AB Impact 1336 no DC bus reading/blown fuse

[cor2man]

I have a 150HP AB Impact 1336 drive that has started giving me faults for DC bus precharge timeout. After looking through the boards I found a flown F3 fuse (in picture)

Drive can be powered up and all voltages on the gate drive board tests good. Everything works on drive but there is a enable inhibit because of the DC bus precharge timout.

When measured the DC bus measures the proper +-700VDC

If I monitor the DC bus from the drives interface it claims that the BUS voltage is zero.

I am assuming that the fuse that blew (as drive was powered up) is connecting to a circuit that is directly being used to measure my DC bus. I cannot understand how this is working and so far have not found any issues with any components in line with this circuit. It appears to input the DC bus voltage and run it through a series of resistors and an op-amp which then switch the voltage out via a switcher.

Any information or help on this drive would be appreciated, I have attached pictures of the gate drive board and a closup of the circuit and fuse giving me problems. Any information about how a 1336 this size senses DC bus voltage would be much appreciated

 

[petersonra]

I think your best bet is to talk with AB tech support.

In any case, these are relatively ancient drives and may not have a whole lot of life left in them.

 

[cor2man]

I'm afraid AB tech support is requiring a paid subscription to get help on this drive, Honestly I'm just trying to understand the overall DC sensing circuit better so I can narrow down the cause of my problem...

 

[Jraef]

Not sure what you are after here though. Are you wanting an explanation of how a pre-charge circuit works? Basically when you first power up a converter that goes to a filtered bus, such as a VFD, the cap charging current rises so fast that it looks like a short circuit to things like fuses and circuit breakers, plus it can stress the capacitors themselves. So a pre-charge circuit is engaged whenever the drive is powered down such that on the next power-up, the rectified DC voltage goes through a set of current limiting resistors at first, then when the bus is charged, a contactor or relay shorts across the resistors, removing them from the circuit. From what I know of the old 1336 design at the frame size that would have had that, there is a fuse feeding the pre-charge circuit components, which protects against collateral damage should one of the resistors fail. Is the DC bus measurement taken from behind that fuse? Probably, that would make sense because that would be HOW the system decides when to short out the resistors and could be included in that "collateral damage".

So did you replace the fuse and it immediately blows again? If so, that's usually the result of a failed resistor or maybe a board trace for one somewhere. I don't have a circuit diagram for those any more, but I have encountered that in the past. It will be difficult to find if there is no obvious discoloration because I believe there are multiple resistors in parallel, so you have to know what the correct value was supposed to be in order to detect that it is different. By the way, on a 150HP drive, the resistors on the board are NOT the pre-charge resistors, those would be probably two large resistors on the chassis.

They stopped making those drives in 1999, they are at their end of life now and component parts are no longer made, that's why A-B stopped supporting them. If you were unaware, there is a program available by which you can get partial credit towards a new PowerFlex 750 series drive, might be time to think about making the change.