5hp single phase motor from 12kW generator

[Prefix]

Good Day!

I have DuroMax XP12000EH generator that's capable produce 12kW. It has 240V receptacle and 50Amp breaker.
My generator front panel picture


I thought it will be enough to power 60 gallon air compressor, so I bought HarborFreight one with the Century 5hp motor.
Motor plate picture

Once I wired it up, I turned the compressor on, the motor started spinning and in a few seconds blew up start capacitor.
Start capacitor picture

I repeated the same procedure 2 more times with replaced start capacitor and had no luck in starting the motor - another 2 capacitors also blew up.

After researching, it appears that the motor doesn't reach enough speed so centrifugal switch still feeds the start capacitor more than ~3 seconds and this obviously destroys it.

I didn't really understand why it happens because as you can see the motor is rated for 23Amps and the 50 Amps breaker on the generator never trips.

That's where I started to learn about in-rush current

So I removed the belt from the motor and repeated my test with no load on the motor (although I could easily rotate pump pulley with my hands).

The motor started with no issues, I almost immediately heard that click sound produced by centrifugal switch, the motor reached full speed.

I've also noticed that once I turned it on, the arrow on the volt meter built in in my generator momentarily dropped from 240V to ~120V-140V (hard to tell cause it's half second drop), and then returned back after the click from the centrifugal switch.

So it's obvious that I had to learn about inrush current before buying a generator.

However, here is my question: since the generator is able to start the motor with no load, is there anything I can do to make my compressor working as it supposed to be? Perhaps, soft start device or something? I don't have the access to the utility electricity there, also gas powered air compressor is not an option.

 

[American Locomotive]

Couple things:

1. Where's your compressor motor protection? The compressor should have some kind of motor-starter or protection circuit that would cut power to the motor well before the start capacitor pops.

2. Air compressors are hard to start, because you're simultaneously spinning up a heavy flywheel while putting the unit under load (compressing air). We need to remove the load component so the motor can actually get up to speed.

The only solution I can think of is an electronic time-delay unloader. The unloader your compressor comes with turns off as soon as the motor starts. An electronic delay unloader will keep the compressor unloaded for a set time, giving the motor time to spin up.

 

[mm08822]

Couple things:

1. Where's your compressor motor protection? The compressor should have some kind of motor-starter or protection circuit that would cut power to the motor well before the start capacitor pops.

2. Air compressors are hard to start, because you're simultaneously spinning up a heavy flywheel while putting the unit under load (compressing air). We need to remove the load component so the motor can actually get up to speed.

The only solution I can think of is an electronic time-delay unloader. The unloader your compressor comes with turns off as soon as the motor starts. An electronic delay unloader will keep the compressor unloaded for a set time, giving the motor time to spin up.

I would do this^^^^. Get a 240v solenoid valve to keep the unloader line vented to atm. Control that sv with an on delay timer set for 5 seconds. This will split the inertia up that the motor/gen is trying to start all at once.

Might want to try this with a manual valve before you drop bigger $$$.

Motors can draw 5-7 fla's on start up and your gen cant handle that spike.

 

[Prefix]

1. All it has is the standard pressure switch. As I understand, centrifugal switch on the motor is the devise that supposed to disconnect start capacitor. I've never seen before any devices that would analyze if the power should be cut because the motor hasn't reached target rpm during start up. At least, not on the air compressors. But I haven't seen too much air compressors, so who knows.. The instruction doesn't mention any additional devices.
2. What I think is that voltage drop is the reason why the motor can't reach target Rpms and disconnect start cap. As I read, soft starters may significantly decrease the voltage drops. So I'm thinking if it makes sens to try soft starter, or if it's not applicable for my application at all by some reasons.

Thanks, I got your idea about an electronic time-delay unloader, but I can't imagine how it would engage\disengage pulley. Because the compressor doesn't start when it's empty, meaning that once it has to rotate pump pulley, even not under load, it can't.

 

[Prefix]

I would do this^^^^. Get a 240v solenoid valve to keep the unloader line vented to atm. Control that sv with an on delay timer set for 5 seconds. This will split the inertia up that the motor/gen is trying to start all at once.

Might want to try this with a manual valve before you drop bigger $$$.

Motors can draw 5-7 fla's on start up and your gen cant handle that spike.

Thank you, I'll research your ideas with the unloader.

But honestly, I'm thinking about soft starters. As they are actively used in HVAC, I'm trying to understand if it's applicable to my situation.

