1336 drive dc bus failure

IPSI John

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Join Date
Jun 2007
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Alabama
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I've got an AB 1336 AC drive that failed and had no DC bus voltage.

The DC bus fuse was fine. The incoming AC power was fine and the AC fuses were fine on the rectifier firing board.

We bench tested the SCR bridge for the rectifier each SCR in the device conducted when the gates were fired, and they all meggered fine.

We partially charged the capacitor bank with a crank megger, and they held a charge and seemed to discharge at a reasonable rate.

We replaced the rectifier firing board and the main control board, and we still have nothing. Could there be another condition that would keep the recifier from chargin the DC bus? Thanks.
 
Refresh my memory.... I thought the "rectifier" semi-conductors worked on their own and the "firing board" was for the output section.

I'll admit it's been quite a while since I worked on a 1336.

You didn't mention the choke, I trust IT checks okay?

Do you have a link to the schematic?

Stationmaster
 
Okay, I downloaded the manual at

www.rockwell.sjtu.******/web/manual/1336-6.1.pdf -

Page S-2 clearly shows that the rectifier diodes have no "firing" or "gating" going on. The MOVs are just surge protection. There are no connections from the rectifiers to ANY of the ckt boards.

So from your description, it sounds like you tested the OUTPUT semi-conductors instead of the INPUT Semi-conductors. It is good to know they are good, but they don't produce the DC voltage. There is a step-by-step, meter lead by meter lead instruction set on how to test BOTH in the manual.

Even still, one open rectifier module will not eliminate ALL DC voltage on the buss. All THREE would have to be open for that.

The CHOKE however would theoretically cause zero DC voltage on the buss if it were open. (I say "theoretically" because I've never had that happen.)

Stationmaster
 
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I've got an AB 1336 AC drive that failed and had no DC bus voltage.

The DC bus fuse was fine. The incoming AC power was fine and the AC fuses were fine on the rectifier firing board.

We bench tested the SCR bridge for the rectifier each SCR in the device conducted when the gates were fired, and they all meggered fine.

We partially charged the capacitor bank with a crank megger, and they held a charge and seemed to discharge at a reasonable rate.

We replaced the rectifier firing board and the main control board, and we still have nothing. Could there be another condition that would keep the recifier from chargin the DC bus? Thanks.

You did the meggering in accordance with factory manual??
Reason I ask is from way back when
- never megger solid state components -
the only VFD manual I have seen so far which gives you directions on how to megger it is Hitachi. Even there they require you to disconnect or short out a lot of stuff.

Dan Bentler
 
I've got an AB 1336 AC drive that failed and had no DC bus voltage.

The DC bus fuse was fine. The incoming AC power was fine and the AC fuses were fine on the rectifier firing board.

Most VFD's have a resistor to charge the cap bank before the line contactor "kicks" in. This would be the click you hear when the VFD is connected to the line. If the full wave bridge that charges the cap bank were to be connected straight across the line it would appear to be a dead short. So most manufacturers use a resistor to start the charging process slowly. Look for a resistor that would connect the full wave bridge to the line. my guess that it is open. The service factor on these resistors is not very high. If a VFD is "jogged" at the line terminals it will fail.

We bench tested the SCR bridge for the rectifier each SCR in the device conducted when the gates were fired, and they all meggered fine.

We partially charged the capacitor bank with a crank megger, and they held a charge and seemed to discharge at a reasonable rate.

I agree with leitmotif a meggar anywhere near the electronics could be fatal.
 
1336 plus

Sorry about the confusion. It is a 1336 plus with an active, SCR controlled rectifier. Part number 1336S-BX040-AA-EN-GM1.

An SCR in a rectifier circuit is a solid-state device, but it is rated to withstand in excess of 700V differential. Meggering it on the bench is the only way to verify minimal leakage, and 500V is less than the voltage differential it sees in use. Testing resistance in the unfired state with merely an analog meter, or worse a digital meter does not give you the full picture of the health of a high-power solid-state device.

But, debating how to thoroughly bench test a power solid-state device is off subject.

In all seriousness, does anyone have any ideas regarding the lack of DC bus voltage? The active rectifier bench tests fine, there are no blown fuses, the capacitor bank holds a charge, the active rectifier firing board has been replaced, and the main control board has been replaced? I'm going to take a close look at the DC choke when I get back to it.

Thanks.
 
On page 2-11 of "Bulletin 1336 PLUS Adjustable Frequency AC Drive Troubleshooting Guide and Renewal Parts", "Publication 1336 PLUS-6.2 October 1995" it lists a troubleshooting flow chart for "No Display". Following through the flow chart, we get to no backlight, no fan running, yes voltage TB1-R, -S, -T, no fuse blown on power driver board, and finally no DC bus voltage present. The solution is to "replace damaged components", which I am attempting to do.

