Converting Bandsaw with VFD, but also has 3 phase blade grinder?

So I am converting a band saw for single phase operation. I started looking at the schematic and it turns out the grinder motor as well as the main motor are 3 phase. Everything else can be ran on 110 or 220 single phase when I rewire it.

I do not believe I can make both of these work with one VFD, correct?

This complicates things a bit. I do not know the RPM of the grinder motor yet. I guess I could try to find a single phase motor with the right RPM and replace it and then just use the VFD on the main motor.

I would also consider just changing both motors and forget about the VFD, but the main motor does not have a spec plate on it that I could see. I am going to get my mirror in there and see if it is more hidden somewhere. Matching the RPM with a single phase motor could be a problem. Not sure.

I do not need to use the VFD for variable speed. The saw has mechanical variable speed already.

Any advice?

Schematics attached.

I assume the 2 boxes in dotted lines that say Welding Device connection are options not included.

If that is the case I would consider this:

OK, I would run over 220 and a neutral.

I would hook up the to L1 & L2 and put a VFD for each motor (2 VFD's)
between the breaker and the motor.

This would power the control transformer and power each VFD

(and I'd hook up the Neutral as indicated)

Are both of these diagrams for the same unit?



If I had diagram # 2 I would ask myself if they put the single phase devices on L2 &L3 were routed there just to balance the load and could they be moved to L1 & L2

I do have the "options", but they should run on single phase as is, so they are not really a concern. Just that second 3 phase motor makes it more complicated.
These schematics are the same machine. One is more of a connections schematic and one shows the machine wired in its 220 3 phase configuration. It can also be connected to 440 as well, but there was no need to attach that.

And yes I assume there were load balancing considerations for the single phase device connections.

I am trying to avoid two VFD's, but it is a solution that would work. Seems overkill for a grinder that most people probably don't even use though.

I think I would search for a grinder replacement motor first. It is not much of a motor. The RPM would be the only thing, but it draws so little current that a Pot could be used probably or a simple speed control (assuming the single phase replacement is higher RPM).

I really need to find the RPM specs on these two motors. It might turn out that replacing both motors with single phase motors is the easiest method. The main motor is barely over 1HP, but the RPM could be a problem.

I am going to have to get more info from the motors I think to figure out the most cost effective method.

Two VFD would certainly work, but that would be $250 give or take for cheapos I think (did not price them out). It would also take more real estate to get them on the machine.

Although technically since you are not going to vary the frequency, you COULD use a single VFD to run both motors, you should NOT do that. For that to work, you would have to control the grinder separately from the blade drive, and turning a contactor on below a running VFD is a great way to smoke the VFD transistors. You are going to want to remove those motor starters and REPLACE them with the VFD(s) anyway, otherwise your controls get a lot more complicated.

Yeah, I already figured that.
And I would not play with contactors after the VFD. Even it if did work the programming of the VFD would not be optimal for each motor although it could be tweaked to work I suppose. I was just curious if someone had any better more cost effective ideas.

I think my options are:
1) VFD main motor and replace grinder motor
2) Replace both motors
3) Two VFD's.

Not sure there is much else to be said about it really....unless there is some magic out there I don't know about. I refuse to use a RPC, which could be a forth option.

2hp RPC.

Or, run the main motor off a VFD, and put a couple run capacitors on the grinder motor and power it with single phase 220. Fooling around with different capacitance values will make it run well enough to grind.

Lots of options here, but if you're contemplating ever running other 3 phase machines, they can be wired to the existing RPC, as opposed to buying another VFD for every machine.

I believe that the advice of others to install 2 VFDs is sound.
The grinder motor is fractional, at .18HP, and you can get low cost ($70-$80 less if your lucky) VFD for sub fractional HP motors.
I know it seems over complicated. I did this with a coolant pump on my lathe. Easier then finding a single phase motor and adapting.

try this ebay search
inverter -keypad (220, 230, 240) -display -car 3phase | eBay

or
vfd -keypad (220, 230, 240) -display | eBay

That blade grinder doesn't need a VFD, Just a "starting capacitor". I mean it will run so seldom, and when it does, a light touch will take care of any HP loss.
A static converter is a sure solution, but some small motors will spin up with just a small run cap between the line in and the mfg phase.

It would be possible to "bring in" the small blade grinder while the main motor were running off a single VFD. The added load most likely would NOT cause harm or fault to an oversized VFD. But, such a scheme does have it's risks. I would do it ;-)

A blade welder? That's going to take some creative transformer rewiring ;-)

The blade welder is single phase 220v. Not much to do there.

You can get a tiny little basic VFD for that grinder motor for under $100, maybe less if you find a used one on Fleabay. Then you don't have to worry about the shaft speed. You can't really use a pot to slow down that type of single phase motor, that only works for things like fans. A grinder is most likely a 2 pole motor, so 3600 RPM (nominal). Might not be that easy to find one that small in single phase.

jevs said:

The blade welder is single phase 220v. Not much to do there.

Click to expand...

There was a smile at the end of that sentence ....

I just took it out. It is 0.12kW 2650-3230 RPM (dependant on voltage).

I also found the main motor plate. It is Siemens motor. It only says 0.75 kW even though it is pretty big.

This is a 1997 Dake Johnson V-16 by the way. Same colors and looks like the new ones. I think I got a pretty good deal on it. Only thing is I thought it was made in the USA. It says made in Slovenia though. It's heavy. 1000 lbs.

jevs said:

I refuse to use a RPC.

Click to expand...

I was wondering what objection you have for running a RPC?

I agree with neilho and CalG. The grinder is starting with no load, so starting is just a matter of getting it to run well enough to get up to speed. Try a run capacitor permanently connected and adjust it so the grinder will handle a small load and doesn't make strange noises or draw excessive current.
I ran a mill with a two speed motor that was rated at 1 hp at low speed that way for years. I set up the starting relay to pull in on the starting load when on high speed but not on low speed. Low speed started and ran on the run capacitor only. It may not have been optimum, but I made a lot of parts that way.

Bill

swatkins said:

I was wondering what objection you have for running a RPC?

Click to expand...

Loss of horsepower. Noisy. Waste more electricity. Big. All my other machines use single phase already. I only need to convert this one.

After looking around a bit last night. I think I am just going to go with two VFDs.
Even if I found a motor that would work, it might be as much as a Vfd anyway. Trying to finding one that will work is going to waste too much time.
I doubt I will ever need to, but switching back to 3 phase would be faster.
I got the saw for half what it is worth so spending 250 or so on a couple VFDs will still be OK and it will run without hassle and much tinkering. I can't afford to spend much time on this because I have other bugger projects to do.
Now finding a couple VFDs to do the job is the challenge. Not sure which ones I will get. I could just get two new Chinese ones that match, scour for used ones, or pay even more for two new name brand ones.