Wiring an Agazzani

[ian maybury]

Hi guys, pardon my coming back to the well again. :) As posted before I sourced a used 5.5KW Transwave (UK maker) rotary phase converter to run the 400V/50Hz/3kW/3ph UK spec Agazzani NRA-600 (very sim. to the B-24) I bought some time ago.

The workshop isn't ready yet, but I've been (with help from various generous people) figuring how to wire it and the above two items in the meantime. I'd appreciate a little confirmatory input though. The problem is that my electrical knowledge is limited, and the wiring diagram in the manual is fairly basic. (no names for components, no wire numbers or colours)

The converter maker says that L3 is the 'synthetic' phase the converter creates, and that it's best to take the 400/230V transformer connections for any 230V emergency stop and/or control circuit from the full voltage phases L1 and L2. It also says that when starting the machine that it's best to switch straight from the start/star setting on the manual starter into delta/run (not to delay in star) - as the converter prefers this.

Also there was a badly burned out 25micro F 40mm dia x 93mm long capacitor wired across the Y/T8 and Z/T9 terminals on the star delta switch which I'm proposing to remove. It was fairly clearly fitted in the field (not in the Aggie wiring diagram, no mounting, no proper cable terminations) - maybe by the UK supplier to help the saw get started on the (different and possibly static) converter the previous owner was using.

I've already had help from some generous friends, and think we've identified that the transformer connections are made by inserting the two wires into the L2 and L3 input terminals respectively on the main start/stop rotary switch. So re-connecting the transformer to suit the converter should only be case of switching one transformer connection from the L3 to the L1 terminal. So......

1. Is re-connecting the transformer as above likely to cause any unwanted problems? I don't think so, but there's normally open and normally closed switches in the 230V circuit with dotted lines from them (in the diagram) to the start/stop switch (N/O) and star delta switch (N/C), and I'm not quite sure what that's all about.

2. Any ideas on what the stray capacitor was about, and how it might have been intended to work?

3. Will switching quickly into delta immediately after starting cause any problems, and why is it recommended by the maker of the converter?

Thanks,

Ian

[Stephen Cherry]

Ian

For electrical diagrams, a picture says a thousand words. It's really not difficult to run a motor, but there are a few ways to do it, so without knowing the components involved, it's hard to comment.

That said:
1. All the transformer connections should come from the non-synthetic phase. My machines won't work exactly right if the controls use the synthetic phase. Usually when you wire a three phase machine, you just wire each of the three phases arbitrarily. If the motor turns the wrong way, you reverse two of the wires. With the phase converter the two of the three wires that the transformer are taken from come from the non-synthetic phases. If the motor turns the wrong way, switch the two non-synthetic wires, leaving the synthetic connected.

2. It sounds like someone had a start capacitor wired in. This could be used to help the machine start using a phase converter, or to just start it as a static phase converter (the motor can be started from single phase if you connect the right capacitor to the non-wired phase during startup). The idea would be to run a capacitor from one of two non-synthetic connections to the synthetic connection during start up. This is how a rotary phase converter typically starts. The problem is that these capacitors can only run for a short time before they burn out. Just a few seconds is all that it needs, and some longer time will cause problems. With a phase converter, you probably won't need this.

3. Switching into delta immediately is the way that most motors start. Star delta is the exception, and typically not done in the US. I worked as a control system engineer for a long time, and did not run across that configuration until I bought a European sliding saw. My guess is that it is used to meet regulatory requirements, or to allow the use of skimpier wiring. A bandsaw needs all the help it can get thought- highly inertial.

[ian maybury]

Sorry Stephen, I forgot to post the wiring diagram - it's attached now. It's for the US spec saw, but seems the same as what's physically in mine except for the voltage and frequency difference. (our 3 phase is 400V/50Hz, with 230V/phase. There's no neutral wired to the saw)

On mixing phases. The transformer issue could presumably also be solved by exchanging L3 and L1 back at the plug where the saw cable connects to the converter, but I was presuming that I shouldn't do that as it would leave the phase labeling on the plugs and other components conflicting with the reality. On the other hand maybe nobody bothers with this. There presumably would still be the question of whether or not this might cause unintended consequences elsewhere??

If my fuzzy recollection is correct star (in a normal mains supplied three phase installation) gives reduced torque from a standstill, but it's used because it gives a reduced current draw too.

The converter leaflet is a bit cryptic, but seems like it may be recommending a fast switch to delta because converters themselves inherently limit the current draw (????) in a direct on line start to x3 the plated motor current, but at the expense of similarly reduced torque to that available when connected in star. i.e. it's apparently for this reason best to start direct on line off an inverter - because starting in star with a converter amounts to a double whammy (the effect of the converter, plus the low star voltage together) that gives very low torque, and an extended wind up.

The capacitor was a typical cheap plastic cased motor start type. My instinct would be to replace it only if we could see another reason for it being there beyond assisting a converter to start - the example I have bought is a rotary and might well be OK without one. If it turns out to need one, then I'm surmising (?) that it might anyway be best to first measure some phase voltages and proceed from there??

