digi phase converter for 10 machines.....

3 times load with a 50% overload capability gives a 2 times de-rating for the drive, which is what they specified. No one using this sort of drive is going to be driving a Lumsden grinder or similar.

Edited By Mark Rand on 04/10/2023 01:24:06

That is not what DD say. Quote :

"All this range of DIGITAL Plug and Play Converter allow you to take a 150% overload for 30 seconds so the 6HP starting requirement of the 2HP mill can be accommodated by this 7½ HP converter"

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

https://www.ebay.co.uk/itm/154157588494

Robert

My take on this thread is that if you want simplicity, in both installation and use, then a passive static converter is a good contender. The main components are just an auto transformer to convert 240V to 440 V which powers 2 of the 3 phase wires and a bank of capacitors to "generate" power on the 3rd phase wire. They are robust although not necessarily efficient but are very easy to fix by oneself or an ordinary electrician.

Their common failure mode is that the capacitors degrade with time but it is relatively cheap to replace a set for £50.

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.

Active 3 phase converters can be more efficient and compact but may need to be overrated to allow for DOL motor startup loads.

Converting each machine to be driven by a VFD is the most complex option. For those wishing to benefit from the variable speed they provide this is a price worth paying.

CS

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..

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

Emgee

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

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

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.

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

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

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.