Mains power supply? How have you done it?
I mostly just read on here,
I've started collecting parts for my build mechanically I have my head round it all,
But electrically my main supply I'm struggling with,
obviously in the UK we have 220v 13amp supply in the house, I'm thinking this won't be enough to run a 2.2kw spindle/VFD inverter, my pc, main power supply for the steppers and a coolant setup.
Maybe I'll need to separate it out and split it between two sockets?
How is every one else doing it?
Also when I look at 2.2kw inverters single phase to 3 phase most advice an input current of between 16-20amps ? How are people running them on normal feeds?
Hopefully I don't sound to stupid :)
Many thanks
Gary
Re: Mains power supply? How have you done it?
If you add all the power consumptions together, it will still be under the 3KW max you can reasonably draw from a 13A socket. The main reason people use a minimum of a 2.2KW spindle is because it takes ER20 collets which allow you to use up to 1/2" shank cutters. I doubt if there are many home-built machines that are strong enough to load these spindles to max power, so in practice you will be drawing much less and you will be even further under the max permissible for a 13A socket. Consider plugging the VFD into one socket and the rest of the electrics into another. Each will be way under max load, and behind the covers a normal UK ring circuit feeding them will be fused (MCB'ed?) at 30A which is plenty.
Re: Mains power supply? How have you done it?
House consumer unit --> 32A RCD --> shed consumer unit --> 16A CB --> cnc machine (all electrics in one panel)
cnc PC fed from a 13A socket in shed.
Re: Mains power supply? How have you done it?
Normally You won't have any trouble running everything off a single 13a circuit or socket even when spindle is under full load or even stalled pulling max amps. But if running direct from mains ring then you have to factor in any other electrical items that can affect and pull high loads. Ie Fridges, Kettles, emerson heaters etc.
It's not uncommon for machines running off domestic supplys to be work fine for months or years then for no apparent reason start locking or tripping breakers. (often it's PC that crashes first) 99% of time when this happens it's nothing to do with CNC machine or it's PC. It's a scaled up kettle or Fridge motor failing so pulling higher loads and the combination pushes the whole circuit over the edge or in most cases the PC PSU is sensitive to power drop and will shut down to protect it's self or lockup.
If your system is running on it's own 13A circuit ie for workshop then you won't have any troubles at all, even with a small/med compressor or dust extractor running.
Re: Mains power supply? How have you done it?
One reason why you sometimes see higher ratings required for inverter power supplies is if they are designed to switch on at full load. The kinds of VFD/inverter you use with these spindles will ramp up relatively slowly, though, and that keeps the initial surge under control which might otherwise trip a breaker. My machine runs off a single 13A socket with VFD, PC, stepper drivers, etc, all running from that. The same ring supplies the wet-and-dry nominal 1200W vacuum cleaner for dust extraction, and I have never had a problem with any of that. The garage ring is separate from any of the house ring circuits, to avoid the kinds of problem that Jazz mentions (and the possibility of a problem with a machine in the garage tripping the house ring that feeds the television or my wife's sewing machine, which could lead to drastic loss of privileges).
Re: Mains power supply? How have you done it?
Sound s promising! Cheers guys.
I won't be using the Chinese VFD as I've seen alot of people have issues.
I'm also planning on having a slower spindle as well, 6000 rpm with a 1.5hp motor and pulley drive, so I guess I keep the ramp up speed ill be just fine as that's what 1.1kw max.
Sadly I live in rented accommodation currently so can't go changing the wiring lol! But do have about a 2 metre extension to my shed from the house so should be fine.
Re: Mains power supply? How have you done it?
what thickness cable is the extension lead.
Re: Mains power supply? How have you done it?
Being only 2 metre I'd be fine on 1.5mm but I over engineered it incase, 2.5mm 3 core artic flex, I run my 180 amp welder off a 40 metre version i made up at work on advice of electrical dept, with no issues on full whack so assumed I'd be ok.
Re: Mains power supply? How have you done it?
Quote:
Originally Posted by
gary_808
Being only 2 metre I'd be fine on 1.5mm but I over engineered it incase, 2.5mm 3 core artic flex, I run my 180 amp welder off a 40 metre version i made up at work on advice of electrical dept, with no issues on full whack so assumed I'd be ok.
