Which VFD for disc sander

[Ben Grefe]

I bought a 3HP 3ph disc sander a few months ago at auction, came up with a plan for the VFD and got busy....

I was planning to buy a Huanyang GT series VFD with the external braking resistor terminals (https://www.amazon.com/dp/B077KS9LRY).

Looking through the seemingly successful VFD thread for a Delta jointer I see some good comments on the Lapond VFD’s. I know the Huanyang’s don’t get the best reviews, are there any better (cheaper?) options that I should be considering?

[Bob Riefer]

I'm nowhere near the expert on this topic, but I'll say this... it seems like including the details of my motor plate helped the actual experts give me the right advice during the jointer thread that you reference. I think besides the horsepower, some of the other details are worth including.

[Matt Day]

I’d stay away from the HY ones, which I did when I got the Lapond one I recommended in Bob’s thread. It’s $85 by the way. It accepts breaking resistors.

[Ben Grefe]

Good point Bob.

The motor plate specifies:
Induction Motor
3 Phase
3 HP
220/440 Volt
60 Cycle
9 / 4.5 Amp
4 Pole
1725 RPM
Built in 1993

Matt,

I see multiple models (series) offered by Lapond in different sizes. Any idea which one I need?

[Matt Day]

https://www.amazon.com/LAPOND-Performance-Inverter-Variable-Frequency/dp/B07T96TG9F?ref_=ast_bbp_dp&th=1&psc=1

[Bob Riefer]

Matt - from that link, two products are available. Which one will he want to suit his scenario? One of them notes 3 hp (seems like he'd want that one?), the other 2 hp (which is the one I have since my jointer is only 1.5 hp)

[Matt Day]

He has a 3hp motor, so he’d want the 3hp VFD. Over 3hp you’d have to consider derating the VFD, meaning getting a higher hp rated VFD than the motor, but for 3hp and less get the same rated VFD.

[Tom Bussey]

Another thing to consider is since it is 3ph you can use instant reverse to brake. Instant reverse is not as good as a brake but almost as good. And there is always a reason to sand from both sides of a disc, so a reversing switch is awesome. I bought an old disc sander that had a reversible single phase motor on it. Paid $50 for a motor repair shop to put a reversing switch on it. It has to come to a complete stop before reversing but having it reversible is worth every penny spent.

[Ben Grefe]

Well, I bought the Lapond 3HP model linked by Matt - thanks for the help.

For the life of me I can’t find the manual online for this unit, so I’ll just have to wait for it to arrive to figure out how to size the braking resistor. I’m pretty sure I need a 300w resistor, but I can’t figure out which ohm rating without the manual.

Thanks for the help so far.

[Bill Dufour]

I do not know why you would need any brakes on a disk sander? Be careful, my cheap HY VFD has brake resister terminals but they are not actually connected to anything. they are just for show. This is fairly common on the cheap ones.
Be very careful using brakes or reverse on a disk sander. It is possible the disk is just threaded onto the shaft and can unscrew if run backwards or braked too fast. It is not unknown for lathe chucks to unscrew and missile off when stopped too quickly.

[Matt Day]

Bill makes a good point about using a VFD and brake resistor with a disc sander while in reverse. All that mass could (pretty easily?) unscrew the disc, if it is indeed screwed on.

My 20” will take about 16 minutes to spin down. I forget the max time you can program decel, but if you make it say 1 or 2 minutes that might be a slow enough to not unscrew it. I would t want to be the one doing the testing on my theory though. ;-)

[Ben Grefe]

Bill,

I actually contact HuanYang months ago when I bought the disc sander about braking terminals.

Turns out they make 2 models of their VFD’s. One with braking terminals present but not connected, one with braking terminals wired. You have to special order the one with braking terminals wired. You do this on amazon by clicking ‘buy from another source’ and selecting the slightly more expensive model. Stupid? Yes.

I don’t plan on using the brake to suddenly stop the disc, I just don’t want to overload the VFD. I’ve read that’s what kills the cheaper versions quickly. I guess I can start with a 5-8 minute spin down setting and see how it goes.

[Tom Bender]

I stop my table saw in 1 second without a resistor. This is fine per the VFD manufacturer's rep. It's another brand.

A sander is a lot more mass so it will take longer but 5 minutes seems excessive. Then again why stop it fast? It's great on a TS but not important on a sander.