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
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....
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.
Unfortunately, you are at the point where there is a big jump in VFD
cost. A 3HP/2.2kW 220 single phase to 220 three phase inverter can be
had new for $250, but the same thing in 5HP/3.75kW is $600.
You could probably ebay those inverters you have for enough funds to buy
the proper VFD. What are the actual specs on the inverters?
I wont actually have the inverters here till this weekend but I know that
they will run this compresser because both the compresser and inverter are
the same as used on service trucks in the army. I got this from a guy who
had 2 of each of the compressers and inverters, he used one compresser
hooked to mains power because he has 3 phase. I got a good deal on both
inverters and the compresser I bought. I was told these inverters would
retail for over 1500 dollars apiece. I'm not sure of the specs till Friday
or Saturday but I'll post as soon as I know more.
On Wed, 10 Feb 2010 23:19:09 -0600, the infamous Ignoramus5008
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
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 21:00:40 -0500, "Dixie Drifter"
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
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...)
--<< Bruce >>--
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.
On Fri, 5 Mar 2010 15:05:04 -0500, "Dixie Drifter"
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.
--<< Bruce >>--
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