500 / 51X series meltdown need protection

So I have this 51x rack, actually more then one, however I am using retail API 500 units in it and when somehow Mr. Neve's Portico 517 shorts the rails to the 48v it seems to burn out and smoke the 48V part of the circuit.

Then to make matters worse it (the short) causes the other Portico to Smoke ....
And then the AMS NEVE 1073  starts smoking...

BTW , the 4  API 512s are fine.

Really disapointed in the lack of protection from this sort of thing!!!!

Who can help me put in a way of protecting the rails form cascading failures??  I would like to mod the powersupplies to avoid any more money lost. These are very expensive  modules melting. If something like this could be detected and fused It would have saved a lot of money and repair time.


Ideas?? Thanks


Chuck

I have noticed that in the new REV2 of the PSU design there are output fuses. Which would limit against current but since the voltage limits are 250V would this protect against what I am talking about here?

Are you saying the 48v rail was directly connected to the power rails (+/-16v, +/-24v) by one of your Porticos, causing the rail voltages on other equipment to go high (~48v) and fry components?

Output fuses would be good, but wouldn't stop this problem in all scenerios. If the -16v and 48v were shorted together, and the -16v fuse blew, the -16v rail would still become 48v.
To protect each power rail from overvoltage, zener diodes could be installed to shunt current for overvoltage situations.
For instance, the 24v rail could have a 27v zener diode, which only turns on if the rail voltage > 27v.
The zener diode current rating would have to exceed the fuse ratings. (To cause fuses to blow before allowing an overvoltage situation)

If I'm understanding the situation correctly.

Weird fault.....

Trying things out and Blowing some fuses as we speak, the crowbar seem to be an easy solution, some other protection would be nice as well.

http://www.groupdiy.com/index.php?topic=49831.0

Ah

Sorry I didn't see your thread. Didn't mean to duplicate this.
Maybe an admin can merge the two together as we are dealing with the same thing.

Yes I think a solution is a must here. Zeners sound like a good idea. In fact I thought I read somewhere that was a requirement on the input power rails of API compliance 500 series modules.

Zayance can you update with your findings?  And solution?


Chuck

Zayance can you update with your findings?  And solution?

Click to expand...

Yes i'll do.

Sorry to hear that Chuck.

250V rating of the fuse has no bearing on this.

My understanding is that the +48V rail has a fuse rating of max 125mA and in the case of a short it would blow instantly. So putting that fuse on the unregulated side and having a crowbar will not make it blow quicker.

To be frank this is the first time in my entire professional life I have seen +48 shorting with any of the other rails. How did this happen in a Portico?  I think you should first look into having protection on the modules. I'll try to simulate the fault on the bench this weekend and look into a suitable solution.

I wonder if I am wrong then? Maybe something else has gone wrong here....

What could make the PSU :

1) the +16 , -16 , 48V rails all go to approx. zero.
2) some  preamps with Phantom power circuits start smoking !
3) a smoking preamp in a known good rack by itself now has the 48V led always on. Meaning the 48V circuit must be fried.

Sounds like a short but any ideas or thoughts would always help.


Chuck

Chuck,

I am definitely not blaming but we must accept that this is really an unusual occurance.

However, I actually made a similar mistake but not in the 511 rack. I cut up an old version of the motherboard in individual strips and made some adaptors for testing  modules on the bench. I connected the module upside down to the edge connector by mistake but +48V blew immediately. So in a similar situation it should not make much of a difference. The +48 fuse will blow.

Otherwise I am thinking how and where on a complete module you can short the rails to eachother.

Since the +48V is pretty near the -16V, could be mechanical misfitting of the unit maybe??
Seems like Chuck's PSU didn't include any secondary fuse if i get it right, so......nothing would have blown in case of an error.
That should be first upgrade to your existing PSU.
And as Harpo corrected me, it's possible to use fast blow fuse on secondary, since it's after Rectifier/Loading caps, so that would
make an even better protection....

maybe a silly idea, have you checked the 7pin connector cable?

I had a marshall footswitch that did all funny stuff when the wires were twisted and shorted inside at the plug

dmp said:

Are you saying the 48v rail was directly connected to the power rails (+/-16v, +/-24v) by one of your Porticos, causing the rail voltages on other equipment to go high (~48v) and fry components?

Output fuses would be good, but wouldn't stop this problem in all scenerios. If the -16v and 48v were shorted together, and the -16v fuse blew, the -16v rail would still become 48v.
To protect each power rail from overvoltage, zener diodes could be installed to shunt current for overvoltage situations.
For instance, the 24v rail could have a 27v zener diode, which only turns on if the rail voltage > 27v.
The zener diode current rating would have to exceed the fuse ratings. (To cause fuses to blow before allowing an overvoltage situation)

If I'm understanding the situation correctly.

Click to expand...

good for the zeners , it is the a very good solution

the matter is that if the -16V or -24V rails are shorted with the 48V rail, is the +48V rail that became -16V or -24V because in the 500 or 51X racks the negative rails' current limit are bigger than the +48V current limit. When the +48V rail exceeds its current limit, its IC reg reduces its out voltage until negative voltage if there is a negative rail that can give this current.
If is shorted the +16V (or the +24V) rail with the +48V, is the +16V rail that assumes the +48V.

In any case the zeners plus fuses give a good protection if the fuses are so fast before that the zener diodes are destroied by current.

Chuck, do you have 18 pin card edge connectors in your rack? Is it possible that the 15 pin Portico modules were not perfectly lined up and multiple rails shorted out at once? I have heard of a similar occurrence and yes the fuse on the 48V rail blows instantly. If this is the case, the -16V rail will be shorted directly to ground and the +16V rail will short to the 48V rail. All kinds of not good things can and will happen.

How do you guys handle making sure the extra 3 pins don't connect on a 15-pin card?  Do you put something in the card slot over those 3 pins, like a piece of cardboard or soemthing?   

mulletchuck said:

How do you guys handle making sure the extra 3 pins don't connect on a 15-pin card?  Do you put something in the card slot over those 3 pins, like a piece of cardboard or soemthing? 

Click to expand...

Yes that's how you'd do, not with Carboard tough, but with piece of plastic, or piece of PCB but without any copper on it of course.

jsteiger said:

Chuck, do you have 18 pin card edge connectors in your rack? Is it possible that the 15 pin Portico modules were not perfectly lined up and multiple rails shorted out at once? I have heard of a similar occurrence and yes the fuse on the 48V rail blows instantly. If this is the case, the -16V rail will be shorted directly to ground and the +16V rail will short to the 48V rail. All kinds of not good things can and will happen.

Click to expand...

yes, the +48V rail forced the +16V rail to +48V infact its fuse (of the same +48V rail) blowed for this forcing.