Boxford TCL125. (Fresh start )

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Originally Posted by Doddy

John - firstly, these are usually infra-red, so it may well have been illuminated even if you couldn't see it (hint - you can often get a mobile phone camera live-view to witness IR LEDs).

Reverse voltage?, yup, a good way to fry an LED.

The good thing is these are generally fairly standard devices, although pin-outs may vary. And drive voltages?, can be pretty much whatever you need. I'll assume you've not hit this before otherwise you'd not be asking.. Take the supply voltage, and subtract the forward voltage drop of the LED. Then divide that by your chosen forward current. That gives the value of a resistor to place in series with the LED for it to operate at that voltage. That Datasheet indicated a max forward current of 40mA - that's an absolute max rating, a rough rule of thumb is around 10mA.

So, if you're trying to drive at 5V, and the Forward Voltage is 1.8V, with a Forward current of 10mA (0.01A), that's (5.0-1.8)/0.01 = 320 Ohms, nearest easy found value is 330 Ohms. If you want to drive at 12V, then (12.0-1.8)/0.01 = 1020 Ohms, nearest easy value = 1000 Ohms (1k).

Whichever resister value you calculate, you place the resistor in series with the LED then drive that from the DC supply.

Note, its generally considered unhealthy to reverse bias an LED - they go pop at quite a low reverse voltage. Even if they don't pop, then can be significantly degraded.

Amazon sell reflective opto-couplers - there's generally not a huge difference in the 4-pin devices (2 pins for the LED, 2 pins generally for a photo transistor). They should be pretty much interchangeable.

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Hi again folks
Have replaced the opto switches but i am struggling to follow the calcs above
Taking figures from page 5 of the datasheet Forward voltage is 1.7 v max with a forward current of 20mA, so with two lamps in series we have a forward voltage of 3.4.
Not sure how I choose the forward current but 20mA is the figure given in the conditions column so will go with that.

So cautiously driving with a 5 v supply 5- (2x1.7) = 1.6V and at 20 mA I calculate a resistor of 80 ohms and I dont have one.
And I still cant quite understand why Boxford were driving the same rig with a 10v output and no apparent resistor , so with tongue firmly in the cheek and having a couple of spare opto switches my inexperienced mind thinks why not give it a shot without resistor anyway.

So I wired to plus 5 v and brought the single pulse (blue wire) back to pin 12 , set this up in Mach 3 I am not understanding the other settings I see in Mach.
I get figures flashing up for true spindle speed as I switch on with say S500 but these figures die away to zero as spindle runs up.

I am bewilderd by the range of settings I may need to address so if any one can guide me I would appreciate.
I presume that spindle pulleys just selects a speed range so I think I am OK with that
But Ports and pins , spindle setup , spindle motor , motor outputs , PID settings have lost me, even before I get into Encoder settings :sorrow:

20mA is usually around the max rated forward current. It's a fairly conventional rule of thumb to select 10mA. That'd give a resistor of 160R, or thereabouts (selecting 10mA as the basis of the resistor calculation gives you a lot of wiggle - you can halve it and still be within the working limits, chances are you could double it and it'd still work). You get less flexibility as you chose a resistor for a larger forward current, of course.

An idealised, simplified model of an LED would presented a voltage source of V-forward (1.7, above), and 2 in series would be 3.4V. That then would mean without a series resistor you're presenting 1.6V (as you say) into a dead short - theoretically infinite current and the blue smoke escapes. Of course, the real model of the LED would have some internal series resistance, and there's the series resistance of the cabling, and the PSU. It might work. It might work for a while. It might work for not very long. But you have spares!, and if you want any resistors thrown in the post I can do that. It's an interesting experiment in any case, and you can but learn from it.

With Mach, can you confirm that with stationary spindle you get 0 RPM. Then at very low RPM you get some RPM (maybe not the right RPM, but some). The first thing you want to make sure is that the encoder input is working before getting too hooked into the inner workings. You should be able to monitor P12 input on diagnostics page and rotate the spindle by hand to find the index position - just confirm that is working with 1 PPR.

