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Thread: Weird voltage problems on 4020

  1. #21
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    Default No dice...

    Quote Originally Posted by fadalman View Post
    BTW
    my ps that failed(looks like a PC type)said 5+vdc 25.0 AMP.+12vdc 10.0 AMP,-12vdc 0.3 AMP
    Hmm. It powers up but still the same problem. Ok I dont have any AC ripple on the 5VDC that I can see, but the voltage drops from 5,3VDC with out load to 4,6VDC when it is hooked up to the CNC. this means same problem as before, but more voltage drop than before. Almost like something is really pulling loads of amps, but what?

    Andy



  2. #22
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    If I feed each of the 5 wires from the CNC that requires 5VDC with its own red 5V wire from the PC power supply the load drops the voltage to average 0,03 V per card. that is CPU, VIDEO, INTERFACE, MILL INTERFACE, SPINDLE and the XYZ axis cards. The others dont pull much. Still that puts me just below 5VDC so I am still stuck.

    Since I cant feed each card with its own dedicated power supply would it work to use say 3 power supply units to all feed the various voltage groups?
    would this result in smoke and flames?

    The problem is that not until I can get over 5VDC with every thing hooked up will the control go beyond the intitial Fadal logo and report which axis is causing problems.

    Andy



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    071211-1713 EST USA

    andy.f:

    Usually most 5 V logic systems will work down to about 4.5 V (a 10% drop). However, I would expect any 5 V system to work at 4.75 V. You have indicated a supply drop of 0.03 V per card and there are apparently 5 cards. So on this average basis you have a drop of 0.15 V, or 4.85 V if you had an unloaded output of 5 V.

    If your supply is actually a 25 A at 5 V unit, then I would expect a well designed unit to drop maybe 0.1 V at 25 A, or an internal impedance of 0.004 ohms.

    Possibly there is a trimmer adjustment on the supply for voltage.

    You do need to make current measurements. For a machine controller 25 A would sound high.

    Apparently you found the original power supply to be defective.

    .



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    Hi Gar, Thanks for the reality check. I am still not sure the original PS is defect. that does have a 5V trim pot that I have open full whack.

    Also the PC power supply will not carry all cards in the cage. Right now I am using only the 5VDC and Ground from the original PS for the cage. At the moment the wall AC is very high at 225 - 250VAC so I am actually getting 119V freeding the DC PS which means with all cards in the cage I am at 4,94VDC so all cards are blinking.

    the rest of the CNC gets 5V, 12V+ and - and ground from the PC PS.
    I checked the voltage going into the 1100-1 board and it is 5,2 VDC so should be enough.

    so for the first time I can operate the control, but as soon as I release Estop the control freezes up so I can t jog any axes yet. I have jumpered F14 an F16 on the 1100-1 board to by pass the fault circuit so I can force open the control voltage to the ampchassis and get 140VDC accross the blue capacitor. Strange thing is that I get over 1000VAC between the phases on the breaker in the top right corner of the ampchassis. Or is that DC maybe? Anyway it has not tripped and there is no smoke!

    I am starting to think there might be some ground loop or stray current screwing up the CPU when the E-stop is released.

    The PC PS dont give AC ripple I can measure as the resolution of my clamp meter is only down to 0,1VAC, so dont know.

    It is clear that some thing is eating current. I did a contiuity check on the 5V fuse on the Fadal DC PS under load and got 021 on the DMM. If I am not mistaking this means 21 ohms resistance. It is not the fuse as it reads 0 with out load. This means I have resistance one the 5V ciruit...

    Andy

    Quote Originally Posted by gar View Post
    071211-1713 EST USA

    andy.f:

    Usually most 5 V logic systems will work down to about 4.5 V (a 10% drop). However, I would expect any 5 V system to work at 4.75 V. You have indicated a supply drop of 0.03 V per card and there are apparently 5 cards. So on this average basis you have a drop of 0.15 V, or 4.85 V if you had an unloaded output of 5 V.

    If your supply is actually a 25 A at 5 V unit, then I would expect a well designed unit to drop maybe 0.1 V at 25 A, or an internal impedance of 0.004 ohms.

    Possibly there is a trimmer adjustment on the supply for voltage.

    You do need to make current measurements. For a machine controller 25 A would sound high.

    Apparently you found the original power supply to be defective.

