New smart meter makes me question 3hp Vs 5hp Running Costs!

Hi all,

Just had a smart meter put in today - Don't ask. Anyway am glued with interest to the usage display. Believe me its as addictive as my curry.

My question is simply this, I have assessed possible lathe purchases based on a few things as contributors to some of my earlier posts will know. One of those things is size of motor - 3hp my thoughts are the maximum. P.S I am also not trying to take10mm (you get the idea) large cuts......

Putting wiring aside for the moment as I have a 60 amp supply into my workshop, I have always shied away from motors larger than 3hp based on running costs........am I being to frugal ?

What would you expect to pay typically when running a 5hp or 7hp lathe per hour......would my smart meter reading scare me to death?

Gary

Sorry the curry has gone to my head.  My Electrickery cost is 12p per kWh x 3.7 approx 5hp = £44.4p per hour on full load......

Edited By Absolute Beginner on 24/11/2017 18:53:44

Edited By Absolute Beginner on 24/11/2017 18:54:49

It all depends on load when you are cutting

A 5hp motor would probably show a FLC of 12 amps per phase. But that’s full load

as an example my 3hp motor running on an inverter shows 3 amps idling mine has a clutch and 10.27 whilst running these are figures on the single phase supply

Have you 3 phase?

Edited By Ian Parkin on 24/11/2017 18:59:39

I think you will find the cost is £0.44 per hour and not really worth worrying about when you think of some other hobbies.

In my example if it was running all year that would be just short of £600

Hi Ian,

Like your style and meter. I have a Digital Drives deice to supply my 3 phase at 415v. I see around 2.4A per phase on the supply when running. So I guess similar to yours.

Having the pound and pence in front of my face with the smart meter display just got me thinking

Gary

Gary

2.4 amp on the single phase supply? Or 2.4 on the output phases?

Hi Ian,

2.4A per phase...Thats correct I am sure.

Gary

Don't worry about the electricity cost of running the lathe at full power. You are extremely unlikely to be doing that for more than a tiny fraction of the time unless it's a bar fed CNC machine doing production work! Using a common approximation, 5hp is equivalent to removing 5 cubic inches of steel per minute. That's quite a lot of swarf to dodge. On the other hand, a more powerful lathe will almost always be more useful just because you can take a decent cut with it, or run carbide tooling at a sensibly high speed.

Interesting one i did some tests on 8 years ago for comparisons.

2.2KW motor fed by a 240v 1ph to 3ph 5.5kw Rotary Convertor was using 35p/min on no load. Mild cut on went up to 56p/hr. Will be dearer nowadays.

2.2KW motor fed from a 240v 1ph to 3ph 7.5kw inverter was running 4p/hr on standby, 12p/hr ready to go. 25p/hr cleanup cuts and ramping up to37p/hr putting a 1/4" cut on.

Food for comfort. Just replaced that lathe motor, always had doubts and dare say can now put heavier cuts on. Used to struggle spindle slow at 1mm cuts with 5.5hp Rotary Convertor, bigger cuts taken with 4kw inverter still useless and managable with the current 7.5kw inverter.
Previous lathe Harrison 140 1ph 1.5hp could power feed 1/2" cuts off where at 10mm it started to groan.
Long term approach is wire in a Mitsubishi 3ph 220v 10A as a VFD, no one any where has compared all 3 ways.