field day question?

[N2EY]

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.

Not exactly. The alternator isn't 100% efficient, and neither is the battery. More like 500 watts out, tops. And you won't get to use all of it due to battery inefficiency.

But the concept is right - and it isn't new.

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?

Depends on what it costs overall. Three batteries, an engine-alternator setup, cables, etc. Plus you're connecting and disconnecting, moving batteries, and more work.

4 hours is rather optimistic charging time, too.

A simpler setup would be to have one battery, the engine-alternator setup, and some long cables so you're not sitting on top of the running engine. The trick would be to have the alternator output voltage set to compensate for the voltage drop in the cables.

You hook everything up and run till the battery voltage gets low, then run the engine-alternator setup to recharge. Most small engines have small gas tanks so you just let it run and charge till it runs out of gas.

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.

You have to analyze the whole system by-the-numbers. The inverter-type generators run at high efficiency on light loads, have good regulation, and are amazingly quiet. W6OGC's system with propane eliminates handling the gasoline, too.

This isn't a simple problem; there's no one-size-fits-all solution. If you have to buy batteries, but have a generator, the gasoline cost starts to look pretty reasonable. Etc.

There's also the "accessory issue" - what will you run besides the rigs? FD rules only require that the rigs themselves be on emergency power; the lights, computers, cooking, etc., can be on commercial mains and you still get the bonus. But in many FD setups, commercial power isn't available.

So the question then becomes: can you run FD without 120 volts AC?

73 de Jim, N2EY

[K2XT]

So the question then becomes: can you run FD without 120 volts AC?

Good points all around Jim. We're on to something here. I like your configuration with the single battery and remote alternator setup.
Answer to your question, yes you can. Two years ago we ran 1 station, a K3, at 100 watts on battery, at a park in Ocean County, NJ. We had 2 car batteries. One of them was huge, out of a Mercedes, and Mercedes uses BIG batteries. Not being deep cycle batteries of course we didn't discharge them completely, but the K3 runs down below 11 volts if I remember correctly. We took the depleted battery home for recharging and I think we only used 3 cycles total meaning we charged the big battery once and took both batteries home depleted. One guy had a tiny little inverter to power a laptop, and we used a Coleman lantern for light running on propane or kerosene, I forget. Today there may be efficient LED lamps that would be ok on batteries.

[AG6JU]

charging battery or using inverter by car stead of using small engine generator is false economy, car at idle take much more gasoline than 400 watts generator does. I think many car takes 1 Gallon per Hour even at idle. while generator are 0.2 Gallon / Hour if club member has Prius, I heard they have internal Inverter, about 1kW, to convert high voltage drive battery to 12V auxiliary battery, and engine turn on/off automatically when high voltage drive battery needed charge as long as car is in ON position.

[N2EY]

Good points all around Jim. We're on to something here. I like your configuration with the single battery and remote alternator setup.

It is only an idea. The limiting factor IMHO is that you need some serious cabling between alternator and battery, to prevent excessive voltage drop.

Answer to your question, yes you can. Two years ago we ran 1 station, a K3, at 100 watts on battery, at a park in Ocean County, NJ. We had 2 car batteries. One of them was huge, out of a Mercedes, and Mercedes uses BIG batteries. Not being deep cycle batteries of course we didn't discharge them completely, but the K3 runs down below 11 volts if I remember correctly. We took the depleted battery home for recharging and I think we only used 3 cycles total meaning we charged the big battery once and took both batteries home depleted. One guy had a tiny little inverter to power a laptop, and we used a Coleman lantern for light running on propane or kerosene, I forget. Today there may be efficient LED lamps that would be ok on batteries.

So you effectively had 3 batteries to power one station, and the rig used has very good tolerance for low supply voltage and very low receive current draw. Good stuff!

The problem is that, in the general case, folks may want to use rigs with higher receive current draw (some popular rigs draw 2-3 amps just on receive!) and with less tolerance for low supply voltage (11.5 or even higher). Plus "regular" car batteries....

All depends on the situation.

Another big factor was that you didn't use electricity for anything other than the radio and laptop.

73 de Jim, N2EY

[K7JEM]

I think the cheapest way to power 2 100 watt radios would be a small (800-1000w) generator and a few gallons of gas. Maybe only 3 or 4 gallons would run all field day. The max power that would be drawn by a 100 watt radio would be about 300 watts. Two would be 600 watts. Add a couple hundred watts for computers and high efficiency lighting, and you are only at 800 watts, max.

You can buy a 900 watt 2 cycle generator for about $100. I don't know about their quality, but they should be able to do this OK. 5 gallons of gas is about $20, that should run the entire time.

Joe

[K2XT]

and the rig used has very good tolerance for low supply voltage and very low receive current draw. Good stuff!


Another big factor was that you didn't use electricity for anything other than the radio and laptop.

A K2 draws about 1/3 to 1/4 of what a K3 does on receive.

