field day question?

[N2EY]

Why not just run your rigs on batteries? You could do as WY5Vs suggests (a good idea, swapping out batteries from cars) or go to a junk yard and get 2-3-4 old batteries, charge them up before FD and run on them.

The cost of the batteries, even junkers, is likely to be more than cost of gasoline for a generator. Junker batteries are a real roll of the dice, too.

Add to that the fact that the typical YaeComWood rig has a certain minimum voltage below which it won't work right. That voltage is typically about 11.5 volts, depending on model. Those junker batteries won't last long before they drop below that voltage on transmit.

You can take them to a vehicle and hook a set of jumpers up to them and fast charge the old junker batteries if they run down. Generators and inverters are a big waste of energy.

Running a car engine just to charge the battery is a big waste, too.

It needs maybe at most 1 amp (if it was a K3 for example), 12 watts. Yet typically a generator is running, generating a lot of heat.

Elecraft rigs are designed to use very little power on receive. Most other rigs are much less efficient - typically 2-3 amps on receive.

Wild guess - 90% of all energy consumed by generators on FD or DXpeditions is wasted.

Very inaccurate. Depends entirely on the generator and load. Running a car engine just to charge batteries (which aren't all that efficient either) is at least as wasteful.

Reading the original post, it seems to me that the big issue is the cost of gasoline for the generator. If the goal is to run two 100-watt-class HF rigs, the alternative solutions cost a lot more than the gasoline would, unless somebody has some really big batteries around, charged, that they will lend.

----

I went to the Home Depot website, and checked out some generators.

The Generac GP3250 ($439) is more than adequate for the application. According to the specification, at half load (1600+ watts), it will run 9.7 hours on 3.5 gallons. That's about .37 gallons per hour. 9 gallons should be more than enough for Field Day.

Home Depot also rents generators (though I couldn't find a price on the website). The 3000 watt Honda they showed as a rental is rated 9.3 hours on 2.7 gallons at half load (1500 watts). That's about 7 gallons for 24 hours.

Now of course if somebody brings along a big generator (say, 10 kW for a 2A setup) and everybody plugs in all sorts of stuff (lights, fans, computers, portable refrigerators, coffee urns, electric griddles, etc., etc., ) all bets are off on gasoline use.

73 de jim, N2EY

[W6OGC]

The Coronado Emergency Radio Operators have a member who last year had a generator that was tri-powered, runs on gas, propane or Jack Daniels, or something like that. Maybe it's grapefruit juice.

Anyway, last year this generator ran all weekend on a fraction of one of those home bar-b-q tanks of propane, quiet, clean burning and none of the hazards associated with gasoline handling and storage, etc. It was considered a terrific improvement over what had been used before.

[N2EY]

The Coronado Emergency Radio Operators have a member who last year had a generator that was tri-powered, runs on gas, propane or Jack Daniels, or something like that. Maybe it's grapefruit juice.

Anyway, last year this generator ran all weekend on a fraction of one of those home bar-b-q tanks of propane, quiet, clean burning and none of the hazards associated with gasoline handling and storage, etc. It was considered a terrific improvement over what had been used before.

TERRIFIC! Plus it ran without interruption, start to finish.

I wonder what the total fuel cost was? One of the hidden costs of a gasoline-powered generator is that you're paying all the motor-vehicle taxes for fuel that isn't being used to power a vehicle.

The ultimate generator, for my dream setup, would be a diesel unit that could run on veggie oil.

73 de Jim, N2EY

[W6OGC]

The generator used is a Yamaha Tri‐Fuel EF2000i Generator.

We had a local test between this one and a Honda ES2000is Generator. A test of these two was video-taped and is available to watch. Pat WA6MHZ was involved in this project, too.

[KG4NEL]

Another advantage for QRP - the contacts are worth more

You get a x5 mult that the 100W guys don't have.

[WA7PRC]

My station normally runs on a float-charged battery pack that uses four flooded Group 27 batteries in parallel in my attached garage. The float charger is a homebrew regulated linear supply that can handle just under 30A. Preparation for FD involves turning the float charger off.

