PWM signal causing problem for battery pack BMS  - Page 1
Forum section: electronics / beginners

author: Adhith
author_rank: Frequent Contributor
timestamp: May 29, 2018, 02:58:33 pm
content: hello friends...I have a battery pack arranged in 4S1p configuration. It is connected to a BMS as well. The output from the BMS is connected to an amplifier board and a LED driver. While using the battery pack to power the amp, everything works fine and I have no trouble. But, when I power the LED driver (with amp turned off)which drives a few led strips, it works for around 5 minutes or so and then suddenly turns off. The small digital voltmeter attached to the output terminals of the BMS also goes dead. After waiting for around 10 mins, the BMS is back to normal and could be used to power the LED driver till the problem is repeated afte the next 5 min. So what would be the reason for this?? I'm very sure that The led strip wont consume a current more than 400mA ,so i think there won't be an over load issues for the BMS.

author: jeduffy
author_rank: Contributor
timestamp: May 29, 2018, 11:22:47 pm
content: Does anything get hot? Something that slow sounds like it's likely to be overheating. Any details on the BMS, LEDs, amplifier, LED driver?

author: Adhith
author_rank: Frequent Contributor
timestamp: May 30, 2018, 12:38:19 pm
content: Quote from: jeduffy on May 29, 2018, 11:22:47 pmNo, nothing gets hot. The BMS, the battery pack and the driver stays cool. Another thing is that, the driver and LEDs work perfectly when powered by a 12v wall adapter. So the problem is definitely with the BMS i guess.The BMS is the one with added balancing option. I have attached a pic of it. The LED driver is a 12V WiFi controlled driver which lights up the 12v LED strip. The led driver is in fact powered by a buck boost module (set at 12V) which is connected to the output pads of the BMS.

author: Adhith
author_rank: Frequent Contributor
timestamp: June 01, 2018, 07:06:04 pm
content: Should I try replacing the BMS??

author: C
author_rank: Super Contributor
timestamp: June 01, 2018, 07:22:57 pm
content: Some of the USB battery packs will turn off on to small a load.The idea is that such a small load is a leak that is just draining the batteries.Need to remember that electronics can be fast and could be shutting off on no current if your leds are PWM driven.A smoothing cap might help here.You check the difference in current for the loadsAdding a large capacitor will present a more constant load to BMSAdding a resistor load would work around the too small current load.C

author: Adhith
author_rank: Frequent Contributor
timestamp: June 02, 2018, 06:55:57 am
content: Quote from: C on June 01, 2018, 07:22:57 pmThank you for kind reply. I just fed the BMS output pads to the voltmeter terminal to simulate a small load. But the BMS doesnt turn off after a while. So this means that the BMS dont turns of by itself on smaller loads right??So you are saying the Buck/boost module which is used to power the LED driver is creating the problem right?? So about smoothing caps..what value would you suggest??. I have some 1000 and 2400 Mf electrolytic caps lying around.So smoothing caps is connected parallel to the output pads (P+, P-) of the BMS right??

author: Adhith
author_rank: Frequent Contributor
timestamp: June 02, 2018, 10:33:49 am
content: I figured out the problem. The buck/boost module is causing the trouble. I powered the amplifier module with and without the the Buck/boost module from the BMS and found out that by using the buck/boost module the BMS turns off after a while.

author: Rerouter
author_rank: Super Contributor
timestamp: June 02, 2018, 10:34:48 am
content: Yes, something like 0.33 ohm series resistor and a 1000uf cap parrellel to you led drivers inputs should be ok

author: Adhith
author_rank: Frequent Contributor
timestamp: June 02, 2018, 11:06:26 am
content: Quote from: Rerouter on June 02, 2018, 10:34:48 amThank you for your reply. So please correct me if I'm wrong. Do I need a series resistor?? The BMS wont shut down for low current draw(since it wont shut down even when driving a voltmeter). So There no need for the load resistor right?? just the 1000mf caps will do the work right??Since the LED driver is powered by the buck/boost module, I should place the caps at this module's input right??

author: Rerouter
author_rank: Super Contributor
timestamp: June 02, 2018, 11:41:56 am
content: The series resistor was just an old habit of mine, to make the supply regulator not suffer if it cannot handle a low ESR cap on its output.

