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VFD - Do I understand this correctly???

YYCHM

YYCHM

(Craig)
Premium Member
 
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ok.... kinda... I'm NOT a VFD expert. I've implemented a good setup and researched the crap on VFDS, and I understand that you'd be sensible to overbuy the capacity on a VFD from Offshore sources....

I bought a 2HP TECO 510 to power a 2HP motor (1500 watts)...

When I asked several guys that do this thing professionally, they said I'd need a 2,5KW offshore VFD to to the same job. When pressed, they made sounds like 'lower component quality, and poor quality control...

I'm looking at an offshore VFD for my 7.5HP lathe. I'm looking at 10 and 10.5 HP VFDs. My 2 cents.
 
I also went the Teco route for my mill. Primarily because I wanted as close to plug and play as I could get. I watched a series by Clough42 on Youtube where he replaces his lathe motor with a 3 ph and vfd. I highly recommend watching it.
 
I have a 2.2kW Chinese Vfd on a 1.5hp motor and it works great. As far as Chinese sizing vs American sizing I really don’t know. Over rating the specs does not seem to be just a Chinese problem although sometimes they are the worst.
what do you have a 3hp motor on?
 
Johnwa said:
What do you have a 3hp motor on?
Click to expand...

Nothing yet. This is what I'm contemplating. My mill has a 2 HP 1 PH 220 V motor. I'm thinking of upgrading the motor to 3 HP 3 PH 220 V and using a 220 V 1 PH to 220 V 3 PH VFD for speed control. By the sounds of things I should be looking at a 5 HP VFD for a 3 HP motor? Are all 3 PH motors VFD compatible? Am I missing some key detail? Just trying to figure out if this is feasible and what the cost would be.

Craig
 
YYCHobbyMachinist said:
@David_R8 When you installed your VFD what did you need a POT for?
Click to expand...

For the variable speed control.
Edit: added pic.
The knob is for changing the frequency/speed and the switch is reverse/off/forward


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@YYCHobbyMachinist if you want to see/touch/discuss in person let’s line up a visit. I have a similar setup on my mill and can go over the individual components


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Long time ago - before I discovered the joy of rotary converter I used 2 VFDs - one burned out one is till collecting dust somewhere.

You are correct - they allow you to run 240 3ph on 240 1ph and have speed control as well. Very easy to wire up - almost trivial. Unless you need to run a break capacitor or do some strange stuff (you can do a lot of cool things - like have VFD hidden in cabinet and remote on/off + remote speed control).

What most pp are missing is that a VFD has a rating for going from 240 1ph ==> 240 3ph and there is usually no de-rating for small stuff at 5hp and under. This is *full power*.

What is another thing that most pp miss is that VFD that is tiny can start a huge motor - you can start 15 hp motor with 3hp VFD no issues at all - you will just start it very *slowly* and cannot get 15hp out of the motor peak power (it will be around 6hp for say 30 seconds). The bigger the VFD the faster you can start a motor - so a 5hp VFD can start 3hp motor a bit faster. A 15hp VFD should start 3hp instantly. This is related to motor starting power needed for say 1st second or so - VFD simply is a little power plant and cannot take a 3x overload even for 1 second.

All 240V VFDs will work with all 240V motors - just make sure the VFD can do 240 1ph to 240 3ph - most Chinese stuff can but a lot of western stuff cannot (Chinese stuff is newer tech usually).

I think VFD failures are usually just some component that is weak or poorly connected or has manufacturing defect - other then that heat can kill them. I had zero issues running 5hp on 5hp when it worked. They also have an overload protection. Main issue with China's cheap stuff (you can get brand name) is that you have zero warranty and stuff can either blow or keep on working for 5 years - do you want to re-wire if not lucky? I would not worry about the rating unless you think you can run your upgraded lathe AT 3hp full load for say more then a minute - same for dabler. I would not go so much "bigger" as would rather invest more in quality --- i.e. 3hp VFD for 3hp lathe that is of better make >> 5hp VFD that is cheap for 3hp lathe.

