How long will a Farmall A idle for on a full tank of gas?

PretendFarmer

Well-known Member
So I will be converting my 41 Farmall A to a 12 volt Alternator and battery. It is a mag ignition, so I will not be messing with that. Easier starting in cold weather is one reason, but another is because I have a 1500 watt inverter that I use as backup power when the lights go out.
How many hours do you think the A will idle for on a full tank of gas? If the power goes out, as it so often does these days in the north east, I want to power my lights and fridge off the inverter running from the tractor. Looking at a 55 amp alt from Napa. Opinions? Concerns?
 
Unless you have an aweful small fridge and not many lights , you won't run much off a 1500 watt inverter. also how much output will your alternator have at idle? I find I have to spin mine up pretty fast to get good output.
 
I would imagine an A could idle for literally days on a tank of gas.

An alternator needs RPMs to charge effectively, though. Cars normally idle at around 1000RPM, while an A is more like 450RPM. Full throttle for an A is barely off idle for a car.

I would recommend a bigger alternator, like a 105 Amp, and a way to spin it faster with the tractor at idle. Since the pulley on the alternator itself is about as small as it can get, all you can do is go bigger on the crankshaft, or introduce another multiplying pulley in between. What I mean is two pulleys connected together on a common shaft. Crankshaft drives the small pulley, big pulley drives the alternator.
 
I currently run a 1200 watt generator. When we lost power for a week, it ran my fridge, freezer and most lights in the house. Hot water heater is gas and I heat with a coal stove so, no real need for more power.
 
All at once?

It never hurts to go bigger, though. If you can afford a larger inverter like a 2000 Watt, running it at less than full capacity will keep it cooler.
 
You are going to run the tractor faster than idle to get the alt to put out more power. The pulley on the A isnt that big so to get the Alt running fast enough for its output makes running at idle wont work you need to see how fast the Alt needs to turn for its potential. Due to the crank pulley on the A you cannot attach a pulley there. Now how about running the Alt off the belt pulley as you can easy do that. You can get a Browning bushing on the splines and run as large a pully as needed for the alts output and use a 12v batt in the circut leaving the As system apart from the Alts circut now you wont need as much motor RPMs.
 
A 55 amp alternator will provide about 750 watts at full speed - ie. with the rotor spinning faster than about 3,000 RPM. However as the alternator heats up its output will drop off a bit. Also you must subract the 100+ watts "lost" inside the inverter (heat).

Bottom line is the BEST you might expect is about 600 watts continuous from your 55 amp alternator/inverter combination.

Now a 105 amp alternator (about 1,450 watts max) gets you closer. But you still have the inverter loss.

Also you need a way to spin the alternator at full RPM. To achieve this with the engine at idle requires significant (7:1 or 8:1) step-up from crankshaft RPM. Not a simple exercise!

----

As for fuel consumption at idle it should be easy to test. Simply rig a temporary gas supply (an old lawnmower tank will do) to the carburetor. Accurately measure a quart of gas and dump it in temporary tank. Now start the engine and note how long it takes to out of gas. A quick calculation will then tell how long you can expect from a full tank.
 
Inverters are made to run small things like a drill or light and that is for short periods of time. You would be better off buying a PTO drive type generator set up and run it off the PTO of that A but then again you will only be able to maybe have a 5KW unit or it would be to much for that A to handle
 
I have an F-12 that I run at idle to buzz firewood
with. I get about 6 hours on 2 to 2-1/5 gallons of
gas. The F-12 has essentially the same engine on
the inside as that of the Farmall A.

On another note, you can get some pretty big
alternators for a Diesel truck, such as 235amps and
up, that you could make an adapter to hook on to the
PTO (belted of course to get the desired RPM; run it
through a battery and then the inverter.
 
The alternator will produce 55 amps at higher speeds, doubtfully at idle.

You are MUCH better to just get a small gasoline powered portable generator, could get a 5KW unit for a few hundred dollars
 
(quoted from post at 08:40:07 11/12/12) I currently run a 1200 watt generator. When we lost power for a week, it ran my fridge, freezer and most lights in the house. Hot water heater is gas and I heat with a coal stove so, no real need for more power.

Funny, I have a 5500 W gen and it won't (or I don't let it) handle my whole house at one time. I know, you say you only want a refrigerator @ about 6-800w. (depending on how old it is) and lights, and I know the refriig compressor won't run 100% of the time. Getting a big enough alternator to put out enough for the invertor to operate at close to full capacity sounds like it would buy a generator and a lot of gas. Those 235 amp diesel alternators will cost more than my 5500w did and to get a smaller one to put out enough sounds like it will cost you in parts to set it up. A 1500w invertor is meant to power a small camper at best, or a saw or drill for a short time. Also, if you have ever looked at the output from an invertor on a scope, it's usually not very "clean", so might be hard on your refrigerator.
You can get a 3500W gas generator for around $300-350... sound like a much better way to go.
 
I would think you could idle a good day and half maybe longer. As for battery and alternator once you have engine running there is no draw on battery because you have a mag. ignition (which produces its owen spark).I have a Farmall B with a 6 volt alternator and mag ignition and it will charge at idle.
 
Bob M is correct.

Watts is Volts times Amps.

1500 Watts divided by 13.8 Volts is ~109 Amps.

A 55 Amp alternator running at full output will not keep up with the demand when the inverter is running at full output.

With electricity, there are losses and duty cycles to think about. Available supply should ALWAYS be greater than anticipated demand. How much greater depends on duty cycle.

Most cheap inverters are not rated for 100% duty cycle. In other words a 1500 Watt inverter is not designed to output 1500 Watts for hours on end. To get 1500 Watts out you would want to get a much larger inverter, 2000 Watts minimum, ideally 3000 Watts.

Now your 105 Amp alternator is not rated to put out 105 Amps 100% of the time either. You really need TWO 105 Amp alternators to do the job.

By the time all is said and done, you've got way more into it than a cheap clone 2000 Watt inverter generator, which only run about $500.
 
also if it is an early A, idling will not lubricate the shafts without moving or pto
runing and will run bearings dry, stumper
 
If you didnt get proper lubrication at idle, then how do people get away with running PTO water pumps for irrigation for hours on end?
 
(quoted from post at 09:59:04 11/13/12) If you didnt get proper lubrication at idle, then how do people get away with running PTO water pumps for irrigation for hours on end?

Because the PTO was running, and I don't know that they were at an idle. Pump we ran in SD behind a U-4 power unit did not idle. Pump would not have had enough suction until you throttled it up.
Not that I think it would really hurt to idle for long periods, but how do you intend to get much output from the alternator at an idle?
 
http://www.harborfreight.com/engines-generators/gas-engine-generators/800-rated-watts-900-max-watts-portable-generator-66619.html

I have seen the 900 watt one go for even cheaper. With the 20% off coupon you could get it for a tick over $100 or get the 3k one for about $220.
 
the i h salesman sold the A s, B s and C s on the premise that they would work all day on a tank of gasoline. approximately 1 gal per hour.

my C will just about do that.
 

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Back
Top