Vfd on Bridgeport mills

[ronan]

I bought a vari-speed bridgeport head off a member here last year with the intention of mounting it on my Tom Senior mill. To drive it i was going to use the ABB vfd i have on the Senior, and then buy a cheap chinese vfd for the horizontal shaft for the very rare time i would need it.

But i was reading on one of the modellers forums about a guy who reckons a vfd has a hard time driving a Bridgeport head as the motor is always engaged with the spindle and rest of the head, the starting torque on the motor and current draw on the vfd is too much.

Anyone here running a Bridgeport on a vfd having an issues or problems ?

 

[Hood]

Ran a VFD on a manual step pulley BP for years, also had one on a Vari Pulley CNC one for years, no issues at all.

 

[ronan]

Thats good to hear Hood. Probably some old woman getting their panties in a bunch over something imagined rather than real. I am looking on youtube now and there are plenty of lads running bridgeports on vfd's.

 

[WorkshopChris]

I cant speak for the Chinese vfd's on the market, but i see vfd's from the main suppliers driving things far heaver than a Bridgeport all the time, compressors and pumps running 24 x 7.
Personally have never come across anything like that and can not see the issue.

 

[Maker]

My lathe starts up just fine off an inverter (Albeit not a Chinese one), even with heavy lumps in a 4 jaw, which I'm sure takes more oomph than a milling head.

I suppose if you were using an inverter of the or lower same capacity than the motor, especially if it was a cheap inverter, there could be issues with the inrush current but I don't think it's likely.

 

[ronan]

No the inverter i will be using will be the ABB which i have driving the machine at the moment, it drives the horizontal milling shaft and the vertical knuckle head. What i want to do is use the ABB on the Bridgeport head and then use a cheap chinese one on the horizontal shaft, because it will be rarely used.

 

[Maker]

Why not use the ABB inverter and a 3 phase changeover switch to connect both motors? As long as you don't change the switch while a motor is running it'll work fine.

 

[Fazerruss]

I bought a vari-speed bridgeport head off a member here last year with the intention of mounting it on my Tom Senior mill. To drive it i was going to use the ABB vfd i have on the Senior, and then buy a cheap chinese vfd for the horizontal shaft for the very rare time i would need it.

But i was reading on one of the modellers forums about a guy who reckons a vfd has a hard time driving a Bridgeport head as the motor is always engaged with the spindle and rest of the head, the starting torque on the motor and current draw on the vfd is too much.

Anyone here running a Bridgeport on a vfd having an issues or problems ?

Well if it doesn't work I'm stuffed cos that's exactly what I'm doing with my tom senior

 

[oilyneil]

What a load of nonsense on the modellers forum
,,the rotating mass of a bridgeport, even with all the varispeed bits is light compared to a lathe with the weight of a chuck and whatever is in it.
I run my bridgeport off vfd,been 7 years so far with no problem, just make sure you size the vfd correctly for the motor.
Before you buy the vfd, just check the motor on your bridgeport, some of them have the motor star point buried deep in the windings, your choice whether to try and dig it out or go for a 240 to 415 vfd.

 

[penfold]

VFDs control the output current so the rotational inertia is irrelevant provided it's within the VFD's capacity, whereas soft starts or star/delta starters have to deal with surge current and generally die through the contact surfaces getting tarnished, which causes resistance, heating up and ultimately contact burn-out.

 

[thinfourth]

Just adjust the ramp up to be as long as you want.

 

[rikrobson]

A vfd is designed to run one motor. You set the parameters t9 the motor you are running. If you want to drive 2 motors you need. 2 vfd. If you want to drive more off one motor then you'll need t9 compensate in the vfd for that. If you want a 3 phase system for the workshop you'll Need a phase conveter

 

[Seadog]

Buy a VFD that rated above your needs. I bought a 1hp Teco from Drives Direct and used it on a 1hp motor. It definitely wasn't happen under certain condition, often slower speeds. Spoke to DD and the very helpful man out me right. Bought a 1.5hp one, Invertek, and I've not had a problem since.

 

[rikrobson]

There is drop in power when you convert something. That needs to be taken into c9nsideration. Also induction motor sink a large inrush current.

 

[oilyneil]

How does this work with the ramp up in frequency of a vfd output? Do you still get the large inrush?

 

[Seadog]

Most inverters will/should handle an overcurrent condition at start up. The amount is determined from the parameters you enter for the motor. In addition the speed can be controlled, as in ramp up - ramp down, for a more controlled start by starting from a pre-determined lower frequency.

 

[rikrobson]

You have still to charge the coils up.. let the vfd programming do the work. That's why it's one per motor

 

[ronan]

There is drop in power when you convert something. That needs to be taken into c9nsideration. Also induction motor sink a large inrush current.

I often wonder what the percentage power loss is with vfds. Doesn't really matter though as i will never be working the machine that hard.

 

[daleyd]

Vfd are generally quite efficient, here's some info from Schneider website. Generally the larger the drive the better the efficiency. When we looked at fitting some big (75 kw) ones on furnace fans some years ago the payback time was about 12 months (that was running them controlling via a pressure sensor rather than running flat out all the time).

The inrush when a vfd starts is negligible compared to direct on line starting or even star/delta. Direct online puts 240 (or 440) volts across windings of typically a couple of ohms resistance (say 4 for ease of calculations) so the current will be something like 60 amps at the instant of the contactor coming in, and will be hundreds/thousands of amps for bigger motors on higher voltages. This initial spike decays as the windings build up inductance.

When an inverter starts its ramp up the voltage it provides to the motor is much lower, hence the current it will draw is also a lot lower. This is simplifying it somewhat as well, as the inverter had the ability to limit the current it supplies to the motor windings so can reduce this effect further.

 

[daleyd]

With regards to sizing inverters relative to motor size, there shouldn't be any need to oversize a vfd - decent ones should have the ability to supply more than their rated current for short periods, altivar are typically 20% more for a couple of minutes and 50% for a few seconds. If your pulling more than this (remember this will be above the motor rated current) as a matter of course really you need to look at the motor size for your application.