gasoline electric hybrid air compressor

[oil pan 4]

I am building a replacement for my old 8 gallon wheelbarrow style gasoline powered air compressor with real old 5hp briggs and Stratton with 11 to 12 cfm compressor.

Some people will say just get an electric. I already have about 10 horsepower worth of electric compressors finely tuned and staged to work together on tap ready to go. This is for when I am away from my home base.

The replacement engine will be a more efficient and powerful honda GX200 engine and a larger 19cfm compressor. I was considering hauling around my little blue oilless air compressor for when I just needed a little bit of air to fill a tire or shoot a nail gun.

Then I picked up a used 1.5 horsepower 3600rpm craftsman 120 volt electric motor for almost nothing and had a thought.

Obviously a fixed 1 belt system where the electric motor would be turning the compressor and gas engine wouldn't work, plus that would be stupid. I was already planning to do a quick tensioning system. I found it very difficult to start my 5hp/11cfm compressor on cold days, but found the gas engine very easy to start when all by its self. I have a feeling that a larger, higher compression engine pushing twice the compressor will be even more fun to start. It would be nice to be able to start the engine by its self and apply belt tension to engauge the compressor with out losing several fingers.
The hillbilly way would be to pop the belt off, yank the engine till it starts, let it warm up a bit, shut the engine off toss the belt on and then re start. I am going to say that sucks, it wastes time in a game where time is money and it wastes gasoline.
With a little more adjustment a quick belt tension rig becomes a belt quick removal rig.
I could set it up to where the belt could be rerouted or replaced to incorporate the electric motor to slowly turn the 19cfm compressor at greatly reduced capacity. A capacity about equal to that of my 1hp oilless compressor.

I like efficiency so each motor will have a control system. The gasoline air compressors unloader/throttle down valve vents to the atmosphere when it trips. So the electric motors pressure switch will have to be set below this, or the electric motor will build up the presssure and then have it released to the atmosphere.
I thought about just using the mechanical unloader/throttle down only and running the electric motor all the time, but I dont like it, that is especially wasteful if powering it with a remote generator. The electric motors pressure switch has an unloader too that will pop and release pressure before the mechanical unloader/throttle down valve kicks in. A manual valve on the electrics control switch can fix that.
If some dumby forgets to throw the manual valve that enables electrical controls the mechanical unloader valve will still vent to atmosphere.

I have the GX200, 1.5hp electric motor, tank but not the compressor. I can put up pictures tomorrow of at least what the motors look like together.

[Daox]

That sounds like an interesting setup. I'd like to see pics and hear more.

[oil pan 4]

Well my original idea wont work. The gasoline engine and electric motor spin opposite of each other. Obviously I could turn the motor 180 degrees but then the thing would be super wide.
I think what I will do is take my blue oilless air compressor and build the 6.5hp engine and compressor on to it. That way I will have an compressor I know can be run off as little as a 750 watt power inverter, the gas and electric will be able to operate independent of each other or together.

In the picture is the new Honda GX200 on my motor testing plank next to my little oilless electric air compressor.
It will be a long rig but that's ok since it will be doing the job of 2 air compressors and it will be cheaper to build this way since the electric side is done, the oilless air compressor already has its pressure switch control, a tank, regulator and wheels.

[oil pan 4]

I found the compressor I want to use for my build.
Its a V cylinder setup compressor for a "7.5hp engine". Its max speed is 1400rpm, if your engine can turn it that fast.
I like the separated V configuration, it dissipates heat better. The plan is to put a pulley that is one size below "too big". There are 2, 3, 4, 5 and 6 inch pulleys in my collection.
The 6 inch will drive the compressor at something like 1700rpm, which is way too fast so that one is out. The 5 inch will drive it right around 1400rpm, if the engine has the power.
The 4 inch sheave will drive the compressor at a fairly reasonable and sane 1100 to 1200 RPMs. I want to run the engine for all its worth, don't want to mismatch anything and under utilize too much engine with too small a compressor, I would rather get too much compressor and run it slower.
Engineering tool box says its rated output, 24cfm@90psi will take something like 4.5hp to turn. So add 10% to 20% for "friction" and the fact that the gasoline engine only makes power briefly every 2 rotations should mean its at or over its limit with a 5 inch pulley.
So this GX200 should be able to turn the 5 inch pulley at 90psi maybe, but at 125 to 135 psi where the diverter valve will kick on maybe not....

