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Old 02-25-17, 04:49 PM   #21
Elcam84
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The clutch was just an idea.... But will be interested to see how it works out and what works best.

I have never liked the magnetic clutches on mowers not just because they readily fail and are expensive but because of the harsh engagement. I can see that need on something that needs a big jolt to get it going but not on a couple blade as they aren't that heavy.

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Old 02-25-17, 11:43 PM   #22
oil pan 4
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I pretty much have to start the single phase motors unloaded so it needs a clutch of some sort.
The 3 phase motor on a VFD is going to just be belted to the compressor with solid pulleys and no clutch. Just like a normal compressor with solid pulleys.

Last edited by oil pan 4; 03-07-17 at 11:40 PM..
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Old 02-28-17, 12:45 AM   #23
oil pan 4
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Alright I have my ABB drive and motor working in hand control only.
The ABB drive has digital input that could be controlled with pressure switches and used to ramp up the speed.
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Old 03-01-17, 06:28 PM   #24
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Turns out the cheapest most effective way to reduce start up inrush was sitting in front of me the whole time.
I put the gocart clutch on my 2.5hp 2pole compressor. I knew it was going to need a smaller belt. The cart clutch is a 3.2 inch pulley and the solid pulley I had on there was a 4 inch. I had a slightly smaller belt, but it wasn't small enough.
The original belt was way too big and I didn't have enough adjustment built in to my design to take out the slack, the next size smaller belt was just too small with the motor adjusted all the way in. I finely got around to taking both belts to the store and selecting a size between the 2.

The results are that the motor which had a start up inrush of 45 amps is now down to 23 amps with the smaller clutch pulley.
Now if I welded on a bigger pulley added mass and lowered the mechanical advantage the motor has on the compressor even further with a bigger pulley it might peak at 25 amps.
Still down 20 amps from the original inrush is amazing.
I may even be able to use resistor start to further lower inrush if needed.
But I'm replacing this 2.5hp 2pole motor with a 2hp 4pole and electromagnetic clutch. They're already on the way.
I should say the magnetic clutch is already here, just waiting on the motor.
The end?
No not even close I still have a 3 phase 4pole motor on an ABB drive to get going and the 4pole electromagnetic clutch to make happen.
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Old 03-04-17, 01:08 AM   #25
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The 2hp 4 pole motor I ordered came in.
Full power starting it free spinning with no power factor correction it hit 14 amps. Resistor starting reduced it to 11 amps. Power factor correction should reduce that by an amp or 2.
That's half of what the 2.5hp 2 pole motor was drawing with the go cart clutch.
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Old 03-05-17, 06:27 AM   #26
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I tried putting the go cart clutch on a 4 pole motor and as I expected running the clutch at half speed would not engage the clutch at all.
I took the very strong spring out of the clutch and replaced is with a much weaker spring and it works very well. It looks like it will reduce inrush current from 15 amp down to 9 or 10 amps.

I was told that there wasn't anything I could do to soft start or reduce starting current on an air compressor with a single phase motor (not on here, you guys are npt so negative).
Well on my original 45 amp inrush compressor, just adding a simple go cart clutch cut its inrush in half. For $50 to $60 this will likely be the simplest one step, most bang for the $ way to reduce starting amps.
I am going to replace the 45 amp inrush 2.5hp 2 pole motor with a 2hp 4 pole motor and magnetic clutch and likely further reduce inrush to between 10 and 15 amps. Yes I will have to give up about a half horse power but I will be reducing inrush by up to something like 77%. It wasn't cheap, it wont be super simple but it will happen.
So its not looking good for the nay sayers.
I'm glad I don't listen very well.

Last edited by oil pan 4; 03-07-17 at 11:31 PM..
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Old 03-09-17, 05:47 AM   #27
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The armatures of induction motors are not designed to work in excess of 6Hz more time spent below about 3,300rpms will build extra heat in the rotor.
This soft starter appears have terminals for the start circuit so I'm guessing it's on a timer to prevent burning out the start cap.
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Old 03-09-17, 11:51 PM   #28
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I needed a much larger than normal 56 inch belt to connect the 2hp 4 pole motor with 6 inch pulley to the compressor. It came in and I finally tested it.
The motor inrush full power starting the compressor and motor together is about 17 amps.
That's a huge reduction from the 2 pole 2.5hp motor that was hitting 45 amps on start up.
Free spin starting the motor hits 14 amps.
Free spin starting the motor with resistors is hitting 10 to 12 amps. But I have not tried all my methodsto reduce starting amps like trying a slightly smaller start capacitor or different resistance values.
When I engage the clutch on the motor running at full speed to the unloaded compreasor the motor only surges up to about 6 amps.

Compared to go cart clutch starting the go cart clutch start hits about 110 to 120% of unloaded starting amps. Which works pretty good for only changing one $50 or $60 part.
Only thing is the go cart clutch comes in one size, 3.2 inches which doesn't work real well with most 4 pole motor setups.

Quote:
Originally Posted by LarryBertsc View Post
The armatures of induction motors are not designed to work in excess of 6Hz more time spent below about 3,300rpms will build extra heat in the rotor.
This soft starter appears have terminals for the start circuit so I'm guessing it's on a timer to prevent burning out the start cap.
I know I said that on post #2.
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Old 03-20-17, 09:46 PM   #29
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I took the 2hp motor put in a smaller start capacitor, with some testing I found the smaller capacitor starting amps trending slightly lower and we're being more consistent.
I also took my big 8 amp 25 ohm rheostat and hooked it up to my resistor start test rig in place of one of the 5 ohm resistors. Found that this motor likes closer to 15 ohms of start resistance.
This lowered staring amps to a consistent 8 amps on the unloaded motor.
Energising the magnetic clutch to the motor running at full speed only peaks at 7 amps.
Tested the pneumatic unloader it drops running amps to 4.5
Full load shut off is at 7.5 amps. With a .96 powerfactor.
Going from 45 inrush amps down to 8 is pretty darn impressive.

Last edited by oil pan 4; 03-20-17 at 10:21 PM..
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Old 03-20-17, 10:42 PM   #30
Elcam84
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That's a nice big drop in amps. Been looking at a new planer and cyclone and the 3 hp and 5hp both pull the same amps on the label... The import motors are horribly inefficient and pull more and most than they should for a given hp.

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