Author Topic: Real Bull controller, adjusting the trim pots  (Read 716 times)

Offline Gazz292

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Real Bull controller, adjusting the trim pots
« on: December 20, 2020, 05:34:53 PM »
I have a real bull CJ18 lathe,

I bought it second hand in about 2012, and shortly after i got it one of the pcb's died... it was the board that made you turn the speed control knob to zero every time you wanted to start the lathe up, and braked the motor when turned off etc.

I removed and bypassed that board to get my lathe working again, i just followed something i read on the internet back then on how to bypass the board as they were unreliable.
i did plan on maybe adding back motor braking using a simple relay and resistor, but never got round to it,

I was actually glad to have got rid of the need to turn the speed knob to zero every time i start the lathe up, i just use the NVR switch like you would any other bit of machinery, and know that it'll start up at the last speed i used it,
i assume that if i was daft enough to change the direction switch with it running it'd go bang.


Anyway, this lathe has always needed its power board's trim pots 'tuning' so to speak, the motor will speed up when it's under load... i.e. it speeds up too much, as in too much current compensation or something,
and below 200 rpm it goes the other way, apply load and it'll reduce power to the motor, i'm only now remembering these issues as i've only just replaced the high - low gear with a metal one, the plastic one having lost low gear 4 years ago.. and the lathe being in storage for most of the time after.

I've read on another post that John Rudd knows these controller boards very well,

Can i get some pointers on which trim pots to twiddle and which ones to leave alone,


Offline John Rudd

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Re: Real Bull controller, adjusting the trim pots
« Reply #1 on: December 21, 2020, 03:06:17 AM »
Gazz,
Could you post up a picture of the board you have please?

The Sieg boards have 3 presets on the XMT series, while the KB Controls boards have 5 ( and their Chinese clones..).
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Offline Gazz292

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Re: Real Bull controller, adjusting the trim pots
« Reply #2 on: December 21, 2020, 07:15:52 AM »
it deffo has 5 trim pots, i'll get a picture shortly.

Offline Gazz292

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Re: Real Bull controller, adjusting the trim pots
« Reply #3 on: December 21, 2020, 09:42:39 AM »
Here's the pcb

Offline John Rudd

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Re: Real Bull controller, adjusting the trim pots
« Reply #4 on: December 21, 2020, 01:10:44 PM »
The CL Trimpot sets the current limit (overload), which limits the maximum current (torque) to the motor. The CL also limits the AC line inrush current to a safe level during startup. The CL Trimpot is factory set to 1.5 times the full load rating of the motor. To increase the current limit, rotate the CL Trimpot clockwise (do not exceed 2 times (200%) motor current rating (maximum clockwise position)). To decrease the current limit, rotate the CL Trimpot counterclockwise.

Ideally, the CL adjustment should be carried out using a DC Ammeter if you have one, adjusting to around 1.5 times the current draw of the motor...( if your motor is the 550Watt version, that should be around 4.5 Amps....I'd set it so that it is mid way between the min and max settings of the preset, if someone has twiddled with it...and you dont have a suitable means of measurement

The ACCEL Trimpot Is normally set to 2 seconds, which is the amount of time it will take for the motor to accelerate from zero speed to full speed. To increase the acceleration time, rotate the ACCEL Trimpot clockwise. To decrease the acceleration time, rotate the ACCEL Trimpot counterclockwise.

The MAX Trimpot sets the maximum speed of the motor when the Main Speed Potentiometer is set fully clockwise. The MAX Trimpot is factory set to 100 % of base motor speed. To increase the maximum speed, rotate the MAX Trimpot clockwise. To decrease the maximum speed, rotate the MAX Trimpot counterclockwise. I normally adjust the Max speed by measuring at the motor leads, for 180V DC, corresponding to the speed of the motor and what it normally runs at.

 The MIN speed trimpot sets the minimum speed of the motor when the Main Speed Potentiometer is set fully counterclockwise. The MIN Trimpot is factory set to 0 % of base motor speed. To increase the minimum speed, rotate the MIN Trimpot clockwise. To decrease the minimum speed, rotate the MIN Trimpot counterclockwise.

