Maximum Capacity of a 12V Air Compressor?

The shaft power required for any fluid mover = pressure increase x volumetric flowrate, all expressed in compatible units.

In the case of a vehicle electrical system, the electrical power available is limited by the fuse in the circuit. So if this fuse were, say 10A, then at 12V the maximum electrical power that can be sustained is 120W or 0.16hp.

Multiplying by a compressor efficiency, say 75%, that makes typically 90W or 0.12hp shaft work.

Choose a CFM. Let's say 100CFM = 4.7x10^-2m³/sec.

Divide by 90W = 5.2x10^-4N/m² pressure increase (7.6x10^-8psi).

Enough to illustrate?

As to the question regarding charging batteries, I had figured on checking what the power consumption was going to be (if it were possible), and possibly connecting a generator to the serpentine belt of the vehicle.

Thanks for the replies. I suppose it was just wishful thinking.

Can you rig a PTO [power take off] & run off the trucks motor?

I'm willing to try it.

I would also have the problem of how it would regulate when to engage and/or disengage as it would not need to be continuous duty - then again if I had to I could create a bypass for the "extra" air not being used when idle.

I would either need to make it to where a secondary drive shaft could power the screw compressor at the rear of the truck, or maybe add a pulley and have the screw compressor at the front of the truck...?? Do you think the v-belt will handle the load?

I don't know if that's what you had in mind. Any suggestions?

Thanks

Tractors have power output shafts that are there to turn anything you mount on it, if you cannot use a tractor, then your only other possibility is to buy a new ( or used ) petrol or diesel pump, sorry.....all 12 volt suggestions are useless......the generator you would need (let alone the connection problems) would probably be more expensive that a complete new engine driven compressor!

Checkout ebay and make sure you buy something that spares are still made for!!

Maybe ebay will have spares for your present unit also!!

You can use a transfer case from a 4wheel drive

You would hook it up in series w/the existing transmission

you would be able to disengage the drive wheels & just run the compressor or run both.

Semi's that have pumps or compressors have a PTO built in for unloading tankers

Your compressor should already have a bypass valve

PWSLACK gave you about as thorough of an explanation as possible. Its not really feasibile. You can't deliver "work output" without at LEAST as much work input, (efficiency losses.)

Summarizing, even if there were a 12 vdc motor large enough to produce 85 to 100 bhp., (to replace the probable HP or your old 6 cyl engine), how would you recharge your batteries? Using an engine with a generator ?

What size (cfm and bhp) is your current compressor? What manufacturer? Is it the engine that is going bad? Depending on the age of the unit and the control systems, you might be able to substitute another engine or drive system, but the controller will want to throttle down the unit when you reach pressure. If you keep running full speed with the unit unloaded, you will mainly be wasting fuel. Standard industrial electric units don't usually change the motor speed. They typically run with wide open speed, but they unload the compressor to reduce the horsepower use (i.e. power drain) of the system. On a gas powered version you won't save a lot of gas just by unloading the compressor. You would need to throttle down the engine to see significant savings. Also, be careful about making your own unloading valve system. You need to keep enough pressure to the separator tank (typical of screw compressors) to keep the oil flowing to the compressor. Starve the screws of oil and you will have no choice but to buy a new compressor. Using a separate drive system that the controller can't disable in case of a critical situation (over temp, no oil flow, over pressure, etc.) can be dangerous if you don't think it through.

"Does anyone know of an air compressor that could run off of a vehicles electrical system, and still output the same CFM's that an industrial compressor would?"

In a word, NO, definitely not. UNLESS it is one big mother of a vehicle electrical system>

The Neal Air Compressor

You didn't tell us whether it is the engine or compressor that is going bad. If it is the engine, I can tell you that you probably have a 300cu.in Ford industrial engine, kissing cousin to the 300 Big Six that was in a lot of trucks and vans in the 60s,70s,and80s. Although Ford discontinued manufacturing this engine in the late 80s or early 90s new parts for overhaul are available anywhere in the U.S. You can even get heads equipped for fuel injection. I am not sure about the electronics though. There are even complete engines available. Check powertechengines.com also of course j.c.witney and ebay. powertech can also probably help you with that sludged up governor on your unit which may be the root of you problem if the compressor is o.k.

Your assesments seem to be very accurate. The engine is more than likely from the 70's, and by looking at it, would be around 300 cubic inches.

One of the parts that gave us a lot of trouble was the carbuerator. We've spent about a year looking for places to either rebuild it, or sell us a new/rebuilt one. Maybe powertech can help us with that also.

I will look into the site you've listed and see what I find out.

Thanks for the help

Sorry everyone, I suppose I should have mentioned this: The problem I'm having with this unit is that sometimes it bogs down and dies. Then can be hard to start on occasion. The engine's governing system seems to be the problem. It has several linkages, spings, and other pieces to keep the proper throttle as load changes. I believe it operates on air pressure alone. We can not afford to tinker with it too much as this equipment is much needed on a day-to-day basis. At least until we can "afford" to buy a new one.

Thanks