Would appreciate a couple of resistors suitable for the task Doddy. You still have my address I presume.
And yes spindle speed shows as zero

Not seeing any illumination on pin 12 as I rotate the disc past the single slot:confusion:

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Originally Posted by John11668

Not seeing any illumination on pin 12 as I rotate the disc past the single slot:confusion:

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I suspect with no resistor you have blown the new optical sensors
Take the pin 12 and touch it to ground. See if this triggers the pin in mach3
If it does then you have likely popped the new sensor

Paul


Sent from my iPhone using Tapatalk

Are there optical switches with a better voltage tolerance ?

That's the purpose of the resistor.

EDIT: I'll get a selection in the post on Monday morning.

Am currently trying to set up a profile in Linux cnc .
Would that be an easier to place to start .

RS Components do free delivery on all online orders which makes it economical to order only a few LEDs, resistors etc. of various values costing next to nothing for experimenting. I used to feel guilty about this and try to wait until I had a larger order, but they end up sending your order in 5 envelopes from 3 different countries anyway so don't worry about it. RS are not always the cheapest supplier but for small orders the free postage is very useful and delivery (here in Australia anyway) is quick.

If you're not sure what you need I'm sure there are several readers who could scan the online catalogue and suggest RS part numbers for you even if we don't have components we can send you directly.

(Deleted - retreats with egg on face due to not being able to count on fingers and get same answer twice)

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I am still in bed. Maybe that's the problem. I really need that first cup of coffee!

Sorry, guys - I promise not to try mental arithmetic in public again...

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Originally Posted by Kitwn

RS Components do free delivery on all online orders which makes it economical to order only a few LEDs, resistors etc. of various values costing next to nothing for experimenting. I used to feel guilty about this and try to wait until I had a larger order, but they end up sending your order in 5 envelopes from 3 different countries anyway so don't worry about it. RS are not always the cheapest supplier but for small orders the free postage is very useful and delivery (here in Australia anyway) is quick.

If you're not sure what you need I'm sure there are several readers who could scan the online catalogue and suggest RS part numbers for you even if we don't have components we can send you directly.

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Looks like lots of options on there https://uk.rs-online.com/web/c/displ...ect-relevancy-
but I wonder I may not have the right spindle and encoder settings .
Until I am confident of those then I might be flogging a dead horse replacing opto switches .
If I were confident of my settings being correct in Mach 3 then I could happily mess about with resistors and adjust positions until I can get light shining through the hole. and the little Indicator of the diagnostics screen illuminating

Still puzzles me how Boxford could supply this setup with 10v and not a resistor in sight

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Originally Posted by depronman

I suspect with no resistor you have blown the new optical sensors
Take the pin 12 and touch it to ground. See if this triggers the pin in mach3
If it does then you have likely popped the new sensor

Paul


Sent from my iPhone using Tapatalk

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Have tried that and the yellow light goes out so sounds like I am stuck until I get some resistors .
Will look out for my mail early in the week.

Had a look on RSwww and literally pence each but with £4.95 postage

so at least you have proven the wiring is correct and the setup in Mach3 is also correct

just need the resistors and fit a new pair of optical sensors and you should be good to go

Paul

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Originally Posted by John11668

Have tried that and the yellow light goes out so sounds like I am stuck until I get some resistors .
Will look out for my mail early in the week.

Had a look on RSwww and literally pence each but with £4.95 postage

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That's interesting, I must have been given a business account (which has free postage for all orders) for some reason without realising it. I've been a customer for donkeys years and have never been charged postage.

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Originally Posted by Kitwn

That's interesting, I must have been given a business account (which has free postage for all orders) for some reason without realising it. I've been a customer for donkeys years and have never been charged postage.