For example (don't want to mention exact brands that I googled):

Before: soft starter installed:
- 72 amps peak inrush current on mains power
- Would not start on Honda 2000i portable generator

After: soft starter installed:
-32.5 amps peak inrush current on mains power
-Started easily from Honda 2000i portable generator

Result: soft starter reduced starting surge by 55%

 

[American Locomotive]

1. All it has is the standard pressure switch. As I understand, centrifugal switch on the motor is the devise that supposed to disconnect start capacitor. I've never seen before any devices that would analyze if the power should be cut because the motor hasn't reached target rpm during start up. At least, not on the air compressors. But I haven't seen too much air compressors, so who knows.. The instruction doesn't mention any additional devices.

The capacitor popped because the motor stayed on the start-winding too long. There should be some kind of circuit breaker or thermal-overload that should have disconnected the motor long before the capacitor popped.

Thanks, I got your idea about an electronic time-delay unloader, but I can't imagine how it would engage\disengage pulley. Because the compressor doesn't start when it's empty, meaning that once it has to rotate pump pulley, even not under load, it can't.

It's still forcing air through the small feed pipe to the tank and through a check valve.

Here's a test for you: Disconnect the pipe going from the compressor pump to the tank. Make sure you disconnect it on the compressor side and move the line out of the way. Then see if the generator can start the compressor. If it can, a time delay unloader will solve your issue.

 

[Prefix]

Here's a test for you: Disconnect the pipe going from the compressor pump to the tank. Make sure you disconnect it on the compressor side and move the line out of the way. Then see if the generator can start the compressor. If it can, a time delay unloader will solve your issue.

Great idea, will do, thank you.

 

[Milton Shaw]

Wonder if you could find a clutch system that doesn't engage until motor is at say 1200 RPM and then fully engage by 1500 RPM. Electrical clutches like on auto air conditioner compressors might could be modified to give delayed engage but would be an expensive thing to rig up. I know some air compressors on large truck have unloaders built into the compressor head that all the compressor is doing is moving pistons and the air moves back and forth between the two cylinders until the unloader lets them build pressure. Those unloaders typically work off a pressure regulator that keeps the air system in brake operating pressure.

 

[mike93lx]

Great idea, will do, thank you.

It would be a heck of a lot easier and have the same effect to just open up the tank's valve, but this won't solve the problem if the tank was already empty.

 

[Prefix]

It would be a heck of a lot easier and have the same effect to just open up the tank's valve, but this won't solve the problem if the tank was already empty.

Well I don't really know internalls of the pump and where is the bottle neck. When I did my tests where the capacitor had been blown, I had an empty tank and opened tank's valve.. So it's a 'first run' test, not even that one when the compressor is almost full and just tries to refill..

 

[larry_g]

Another thing to consider is going to a smaller motor pulley. It will deliver less air but also reduce the load on the motor. Figure out the speed of the PUMP and then shoot for a pulley that will spin the pump at about 60% of the speed it is running now.

lg
no neat sig line

 

[American Locomotive]

Well I don't really know internalls of the pump and where is the bottle neck. When I did my tests where the capacitor had been blown, I had an empty tank and opened tank's valve.. So it's a 'first run' test, not even that one when the compressor is almost full and just tries to refill..

Try disconnecting the pipe first and see what happens.

 

[alwaysFlOoReD]

What about a centrifugal clutch like on a mini-bike or go-kart?

 

[mm08822]

Good Day!

I have DuroMax XP12000EH generator that's capable produce 12kW. It has 240V receptacle and 50Amp breaker.
My generator front panel picture


I thought it will be enough to power 60 gallon air compressor, so I bought HarborFreight one with the Century 5hp motor.
Motor plate picture

Once I wired it up, I turned the compressor on, the motor started spinning and in a few seconds blew up start capacitor.
Start capacitor picture

I repeated the same procedure 2 more times with replaced start capacitor and had no luck in starting the motor - another 2 capacitors also blew up.

After researching, it appears that the motor doesn't reach enough speed so centrifugal switch still feeds the start capacitor more than ~3 seconds and this obviously destroys it.

I didn't really understand why it happens because as you can see the motor is rated for 23Amps and the 50 Amps breaker on the generator never trips.

That's where I started to learn about in-rush current

So I removed the belt from the motor and repeated my test with no load on the motor (although I could easily rotate pump pulley with my hands).

The motor started with no issues, I almost immediately heard that click sound produced by centrifugal switch, the motor reached full speed.

