I've measure some of the bad chips. I haven't found an open or short yet. I must reiterate that when I get the board back to the bench it works fine. I think this is being overlooked. What type of failure is it when is fails 50% of the time in the machine then passes 100% of the times when its removed and tested on the bench?Got an ohmmeter? Next time, every time a unit blows make these measurements:
With the ohmmeter in normal (low voltage) mode, read each pin to Vdd, then repeat each pin to Vss. All should read open.
With the ohmmeter is diode mode (higher voltage) read each pin + to Vdd -, then again pin - to Vss +. In every case you should read a diode.
If a pin fails the first group of tests you have a shorted pin.
If a pin fails the second group of tests you have an open pin.
It was one of the first things that crossed my mind and everyone elses mind here. I soldered a cap to the back of the board, a ceramic 1uF. The board still failed.And fer chissake, just add the friggin bypass caps already.
J3 goes straight through to J2 on the next board/battery with a cable. There it is isolated by optocouplers. The top pin on J2 goes to the top pin on J3. The second to the top pin on j2 goes to the second to the top pin on J3 ... etc. I've put a hipot tester to J2 and connector J1 and J3 on the board. It never breaks down.Where does J3 go? It seems to be the only place that is not isolated by an opto.
Its a huge board. Its not necessarily the point of failure, either. The last problem I had was on a board almost right in the middle of the string. It was board number 12 of 20. There was one of the boards I've shown on the right and left of it. Each board was connected to another battery. I don't think the external board can cause a problem, because it wasn't connected. The board I've shown fails when connect to the other boards that follow the same layout, schematic, BOM.how about showing what the external circuit looks like?
Obviously the bench is not a proper simulation of the system.What type of failure is it when is fails 50% of the time in the machine then passes 100% of the times when its removed and tested on the bench?
I guess not. Some differences are the input into J2 shares a ground with the board/battery, which would not be true in the machine, but those are fed into optocouplers, so it shouldn't matter. The 12V supply has more impedance behind it, since it isn't a car battery. The big difference that comes to mind is that in the system the board can be hundreds of volts below earth ground. This is the most obvious difference, but I cannot think of why it would cause this failure.Obviously the bench is not a proper simulation of the system.
Yes.Do units that fail in the machine then pass on the bench?
I'm interested in this phenomena. The two articles I have read have given conflicting causes of latchup. What could cause latch-up in your opinion?Sure sounds like latch up.
The grounds and vcc have been confirmed on the layout and I got a board and toned it out. The ICs are connected to the battery terminals.The only other thing I can think of is maybe the inverter doesn't have ground or 15 volts to the ground or Vcc pin. Sometimes it's possible to run thru a substrate diode form an input.
The signals go through maybe a dozen other boards then to the monitoring board.Since everything is isolated by an opto the battery shouldn't make a difference. How does the signal finally get of the boards to where you can see a failure?
It's false economy to omit bypass caps in a circuit like this.It is good house keeping to include bypass capacitors, but you need understand why they are unnecessary here.
1. The ripple on the supply is 10mV from the charger
2. The battery is a 40F capacitor with only .005ohms source impedance and is the source
3. the logic transition @5Hz
there is little reason to put capacitors where there is no AC and the source is already so stiff(a car battery).
If I put a cap on the board I'd have 40F(battery) + .00001F(electrolytic) = why even bother?
You need a bypass capacitor. You see your ICs are failing right?It is good house keeping to include bypass capacitors, but you need understand why they are unnecessary here.
1. The ripple on the supply is 10mV from the charger
2. The battery is a 40F capacitor with only .005ohms source impedance and is the source
3. the logic transition @5Hz
there is little reason to put capacitors where there is no AC and the source is already so stiff(a car battery).
If I put a cap on the board I'd have 40F(battery) + .00001F(electrolytic) = why even bother?
So you put 0.1uF ceramic bypass capacitors from every IC power pin directly to ground with as short a lead as possible?I put a bypass cap on the ICS it did nothing.
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I have experienced problems with opto-couplers in the past when I wrongly assumed that they truly isolated things perfectly.I put a bypass cap on the ICS it did nothing.
I am not confused by capacitors and batteries.
I have made a board that monitors a battery in a battery stack that is connected to an inverter through a circuit breaker.
I'll reiterate I put in a bypass capacitor. It did nothing. Somehow when the circuit breaker between the batteries and the inverter is closed the noise comes out of the optocopler.
The board members s completely isolated through optocouplers and transformers from the batteries and the inverter. No radiated noise is present to n the supply or anywhere else.
I put in bypass capacitors
It did nothing.
by Aaron Carman
by Aaron Carman
by Jake Hertz