Dc power supply in cnc not working

[sam_sam_sam]

Re: Dc power supply in cnc not working

Hi redwine
Thanks
I didnt want to spend 50$ total inc shipping....however i did get lucky and found exact part number on ebay used

I typicslly eould never buy a used cap but sibce this one is so costly new i made an exception

)

You need to reform this capacitor before you put it in service

If you have a adjustable power supply put the capacitor on the power supply at 5 volts to start with and the current set at minimum and when the current goes to zero then slowly increase the current until the current goes up a little bit and keep doing this until you get at the working voltage rating of capacitor and leave it at this voltage for at least an hour

Then you would be able to use it now if the current will not go to zero then there might be an issue with this capacitor

[shelby5041]

Re: Dc power supply in cnc not working

Hi samsam...thats possibly beyond my skills...i have installed many smaller caps (from new stock stored for over 5-10years) and have never done that procedure...i do have an adjustable dc power supply but only goes to 30v 10a

[sam_sam_sam]

Re: Dc power supply in cnc not working

That will still work just leave it at maximum voltage of your power supply for at least an hour you would still do it the way I describe earlier

The most important part of this is at the beginning is that you limit the the current to 100 milliamperes

Smaller capacitor do not need to be done however larger capacitor with higher UF value do need to be done especially if they have not been used for long periods of time time

This is not a very difficult to do for the voltage to get to 30 volts and current to basically zero this might take a few minutes to do this once you have zero current you just leave it at those settings for a hour or more then you are ready to use it

[shelby5041]

Re: Dc power supply in cnc not working

ah ha now i see...this is recommended for larger value uf caps

i will try it once i get it

you should have seen when this thing exploded...it startled me pretty good..i thought it was going to shoot off like a rocket as much smoke that poured out of it

thank you

[eccerr0r]

Re: Dc power supply in cnc not working

Only seen people explode small caps, pics or it didn't happen!

[shelby5041]

Re: Dc power supply in cnc not working

well im super dummy..i screws terminals on backwards and it exploded pretty good

looked like a big smoke bomb was set off...

[eccerr0r]

Re: Dc power supply in cnc not working

oh just smoke and no rapid self disassembly?

[shelby5041]

Re: Dc power supply in cnc not working

yes the actual body of the cap looks fine..you would never have known it exploded.....not sure how it leaked all out without showing any signs of damage but it did

i call it explode...but in reality it didnt get damaged it just looked like an explosion...when it happened .it looked like a fire extinguisher was being used..

Now that im looking at it closer it may have a pressure release vslve in it ...there is a red plastic piece with a hole in it.thats on bottom of cap.....i bet thats a release valve

[eccerr0r]

Re: Dc power supply in cnc not working

Indeed it's a release valve.

Oh well. Thought you had a more spectacular sight. I do wonder about one of my Sangamo capacitors, which I think is a bit larger physically (0.3F 7.5VDC), would do if it were "misapplied" when there's a whimsical warning on it that says "Misapplication Hazardous"...

[redwire]

Re: Dc power supply in cnc not working

I double-checked and the LM338 is configured with nearby resistors R3 VOUT-ADJ "3160F" R2 "1072F" ADJ-GND confusing resistor labelling.
Vishay Dale CCF55 so it's likely 10.72k and 316R giving 43.3VDC out. I thought it was around 5V 3.16k/107.2R but that makes no sense either so gotta be wrong.

LM338 needs a minimum load of 3.5-10mA but R3/R2 provide that. The IC's max is 40V so any mains surge on power up, or short on the output would damage it. Original part is National Semiconductor and these guys must be pushing it past the limit in this product.
The 12V reg U2 is fed from another transformer winding (orange wires). The 12V reg U3 is fed from another transformer winding (yellow wires).

P.S. I've blown up big electrolytics like that and the safety vent pops out and it rains electrolyte. Very loud and scary. What a mess.

Lab-Volt MY92924 power supply board

[shelby5041]

Re: Dc power supply in cnc not working

Hi redwine

U very smart...how did you get all the technical info?...just by my photo?

