Static 3 phase converter help

[tonygarner1Participant @tonygarner1]

Came across this static converter at car boot sale.

Didn’t overpay but when home took the lid off, the start and run caps are missing.

It is identical to this pic cribbed from an earlier post.

Can anyone help me with the size (uf) of the start and run capacitors

It is a 2hp Motorun static converter.

[duncan webster 1Participant @duncanwebster1]

Wot picture?

[tonygarner1Participant @tonygarner1]

OOps!! Sorry

[not done it yetParticipant @notdoneityet]

Try the internet?  Often suppliers of spares, if not the actual machine.

What model?  It might help those that might reply/search for you.

Maybe look on the internet for similar sized  machines?

Look for reviews – maybe find those are poor for that machine.

I have a fully working Transwave static converter for sale.  £150.  Video available to show it working.  About 3.2m outlet cable and socket, ~ 1.2m 2.5mm^2 mains cable (will be disconnected because it needs better cable restraint).

1.5kW single motor, 2.25kW (multiple motors), 0.37kW minimum.  I suspect yours may not be such a good value purchase.🙂

It’s not eating anything, just taking up space, so no rush to dispose of it – but it’s there if wanted.

[noel shelleyParticipant @noelshelley55608]

It looks like a late model 2Hp unit. I take it that’s not your machine as the caps are there ? Noel

[noel shelleyParticipant @noelshelley55608]

OOP ! Must pay attention to the question ! Noel.

[SillyOldDufferModerator @sillyoldduffer]

If you don’t mind taking a punt based on a bloke on the internet guesstimating:

• Big one – 250uF
• Little one 32uF

Exact values not critical provided you’re not too worried about phase balance, so ±25%.  Both rated 450Vac,

Risk is the values given turn out to be not “good enough”.  Suitable capacitors are expensive.

With luck someone else will recognise the model, and have a circuit or will look inside.   Replacing with what the manufacturer used is always the best place to start – if you can.

Dave

 

[tonygarner1Participant @tonygarner1]

Interesting.

The values of 32/250uf seem huge.

I have another earlier Motorun converter that has 20/40uf and that starts the lathe and mill quite successfully.

I have tried transposing those but on switch on it engages but wont turn the machine….just hums.

Just beginning to wonder about that pesky pcb not quite sure what that does.

Just hoping someone has similar machine with pcb whoc can tell me start and run cap values.

 

[tonygarner1]

On tonygarner1 Said:

Interesting.

The values of 32/250uf seem huge.

It’s to do with how much power the motor actually consumes.   Motors often pull massive amps when first switched on, before settling at tick-over power.  When the user loads the motor by doing work, the amps increase again.   How far third phase shifts  depends on the current, so the capacitor values are a compromise.   Static converters usually allow the user, or a digital controller, to switch more capacitors in and out for best effect.

Results are mixed because they depend on the motor and what you do with it.  If the capacitors are too small, may not start at all, or be unable to supply full power to a big motor.  Especiall one that likes it’s phases to be power balanced 120° apart, not a wobby 180°.      The values I suggested should be big enough to start most motors in the 2HP range, fingers crossed!

Might well get away with smaller capacitors if the motor is friendly (low start amps), and isn’t called on to deliver 2HP.   In practice a heavily loaded 2HP motor will output a lot more than 2HP, for which big capacitors help.

The transformer is good.  It helps the capacitors balance the phase, maybe allowing smaller ones to be used.

Just hoping someone has similar machine with pcb whoc can tell me start and run cap values.

 

That’s the best answer.  Judging by the size of the big one in your photo though, it’s lots of uF.

Static converters are great when they work, but there’s always a chance they won’t.  It’s why rotary converters exist.  VFDs are even better.

They all have pros and cons.  Static converter capacitors often fail after a few years because they take a real beating, and replacements are expensive.

Dave

[noel shelleyParticipant @noelshelley55608]

For what its worth my early Motorun has 8 caps but it is an 8Hp unit in essence 2x4Hp.. With out dismantling I can only read some of the values. 75uf at 440v, 105-130uf at 280-350, and 8uf at 440v. There are 2 bigger ones and 2 smaller ones. As to the life of caps in this application my transwave is about 25 years old and never failed. The motorun starts at .5Hp to 1.25, then 1.25 to 2.25 and then 2.25 to 4hp by switching in caps. Good Luck. Noel.

[tonygarner1Participant @tonygarner1]

Thanks for everyones input but still not got a definitive answer.

Still trying to make sense of whats happening.

Am I correct in thinking on powering the unit the run/start caps that are in parallel should be energised.