Ian

[Stephen Cherry]

If my fuzzy recollection is correct star (in a normal mains supplied three phase installation) gives reduced torque from a standstill, but it's used because it gives a reduced current draw too.



The capacitor was a typical cheap plastic cased motor start type. My instinct would be to replace it only if we could see another reason for it being there beyond assisting a converter to start - the example I have bought is a rotary and might well be OK without one. If it turns out to need one, then I'm surmising (?) that it might anyway be best to first measure some phase voltages and proceed from there??

Ian

Looks like a basic start circuit- not sure about the configuration of the switches- how the physical devices align with the drawing.

Right, star reduces inrush. I've used normal starting on some pretty humongous motors without even considering it. In the three phase motor world, a bandsaw is a drop in the bucket. (no offense intended, I have a very similar saw)

You really shouldn't need the capacitor. If the converter can't deal with the inrush, you may want to consider it. In which case I would recommend wiring the machine with a momentary start button, which would feed a supplemental contactor to switch in a capacitor. Purely speculative though. I think that it will start. If it does need this, you don't really measure any voltages, it is just the inrush period where a start capacitor has any effect. There is not enough time to measure anything with a normal meter. Where you can measure voltages is if you want run capacitor. These are completely different, and stay connected to balance things out. Check practical machinist for this type of information, they have everything, as well as expert talent.

Does your saw have a rotary on-off switch and an emergency stop? That's what mine has and I have always wanted just a start button, stop button, and estop. I haven't wanted it enough to even think about doing anything about it though.

It sounds like you are asking all of the right questions. I am just finishing my phase converter. It has a 15 HP idler; I scrounged just about all of the parts, but is still was not exactly inexpensive. I opted towards the robust side as far as construction goes. To really do this right with all good commercial quality parts would cost a ton. One thing- don't skimp on the wire gauges. There is a lot of current moving around, so you don't want to get caught short.

[ian maybury]

Ta Stephen, sounds like we're at least seeing it the same way.

My controls sound the same as yours too - I've a rotary manual start/stop, and a separate emergency stop button. Plus an rotary isolator round the back of the machine.

EM I guess is the emergency stop, and the symbol used for the next switch along I'm told is for a foot operated switch - it possibly cuts the power to the motor (by cutting the power to the coil holding FS1 closed) if you use the foot brake on the US models (?) - so that you can't brake against motor power. Euro saws usually have some sort of electrical braking, but since I haven't had any luck yet in sourcing a Euro drawing I don't know how this is done on mine. It definitely has no foot brake. (wonder if this could cause a problem if the transformer tapping is moved from L3 to L1?)

Like you suggest the bit I've not been able to figure out either is exactly how the two parallel switches work with the main manual start/stop and star/delta control switches. I'm guessing that when you rotate either control switch manually that you make/break the N/O 230V switch FS1 (in the case of the start/stop), or the N/C 230V switch Q1 (the star/delta).

The 230V switch FS1 looks like when closed that it powers the coil that closes the contacts in the main start/stop switch FS1. i.e. so that power is fed to the star delta switch.

The 230V Q1 switch I'm guessing may somehow depending on whether it's open or closed (depending on whether the rotary switch is set to star or delta) either actuate or at least enable the manual selection of star/delta by the main Q1 starter switch? (maybe it is the basis of an interlock that prevents it being started in delta)

This electrical stuff takes a bit of figuring out when you're a mech guy!!

Don't worry about it - it's just turned out today that I'll have a good industrial electrician in next week to do some wiring in a building I look after for somebody - he'll probably know the score at a glance.

On your building a rotary phase converter - with a 15hp idler motor it sounds like you are planning to power your entire shop from it. (10 - 12hp output?) I came close to building one from the web too, as I had to wait for several months to find a used rotary - there's lots of info on the web.

It was looking expensive to do that over here though, and I figured that by the time I got it humming that it could prove very time consuming too. A scrapper motor with a damaged shaft seems to be the plan. I get the impression that you guys have much readier access to the right sort of surplus capacitors and other components in the US - new over here is very expensive. Another issue here is that we need an auto transformer to step up to 400V 3 phase - and the motor in my saw turned out to be a delta connected 400V item so 230V wasn't an option. I guess you won't need that.

An inverter would have been attractive (cheaper, variable speed, good control of start up current) if the saw had a 230/400 dual voltage motor - the down sides with that would have been its inability to run more than one load at a time, and the need to control the saw using the inverter's controls.

Something that might just be of interest. These guys use an electronic controller on their high spec rotary converters that automatically switches capacitance in and out to balance the phases with changes in load: http://www.digi-phase.co.uk/digi.htm (see F range, <2% voltage variation) They will sell kits and parts separately, but they source the controller from a company called Eurotech in New Zealand run by some German guys that developed it: http://www.eurotech.co.nz/Home.html

Thanks again for the help.

Ian