[DLawrence]

Found out the hard way the 4th axis on the 1100 can't be unpluged while the machine is on , even if the 4th is not under power.
Tormach tech said, oh yeah thats gonna happen, it says not to do that, in the printed literature. . . . . OK and it does , and so order a new driver , the new leadshines, are not marked for polarity , simply say AC on the input power terminals, called Tormach again , they say " POLARITY DOES NOT MATTER " on the new leadshne drivers. . . .
So I hook it up , and it blows upon power up. . . . .. ??????
OK so tormach tech says board musta been bad they send me another checking everything very carefully and rechecking
It fizzles upon power up too . . . .

Tormach tech didnt know what to say, I free dumb about the whole situation and just put it all aside for a couple months

Any ideas or insights ? Its a series 1 from 2008 seriel 1278

Dave Lawrence

[smokediver576]

So.... as a new owner of a machine with 4th axis. Please advise what plug you are talking about when "unplugging"... Is this the auxiliary plug that's attached to the 4th axis that you plug into the front of the cabinet? Wish I had info to help you but I only ask in order to help me and other new guys will not screw up....

Thanks

[SCzEngrgGroup]

In general, it's a bad idea to just un-plug ANYTHING from most motor drivers - input power, output power, control signals - when it has power. Most will include explicit warnings about this, and doing so will void warranty. The electronics is quite robust, but can't protect against everything. Sudden disconnection, when current is flowing to an inductive load, really creates havoc, as it can instantaneously generate voltages FAR in excess of the supply voltage.

Regards,
Ray L.

[smokediver576]

Just so I understand fully. If I put my 4th axis on the table, plug it in prior to turning the main power on (red switch on the side of the cabinet)?

Thanks,
Awall

[R.DesJardin]

Not sure what caused the first issue but it sounds like you bought a Series 3 driver to drive your 4th. If so that won't work they are wired totally different and not interchangeable.

[kirk_wallace]

I suspect the connector on the side of the electronics cabinet was unplugged while the drive was powered up. This is the cable than goes between the rotary table and the machine cabinet. The VFD and other motor drives can be damaged the same way except they don't have a cable that can be easily removed.

A stepper motor is fully on all of the time that it is under power, since it is trying to hold a position. To get motion one just changes the position that it needs to hold. Some stepper drives have an option to reduce the motor current if there has been no call for motion for a while, but the unplugging danger is still there.

The power input to this particular driver (if does say AC on the power terminals) has a diode bridge that changes AC into DC. Feeding the input with DC of either polarity is not a problem because AC has both polarities and the bridge is designed to deal with it. Common VFDs are the same way. Most VFDs are designed for three phase AC power input, but the diode bridge can make DC from single phase AC or DC input. There are other issues that make this a bad idea, but it does work.

For the problem with the replacement drive, stepper drives are designed to overdrive the stepper in order to get fast stepping rates. The drive senses current in the motor and turns back the output in order to keep the output within limits. At high stepping rates, the drive senses that it can drive the output harder and does so, but the drive needs to keep a very close eye on the load. If a motor coil is shorted out the driver has a hard time figuring out what the output should be and may overload. It might be wise to check the motor coil resistance to make sure the motor is properly loading the driver. Plus check to see that the coils are not shorted to ground and that the wires are connected to the proper terminals. Also the driver switch settings need to match the motor being used. This is covered in the manual.

Hmm, page 16 of the manual
http://www.tormach.com/uploads/738/U...A_web-pdf.html
seems to indicate the AC input wiring does matter, but I don't know why. Paragraph 3.12-4 talks about two issues 1) the motor power wires 324 and 325, and 2) measuring motor coil resistance at the driver connector, which is a good idea.

At this point, with the driver (P2) disconnected, I would check the voltage coming out of the DC Bus Board on wires 324 and 325. Check with the volt meter on AC and DC. Then I would check the motor coil resistance. First check with the meter on the lowest resistance setting and just connect the two test leads together to get the resistance of the test leads. They might have somewhere between .2 Ohms to maybe 1 Ohm. Then measure the coils and subtract the test lead Ohms from the coil Ohms. Also check between each coil terminal and ground and from one coil to the other. Then check that the driver switches are set properly.

