VFDs, educate me

[Tim Hoyt]

Hi my name is Tim Hoyt and I am fairly certain this is my first post. I have lurked and learned a lot for several years.
Anyway, I am in a serious search for a nice wood lathe. I suspect I will end up buying a Powermatic 3520b brand new. But I have been checking the used market diligently. So, of course, I ended up buying, sight unseen what I think is a Delta 28-350 bandsaw in a government auction. They claim it runs (snicker,snicker) and the only "problem" is a 3 phase motor.
I have not really paid attention to discussions about how to solve the 3 phase conundrum. Yea, I have read a little, but......
my assumptions:
1. The only way to go is a VFD.
2. A phase converter, would "rob" about 1/3 of the horsepower which I suspect is 1 horse.
3. One of these new fangeled VFDs shouldn't run more than $200 for a decent one.
4. The installation of said VFD will be a piece of cake.

So am I headed in the right direction? I'm only looking for the "big picture" at this point. i plan on much more research before I do anything.
Thanks
tim

[Simon Dupay]

check out owwm.org they have the info you need BTW nice saw

[Matt Day]

I think VFD's are the way to go as well.

Static phase converters rob 1/3 hp, and VFD's are coming down in price that SPC's are on their way out I think.

I just bought a $116 (shipped) 3hp VFD off eBay (a131). I'm struggling with a language barrier with the seller and company to get it to work like I want it, so it might be returned. I figured it was worth a shot. I'll try a huanyang if I return it, which are around $140. The TECO fm50 is around $200 w/o shipping, and I have one of those on my bandsaw. Simple and good CS, I just tried to save a few bucks this time.

[David Malicky]

1. Phase converters still have a place, but less and less now that VFDs are so inexpensive. Personally, I always use VFDs. http://www.hobby-machinist.com/threads/static-phase-converters-vs-vfds.14625/
2. Yes for a static phase converter. A good RPC gives full motor power but that is more $ with additional issues.
3. Yes, for reasonable HP.
4. Depends on one's experience with wiring and controls. The wiring is not complex if you've done similar work. To program the VFD, it takes time to read the manual and go through the many menus. Agreed that a Teco manual is easier to read than a generic one.

With an old motor, there is a possibility that its insulation won't stand up to the voltage spikes put out by a VFD. Modern motors have Class F (or better) insulation which is plenty good. If the motor is rated for 460V and your VFD outputs 230V, and the line lengths are not long, and this is home shop duty, it will likely work fine.
http://www.practicalmachinist.com/vb/transformers-phase-converters-and-vfd/vfd-older-motor-what-issues-200426/
As you probably know, 1 HP is not much for that size bandsaw; an upgrade would be $100 used - $300 new.
If running below 30-50% rated RPM at high amps for extended time, the motor should be derated so it doesn't over heat (program the VFD to put out less amps). Or add a cooling fan.

[David Kumm]

If you are running 240 volts you are unlikely to have motor problems with a vfd. Old motors may have had worse insulation but generally used big enough frames that overheating isn't an issue. If you are running a 460 v motor, you might as well swap it out. You don't want to run a 460 on 230. It might run, but won't for long when under load. Dave

[Dennis Ford]

I very much like VFDs but have a couple of cautionary comments about your situation;
* Band-saws don't benefit much from variable speed if you are only cutting wood (metal cutting is a different ball of wax)
* Wiring and setting up a VFD is easy IF you have electrical skills and can understand the manual (often technical and MANY pages). The name brand VFDs have better manuals.
* If it is really only a 1 hp motor, you would be better off replacing the motor with a larger single phase motor.

[David Malicky]

Sorry, I wasn't clear -- I didn't mean to run a motor that is wired for 460 at 230. Rather, that if it's a dual voltage motor (230 and 460), then its wires are rated for 460, and so wiring and running it at 230 (with VFD spikes) should be ok.

Edit: and Dennis has a good point -- unless you need the variable speed, consider using the VFD $ to buy a bigger single phase motor.

[Andy Booth]

A VFD is a great way to go however there
- Older insulation is more than likely to fail over time. Most old motors I have connected to VFD's eventually fail.
- I have almost always had to increase HP when replacing an older motor with a new motor.
- Pay attention to safety and the mfg's recommended circuit.
- Go for a better quality unit that has UL approval.