    .




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    071211-2215 EST USA

    andy.

    What do you mean by "continuity test" ? When current is flowing thru some element you can not use an ohmmeter to test for continuity, and should not. You can use the voltmeter to check the voltage drop across the element. This you should do. Check the voltage drop from one wire to the other to the fuse and not directly across the fuse. You want to see if there are some high resistance areas around the fuse. Is this fuse in the output side of the 5 V power supply?

    .



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    Quote Originally Posted by gar View Post
    071211-2215 EST USA

    andy.

    What do you mean by "continuity test" ? When current is flowing thru some element you can not use an ohmmeter to test for continuity, and should not. You can use the voltmeter to check the voltage drop across the element. This you should do. Check the voltage drop from one wire to the other to the fuse and not directly across the fuse. You want to see if there are some high resistance areas around the fuse. Is this fuse in the output side of the 5 V power supply?

    .
    I know the power should be off for continuity test, but just noticed this and thought it would indicate something. The same test under power on the 110V fuse does not pick anything up. If I put the probes on the fuse and ground the reading is same before and after the glass body like expected. The fuse is after the 5V output.

    I dont know what else to check. It is clear the cards seem to use more power than normal. If I use individual wires from the PC power supply the voltage drop is same as when using the fadal PS. Using both the Fadal and the PC power supply gives enough amps to run all cards. There is not one particular card using a whole lot more than another other than what is expected meaning the CPU cards and axis cards should use a bit more than the M and clock cards etc.

    I will leave this as it is for now and focus on finding out why I get over 750VAC on the amp chassis overload relay and why it doesnt trip.

    I will check the bridge rectifiers. the make a swirling noise when powered and I am not sure that is normal or not.

    Andy



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    071212-1539 EST USA

    You want to make the voltage measurement across the fuse, not from each side of the fuse to ground. I suggest maybe 0.01 V maximum would be good, but I have not looked at fuse holder voltage drops.

    .



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    Quote Originally Posted by gar View Post
    071212-1539 EST USA

    You want to make the voltage measurement across the fuse, not from each side of the fuse to ground. I suggest maybe 0.01 V maximum would be good, but I have not looked at fuse holder voltage drops.

    .
    Right. It is 23 mV so a bit more and now I only feed the cage from this power supply. The rest of the machine that needs 5V get it from the PC PS.
    It seems like everything is a bit shaky and just on the minimum limit. It can work ok for a few minutes and then the CPU stalls or reboots or an axis card stops responding. then I check and the 5V is around 4,82 or so.
    I talked to Gary at Fadal and he says it needs to be 5.01 - 5,1VDC.

    I feel like going back to wood carvings....



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    071217-0924 EST USA

    andy.f:

    Most 5 V integrated circuits will be at least as good as the following specification from TI for the 74LSxx devices: Recommended operating conditions 4.75 to 5.25 V. This dates to the early 1970s and earlier for other 7400 series devices. This does mean the voltage at the integrated circuit.

    There is voltage drop between a power supply and the integrated circuits.

    The voltage drop across your fuse is higher than I guessed at, but I have just run an experiment, and the results are:
    7.5 A AGC fuse in a holder with high contact force. Initial voltage drop at 200 MA was 130 MV, but the drop across the fuse was 2 MV. I then rotated the fuse to clean up the contact surfaces and the drop across the holder dropped to 3.8 MV. Extrapolating to 5 A the fuse drop would be 25 * 2 = 50 MV assuming the fuse resistance was constant. Thus, your 23 MV drop is reasonable, but we do not know your current.

    The Fadal spec of 5.01 V instead of 5.00 is sort or silly, but 5.00 V for a low limit as measured at the power supply does make sense, because of the voltage drops from the supply to the integrated circuits. You need to measure the voltage directly on your circuit boards. If the voltage across integrated circuits on your boards is above 4.80 V, then it is likely you have some defective components. You might blow cold air, 70 deg F., over your boards and see if this keeps the system running longer.

    .



  10. #30
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    Hello. I have the same problem on a 4020 ht. I have 12 volts and 4.54 volts. I have garbage on the screen and I cannot start the machine. the power supply transformer has varnish as if it has leaked



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Weird voltage problems on 4020

Weird voltage problems on 4020

Weird voltage problems on 4020