Motor ID & VFD Selection

[Rod Ango]

I bought a fairly antique 20" Monarch bandsaw. It came with a gigantic (~16" diameter) 5HP electric motor.
I'm not sure a bandsaw of this size needs this much motor, but since I have it, I'll try to use it.

The motor appears to be 5HP 3Phase, and probably 1730RPM. It is old enough that I can't find information
about it on the 'net. In the US, power is supplied to residences in single phase, so I would like to size and
buy an appropriate VFD/Inverter/starter to run it from 240VAC 1-phase at 220VAC 3-phase. It would be great to choose the run speed, have soft start so there's not a huge inrush current, and possibly use
dynamic braking.

I've seen less expensive Chinese manufactured VFD's on ebay, but there's typically no consultation
with the vendors, and caveat emptor. I have seen recommendations for sizing at multiples of up to 6
or 8 times Full Load Amps. Also I've seen it said with 1 to 2 HP motors that 2 x FLA is sufficient.
The label is faded enough that I can't be sure about the listed FLA (12? 12.68? 12/6.8 at 220/440?)
nor the motor efficiency.

One formula I found online shows to use ((HP x 746watts/HP) ÷ Efficiency) x √3(for 3phase) to get the
KW required to size the VFD properly. It sounds right, but I can't read the necessary info from the motor
badge so I wondered if anyone is familiar with this gear enough to make a recommendation?

Thanks.

 

[Darkwood]

If you get this bandsaw updated and working what is your intention with it, who will be using it?
It might sound a strange query but it changes how we respond to you.

Just for useful info can you take a pic of the terminal connections and arrangements of any links, it may help to decipher some of the plate.

 

[Rod Ango]

If you get this bandsaw updated and working what is your intention with it, who will be using it?
It might sound a strange query but it changes how we respond to you.

Just for useful info can you take a pic of the terminal connections and arrangements of any links, it may help to decipher some of the plate.

Ok, will get and post the photos.

I intend to use the saw primarily in 'hobby' woodworking. It clears >= ~11.5" under the guides. I intend to use the saw for basic cuts on hardwood, softwood and ply. I also plan to resaw some interesting, air-dried woods I've collected over time. Right now I have some larger pieces of an unusual cherry that was felled decades ago and pushed into a burn pile. I also have some large rounds of cornus florida, and a piece or two of hickory, all very hard woods.

Eventually, if I can get a low or variable speed, I might consider some use in light metals, esp. aluminum (angle or sheet, up to 1/2"), sheet metal or mild steel up to 1/8" or so, plastic and some composites. I say 'eventually' as there may be other options, and wood sawing is primary.

 

[Darkwood]

The point in asking here is that this is usually out of the scope of what we would class as DIY advice, you are located in the US by the looks of it and I can only imagine you will have similar legislation and safety guidance as here in the UK on these matters, that been said, in upgrading this machinery (if this was the UK) you would be required to bring it up to current standards for safety and machine control regulations, this is a minefield of requirements that need an in depth knowledge of and not only regulations surrounding the building and updating of control systems but also an understanding of the safety aspects around such systems.
There are many other areas that may overlap into the design of this upgrade especially the need for a braking system in the event of an emergency, this however should be designed and implemented so as not to impact on the structural integrity of the machine when operated, IE - I can stop a large lathe turning a high inertia load on a dime by design but it is highly likely that doing so would sheer the shaft and present a larger hazzard than a controlled emergency stop would do, although this is unlikely to be a issue with a saw it highlights what I mean and the saw would have its own considerations.

At a minimum and only for the control section of this you may be looking as $2000 to upgrade it and that is only the materials, that will include the drive, the appropriate safety system and safety rated controls, additional guards and limits would be extra if needed, gone are the days where you can build a simple control box with a latching contactor and a start stop button.

We don't discriminate here on title, if you can show your knowledge of a particular field we would happily assist and advise, however in asking a basic question here we would deem your understanding and knowledge would fall far short of what we require thus our help is limited.

