Running a 3 speed motor from a converter

I'm trying to get a Holbrook C10 running on a 3.7kW Transwave converter; has anyone managed to get multi speed motors working OK on a converter?
The C10 has a 3 speed (2860, 1430 and 925 RPM) 2HP motor that drives a 2 speed clutch/gearbox assy; with backgear this gives 12 spindle speeds.
Without a pilot motor it's difficult to find a switch setting on the converter that will run the motor at sensible voltages at all 3 speeds and when the fast clutch is engaged at 2860 the motor slows significantly and won't come back up to speed - after a few seconds the motor protection trips.
With a pilot motor (5HP 2800RPM) the voltages are more sensible at the 3 motor speeds but the lathe still won't run at the highest spindle speed (2000 RPM). These tests were done without a chuck mounted so the problem may occur at other speeds with the extra inertia to be overcome.
Any ideas?
Dave
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converter;
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Dave,
Those exact symptoms were my experience with a two speed on a Colchester Student Mk2. Never did get a working set up using my otherwise excellent Transwave. Problem now solved by trading lathe in for Colchester Master 2500 with 7.5 HP Transwave rotary <G>
AWEM
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Hi Dave. Cant remember the exact formulae for current calcs, but that aside a few things spring to mind. Obviously it would appear on the face of it that your converter dose not have a sufficently high current output to run the motor at high speed, while you may be able to fiddle with it to some extent to force it to run, you cant get round ohms law which basically means that while you are under running the motor the windings will be generating more heat as the voltage drops, this is because the heat generated =I R squared. Basically what happens is as the voltage drops the current increases, and current is the heat generator. What this means is shorter service life of both motor and converter.
Next thought is that the converter is really only suited to small ish loads, and a more suitable unit would be a static converter, which is basically a toroidal transformer and capacitor bank, which gives much closer to a true three phase supply {even though far from perfect}and it dose not suffer from voltage wander in the same way as the transwave unit, as this uses the other motor as an inductive load and so is tuned in this manner to a specific current and phase angle, once you go outside the current range the phade angle dies fairly quickly. What this means is to some extent they stop generating the phase angle and instead the generate 3 phases with less angular differance, or more simply all three phases become more or less the same. Hope this helps

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Dad wrote: ... snipped

The Transwave converter IS a static converter - did you mean rotary converter? The converter is rated at 3.7kW, I'm using it with a 2HP (1.5kW) lathe motor and so far the only load is spinning the gearbox and spindle. Admittedly the pilot motor is 5HP but it's running with only it's integral fan as a load.
It feels like it should be possible to "tune" the converter by switching-in additional capacitance with the motor selector so maybe I'll look at this if I can't find someone who's already solved the problem.
Has anyone made (or found a source for) signal transformers so the phase angles can be safely seen on a 'scope?
Dave
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Dave wrote:

Just a thought. Could it be that your motor is expecting 415v and your converter is sending out 240v? This would certainly give the symptoms you're experiencing. If this is the case, then it _might_ be possible to change the motor from star to delta wind. If not then you'll need a 240-415 stepup transformer between the converter and motor.
--
Regards, Gary Wooding
(To reply by email, change feet to foot in my address)
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lemel_man wrote:

These converters have a 230-415 auto transformer in them to generate 415 across 2 phases. A capacitor to the third phase generates a phase shifted current to start the motor and (I think) they then monitor the synthetic phase current to switch in/out capacitance appropriately. Unfortunately multi-speed motors do not have the provivision to change between star/delta.
Dave
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wrote:

Rather perversely I found that I got better results on my mill when I used a smaller pilot motor. Not sure why. I also wired in an extra load of capacitance to give the wack needed to overcome this issue when needed.It come in on a push-to-make switch. I have an old Motorun 4 HP static converter that has a button marked "PUNCH" on it to achieve just this aim. Not sure if Transwave ones are the same.
Regards
Charles
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Charles Ping wrote:

... snipped

Apparently the Transwave has a voltage sensor which switches in additional capacitance when the voltage falls below 380V (they call it a "boost" circuit). The pilot is only resulting in about 1A on the converter input so it's not wasting much of the available power. I'm an Electronic Engineer by training (although rarely design anything these days) but I admit to not fully understanding the role of a pilot motor when it's running at no load - can anyone explain?
Dave
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wrote:

As a matter of interest Peter Neill bought a new Transwave a couple of months ago and found that the boost relay was missing. That really didn't help him much.
Read the story at the bottom of this long thread
http://tinyurl.com/ja54f
Charles
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<Snip lot of stuff about it not working>

As I understand it ( im a software engineer nowadays, so its likely Im wrong) The idle motor generates the third phase. It runs on 2 phases, (istr all 3 phase motors will do this, but on big ones the protection relay trips in to prevent it, as it causes a big heating effect....) and 'generates the third. This is supposed to give a better phase angle compared to capacitors, something to do wit the phase shift of the capacitor bank being related to the slip angle of the motor (and therefore indirectly the load applied) There is a good Model Engineering article about this here: http://www.boost-energy.com/boost/files/MEWed200401merged.pdf and a shorter one here: http://www.boost-energy.com/boost/files/MODEed200431merged.pdf
hth
Dave (who works for Brush Electrical Machines, who make BIG motors and generators, but only actually writes control software...)
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snipped-for-privacy@bem.fki-et.com wrote:

