Bridgeport boss 4 Spindle not powering up (continued)

Hi Jak. Would you mind answering a few more questions?

Are these three wires connected directly to the motor, or do they pass through a transformer/rectifier first? Did you take the measurements with the wires to the spindle disconnected or were they still connected?

If a machine has a 3 phase motor, in the circuits I'm familiar with, when the contactor closes there is supposed to be an unbroken path from the main breaker to the motor. If the path on one of the power legs is broken somewhere and you measure for voltage presence you can still measure voltage at all of the overload to motor connections because on the missing leg you will measure power flow coming back on that leg from the motor because all three legs are connected within the motor. I suggest you disconnect the 3 leads to the motor before checking for voltage at the bottom of the overload relay.

The only "heaters" I see in the pix are the ones shown (I think) in the bottom right of the other photo you posted. The large orange cylinders you mention look like part of a transformer or rectifier circuit. Do the leads from the spindle motor attach at this point? Is your spindle motor DC?

Can you obtain and post some schematics or do you know where they may be available for viewing online?

dennis in nca

These wires are connected directly to the motor, they do not go thru any transformers or rectifiers that I can see, only a switch of some sort. I took the measurments with the wires to the spindle still conected and the spindle motor ON.

Will do tonight.

No the leads going to the motor do so right after the main fuses.

The spindle power diagrams are convienently missing from my stack of prints, will try to find one online.

Thanks dennis

According to jak :

O.K. Though low spindle oil would simply make it noisy, not keep it from turning.

Easy enough to replace.

Hmm ... in that photo, I see the interlocked pair of contactors (on the left) which select for forward or reverse operation, and the heaters (bottom right) which sense excess current through the motor and disable the contactors so there can be no power to the motor.

Is it possible that one of the axes is hitting a limit switch? If so, the interlocks may prevent powering up the motor.

Hmm ... a bit low. Is this from a rotary converter? I think that it perhaps needs to be tuned with capacitors for a better balance.

What are the voltages with the spindle turned off? That poor balance will perhaps make it more difficult to start the motor, and will certainly introduce problems for the axis stepper drivers. And -- if the one phase gets *too* high, you are even likely to blow the transistors on one of the three axes.

If the three phase is coming from the power company, and is that far out of balance, you have serious problems. (Or perhaps some terminal screws between the three phase power source and the input to the back are loose.

I presume that you've checked all three of the big cartridge fuses in the upper right of the "boss4back.JPG" image. The ones which look lie black sticks of dynamite. :-) I see that at least one has been replaced, since it has a different color of label than the other two.

No! What that looks like is the big three-phase transformer, which provides the power for the three stepper motor drives for the three axes.

The heaters are actually quite small. They are not to heat the box of electronics, they are to heat devices which sense (by the heat) overcurrent in the power to the three-phase spindle motor. They are part of the small black object in the "boss4_to_motor.JPG" image at the bottom right. I think that they are the three objects on the top (that is, the surface towards you as photographed). You remove them with the two screws each, to change them for different current ratings if you re-wire the motor (and all of the transformers in the system) for 440 VAC operation instead of 220 VAC. Below them are the things which they heat and which release to interrupt the circuit.

Anyway, that box is where I plan to install my VFD to drive the motor, and all of the rest will run from 240V single phase. (But it won't, and *can't* be the original BOSS-3 or BOSS-4 electronics. --

*That* needs the full three phase, and well balanced, to drive those big stepper motors from power derived from the big three-phase transformer. Servo motors and separate servo amps will draw a lot less power than this does.

When this happens, you will have to get into the box on the side and reset whichever of the three has tripped, as you can't get power to the motor until that has been replaced.

Below the big orange three-phase transformer are three saturable reactors (two side by side in the bottom, and one above them sort of towards the center), which are used to reduce the voltage fed to the stepper motor drivers when the steppers are stopped, or moving slowly, to keep from burning out the windings in the stepper motors. They need a lot more voltage when being stepped fast, and the saturable reactors allow switching between the higher voltage and the lower voltage.

