What's new
What's new

Rate my RPC

PHULL

Aluminum
Joined
Mar 26, 2008
Location
Australia
Ok I made a RPC last night and I will post photos of it tonight.

So far I have a 3 hp three phase motor for a idler motor, a motor start switch and a 4 pole three phase 10A switched outlet.

the basic structure is a arch of aluminum stirp bent around the motor cage and secured at the motor base. the motor was a Junk one and it must have been used as a pump motor in a previous life it came with a mild steel plate base and sheet metal guard over the shaft with a lovejoy coupling.

On the aluminium stirp I have mounted the three phase plug and the box containing a 370 uf start cap, a momentary push button and some terminal strip.

so far I have the single phase coming from the motor start switch to (l1, L2 straight to the motor and then off L2 a push button and then this is connected to the Start cap ( Am I ambitious about this switch surviving the first test? )

anyway I will post photos tonight so you can give me some constructive input.

CHeers
 
Remember in Australia 3 phase power is 415V not 240V, these US RPC designs will produce 240V 3 phase on local power, there will be very little that this RPC will run except some small motors ( up to 5 HP) which have been rewired for 240V operation, you need to hunt up a 240/415V transformer preferably isolating but not essential. If your property has 2 phase 415V power you are laughing
 
all it has to run is a bandsaw and maybe a lathe, considering I made it out of scrap materials for about $30, i'm not powering a factory with it the largest machine motor I run is about 1 hp anyway. looking at the ebay VFD's and the features the have I might just snap one up
 
phase1oy0.jpg


here is a photo of my phase converter, so far I have managed to get it to fire up. next step is to make it run something.

phase2do1.jpg
 
"Remember in Australia 3 phase power is 415V not 240V"

I was shocked ... SHOCKED ... when I first traveled to Australia to install the first Amdahl mainframe computer in Australia, at QANTAS.

The electricians insisted on running Type MI cable for the machine's three-phase power, which, as usual for mainframes, was 208 volt, 415 Hz power ... not 415 volt, 50 Hz power.

Now, Type MI is almost exclusively found aboard ship, and is a copper tube with mineral insulation which separates the enclosed conductors.

Special termination are needed.

And, this was for an interior installation, at QANTAS Centre in downtown Sydney.

Possibly required because the wiring was run in an underfloor plenum.
 
Peter
The electricians insisted on running Type MI cable for the machine's three-phase power, which, as usual for mainframes, was 208 volt, 415 Hz power ... not 415 volt, 50 Hz power

Pyro, my fathers favourite sort of cable, this was common on fireproof applications 25 or more years ago, 40 years or more ago it was common for general purpose industrial wiring in arduous locations. It is not uncommon for cable to be specified which is capable of withstanding much greater environmental extremes than the equipment that it supplies, somebody in engineering was just overspecifying or was an engineer with an english background where pyrotenax was widely used. IMHO it is still one of the best extreme environment resistant cables.


PHULL did you rewire your motor delta? if not you should because you will only be using a fraction of the motors capacity otherwise. If you do not understand this post a picture inside terminal box on the motor and I will explain it.

4 problems you will encounter running a typical 415V bandsaw off 240V

1 The motor starter will not hold in Solution, change the coil in the starter contactor to a 240V one

2 The motor will lack power Solution wire the motor in delta

3 Once the motor is wired in delta the thermal overload keeps on tripping. Solution increase the Amps setting on the overload by 1.73x

4 The blade welder doesn't work properly, solution get a 240 to 415V single phase transformer just to run the welder transformer.

You will encounter the first 3 problems with almost any 3 phase machine, getting a 240V to 415V transformer to run your rotary convertor will avoid these problems also you will not need to rewire your rotary convertor motor to delta.


A cheap and nasty source for a 240 to 415V autotransformer is the CIG transarc tradesman welder, they are usually both 415 and 240V, just a matter of putting 240V in the 240V tap and taking 415V out the 415V tap. You can still use if for welding as well, these machines are cheap secondhand.

Unlike in the US rotary convertor power is quite a bit different to utility power in Australia, care and understanding is needed before using it to power a machine OTOH 3 phase power is easy to get in most residential premises
 
Last edited:
Cheers for that Helical

The RPC was wired for Delta, it was originally wired that way, now I'll go take a few photos of whats inside both boxes to show you (RPC and the Band saw box). The first point you made about the motor starter coil not engaging sounds right. I will also dismantle the starter switch and get some photos of that too.

thanks for your help.