I've also noticed that once I turned it on, the arrow on the volt meter built in in my generator momentarily dropped from 240V to ~120V-140V (hard to tell cause it's half second drop), and then returned back after the click from the centrifugal switch.

So it's obvious that I had to learn about inrush current before buying a generator.

However, here is my question: since the generator is able to start the motor with no load, is there anything I can do to make my compressor working as it supposed to be? Perhaps, soft start device or something? I don't have the access to the utility electricity there, also gas powered air compressor is not an option.

Couple things:

1. Where's your compressor motor protection? The compressor should have some kind of motor-starter or protection circuit that would cut power to the motor well before the start capacitor pops.
It has internal OL. Cap is in circuit too long and overheating.
2. Air compressors are hard to start, because you're simultaneously spinning up a heavy flywheel while putting the unit under load (compressing air). We need to remove the load component so the motor can actually get up to speed. Only load to remove is whats already in the compressor bore being compressed.

The only solution I can think of is an electronic time-delay unloader. The unloader your compressor comes with turns off as soon as the motor starts. An electronic delay unloader will keep the compressor unloaded for a set time, giving the motor time to spin up.

I would do this^^^^. Get a 240v solenoid valve to keep the unloader line vented to atm. Control that sv with an on delay timer set for 5 seconds. This will split the inertia up that the motor/gen is trying to start all at once.

Might want to try this with a manual valve before you drop bigger $$$.

Motors can draw 5-7 fla's on start up and your gen cant handle that spike.

So you are in the 110 - 170A range with your generator at startup.

1. All it has is the standard pressure switch.
And that has an unloader built in to it.
As I understand, centrifugal switch on the motor is the devise that supposed to disconnect start capacitor. The centrifugal switch opens above a certain rpm – assuming the motor reaches and passes that speed.
I've never seen before any devices that would analyze if the power should be cut because the motor hasn't reached target rpm during start up. At least, not on the air compressors. But I haven't seen too much air compressors, so who knows.. The instruction doesn't mention any additional devices. They exist but not for your needs/budget. The instructions would not be expecting a 50% or more voltage sag on startup.
2. What I think is that voltage drop is the reason why the motor can't reach target Rpms and disconnect start cap. It probably could reach speed eventually with a different cap, but the existing cap wasn’t rated for that duty cycle. Your motor windings would also be taking a beating with the excess heat generated.
As I read, soft starters may significantly decrease the voltage drops. Yes by limiting the inrush current and initial torque. So I'm thinking if it makes sens to try soft starter, or if it's not applicable for my application at all by some reasons. I’ve only used 3 phase soft starts on much more stable distribution systems. Not sure single phase exists. Even if they do, you have break away torque to overcome.

Thanks, I got your idea about an electronic time-delay unloader, but I can't imagine how it would engage\disengage pulley.
It does not disengage anything in the drive train. You are not understanding what the unloader is doing.
Because the compressor doesn't start when it's empty, meaning that once it has to rotate pump pulley, even not under load, it can't. ??? If the unloader is working properly, it opens the compressor cylinder to atm upon set point pressure being reached. The air in the cylinder bore (only) is released so the motor can start under minimal load, instead of having to continue to compress air still in the cylinder. The compressor would start to compress air on the next compression cycle after it draws in new air on the suction stroke.
The unloader line is the small ¼” line going to the PS. The larger line fills the tank from the compressor head through a check valve.

Thank you, I'll research your ideas with the unloader.

But honestly, I'm thinking about soft starters. As they are actively used in HVAC, I'm trying to understand if it's applicable to my situation.

For example (don't want to mention exact brands that I googled):

Before: soft starter installed:
- 72 amps peak inrush current on mains power
- Would not start on Honda 2000i portable generator

After: soft starter installed:
-32.5 amps peak inrush current on mains power
-Started easily from Honda 2000i portable generator

Result: soft starter reduced starting surge by 55%

What type of loads? What type of cycling do they do? How long been running this way?

The capacitor popped because the motor stayed on the start-winding too long. There should be some kind of circuit breaker or thermal-overload that should have disconnected the motor long before the capacitor popped. OL protection is integral to the motor. See OP's pic. However, with the voltage dipping that low, the current is below the OL setting.

It's still forcing air through the large feed pipe to the tank and through a check valve.

Here's a test for you: Disconnect the pipe going from the compressor pump to the tank. Make sure you disconnect it on the compressor side and move the line out of the way. Then see if the generator can start the compressor. If it can, a time delay unloader will solve your issue.

