KBCC-125R DC tach question (new CNC mill build).

[krakenatwork]

Hi!

IMHO I don't think a diode is required for this use, the only current flowing through the coil will be provided by the C11 (@5VDC), and this should be minimal.  The current going through the reed switch won't interfere with the coil's voltage (relays and reed-switches are an isolation method based on magnetism, another isolation method being opto-isolation).

Just make certain your coil doesn't pull more amps than the C11 can output, and my guess is you're good to go.

Bye!

[krakenatwork]

Good news: I got my DC motor!

I did connect the minimum stuff and it ran great; I was able to make fwd/brk and fwd/rev moves with the small relays connected into a 5VDC power source (they switch the signal for fwd/rev/brk on pins S1, S2 and S3)

I had to take care; the pulley is screwed to the shaft using a left-thread, so when I put the motor in reverse the (cast-iron) pulley unscrews itself out; nothing a little bit of thread-lock couldn't take care of (for tests) or a keyway (in the future).  The motor has a small shaft that protrudes in the reat (1/4"), tht'll come handy to connect the tach to it.

The bad news: I blew up the KBCC...

Since it ran great in open-loop (but it was making the motor overspin then freewheel for some time), I wanted to go the next step; connecting the blue wires I thought were the field coil out of the motor.  Big error; the mains fuse blew up.  (read afterwards the wires are for a thermal switch to protect the motor)

I then removed the "field wires" from the KBCC, but a blown mains fuse happened again.  I saw/smelled nothing burning, but since the motor still seems OK (it still has a bit of "notchiness" in it when spun by hand, and it produces voltage when I spin it).

The KBCC was "off" (pins S1-S3 opened; brake mode) when I connected it the second time, so I guess something grounded itself.  There's no troubleshooting manual for these drives, so I guess I'm stuck and I have to buy another one. 

Morale of the story; never short out pins F+/F- on a KBCC...

[DICKEYBIRD]

Ouch!  Man, I'm sorry to hear that.  Sounds like some of my exploits with electrical stuff.  You should be able to fix it though or get just the KBMM-125 speed control by itself without the A.P.R.M.

I have a treadmill motor on my little lathe and almost made the same mistake.  Fortunately someone educated me about the extra 2 wires & thermal switch. AFAIK all the inexpensive treadmill motors are permanent magnet types without wound fields.

I discarded the flywheel/fan, cut off the threaded section, turned a small pulley to fit and milled a flat on the shaft for setscrews.  I also made a plastic duct and mounted an 80mm server fan for cooling.

[krakenatwork]

Well, I just purchased another one on ebay.  My wallet hurts.

I'll try to debug the old one, or sell it for parts, but I am thinking about keeping the beefy heat sink for the stepper drivers...  They'll remain cool 

Since both boards are mostly made of simple components (discrete transistors, a few op-amps), it might be not-too-tough to locate the blown parts; the manual lists the replacement parts required; I even have an old toaster-oven I could hack as a SMT soldering oven... (google "homemade reflow soldering oven toaster arduino" just for the heck of it  ) It would be a project in itself.

Looks like more delays 'till the working CNC mill...

[krakenatwork]

Okay, new KBCC came home this week, plugged-it in, worked better than the previous one, even though the KBMM is of the earlier model (with through-board ICs rather than SMT ones (smt = surface mount).

I tested it on the same motor; motor's really fine and runs very smooth.

Next step: do not blow it... 

I machined a coupler to join the servo-tek DC tach to the motor; mounted the tach and gave it a spin (without connecting it to the KBCC).  Not only does the motor runs smooth, with the KBCC's help it runs steady (without load).

I hooked the tach's wires to my multimeter, and gave the motor a go; at full speed I get 35.6V from the DC tach; this in turn leads to a nice 5085RPMs 

Following the math on the KBCC manual, I get a value of 28906 ohms for the tach resistor; in the 5% resistors world, this leads to a 30000 ohms.

