380v Output Inverter Braking.

[Zadig]

I’ve been looking at purchasing a couple of 220-380v 3 phase inverters for the mill I have. I’ve been in touch with the Chinese supplier and they say you cannot brake the motor using a braking resistor, however, their literature clearly shows the implementation of a resistor in the schematics and wording. The VFD is one of the 9600 series 4 and 5.5kw output. I’ve also spoken to another gent who seemingly confirmed that you couldn’t use a braking resistor but it would be nice if someone with more knowledge than myself could clarify the facts. Any help would be appreciated, cheers, Mike

[Muzzer]

I don't know this VFD but generally, to implement a braking resistor there needs to be an additional switching device within the VFD that is activated when the internal DC bus exceeds a threshold. I've seen some examples of VFDs where the components haven't been fitted and other examples of the same basic product where they have. This manufacturer may be telling you that this particular model doesn't have them. There's no reason why one couldn't implemented, so it must be a choice the manufacturer made.

It's possible to obtain standalone braking modules that can be added to an existing VFD, being connected across the DC terminals that are usually accessible. That's possibly an option for you but unless you bought second hand, it could cost you rather a lot.

[Zadig]

Cheers Muzzer, that’s just what I wanted to know. On a similar note, I’ve always been under the impression you cannot manually brake a motor that is controlled by a VFD, mainly because it has a programmed ramp down. Today, I’ve been told by someone that they successfully brake both of their lathes with foot brakes (via a physical braking system). Can this be done?

[m_c]

Out of curiosity, which supplier did you speak to?
I've bought a few boost VFDs from CNWeiken, and they've supplied braking resistors to go with the VFD.

Regarding manually braking, you can set the VFD to simply let the motor freewheel, then you can brake it manually.

[Zadig]

I’ve been asking a few Chinese suppliers questions but I suspect they’ll come through during the night. I know the supplier you mentioned I’ll bear them in mind. I’m looking at the 380v output models rather than 220v, have you purchased one of these with the resistor braking capability? I didn’t know about the freewheeling aspect of the VFD that’s really handy to know, cheers. Do you still have your Shizuoka mill?

[m_c]

Yes, I still have the Shizuoka.
t's still very much a work in progress, but I think I've got 90% of the bits to actually get it functional, it's just life, work, and business keep getting in the way. If I can get if working, I do have a big pet project lined up that I want to do, but making money is the current priority.

[Zadig]

Do I remember correctly that you replaced the impact gun drawbar on it. The brush housing on mine is coming to the end of it’s days so if you have one to sell I might be interested. I really do like my Shizuoka, I replaced the CVT drive with a 7.5 hp motor and vfd and it works a treat. I’ve pondered getting a bed mill at some point but I’d be loathe to get rid of it.

[m_c]

You sure do. Well, I've at least got most of the parts, with the trial machining done to replace the electric impact driver with an air impact gun.
If I could find the electric driver, you could have it, but I had a look earlier and couldn't see it. I'm pretty sure I never threw it out, but it isn't where I thought I'd left it. If it turns up, I'll give you a shout.

[Zadig]

Thanks for looking and thanks for the offer too. I’ve bought a 3/8” butterfly impact driver with an idea of making one like the kurt design and if I can’t get a replacement electric one that is easy enough to butcher I’ll probably go down a similar route to yourself. My old Black and Decker one works quite well and get lots of use, I’m just predicting it’s going to let me down half way through a job. My only criticism of it is it’s a bit loud and when a job has twenty or so manual tool changes your ears ring after a while. I can’t recommend getting a big motor and vfd highly enough. A direct drive and getting rid of the noisy back gear makes the mill almost silent. I made up a large resistor bank for it and the spindle stops in half a second.

[Muzzer]

I don't know if I mentioned it here but I'm a fellow Shizuoka owner. Mine's an AN-SB which is almost identical to the more common AN-S. Mine came from the factory with a fixed belt ratio and VFD although I had to replace the original VFD.

I've got the manual / parts list with section drawings if that would be useful. I've also stripped down and rebuilt most of the machine apart from removing the actual saddle and table for understandable reasons. I took lots of pictures if you want to know what I encountered.

The machine's where I live near Blackpool although I work in Leamington.