- You could just buy a 1.5HP 230V, 1750 RPM, single phase motor and not have all the extra hardware. Check frame size to make sure it fits.

[Anthony Whitesell]

I wouldn't call the installation and wiring of a VFD a piece of cake. It takes due diligence, a little know how, and a bunch of reading to not only wire the VFD but also figure out what all the parameters do and which ones you need. In the case of a bandsaw, where a single speed is enough (unlike a drill press where variable speed is a must) will simplify the setup of the VFD and it can be mounted out of sight and out of the way. I have not found a VFD that is capable of single phase 120 or 240 input and output more than 240V 3 phase. If you have a 380V or 460V three phase motor, you will have to change it out. In which case you might as well drop to a 120V or 240V single phase motor and save the money and hassle.

[Keith Weber]

Sorry, I wasn't clear -- I didn't mean to run a motor that is wired for 460 at 230. Rather, that if it's a dual voltage motor (230 and 460), then its wires are rated for 460, and so wiring and running it at 230 (with VFD spikes) should be ok.

David, I think you have that backwards. If the motor is 230/460V, then its internal wires are rated for 230V, with 460V being OK. The wires are limited to current (amperage), not voltage (which is probably closer to a 600V limit). The current will double at 230V (compared to 460V), so you need heavier wires to run a machine on 230V. A 230V motor will have heavier gauge wiring than a 460V only motor. A 230/460V motor will have the internal wiring size to run on either voltage, but 2 things need to be done first.

Firstly, you need to rewire the motor according to the wiring plate on the motor. Secondly, you need to swap out the heaters on the motor starter. If you run a motor on 230V with 460V-appropriate heaters, you can melt the heaters. If you run a motor on 460V with 230V-appropriate heaters, you don't have proper overload protection.

[David Malicky]

David, I think you have that backwards. If the motor is 230/460V, then its internal wires are rated for 230V, with 460V being OK. The wires are limited to current (amperage), not voltage (which is probably closer to a 600V limit). The current will double at 230V (compared to 460V), so you need heavier wires to run a machine on 230V. A 230V motor will have heavier gauge wiring than a 460V only motor.

Oh, by "rated for 460", I was referring to the voltage capability of the wire insulation, not the current. With a VFD, the motor will see voltage spikes well above the nominal line voltage (roughly 2x, depending on many factors). Insulation is very good in modern motors, but more variable in older ones. Like Andy's experience, above, the insulation in an older motor may break down from these voltage spikes. If the motor/insulation is only rated for 230V, running a VFD at 230V (nominal) is more risky. But if the motor/insulation is rated for 460V and the VFD outputs 230V (nominal), there is some insurance the insulation can handle the spikes. No guarantee either way, of course. This is my understanding from practicalmachinist and other sites.

[Erik Manchester]

Tim,

I have a shop full of older tools with three phase motors and many run on VFDs. A good three phase motor is a reliable beast, it has no capacitor or start circuit to be concerned with and as long as the bearings are OK and the power within spec it will run.

As others have mentioned you will want to see the motor tag to see what you are dealing with and hopefully the motor is a 230v or dual voltage which makes running off a VFD easy.

It is likely easy to swap out the motor for a single phase motor but this will require new motor heaters or possibly a new starter in addition to the motor.

If you go with a VFD and retain the existing motor, you don't require a magnetic starter as the VFD can provide the motor overload protection.

The simplest way to run this saw is likely to swap out the motor for single phase, but if you like to tinker with tools and have time to do a little reading the VFD will provide excellent three phase power and run your saw (assuming a 230v motor). As you will just be running the saw at a constant speed without braking, etc I would not be concerned with voltage spikes, etc.

The flood of Asian VFDs are both cheap, and in my experience, reliable. I have a rotary phase converter that I use with a transformer to run larger motors but all of my smaller motors (3 hp or less) are on VFDs.

In your case, soft start, speed control and electronic braking are not so useful on a bandsaw so you would be using the VFD for phase conversion only. There are VFDs available that take single phase 230v input and provide 230v three phase output.

There is a lot of good info available online to help you and you are on the right track doing your research before buying anything.

Good luck.

[Anthony Whitesell]

Tim,

In your case, soft start, speed control and electronic braking are not so useful on a bandsaw so you would be using the VFD for phase conversion only. There are VFDs available that take single phase 230v input and provide 230v three phase output.