Yes, but OP needs to be able to close off the unloader line once compressor flywheel is up to speed (few seconds) because the motor needs to then see the true load from the compressor as it is building pressure. This is where the generator will see the second load spike. If the unloader line stays open, it wont be the same pressure developed in the bore.

Great idea, will do, thank you.

Wonder if you could find a clutch system that doesn't engage until motor is at say 1200 RPM and then fully engage by 1500 RPM. Electrical clutches like on auto air conditioner compressors might could be modified to give delayed engage but would be an expensive thing to rig up. I know some air compressors on large truck have unloaders built into the compressor head that all the compressor is doing is moving pistons and the air moves back and forth between the two cylinders until the unloader lets them build pressure. Those unloaders typically work off a pressure regulator that keeps the air system in brake operating pressure.
A clutch system is a PIA and needlessly complicated in this application.

It would be a heck of a lot easier and have the same effect to just open up the tank's valve, but this won't solve the problem if the tank was already empty.
The unloader valve works the same way, whether the tank is empty or at a high pressure. The unloader only unloads the cylinder bore. There is a check valve between the cylinder output and the tank inlet.

Well I don't really know internalls of the pump and where is the bottle neck. When I did my tests where the capacitor had been blown, I had an empty tank and opened tank's valve.. So it's a 'first run' test, not even that one when the compressor is almost full and just tries to refill..
If the valve you are referring to is the pressure relief valve or the drain ****, then neither do anything similar to the unloader valve.

Another thing to consider is going to a smaller motor pulley. It will deliver less air but also reduce the load on the motor. Figure out the speed of the PUMP and then shoot for a pulley that will spin the pump at about 60% of the speed it is running now.
This would lower the scfm rating of the compressor and only help the running current. The “locked rotor” condition may or may not still exist.
lg
no neat sig line

Try disconnecting the pipe first and see what happens.
Then put a manual temporary valve on it as a second step and close it 5 seconds after startup or clamp a small hose on it and fold it over to pinch it off. Open the valve (hose) after compressor shuts off on high Set Point.

 

[larry_g]

Quote:

This would lower the scfm rating of the compressor and only help the running current. The “locked rotor” condition may or may not still exist.
lg
no neat sig line

You are wrong in thinking that a smaller motor pulley will not reduce the startup load. If the motor will start without the compressor head load then some reduction of the pulley ratio will start the pump. And as I said in my original post, it will reduce the air delivered. If the OP is really isolated and needs air then I'd bet he would make do with a reduced delivery system rather than none...

lg
no neat sig line

 

[mm08822]

You are wrong in thinking that a smaller motor pulley will not reduce the startup load. If the motor will start without the compressor head load then some reduction of the pulley ratio will start the pump. And as I said in my original post, it will reduce the air delivered. If the OP is really isolated and needs air then I'd bet he would make do with a reduced delivery system rather than none...

lg
no neat sig line

I never said it would not reduce the start-up load. I said it may not eliminate the problem......"The “locked rotor” condition may or may not still exist." If the motor still cant turn the load presented at start-up, then it's not starting. As far as the Op is concerned, he will still be in the same situation - no air, just money spent on a new belt and pulley adding no extra value.

You originally stated "another thing to consider". I interpreted that as something different to do instead of...... Now you reply as though it is in addition to modifying the unloader valve timing. Well sure, if in addition to, it will probably work, but why would anyone want to randomly throw away 40% capacity based upon a SWAG? What is your basis for determining 60% as the new pulley diameter?

 

[larry_g]

but why would anyone want to randomly throw away 40% capacity based upon a SWAG? What is your basis for determining 60% as the new pulley diameter?

Right now the OP has NO capacity. And 40% is a SWAG. Cheap compressors typically spin the pump quite fast, in the 1200+ rpm range. Better compressors are in the 800 rpm range. So give it a try in that range. We have no information on the compressor the OP has other than tank size and motor plate. I can only give a swag based on my experience and some guessing.

Right now the OP has wasted his whole investment, and a few more bucks may salvage the investment. Bottom line is the OP should have invested in a engine powered compressor.

To the OP, have you seen this compressor run on mains power? If not you may have a defective compressor out of the gate. Not unheard of.



lg
no neat sig line

 

[mm08822]

Right now the OP has NO capacity. And 40% is a SWAG. Cheap compressors typically spin the pump quite fast, in the 1200+ rpm range. Better compressors are in the 800 rpm range. So give it a try in that range. We have no information on the compressor the OP has other than tank size and motor plate. I can only give a swag based on my experience and some guessing.

