Potentiometer

[hunter27]

Yesterday I was trying to get my head round screw cutting on some scrap material on my Boxford BUD lathe. It went okay after a few mistakes but halfway through the day I lost the variable speed function from the remote inverter control box fitted to the headstock.
The lathe has a 3 phase motor converted to run on single phase through an inverter (I bought it like this a couple of years ago) now I can only adjust speed using the pulleys.
I suspect (hope) it's the potentiometer in the control box which has stamped in it =
"Lin A RS 10K made in UK" and nothing else.
Can I just replace it with any Linear 10K mono potentiometer to see if this solves the problem?
Cheers Pete

 

[daleyd]

Yes, though have you got a multimeter to check whether this one is actually faulty?

If not and the inverter itself has got an issue then you could possibly reprogram it to set the speed via the front panel (I don’t know which inverter you have so maybe it’s not possible) - but hopefully if it’s just the pot then it should be an easy fix.

 

[fizzy]

That is as about bog standard as it is possible to get. Fairly rare for a pot to just stop working - they get noisy first so would perhaps have caused speed fluctuations in the past.

 

[Pete.]

More likely to be a wiring issue but could be the pot. Did it go to minimum/maximum rpm or just stay at the one you had set?

 

[Dieselman 63]

Mine went haywire twice, it was quite scary to not be able to control the motor at max rpm. It turned out there was a loose connection which shook free from vibration when the motor was running. All sorted now

 

[Hopefuldave]

As said, that's a pretty basic pot, there are more reliable/durable ones e.g. 2 watt wirewound, but they tend to be a bit larger (and a couple of Local Currency Units less cheap) and might be a tight squeeze in the box...
I've set my VFD up to use the fixed frequency settings as well as the variable, usually just needs a 2-pole 4-way switch (full, half and jog plus variable) or similar connected to digital-in on the VFD and configuring the fixed speeds though a billion menu options. If you're flash you can use a fancier switch and light up speed selection LEDs on the box, or have a slider pot on the cross-slide for nearly-constant surface speed like the youngsters have on their CNC lathes....

Dave H. (the other one)

 

[hunter27]

When it packed up It wasn't dramatic but I think it just ran up to full speed and wont slow down. Readings (still wired up)seem a bit erratic from middle post to the input the resistance reading goes up and then back down. I will check the reading again when I get home and disconnect it first. At least I know I can just replace it, and may be try to incorporate a jog switch to the panel.
Thanks for the replies.
Cheers Pete
.

 

[Seadog]

If it's erratic then it's faulty.

 

[MBB]

10 k pots aren't very expensive, try new on and see if its any different.
What is the make of the inverter?

 

[hunter27]

Will have a look when I get home and report back. I have ordered a potentiometer and a momentary switch to see if I can add a jog switch to the forward / reverse / speed/ on/ off control box

 

[hunter27]

I have ordered one of these
https://cpc.farnell.com/bourns/93r1...&ddkey=https:en-CPC/CPC_United_Kingdom/search

and one of these
https://cpc.farnell.com/itw-switche...key=https:en-CPC/CPC_United_Kingdom/searchfor
a jog switch hopefully. I thought I could bridge the on / off switch with it?

 

[Hopefuldave]

Jog wants to bridge forward and common on the control input terminals, if you want a low-speed jog then have a look in the manual (https://inverterdrive.com/file/IMO-Jaguar-Cub-Manual) at the X1 - X3 terminal settings, an input for a low-frequency output should override the Pot setting (you need the jog switch to also route the common terminal to one of the Xs, a pair of diodes on the switch output connected to the X terminal and forward terminal would do it)

Dave H. (the other one)

 

[daleyd]

You know the manual says to use a 1 - 5k pot?

 

[Hopefuldave]

You know the manual says to use a 1 - 5k pot?

well spotted that man, just testing...

Dave H. (the other one)

 

[hunter27]

Jog wants to bridge forward and common on the control input terminals, if you want a low-speed jog then have a look in the manual (https://inverterdrive.com/file/IMO-Jaguar-Cub-Manual) at the X1 - X3 terminal settings, an input for a low-frequency output should override the Pot setting (you need the jog switch to also route the common terminal to one of the Xs, a pair of diodes on the switch output connected to the X terminal and forward terminal would do it)

Dave H. (the other one)

Hi Dave Thanks for looking up the info.
I have no instructions unfortunately for my inverter and I think the one you posted a link to are for newer models but probably not that different overall. I have had a look at it but am more baffled than ever now.

My set-up has been working fine since I bought the lathe and I am a bit scared that I will upset the inverter settings so have left well alone

I perhaps naively thought a momentary between the on/off switch would jog the lathe, will it not? I have just removed the bottom panel from my inverter and it mentions jog but they are not cable terminals "thermistor jog preset etc" they look like they require links like they use on old hard drives


Cheers Pete

 

[daleyd]

I’d be tempted to get a pot of the right value (between 1 - 5k according to the manual) before doing anything else. You can as you say use a button across the start but that’s not a true “jog” function as it will run at the pot set speed with all the associated ramps etc, though to be honest it would probably be fine for a lathe. If I get chance I’ll have a look at the manual but it shouldn’t be hard to assign a jog function to one of the terminals - it will probably need some programming to set the terminal up but should be doable.

A jog is *generally a lower (*though not always) preset speed.

 

[hunter27]

I’d be tempted to get a pot of the right value (between 1 - 5k according to the manual) before doing anything else.

Hi daleyd
On the last picture of my inverters bottom panel (different model than the link posted by hopefuldave) it says 10k pot between 8,11 and 12. There is no wire connected to No12 ?
I have ordered a 10K pot (only because I saw it stamped on my speed control pot)
Is this right or is it a different unrelated pot?
Cheers Pete

 

[daleyd]

Hi daleyd
On the last picture of my inverters bottom panel (different model than the link posted by hopefuldave) it says 10k pot between 8,11 and 12. There is no wire connected to No12 ?
I have ordered a 10K pot (only because I saw it stamped on my speed control pot)
Is this right or is it a different unrelated pot?
Cheers Pete

Sorry, I didn’t look at your pic - it looks like that’s right, like you say the manual is possibly for a later model - might be worth doing a bit of digging to find the right one for yours? I guess if it’s worked previously then it must be correct so disregard everything I said ha ha

 

[hunter27]

Sorry, I didn’t look at your pic - it looks like that’s right, like you say the manual is possibly for a later model - might be worth doing a bit of digging to find the right one for yours? I guess if it’s worked previously then it must be correct so disregard everything I said ha ha

No worries, at least I have ordered the right size then, hope it's just as simple as replacing the pot.
Cheers Pete

 

[Pete.]

5k or 10k shouldn't matter, all it does is split the voltage to give you a variable output. Too low an ohms value is worse than too high, usually.