Surge protection?

Hi,

Would "surge protection" be wise for a lathe with electronic speed control? If so, what would you wise people suggest?

It should be built-in, but almost certainly won't be due to cost. I assume that by surge you mean high voltage, fast and short spikes, as opposed to longer term over-voltage. If I remember correctly the standard surge tests have repetitive patterns of both polarities with peak voltages of 500V, 1kV and 2kV.

If the lathe runs off a single phase 13A socket then one can buy plug in surge protectors intended for computers. Provided they are rated for the current then they should be fine. Or one can buy more involved EMC filters that may also contain surge protection, but they're likely to be more involved to wire in safely. That's a caveat bearing in mind the brouhaha going on in the VFD thread.

Andrew

Ketan advised me to feed a mini lathe via a surge protected supply. I use an extension lead with built in surge protection.

I know what a spike in the supply can do, so anything that lessens the risk has to be worth having.

It may only last for a millisecond, but it will do the damage, just the same.

My big one's VFD is fed through a surge protection, and a filter, to prevent any nasty from being fed back into the mains. Would hate to mess up TV for someone on the same phase, three doors away

Howard

What sort of motor, how big, and what sort of electronic control?

If a DC Motor in the 500W to 1500W range, PWM controlled as fitted to a mini-lathe up to some large hobby mills, then no starter is needed. Except make sure the operator knows to stop by winding speed down and never to start with the speed control at high. (The operator is the starter!)

If a 3-phase motor with a VFD, then the VFD can be configured to accelerate, decelerate, and detect over-current, So in addition to controlling speed, VFDs are also excellent for managing start surges. It seems most modern VFDs come pre-set with reasonable surge parameters, otherwise read the horrible manual!

Single-phase motors briefly draw an exceptionally heavy current when starting. Big ones, say more than 1kW, need a starter, either electromechanical or electronic. (Given the choice, avoid single-phase motors.)

Similarly, big 3-phase motors connected to a 3-phase supply also need a starter. These days it's becoming common to fit a 3-phase to 3-phase VFD because of the extra control they give compared with an electromechanical starter.

Often as not the motors on small machines don't have starters because the supply can handle the surge. It may be necessary to help with a slow-blow fuse or a suitable trip - if so, the machine's manual should have all the details.

Dave

PS Just read other replies which focus on transient protection, i.e. voltage spikes that might upset the electronics.  If that's the issue, the power leads sold for computers will do the job.  They vary in sophistication from cheap and simple (effective for mild problems), more expensive for more difficult cases, up to serious money for a professional box sold by RS and others.   What's the problem?  Kit in your workshop, or coming in from outside?

Edited By SillyOldDuffer on 22/03/2020 17:14:40

The motor is 1100W brushless.

My concern in using surge protection is not for the motor, but for the electronics in the board that control the speed and commutate the brushless motor.

The motor may be pretty robust, but FETs and the like are not min the same league for withstanding over voltages.

Howard

Brushless motors need an electronic driver that should deal with surges on the motor side. How good the electronics is at protecting its input is anybody's guess.

If there's an input spike problem that can't be fixed with a computer type surge extension lead then try one of the posher protections available from RS on this page

Dave

Hi Guys,

Varistors are cheap and are easily soldered across the mains supply inside the machine. You need two. One from live to earth and one from live to neutral. 275 volt ones are available from RS or Farnell, in fact almost any electronics components supplier. They should be wired on the supply side of any filter that may be fitted.

https://uk.rs-online.com/web/c/passive-components/variable-resistors/metal-oxide-varistors/?searchTerm=275 volt varistor  NOTE: this is in bags of 250.  Farnell do them in tens, much cheaper.

Edited By John Baron on 22/03/2020 19:23:51

Edited By John Baron on 22/03/2020 19:27:15

The estimable John Ward recently uploaded a series of videos on YouTube about surge protection for electronic apparatus - well worth watching.