Right now the OP has wasted his whole investment, and a few more bucks may salvage the investment. Bottom line is the OP should have invested in a engine powered compressor.

To the OP, have you seen this compressor run on mains power? If not you may have a defective compressor out of the gate. Not unheard of.

lg
no neat sig line

His generator is way undersized for this motor load. All of this discussion is seeking a band-aid around that error. An unpredicted 50% reduction in line voltage would make any properly sized motor scream during start-up. We don't know why he purchased what he did, or shoulda, coulda.

Since his prime mover doesn't have enough peak reserve to get the existing compressor load up to speed, testing the delay of the unloader valve closing is the quickest and cheapest thing to test to split the load spikes imposed on the generator. If that alone works, it is not worth reducing the compressor output. His compressor loads are not known either - maybe he cant operate with lower scfm......

 

[donpauli2]

My "Puma" 3HP 60 gallon does this also on the generator. Which is aB&S 13.5 kw start and 10.5 run with 27 HP Honda engine. Completely disconnecting th 3/8s discharge line from compressor head it cannot overcome the compressor friction and inertia on startup. The genset doesn't even pull down while trying to start it. Just not big enough inrush capacity. I ended up installing a subpanel w #3 copper from house and the compressor starts up like a shotgun blast no sweat. I guess you have no line power access so the smaller motor pulley may help that probably the cheapest fix if it works.


Sent from my iPhone using Tapatalk

 

[sberry]

Something is wrong with the genset or genset settings. I start 5 hp motors on my welders, one a 6KW and one 8. I havnt tried it on comps but pressure washer and well. 16 hp engines.

 

[jblnut]

When we install a compressor on our robotic milking farms we install a 15hp Cast Air head and a 5hp motor with different pulleys. The compressor sounds like an old John Deere two cylinder but they run forever. We have a few dozen that have been running 8,500hrs a year for 7 years with very basic maintenance.

The point being that lowering the compressor RPM's will lower the power requirement from the driving motor. A smaller motor could be used as well with smaller pulleys to lower the startup draw.

 

[Junkman]

Unless the compressor head has un loader valves installed in it, when the tank comes up to its desired pressure, it is going to shut off the motor, and he will be back in the same boat, when the compressor wants to start up again. On my Quincy, I can turn a valve, which will open the compressor valves and allow the motor to continue to spin the compressor flywheel, until air is needed again. Then the valves close, and it starts compressing air.
I will also say that the one time that I tried to start my compressor off my 14 KW generator, it wouldn't start the Quincy. This is a whole house generator, and I don't know if it might have, if I turned off all the lights in the house. It has a Baldor 5 HP motor on it.

 

[Prefix]

Hi Everyone!

The compressor is Central Pneumatic 60 Gal from Harbor Freight.

Link to the compressor on HF site

The reason why I bought that 12kW generator is just because I thought it will be enough to start the compressor (at that time I didn't know about x7 amperage at start up).

I also use this generator for my welder, so that's why I don't want a gas powered air compressor - I though generator will resolve both issues.

Ok, so I had a chance to perform some tests over the weekend. All test were performed with the empty tank and opened shut off valve.

First, I disconnected the copper pipe that goes from the air pump into the tank.

Test 1. Cooper pipe that was disconnected

With that pipe disconnected, the compressor started with no issues. I was surprised, so I repeated the test, and it started again. Then I've decided to record the video that shows what happens with the volt meter on my generator when I start the compressor, so here is the video (the compressor has started successfully too):

Test 1. Video, volt meter readings

Then I decided to connect the copper pipe back, but this time disconnect a small plastic pipe that goes from the tee that goes into the tank to the pressure switch:

Test 2. Plastic pipe that was disconnected

So now I tried to turn on the compressor, and surprisingly, it also started. I repeated the test and it started again. After that I also decided to record a video of volt meter readings, and going forward, during that 3rd attempt while I was recording the video, the capacitor blew up:

Test 2. While recording this video, the capacitor blew up

So as you can notice, in that test the voltage didn't return to the normal reading (was around 200V). That's actually why I turned it off, since it already was clear that something wrong. But when I turned my head on the compressor - it was too late - there was a smoke coming from the capacitor.

So, results are: 3 successful attempts to start the compressor without the large cooper pipe, and 2 successful attempts to start without small plastic pipe.

Based on that, I assume that some kind of unloader solenoid mentioned in the previous posts that can be integrated into the copper pipe might resolve my issue.

Any thoughts?