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I think it depends where you live. In the UK postage is normally charged unless you order is over a certain amount at which point postage becomes free
I have a deal through work where by I get free postage and on most thinks a little off the price

I normally use CPC as they are local and if I need it quickly I can collect at their counter I find that I normally need something immediately so this works for me

Paul


Sent from my iPhone using Tapatalk

Some of you are privileged but we have no branch of RS or CPC within range .
I do use RS for stuff like relays or Capacitors and the min order which I believe is £20 is usually covered
And I have ordered at 9 pm and found the goods on y doormat by first post following morning. Brilliant

I'm a grumpy old git, and rarely have much good to say about anything. But, to be fair, both Farnell and RS have in recent years come along in leaps and bounds for supplying to the general public. As with John's experience I've had good next day delivery on small orders. I do think both trade better in volume, more so RS and MoQ can sometimes be prohibitive, and the supply chain rigour can mean that you can find cheaper elsewhere on some things (connectors and cables especially). Farnell pee'd me off at work with two switches (£140 each) taking over 6 months for delivery - but that's exceptional.

What I'm trying to say is that both RS and Farnell are very accessible to Joe Public.

CPC - yeah, like Depronman, is local to me - it was bought out by Farnell years ago but is a poor substitute. Very handy for picking up bits on-the-day, but with my laziness it can be easier just to throw an order out for next day delivery from the big-two (particularly as CPC closed their trade counter at the weekend under Covid).

Rapid, also springs to mind as a good supplier.

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Originally Posted by depronman

I think it depends where you live. In the UK postage is normally charged unless you order is over a certain amount at which point postage becomes free

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I've just checked both the UK and Australian RS websites and you're right. Free delivery for all online orders for those of us living down under but not for you poor souls still living in pommieland.

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Originally Posted by Kitwn

I've just checked both the UK and Australian RS websites and you're right. Free delivery for all online orders for those of us living down under but not for you poor souls still living in pommieland.

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It’s a long way to come to Oz to get free delivery from RS [emoji2957]. Sounds like a good excuse though...

Paul


Sent from my iPhone using Tapatalk

For the sort of quantities I need , ebay is sometimes a reasonable route

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Originally Posted by depronman

It’s a long way to come to Oz to get free delivery from RS [emoji2957]. Sounds like a good excuse though...

Paul


Sent from my iPhone using Tapatalk

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Any excuse is a good excuse for moving here, especially now.

Another lesson this evening!
I decided to take a supply to the driver board from my 5 v PSU rather than regularly falling over a Usb lead from the computer.
And I took the opportunity to make some of the other wiring a bit more compact. So I had the power switched off , and unplugged for (I think) more than 20 mins when the 24 v supply cable touched the chassis giving me a hefty flash and lightly welding itself . Maybe need to be careful of big capacitors .
I think it has taken out the driver board as the traverses dont seem to be working. :dread: Spindle controller still OK though .

Is there a way to quietly discharge the capacitor when I switch off??

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Originally Posted by John11668

Another lesson this evening!
I decided to take a supply to the driver board from my 5 v PSU rather than regularly falling over a Usb lead from the computer.
And I took the opportunity to make some of the other wiring a bit more compact. So I had the power switched off , and unplugged for (I think) more than 20 mins when the 24 v supply cable touched the chassis giving me a hefty flash and lightly welding itself . Maybe need to be careful of big capacitors .
I think it has taken out the driver board as the traverses dont seem to be working. :dread: Spindle controller still OK though .

Is there a way to quietly discharge the capacitor when I switch off??

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Big capacitors?, I always fit a bleed resistor across the terminals - nothing too exotic - for exactly that reason. Others here will argue against that... we agree to disagree.

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Originally Posted by Doddy

Big capacitors?, I always fit a bleed resistor across the terminals - nothing too exotic - for exactly that reason. Others here will argue against that... we agree to disagree.

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Not as bad as initially assumed .. Board IS working but amazingly the jog function works better when some "plonker " does not forget to check that the "Jog on" function is selected Dooohhhhh!

Nonetheless I do feel it would be a good idea to bleed away charge from the capacitor when the the supply is broken . What size of resistor would be approprate ??