What else would you need electricity for on FD? An air conditioner? Yeah I guess some guys would! Maybe a fan to keep the mosquitoes away. As you can see we do a rudimentary FD operation, really out in the field, with only stuff that we could carry in 2 trips from the car. No cooking, no showers, no comforts. Heck, for that matter, chairs were a luxury.
Last year we ran a different type of FD (a different buddy). We operated 1D (or is it 1E?) from home, with a K3 at 5 watts, on 7 AH gell cell batteries. Had as much fun.

[KK0G]

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.

That's exactly what we've done for the last 5 years. I Built a 12V generator from an old Delco 10SI 60 amp alternator which is belt driven by a 3.5HP Briggs and Stratton engine, built the whole thing for under $30 to purchase a pulley and belt. Granted I had the engine and alternator already in my junk pile but scrounging up used ones wouldn't cost too much. We set it up away from our operating position and run power cable from it to a pair of batteries located at the radios. With the engine running at just above idle it easily powers our 3 rigs at full power using about 3-4 gallons of fuel for the entire weekend. We now have 110V utility power at our location to run other stuff but in the past I have even powered a 12V - 110V inverter from my generator to power a computer for logging.

It never did make any sense to me to generate 110V then run that through a 12V power supply. If what we need is 12V then why not just generate it in the first place? Far more efficient.

[N2EY]

That's exactly what we've done for the last 5 years. I Built a 12V generator from an old Delco 10SI 60 amp alternator which is belt driven by a 3.5HP Briggs and Stratton engine, built the whole thing for under $30 to purchase a pulley and belt. Granted I had the engine and alternator already in my junk pile but scrounging up used ones wouldn't cost too much.

It's an idea that goes back to at least the 1960s.

The Big Question is how much the engine and generator cost. Because if you have to buy them new, pretty soon there's no economy to it.

We set it up away from our operating position and run power cable from it to a pair of batteries located at the radios. With the engine running at just above idle it easily powers our 3 rigs at full power using about 3-4 gallons of fuel for the entire weekend. We now have 110V utility power at our location to run other stuff but in the past I have even powered a 12V - 110V inverter from my generator to power a computer for logging.

The batteries handle the peak and the generator handles the average. You still need fairly heavy cable from the generator, to avoid excess voltage drop.

It never did make any sense to me to generate 110V then run that through a 12V power supply. If what we need is 12V then why not just generate it in the first place? Far more efficient.

Not really all that more efficient because the main inefficiency is the engine.

The use of 120 volt AC power means the DC sent to the rig is regulated and isolated. Plus you have AC for other purposes.

Where it really makes sense is in big FD operations where you have many rigs and other power requirements.

73 es good show de Jim, N2EY

[N2EY]

A K2 draws about 1/3 to 1/4 of what a K3 does on receive.

I know; BTDT.

What else would you need electricity for on FD? An air conditioner? Yeah I guess some guys would! Maybe a fan to keep the mosquitoes away.

It's like "camping". Different folks have different definitions of what the words mean.

Ask some folks, and to them "camping" means backpacking miles beyond the end of the road, into the wilderness, where you carry in (and out) everything you need.

Ask other folks, and to them "camping" means finding a place where the air-conditioned RV can have electric, water, sewer and broadband internet hookup for not too much money, and where it's not much of a drive to a supermarket and Wal-Mart.

All depends who you ask.

I've been on Field Days where the accessory load far exceeded the radio load. Lights, fans, computers, electric cooking, refrigerators, and yes, air conditioning.

As you can see we do a rudimentary FD operation, really out in the field, with only stuff that we could carry in 2 trips from the car. No cooking, no showers, no comforts.

Luxury. Try loading an entire 100 watt station (homebrew and hollow-state), including tent, shack table, generator, 42 foot mast, ropes, tools, food, etc., into a VW Rabbit and doing FD single-handed at a site with no facilities. Did that in 1995 and made 629 contacts.

Heck, for that matter, chairs were a luxury.

What are these "chairs" of which you speak? Wooden packing box did the job.

Last year we ran a different type of FD (a different buddy). We operated 1D (or is it 1E?) from home, with a K3 at 5 watts, on 7 AH gell cell batteries. Had as much fun.

1E. Home station, emergency power.

It's all good; I've done big multi-multis, 1B1-battery and many things in between. Most memorable was that 1B1 operation in 1995.

The main point of my posts is for folks to really do the planning and preparation rather than being disappointed or worse. Often (but not always) a generator is the best solution!

If you have QST for June 1994, look at page 55.

73 de Jim, N2EY

[W6OGC]

The most fun I've had on Field day involved a marine battery, an Argonaut, a Dentron MT2000 tuner and a looooooong wire at the NEL site up on Point Loma. A couple of outstanding CW ops stopped by, and it was a blast.

I wish I could find the picture of that Argonaut sitting there by the Dentron tuner.... pretty funny looking, actually. You use what you have!

This was probably 35 years ago or so.