digi phase converter for 10 machines…..

[Robert Atkinson 2Participant @robertatkinson2]

One problem with simple* "passive" converters is they do not provide 120 degrees of phase shift. This means you loose the low torque ripple advantage of 3 phase motors. This can affect surface finish and generate noise.

Robert.

* You can generate proper 3 phase passivly using capacitors to generate phase quadrature and then a a Scott-T trhansformer to get 3 pahases but as far as I know the low cost units don't do that..

[EmgeeParticipant @emgee]

Posted by martin haysom on 04/10/2023 11:54:55:

Posted by Clive Steer on 04/10/2023 10:48:18:

Adding a motor to turn it into a rotary converter improves the phase balance and provides a degree of energy storage beneficial for starting machines with direct on line motors. The downside is that the motor adds a level of noise and inefficiency. Static converters are reasonably tolerant of supply issues that some countries power distribution systems may provide.

could this be done by letting a machine not being used run.

That would be OK if the motor was not driving the machine otherwise you will wear 2 machines out at the same time. !!!!

Emgee

[Clive SteerParticipant @clivesteer55943]

Absolutely and you could use your smallest/simplest machine such as a pillar drill to act as the idler motor. However you need to be aware that the motor may be the other side of a no-volt release and motor protection arrangement.

CS

[Clive SteerParticipant @clivesteer55943]

There are short comings with the normal converters as RA2 points out but many wouldn't notice these. To get the best finish I'd use a 5 phase motor. I've only seen one machine with these and it was eye watering expensive.

CS

[Mark RandParticipant @markrand96270]

Posted by Robert Atkinson 2 on 04/10/2023 01:58:13:

So they say to use a 71/2 HP inverter for a 2 HP motor i.e. > 3 times de-rating.

Whatever. The voice of hypothesis obviously trumps the voice of experience…

[Dave HalfordParticipant @davehalford22513]

Posted by Mark Rand on 04/10/2023 13:26:40:

Posted by Robert Atkinson 2 on 04/10/2023 01:58:13:

So they say to use a 71/2 HP inverter for a 2 HP motor i.e. > 3 times de-rating.

Whatever. The voice of hypothesis obviously trumps the voice of experience…

And the voice of hypothesis is of course the voice of the equipment supplier who ought to know what he's selling and why he's saying it.

[clogsParticipant @clogs]

originally thought one machine was 5HP but it is def 4……

as for the supply cables from the pole there are 5 cables wound / twisted around each other and after going up to look each cable is almost as thick as my index finger…..alowing for double insulation it is still a heavy cable…..

the elec supply ends at my house *it's the last pole*…

what's there now is five tails with ony 3 connected and what looks like a 4mm'ish x 3core cable that drops down from the pole to the outside meter box….10m distant from the pole…….

cannot see any difference in my supply cables 5 core twisted as to whats used at a couple of local small industrial units…..

perhaps I'm wrong but I thought it would be straight forward to replace the orig supply 3 core cable for a 5 core cable plus a new meter….plus the new junction box and their sealed mains fuse/rcd or mcb …??

happy to learn if I'm wrong……

so the cost for that at €12,000 seems like a con…..on occ you get local prices and foreigner prices tho…..

thanks again still studying…..

an old industrial elec freind who's no longer here said that 3 phase is a black art……mmmmmmm

[SillyOldDufferModerator @sillyoldduffer]

Posted by clogs on 04/10/2023 16:21:05:

…

perhaps I'm wrong but I thought it would be straight forward to replace the orig supply 3 core cable for a 5 core cable plus a new meter….plus the new junction box and their sealed mains fuse/rcd or mcb …??

happy to learn if I'm wrong……

so the cost for that at €12,000 seems like a con…..on occ you get local prices and foreigner prices tho…..

…

If that's correct, installing 3-phase should be relatively easy. Problem is it's guesswork. Unfortunately only the supplier knows what work needs doing, and how much it will cost the customer. Possibly they are quoting high because they don't want the work – fair bit of bother for them, and very little profit in it when the customer is obviously only going to buy tiny amounts of power.

Supplier reluctance to provide 3-phase to low power users is one reason VFDs exist.

Why suppliers are reluctant or helpful is unknown; quotes vary wildly. I suspect it's down to how easy or difficult it is for the supplier, maybe plus external factors like how the cost of new infrastructure is shared between customers. Domestic single-phase installations might be subsidised by the government whilst 3-phase isn't. A single small customer in a remote location might be charged much more than a big customer on an industrial estate, simply because large consumers are a fast return compared with the little guy. Dunno.

Dave

[Mark RandParticipant @markrand96270]

Posted by Dave Halford on 04/10/2023 16:17:58:

Posted by Mark Rand on 04/10/2023 13:26:40:

Posted by Robert Atkinson 2 on 04/10/2023 01:58:13:

So they say to use a 71/2 HP inverter for a 2 HP motor i.e. > 3 times de-rating.

Whatever. The voice of hypothesis obviously trumps the voice of experience…

And the voice of hypothesis is of course the voice of the equipment supplier who ought to know what he's selling and why he's saying it.

Sorry, but the 7.5 hp Teco that is used has a rated output of 10.1kVA. with a 50% overload capacity for one minute on top of that. If you assume a 3 times rated current starting current, then you end up with the 7.5hp unit being happy to start 6.75hp motor.

That's my last post in this thread…

[Robert Atkinson 2Participant @robertatkinson2]

Posted by Mark Rand on 04/10/2023 19:29:32:

Posted by Dave Halford on 04/10/2023 16:17:58:

Posted by Mark Rand on 04/10/2023 13:26:40:

Posted by Robert Atkinson 2 on 04/10/2023 01:58:13:

So they say to use a 71/2 HP inverter for a 2 HP motor i.e. > 3 times de-rating.

Whatever. The voice of hypothesis obviously trumps the voice of experience…

And the voice of hypothesis is of course the voice of the equipment supplier who ought to know what he's selling and why he's saying it.

Sorry, but the 7.5 hp Teco that is used has a rated output of 10.1kVA. with a 50% overload capacity for one minute on top of that. If you assume a 3 times rated current starting current, then you end up with the 7.5hp unit being happy to start 6.75hp motor.

That's my last post in this thread…

I was only quoting what the supplier says their equipment is capable of. Don't blame the messenger.

A lot of people including suppliers suggest de-rating the low-cost drives even when used as a normal VFD. I assume this is to improve reliability. The quality branded drives will of course run at their full rating 24/7 365 days a year with no issues…….

Robert.

[Stuart Smith 5Participant @stuartsmith5]

I was going to post before the old site went down but here are my thoughts.

Dave (SOD) – if the cables near the house are actually 3 phase, installing a 3 phase  service cable should be straightforward as you say. However, in the UK, any load such as motors and welders need to be considered to make sure that the starting current does not cause the voltage to other customers to dip outside certain parameters. ( to stop nuisance to others).

To do this, it is necessary to know the maximum starting current of motors and the maximum current of welders. Using the network impedances (ie HV network, size of transformer and length and sizes of LV network). Also the position of connections to other customers and the customer with the motors.

Depending on the existing network, it may be that the transformer and/or LV network would need to be upgraded. The cost of this would be have to be paid by the customer.

As far as I am aware, there is no reluctance to provide a 3 phase supply to domestic customers, it is purely an issue of cost. If a customer is prepared to pay, a 3 phase supply will be provided.

In the olden days (before suppliers and distributors were split), the projected income from energy usage was indeed taken into account, but not now.

Stuart

 

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