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PWM signal causing problem for battery pack BMS
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C:
Think you testing has shown
as loads
voltmeter & amplifier board work ok

and
buck/boost module LED driver by it's self is a problem.

Now the buck/boost uses on/off switching to save power which can create high current/ no current load to your BMS.


--- Quote ---I have some 1000 and 2400 Mf electrolytic caps lying around.
--- End quote ---
Now no electronic part is simple, your two cap's have a internal series resistor and it's value is listed as ESR.
Rerouter suggested adding a 0.33 ohm series resistor to the cap. One thing this does is when the cap is discharged, change from 0 volts is less with that 0.33 ohm resistor.

Remember that nothing is simple, wire has resistance and has some inductance and could have some capacitance.
You place the parts to get the most advantage using what is there.
Your BMS will not like huge loads or huge current pulses
Your buck/boost needs huge currents pulses.

Placing the Cap closer to buck/boost is a small change to the better.
Shorter and larger conductor from cap to buck/boost is another easy change(lower resistance & inductance).
Smaller and longer conductor from cap to BMS is adding resistance to this connection(more resistance & inductance) .

Now think of what a capacitor is.  A simple two conductors separated by an insinuator..
An inductor is a coil of wire where you have the magnetic field of one coil effecting another.

Remember that resistors turn power into heat.
So to reduce and smooth the BMS load from the buck/boost some inductance & resistance is good.

Would be easy for you to make an air core inductor by just putting a coil in the wire connecting the BMS to buck/boost.

It is always good to do what is easy first.

C

Adhith:
The 1000mf electrolytic cap at the input side of the buck/boost module doesnt make any difference. What should I do??
Rerouter:
Ok, time for much more info.

What is the current limit for your BMS (max)
You say your leds draw 400mA, but what is the input current drawn from the bms.

What is your pwm frequency, and are you able to change this?

Does the same issue occur at 100% brightness

What bms exactly. And which pwm controller?
Adhith:

--- Quote from: Rerouter on June 02, 2018, 01:10:04 pm ---Ok, time for much more info.

What is the current limit for your BMS (max)
You say your leds draw 400mA, but what is the input current drawn from the bms.

What is your pwm frequency, and are you able to change this?

Does the same issue occur at 100% brightness

What bms exactly. And which pwm controller?

--- End quote ---
Thank you again for your reply.
The current limit of the BMS is 30A.
Like I mentioned before 400mA was a round estimate and the actual current draw is around 250mA. Yes it occurs for 100% brightness as well. connected an amplifier as the load to the buck/boost module and the same problem occurs.
In the specification, the PWM frequency of the buck/boost module is given as 400kHz. It is fixed and cant be changed.
The BMS is a 4S li ion BMS with balance charging function. I have attached a pic of it.
I didnt get what you meant by which PWM controller. It is buck/boost module based on XL6009. Rectification is of Non- Synchronous Rectification.
This is the link to the product specification
https://www.banggood.com/DC-DC-Boost-Buck-Adjustable-Step-Up-Step-Down-Automatic-Converter-XL6009-Module-p-1087346.html?rmmds=myorder&cur_warehouse=USA

So what would be a possible solution for my problem??

Adhith:
Thankyou very much for your reply. So I have made a quick sample circuit digram for it. Could you please check that its correct or not.
Right now I have only attached a 1000mf capacitor at the buck/boost module input side and it doesn't work, the BMS still turns off after a while.
Since placing the cap didn't solved the problem then should I try this circuit or not??
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