Electronics > Beginners
Effect of switching current on Li-ion battery packs
ogden:
--- Quote from: VEGETA on February 09, 2020, 09:20:31 pm ---Is this ripple good enough?
--- End quote ---
That is current ripple of battery, right? Where is voltage ripple on input capacitors? You have to look at both.
--- Quote ---Also, see the very first +40A overshoot thing... I couldn't fix it even by putting 4.7u inductor.
--- End quote ---
Ignore it. It is inrush current of input capacitor charge.
VEGETA:
--- Quote ---That is current ripple of battery, right?
--- End quote ---
Yes.
--- Quote --- Where is voltage ripple on input capacitors? You have to look at both.
--- End quote ---
I have attached photos for the voltage ripple, the 2nd photo is when output is stable. voltage ripple is about 0.15V, so is it good?
--- Quote ---Ignore it. It is inrush current of input capacitor charge.
--- End quote ---
I would ignore it but isn't it harmful to the batteries and supplies in general? It was oscillating and doing some overshoot then stabilize before adding caps though.
ogden:
--- Quote from: VEGETA on February 10, 2020, 07:04:19 am ---I have attached photos for the voltage ripple, the 2nd photo is when output is stable. voltage ripple is about 0.15A, so is it good?
--- End quote ---
You mean 0.15V? - Yes, looks good. To me seems like input caps size is right. Why you are refusing to reconnect simulation ground to "OUT-" so you don't have to use math like in this case?
--- Quote ---
--- Quote ---Ignore it. It is inrush current of input capacitor charge.
--- End quote ---
I would ignore it but isn't it harmful to the batteries and supplies in general?
--- End quote ---
That "short circuit" is very short. In real world some spark will fly but nothing bad will happen. Obviously do not overdo capacity of input capacitors. The bigger they are, the louder bang will be when you connect battery :)
VEGETA:
--- Quote ---You mean 0.15V? - Yes, looks good.
--- End quote ---
yes I modified it to be "v". I guess this is the best it gets.
--- Quote ---To me seems like input caps size is right.
--- End quote ---
Yes since increasing them will increase the inrush current plus will make it slower.
--- Quote ---Why you are refusing to reconnect simulation ground to "OUT-" so you don't have to use math like in this case?
--- End quote ---
what math?
This simulation is exactly as the one it should be in real-life, that is how this design is.
If I connect ground to OUT-, then I will have to modify a lot of stuff like the isolated DC-DC ground and the ground at the output... since all referenced to it. It looks like negative current and so on but in real-life it is typical behavior. Check the thread where this thing got developed in for more info.
Why do you differentiate between real-world ground and simulation ground?
You can do this modification as a gift to you brother if you want to xD. :-+
fcb:
From your earlier description I’m assuming you are permenatly connecting the battery to the converter? So no switch?
Back in the 90’s we built high power dc boost converters (250W+), these were connected to large NiMH packs as and when needed using expensive Fischer connectors. As the topology was basic ‘boost’ we needed to (1) protect against high in-inrush current when connected (2) disconnect under low voltage battery conditions and (3) disconnect under output short conditions.
We used a big MOSFET in series with the battery and drove it from the microcontroller. It had no measurable impact on converter efficiency and allowed us to gently fill the front end filter capacitors and bring up the converter. We could detect shorted outputs, etc.. easily and protect battery and converter.
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