The diode check is always the first thing to be done because shorts on the input side or sometimes even the output side cannot be saved by the drive just faulting. What you are actually checking are the 6 input rectifiers as well as the 6 reverse polarity freewheeling diodes built into the modern IGBT's. What you do is follow the current path from the meter through the component. When you place the negative meter probe on the DC bus Negative, then the positive on any of the inputs or outputs, you are reading OL because you are charging the bus capacitors with the output voltage of the meter. This is what you want to see. When you place the negative meter probe on the DC Positive and then put the positive on any of the inputs or outputs, you are then measuring the drops of all the diodes in the corresponding half of the drive. The three input rectifiers on the 'top', and the three reverse polarity diodes on the IGBT's on the 'top'. When you reverse the probes (positive of meter to DC bus Neg) and do the same operation, you are then measuring all 6 diodes on the bottom half. So you want to see healthy voltage drops typical of those rectifiers, such as above ~300mV or so. Anything below would indicate one of those diodes has failed shorted, and something is going to blow up either powering it up, or giving a run command (if it can't just fault).
Place that I retired from had over 100 ABB 6 & 18 pulse drives. We had about 45 5 HP garbage ABB drives in a 5 story garage that over 25% burnt up first year. Told us they are throw always and have to purchase new ones. ABB tech support were prima donnas that always gave me a hard time when I only asked them 1 or 2 questions. A&B & Danfoss tech support were best in class.
If you look at the schematic, the diodes are forward biased (should act like a closed circuit) relative to the negative terminal. When placing the positive probe there you're generating a small voltage between the negative terminal and any of those l1 l2 l3 u v w terminals. If the diodes work correctly you should see a voltage drop (between 0.5-0.8V or 0.2-0.3V depends on the type of diode) or small current passing (which translates to some resistance if you're reading in ohm mode). When reversing the probes (positive probe on any of the l1 l2 l3 u v w terminals and negative probe on dc negative) you should read OL in resistance, as the diodes should block currently from flowing back.
Easy way is remove three out put wires that goes to motor and start the vfd. If vfd is giving out put voltage means vfd is ok if still vfd faulted out at ground or other fault then vfd is bad otherwise motor or cable that is connected to motor
@@Josh-px6xb we have Allen Bradley drive like power flex 525 and 40 P starts if load is disconnected last time I have ground fault and i figured by disconnecting load
i think hes using the how to test a diode technique to tell whether the diodes are bad or not because if they are bad they wont convert the ac to dc properly and i believe fry electronics. if i remember right the anode is the positive side and cathode is negative if you put your black on the negative end and red lead on the positive end electronics flow should be .6 voltes for a silicone diode. reverse the leads and you should see OL no voltage should flow if its working correctly. diodes only allow voltage to flow one way so when you see them flow both ways or not at all you know they are bad. he could probably open it up and desolder and solder the correct rated diodes but if your an amatuer and dont want to risk damaging expensive motors id take it somehwere to be done if its cheaper.
Im still confused on why you're testing between AC and DC. I understand the drive is converting the AC to DC, and then back to AC. But its done all internally. Aren't those DC terminals used for 24v for the drive? I guess i just don't understand the relationship between the AC and DC terminals.
The DC terminals are for the DC bus, not 24VDC IO power. Those would be on the IO terminals. This is the rectified DC bus shown on the center of the schematic that the VFD uses to invert to PWM AC.
The diode check is always the first thing to be done because shorts on the input side or sometimes even the output side cannot be saved by the drive just faulting. What you are actually checking are the 6 input rectifiers as well as the 6 reverse polarity freewheeling diodes built into the modern IGBT's.
What you do is follow the current path from the meter through the component. When you place the negative meter probe on the DC bus Negative, then the positive on any of the inputs or outputs, you are reading OL because you are charging the bus capacitors with the output voltage of the meter. This is what you want to see. When you place the negative meter probe on the DC Positive and then put the positive on any of the inputs or outputs, you are then measuring the drops of all the diodes in the corresponding half of the drive. The three input rectifiers on the 'top', and the three reverse polarity diodes on the IGBT's on the 'top'. When you reverse the probes (positive of meter to DC bus Neg) and do the same operation, you are then measuring all 6 diodes on the bottom half. So you want to see healthy voltage drops typical of those rectifiers, such as above ~300mV or so. Anything below would indicate one of those diodes has failed shorted, and something is going to blow up either powering it up, or giving a run command (if it can't just fault).
