VFD Maximum Motor Speed

[rtcosic]

Finally wired up the VFD on my 370W drill motor.

All works - speeds up, slows down, stops, starts and runs backwards.

The motor is a 1425 rpm Hawker Siddeley Brook Crompton Parkinson motor to BS3000/11 according to the data plate. It is huge compared to the 370W single phase motor on the cheap DIY shed pillar drill.

I have replaced the bearings with new SKF ones rated for 19'000 rpm.

I have the speed range set from 5 to 75 Hz or 143 - 2140 rpm. The motor sounds quite happy at those speeds.

What is the maximum rpm I should try?

The drill data plate has the highest quill speed over 4000 rpm which I don't plan to exceed.

 

[daleyd]

What speed do you want to try?

If it works and does what you want leave it as is - you can go faster but you end up increasing the frequency without any increase in voltage which means the motor starts to make less power as you go faster (over the 50hz point), so while it’s possible to over speed the motor it’s debatable whether you gain much, unless you really need the extra rpm. I find most of the stuff I do on a pillar drill I want lower speeds for, higher is almost irrelevant, though of course you might have different needs to me.

 

[brightspark]

no need to go over 2140 and if you do that's only on small twist about 1.0mm you still have the belt speed change as well

 

[Pete.]

Most 4-pole motors have a 2-pole variant which puts the base speed at 2800rpm. If yours does then you could infer that 2800rpm was safe.

 

[daleyd]

Most 4-pole motors have a 2-pole variant which puts the base speed at 2800rpm. If yours does then you could infer that 2800rpm was safe.

I’d say the motor wouldn’t be the limiting factor, but the drill itself. I’d just be wary that over speed too much will reduce the amount of torque - though it’s probably not a big consideration for a drill (as you would be using the higher speed for smaller drill bits anyway).

To be honest if it sounds ok then I’d just use it as it is.

 

[eLuSiVeMiTe]

I set my Max to 70 hertz
No complaints from my motor and seems a lot use 70 as a limit from my searches

 

[rtcosic]

2800 would do me fine. The smallest pulley on the quill is damaged and to avoid damaging the belt I don't want to use it.
The only time I would need high speed is 3mm or so drills into aluminium.

At 2800 maximum for the most common bit diameters I could leave the belt on the second pulley for mild steel.

Very occasionally first pulley for very low speeds.
Third pulley would then only be used for small bits into aluminium - about once a decade!