Note that I think that I see a diagram printed on the inside of the back door which should identify the various objects in there.

I believe that the objets shown in the "boss_4_to_motor.JPG" image are in a second box attached to the right (as viewed from the back) of the main electrical box on the back.

Probably looking for loose connections. Power it off, disconnect from the power entirely, and tighten the screws on all of the terminal strips, and those which are awkward to reach (such as the contactors in the "boss4_to_motor.JPG" image, at least try wiggling them. If any of those move, you'll need to pull the contactor out to where you can tighten those terminals.

We're *trying*. But it is rather difficult to do a good job of troubleshooting something this complex at a distance, when you are having difficult identifying the various parts about which we are asking.

Note that this also depends on the proper relays being in the sockets in the base of the computer chassis on the right side of the machine (as viewed from the front). And -- if a safety fix has been installed, you need to reset a safety interlock on the motor switch pod to confirm that you have changed the tool and have your hands safely clear again -- *each* time the system thinks that a tool needs changing, which probably includes when it boots up.

Have you ever seen this operate? If not, you may not know how to reset the CPU on initial power on.

Good Luck, DoN.

Good ideas DoN. I was hoping someone with more specific information would show up to help jak. I can work my way through the average power circuits but there's sure nothing like hands-on experience.

I think jak will be ok on things like relays and logic boards because, during the first series of this topic, he said when he tried to activate the spindle all he would get would be a buzzing sound. Also I understand there are two mechanically interlocked contactors for the spindle. So, if I understand the circuit correctly, all of the rest of the circuitry is used for control; which kind of leaves us with a power problem.

However IHBKTBW.

On the other hand I worry a little bit about that fan problem. In the past I've seen things like a fan set off a chain reaction, which in the case of this type of electrical system where you have a TON of power conversion (in a relatively small enclosure), would be the effect that much heat would have on other components in the box. I'm guessing a little here because I have no way of knowing if the fan and spindle are powered by inter-related circuits which could mean when you fix the spindle problem the fan will run.

dennis in nca

p.s. Hey jac. Are you doing the voltage measurements at the motor and while someone is holding down the motor start switch? Or are you holding in the contactor mechanically?

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My experience is with a BOSS-3 (old enough so the logic cards were wire-wrapped, not custom PC cards. :-) But the basic principles are the same, though the power supplies change a bit.

On mine, there were two muffin fans (24 VDC, IIRC, though they might have been 230 VAC instead) mounted in the bottom of the logic cage

-- where they were very difficult to get to and replace. Both were gummed enough so they did not run.

Not really much power conversion going in in the big back box. The three-phase transformer was connected to three bridge rectifiers (one per phase, each for a different axis stepper motor drive). In series with the AC feed from the transformer to the rectifier is a saturable reactor (transformer whose AC impedance is changed by DC through the other winding saturating the core), which is used to reduce or increase the voltage actually reaching the bridge rectifiers -- on an axis-by-axis basis. None of this dissipates much power, unlike trying to control that much current (7A per stepper) with transistors of the day.

The logic cage on the side includes a hinged back door which is a large heat sink loaded with transistors to drive the steppers. The drive boards are in a smaller card cage in the logic cage, and are eventually driven with TTL level signals. The CPU is a quad-wide LSI-11 with custom firmware. The whole thing could be replaced with a lot more power efficient circuitry these days.

Pretty much everything in the back box is pretty immune to heat problems. Even the filter capacitors are moved to the logic box instead. The interlocking three-phase contactors to control the spindle motor, and the heat coil assembly which accompanies it are in a third box (which he showed in a separate photo. In the bottom front of the box is (maybe) an optional AC outlet to power a coolant pump, and to power a work light.

I *think* that box has enough room to accept the Mitsubishi VFD, which will let me control spindle speed and direction with logic signals -- and eliminate the contactor entirely. The later models than mine have a compressed-air powered motor which turns the variable speed pulley crank, and an air solenoid to operate the spindle brake. Mine does not have those.