Then when the load is switched on they dump their charge and help the torque needed to start the load(lathe)

 

 

[John HinkleyParticipant @johnhinkley26699]

Tonygarner1,

You state in your first post that the photo was “cribbed” from an earlier post.  Does that thread not reference a make/model number of some sort?  Or maybe contact one or more respondents in that thread for information via PM.

John

 

[tonygarner1]

On tonygarner1 Said:

Thanks for everyones input but still not got a definitive answer.

Still trying to make sense of whats happening.

Am I correct in thinking on powering the unit the run/start caps that are in parallel should be energised.

Then when the load is switched on they dump their charge and help the torque needed to start the load(lathe)

 

 

Err no.

3-phase motors are fed by three wires carrying alternating currents phased 120° apart, i.e shifted relative to each other in time. Connecting them to the 3 windings inside the motor creates a smoothly rotating magnetic field, which spins the rotor.

Not easily imagined!

Single-phase has no phase shift.   A static converter bodges 3-phase with a circuit that arranges Live and Neutral in opposition, giving two phases 180° apart.  The third phase is obtained by passing Live through a capacitor.  As capacitors take time to charge and discharge, the output is shifted by up to 90°.  The actual shift depends on the amps flowing and the size of the capacitor.  And because the amps drawn by the motor varies, the third phase bounces around.

Ideal 3-phase is three equal power sources spaced 120° apart.  A static converter produces two equally powered phases 180° apart with an underpowered phase at about 90°.  It’s a compromise, with an extra wobbly third phase    Performance is improved by using bigger capacitors and a transformer, but static converters are a trade-off.  If only allowed one word, I’d say “yuk”.

May not matter.  Though far from ideal, static converters are often ‘good enough’ to run a motor or other not too fussy 3-phase device.

Motorun’s designer will have identified suitable capacitor values based on:

• motor power
• an assumption that the load had ‘normal’ characteristics
• a notion of what constitutes acceptable start/run
• the presence of a transformer and control electronics
• cost

There is no simple right answer unless someone has the same Model or Manual.  This is an old machine, made by a firm who shut down about 15 years ago.  If no-one here has the as designed answer, options:

• ask on other fora, one of their members might know.
• Try the values I suggested.  Pro: will probably work.  Con: expensive.  OR
• Try the smaller values others have suggested.  Pro: money saved, provided they work.  Con: Higher risk money will be wasted buying the wrong capacitors.  And they’re not cheap!

I don’t think trying to work out what’s needed from first principles will be fruitful.

I guess a previous owner took the capacitors out after the converter broke down in the past, intending to replace them.  Then he found out how much they cost!  Pity he didn’t leave them in place, or write their values on the chassis.  Be aware that the capacitors might not be the only problem.   Is that control board OK?

Dave

 

 

 

 

[tonygarner1Participant @tonygarner1]

dave

Thanks for your advice but I really need to get this converter working.

I’m pretty sure about 120°  x 3 for 3phase.

But I am not clear what happens at start. Does the motor try and start and then the start leg kicks in.

Must be pretty quick to charge start cap.

But that would explain why you sometimes have to wait for the converter to work. ie Cap charging after discharge.

That pesky pcb board is a worry.

It has 2 x red wires labelled 20volt go direct to transformer,

It has  2 small black wires labelled con and yel they go to the start contactor.

It has 1 small black wire labelled blu that goes to the cap bank.

And it has a potentiometer labelled volt adjust.

I just don’t know how to test this………yet but i’m not giving up.

What I do find disconcerting is label blu but its black and goes to the cap bank wired red.

Then label yel is black?

Presumably they didn’t have the right colours availble.

 

 

 

 

[tonygarner1Participant @tonygarner1]

Dave

This is the junction block on pcb

[tonygarner1]

On tonygarner1 Said:

…But I am not clear what happens at start. Does the motor try and start and then the start leg kicks in.

At startup the start capacitor and relay temporarily provide a crude third phase to create a rotating magnetic field to get the motor running. Once running the third phase is disconnected and the motor is said to be ‘single phasing’. In reality it is running on two phases 180 degrees apart providing a pulsating magnetic field rather than a rotating one.

There are some disadvantages. The current draw on the remaining two phases will be higher than plated on the motor possibly leading to overheating. Maximum power will be about two thirds of the plated value and torque ripple will be significant.

A 3-phase motor will start, and run, on two out of three phases from a true 3-phase supply, albeit rather lumpy and noisy.

Julie

[noel shelleyParticipant @noelshelley55608]

Car boot sale, and 2 caps missing and you’ve never had it running ? What else have they messed with ? The 20v may well be the control circuit, eg the board. From the info on here take a punt at the cap values and try it is your only chance and hope the board is ok, or car boot it ? Noel.