I would finish by answering the basic query you originally asked as it is easily sourced and a simple calculation to work out, the appropriate sized inverter for the motor would be a 4kw however most manufacturers cap their single to three phase models (the kind you are looking at) under that rating and you may struggle to find a suitable one as there isn't a large market for them at this size, given that the demand on your own power if you have 2 lines at 220/230v ish would be 40 -50amps then you may not be able to go down this route for use on a standard supply.

 

[Andy-1960]

I think I would avoid putting a VSD on a motor of that age as the insulation of the windings probably would not be able to withstand the peak voltages generated by the VSD.

 

[Darkwood]

In theory @Andy-1960 you are right, in practice I find even some of the oldest buggers out there cope very well, got a load fitted on old motors with the understanding they may fail prematurely because of their substandard (by modern standards) winding insulation yet 10yrs later they are all still going strong and no depreciation in insulation values.

 

[Strima]

You need to check how the motor is configured to run, star or delta, this will influence what type of VFD you require.

TBH I would look at fitting a modern motor an use a suitable VFD, keep the old motor so the saw can be reverted back to original if required.

 

[Rod Ango]

You need to check how the motor is configured to run, star or delta, this will influence what type of VFD you require.

TBH I would look at fitting a modern motor an use a suitable VFD, keep the old motor so the saw can be reverted back to original if required.

Strima, thank you, I believe I will be doing that. I'm considering going with a used-condition 3 or 5 HP 3-phase motor as replacement. For below US$200, I can easily find a new-condition 5.5kW VFD. I'll buy that first and try using with the old motor, but without great expectations. The rating is typically for a 7.5HP motor, so it should handle starting (or in-rush) current, and they state the devices have overcurrent and other protections. Most of the parameters are settable - direction, hz, voltage output <= Vmax of the unit, etc.

The motor that came with the saw had been bolted to a floor separate from the bandsaw (also bolted to the floor.) As such, any mechanical connection I make to drive the bandsaw will be a 'new' one. It will have a belt drive, in this case, to match the previous arrangement. I will put the saw on a cart with casters and brakes, and a frame will hold the motor in relation to the saw. So with some mechanical adjustment, most motors can be fitted with a pulley and made to work. I believe a modern 3HP (2.2kW) motor will be sufficient, - if the test on the motor supplied fails. 3-phase motors in the 1740~RPM class are common and cost < ½ the price of single phase motors of that class that I've been able to find used...new, the price difference is more striking and the options are fewer.

@darkwood thank you for your in-depth response. You speak, I realize, largely from the UK/EU rule-set for commercial environments (shops with employees) and commercially sold goods. For all that I know, some of the same extensive rulesets apply to hobbyist shops, and may even apply retroactively! We satisfy a less stringent set of rules here, which are mainly dicta from concerned regulatory agencies, not set forth in a single code document but in many, many different ones, even varying by jurisdiction. Commercial shops and jobsites (ie with employees or operators) must meet Federal standards as set forth by the Occupational Safety and Health Administration (OSHA) or suffer dire penalties.

Greyer zones include personal and hobbyist shops. Here you must satisfy the AHJ* for instance for building wiring, if modified. If changes are made to a strucure, or a new space is created that is adjoining or freestanding with any utilities: electric, plumbing, gas, DVW (Drain, Vent and Waste), they must usually be permitted then inspected. New construction, and addition and modification of any utility or significant/structural change to existing structures with utility(ies) connection must also usually be permitted and inspected, depending on the jurisdiction. In practice, one studies the requirements of the AHJ. And it's still confusing! Many locations in the US allow and issue permits for owners to do most, if not all work for their own residence. Frequently, natural gas is an exception.

Lathes, bandsaws, jointers, tablesaws, and so on are not preyed upon by regulation to the degree that I've read about in the UK/EU. I've read that because of the time required to spin down being considered a hazard, tablesaw-dado blades are not a frequent item. Without that requirement, they are commonly used here. People more frequently are injured due to kickback and improper setup than because they didn't realize a dado blade was still spinning, I have read.

If a lathe is made more dangerous because of a rule intended to make it safer, do you have the regulators personally prove they're actually right?