My former KBMM board didn't have a J1 jumper wire (there was a set of holes where standard jumper pins could be installed on the board, but nothing connected to them).  My new one does have a 20-ga (or so) wire.  Did you have to cut a wire on your board to enable the DC tach?

On the other hand, I used alligator clips to connect to the APRM relay's coil pins.  The relay has around 110VDC between coil pins and activates my 2 SPDT relays (couldn't find DPDT 110VDC relays locally so I "created" a DPDT from 2 parallel SPDT relays...)  I'll use these to reverse the relay's polarity.

I'll try to locate some terminals that could be used instead of alligator clips, else I'll build terminals myself out of thin brass sheet.  There are 2 designs I'm thinking about; either "j" shaped terminals that'll slip over the flat pins on the relay (and hopefully lock in place) , or spring-clamp style.  I'll let you know about these when I'll get there.

[krakenatwork]

woopsie!  double-post...

[DICKEYBIRD]

Mine has a simple jumper you move to set it up for tach use...nothing to cut.  Not sure if yours has the jumper??

Here's the manual http://www.kbelectronics.com/manuals/kbmm_smt_manual.pdf

[krakenatwork]

My new KBMM is this model: kbelectronics.com/manuals/kbmm_manual.pdf

My former one didn't have a jumper, it was an SMT like yours, with a twist; it had the place to solder a jumper base but nothing soldered there.  My new one (older model) has a jumper wire ("J1" being a loop of ~20ga wire to and from the board.)  It's old technology for jumpers, first Commodore 64's "1541" floppy drives had these to set the device number, you had to cut a wire to change it, or get your soldering iron to set it back.  Many people soldered a block of 2 dip switches instead of the jumper wires.

I'll probably solder a small switch to the loop; old ideas have a long life

[DICKEYBIRD]

Finally pieced together enough shop time to get the tach-generator & relays setup working.  I really gotta thank Kraken for educating me on the proto board & DIP sockets stuff.  I had never really done that sort of thing before and it made wiring up this project a breeze.  I got a few boards, a bag of DIP sockets, terminals and some relays from Electronic Goldmine very reasonable.  http://www.goldmine-elec-products.com/  The relays came with built in suppression diodes.

Here’s a few pics of what I cobbled up.  The larger board mounts inside my lathe’s base unit.  The 2 small 5V relays are switched by Mach via pins 9 and 16 on my C11 B.O.B.  Pin 16 pulls in one of the relays & switches on the 12V DPDT relay in the tach output when M4 spindle reverse command is called.

The other (pin 9) relay pulls in the big onboard relay when M8 is called and sends 12V to the cutting oil pump on the back side of the enclosure.



The back of the boards ain’t real pretty but hey, they work great!





Here’s a pic of the tach polarity reversing board mounted in an auxiliary box on the back which houses the KBCC-125R speed control.  Initial tests showed that the reverse polarity spike that occurs during spindle deceleration after powering down from a reverse spindle run did give the control a big jolt.  Never did pinpoint what happens exactly but it sure didn’t like it based on the short ”ka-whiz” noise it made every time.  Fortunately no smoke was lost.  I added a couple diodes in the wires between the relay & the KB terminals T & I2 and the problem was solved completely.  There was a .6V drop across the diodes but a simple adjustment of the min/max speed pots had it working perfectly.



Here’s the tach-gen mounted on the back of the Baldor ¾ hp motor.  Crude but effective mount system.  I used a short bit of rubber tubing as a coupler.



 

Here’s the acetal plastic motor shaft adapter I made using a Mach3 wizard…one of the first items I made on the CNC lathe.



Here’s the cutting oil pump.  It’s an old Suzuki 250 dirt bike oil injection pump mounted on a homemade housing & coupler driven by a 12V auto sunroof motor I had lying around.  It pumps just enough cutting oil to keep the work shiny with oil but not so much that it makes a huge mess.  The output is easily adjustable via the bellcrank that used to be hooked up to the throttle cable.  The Denford ORAC lathe sits on top of it’s controls cabinet and wouldn’t do well with flood cooling.