Tannewitz GH36

[John Pendery]

Hey Everybody,

I posted this over on owwm just a bit ago thinking it pertained to that site, but want to get as much feedback as possible, and I think there’s more traffic here. I try not to make duplicate posts on different message boards, but here goes:

Interested in feedback from others that are running large bandsaws off rotary phase converters or vfd’s. Recently moved shops and lost utility company three phase and am running my equipment off an American Rotary ADX 20 hp. My Tannewitz GH36 has a five hp direct drive motor, but it pulls a ton of amps on startup and I keep tripping breakers. My electrician buddy suggests I buy and wire it with a 80 amp breaker to handle startup, but the breaker alone is close to $500 (local supply store price, can likely get much cheaper online) and I feel like it’s somewhat of a shot in the dark if that will improve the startup issue. Is anyone out there running this saw off a vfd with success? Would you suggest I follow the advice of my electrician? Curious what others are doing with large bandsaws that are lacking three phase from the street. Thanks

John

[Kevin Jenness]

Hey Everybody,

I posted this over on owwm just a bit ago thinking it pertained to that site, but want to get as much feedback as possible, and I think there’s more traffic here. I try not to make duplicate posts on different message boards, but here goes:

Interested in feedback from others that are running large bandsaws off rotary phase converters or vfd’s. Recently moved shops and lost utility company three phase and am running my equipment off an American Rotary ADX 20 hp. My Tannewitz GH36 has a five hp direct drive motor, but it pulls a ton of amps on startup and I keep tripping breakers. My electrician buddy suggests I buy and wire it with a 80 amp breaker to handle startup, but the breaker alone is close to $500 (local supply store price, can likely get much cheaper online) and I feel like it’s somewhat of a shot in the dark if that will improve the startup issue. Is anyone out there running this saw off a vfd with success? Would you suggest I follow the advice of my electrician? Curious what others are doing with large bandsaws that are lacking three phase from the street. Thanks

John

I'm surprised you need that much current to get it moving. We had an 18 hp three phase single head widebelt running off a 60 or 70 amp breaker and I ran a Crescent 36 with Carter fabricated steel wheels with a single phase 3 hp motor on a 20 amp circuit. It took a while to ramp up and definitely could have used more power for resawing but I never tripped the breaker. With a vfd (single or three phase input) you can adjust the acceleration time and lower the initial current draw but I would suspect something else going on, maybe an old worn breaker. Have you checked the actual current flow and voltage on the bandsaw circuit? Is the wiring correctly sized? Do the wheels spin freely with hand power? Did you have any problems prior to running the saw off the rpc? Are you having problems with any other three phase equipment?

[John Pendery]

Hey Kevin, in the past the saw was not run off of a rpc. The breakers are brand new, but I’m on a 40 amp breaker with according wire gauge. I think my first step will be to throw a 60 or 80 amp breaker in the panel ordered online to see if that helps. On startup the inrush amp draw is around 140-50. Wheels spin freely and the saw is in good operating order, but the wheels are big heavy suckers. No other problems with other machines up to 13hp. Maybe just running 6 awg to a 60 amp breaker or 4 awg to a 80 amp breaker would do the trick. I think it’s just the mass of the wheels that lead to a long startup time and big amperage inrush causing an undersized breaker to trip. I was hoping someone out there had a big bandsaw in a similar situation to avoid guesswork. Thanks for your feedback!

[Bill Dufour]

A 5Hp VD will cost less then that giant breaker and extra wire. You have two choices get a 5hp vfd and supply it with three phase power or get a larger then 5hp and supply it with single phase. A VFD set for say 7 seconds acceleration should not trip the circuit breaker.
The VFd also gives you the option of power braking.
You can use the existing switches to control the low voltage VFd switching or add as many extra as desired. I like to add an extra off switch on the outfeed side of many machines.
BILL D

[John Pendery]

Bill, will I experience any loss of power if I choose to run the saw with a VFD? The only VFD in my shop is on my lathe, and that came installed from the factory, so really no experience with them. Thanks for your input.

