I just got an Atlas Copco LF3-10 compresser at a GREAT price. It has aLeroy Somer LS100lt 3 phase motor. My problem is I have no experiance with 3 phase wiring however I do have 2 24 volt dc in 230 volt 3 phase out inverters. My question is should I try and build a rotary converter or just run from a battery bank and inverter? I am in South Carolina and I only have 220 single phase service here.This is an oil-free unit from a mobile service truck it was new on the pallet when I got it.
750 watts per horsepower, so that's about three HP, no way you will run that off batteries. change motor, or you might try a static converter, or even a VFD - I run my 6 HP mill on a static converter (that's a fancy name for a capacitor and a relay), it may work for you
Why not? Yer basically just providing start caps for a 3 ph motor so it will start off single phase, as if it were a rotary converter, no?
the relay Bill mentioned would be NC in series with the start capacitors, and then would open when the third leg generates enough juice. ie, the coil of the relay would be between either line leg and the generated leg. Or so I think....
Get a single phase motor or peddle the compressor and get a 220 volt single phase compressor. There are lots available. And if the oil-free unit is as loud as most of the oil-free units then for sure peddle the compressor and get a conventional one.
On Wed, 10 Feb 2010 23:19:09 -0600, the infamous Ignoramus5008 scrawled the following:
2,600w divided by 746 = 3.48 horsepower +- efficiency rating.
-- In order that people may be happy in their work, these three things are needed: They must be fit for it. They must not do too much of it. And they must have a sense of success in it. -- John Ruskin, Pre-Raphaelitism, 1850
You can use a rotary converter that runs continuously while you are in the shop, but NOT a static inverter like a Phase-A-Matic - compressors need all their horsepower as they approach peak pressure shutdown.
And they start too often, and automatically - if something goes wrong with a static inverter and the motor fails to start... No matter how fancy, I have seen staged systems that pre-start a rotary converter idler first fail, and static inverters fail, and the results can be disastrous. You really need to be there to cut the power.
The best bet is a Variable Frequency Drive, if the motor is rated to handle it - most newer motor are, but you have to check the paperwork to be sure. That's the ONLY way that I consider safe for unattended operation, as the VFD will go into protective mode and shut down.
And the VFD you buy has to be rated for single-phase input at the needed load, too. Some are, some aren't. Some are, but you have to derate it and a nominal 10-HP drive can only handle 5 or 7.5 with single phase input. Read The Friendly Manual.
Special hookup is needed. You NEVER put any switches or controls between the VFD and the motor (unless specifically allowed by the VFD builder), or the VFD blows up when the load suddenly disappears and the contacts in the starter start arcing over.
You want to wire the pressure switch on the air receiver tank to the remote Start/Stop leads on the VFD, not inline between the power source and the motor. The VFD will handle all the starting and stopping for you.
(But you still need a safety switch on the wall to cut the power feeding the VFD, so you can lock out for service. Having the motor start in the middle of a compressor oil change, or with your hands inside the belt cage replacing the vee belt is a bad thing...)
OK I know the inverters I have will run this compresser because they are used togather on military service trucks. I was just wondering if the loss of going from AC to 24VDC back to 2203 phase AC will be more than the loss of letting a rotary converter run an idle motor. I had actually thought about using a 24VDC alternator off a semi truck running from a 5 hp 220 motor with a couple deep cycle batteries inline to the inverter.
For the next month or so I'm putting this off as my sister and brother-in-law had to postpone bringing me the rest of the accessories to hook this up. I still need the tank, pressure switch, and the inverters I bought out in Kentucky. I could kludge something to work but as I already have 3 other working compressers I'm in no hurry. I'm thinking of buying a leblond lathe with a busted gear in the drive box for 100 bucks so that will probally keep me busy at least a week or two.
If you need to use this in a domestic truck (not an Ex-Military that came with a 24V electrical system) I hope you have plenty of room under the hood for a second alternator...
The easiest way is to rig two 12V Deep Cycle batteries in series in the back, hang an independent alternator off the engine somewhere, and come up with a serpentine belt that's a just the right value of "just a bit longer". After that, all you need is a relay to slave the alternator excite line off the 12V Accessory circuit, and a 24V pilot light or two for the Alt Fail light.
(Trying for a true "Self Exciting" 24V alternator might be a bit much to ask. They barely get it right at 12V for street rods.)
A 24 VDC to 240 VAC 3Ph inverter and battery bank COULD be rigged up to recharge (not run) from a 12V alternator, but it will A) put a hell of a strain on the regular alternator unless you start stealing
300A units from a Class 8 Truck, and B) the wiring of series-parallel changeover relays will be complex and error prone if you can't use one big honkin' contactor to do it all at once.
If you try doing it with a half dozen starter-style relays (and get the ones rated for Continuous Duty!!)... One relay hangs or welds on the change-over, and you'd better have everything fused with Mega Fuses or big breakers. Cause the fireworks are about to start.
Myself, I'll save the conversion losses and get a 56C frame 12V DC motor to run a compressor from, or a direct-drive compressor using the same motors - they are easily available 1/4 HP up to 1 HP, but they are not cheap.