I'm in the opposite camp to Doddy in that I don't use any bleed resistors. Why? Because they only matter in practice if you are running the PSU with no load. Once it's all in and working, the load on the PSU is going to discharge the capacitors anyway. If it's a switch-mode supply, then the actual capacitor value is quite small - my 24V supply feeds, amongst other things, the "Mains On" LED on the front panel and that and the motion controller between them discharge that supply very quickly - the LED goes out with no measurable delay when you hit the mains off switch. The 68V main driver supply has four stepper drivers permanently connected; even in "disable" mode when the output devices are presumably switched off, they draw power for their internal electronics and again, that's enough to bring the volts down fairly quickly.

While a bleed resistor won't do any harm, it's something else to house, it wastes power whenever the PSU is energised, and it can get hot.

There are different ways to look at the problem and estimate associated risk. For example, I don't have an interlock on my control cabinet that cuts mains power when it's opened. You pays your money and you takes your choice!

Although a bit of a belt-and-braces man, I personally stop short of the electric trouser hoist!

For the benefit of others: This addresses a particular question posed, based on the OP's determination that having a charged capacitor is something that he wants to avoid and because of the observed behaviour. It's not intended as a 5 page debate over bleed-resistors-or-not.

"what size of resistor would be appropriate"

You need to solve a couple of equations...

Tau = RC

(R is the resistor value in Ohms,
C is the capacitance, in Farads
Tau is the value of time taken for the voltage in the capacitor to fall by 63% (or to 37%) of the original voltage).

So, for example a 20,000uF (0.02F) capacitor, and a 1k resistor (1000R), Tau = 1000 * 0.02 = 20 seconds to discharge a 100V to 37V. Then another 20 seconds to discharge to 14V (37% of 37V) and so on. The lower the value of resistor, the quicker the rate of discharge.

However, the lower the value of resistor, the higher the power dissipation that resistor endures whilst powered on, until the capacitor is discharged.

P = V^2 / R

(where V is the voltage across the capacitor)

Assuming your 24V supply.

P = ( 24 * 24 ) / 1000 (using the 1k resistor above).
= 0.576 Watts.

Therefore you'd need a resistor rated at above 0.576 watts - there are a 0.6W rating, then you typically find 1W, 2W, 3W, 5W etc...

Also consider then that you're dumping that power into your PSU enclosure as heat whilst the PSU is operating. To be honest, a couple of Watts is 2/3'rds of cock-all, but you need to be aware.

Myself - I have 72V DC power and, I think 10,000uF capacitors (x2, dual secondary/supply) - I really can't remember but expect I've used in the order of 2k2 wirewound 3W resistors. But that's just my choice/wet finger.


EDIT:

AHA, Neale - you posted first. Part of my rationale is that my cabinet is modular in design - as you say, if I isolate the drivers whilst I'm working in the cabinet, it's reassuring vs spot-welding the wedding ring to chassis.

OK points taken and it seems that no damage was actually done but the arc was a bit intimidating.
The wedding ring seldom gets into exposed positions (fat fingers) but I am never without the trusty old (and thoroughly abused )Seiko Titanium, and the idea of it being welded to the chassis does not appeal.
However I am not sure if I can accommodate one of these https://www.cpaltd.net/dynamic-braki...l?options=cart

If I choose to dispense with the old Boxford control panel then that will vacate some space where the junction strip now resides so may think about it .
Laterally thinking, might it be possible to make the E stop a changeover switch which when it breaks connects the capacitor via the NO terminal to the heater to and thus on to earth , thus avoiding having an electric heater going continually in the panel as the machine is operating??

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Originally Posted by John11668

OK points taken and it seems that no damage was actually done but the arc was a bit intimidating.
The wedding ring seldom gets into exposed positions (fat fingers) but I am never without the trusty old (and thoroughly abused )Seiko Titanium, and the idea of it being welded to the chassis does not appeal.
However I am not sure if I can accommodate one of these https://www.cpaltd.net/dynamic-braki...l?options=cart

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Check your decimal point.

Attachment 29128

These are 3w...or maybe 5w from the look of them, across the capacitor terminals.

Sorry doddy
I read "Kw "