[Bill Dufour]

A 5hp vfd will output 5Hp. They are about 95% efficient. They generate full 100% real sine wave three phase so the motor runs at full power. Unlike a static phase converter or a poorly balanced rpc. You could run it off a 3Hp vfd then the motor would only make 3hp at maximum load.
I do not think variable speed is much use on a bandsaw. Lower speed is lower horsepower. To cut iron speed must drop by times ten or so not enough Horsepower left over to do any work and the motor will overheat unless you add forced cooling.
For your use think of a VFD as a soft start unit.
BilLD

[Bradley Gray]

I have a 32" Crescent 5hp running on a 10hp Kay RPC with no start issues. I also run a 3hp table saw that had issues until I changed the starter heaters.
Southland Electric sells used starter parts.

[Jonathan Jung]

John, I'm concerned you may be led a bit astray here. Only certain VFDs can only be matched Hp-Hp, others need to be oversized. Also, usually the power loss of a 3ph motor on a VFD is normally when run at slower speeds, as only certain motors will sustain power at slower speeds. Call Automation Direct. They are so helpful and their VFDs are good, if you go that route. My big bandsaw and other machines are powered by a RPC but I have others on VFDs too.

[Malcolm McLeod]

Bill, will I experience any loss of power if I choose to run the saw with a VFD? The only VFD in my shop is on my lathe, and that came installed from the factory, so really no experience with them. Thanks for your input.

John, I'm concerned you may be led a bit astray here. Only certain VFDs can only be matched Hp-Hp, others need to be oversized. Also, usually the power loss of a 3ph motor on a VFD is normally when run at slower speeds, as only certain motors will sustain power at slower speeds. Call Automation Direct. They are so helpful and their VFDs are good, if you go that route. My big bandsaw and other machines are powered by a RPC but I have others on VFDs too.

I'll 2nd Mr. Jung's suggestions/info. Assuming you run your BS at rated speed, the VFD is basically operating as a soft-start, and once at speed, will develop rated power.

If used as a phase converter, 'oversized' is perhaps a better term than the more common 'de-rate', since most here are speaking from the beginning perspective of the motor. Your 5Hp will need 15.2FLA at 230VAC/3ph, so 28FLA on the 230VAC/1ph input (motor tables still use 230VAC, regardless if archaic). So, a VFD in this case would need to handle the 28A input. Some manufacturers have addressed this 'small end' phase conversion of the consumer market by increasing the size (amperage handling) of just the input section of their VFDs. If so they will usually state that a 5Hp VFD can run on single phase, or words to that effect.

If they do not state this, then you'd need a VFD sized for 28A - - this is typically a 10Hp VFD, but you might get by with 7.5Hp ratings if you don't run the BS too hard.

** You could look at true soft-start set ups, but for only 5Hp I'd not recommend it.

[John Pendery]

Thanks for all the input guys. I was curious what experience others had with vfd’s, but I’m going to steer clear as I think it might just complicate things. I agree variable speed for my application has no benefit aside from soft start. I’m not sure why my electrician undersized the breaker and wiring so much, but that’s got to be the root of the problem. I’ll bite the bullet and simply get a larger breaker with according wire size and rewire it properly from the panel as my rotary phase converter provides pretty clean and balanced 3 phase power. The saw has always run great and has a baldor electric brake that I would like to keep in use, and I assume switching over to a vfd would render it useless. Thanks again guys

[Richard Coers]

I had a 32" Yates American years ago. First tried a homemade static phase convertor and one of the capacitors blew like a volcano. Then went to a homemade 7.5hp rotary phase convertor. Worked perfectly. I would definitely not buy a cheap 5hp VFD to run it. The start time is slow enough on those big bandsaws, let alone try to soft start it. Has anyone suggesting a phase convertor ever used one on a big old bandsaw?

[lou sansone]

I have a 36” Moak bandsaw with the super slow speed 5 hp motor ( 30 hp frame size ) and run a rotary phase converter with no problem. I think I only have the saw on a 30 amp breaker. Never a problem

I have a 37” timesaver wide belt with the heavy 12” drum with a 20 hp motor on a 60 amp breaker with no problem either