[John HinkleyParticipant @johnhinkley26699]

I posted this on a similar thread:

After a (very) little searching, I found this old thread  in which the contributor “Mrfixit” helpfully supplies the values for all the capacitors and even a schematic diagram about halfway down page three of the thread.  I do not have sufficient electrical knowledge to verify his reports, but a number of respected respondents appear at various points in the narrative.

John

[tonygarner1]

On tonygarner1 Said:

dave

Thanks for your advice but I really need to get this converter working.

Understood, and I sympathise, but what do you expect the answer to be?

Ideally go with the values fitted by the manufacturer, but, so far, no-one knows.  Other options:

• Fit the values recommended by me.  They are more likely to work than smaller capacitors.  Best bet if you ‘really need to get this converter working‘.  Why not go for it?
• Fit the smaller values found in other units.  The risk is smaller capacitors might not work, either by failing to start the motor, or not delivering enough power to the motor so it can perform adequately.  Why not take the risk – it might well be ‘good enough’

I’m pretty sure about 120°  x 3 for 3phase.

But I am not clear what happens at start. Does the motor try and start and then the start leg kicks in.

Must be pretty quick to charge start cap.

But that would explain why you sometimes have to wait for the converter to work. ie Cap charging after discharge.

That pesky pcb board is a worry.

Electric motors need a lot more power to start than they do when running. The surge doesn’t last long, seconds, but the power supply has to deliver.  Hence big start capacitors that are switched out after the motor is running.

It has 2 x red wires labelled 20volt go direct to transformer,

It has  2 small black wires labelled con and yel they go to the start contactor.

It has 1 small black wire labelled blu that goes to the cap bank.

And it has a potentiometer labelled volt adjust.

I just don’t know how to test this………yet

Neither do I!  Can you trace the circuit?   What it does is simple enough in principle – it switches capacitors in and out to match the motor’s actual needs.   Simple units provide switches and expect the operator to find the match experimentally.   More expensive units are semi-automatic, or automatic.  Much harder to reverse engineer.

 

but i’m not giving up.

What I do find disconcerting is label blu but its black and goes to the cap bank wired red.

Then label yel is black?

Presumably they didn’t have the right colours availble.

Maybe, or more likely the colour scheme is explained in the Service Manual!  Don’t take colour coded wiring too seriously, it may simply be to allow maintenance man to trace what connects to what – no other significance.  Conventions, like RED for hot power, and BLACK for ground, are often followed loosely, but don’t assume anything.  In a control circuit, GREEN may not be earth, BROWN is not Live, and BLUE is not neutral.

 

 

 

We’re able to explain why there isn’t a simple answer.  That leaves taking a risk, either buying big expensive capacitors, or smaller cheaper ones.  And hoping the capacitor are the only problem: broken electronics are another can of worms.

You’ve been torpedoed by whoever removed the capacitors, and though not as expensive as they were, not cheap,

What’s your budget? Gambled at a car-boot sale and lost.  Lots of time, trouble and dosh to fix. Danger of throwing good money away after bad.  Personally, I’d walk away, even though I know how.  NDIY’s offered a working unit for £150, a good price, given a new Transwave is about £600.

Dave

 

 

[Maurice TaylorParticipant @mauricetaylor82093]

Hi, Will this be of any use

 

https://www.researchgate.net/profile/Noor-Mohd-Yunus-2/publication/286582066_Design_of_single_phase_to_three_phase_static_power_converter/links/5c8b1366299bf14e7e7ca38a/Design-of-single-phase-to-three-phase-static-power-converter.pdf?origin=publication_detail&_tp=eyJjb250ZXh0Ijp7ImZpcnN0UGFnZSI6InB1YmxpY2F0aW9uIiwicGFnZSI6InB1YmxpY2F0aW9uRG93bmxvYWQiLCJwcmV2aW91c1BhZ2UiOiJwdWJsaWNhdGlvbiJ9fQ

[tonygarner1Participant @tonygarner1]

Dave

Neither do I!  Can you trace the circuit?   What it does is simple enough in principle – it switches capacitors in and out to match the motor’s actual needs.   Simple units provide switches and expect the operator to find the match experimentally.   More expensive units are semi-automatic, or automatic.  Much harder to reverse engineer.

This Motorun unit has switches for power selection(switching caps) and a high low switch for start.

The control board I have pictured I think maybe some sort of delayed start together with a voltage sensor cut off.

I suspect this may be faulty but its way above my pay grade.

I have to decide now what to do, either get to grips with the control pcb or use the  parts to make a simpler converter.

Seems my little buy wasn’t so good.

But thanks everyone for helping out keeps the grey matter functioning.

[The Mad ProfessorParticipant @themadprofessor]

Have a look at the Workshop Practice Series book No.47 – Three-phase Conversion – it will help you start from a dead one. At least you have the transformer and the case…

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