Yes you will be ok. Often the machines I build for people or help people with end up in sheds or Car garages running from an extension cable reel from house and very few have any issues. This includes Vfd and dust extraction, lights everything.
Re: Mains power supply? How have you done it?
Quote:
Originally Posted by
JAZZCNC
Normally You won't have any trouble running everything off a single 13a circuit or socket even when spindle is under full load or even stalled pulling max amps.
If the spindle is stalled and drawing rated, or even higher, current from the VFD, that's actually requires very little power from the mains. One way to think of it is to recall that power is the product of torque and speed, so when the spindle is stalled the speed is zero so the mechanical power required to apply rated (or any) torque is also zero. From an electrical point of view, you still have to put current through the winding to get torque, but that current in this situation is only supplying the losses in the motor ... so the power, and thus current, drawn from the supply is low - I'd guess an amp or two at most.
Assuming you're operating within the motor's continuous ratings, you can only draw a rated power from the supply when the motor is driving a load (be that a tool or just accelerating itself), at around rated speed. This is obvious when you consider that the cooling power of the water cooling system is limited, so for the input power to the system to be much higher than the cooling power there has to be a significant mechanical power draw, otherwise the motor would be fried as the extra power has to go somewhere.
Re: Mains power supply? How have you done it?
Quote:
Originally Posted by
Jonathan
If the spindle is stalled and drawing rated, or even higher, current from the VFD, that's actually requires very little power from the mains. One way to think of it is to recall that power is the product of torque and speed, so when the spindle is stalled the speed is zero so the mechanical power required to apply rated (or any) torque is also zero. From an electrical point of view, you still have to put current through the winding to get torque, but that current in this situation is only supplying the losses in the motor ... so the power, and thus current, drawn from the supply is low - I'd guess an amp or two at most.
Ok well I'm not arguing here as I'll bow to your superior knowledge of electronics but what your saying if I drive the spindle into the bed it won't pull any more amps cos it's not spinning.? So why does the VFD have current limit setting and trip when spindle embeds it's self into material.? Surely that power that trips the VFD is being pulled form some where.?
Re: Mains power supply? How have you done it?
Quote:
Originally Posted by
JAZZCNC
Ok well I'm not arguing here as I'll bow to your superior knowledge of electronics but what your saying if I drive the spindle into the bed it won't pull any more amps cos it's not spinning.? So why does the VFD have current limit setting and trip when spindle embeds it's self into material.? Surely that power that trips the VFD is being pulled form some where.?
Not quite - the spindle will draw more current as the tool driven into the bed, but once the motor speed is very low, or it has stalled, the input power required for the VFD to get the motor to output a given torque is small, so the current drawn from the mains supply is also small. However, in getting to that point you will momentarily get a higher power demand, as the motor takes some time to slow down and the VFD tries to respond. The VFD will allow higher than rated current to be used for a short time, as sometimes you need that.
The VFD does not trip on power measurement, only current. The VFD protection is done with two different current measurements:
- To protect the motor it will sense the current in one (or more) of the 3-phase wires to the motor, and shut down if this exceeds the motor peak rating.
- For the VFD to protect itself, it will sense (or calculate) the input current from the supply and shut down if this exceeds some limit.
These two currents can be very different values - e.g. if operating at a low speed you could have 1 amp drawn from the supply but 10A line current in the motor, but with only a low voltage applied to the motor.
One complication is whether the VFD is doing Vf control (like the cheap ones), or vector control. If vector controlled, then the torque and thus current is measured, calculated and set thousands of times a second, so if the motor is set to run at a constant speed and it suddenly experiences an increase in load torque, the VFD will output more current to try and get the speed back to the setpoint. If the load torque required to do this is too big, the current required will be too high so the VFD will trip and display an error.
The difference with vf control is it's open loop - the current and speed aren't controlled, so if you apply a bigger load the motor just slows down and draws more current, whilst the VFD happily keeps applying the voltage and frequency you set. That's why the current limit is there - to stop the current increasing indefinitely with load.
This concept also applies to stepper motors - notice how little power they draw when stationary, even when the driver is set to apply rated current? If you apply a torque to the stepper motor when stationary it'll still draw the same current.