*Authority Having Jurisdiction (code inspector for city, county, even state?; mayor, town council, fire chief, sometimes industry associations' rules are applied by inclusion, etc)

 

[Rod Ango]

Here are VFD's for sale up to a claimed rating of 7.5 HP or 10 kW,

VEVOR 5.5KW 220V 8HP 25A Variable Frequency Drive VFD AC 1-3 Phase Converter | eBay

Find many great new & used options and get the best deals for VEVOR 5.5KW 220V 8HP 25A Variable Frequency Drive VFD AC 1-3 Phase Converter at the best online prices at eBay! Free shipping for many products!

www.ebay.com

With some searching around, I found them all over the place. I started the thread because from the motor plate, I had insufficient information to size the VFD. After studying various sources, I see that with a relatively low starting torque, there is not too much need to oversize the drive's capacity - 5.5kW should be good. Neh?

 

[Darkwood]

I am bemused why you are choosing a 5.5Kw on a 5 HP motor, you are setting yourself up for issues down the line here, you will need to detune the drive to the lower rating and this can cause some issues. Also you may have to do this anyway even with the correct drive as you have a continuous rating of 4 HP not the 5 HP it can deliver in brief periods, this needs thus a much more complex set up to ensure the motor is protected correctly and one where you may need a drive that can give the information needed to set it up correctly like the magnetising current and the torque current, if this motor was rated continuous at its 5HP rating then none of this would be an issue.

The sizes I mention are related to household names in the VSD industry, popular well known brands that have a good standing in the market, you have basically posted an Ebay link to an imported chinese product that has no paperwork to peruse, no mention of EMC filters fitted which may be required in the US as they would be in the UK, goes under several names of which I do not recognise any and has some questionable translated terms that even confuse me.
You get what you pay for and although I cannot directly comment on this product I can give you many stories of people who import machinery control equipment direct from China and there are many bad stories out there so do your research and stop looking at the price first, look for a quality brand.

Like I said before, happy to nudge you in the correct direction here but we cannot really advise any further after that, this fall beyond DIY and especially when we are discussing machine control and safety.

 

[Rod Ango]

@darkwood My impression from reviews and FAQs is the newest crops of electrically programmable drives (VFDs) allow entering the motor characteristics, setting the power-on slope, adjusting frequency supplied, attaching brake-resistors. This includes de-rating.

The point in buying the larger size unit is that the initial test motor is older and likely less efficient. An oversized VFD-drive (it is not: I'm told that book size for this motor is 28.8 AMPs) is easilyset to correct parameters. I am looking at several, but have seen good results with the inexpensive controls...still looking though.

Can I use a larger HP Variable Speed Drive to run a smaller HP motor? | Schneider Electric Global

 

[Darkwood]

To some extent yes you can derate most drives to fit a smaller motor within reason if it is serving a basic simple function, and in some cases there is actually a need to uprate the drive which we needn't go into here, my caution is that this is a complex subject that in it's easiest format can be a quick setup and away you go, but if/when other factors are brought into play it can get very complex very quick, be careful that you are not given a false sense of simplicity by doing a crash course by searching the internet, even the link you posted highlights certain scenarios where you may need external monitoring but this is barely touching on the subject.

Again I will reiterate that we cannot advise here as this does not fall within DIY and the regulations that are needed to be followed are extensive when you realise all the standards you are crossing into here by altering a motor control circuit.

I am merely trying to open your eyes here that there is a lot more to this subject and this project than what you may be picking up off the internet and foremost as a DIY project you are attempting I almost can guarantee you will not comply to local machine control regulations and safety codes, you could even dirty the power supply network if you purchase a drive that doesn't have the necessary filters and you don't fit external ones.

I will however wish you luck on your project and if you can I would advise getting some local professional onboard just for guidance if you can just to ensure you are not exposing yourself to unnecessary dangers.

 

[norcal]

While have read where people have used 3 HP VFD's on 5 HP Rockwell/Delta 12/14 table saws, I don't like it, just not right, most drives w/ single phase input stop at 3 HP, & a quality drive can be bought pretty cheap but over 3 HP with some exceptions* means using a 3 phase input drive that phase loss protection can be disabled, and derating 50% so for a 5 HP motor a 10 HP drive would have to be purchased.

*There are larger VFD's out there that are suitable for single phase input, but be prepared to shell out some serious coin.