Actually for a bandsaw, the electronic braking may be very useful. Not so much for the soft start and speed control. I wish my big 17" grizzly had some sort of help getting stop. It takes close to 30 seconds to wind down, but only a fraction of that to start up.

[Cary Falk]

Since this is a bandsaw and you don't really need any features of the VFD, I vote with putting a BIGGER single phase motor on it and calling it a day.

[Rod Sheridan]

Since this is a bandsaw and you don't really need any features of the VFD, I vote with putting a BIGGER single phase motor on it and calling it a day.

Cary, electronic braking is a very useful feature on a band saw, which the VFD will provide...........Regards, Rod.

[David Kumm]

If you go the vfd route, talk to someone about what you need. I'm not sure a small vfd will have enough braking torque to stop a bandsaw very quickly without a braking resistor added. You can order a vfd with additional braking for not much extra. Get some advice about the application. Dave

[Cary Falk]

Cary, electronic braking is a very useful feature on a band saw, which the VFD will provide...........Regards, Rod.

I would still take a bigger motor over the braking. Sounds like some of them came with a 1hp motor.

[Bradley Gray]

+1 for a bigger single phase motor. I have lots of 3 phase motors run on 2 different RPC's, but for 1 tool I would spend the money for more power. I can envision going to all the trouble to set up a VFD for the 1hp motor and then finding out I needed more power. KISS (keep it simple..)

[Allan Speers]

I think VFD's are the way to go as well.

Static phase converters rob 1/3 hp, and VFD's are coming down in price that SPC's are on their way out I think.

I just bought a $116 (shipped) 3hp VFD off eBay (a131). I'm struggling with a language barrier with the seller and company to get it to work like I want it, so it might be returned. I figured it was worth a shot. I'll try a huanyang if I return it, which are around $140. The TECO fm50 is around $200 w/o shipping, and I have one of those on my bandsaw. Simple and good CS, I just tried to save a few bucks this time.


The TECO's are great. Known to be dependable for a very reasonable price.

However, that other Taiwanese junk, sold under all sorts of brand names, is known to be complete garbage. The internet is full of rants and long cuss words from folks who wasted money on them.


Ans yes, OP, they are easy to install and use. You also get some vari-speed in the bargain, plus dynamic (electrical) braking. If you get TECO, consider adding extra heat resistors, (the dealer can sell them to you) as this will increase the braking action, and that's a very good thing with a bandsaw.

[Tim Hoyt]

Hey thanks everyone for some excellent comments. It is my understanding that these saws came equipped with either 1 or 1 1/2 hp motors. I do not know if the original motor is present or not and what size it is. I suspect if it is 1 hp and old, I might just swap it out for a 1 1/2 hp 220v single phase motor.
I was not aware that a VFD offers soft start and some sort of braking and I doubt I would ever change the speed once set up. Not worried about braking, the saw has a foot brake.

i guess my biggest problem right away is how to move this 700 lb monster.

Thanks again everyone!

[Keith Weber]

If you want a VFD that's not made in Taiwan or China, look up Lenze SMVector AC Tech drives. I bought a couple of them from the Precision-Elec website. They seem nicely built, the buttons are more robust than most, and best of all... they're Made in the USA. The manuals are in English, and are easy to follow. Customer service and knowledge at Precision-Elec is top notch, too. They answered all my questions instantly via Internet chat from their website, which made my decision to buy from them very easy. They've also posted some YouTube videos on wiring them.

I haven't got them hooked up quite yet because I've been sidetracked on building the machines that they will power, but from what I've researched, I'm not anticipating any problems. Hopefully, I should be ready for wiring the first one soon (which for me, means in a month or two).

Anyway, I just thought I'd mention them. No affiliation. Just a customer who appreciates good customer service, and American-made products.

[Matt Day]

The TECO's are great. Known to be dependable for a very reasonable price.

However, that other Taiwanese junk, sold under all sorts of brand names, is known to be complete garbage. .

You should do some more research before making blanket statement. Check Practical Machinist for instance. . There are lots of happy users of Huanyang VFD's, and I finally just got my A131 setup (wasn't easy but saved me $80+ Over a TECO). I also have a TECO which was easy to setup and use.