Can anyone see anything wrong with this wiring schematic?

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Good Afternoon,

I am building this battery pack with 64 aa cells (QU1500 AA) It is split in a series parallel configuration. Each series string has a Diode and a fuse. When I perform the diode test (add the OVC 50.4V plus 0.5V to the circuit) the fuse keeps blowing? I have looked at this for a couple weeks now off and on and I cant seem to pin point the problem.
Any help in solving this mystery would be greatly appreciated.

-Thank you
 

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  • #2
berkeman
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Welcome to the PF. :smile:
When I perform the diode test (add the OVC 50.4V plus 0.5V to the circuit) the fuse keeps blowing?
What does that sentence mean? What is a diode test in this context? What is the load that is blowing the fuse(s)?
 
  • #3
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The test is to check the diode will not leak any voltage or current. The Diode is a blocker of current and voltage in one direction. Looking at the schematic, I would attach the power supply (50.4 Volts + 0.5 Volts) to pins 1 and 5 then check the voltage across pins 3 and 5. I should not get any voltage reading at all if the diode is working properly. Its to verify that the voltage amplitude is less than negative 0.2 Volts. (Example 0 Volts is Pass; -0.3 Volts is Fail) In this case the fuse just keeps failing.
 
  • #4
berkeman
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What Schottky diode are you using? Can you link to the datasheet?
I would attach the power supply (50.4 Volts + 0.5 Volts) to pins 1 and 5 then check the voltage across pins 3 and 5. I should not get any voltage reading at all if the diode is working properly.
Between pins 3 and 5 you get the sum of the battery voltages, no?
 
  • #5
berkeman
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  • #6
berkeman
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I would attach the power supply (50.4 Volts + 0.5 Volts) to pins 1 and 5
Are you sure you are connecting the + of the power supply to pin 1? Any change you are connecting it backwards?
 
  • #7
Averagesupernova
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Sounds to me like you don't have something hooked up the way you think you do. If you are hooking the negative of your power supply to pin one with positive to pin 5 I would expect the fuse to blow. You don't mention the size of the fuse or the configuration of the power supply.
 
  • #8
berkeman
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You don't mention the size of the fuse
I found that in another hand-written note on the schematic -- looks to be 375mA

upload_2018-8-28_10-30-45.png
 

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  • #9
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What Schottky diode are you using? Can you link to the datasheet?

Between pins 3 and 5 you get the sum of the battery voltages, no?
Im sorry, i meant i would hook up the DVM to pins 3 and 5 to get the voltage reading. It should be 0 if the diode is working properly.
 
  • #10
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Sounds to me like you don't have something hooked up the way you think you do. If you are hooking the negative of your power supply to pin one with positive to pin 5 I would expect the fuse to blow. You don't mention the size of the fuse or the configuration of the power supply.
I am attaching the positive to pin 1 and the negative to pin 5. I have the P/N of the fuse and the diode hand written at the top of the schematic.
 
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  • #11
berkeman
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Im sorry, i meant i would hook up the DVM to pins 3 and 5 to get the voltage reading. It should be 0 if the diode is working properly.
Why wouldn't you read the sum of the battery voltages between pins 3 and 5?
 
  • #12
Averagesupernova
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I am attaching the positive to pin 1 and the negative to pin 2. I have the P/N of the fuse and the diode hand written at the top of the schematic.
You said pin 1 and 5 in a previous post. Which is it?
 
  • #13
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  • #14
berkeman
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So if you are putting 50.9V reverse bias across the Schottkly diode plus the battery string, you will measure 50.9V on the power supply side of the diode (cathode) and 48V on the battery side (anode). Why do you think you will measure 0V somewhere?
 
  • #15
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Why wouldn't you read the sum of the battery voltages between pins 3 and 5?
The voltage amplitude should be 0 Volts. When I increase the voltage of the power supply to 0.5 Volts (across pins 1 and 5) above the battery pack voltage, I would check the voltage across pins 3 and 5. The voltage amplitude should be 0 Volts. The amplitude should be less than negative 0.2 Volts.
 
  • #16
berkeman
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The voltage amplitude should be 0 Volts. When I increase the voltage of the power supply to 0.5 Volts (across pins 1 and 5) above the battery pack voltage, I would check the voltage across pins 3 and 5. The voltage amplitude should be 0 Volts. The amplitude should be less than negative 0.2 Volts.
Sorry, this still makes no sense to me. Pin 3 is the + end of the 48V battery string, and pin 5 is the - end. Why won't you measure 48V between pins 3 and 5?

Edit -- fixed pin numbers
 
  • #17
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Sorry, this still makes no sense to me. Pin 3 is the + end of the 48V battery string, and pin 5 is the - end. Why won't you measure 48V between pins 3 and 5?

Edit -- fixed pin numbers
Pins 3 and 5, should read 50.4 Volts If the diode is working properly? When I perform this test, I seem to not get a reading at all? Then i check the continuity of the fuse and it has failed me now 3 times. Not sure what I am doing wrong.
 
  • #18
berkeman
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Pins 3 and 5, should read 50.4 Volts If the diode is working properly? When I perform this test, I seem to not get a reading at all? Then i check the continuity of the fuse and it has failed me now 3 times. Not sure what I am doing wrong.
It looks like the voltage between pins 3 and 5 should be the battery voltage, unless the diode is bad.

Are you sure you aren't using current mode on your DVM? With such a small value fuse, if you are trying to measure current instead of voltage, your DVM will short out the circuit and blow the 375mA fuse.
 
  • #19
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Seems like an odd way to test the diode when you have direct access to test it via pins 1&3.

Testing it the way you are runs the risk of popping the fuse if the voltage you apply is not high enough to reverse bias the diode, ie the fuse could be blowing because the battery pack is trying to supply current to the power supply.

If you must test it the way you are, I would apply a voltage that is statistically never expected to be reached by the battery packs(s), but from a test perspective will give you a bit of variability in the diode reverse voltage result.

Were I doing the ICT for this I'd look at pin 3 to 5 to check battery pack voltage, for full test coverage you would also put in test access for the fuse to check its resistance. Then diode test between pin 3 and 1, a Vf test under some nominal forward current, and a reverse leakage test.
 

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