Hi,

I'm currently trying to troubleshoot an issue I'm experiencing with custom design. The problem only exist when I connect the device to a battery (24V 100aH LiFePO4 custom battery - it has a BMS). I tested both blown boards with a 24DC supply before connecting the battery and no issues occured.

Once I flip the switch on the battery, a part on this DCDC converter illuminates:
https://www.cui.com/product/dc-dc-converters/non-isolated/pxo78-500-m-series

 

More details please.
The schematic of the custom power supply would probably be most helpful at this point

 

More details please.
The schematic of the custom power supply would probably be most helpful at this point

The DCDC converter isn't a custom design and link to the part is in the orignal post.If you were referring to the battery, I unfortunately don't have much infomation other than it uses a BMS from this manufacture:
https://xiaoxiangbms.com/product/6s-21s-smart-bms-100a-200a/

 

Are you sure the battery polarity was correct when connecting the supply?

Did you measure the battery voltage?

 

Are you sure the battery polarity was correct when connecting the supply?

Did you measure the battery voltage?

Unfortunately, I didn't make the rookie mistake (even though the symptoms are very similar to what you would expect in a reverse voltage situation).

and yes, battery voltage is at the expected value of 26.67V.

I just wonder if the BMS is allowing a voltage spike or worst a reverse voltage spike when switched on (I'm not risking destroying a scope with this battery - so fishing for anecdotal experience here because I'm not finding good info on the world wide web). The battery is found here: https://www.facebook.com/ProfSylvester/. I'm in the process of talking with the customer about getting another LiFePO4 battery that is readily available. I've used these types of batteries with systems I've designed in the past and I've never have had this issue.

 

Hi,

I'm currently trying to troubleshoot an issue I'm experiencing with custom design. The problem only exist when I connect the device to a battery (24V 100aH LiFePO4 custom battery - it has a BMS). I tested both blown boards with a 24DC supply before connecting the battery and no issues occured.

Once I flip the switch on the battery, a part on this DCDC converter illuminates:
https://www.cui.com/product/dc-dc-converters/non-isolated/pxo78-500-m-series

Just a WAG
Are you using the recommended external capacitors when connected to the battery? I've seen these modules go into self-destructive mode without them while on low source impedance batteries.

From the datasheet.
The required C1 and C2 capacitors must be connected as close as possible to the terminals of the module.
2. Refer to Table 1 for C1 and C2 capacitor values. For certain applications, increased values and/or tantalum or low ESR electrolytic capacitors may also be used instead.

 

Incorrect wiring is still the most likely cause. I suspect a current limit on the power supply saved him. No such luck with the battery.

 

Incorrect wiring is still the most likely cause. I suspect a current limit on the power supply saved him. No such luck with the battery.

First time high probability, second time lower probability and the OP says the power input indicator is lit when connected to the battery. That normally indicates a correct voltage polarity input connection.

 

First time high probability, second time lower probability and the OP says the power input indicator is lit when connected to the battery. That normally indicates a correct voltage polarity input connection.

I am thinking the PCB is incorrect. Not the battery connection.

 

I am thinking the PCB is incorrect. Not the battery connection.

"I tested both blown boards with a 24DC supply before connecting the battery and no issues occured"

I hope the OP can find some sort of solution.

 

I am thinking the PCB is incorrect. Not the battery connection.

I'm confident that design is acceptable for the application. I have quite a bit of experience with all the circuits involved including powering my designs with LiFePO4 batteries. Like I mentioned before, the system works for the most part with the meanwell like power supply ( for instance, I have a 3.3V rail on the board that has ADCs and a MCU/Wifi Radio combo and they work and are quite stable).

I am unfamiliar with the battery (which I'm not a fan of because it seems like it was made in someone's garage) and the DCDC converters that I listed earlier. So I have ordered another battery and some other DCDC converters to test. I will agree with you on the fact the current limiter on the power supply helped me out which leads me to believe the custom battery's BMS current limiting function isn't working as it should.

nsaspook, I'm using the reccomended values for the capacitors but I was considering trying some alum caps with larger values. I might do that after testing the new battery and DCDC converters. The capacitors are located very near the terminals:

 

At least initially, you might add a small resistance resistor in series with the battery to limit its maximum surge current.

An incandescent lamp of an appropriate voltage and power rating can also work for that, since it's cold resistance is about 1/10th of its hot resistance.
It has the advantage of giving a visual indication of a high current.

 

My very first questions are: What is the specified input voltage of the DC to DC devices being damaged? And the second question is what is the actual voltage being provided to the DC/DC module.
And a third question: what is the load connected to the output of the DC/DC module? And what is the intended load?