3 phase machine - buy VFD or replace motor?

[sploo]

I'm hopefully about to pick up a planer thicknesser with a 3hp (2.2kW) 3-phase motor. I believe the motor can be configured for 230v, so with a suitable VFD I should be able to run it from my single phase supply in the garage (I have 16A sockets).

However, for not that much more I could just get a 3hp single phase motor.

Obviously the latter option would be more practical (in terms of not needing a VFD hanging around) but I'm aware that the VFD should allow me to configure a gentle ramp up on start (to reduce initial current requirements).

I understand that 3-phase motors are generally "better" (more efficient and pull less current) but is this not relevant if you're ultimately powering a 3-phase motor via a single phase supply + a VFD?

 

[Ttrees]

I use them to run my 3HP machines on a 13a supply ...they only cost 100 quid for the cheap ones.
What size MCB is your breaker? and what's the run distance to the consumer unit (CU)?
Do you have any machines to get an idea of how big you can go? even a 1HP pillar drill for example.

My lights are on the same circuit as the machines are, both going to house from workshop into a 30a MCB (I cant remember what type the MCB is suited for)
Might be a bad idea to be in the dark if you trip something, and its the same circut as the lights are, as in my case.
Possibly not gonna happen with the 16a supply though, and a good chance of the lights being on a different breaker.
If you have an RCD breaker instead, it possibly will trip from VFD's I believe, this is from the phantom earth emmited that can cause radio interference ...
I have never experienced this phenomonom though.
I don't know if this RCD issue can be fixed, if it can, best chance would be done by having the following....
Having a metal enclosure for the VFD which is recommended anyway for dust...
Having a shielded SY cable going from motor to VFD, with the shortest distance between if in doubt....
and being able to adjust the carrier frequency which you need to read up on and estimate, as adjusting this can heat up the motor (bad news for a motor to be heated up)
I have never needed to do so, and I dont have a shielded cable going from motor to drive/inverter/tomato/tomato...
I do however have metal enclosures around my VFD's with only 3 or 4 feet distance from the motor.
I don't know if the Isacon drives can be adjusted for carrier frequency values like the Huanyang has, (there could be parameters hidden somewhere though)

Another thing is how heavy of work do you envision doing, are you looking for capicity and taking light cuts, or do you plan on doing heavy work with this machine
for long periods?
How dusty of an enviroment will it be in?
I wouldn't want to strain a cheap VFD

Do you know if you can match the shaft size for the motor pully if you do go single phase?

Tom

 

[Sideways]

Tom , your lights being on the same breaker as your sockets is a red flag for me.
Lights are normally wired on 1.0 or 1.5 square mm twin and earth cable, sockets on 2.5mm twin and earth. 32 amp breaker tells me that the sockets are on a ring main not a spur (a spur should be protected with a 20 amp fuse).
If you have a lighting circuit wired in 1.5mm connected straight onto a 32 amp breaker without a smaller fuse in between, that isn't safe and doesn't comply with the wiring regs. It's a shock and a fire hazard.
As you have already realised, having a machine fault of overload knock your lights out isn't safe either, which is why sockets and lights should always be installed on different breakers.
Your house and all that ...so your decision... but it doesn't sound right and no one wants to give the insurance company wriggle room if something were to go wrong.

 

[Ttrees]

Hi
There are a pair of the old style screw in fuses in the shed, but no modern fusebox, so presuming these are for both sockets,
The other socket is for the boiler that I dont use, with an isolator inside hotpress in the house...
I actually haven't knocked off the lights in the shed, but do notice them dim when starting the 1hp single phase pillar drill, and also noticed them dim
when I had a pot hooked up to the bandsaw, and was test running the saw between dressing tires running it at lower speeds...
Only on adjustment of the potitentiometer is when the lights flickered, so I just presumed that it would knock the lights out.
I work by myself, and have custom knee switchgear on the machines.
And I have a nice juicy wire going to the house (not my house BTW) and I was always checking for wires heating up at first.
No hint of heat has ever in the wires.
Another slightly off topic, but I have an Aldi extension reel lead which seems to have some sort of trip switch built in...
I dont see any fuse though so I wouldn't count on it....
This is the first one I would be checking for heat, as its much slimmer than the gauge I chose to put on the machines...
Just for the record, before I got this lead, I was running the saw with a different extension lead...
The fuse blew one day, so I opened it up only to discover a wee 5amp fuse inside, the extension sockets rated for 13a I believe from reading the embossing on it.
I was using this for a good while.

