Discussion between tlfong01 and Cezerb

9:29 AM

Q: SMPS powered DC motor inrush current problem

I stumbled upon a problem when connecting a DC motor to a SMPS. It's a 20W AC/DC converter with an 12V output that powers some 12V DC motors the processor and some LEDs. I needed to speed up the most powerful of the motors so I added a boost converter on the lines of the motor to raise the voltag...

Cezerb

@brhans my mistake. I meant boost. I edited the post.

tlfong01

@Cezerb, your project looks like some of the things I have been doing and some of my thoughts: (1) Using power MOSFET IRL540N driving DC motor 37GB528 motor: raspberrypi.stackexchange.com/questions/94031/…, (2) MT3608/XL6009 boost converter with ICL/thermister NTC-5D7: chat.stackexchange.com/rooms/115057/…. / to continue, ...

/ cont, ... (3) I am just an electronics hobbyists, also a newbie in ICL (Inrush Current Limiter). I know my NTC-5D7 is 5A, but I have no idea about its response time, so I am not sure if it is useful. If my ICL is not useful, I might try your L-C workaround. I also heard experts saying that a simple resistor can do the job, and suggest 300R. (4) I have a couple of SMPS including (a) 7.5V 26A (to simulate Lipo 16450s2), and (b) 12V 20A (my plan is to move up toy motor standard 12V to 24V industrial standard). / to continue, ....

/ cont, ... I also have a couple of step down SMPS, including LM2596 3A, and ZK-JVA-12KX 12A. (5) Perhaps you can suggest something so that we can do some sort of pairing testing and development.Cheers.

Cezerb

@DavidMolony Unfortunately I can't. The added boost converter is only a temporary fix, I'm later going to use a faster 12V with higher power and I suspect I'll have the same issue. I'd like to limit the inrush current to get rid of this problem entirely.

@tlfong01 I've just found another solution that might work for you as well. I haven't tested it yet, but the idea is to slowly switch the MOSFET on using a capacitor between the gate and the source.

tlfong01

@Cezerb, Ah yes, that is called delay start or soft start, which is used if the converter does not have internal delay start. I have checked that both *MT3608 and XL6009 has built in chip soft start circuit. In other words, if we use XL6009 to boost 5V to 12/18/24V, then we don't need any external soft/delay start circuit. (See my comment on the above referred chat record at Oct 15, 11:58 for more details) Cheers.

@Cezerb, By the way, XL6009 has an 47uF external inductor, so your protection inductor of 1uH is very likely too small. I vaguely remember my GB37 motor takes about 350mA steady current and might be over 2A start/stall.

Cezerb

@tlfong01 This is why I asked about the L1 value as I have no idea how to choose the right value.

tlfong01

9:31 AM

Ah yes, in the chat record I reffered earlier, the very first comment made by an expert says the following: "All step-up converters spark unless you have soft start. Do you understand transformed equations for V, I, Z ratios?".

I guess the "Z" in the above comment refers to Impedance, which is the equivalent of combined R, L, C of the boost converter MT3608 or XL6009. I once learned the idea of this "transformed equation idea", when ages ago I studied my rusty EE Diploma at Hong Kong Technical College, I but I did not understand it at all. I only remember they called the mysterious thing "S" transform, or "Z" transform, I forgot. :)

Ah, locking down jogging + supper time. I need to go. See you later. Cheers.

next day → last day (16 days later) »

all rooms