After running two 100W HF rigs 24 hours, the terminal voltage dropped to around 12.35V. The batteries are several years old. If the OP wishes to use less battery capacity or is otherwise concerned about the voltage supplied to the radio gear, he can use a DC-DC boost supply such as the MFJ-4416B. I use a homebrew unit, and when actually portable, the logging PC runs on a homebrew 12V to 16V 4.5A boost regulator. Those are also commercially available.

[K7JEM]

Originally Posted by K2XT
Wild guess - 90% of all energy consumed by generators on FD or DXpeditions is wasted.

Originally Posted by N2EY
Very inaccurate. Depends entirely on the generator and load. Running a car engine just to charge batteries (which aren't all that efficient either) is at least as wasteful.

Well, it depends on how you define "wasted". In technical terms, most energy used by an ICE is indeed wasted. An example is that there are 114,000 BTU in a single gallon of gasoline. There are also 114,000 BTU in 33KWh of electrical power. Using the figure of 288 AH worth of batteries to run the 24 hour FD (as provided by N2EY), that translates to 3.7 KWh of power at 13v, or about .11 gallon of gasoline for the entire 24 hour period, IF the energy from the gas could be directly turned into 12v electric power.

So, I would have to agree that over 90% of the energy consumed by any sort of generator is going to be wasted, since any generator that runs for 24 hours will use much more than a gallon of gas.

The best generators are about 30% efficient in converting fuel to power. But when they are lightly loaded, that efficiency goes way down. Unless you can keep the load on the generator in the "sweet spot", it will be much worse than that.

Joe

[N2EY]

Well, it depends on how you define "wasted". In technical terms, most energy used by an ICE is indeed wasted. An example is that there are 114,000 BTU in a single gallon of gasoline. There are also 114,000 BTU in 33KWh of electrical power. Using the figure of 288 AH worth of batteries to run the 24 hour FD (as provided by N2EY), that translates to 3.7 KWh of power at 13v, or about .11 gallon of gasoline for the entire 24 hour period, IF the energy from the gas could be directly turned into 12v electric power.

Quite true.

However, the big factor is the low efficiency of the engine. Charging batteries from a car engine, as was suggested, is even less efficient because those big engines are running so lightly loaded.

The best generators are about 30% efficient in converting fuel to power. But when they are lightly loaded, that efficiency goes way down. Unless you can keep the load on the generator in the "sweet spot", it will be much worse than that.

There are special inverter generators (like the Honda EU2000i) which adjust to the load. Also small diesel generators.

Most of all, the proposed alternatives are even worse.

73 de Jim, N2EY

[N0AZZ]

I have off road diesel and gas at home here for farm use still although I sold most of the farm but still have small utility size gas and diesel tractors. So no taxes for it and can even mow the yard with it and all other things if off road just don't get caught with it in your fuel tank. Several friends of mine have been when going to the stock yards with cattle using it in there trucks big fine, for those who don't know it's a different color and the HP checks for it.

I have 3 Honda generators 2 of the 2000's and a 7500 that I have had for a long time. For field day I always take my Motor Home and use the diesel generator in it to power it and all the other radio gear. It is a 50 amp service 12kw gen I have to stay inside out of the heat and use oxygen so works well for me I still get to go and not stay at home. Beats staying home and still can go out for short periods of time I have 2 antennas that I use from the MH a vertical 10-40 and a inverted L for 6-80m using an IC-AH4 tuner with my IC-9100.

[K2XT]

Charging batteries from a car engine, as was suggested, is even less efficient because those big engines are running so lightly loaded.

Ok Jim, good point, I yield on that one.
So I'll shift to another scenario- what if we charged the batteries using a car alternator but ran it from a lawn motor engine? A 1 hp output engine puts out 746 watts, right? (746 watts/hp). So a 1 hp engine runs a car alternator at 746 watts. That's 62 amps. So you bring three 12 volt car batteries fully charged to start FD. When the voltage slumps on the first one you replace the battery. When it happens again replace it and take your two partially discharged batteries to the 1 hp engine/alternator setup and run it for one hour, putting 62 amp/hours (ignoring charging efficiency) of juice into them. Do this, what, 4 times during the 24 hours? So the little engine only needs to run 4 hours. Isn't that a pretty efficient use of gasoline and low capital expenditure?
It just seems to me that running a generator to pull only 1-2 amps of receive current for the 80% of time that you are not transmitting is a huge waste, even if the generator does throttle back. The batteries don't have that problem.