My Workman (G0602), my way

fitterman1 said:
Another requirement when I initially went to variable speed on my lathe, was that the spindle had to stop inside of a second when I switched off or hit the e-stop. I built this in to take advantage of the fact that the G0602 doesn't have any form of braking, so screwcutting becomes a hairy proposition. So taking advantage of the contactor which is used for powering the motor I put a resistor rated at 10 Ohms/ 100W across the terminals so that when the contactor is de-energised the motor terminals are shorted through the resistor. Conversely when energized, the resistor is isolated from the circuit and power feeds the motor. This acts as a brake when connected to a DC motor and the energy directed at the resistor is dissipated by a heatsink externally mounted. I also drilled a series of breather holes on that back contactor cover to allow some convection cooling for the contactor and its coil as otherwise temperature buildup would cause the
coil to fail over time.

View attachment 225819 View attachment 225820 View attachment 225821

The contactor is a quality unit so coil replacement shouldn't be difficult. This is also the original contactor by the way.
The resistor choice was my decision and works efficiently. If I had wanted a more gradual ramping down of spindle revs I would have gone for a higher Ohms value but kept the same Wattage.
This mod will work on any dc variable drive unit as long as the contactor has the necessary terminals to accommodate it. Please consult a professional sparky if you don't know what you're doing in this department because electrickery is unforgiving.
Click to expand...
@fitterman1 I need your advice here. I have a Teco VFD ready to install with a Leeson 1hp motor. I was looking forward to having an electronic brake, but my VFD doesn't support. Are you saying there is a way to do that within the stock contactor/relay? How did you manage this? p.s. I'm not an electrician so feel free to dumb it down! Thanks Matey (that's what you guys say right?) ; )
 
Hi Guns, I'm not a licensed sparky either but do have reasonable experience. So I'll try to make sense of it for you in the best way possible... matey.
There is a way of doing it using the stock contactor "only" if you use a DC motor.
The motor I fitted to my lathe is a DC motor (from a treadmill by the way) rather than an AC unit. The reason I did this was threefold.
1) to have variable speed control of the lathe spindle, using the stock contactor.
2) to not have to purchase and wire up a VFD.
3) have automatic braking.
Control was via a potentiometer within easy reach on my headstock panel. Braking is achieved when i turn off the motor, automatically by a resistor which shorts the motor winding.
It seems to be that because a DC motor is
a) a motor to drive something and
b) also a generator of voltage, that when I switch off power to the contactor (which is powering my motor), the motor then becomes a generator because it is still rotating. This voltage generation has to be controlled by having a resistor shorted across the terminals when the switch is thrown, otherwise it will slowly spin down by friction alone.
The value of the resistor ( I used a 10 Ohms/ 100W power resistor) you use determines the rate of slowing down, so by careful experimentation you can work out the length of time it takes to stop the chuck.
Eg 10 Ohms stops my chuck in about a second, if I went to 50 Ohms it would stop in probably 10-12 seconds.
My contactor is the standard Siemens unit that came with the lathe. This contactor has two sets of contacts, one pair being normally open and the other pair normally closed. This is so the contactor can be used for two different functions.
Think of them as two switches that operate at the same time instantaneously, but into two different states.
The contactors state at rest has one pair wired, so that when I switch the motor on they become switched closed and supply power to my motor and it commences rotating my spindle.
Prior to my flicking that switch, those same contacts, which were in a rest state, were actually shorting out the motor windings via a resistor.
I hope this makes sense to you.

Because you have a single phase motor and a VFD, I dont think you can achieve braking in the same manner as my setup just by using a resistor because your AC motor cannot generate.
Someone with electrical instrumentation experience needs to be consulted as to whether its possible or not because its out of my scope of experience. There must be some sparkies on this site with motor control experience that can help.
Let me know how you go, I can help with other stuff if required.
Regards Alby
 
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Sparky?!? Wow, you guys have different words for everything! Thanks @fitterman1 I appreciate the somewhat simple answer you supplied. I'm really bummed that braking isn't an option for me. There is a light braking option...maybe 5 seconds (I think you guys call them little minutes) or so...could still be catastrophic for a newb like myself.
I enjoy your threads...you got another follower.
 
Guns, if you think there is a braking function built in, take advantage of it. The user manual for the vfd must mention something. And it may be adjustable when setting up the vfd. I can only think that there is some kind of phase reversal to create a shift in the magnetic flux of the motor, thereby braking the rotor. In fact if there is a capacity to change direction of the rotor from inside the vfd rather than by contactor control then it may be feasible.
Had a look on the Teco site and got a manual for the E510 unit. Page 4-30 mentions deceleration time settings of 0.1 - 3600seconds. The default on this model is 10s. So it may be feasible.
Don't give up.
cheers Alby
 
VFD braking function depends on the model... Almost every modern one has it. The ones that do quick braking need an external resistor attached (which I will be adding one day to mine - as soon as I buy a 'round tuit')

@GunsOfNavarone please let me know what your model number is, and I can check it out for you. I have only done 2 Teco VFD installs, but i used to build PLCs professionally for a living before retirement, so I'm an 'experienced amateur'....
 
I had a look at your manual online. You have an internal braking resistor. If you refer to the wiring diagram in section 3 of your manual, you may have "P" and "BR" terminals on your power side. If you do, you cna add an external braking resistor. I have a Teco L510, but in the 2HP version, running a 2HP motor, I brake in .5 seconds all, the time. I do not (yet) use an external braking resistor. I am on a milling machine where the stored energy in the spindle and tooling is much less than on a lathe. This is how the need for an external resistor is created. The chuck and the gearing store rotational energy, and the VFD will siphon that energy to an external resistor, but there is no way to do this without the switching in the VFD to do it for you. You may get to brake in shorter time than 5 seconds, but that would take an IR thermometer and some testing to achieve.

[okay- for the nitpickers with EE degrees, there is a very good way to add braking to a VFD without it, but not for a novice]

In short look at your power terminals and look for a BR ternimal and get back to me. Like I said before, it depends on the model, and the manual is for all 510 models.
 
Yeah, I came across that in the manual as well. I do not have those terminals, but there's is some internal braking available, but not a lot. Again, at say 1200 rpm with a 6.5" chuck, it would stop in about 3 to 4 seconds. With what fitterman did with the stock contactor, i didn't know if there was some magic that could be sprinkled in this to get it better than that. Thanks for your looking into that. I have read different things, started questioning what I thought I sort of understood.
 
You can upgrade your VFD, and then add a braking resistor: subsecond stops.
 
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