In other news I converted an electric air compressor to gasoline. Actually I found the compressor at the scrap yard with no motor. I am fresh out of electric motors but have an old 3hp briggs that needs a new home. To me finding a tank and compressor together is a really good starting point.
I am building a few practice gasoline compressors from junk before I build up the stuff I spent a good chunk of $ on.

[oil pan 4]

The scrap yard motorless 1.5hp electric air compressor that I am trying to repower with a 3hp briggs and Stratton hit a snag.
I have always found it easier to electrify a gas compressor then to gas up an electric.
I installed a 2.2 inch pully on the engine. I figured turning the engine about 4.5 times for every one turn of the compressor it would be enough. Nope once the air pressure builds up to about 80psi any thing less than WOT (wide open throttle) the engine slows and stalls.
I found a 2 inch serpentine pulley in my power transmission box and will try that today.
Going to a 2 inch will give me a 5:1 ratio.
If that doesn't work I am going to swap my junk yard compressor with a compressor off one of my smaller electric units, the electric compressor uses V-belt and that gives me almost unlimited pulley size options.

[oil pan 4]

A little bit smaller pulley made a huge difference.
Holding at about 1/2 throttle it popped off the 130psi relief valve. Before with the slightly larger 2.2 inch pulley it struggled hard to build up to 90psi, 100psi seemed impossible.
Edit:
Today I welded an extension arm onto the throttle lever plate and connected the diverter valves "bull whip" and made a rudimentary throttle control and it works perfect. No need for a complex governor. I didn't think it would work but figured I would give it a try.
Now I can sell this and make about $100 over what I put into it.
Craigs List 3hp briggs and Stratton, $30
Scrap yard air compressor and tank, $15
New diverter valve, $50
Idler pulley, $9
Ask $240, but will take no less than $200.

Next project resurrect another scrap yard air compressor.
On this one I was going to junk the compressor and save the tank and 110/220 volt motor for later. Then realized the compressor bores were just a little rusty, not pitted and it was full of dirt. After I drained the slug out of the air compressor (had to keep poking the oil drain hole with a wire to keep the oil/slug draining) I hand honed the bores to restore the cross hatching.
I am going to convert the motor voltage from 110 to 220, by swapping wires around. Then I will power factor correct it, of course.
The motor is getting switched to 220 because I am going to put a 10% bigger pulley on the motor, run it faster and get more air out of it. Right now its rated for 22 amps at 110 volts, put a bigger pulley on the motor and it will surely flip a breaker on any house hold 110v circuit that is up to code.
This is going to be an actual mobile compressor, unlike my other compressors that are in the dungeon and never see the light of day.
As of now my only mobile electric air compressor is the little blue one that is getting assimilated into a gas/electric hybrid.

[philb]

Hi oilpan,
I had a 1 hp 120 vac electric motor turning a 1 hp gast air compressor on a 15 amp curcuit. 15 amps had hard starting problems. I noticed a wiring diagram inside the electrical cover for 240 vac. I rewired it to 220 volts. Now it starts without any lugging.

Oilpan, have you thought about mounting the electrical clutch from an auto aircobditibg unit to the hard to start engine? By the rule of thumb, the ac units take about 5 electrical hp in torque. Maybe mount one on your conpressor side of the belt. Some of the new riding lawnmowers have that system for engaging the blades.

[oil pan 4]

I thought about it but I am trying to avoid any kind of electrical system. Its just another battery that will go bad and have to be replaced.

I think I am just going to use V-belt and movable tensioner. It should only be hard to start during the first few engine run hours and during the winter.

[oil pan 4]

I was driving around and saw that some one had a big old gasoline air compressor with an extra accessory.
This person had added a belt driven vehicle alternator. I am totally copying that idea, but in a way that the alternator wont be turning unless needed. This guy I saw had rigged it up so the alternator spun any time the engine was running, I don't want that.
I would rig it up so it would run alt or air, not both. Only reason I could ever imagine needing air and 12v power is if I had dead battery and flat tires at the same time.

[ICanHas]

Modify it to use chain or timing belt like geared belt like used in some vacuum cleaners, bicycles and motor cycles.

It is a lot easier on bearings and parasitic losses will be quite a bit lower.

Maybe weld a bicycle crank gear on the pulley, then attach alternator through the cog gear giving you an extremely efficient power electronics free variable speed control even though you can't shift under load.