Since the commands to the spindle contactors are derived from the logic circuitry, plus a panic switch in the motor switch box, all the logic and relay power must be working before the contactors will pull in. And -- the CPU has to be in a properly booted state. IIRC, it needs to be reset using some small switches in the top half of the logic cabinet -- which may or may not have a punched tape reader in there as well.

The motor start switch is held down by the CPU, not by a person. And the direction is selected by a switch on a pod just beside the motor, along with the panic switch. (Mine was missing the panic switch, and I had to replace it with one which I could get, plus a relay to provide enough contacts to duplicate the switching of the missing original panic switch.

Enjoy, DoN.

On my Boss low spindle oil will not allow the motor to start, there is a float that prevents the circuit from starting if low, but I checked that and the switsh is working properly and I have oil.

Checked that all all limit switches are OK.

Yes, this is form a rotary convertor. I then send it to a voltage regulator which allegeldly regulates voltage to +/- 5%.

WIth the spindle turned off I am getting 240V. As soon as I turn it on, one leg goes down to 140V

Yes, were removed form the machine and checked.

I missed that part, what can trip?

I have seen it operate, It worked fine 2 years ago and nothing has happened that I can think of.

thanks again. Running out of options.

According to jak :

O.K. An interlock -- that makes sense.

O.K. Both not tripped and making good contact?

Hmm ... what kind of regulator? I'm not familiar with three-phase regulators -- except perhaps the antique motorized three-phase Variacs which General Radio used to sell. That does not regulate on an individual phase basis, but turns all three phases up or down until it is happy with whatever it is checking.

That suggests one of the following possibilities:

1) The rotary converter is not capable of providing sufficient current to start the motor. (What HP rating idler motor are you using?) 2) The regulator is not capable of providing the start current for that motor. 3) Some connection from the rotary converter, through the regulator, and through the circuitry is a higher resistance than it should be. For that, the tightening all of the terminal screws suggested earlier is a good start.

O.K.

O.K. Perhaps it is time to explain exactly what the heaters do:

1) Current from each phase passes through an individual heater. And produces a temperature in a small area proportional to the current through the heater. 2) Adjacent to each heater is a device which holds a pair of contacts closed, but which (when hot enough) can allow the contacts to open. One style which I have seen years ago for telephone wiring has solder surrounding the heater (which is not separate in this case), and a ratchet tooth pattern on an object which surrounds the heater. A spring-loaded leaf hooks on one of the teeth of the ratchet, and power flows through that. If there is too much current, the heater melts the solder, allowing the ratchet wheel to turn, which lets the spring-loaded leaf spring clear of the ratchet, and interrupts the current flow.

I've not examined in detail exactly how the heaters in a contactor work, so some may or may not work like this. But, there is a way to reset it (akin to pushing that leaf back to hook on the next ratchet tooth.

3) Each of these devices which open with the heat from the heater is connected in series, and in series with the coils of the contactors. So -- when there is too much current, one of the three heaters gets hot enough so the associated contact opens, and there is no longer a current path to the contactor's coil, so the contactor opens, and removes power from the motor. This is to prevent the motor from burning out.

Note that the other two heaters will have also been getting hot, so it is a game as to which one gets hot enough to open the circuit.

This is probably the thing which you have been having to reset from time to time.

The heaters, and their associated contacts, are in the smaller black Bakelite device sharing the box on the side with the interlocked contactors for running your motor forwards or backwards. Is is probable that there is something which allows a single button or other control to reset all three contacts associated with all three heaters at once. I can't see it in your photo, but you mentioned something in the upper right corner of the electrical box on the back of the machine. It might be that it could be reached through there somehow.

One possibility is that one of the three heaters has burned out, so you are getting no current through that. That will cause the motor to draw a *lot* of current (starting current), and cause another heater to open its contact after some time of attempting to start.

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O.K. Has it been moved since you saw it run? Was it running from the rotary converter at that time?

Good luck, DoN.

After a little distraction I was finally able to determine the culpret, a bad heater. Thanks to everyone who contributed. I think DoN nailed it first, no surprise, always there with help on a BOSS.

jak