[DLawrence]

Somewhere Tormach has a stern warning about blowing drivers, is a stepper is misconnected, but iss a little vague about the specific conditions. I had done all the normal checks,
( phase lead ohms with compensation for meter lead resistance all ok in the .5 ohm area , phase to ground , DC supply voltage .......was 70 DC

Im thinking there was substantial AC superimposed on the DC, picking it up when using the AC scale, what would be normal limit ? Was it 25VAC will check today.

The replacement drivers TMac is suppling for series one blowouts are NOT series three , however the case looks somewhat like series three, in that input power
terminals have no plus or minus but are marked AC

Kirks explanation of the bridge rectifyer explains how this works.

In TMac file TD10173 Driver Replacement instructions for part # PN32793 it explains procedure for reversing rotation,

" Switch A+ with B+ and A- with B- "

I am fairly sure I reversed rotation by just reversng one set of wires only , A+ with A- ( or was it B+ and B- ? ) and it seemed to work could that be a problem?

Would like to know how to check what is + and - on a phase.

Thanks Dave

[DLawrence]

Smokedriver,

The 4th axis cable that should NEVER be unplugged with power on , is the one that is so easy to do on the side of the cabinet.
Its almost hard not to unplug it if one is removing the 4th off the table.

Dave

[kirk_wallace]

Off hand, one way to guard against this is to maybe have a special connector that cuts the power to the driver before the motor connection comes apart. Maybe have a driver power switch tied to the connector locking ring. Or have a warning light next to the connector that flashes while the driver is on. It really can be an expensive mistake. Especially if one needs to get product out the door.

I have never hooked up the A and B wrong, so I don't know for sure what would happen, but here is my understanding of the issues. The very simplified output of a bi-polar driver is shown below:
Attachment 261422

There are a set of Hi side switches (FET transistors) and Low side switches. To activate the A coil in the motor, one of the A Hi switches is turned on and the _opposite_ A side Low switch is turned on. This makes a connection between the motor supply plus, then motor coil, then to the motor supply minus (shown in green). The driver logic carefully controls the current and timing of the switching. If the A and B wires are mixed up (such as shown in red) the Hi side and Low side control will be wrong and likely will blow out the FETs. One common example of a control error is to consider just one set of Hi and Low switches -- let's say the left A pair. If the Hi and Low switches are on at the same time, the Hi side feeds the Low without going through the motor and becomes a dead short. The control logic has to be careful to never ever have the same pair on at the same time, or poof. There are quite a few other control conditions that can have the same result.

[kirk_wallace]

Oops, I didn't mention the motor coil polarity. In the diagram above, if you hook up the A+ wire to the top of the A coil and - to the bottom, the current and therefore the magnetic field will go in one direction. If you switch the + and - the field will go in the other. There are four ways to hook up the A +/- and B +/-, which produces forward stepping, or reverse stepping, or two modes of mixed up stepping. Getting it wrong, should not hurt anything other than getting the wrong motor motion.

To be more precise, A+ does not indicate a positive voltage since a bipolar driver switches the polarity for different steps. A better designation might be A1, A2, B1, B2.

[Don Clement]

I have used my 8" 4th axis on my Tormach for over six years and never had a blown a driver. I believe that I do turn the power off before removing the plug, but not really sure about that ;-) For sure there is going to be some L di/dt voltage generated though if one were to do a hot unplug. Would hope that Tormach put zeners or at least plain transient-voltage-suppression diode protection in place.

Don C.

[BAMCNC.COM]

I didn't read all of this, but just installed my 4th and found a lot of goofy things between the machine and the manual and the kit.

