Validation of power supply

[Davidh]

If I was having trouble how would I validate my power supply to ensure it is not 'pulling down' in certain running conditions?


18v torodial, bridge rectifier and a jumbo capacitor. All correctly spec'ed at the time of build, the details just escape me now.

If I run to the opposite corner and hit 'go to zero' and it whizzes home sucessfully,x and y both running at max speed is that it tested?

TIA

[Yohudi]

Well it is sort of.. in that it seems everything is working OK...

you can safely measure the voltage output by testing with a meter in parallel but current is a bit more difficult.. as you have to put the meter.. and yourself in series connection with the supply to do this...NOT RECOMMENDED unless you know exactly what your doing..... alternatively you can use a clip on meter designed to measure current using induction... but not many people have one of these lying about...

Best thing to do is try the motion against resistance.... GENTLY try and stop the axes from moving... if they have a good amount of torque then along with the speed test you performed this would suggest that all is working ok...

[Lee Roberts]

Best thing to do is try the motion against resistance.... GENTLY try and stop the axes from moving... if they have a good amount of torque then along with the speed test you performed this would suggest that all is working ok...

Ill give that ago as well, have you got a name or website for these meters your telling us about?

Thx

[Yohudi]

Hi there,

It's just a bog standard electrical test meter.. will detect and report voltage and current output .... you should pay about 2 to 3 quid for a test meter from the likes of ebay...

The DANGER when doing current checks is that this can only be measured with the meter in series with the supply... and if you have hold of it then this means you are also part of the supply circuit. Fine if you know what you are doing and there are no problems.

However, if there were to be a fault on the supply that you were unaware of you could be at risk when measuring current. 40 volts or so DC at current of 10 - ish Amps has the potential to do you harm. There's a special kind of test meter called a clamp meter to test current without being in circuit yourself.. it just clamps around the wire and the electronics perform the necessary wizardry to safely read both voltage and current. They are quite expensive tho... clamp meter is probably in the region of £40 to £50 minimum.

It's the kind of thing a sparks would use on site...

[Lee Roberts]

Ahhh, potential to do you harm.

I didnt really understand what you ment about us being part of it like that so thanks for the warning and explanation, thout it was a good idea to put the above in my post.

I was really refering to giving them some resistance, my motors are 4.2 amps, however my drivers only 2.5 or somthing like that so they will only be running half pace/power.

[Yohudi]

Resistance ....

was the wrong word to use in this context.

NOT Electrical resistance but PHYSICAL resistance.

Can safely measure voltage in parallel to the tested circuit.. so can validate voltage without problem..

Current is the risky bit.. depending on amps coming from the supply... but current generally equates to power or torque in motors and this can safely and easily be tested with a bit of physical resistance to the motion of the motor or whatever it's driving...

I.E. If you get good speed but you can stop the motion with light pressure it's likely that voltage is OK but current is Insufficient. If you get great torque but no speed then that would suggest current is OK and voltage is down. It's all fairly simple stuff really...

[Davidh]

Spent a bit of time investagating this.

System powered up and x,y & z steppers locked .................25.8v 1 amp
X fast traverse, Y & Z locked........................................1.4a mp
as above plus heavy load added manually
( in use it will never be anywhere near this load)..................2.0 amp
Y as above............................................. .................Same
X+Y fast traverse Z locked............................................ 2 amp
z fast traverse x &y locked...........................................1 .1amp

Voltage pulls down <1volt


My motors are supposed to be 2.4amp each so I conclude that power supply is well big enough and motors are never loaded to their full rating.

Conclusion. Power supply 'seems' validated.



Any thoughts?

[JAF Graphics]

Hi,
Sounds to me like the power supply is fine, in fact it sounds very much like the power supplies we have been using for the last 20 odd years without any problem.
Now go start making things....the fun part!!

Simon

[Davidh]

'Now go start making things....the fun part!!'


I'm doing that albeit slower that I would like. My stepper wants to stall in certain conditions. It can 'straight line' at a healthy speed x, y or both but can make only about 1/3 the speed doing circles and curves.

Funny thing it is always in the y- direction it stalls, temporarly then it is away again with the job shifted south.

Talk to me people :?: :?:

[Yohudi]

Hi there,

your cutting prob sounds like a mechanical rather than a motor power issue. I would suggest that under cutting load the integrity of your frame is not being maintained in the Y axis... causing it to distort and making the y axis bind/stall and lose steps. Straight cuts impose some force on the axes but if there is deflection it's primarily in line with the axis (shearing in a plane) so you don't see so much binding. also lost steps are potentially disguised as the next step will make the cut anyway... but a non-straight cut imposes the force in many different directions and you get twist effects which can make the axis bind when a straight cut doesn't, then when the cut changes direction the twisting is reduced, the axis unbinds and moves again but with the lost steps it is out of position.

you can test this out by running a very shallow circular cut on some old MDF which is nice and easy to cut as well..... start at a really low cut amount in the 0.5 to 1mm range.. run your spindle at high speed and use a slow feedrate. See if you can cut the circle complete and check that it is a circle. If so double up the cut depth and run again... repeat until the problem manifests, you may see the beginings of it with the shape of the circle changing. This will show if the problem is down to deflection as you increase the load on the cutting tip... it will also determine a "functional" setup for your machine as it stands, you should be able to arrive at a workable comprimise to avoid deflection and lost steps but still cut at a reasonable speed...

hope this helps.