author: C
author_rank: Super Contributor
timestamp: June 02, 2018, 12:54:43 pm
content: Think you testing has shownas loadsvoltmeter & amplifier board work okandbuck/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.QuoteNow 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 pulsesYour 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

author: Adhith
author_rank: Frequent Contributor
timestamp: June 02, 2018, 12:55:49 pm
content: The 1000mf electrolytic cap at the input side of the buck/boost moduledoesnt make any difference. What should I do??

author: Rerouter
author_rank: Super Contributor
timestamp: June 02, 2018, 01:10:04 pm
content: 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% brightnessWhat bms exactly. And which pwm controller?

author: Adhith
author_rank: Frequent Contributor
timestamp: June 02, 2018, 01:40:46 pm
content: Quote from: Rerouter on June 02, 2018, 01:10:04 pmThank 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 specificationhttps://www.banggood.com/DC-DC-Boost-Buck-Adjustable-Step-Up-Step-Down-Automatic-Converter-XL6009-Module-p-1087346.html?rmmds=myorder&cur_warehouse=USASo what would be a possible solution for my problem??

author: Adhith
author_rank: Frequent Contributor
timestamp: June 02, 2018, 01:50:02 pm
content: 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??

author: Rerouter
author_rank: Super Contributor
timestamp: June 02, 2018, 10:55:13 pm
content: Read throught it better now, seems that dc/dc module should be free from the blame and we should be atfacking the led driver. Can you move your attached circuit to infront of the led driver

author: Adhith
author_rank: Frequent Contributor
timestamp: June 03, 2018, 05:52:29 am
content: Quote from: Rerouter on June 02, 2018, 10:55:13 pmSorry about the mistake. you meant Like this??

author: Rerouter
author_rank: Super Contributor
timestamp: June 03, 2018, 06:22:41 am
content: yep

author: Adhith
author_rank: Frequent Contributor
timestamp: June 03, 2018, 12:53:06 pm
content: Quote from: Rerouter on June 03, 2018, 06:22:41 amOK thank you Sir. let me try it out and I'll let you know.

author: Adhith
author_rank: Frequent Contributor
timestamp: June 03, 2018, 01:48:37 pm
content: No Sir. It doesn't work either. The BMS still turns off after a while. What to do??

author: C
author_rank: Super Contributor
timestamp: June 03, 2018, 04:36:19 pm
content: How about doing a simple load test of the BMS to see if it shuts off.First understand how to create this load.When you change the load on your buck/boost module, you are changing the load on your BMS.If you connect a resistor to the output of buck/boost module, when you change the voltage across that resistor you change the load.You can start with a small load, a small voltage across the resistor by adjusting output of buck/boost module.Run a test to see if BMS turns off.Increase the load by adjusting buck/boost module voltage higher.Run a test to see if BMS turns off.You should not go past the limits of the buck/boost module or the watts limit of the resistor.Just the resistor connected to output of buck/boost module.This is a test of BMS to buck/boost module with a nice load on the buck/boost module.This will identify if the buck/boost module is the problem or the led driver connected to buck/boost module.C

author: Adhith
author_rank: Frequent Contributor
timestamp: June 03, 2018, 06:26:09 pm
content: Quote from: C on June 03, 2018, 04:36:19 pmPreviously I have connected the led driver and an amplifier board to the output of the buck/boost module and for both the cases the BMS shuts down. Connected a voltmeter at the output and it also makes the BMS to shut down after a while. So I believe that this strengthens the fact than the buck boost module is the problem right?? Also the BMS has no problem in powering the amplifier board directly without the buck/boost module and thus there is no problem with the BMS either. So this proves the thing right?? anyhow I'll do the resistor test to confirm this.

author: Adhith
author_rank: Frequent Contributor
timestamp: June 04, 2018, 06:17:37 am
content: Yes, the resistor test confirms it. The buck boost module is the problem. But now the much bigger problem is that i think the BMS has permanently damaged after repeatedly doing these load test. Now it cant no longer power a load even when directly connected since it turns off as soon as it is powered. Ordered a new BMS now. So is there a way to solve my problem?? any help would be appreciated

author: Adhith
author_rank: Frequent Contributor
timestamp: June 04, 2018, 11:21:07 am
content: Does making a voltage buffer solves the problem??