The "1336 PLUS Adjustable Frequency AC Drive User Manual" only has parameter descriptions, wiring instructions, etc., without much in the way of troubleshooting.

If the active front-end rectifier bench test fine, no fuses are blown, the capacitor bank will hold a charge, the active front-end rectifier firing board has been replaced, and the main control board has been replaced, what else can be looked at?

As soon as I get back I will look at the choke on the DC circuit.

Also, I'll start a separate thread on bench testing power solid-state devices, so we stop getting off subject here and stop muddying the water.
 
Thanks for finally getting me to the correct print.

"In all seriousness", check the choke.

As is obvious on your print, it's the only device (other than the well-checked DC buss fuse) that can completely open the DC buss.

The only other possibility seems to be a complete failure-to-fire of the active rectifier (unlikely given the bench test and firing board replacement). You could put a scope on the SCR leads to make sure they are actually firing.

Let us know what you find.

Stationmaster
 
Thanks for the pointer on the choke. The choke coil secondary read fine (~7 ohms), and was attached to the gate drive board. Upon closer inspection of the gate driver board, two resistors had broken loose at one end of them. There did not appear to be any thermal damage, so they may have just vibrated loose (the drive has been running in place for 11 years). We'll attempt to solder the resistors (they're large, maybe 0.25 watt) on Monday and see how it looks. I'll post complete final findings once we know. Thanks again for the pointer on the choke.
 
That sounds quite promising. The gate driver board has MANY connections to the precharge board and could easily cause a problem with the active rectifier.

Your description of testing the choke (L1) leads me to point out that according to the print there IS NO primary or secondary configuration of the windings, per se. There are 2 windings, one for DC+ and one for DC-. If EITHER of them were open you would not get your DC buss voltage at the terminal strip.

Again, that is IF I'm on the correct print.

1336s.jpg
 
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I was looking at a CT on the DC bus and it's secondary. We reattached the resistors, but they heated up again and came loose under load. But, we had DC bus power in the mean time. That being said, we've ordered another Inverter Gate Driver Board that will be here in 2 weeks. I assume it will be fine then, but I will update one way or the other.

I ended up focusing on the measurable problem (no DC bus voltage), and troubleshooting from there. If I had visually inspected everything, I would have cought the resistors on the Inverter Gate Driver Board earlier. That being said, I wasn't looking at the back end of the drive (inverter), since my problem was the active front end (rectifier) wasn't rectifying. It goes to show that taking a step back and inspecting everything can pay off. Thanks again for your input on it.
 
Way to go, Stationmaster. That was a good call. We will have to call you DickDV II.

Thank you Lancie, but it sounds like IPSI John rooted out the problem mostly on his own. I'm still not sure whether he ever checked the actual DC bus choke, but now it doesn't matter. I would wonder what those resistors are powering, since they heated up when reconnected. The fact that he has DC bus voltage (I guess all the way to the terminal block) when they are connected verifies the integrity of the choke. I've never seen one go bad anyway, I was just looking on the print for a component that could open the bus.

I don't have much experience with "active rectifiers" but the concept is clear.

Most recently, I'm pondering IPSI John's report of a Control Transformer on the DC bus..... Those DC transformers are SSSOOOooo cantankerous.

Dick DV has nothing to worry about from me, but I DO wonder why he didn't chime in. I was just tossing out ideas until HE could swoop in and set everybody straight.

: )

Stationmaster
 
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The reason I didn't "swoop" in was because I was trying to learn something. I am an applications and commissioning guy, not a drive repairman. And, for sure, not an expert on the internals of a 1336.

As to the DickDV I and II thing, I'm just here to answer questions when I can. I never set out to be on top of any pile and, if anyone else wants that spot, they can have it.

On the other hand, if all of us are committed to being helpful and responsible, we stand to make this BBS a mighty fine place.

I'd like that if it can happen.
 
IT was all in fun DDV I

The reason I didn't "swoop" in was because I was trying to learn something.

You DO know I meant that in a GOOD way right? Like the caped crusader to the rescue. You may not realize it, but a LOT of VFD threads just kind of flail about until YOU get to the forum and surgically pen the 'answer'. It has become normal for me to think to myself 'where is DickDV?' when a tough drive problem is posed. Apparently for Lancie1, too; and I'm sure he and I are not alone.


As to the DickDV I and II thing, I'm just here to answer questions when I can. I never set out to be on top of any pile and, if anyone else wants that spot, they can have it.

It is exactly THAT humble attitude that allows us to elevate you to 'caped crusader' status.

On the other hand, if all of us are committed to being helpful and responsible, we stand to make this BBS a mighty fine place.

I'd like that if it can happen.

I'll try.

Stationmaster
 

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