I just thought I'd add as much information as I thought what could be relevant to the discussion.
Thanks

Tom

 

[sploo]

Garage electrics hopefully OK - modern CU with individual RCBOs for the ring mains, a separate 20A RCBO for the 16A socket, and a 5A MCB for the lights.

The reason for RCBOs for the mains (rather than MCBs and an RCD in the CU is a long story, but it's been done properly).

I could certainly add a dedicated line for running a VFD if needed, but I do already have a 3hp single phase dust extractor that runs fine from the 16A socket.

Good point about motor shaft diameter though: I'd obviously have to look for the same motor mount/flange, and had thought about the possible issues of removing the pulley from the old shaft, but not the diameter.

The extra cost of a new motor isn't so much of a worry; my question is more related to whether having a 3-phase motor in the machine is likely to be "better" (even if it then requires a VFD). I understand they're "better" if you have a 3-phase supply, but I don't know if the benefits remain when you're ultimately powering it from single phase.

 

[deema]

For what your doing the difference in the motors is negligible, and for a resale perspective your always better off with a single phase motor. People seem to be very wary of inverters....spooky box of expensive tricks that needs a scientist to fix seems to be the perspective rather than simply a jelly bean part!
The main advantages of having a VFD are
1. You can have soft start so that the lights won’t flicker (depending on how well the wiring has been done.....thickness of cable)
2. You can make it regs compliant and for most inverters use the brake function to stop the motor is less than 10 seconds. (Probably need to add a braking resistor)
3.they use less power as the main power spike is at startup where you get a very large inrush current / heavy loading as the motor gets up to speed.

Having said all of the I would swap the motor and the DOL starter (you will need one with a 240V coil and a different sized overload trip) (or the inards if the existing DOL if it’s to maintain the aesthetics of the machine)

Bin the pulley and get a new one, they are about £10 so not even worth the effort of getting the old one off the shaft.

 

[sploo]

I'm not planning on reselling (well, for the moment anyway), so I do wonder if a VFD would be easier - no need to change the motor or DOL. That said, the existing motor might be fairly old, so a new single phase unit could be better.

Decisions decisions!

 

[Ttrees]

Are modern motors as good?
I'm under the impression there not, well when it comes to powered handtools anyway...so I assume its the same with induction motors.

FWIW the huanyang drives dont have the hardware for a breaking resistor, but at least has an input
for the ability to get someone to do it...
I don't know if the Isacon/askpower has the ability for this ?, it does have the terminal though...

I also dont know where you would source a pulley from...
I tried finding a suitable one for my old Startrite saw, because the shaft hole was not on centre
and had badly damaged the keyway...I had to file out the hole to insert a centred sleeve because I
couldn’t find one.

Another thing is I was surprised to read that the Inverter devalues the machine...
I dont believe it, that could be some chancers haggling, trying to get machinery for cheaper.

I have read before that three phase machines will leave a smoother finish n the work, so that might
probably be a factor when a cutterhead is concerned.
I think it boils down to how heavy is the work your planning to do, if you have the supply and the funds to go either way.

Edit
I would be interested to know if you do go the VFD route, if you need to wire up another MCB
for it because of the phantom earth.
It may be a bit of a faff for you to be making enclosures if you can afford a new motor.

 

[sploo]

I can't comment on old vs new motors; especially as I suspect it matters as to who made said old or new motor. It of course also depends if the old motor has had a hard life!

If an inverter devalues a machine I'd just remove it before selling :wink: . Seems a bit daft really as it has no impact on the machine (in the sense that it should be completely reversible if someone wanted to remove it - and then you have a machine plus a spare VFD to sell).

Smoother finish with 3-phase may be feasible, though probably within other margins of error regarding wood type and (human powered) feed rates. A three phase motor is getting more "pushes" per revolution, so theoretically should give a smoother power delivery. I'd be surprised if it was that obvious on the finished results though.

Where this would have made sense would have been for a two motor planer thicknesser (e.g. a Sedgwick); where a VFD would allow the speed of the thickness feed motor to be varied, independently of the cutter head. There's only one motor in the unit I've bought though.