rotary converter – only getting half speed

[capnahabParticipant @capnahab]

[capnahabParticipant @capnahab]

I have a 3 phase problem. I have a 15 HP transwave rotary converter for a lathe with a 7.5 HP motor. The lathe has push button motor start – 2 buttons, slow and fast for the motor. Starts very well on slow but I am limited to about 380 rpm ( it's a DSG 17 ).The lathe is capable of double that on 'fast' motor speed. If I start using the fast button It seems to overload the boost which flickers and chatters. Starting in slow and then hitting the fast button does nought. I would have thought the power of the converter would handle it. Any suggestions welcome, – I obviously can phone transwave Tuesday but wondered if it was something obvious I was missing which is very likely as I know almost nothing about 3 phase.

[JonParticipant @jon]

I have exactly the same problem though a much lower motor to drive 2.25kw. Fine on low speeds plenty of grunt, on mid range fine on first two speeds minimal startup problems. On last two mid range speeds with a small chuck on 80% guaranteed it wont start without tripping main feed fed from 32A C type MCB. Motor draws in excess of 9hp on higher speeds and can take 9 to 10 seconds to reach full speed.

Did have a 4kw inverter lasted 1hr 20mins.
Do still have a 5.5kw Transwave rotary kept as backup, spindle start groans like no tomorrow and takes around 10 secs to reach speed, menial cuts spindle slows rotary even untolerably louder. No way will this startup a 5" chuck on 2500rpm even with a push start.
Change to a 7.5kw inverter no problems on startup up to mid range but does have the ramping and torque the Transwave rotary hadn't. Startup at 2500rpm takes around 9 to 10secs before tripping out the feed but can happen at 2 secs.
Havent tried a new modern motor but next step.

Like a car its like trying to pull away in a higher gear with a timer. Needs more juice.

Had similar off old lathe only a 1 1/2hp motor 1 ph 240V, 1 in 3 would blow a 13A fuse on startup. Bought fuses by the bag load once motor running kept in running but had a clutch.

[capnahabParticipant @capnahab]

So I have spoken to Transwave. Had my multimeter in the cabinet. The supply to the converter and the converter itself are fine. The voltage drop on turning on both fast and slow is negligible. The suggestion is that the phase wiring from the converter into the machine is the problem. I enclose a picture of the electrical cabinet. I need help from someone who can walk me through testing how to change the 3 phases.The electrical cabinet is shown in the attached.

I am hopeful that it could be a matter of re-ordering the 3 supply leads into the switch…

[capnahabParticipant @capnahab]

Hi Nick , what makes you say that ?. I had actually posted this for some help.

[Paul BarterParticipant @paulbarter66156]

Hello there

Looks like one of the capacitors providing the phantom phase to the slave motor has died leaving insufficient capacitance to cope with the startup load or full speed.Have a look to see if it is a dud connection rather than a dead cap but beware even with power off charged capacitors can give you a shock unless they  have been discharged or fitted with bleed resistors, hope this helps

regards Paul

Edited By Paul Barter on 04/09/2016 19:21:21

Edited By Paul Barter on 04/09/2016 19:21:50

[John Stevenson 1Participant @johnstevenson1]

Posted by Nick Hulme on 04/09/2016 18:12:34:

Rotary converters are great if your electric is free or if you're happy to pour money down the can

.

Hardly a helpful reply Nick.

How about an article on the pro's and con's of the various types ?

[capnahabParticipant @capnahab]

Paul Barter – thanks very much. Very helpful suggestion. I have solved the problem so for future help and anyone who's actually interested I will relate the steps I took.

Phoned Transwave – Pete v helpful. Checked supply to converter was man enough for the job – it was. Checked it was still ok when I turned on low speed ( 1000v multimeter on supply in box, all safety precautions etc).

Checked each phase delivered to lathe switch – all ok – 430 volts – Or so. Transformer looking ok.

Phoned Dean Smith and Grace who came up with some fantastic advice and a circuit diagram within 24 hours.

Circuit diagram beautifully simple. Even I could understand it.

Was going to test motor but didn't have a high voltage tester to see if the insulation was bad – see https://youtu.be/Fyd3S1EWfYA

Turns out the motor is a pole switching type. Here's how it works. https://en.wikipedia.org/wiki/Dahlander_pole_changing_motor

So plucked up courage and rotated the phases A>B, B>C and C>A , nb not swapping wires cos that would reverse motor. Must have been my lucky day as that solved it. Actually it was in the Transwave manual if I had read it – RTFM.

