Electronics > Power/Renewable Energy/EV's

SG3525 PWM controller OCP cell

<< < (9/9)

xavier60:

--- Quote from: ym58 on January 31, 2023, 03:23:14 am ---
--- Quote from: xavier60 on January 31, 2023, 02:30:57 am ---If you can adjust the output voltage? you can control the battery charge current.

--- End quote ---
During the CC phase (constant current), I leave the battery dictate the PSU its output voltage and the PSU adjusts consequently (no choice !) while providing the battery the constant current that it's been set for (hence this thread !).
I never thought that I could **still** adjust (slightly) the voltage during this phase to modify the current, I need to test that as it's not a normal procedure for LFP4 technology.
On top of that, voltage range on LFP4 batteries is quite narrow (mostly from 12V min to 14.6V max, no linearity !).


--- Quote from: xavier60 on January 31, 2023, 02:30:57 am ---Needing a mains isolation transformer, the low-side MOSFETs Gate waveforms should be checked first. Because the design uses no drive
buffering, the waveform is going to be normally messy.

--- End quote ---
I don't get it, why do I need a mains transformer ?
Can you clarify ?

--- End quote ---
The suggestion of adjusting the voltage to vary the charge current is for testing reasons.
The PSU needs to be powered via an isolation transformer to be able to take oscilloscope readings on the live side.

ym58:

--- Quote from: xavier60 on January 31, 2023, 04:00:18 am ---The suggestion of adjusting the voltage to vary the charge current is for testing reasons.

--- End quote ---
Yes sure and that's what I had understood but, still, I have to make sure the BMS will like it or not !
Otherwise, I will have to disconnect it.


--- Quote from: xavier60 on January 31, 2023, 04:00:18 am ---The PSU needs to be powered via an isolation transformer to be able to take oscilloscope readings on the live side.

--- End quote ---
Actually, since there is a fourth transformer which does not appear (yet) on my schematics, I have to wait until my reverse eng-ing the board is completed before clarifying how the FET gates drive is really handled ...

Njk:

--- Quote from: ym58 on January 31, 2023, 01:40:30 am ---Just one point though : what's C21 for, is it just there for decoupling HF spikes ?

--- End quote ---
A sort of. "lim" input signal is of square wave. C21 shapes it to a triangle form to prevent false triggering at high (yet acceptable) output current levels

ym58:

ym58:


--- Quote from: Njk on January 30, 2023, 12:29:04 pm ---Well, the theory is quite simple. When the SMPS is operating normally (no overcurrent), T20 and T21 are both closed (not conducting current), so the "dis" output signal is not asserted (is at GND level). In the case of overcurrent, the current sensor voltage at "lim" input became high enough to open T21. It opens and that, in turn, causes T20 to open. Because of that, the "dis" output became asserted (5.1V) causing the SMPS to shut down. Meanwhile, C20 starts charging and that keeps T21 opened even if "lim" signal is no more active. So the C20 charging time determines the pause time. When the charging has finished, T21 closes, T20 closes, "dis" de-asserts enabling the SMPS to start again. Meanwhile C20 starts discharging. D20 speed-ups the discharging to make the OCP cell ready for the next cycle more quickly

--- End quote ---
@Njk
So, if I understood you well, that cell is more an 'OCP' cell than a 'CURR LIMITING' cell, is that right ?
By reducing C20, do you think I could make the controller recover FAST from the OCP state, at least fast enough to mimick a 'CURR LIMITING' behaviour that is to keep the current constant at a certain value (dictated by the choice of R9, e.g.) ?
Actually, my point is more to be able to control and adjust the CURRENT LIMIT than the OCP ...
(you will find the final PSU diagram in my previous post)

Navigation

[0] Message Index

[*] Previous page