

Hi

They still make the units. The now call them CHP combinede heat and power But they are aimed at hospitals, hotels and leasure centers because to be viable they have to run 24/7 at 80% or more load.


Brian

[kitestrings]

Hi aka47,

I'm not sure you will find something in a small package with these type of features, but putting something together might be possible.  I would assume starting with a water-cooled unit would be easier to adapt.  And of course "cheap" (inexpensive, but durable, marinized) will be a reach I suspect.

The goal of course is to be efficient and have the best 'fit' for the application.  Chris O posted an interesting piece on something called "generator support".  It is a Xantrex/Schneider feature that allows the generator and the inverter to combine efforts to serve a load; so a heavier load can be served with a smaller generator (and/or less batteries).  You might find it of interest and can easily google it on this board.

I agree that generating to then turn around and dump it into a resistor for heating something seems long a long way around the barn.  We still cook toast on the gas-top, though I should use a toaster in the summer months.