 IR compensation is provided to substantially improve load regulation. If the load presented to the motor does not vary substantially, the IR adjustment may be set at a minimum level (approximately 1/4 of full setting). The control is factory adjusted to approximately 3% regulation.

Suffice to say, any adjustments should be carried out with an insulated tool......anywhere on these boards should be considered Live... :zap:
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Offline Gazz292

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Re: Real Bull controller, adjusting the trim pots
« Reply #5 on: December 21, 2020, 02:36:26 PM »
Brilliant, thank you very much  :bow:

yes, i have a DC ammeter, got a current clamp type (Uni-T UT210E... very handy little thing, does 100A DC)  and the usual multimeter  wire it in line type... then forget you had the leads set for current and go and do a voltage reading and blow the fuse  :doh:  or is that just me :)

Somewhere i've got a set of mains testing meters including a megger, but don't think i want to subject a chinese lathe motor to that kind of test.

I presume it's mainly the IR trimpot i need to play with, and assume it's been wound too far round,
i just had the lathe running, taking a light cut on some alli bar, speed set at ~650 rpm, as soon as i took a cut the speed went up to ~720 or so, take a deeper cut and it goes even faster, no load and it's back to 650.


It'll be nice to get this little lathe running how it should again, i've just put angular contact bearings in the spindle, and a set of metal hi - lo gears... i've not had low speed for a few years,
Whilst i had the headstock off i added extra jack screws to align the motor properly, when i first got it the motor was sitting at a right old angle, only the side of the drive gear was keeping the belt from coming off, and that's chewed up pretty bad... so got a new one coming, and a slightly longer belt so i have more room to adjust the motor and not have the belt as tight as a guitar string.

Offline John Rudd

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Re: Real Bull controller, adjusting the trim pots
« Reply #6 on: December 21, 2020, 04:08:30 PM »
From memory, if you look at the IR pot, the notch in the screw slot should be about the 9 o'clock position...
Failing that a good starting point is at 25% of the travel of the pot.
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Offline RussellT

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Re: Real Bull controller, adjusting the trim pots
« Reply #7 on: December 22, 2020, 05:17:43 AM »
multimeter  wire it in line type... then forget you had the leads set for current and go and do a voltage reading and blow the fuse  :doh:  or is that just me :)

It's not just you.  I wanted to make some current measurements last week, first, wonder why the meter shows nothing, second, spend half an hour searching for a fuse somewhere near the right rating, third, make the measurements. :doh:

Russell
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Offline Gazz292

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Re: Real Bull controller, adjusting the trim pots
« Reply #8 on: December 24, 2020, 03:14:55 PM »
Thankyou for this great info John.

I spent a little time setting my controller up and have got the lathe running better than i ever remember it.

It will spin reliably at 60 rpm in low gear and has just enough torque down there to actually use it gently,
In high gear with the max trim pot set for 180 volts on the motor, the chuck was turning about 2800 rpm, so i wound that down to 2500, and about 165 volts, it's quite rare i use this lathe in high gear tho except for polishing something.

And once IR pot had been twiddled with with informed reason (i'm not sure if this was just set up badly from the factory, or the last owner had a blind twiddle in there) it's now holding it's speed properly, i get maybe a 15 rpm change from it spinning free to taking a slightly deep depth cut for this little lathe, and it no longer speeds up when i engage the lead screw gears.


Not sure i have the overload set right tho,  as in likely too low?  i had the chuck spinning around 80 rpm and using a length of ratchet strap webbing, made a loop around the chuck and pulled it tight till the chuck stalled,
i saw no more than 2.5 amps with the motor stalled.

Should i have the overload current higher? or is that the controller cutting the current down (thought it would cut power in an overload condition tho) and should i reduce it?

There's no markings on my motor that i can see, i think the lathe was new in about 2008 or so, the motor is just a simple cylinder shape... like a vw beetles dynamo with flat silver end caps, and not the belled end caps, or plastic looking ones i've seen on sites showing how to adjust the motor position for belt tension...

