Running pancake air comp.off a 5500 watt genset

Joht T or other experts,I am trying to run a small pancake air comp.off a 5500 watt genset,to run an air nailer and such.You already know my problem,it will start and build up pressure from zero psi,but it wont restart when the psi drops to 90 and it cycles back on.Just a hum and the breaker kicks out on genset.Can you suggest a capacitor set up to give that extra push. Have used hard start set up on ac heat pumps with good sucsess,would that work in this aplication? Willing to experiment a little if needeed. Thanks Butch
 
This is funny ! Let me see --okay a big capacitor.Yeah I suggest a big one. Get that power factor leadin" not laggin" . It's all good! If you can find an old DeLorean flux type capacitor ? { That should work }
 
Sounds like the "unloader" on the compressor isn"t functioning.

I routinely run a similar compressor off of a 3000 Watt Kipor, and it works just fine.
 
What is the amp draw of the compressor??? Of you do the math and find the draw is higher then 5500 watts then that is your problem but I don't think it would be. Maybe your compressor motor has weak or bad capacitors. Been to many years for me to remember the math as to how to figure amps/volts/watts. But if I do remember right you multiply volts times amps to get watts. So if you have 120 volts and 15 amps that is a draw of 1800 watts which you then should be just fine with
 
I agree with Bob - sounds like the unloader is not opening when the pump shuts off (your 5,500 watt generator should be able to start the compressor with ease).

Note many of those direct drive compressors actually have TWO unloaders:

One is the traditional unloader valve incorporated into the pressure switch. It opens and bleeds pressure off the pump when the pressure switch opens. All small compressors have this one - it's what makes the "psssht" sound when the pump stops.

Some compressors have second "starting valve" teed into the compressor discharge line. This valve is normally open. At startup it allows the motor to spin several revolutions (build RPM) before closing and loading the pump.

If the starting valve is stuck shut it makes the compressor draw excessive current at startup making it hard (or impossible) to start.
 
Without knowing the HP and starting current of the compressor and surge capacity of the genny (even then hard to say) I cant really say BUTTTTTTTTTTT I've seen those compressors start n run off smaller gennys then yours???????

AS the fine gents noted below most compressors have an unloader valve aka head pressure unloader aka load genie etc etc that dump the compressor head pressure without, of course, unloading the tank, thereby the start up isnt much harder then when you first started the unit with no tank pressure whatsoever.

See when it kicks off if you hear a hiss of escaping pressure in some sort of valve, often a brass lookin device between the output and receiver tank. If its NOT working then the inability to start wouldnt surprise me.

Let us know.......

PS Air Compressors and valves n pressure devices arent my cup o tea, best listen to the other gents over me......

John T
 
I'm no expert, just a life time of experience.

If your compressor works on house wiring, then it's your generator or you may be you are trying to use a wimpy extension cord.

My 3500 watt RV genny has 2 110 volt outlets, but they are only rated at 15 amps each. However the RV outlet, when set on 110 volts, is rated at 30 amps. If I try to start a small motor on the 15 amp outlets, the genny doesn't like it nor does the motor.

So, I bougth an RV adaptor to convert it to 110 v plug, NO problem with genny or what ever I plug in to it.

Another possibilty is the air compressor. I had a noisy oil-less air compressor. For some reason it would sometimes trip s 20 amp breaker in the house. I had no love for that compressor. Gave it to my son. Compressor lost compression and it ended up at the recyclers. Try a different air compressor. I have a 1.5 hp portable, not oil-less, that will handle 2 nailers. Had it over 20 years. It has never blown a breaker in the house. Cap start motor.

I use my genny to power my well if I have a power failure. Above ground 3/4 hp pump. It took 200 MFD, ACV, to power factor it. I did that to assist the genny. If you had to buy 4-500 MFD, you may change your mind and buy a gas powered air compressor. My contractor has 3 gas air compressors.
George
 
I too have seen those run off smaller generators BUT they may have been smaller compressors also?? No facts or figures to go by. Does the generator auto idle? If so turn that off and try it, have seen it make a difference starting "iffy" compressor loads in the past.
 
HEY GUYS.... the shut off switch 'PRESSURE SWITCH" should have the little unloader built in. Everyone is correct with the "pissssh" went it shuts off. I am wondering how he hasn't burned the motor up yet if his unloader is not working. Switch busted internaly?
Now if you are a contractor you pick up an EMGLO or the new name is JENNY and with those compressors you can have it "on off" or it will idle with an uloader valve that lets the compressor go around without pumping any air. The pressure drop on/off is like only maybe 5 lbs.and then the pump starts pumpin again. I have one and it is so SWEET!! Like I said I think his pressure switch is broken.
 
Are you by any chance trying to power it over an extension cord? Before you do anything else, plug the compressor directly into the generator.
 
Thanks for all the replies.This comp.is a dewalt brand,label saye 13.5 running amps so probaly 35 to restart it.No capacitor visible outside of motor case.Pulls the same stunt on two different gensets,both 5500 watt,works fine on larger 13500 watt set,no fun to lug that one around though .Dont see anything on thew label obout running on 2220 v.That would utilize the full capacity of genset,I think... Will check out the unloader deal,may be the whole problem,Will keep you imformed,thanks again.!!
 
At 13.5 amps x 120 = 1620 watts
The generator has
5500 watts @ 220 volts but only 2750 watts on each 120 volt leg.
2750/120 = 22.966 amps
Perhaps that is a bit of a load for starting.

Sometimes you can find a generator that has a switch that will give you a full 5500 watts on 120 volts. Just like a dual voltage electric motor. I have a 4000 watt belt driven one.