Mine came with the wrong wires, it had 770 wires, not 1100 wires. (labels) So I got out the meter, and found that it was DC power not AC like the driver shows. So I wired it up correctly even though the wire labels are wrong. I plugged it in and unplugged it while the machine was on (like Don) and haven't had any issues.

[kirk_wallace]

I think the problem comes about with current control. The driver will see a sudden change in current and try to react. At .5 Ohms motor coil resistance driven by 70 Volts and close to 8 Amps, current control is really important. Plus, FETs are easy to blow out. Most all of the drivers I have looked at do have freewheel diodes across the FETs to protect them from the reverse voltage periods of the switching cycle but it's really up to the control logic to keep things in check.

Dave, don't throw your blown out drive away. I'd like to buy it if it is available.

[Don Clement]

I didn't read all of this, but just installed my 4th and found a lot of goofy things between the machine and the manual and the kit.

Mine came with the wrong wires, it had 770 wires, not 1100 wires. (labels) So I got out the meter, and found that it was DC power not AC like the driver shows.

Doesn't really matter if is it is DC current, when the plug is unplugged hot while current is flowing though the stepper inductive coils a L di/dt voltage is generated. I have personally measured several hundred volts generated when 24V DC relay was energized or de-energized due to L di/dt.

Don C.

[SCzEngrgGroup]

Any motor driver with no free-wheeling diodes across the FETs would not survive its first 30 seconds of use....

The problem is, if a motor coil is disconnected while current is flowing through it, the instant either coil circuit is interrupted, the voltage on that coil will shoot up to thousands of volts (it is precisely like the ignition coil in a car engine), which will jump the gap in the connector, and apply that high voltage to the FETs. There is no protection circuit that can save the FETs from that.

Regards,
Ray L.

[kirk_wallace]

Weeel, not exactly, interrupting the current in an ignition coil primary will induce a thousands of Volts pulse on the secondary. The primary _might_ see up to one or two hundred Volts at best.

The 24 Volt relay will have a high voltage spike because it is designed to have a high inductance so it stays energized with AC or unregulated DC and they don't need to switch on and off very quickly.

I don't see getting more than a hundred Volt spike with a stepper motor since they are designed to have low impedance in order to switch the coils very quickly.

The bottom line, in my opinion, is it is a bad idea to unplug the 4th axis connector with the power on.

The real problem is in getting Dave's machine going again.

[Don Clement]

The bottom line, in my opinion, is it is a bad idea to unplug the 4th axis connector with the power on.

I agree!

Don C.

[DLawrence]

Turning the 1100 on , for the first time in a couple months to check power supply voltage , its a solid 70 VDC on the DC scale....

and on the AC scale of my( radio shack autorange only) digital meter it steadliy fluxuates , continuously flashing 23 then all zeros at about 30 changes per minute , equal length of time on the 23 as the zeros

. and it is NOT saying millivolts.

[SCzEngrgGroup]

Turning the 1100 on , for the first time in a couple months to check power supply voltage , its a solid 70 VDC on the DC scale....

and on the AC scale of my( radio shack autorange only) digital meter it steadliy fluxuates , continuously flashing 23 then all zeros at about 30 changes per minute , equal length of time on the 23 as the zeros

. and it is NOT saying millivolts.

Taking AC readings on a DC power supply will tell you nothing of any value. The reading is absolutely meaningless. Same is true taking DC readings on an AC supply.

Regards,
Ray L.

[kirk_wallace]

Taking AC readings on a DC supply gives you an indication of the AC component of the DC. If a diode in the rectifier section of your power supply is shorted or open, it will show up in your AC reading. Taking AC or DC readings cost nothing and if the readings don't match the expected readings, then it can indicate a problem. Taking a DC reading on an AC signal can indicate grounding or isolation problems.

Motor power supplies are generally unregulated, so it should be expected to have a significant amount of AC on the DC output. If you get a lot of AC or none, then there is a problem somewhere. In this case the AC reading is unstable, which isn't much help. It may help to turn the auto-ranging off and try again, otherwise skip it.