 

[American Locomotive]

You're going to need a Delay-On-Make timer, and an normally open solenoid valve connected to the large copper pipe. Something like this http://www.ebay.com/itm/SSAC-TMV800...357165?hash=item51eac876ed:g:wS4AAOSwdIFXzt9~ and this http://www.ebay.com/itm/1-2-inch-NO...hash=item1a047449dd:m:m4zp8Lx-J4YtQNKt_f_N1Pw.

The timer gets connected in series with the solenoid valve, and then the setup would be connected in parallel with the motor terminals on the pressure switch. I could make a diagram to better illustrate it, if needed.

So the compressor would kick on, the valve would be open and venting air, after a set time the timer would engage, closing the solenoid and allowing the compressor to function. It resets when the pressure switch cycles off.

You could also do the same with a normally closed solenoid and an "interval" timer. But the interval timers tend to be harder to find.

 

[Radix2]

Hi Everyone!

The compressor is Central Pneumatic 60 Gal from Harbor Freight.

Link to the compressor on HF site

The reason why I bought that 12kW generator is just because I thought it will be enough to start the compressor (at that time I didn't know about x7 amperage at start up).

I also use this generator for my welder, so that's why I don't want a gas powered air compressor - I though generator will resolve both issues.

Ok, so I had a chance to perform some tests over the weekend. All test were performed with the empty tank and opened shut off valve.

First, I disconnected the copper pipe that goes from the air pump into the tank.

Test 1. Cooper pipe that was disconnected

With that pipe disconnected, the compressor started with no issues. I was surprised, so I repeated the test, and it started again. Then I've decided to record the video that shows what happens with the volt meter on my generator when I start the compressor, so here is the video (the compressor has started successfully too):

Test 1. Video, volt meter readings

Then I decided to connect the copper pipe back, but this time disconnect a small plastic pipe that goes from the tee that goes into the tank to the pressure switch:

Test 2. Plastic pipe that was disconnected

So now I tried to turn on the compressor, and surprisingly, it also started. I repeated the test and it started again. After that I also decided to record a video of volt meter readings, and going forward, during that 3rd attempt while I was recording the video, the capacitor blew up:

Test 2. While recording this video, the capacitor blew up

So as you can notice, in that test the voltage didn't return to the normal reading (was around 200V). That's actually why I turned it off, since it already was clear that something wrong. But when I turned my head on the compressor - it was too late - there was a smoke coming from the capacitor.

So, results are: 3 successful attempts to start the compressor without the large cooper pipe, and 2 successful attempts to start without small plastic pipe.

Based on that, I assume that some kind of unloader solenoid mentioned in the previous posts that can be integrated into the copper pipe might resolve my issue.

Any thoughts?

my thought is that yah, maybe you can get it to squeak by, maybe, most of the time - still not like the conditions when your tank is under pressure - so is it worth pursuing this ? - I say NO.

take that compressor back to HF. Buy a smaller one that starts easily. If you need more air - see if a bigger tank will suffice, if not, get a second small compressor that will work on your generator for those times and run them both with slightly different pressure settings.

Two smaller units will start easier and can give as much or more air then the big unit. Do you really plan long high flow uses like blasting, etc. that need a 5hp sized continuous flow?

 

[American Locomotive]

my thought is that yah, maybe you can get it to squeak by, maybe, most of the time - still not like the conditions when your tank is under pressure - so is it worth pursuing this ? - I say NO.

With a timed solenoid valve, the tank pressure won't matter. The compressor will always start up with 0 load, then after a set amount of time (say 5-10 seconds for everything to stabilize and be happy), the valve will close and the compressor will start compressing.

 

[Prefix]

I have a sandblasting cabinet. Nothing crazy, I'm just a weekend warrior, but that's why I want 5hp continuous flow.

Speaking about the timer, I thought it can be eliminated, because the solenoid can be connected to the start cap. In this case, it's disconnected as soon as the motor will start.

In regards of the condition when the tank is under the pressure - there were advises to install the check valve as well, as I understand it should resolve that issue.

Personally, when I did these tests, it felt like the compressor starts with no problems when the copper pipe is disconnected.

 

[Radix2]

With a timed solenoid valve, the tank pressure won't matter. The compressor will always start up with 0 load, then after a set amount of time (say 5-10 seconds for everything to stabilize and be happy), the valve will close and the compressor will start compressing.

The theory here is that the system is so marginal that the unloader pipe orifice effect is the difference between failure and success (tank is unpressurized so it is not like the built in unloader is doing much at this point).

To me that is asking for trouble and not worth the effort to rig all this up.