The belts tension is done via 2 jack screws under the headstock bearing on the top of the motor, one slightly to the right of the middle of the motor and one above the right hand end, 
I've added 2 more jack screws, 1 at each end of the motor underneath it, and using these i was able to get the belt running straight for the first time ever.

Offline awemawson

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Re: Real Bull controller, adjusting the trim pots
« Reply #9 on: December 24, 2020, 03:32:08 PM »
i had the chuck spinning around 80 rpm and using a length of ratchet strap webbing, made a loop around the chuck and pulled it tight till the chuck stalled,

Blimey - do that with either of my lathes and you'll end up wrapped round the chuck  :bugeye:
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Offline John Rudd

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Re: Real Bull controller, adjusting the trim pots
« Reply #10 on: December 24, 2020, 04:33:57 PM »
If the overload current is set too high, there is a risk of damaging the motor!

The factory setup recommends locking the rotor for a minimum time to prevent this......

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Offline Gazz292

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Re: Real Bull controller, adjusting the trim pots
« Reply #11 on: December 25, 2020, 09:22:54 AM »
I wasn't sure how else to apply a load to the motor, short of building some sort of dyno... which i guess if i anchored one side of the strap to the ways, and pulled on the other end with a spring balance i could kind of do.

I didnt want to take a cut as i had the controller board sitting right where the chips would fly, but these little lathes dont have that much torque i believe,

So.. should i lock the chuck then start the lathe up, and monitor the current? should it cut out fast, or is it a gradual reducing of power when the overload is reached.

Are these boards kind of universal?  i see unused 2 spade connections for F+ and F- next to a big resistor thats got a little warm in the past, i presume the F connectors would be field connections? not used on a permanent magnet motor i have... or was it just the motor braking resistor?
 
i kinda wish i could find the old board that i took out of this that provided the motor braking, so i could try and get just that part working again, i have the little board in the base of the controler box that has the transformer on it and a relay and big wire wound resistor, amadeal call it a filter board, it has wires coming off it that i've taped up when i removed the other board, and a green connector thats no longer used, oh and it takes the tacho pulses and sends them out to the display,

But here is the main board i have.
 

Offline Gazz292

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Re: Real Bull controller, adjusting the trim pots
« Reply #12 on: December 25, 2020, 11:23:59 AM »
Blimey, what a lot of stuff i've forgotten over the past 9 years,

Been searching for things relating to this board and the real bull lathe etc,  and one of the google searches was to this forum, a post i'd put up when i was last having problems with the lathe in 2011, that was when i disconnected that bottom 'filter board' as it was causing a big resistor on the main board to overheat, and kept cutting power to the motor, so turns out there is no auxiliary board i keep mentioning, it's all down to that lower board with the transformer on it just for the tacho it seems.

And.... it turns out that it was me who twiddled the trim pots last  :doh:

I also wanted to put motor braking back onto the lathe 9 years ago... but never got round to it, story of my life.

John Swift did a doodle for me back then of how to wire in a relay to put a resistor across the motor wires when power was off, and i even thought up an alternative way to do it using the inhibit connections on the main board and wiring it to some of the unused switch contacts in the motor reverser switch, so it'd kill power if i ever moved that switch with the lathe running for some reason.


I've also been thinking of putting in a computer fan to blow into the motor all the time the lathe is powered up, others have done this before as they found the motor cooks if you use it at low speed for so long (i am looking for a slightly larger driven gear for the headstock, i believe it's 31 teeth stock, so i might get a 33 or 34 tooth gear on there, and that might help keep the motor running faster for low spindle speeds)

Would it be silly to get the 12 volt power for the computer fan from the 12 volt rail on the main controller board? i believe it's that big cooked resistor that is dropping mains to 12 volts for the boards functions, assuming it's 12 volts DC... there's a point near the max speed trim pot marked +12v, so i presume that will be DC there (but if not i can add a bridge rectifier)

I might also add surface mount led's to the empty solder pads for the power on and overload led's on the board, it looks like the resistors are present, so why on earth did they not add the led's... at least for the overload one.