Thanks Dave. Everything I read confirms that my set-up should work; experimentation needed.
Dave
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Dave
I have a Boost Converter running a TOS FNK25A Mill.
The Boost converter is 4kW capacity, and the quill motor is a 2.5 kW 2/4 pole switchable motor. I had problems with it tripping out when switched to 2 poles (high speed) and also it used to get hot when running on 4 poles.
I am an electrical engineer and I spent a lot of time measuring the phase currents and voltages, and found that they were very unbalanced and this varied depending on the loading at the time. In the end, the people from Boost helped me to solve the problem. They adjusted the run capacitors to optimise things for the mill.
The problem is that the convertor is usually shipped with the optimum capacitance for a full load (i.e. 4kW) with a typical 'typical' motor. As the load changes, or if you run at a much reduced loading like I do, you need different values of capacitance. For a pole switched motor, the loading changes considerably. The only thing you can do is to optimise the setting to get the best compromise.
My problem was certainly reduced to a workable level (but the imbalance was not completely eliminated) by adding about 30uF - not in parallel with the existing run capacitor, but between the artificial phase and the main live leg I seem to remember.
Take a look at http://www.metalwebnews.com/howto/ph-conv/ph-conv.html
This might be helpful in explaining the problem.
Regards
Tony K
Dave wrote:

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tony wrote:

> Dave > > I have a Boost Converter running a TOS FNK25A Mill. > > The Boost converter is 4kW capacity, and the quill motor is a 2.5 kW > 2/4 pole switchable motor. I had problems with it tripping out when > switched to 2 poles (high speed) and also it used to get hot when > running on 4 poles. > > I am an electrical engineer and I spent a lot of time measuring the > phase currents and voltages, and found that they were very unbalanced > and this varied depending on the loading at the time. In the end, the > people from Boost helped me to solve the problem. They adjusted the run > capacitors to optimise things for the mill. > > The problem is that the convertor is usually shipped with the optimum > capacitance for a full load (i.e. 4kW) with a typical 'typical' motor. > As the load changes, or if you run at a much reduced loading like I do, > you need different values of capacitance. For a pole switched motor, > the loading changes considerably. The only thing you can do is to > optimise the setting to get the best compromise. > > My problem was certainly reduced to a workable level (but the > imbalance was not completely eliminated) by adding about 30uF - not in > parallel with the existing run capacitor, but between the artificial > phase and the main live leg I seem to remember. > > > Take a look at http://www.metalwebnews.com/howto/ph-conv/ph-conv.html > > This might be helpful in explaining the problem. > > Regards > > Tony K > > Thanks Tony,
The transwave has an 8 position switch on the front which (presumably) varies the value of the run capacitor. By firtling with this I can get the phase voltages to be fairly good but the currents are 5.3/3.0/2.9 which seem rather high for a 2HP motor; I suspect that phase shift (or lack thereof) is the issue. I'd hoped that having a big (5HP) pilot would prevent problems but I'll do some reverse engineering on the transwave and some experimenting with pilot motors at the weekend.
Did you find a safe way to investigate the phasing? I was wondering about using 3 small isolating step-down transformers so I can scope the voltage waveforms but haven't thought much about it yet.
Dave
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I just used a multimeter and a clamp-on ammeter. Not the best idea, but those were the instruments to hand.
The gentleman from Boost used a special meter (basically a 3 phase power analyser I think) which was able to indicate volts, current and power in each of the phases. I am not sure of the make, but I have used similar ones by Dranetz in the past.
I recommend switching off before making the connections to the meter if you are not absolutely sure of what you are doing, or if space is limited as it is very easy to get an electric shock and at 415 volts that is not good!
The key seemed to be in putting the capacitance on the opposite phase to the normal run capacitors. We tried increasing and decreasing the run capacitor value but that did not solve the problem.
The gentleman from Boost told me that the controller is a design from New Zealand and the guy who developed it did not advise putting capacitance where we put it, however it does seem to work and although the balance is not perfect, the machine has not tripped out since, and everything runs much cooler than before.
regards
Tony
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I don't have a 2 speed motor... but I have fitted extra capacitors to my larger motors, so that the capacitance is right for the motors I am running without my changing the converters settings... could you rig extra capacitors to come in with each stage of your motor ?
regards Jonathan.
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wrote:

I'm running a 2-speed motor on a Bridgy from a static Transwave converter. Being fairly electrically ignorant I spoke to Transwave before I bought it about running high speed on this and they recommended the 3kw model as (apparantly) this has a higher torque transformer.
It will start up at full speed, 4600rpm, with the boost switch set to 4 out of 8 then will happily run with the boost set back down to 1.
There is a voltage sensing relay on the inside of the front panel, have you checked that this is present and set correctly? I only know this as mine was completely missing when it arrived!
It would start and run everything fine on low speed, but when attempting to start on high speed it would run dead slow then trip out after a few seconds. Transwave suspected the problem was due to the relay either coming loose in transit or having a fault, and were quite surprised when it was missing completely:)
Peter
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