My big lathe has 10hp motor and starts without issues at top speed from 15hp rotary. I will never recommend going VFD route for phase conversion over rotary - been to both - rotary is so much better. VFD only for speed control - if you really need it.
 
This vfd has a built in POT. You can install an external one next to your mill.
A regular 3 phase motor will work on a vfd but is not designed for significant under speed or over speed. I think 80% to 120% is considered safe. With your belt drive mill you might want a wider range. Under speed will make the motor run hotter but you can monitor that. I’ve heard of some users running as low as 30%. Over speed failures will be things flying apart.
E390F9A6-1495-4F3A-B260-DE9317A191AD.jpeg
 
You can usually overspeed a 1800 rpm motor by 100% but you should not try to overspeed a 3600 rpm motor by more then say 10%.

You can run a motor at 10% of nominal speed - it will get hot if under load - it does not matter it is "VFD ready" - VFD ready == can take more heat and there is extra insulation to deal with harmonics better - its a bit better then any regular motor.

Main problem with running slow is that you loose power - there is a reason CNC machines have HUGE motors.
 
Tom Kitta said:
My big lathe has 10hp motor and starts without issues at top speed from 15hp rotary. I will never recommend going VFD route for phase conversion over rotary - been to both - rotary is so much better. VFD only for speed control - if you really need it.
Click to expand...

I think the majority of people get into the VFD specifically for speed control (myself included), and a small percentage because they hit the auction/estate lottery and picked up a sweet industrially relic that was wired for 3ph. The speed control is very slick, nothing like cycling up/down by 800rpm on the fly.
 
Even my big 3600lb mill has a 2HP motor (3PH). Normally going to higher HP motors is for more torque. With a round column mill, high torque is your enemy, and will deflect your column. You will get smoother cutting performance and more consistent torque with 3PH, but not enough to install a spendy 3HP 3PH rig.

For the same money, you could install an auxiliary 20,00 RPM ER16 head...
 
I’m running single phase 220v to 3 phase 220v.


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I used to run 1ph --> 3ph few years ago - but now I have 3ph in the shop with rotary so no need. Generally build in mechanical speed control is all I need ... but I admit my little lathe has build in mechanical variable speed & my main mill as well... so mechanical VFD. On mill moving from 500 to 1300 takes like 2 seconds - same on the lathe.
 
@YYCHobbyMachinist : I am running a VFD for the mill and one for the lathe. I don’t use them for speed control per say, more to convert to 3 phase. The mill, however, has a 240 volt motor that runs fine at 50 hz and then the speed adjustment on the dial up drive is right on the money, so I use the VFD to drop the frequency to 50Hz and then use the speed control as intended on the mill. The lathe is a geared one so I use the gear box to adjust speeds.

If your plan is to use the VFD on your mill for speed control, be sure your motor is a VFD rated one as it will then be designed to decrease or increase speed without as much heat build up and horsepower loss. That is one of the biggest issues when running at low speeds is there is a corresponding loss in power from the motor- most VFD speed controlled machines will have a larger motor fitted to make sure there is good low speed power
 
Brent H said:
most VFD speed controlled machines will have a larger motor fitted to make sure there is good low speed power
Click to expand...

That is my understanding as well, and why I'm thinking growing to 3HP from 2HP. On the other hand @David_R8 has the same mill and his was only fitted with a 1HP motor? So far this is looking to be an affordable way to achieve variable speed provided I get a used motor and an offshore VFD.
 
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Long time ago I looked into converting large Horizontal BS from wood only to wood/metal or metal only. So with a single pulley you can maybe decrease speed 6x.

So VFD would need to run at less then say 10% or so. Now with wood BS the motor is 2 -3 smaller then in metal. So need bigger motor... but with 10% speed you have so little power... so now you need huge motor... but even with huge motor running at 10% cutting any meaningful metal == at least 50% - 100% of all power == heat -> need auxiliary cooling motor!

At this point it feels its just cheaper to buy actual wood/metal BS ;) Which is what I did.
 
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