My concern is like u say the lm338 blow due to another issue

I just hope the other issue was just a fluke...1time thing...maybe related to my attempt at wiring up the potentiometer since thats when the main fuse blew and then lost 42v output after that....i was powering machine on and off during potentiometer testing when main fuse blew.

The relief vent probably saved me from getting injured since it would have literally exploded in my face

[redwire]

Re: Dc power supply in cnc not working

I'm just used to figuring out a circuit based on PC board photos, and using the IC datasheet plus math to see what it's supposed to do when it works.

The potentiometer shouldn't have had anything to do with the 42V regulator or fuse really. There must have been a short circuit in the wiring?

Putting in a new LM338 should fix the regulator. But it's a fragile regulator circuit likely killed if its output is shorted or during power up. So if there is still a short on the 42V rail, the new regulator will likely just croak.

[shelby5041]

Re: Dc power supply in cnc not working

thanks
hopefully it was just a fluke...as i said i was wiring a potentiometer on another driver board and when i installed it i turned the knob all way CC so the spindle motor should not turn on..but when i powered on the machine the spindle was immedialtey on...it shouldnt have been..and the pot wiring was correct....it may have been a bad POT...so i powered machine on and off about 3 cycle to test the pot and thats when the main fuse blew and lost 42V.

ill double check my wiring and make sure nothing is out of place

i have done a lot of rewiring on other boards in this machine..i have not touched the 12v/42v ps though ..



i bought 10 LM338 ...so i will have extras if it blows again and if it does i will have to review more..i have done this same exact rewiring on 2 other same machines with no issues

[shelby5041]

Re: Dc power supply in cnc not working

Got the used cap today..will try and teform it today and .will install tomorrow

[shelby5041]

Re: Dc power supply in cnc not working

hi samsam

im not clear on how to reform

i have a dc power supply that i can change voltage and current settings

when i put my voltage on 5V and current at 50mA and then hook it up to the cap and power on the ps

the voltage says 5v..the current shows 0v since nothing is drawing amps

if u change current the voltage does not change

my ps may not be compatible for reforming

[shelby5041]

Re: Dc power supply in cnc not working

If you have a adjustable power supply put the capacitor on the power supply at 5 volts to start with and the current set at minimum and when the current goes to zero then slowly increase the current until the current goes up a little bit and keep doing this until you get at the working voltage rating of capacitor and leave it at this voltage for at least an hour

do you mean voltage instead of current?

i currently have it connected at 30V(my max V on PS) 50mA and its showing 0000 amp drawn ..i will keep it there for 1 hr

thi is the power supply i have

https://www.ebay.com/itm/13386127635...Cclp%3A2334524

[shelby5041]

Re: Dc power supply in cnc not working

update samsam

i left cap at 30V for 1 hour

once i disconnected and tested cap voltage via multimeter...it quickly dropped from 30v to near 0v within about 20 seconds...was the cap being discharged through the multimeter?

is this normal or bad?..note: i only had amp setting at 50mA while connected to power supply

if the used cap is bad i can get a refund

thanks

[sam_sam_sam]

Re: Dc power supply in cnc not working

First of all does this capacitor have a resistor on it if not
It might depend on what meter you are using

What happens when you just turn the current to zero amp and turn the voltage down to minimum use the volt meter on your switching power supply do you get the same results ( some power supply will allow you to monitor a voltage with very little load )

You should be able to light a led light bulb with a current limiting resistor (@ 2 milliamperes @ 30 volts maximum less current would be better ) for a little while on this capacitor if it is any good

It might be okay for 20 second going through the meter

[sam_sam_sam]

Re: Dc power supply in cnc not working

once i disconnected and tested cap voltage via multimeter...it quickly dropped from 30v to near 0v within about 20 seconds...was the cap being discharged through the multimeter

Wait for 5 minutes before you put the meter leads on it does it still have any voltage on it

[shelby5041]

Re: Dc power supply in cnc not working

No resistor


Ill just install cap today...if it doesnt work in circuit ill get a refund