Here it is taking a light facing cut on 3 inch titanium.

Thanks everybody for your helpful replies, and for those non helpful ones …well.

BTW Npower was my only alternative. And before anyone suggests VFD I don't think that's an option. I am v happy with the 11 kW / 15 HP converter which hardly noticed starting a 7.5 HP motor and spinning the 14 inch chuck at 720 rpm. Brake works too.

 

 

Edited By capnahab on 04/09/2016 20:52:07

Edited By capnahab on 04/09/2016 20:53:09

Edited By capnahab on 04/09/2016 21:12:11

[Michael GilliganParticipant @michaelgilligan61133]

Posted by capnahab on 04/09/2016 20:50:55:

Here it is taking a light facing cut on 3 inch titanium.

.

That'll do nicely !!

Good result, Sir.

MichaelG.

[Anonymous]

Glad you've fixed the problem. I thought about mentioning two speed motors, ie, pole changing, but thought it was too obvious, nor do I have any practical experience of rotary converters. Given some recent rather unhelpful one line posts that could invite derision.

My horizontal mill must have a Dahlander style motor as it switches between delta and star when going from low to high speed range. Conversely my repetition lathe must be different, as speed changes by pole changing result in half power at half speed, so no star to delta change.

I don't understand why rotating the phases should alter anything? Did DSG give any explanation? I've just read the manual online, it implies that the three output phases are not identical? Have I got that correct?

Andrew

[john fletcher 1Participant @johnfletcher1]

To capnahab, any chance of a copy of the circuit diagram and other information from Dean Smith and Grace here or via a personal message, as it could be very useful to others. I have a good explanation of how the motor connections are give two speeds all from a 1930 electrical magazine. John

[Peter BellParticipant @peterbell11509]

Good to hear that you've got it sorted. Never heard of that configuration for a motor before so a bit more learned

I've got a DSG 17" as well from 1960 but its only got a single speed motor (7.5hp) giving a top speed of 900rpm which runs on a home made rotary convertor.

I wonder if the two speed motor was fitted on later lathes or if it was an option and what top speed does it give?

[MuzzerParticipant @muzzer]

Posted by capnahab on 04/09/2016 20:50:55:

And before anyone suggests VFD I don't think that's an option. I am v happy with the 11 kW / 15 HP converter which hardly noticed starting a 7.5 HP motor and spinning the 14 inch chuck at 720 rpm. Brake works too.

Don't see any rational reason why not. You could get a rather nifty 4kW Yaskawa drive for under £200 (~6HP) – and before you say it's not enough, this is rated at 6kW (8HP) for 60 seconds, so certainly no problem starting up. Being Yaskawa, it's very well proven and reliable. Tiny as well – 170 x 180 x 118mm – and many other contrasts to the exhibit in the photo.

I'm just trying to imagine what job would require that power on a continuous basis?

[John Stevenson 1Participant @johnstevenson1]

But can that power a two speed motor ?

[MuzzerParticipant @muzzer]

IIRC, the Yaskawa ones are rated for sort of DOL switching up to 2 motors onto the (running) output, so you'd think so.

Not sure I'd try it with a Wing Wah Xmas Cracker Special mind. But the fact is that you can buy decent VFDs for not a lot more than those.

Edit: No, it seems I'm talking crap again. There's a footnote that says "It is not possible to switch between motor 1 and motor 2 during run. Doing so will trigger a "rUn" alarm". Probably not surprising, really.

Edited By Muzzer on 05/09/2016 16:09:00

[capnahabParticipant @capnahab]

Am I missing something?, this Yaskawa VFD only puts out 230 volt 3 phase.

[capnahabParticipant @capnahab]

Andrew , to my simple mind it was explained ( not by DSG) that one of the 3 phases generated by the converter is a bit of a weakling cf the other two and depending which contact it's wired up to matters.

Peter – not sure. I only know mines 2 speed but it's a 17T.

[Anonymous]

Posted by capnahab on 05/09/2016 18:47:26:

Andrew , to my simple mind it was explained ( not by DSG) that one of the 3 phases generated by the converter is a bit of a weakling cf the other two and depending which contact it's wired up to matters.

Thanks for the information. I had a vague notion it was something like that from what the manual said about making sure the correct phases were across any contactors, although I'm not sure what Transwave mean by a rotary transformer. An internet search simply comes up with resolvers, which are indeed rotary transformers, but I'm pretty sure aren't included in the Transwave converter.

Andrew

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