In a perfect world I would lay out the cash and get three phase wired to the house.... problem is it isn't my house, so I have to make do while I can.
 
phasebox1qm4.jpg


phaseplateyt1.jpg

Here are some photos, the first one is inside the terminal box on the RPC motor and the second one is the Name Plate of the motor and it's wiring diagram. it looks like it is wired in delta mode.

More photos to come I am waiting for them to upload

bandsaw1cx2.jpg
photo of the bandsaw for interests sake, a Atlas Brand

img0191bu5.jpg

Photo of the Motor Start switch, I see what you are talking about Helical Cut the coil is 415 volts.

bandsawswitch2yq2.jpg

a photo of the switch with the cover off, I have removed these off old machinery before and the always had the contacts bathed in oil? where is the oil kept in this design? Does anyone know where I find a 240 Volt coil to suit a switch like this?

bandsawswitch3wd7.jpg

The oil goes into the little pots on the bottom of the front of the switch? I would pull it apart but I was thinking it was apart of the saftey cutouf mechanism I think I have a frontal shot of the dashpots and the coils

bandsawmotor1uf4.jpg

some reason the previous owner liked all red wires this makes my life hard... also can't tell what configuration it wired into :( no idea why the terminal block is taped up. the metal box covering the terminals was damaged so I will replace it with a pvc one and fix the terminal block so it can hit the cage of the motor
 
Ypur RPC motor appears to be wired delta as you stated before.

The terminal block should come out and there should be 6 wires coming out of the motor, 3 should be connected together. Check if the insulation on the motor wires is still soft and pliable before even thinking of changing them.
If there are only 3 wires, think about making a 415V RPC. Do not worry about the starter yet, modifying the motor is more important..

Provided there are 6 soft wires, seperate the 3 joined wires and check the resistance between each wire and one of the wires going into the terminal block, you are trying to identify windings, any 2 wires with a low resistance is a winding. Once you have identified the 3 windings, connect the end of one winding to the beginning of the next to form a delta, power is applied to the 3 connections. Hope that makes sense.

The three red wires is very common practice they are all live, you do not need to know what they are, if the motor spins backward swap any 2 to reverse it.

With new equipment changing the starter voltage and the motor voltage is relatively easy but with older equipment it can be a bit of work

I know what needing 3 phase in a rented house is like, I used to run a 3 phase generator every time I needed 3 phase, the neighbors were not impressed.
 
Cheers for you help again Helical,

so if I am luckey enough to find 6 wires that are not brittle coming out the machine I am in bussness and have the machine in delta mode. what would you do about the solenoid coil being 400V to activate... I have been searching for a solenoid to adapt but to no avail. most of them have too much travel and too much force. :willy_nilly:

if i find that it only has three terminals coming out... and I have to go to 415V wouldn'y it be easier to run a 240V to three phase Vfd instead? something like this thing? and bypass the magnetic swtich all together.

http://http://cgi.ebay.com.au/Brand-New-2-2-KW-3HP-3P-415V-VSD_W0QQitemZ280227228421QQihZ018QQcategoryZ57125QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
 
It was good that the motor has 6 wires, the rest is easy, remove all wires from the starter and toss it in the bin, replace with newer starter and scrounge a 240V coil for the contactor or use a 240V vfd, the vfd will give better control over cutting speeds so the saw can be run slow for hard steels and fast for non ferrous.

There are some motor starters which do not have contactors, just overloads they will work on 240V but they rely on the overload to protect the motor from phase failure, not that the the other ones are much better usually if L2 fails the starter will stay in. The contactor style starter also prevents restart after power failure.
 
Ok so I modified the start switch and switched the 400V solenoid coil for a 240V one, and it still makes the same noises, so do I need to adjust the dashpots on the bottom to adjust the trip amps?

I think I will revert it back to original and bypass it all together and go VFD, and I could also use it for my lathe too. the bad news is I found the motor only has three wires coming out of it :( so even if I did managed to get the switches to work I would still have little or no drive.

I will sourced a VFD the other day I will show you the progress, it will give me a excuse to practice my solid riveting technique. ( I am building a monocque race car at the moment using solid rivets)

Cheers
 
If the motor has only 3 internal wires then a VFD will not help, the motor needs to be wired in delta, to operate off 240V. I would not have bothered reworking that old starter, easier to pick up a newer one from a scrapyard or ebay.

I would be looking for a transformer, even if a 240 to 415V isn't available, series connect the secondaries of anything available to get the voltage, the scrapyard is a good source of such things, pity the high price of scrap has inflated the price of motors and transformers.

Let me know how the race car goes, I have a tubular frame one that I am rebuilding, monocoque's are nice and stiff but a PITA to repair after the inevitable bingles.
 








 
Back
Top