Great Video. Thank you.
Excellent tutorial J !
that would be "transistor" not transmitter for IGBT, and thanks for the video
Lol oversight , but yup !
Place that I retired from had over 100 ABB 6 & 18 pulse drives. We had about 45 5 HP garbage ABB drives in a 5 story garage that over 25% burnt up first year. Told us they are throw always and have to purchase new ones. ABB tech support were prima donnas that always gave me a hard time when I only asked them 1 or 2 questions. A&B & Danfoss tech support were best in class.
Great video! Thank you for sharing.
Nice 👍 definitely needed to see this video thanks man
For checking , do i have to remove all the wire OR i can do with wires out
Thanks bro for the info and time share
Very welcome thank you for watching
Great video
I dont understant why your not using the diode feature of that meter to do the troubleshooting.
its the same thing
Thank you man quick question those three dc connectors at the bottom what are those connected to?
Why you choose negative frim drive to make check with l1 l2 l3 and u v w ?
If you look at the schematic, the diodes are forward biased (should act like a closed circuit) relative to the negative terminal. When placing the positive probe there you're generating a small voltage between the negative terminal and any of those l1 l2 l3 u v w terminals. If the diodes work correctly you should see a voltage drop (between 0.5-0.8V or 0.2-0.3V depends on the type of diode) or small current passing (which translates to some resistance if you're reading in ohm mode). When reversing the probes (positive probe on any of the l1 l2 l3 u v w terminals and negative probe on dc negative) you should read OL in resistance, as the diodes should block currently from flowing back.
Can this way of troubleshooting be done while the vfd is still installed in the machine with the main power off obviously?
Easy way is remove three out put wires that goes to motor and start the vfd. If vfd is giving out put voltage means vfd is ok if still vfd faulted out at ground or other fault then vfd is bad otherwise motor or cable that is connected to motor
Some drives won’t start if it doesn’t detect a load . I’ve tried this method
@@Josh-px6xb we have Allen Bradley drive like power flex 525 and 40 P starts if load is disconnected last time I have ground fault and i figured by disconnecting load
I thought when the neg probe is on DC- it should be infinity? Shouldnt you see numbers/measurements at first until it hits O/L?
Do you use positive to negative dc and positive dc to negative terminal
Red on DC Negative gives you numbers that should be the same
Black on dc negative you should read “OL” on all the AC terminals
i think hes using the how to test a diode technique to tell whether the diodes are bad or not because if they are bad they wont convert the ac to dc properly and i believe fry electronics. if i remember right the anode is the positive side and cathode is negative if you put your black on the negative end and red lead on the positive end electronics flow should be .6 voltes for a silicone diode. reverse the leads and you should see OL no voltage should flow if its working correctly. diodes only allow voltage to flow one way so when you see them flow both ways or not at all you know they are bad. he could probably open it up and desolder and solder the correct rated diodes but if your an amatuer and dont want to risk damaging expensive motors id take it somehwere to be done if its cheaper.
thanks bro
Im still confused on why you're testing between AC and DC. I understand the drive is converting the AC to DC, and then back to AC. But its done all internally. Aren't those DC terminals used for 24v for the drive? I guess i just don't understand the relationship between the AC and DC terminals.
The DC terminals are for the DC bus, not 24VDC IO power. Those would be on the IO terminals. This is the rectified DC bus shown on the center of the schematic that the VFD uses to invert to PWM AC.
👍👍👍
Negative or positive meter leads shouldn’t matter where you put on terminals if it’s selected on OHMS.
If you're measuring a diode, polarity does matter.
Thank you
Very welcome thank you for watching I appreciate it
Its not really AC but Pulsed DC that goes into the motor.
Pulse width modulation. Is a good concept to understand. PWM.
Yes, thanks
why negative is ol negative to negative
I can not hear your voice. Increased volume
The video is not bad but I literally don't understand everything..
A...B...C..?
Clark Patricia Hall Daniel Taylor Cynthia
Wilson George Thompson Sharon Moore Elizabeth
Can you speak up I can't couldn't hear.
Gosh darn iPhones sometimes they work other times they don’t I apologize