1 inverter 2 3phase mtors

[rockrose]

Hi iwant to run 2 3phase motors 1 1.1kw 1 3kw from 1 5.5kw inverter,will be using contactors overloads on load side of inverter the reason is to sink the speed of both motors on the 1.1kw motor there will also be a mechanical speed control via a split pulley to give over speed on to the chains the 3kw motor is driving whats your thoughts

 

[Darkwood]

Without knowing the set-up other than what you told us its hard to say whether other options would be better, there are many ways to synch' the speeds of 2 motors all suitable for differing situe's.

Torque control
Closed loop feed back
Slip pulleys

For the sake of saving the extra contactors and overloads you could buy a 1.1kw inverter for not much more and give both drives a common speed reference (1pot - 2 drives).
Synch'ing 2 motors is usually better with a feed back for speed regulation as all a pot does is command a speed output but torque and other load characteristics will mean it can be troublesome to give good speed balance... again these are just blind comments as we have little info of motor duty.

 

[netblindpaul]

You won't sync two motors open loop.

 

[rockrose]

both motors will be running there own gearboxes duty on 1.1kw is light turning 1 roller with cloth pasing over, on 3kw it is turning a chain which picks up the cloth from 1.1kw min seed 90rpm max 300rpm

 

[Darkwood]

Query ... you say you have a a 5.5kw motor at the end of your post ... is this off the inverter as it stands ..are you replacing this with the 2 motors suggested or have you got another inverter ...clarify?

 

[Darkwood]

I work on carding machines (similar task) but id have to see the set up to really recommend whats best ,there's too many unknowns ... not the kind of advice that can come of a forum with accuracy.

 

[rockrose]

sorry my mistake the 5.5kw should read 3kw motor at the end of first post
now changed

 

[netblindpaul]

I still say that you cannot synchronise two motors open loop.

 

[Darkwood]

Im heading out on call now ill see if anyone has furthered you with advice later .... a pic or diagram of machine layout can save a thousand questions its hard to imagine the set up without ever seeing it and give meaningful advice.

 

[rockrose]

job will not be done for while jue to down time required may do amock up beforehand to see what is best

 

[Darkwood]

Just a question - might sound stupid but why can't you chain link with a suitable sprocket size to the 1.1kw roller from the 3kw.... this gives accurate speed management through mechanical means or do you have a need to speed control giving you an option to run one motor faster/slower.

Another method although quite expensive motor gearing with mechanical speed adjustment , you match your speeds roughly with gear ratio then fine tune when running, this method is prone to speed variation between motors when load may increase or decrease due to torque take up.

What are the consequences of the small motor running too fast and vice/versa - this can have implementations, we don't want to over engineer the wheel or try reinvent it 'so to speak'.

 

[rockrose]

Hi almost impossible to link both motors mechanicaly was done before with some sever problems ,2 motors only way to go There is a need for speed control on 1.1kw motor faster/slower than the given control by inverter achived by the split pulley mechanicaly which will be left in place.
Both motors will be matched as close as possible speed wise by ther gearboxes and pulleys the fine tuning of the speed will be got from there mechanical split pulley arangment on both motors

 

[Darkwood]

Terminology here... when you say split pulley do you mean 2fixed pulleys and a central floating pulley which lifts and falls with the tightness of the cloth?

I refer to this as a dancer set-up and if you convert the mechanical movement into rotational to operate a pot or have a transducer to give vertical output this tells the drive what speed to go at.... normally in this set up you class 1 motor as master and has its speed detailed by chosen line speed on a closed loop set up and then slave motors operate off the dancer positions giving overall line speed and as many motors as you require acting as slaves.

Im struggling to envisage your set-up as this one above has the inverter controlling 1 motors speed while the other motor is fixed or through closed loop line speed set up.

 

[rockrose]

Hi the split pulley arrangment is 1 pulley on the load side(not on motor)1 half of the pulley(vbelt c section)is fixed the other is adjustable by mechanical means in and out varing the diameter of the pulley thus given slower/faster roatation this is non electrical and will not be linked electricaley to the circuit.Both motors will have this arrangment

 

[Darkwood]

Kind of get you ive seen similar pulley set up -spring action style it was just split pulley is ambiguous as you may now have realised it applies to different pulleys and pulley systems it also can mean a pulley that is physically in 2 halves that bolt together around a shaft when access for fitting a standard pulley is limited.

Back to the original query... now i think i ca envisage your set up..

-2 motors common drive and speed signal
-Motors run separate sections of machine and are associated with a cloth been fed or pulled around a machine.
-Each motor goes to a 'split' pulley that will self adjust the speed locally by mechanical means (pulley ratio self adjusting).
-Motors are originally set up and geared to be as close as possible to sych' with regards to take through of the cloth.

If the above is correct it should in theory in my mind work although I haven't really used this type of split pulley myself and would be intrigued to see how the pulley reacted in series on the machine (Would they control the cloth correctly without damaging it).. this would be down to reaction time etc... also having 2 motors 1 speed command may create issues as both motors are subject to different loadings and internal losses meaning getting an accurate gear ratio on both motors to match may be trickier than you think.

If im honest a closed loop feed back set up maybe looking at the floating roller would be more precise and accurate, or as discussed before another inverter and loose the outgoing contactors and overloads ... you can then fine tune each motor speed leaving the split pulleys to take up any variations.


Your idea may work but im skeptical tbh because your only sending out the same frequency and voltage to both motors but been totally different sizes working under different duty's the actual output speed may not match regardless of gear and plated ratio's due to slip and whether this can be compensated by the pulleys is a try it and see imo.