As the starting cap ages, temp varies, gen timing varies, etc. the thing it liable to fail.

It looks like the gen is on the margin of being able to start the motor and flywheel load, no need to go further. IMO.

 

[Radix2]

I have a sandblasting cabinet. Nothing crazy, I'm just a weekend warrior, but that's why I want 5hp continuous flow.

Speaking about the timer, I thought it can be eliminated, because the solenoid can be connected to the start cap. In this case, it's disconnected as soon as the motor will start.

In regards of the condition when the tank is under the pressure - there were advises to install the check valve as well, as I understand it should resolve that issue.

Personally, when I did these tests, it felt like the compressor starts with no problems when the copper pipe is disconnected.

You will certainly need a check valve after your solenoid valve...otherwise it would vent your whole tank...

About how easily it starts... what is the real diff beween copper pipe and no? - with it, the pump flows into a empty tank, without it flows into the air...so it is just the flow restriction (and maybe a check valve if it is in the tank fitting) - that is not much margin for you to live by ...

 

[American Locomotive]

As the starting cap ages, temp varies, gen timing varies, etc. the thing it liable to fail.

It starts fine 0 compressor load. It takes it a bit to get the big flywheel spinning, but it's no big deal. Even in the vent it doesn't start what's the worse that happens? It pops the cap and trips the motor overload/breaker? Maybe smokes the motor?

I have a sandblasting cabinet. Nothing crazy, I'm just a weekend warrior, but that's why I want 5hp continuous flow.

Speaking about the timer, I thought it can be eliminated, because the solenoid can be connected to the start cap. In this case, it's disconnected as soon as the motor will start.

Do not tie into the start capacitor.

You will certainly need a check valve after your solenoid valve...otherwise it would vent your whole tank...

About how easily it starts... what is the real diff beween copper pipe and no? - with it, the pump flows into a empty tank, without it flows into the air...so it is just the flow restriction (and maybe a check valve if it is in the tank fitting) - that is not much margin for you to live by ...

No, it would not vent the tank. There already is a check valve is located on the fitting in the tank itself. So the entire copper tube, etc... all gets vented when the unloader opens. The problem is when the unloader closes, the check valve has a certain pressure required before it pops open. This extra pressure is a little bit too much load for the motor during startup.

 

[mm08822]

Prefix,
If you can provide the answers to the below q's, I might have an easier solution for you........

I tried to find the exact PS cut sheet and not certain that what I found is fully correct as website doesn’t show MDR11/11EA. Can you confirm the part # inside the pressure switch? See screenshot below

Please confirm your pressure switch does have an unloader valve on it, probably one of them as pictured in the screenshot below.


The compressor already has a check valve installed (part #4).

Is the plastic tubing you disconnected from part #33 to the port on PS (part #22) or the unloader valve (if present)?

 

[Prefix]

I don't remember exact part number, but the PS is actually not original, but replacement part that I've bought here:
Powermate Vx 034-0184RP Pressure Switch
I clearly remember it's 125-155 or 120-150psi. I bought it as exact replacement for the original one that I accidentally broke during wires installation.

I confirm that it has a port where that plastic pipe was going that I had disconnected in the test #2. That port looks like Г located under PS box, however I don't know it's purpose.

PS under slightly different angle. There you can see a blue end of that port.

This is the link on the ORIGINAL PS that was replaced with the one above (had the picture in my phone):

Original PS

But the are literally the same except small details (the original shows that it can withstand 165psi, but I do remember it was setup for cut-in \ cut-off 125-155 or 120-150 as it had another label underneath so that's how I bough my replacement PS).

The compressor already has a check valve installed (part #4).

I do remember that part, that's what I meant when I mentioned 'tee' between the tank, copper pipe and the plastic pipe.

Is the plastic tubing you disconnected from part #33 to the port on PS (part #22) or the unloader valve (if present)?

The plastic tubing was going from 33 into 22, in that Г-shape under PS with blue end.

UPDATED: I found more details about that PS in the Internet and it says:
* Q: Does this pressure switch also include an unloader valve as part of the assembly?
* A: Yes it does, located under the pressure switch assembly.

So yes, that Г-shape port is unloader valve.

 

[mm08822]

Prefix,
In test #1 with the large copper tubing disconnected, the compressor head open is open to atm. There was no back pressure present on the flywheel when you started it each time.