Dusty
 
That 13.5 running amps is a bit higher then I was as thinking in my original post below NOW IT MAKES MORE SENSE WHY "SOME" GENNYS MIGHT NOT RESTART IT. However still if its unloading it should re start the same as the initial start so Im afraid I cant explain this. Good heavy short cords and quality connections and insure theres some sort of head pressure unloading going on. I think theres some hype in genny ratings especially as far as surge capacity etc. Matbe alls well but the genny just aint got the "poop" lol it needs

John T
 
JohnT,
My guess is the lock rotor amps is more than the genny can handle because of the internal resistance of genny, extension cords and yes could be unloader. The unloader test could be very easy to confirm. If compressor starts with no air pressure in tank and won't re-start later, unloader.

Some gennys only use half the winding on 110v, so they can have two 110 outlets.

The instructions may say gennys can't be used on motors.

Doesn't your RV genny handle an A/c? Does it have one RV out rated at 30a?
George
 
"Doesn't your RV genny handle an A/c?"

My Onan 4000 has no problem with my 12,500 BTU Rooftop AC, and it can run the Microwave at the same time. HOWEVER some cheaper still so called 4000's sold at Big Box Stores for 1/4th the price might not. Thats why I questioned his gennys surge capacity and agree (since he listed 13.5 amps run current) it may simply not have the "poop" to run his compressor unless he has some unloading problem we all talked about.

John T
 
"have used hard start ac set ups with good success" Once you said that I figured anybody who takes parts from an AC unit to make ones compressor sart better already is like an Edison or Tesla and will figure it out. I got nothin".
 
Totally agree, if the bigger genny can do the job, then not enough poop. He said it would kick out after it try to restart at 90 psi. Could be unloader, but then why does the 13500 do the trick?? Still think his 5500 watt is rally only half that amount per 110v out..

My money is on the genny and it's likely to be an oil-less compressor.
 
I think you have it pegged, George. Locked rotor (startup) ranges 3 to 10 times run current and the 13500 just about covers it, but 5500 doesn't. Also, I would add that the unloader function is "barely there" when it is working. It closes before motor shaft moves and leaves compressor partially unloaded for whatever partial revolution (we could argue about partial vs more, but I wont) is needed in the way of compressor output to fill and pressurize probably less than a foot of line between unloader/check valve and the compressor head. Like I said, "barely there".
BTDT. Built a small (approx quart or two) tank & inserted it between compressor & unloader/check. This made compressor start off generator, where w/o tank, it would not, because now, it actually remained 'unloaded' long enough to get up to speed on the marginal generator.
 
Jessie,
I was thinking the same, a tank. All compressors I've seen have the unloader built is a part of the pressure switch, So as soon as the compressor is powered up, the decompression valve is closed. Compressor wouldn't even budge if it had a head pressure of 90 psi.

I have an old 2 stage air compressor, guessing 60 years old, that has a set a weights on pulley and as the compressor comes up to speed, the weights move, and a lever closes the decompression valve on the pump. This compressor has a unique motor too, no capacitors. It's a repulsion start, induction motor. The brushes lift off the commutator when motor comes up to speed.

I'm still betting the compressor is an oil-less and my limited experience says they have a large LRA. Also betting that only half the generator is feeding the 110 outlet. So he is really only getting half the power to the compressor, not enough. He should look at the round plug for a 110 volts and a larger amp rating.
George
 
I have a 1927 Curtis compressor that sounds just like yours with flyweights in compressor pulley, linkage to valve on head and the repulsion start-induction run motor. Only about 2 or 3 CFM on estimated 20 gallon tank, but it just keeps on ticking! Compressor pulley looks like designed for flat belt, but motor v-belt,........ but it has worked for 86 years!
 
Good points I have to agree, as I said up above there after he noted it took 13.5 amps THE GENNY MAY JUST NOT HAVE ENOUGH POOP LOL

My Onan 4000 starts my AC even if the Microwave is running, but its has more surge capacity I bet then some cheap big box store genny rated at the same 4000 I betcha.......

Im sure it either lacks capacity and/or some sort of an unloader problem, but being short on capacity moves right up there after his telling us it draws 13.5 amps........grrrrrrrrr

Fun chat yall

John T
 
Jessie,
My compressor is a little newer, it has side by side v-belts. I've had to sand the commutator a few times, when it has difficulty starting. Mine is only a 1.5 hp 2 stage. Yes, it keeps on going. However, I have 3 other compressors located in 3 different shops. Biggest is a 5 hp 2 stage.
George
 
JohnT,
Does your Onan 4000w have only one 110v out?

My 3500 watt RV genny can put all it's power to one 110v outlet.

I'll bet the 5500 watt genny can't put all it's power to one outlet unless it's a 220v out. If I'm right, then he is trying to start a compressor with only 2750 watt genny. Won't work.
George
 
George,you are right on both counts.It is an oilless compressor and the genny feeds half its output to each half of a duplex receptacle.Found book that came with it and it can easily be changed to send full output to just the 120 v receptacle> Will lose the 220 recep,but no big deal.Will let you know what happens..Thanks very much for all of you helping out,John T I wish you happy travels and please keep sharing what you know.Thanks Butch
 
Yep, theres ONLY ONE hard wired 3 wire (Hot, Neutral, Ground) output that leads to a 120 VAC 30 amp grounding RV type receptacle.........

Fun chat George, looks like most of us here agree his genny may just not have the "poop" lol (unless a mechanical problem)

John T
 
Thanks for the kind words. Yep what you describe I classify as a "multi wire branch circuit". On those a common Neutral serves a split duplex receptacle where Phase A feeds the top outlet and Phase B the bottom. Since the two are 180 out of phase if both outlets current were the same, the Neutral current would be zero. Unlike yours, my Onan has only one outlet, a 120 volt 30 amp RV type.

Fun chat

John T
 

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