After you connected the large copper tubing and disconnected the ¼” plastic tubing, there was no back pressure present on the flywheel.
In test #2, you then started the compressor with no initial back pressure. As the compressor ran, the ¼” line was bleeding off some compressed air. When the compressor was stopped, the ¼’ line continued to bleed off any air pressure remaining in the head.
Resulting in no back pressure present on the flywheel.
You then repeated this.
All reasonably good so far.

Upon the 3rd restart, is where it gets a little concerning. Here the cap blew and the voltage remained at ~200V so you shut it off?
I don’t know if you repeated these tests too quickly or the cap was going out anyway. (This whole test is a band aid on properly fixing the mis-match between load and generator.)
How much time in between restarts occurred?
How long after the ¼” line was fully done blowing off (no more hissing) did you restart the compressor?
Was the 200VAC still seen after the compressor was disconnected and generator running or do you get 240vac again?

Here is how I think you can simplify accomplishing the same effect of the unloader valve closing delay while the motor gets up to speed:
Replace the ~6” of ¼” line with 50’ of ¼”plastic/copper line (psi rating above compressor max). Once the unloader valve closes on start-up, the 50‘ of line will take some time to reach high pressures that is now quickly built up after a few revs and that load quickly impressed against the flywheel never allowing the motor to get up to speed.

If this works, it will be an annoying release of air at end of each cycle. The pssst you may now hear will grow to psssssssssssssssssssssssssssssssssssssssssssssst! But there wont be any electrical parts to add – purely mechanical.

Even if this works for you now, I still don’t know if you will be needing caps by the dozens or soon smoke your motor/generator.

 

[66cj225]

Following the genset theme, what gauge wire, how long, what is it made of? I use a marginal gen- motor combination with rated twist locks, copper SJO cord about 6 ft long, and the motor contactor is the weak link (in this case it sounds like your pressure switch). The coil voltage in the contactor will be wrong for the draw down of inrush and will fry the contacts. Been there.

 

[Prefix]

mm08822, there were few minutes of delay between my tests. For the last one or two tests (when only plastic tubing was disconnected) I couldn't start my generator for 3 minutes, it didn't react on key, could've been some thermal protection after previous 4 start \ stop tests.

But then it obviously started when I waited a little bit more. Unfortunately, I don't remember it the cap died after that or I had another successful attempt for test #2 and it died the next time. I didn't check my gen after that because it was the last capacitor I had.

Anyway, I see your point. Also, my generator has 50Amp breaker and it never tripped.

Speaking about wires, it's a Home Depot 4 ft. I believe 6 gauge wire:

Home Depot cord

 

[66cj225]

When the 50 amp breaker pops, the connections are good! I start 3 hp motor with 5 kw but it's a lightly loaded hydraulic pump.

 

[American Locomotive]

Can you do one more test? Disconnect the copper line at the compressor pump. Start the compressor up, and then reconnect the copper line with it running. The idea here is to verify the generator is actually capable of carrying the load of the compressor before we go any further.

 

[nsula_country]

I have been following this. Many good points.

I built a 150 gallon, 13 hp, gas compressor in the past. Pneumatic unloader.

I cannot believe that you have a 5HP compressor going thru a pressure switch alone, even though it is rated 26 FLA. I would assume it would need a contactor or starter.

I like the idea of using a long coil of tubing to create a pneumatic delay. This may be the simplest, cheapest test yet.

Capacitors... Have you tried a higher voltage rated cap? Like 370V or 440V? I saw that the original was 250V. With caps, one can replace with a higher voltage rating, but not lower.

Subscribed...

CT

 

[Prefix]

At this time I can't make other tests because I'm out of capacitors

Going to order a new one.

I honestly don't think that higher voltage capacitor will help because the issue is that the voltage even lower that required. But since I have to order new capacitors anyway, I can order 370V, just for fun.

Speaking about PS and contactors - well, it's Harbor Freight, you know.

 

[larry_g]

At this time I can't make other tests because I'm out of capacitors

Going to order a new one.

I honestly don't think that higher voltage capacitor will help because the issue is that the voltage even lower that required. But since I have to order new capacitors anyway, I can order 370V, just for fun.

Speaking about PS and contactors - well, it's Harbor Freight, you know.

I would have thought that you might have considered at this point your not able to start this compressor with an empty tank, how are you going to start this with a load in the tank. An unload er can only do so much.

Check out the engine HP on an engine driven compressor with the delivery specs of your compressor and see what it is. Now compare that engine to the engine on your generator. Now add in say 20% to 50% for electrical losses in the conversion of the generator and motor. If the engine on your generator is not bigger than the one on a comparable compressor it ain't happin in my opinion.

lg
no neat sig line