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High power current sense resistor resistance/voltage drop during inrush current

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tszaboo:
It is either the transient response of the current sense amplifier. It is not that great, some of them go up to a 100 KHz, but that's it. Some of them have terrible offset or non linear gain.

Or it can be the current clamp also. They are even worse. The ones with banana jack are instant disqualified for any inrush measurement. They work fine in DC, they work fine in AC, they dont work fine with anything in between. I give you an example, a Fluke i30 (or some other Fluke clamp) was showing current in the wrong direction when you applied a step response to it. The ones with BNC connector might work, but they will have some problems.

aiq25:

--- Quote from: T3sl4co1l on February 19, 2019, 11:54:28 am ---What dI/dt is this inrush, and what's the layout look like?

Related question: can this inrush be much more than the circuit is designed for?  Are you not limiting it with a current mode controller?  You've got a whole H-bridge there, with current sense -- it would be a shame to throw away such an excellent opportunity. :)

Tim

--- End quote ---
The dI/dt is typically ~10A/5us. Unfortunately I cannot share the exact layout. Maybe I can draw something and share, which parts do you think would be helpful?

This inrush can be more but there is a overcurrent protection circuit that kicks in and pulls the H-Bridge driver low when the inrush is more than the set value. There is no controller though. Do you have any suggestion of a controller?

aiq25:

--- Quote from: NANDBlog on February 19, 2019, 04:04:18 pm ---It is either the transient response of the current sense amplifier. It is not that great, some of them go up to a 100 KHz, but that's it. Some of them have terrible offset or non linear gain.

Or it can be the current clamp also. They are even worse. The ones with banana jack are instant disqualified for any inrush measurement. They work fine in DC, they work fine in AC, they dont work fine with anything in between. I give you an example, a Fluke i30 (or some other Fluke clamp) was showing current in the wrong direction when you applied a step response to it. The ones with BNC connector might work, but they will have some problems.

--- End quote ---

I'm measuring this right across the sense resistor, so not taking into account the current sense amplifier.

The current clamp is calibrated and I have tried different ones. I have been using this for other projects and it worked, so most likely I'm thinking it is not the clamp. This is with BNC connector and amplifier, 50A Tektronix probe.

aiq25:
Today I tried something different: I soldered a wire loop before the current sense resistor (I know not the best practice but I wanted to see) and the current through the loop was different than what is measured on the output AC lines HOWEVER the current matched the voltage reading I got across the sense resistors. I'm thinking it is probably not the sense resistors. Everything is pointing towards there is another current path somewhere in the circuit but I cannot figure out what it could be.

tszaboo:

--- Quote from: aiq25 on February 20, 2019, 04:04:57 am ---
--- Quote from: NANDBlog on February 19, 2019, 04:04:18 pm ---It is either the transient response of the current sense amplifier. It is not that great, some of them go up to a 100 KHz, but that's it. Some of them have terrible offset or non linear gain.

Or it can be the current clamp also. They are even worse. The ones with banana jack are instant disqualified for any inrush measurement. They work fine in DC, they work fine in AC, they dont work fine with anything in between. I give you an example, a Fluke i30 (or some other Fluke clamp) was showing current in the wrong direction when you applied a step response to it. The ones with BNC connector might work, but they will have some problems.

--- End quote ---

I'm measuring this right across the sense resistor, so not taking into account the current sense amplifier.

The current clamp is calibrated and I have tried different ones. I have been using this for other projects and it worked, so most likely I'm thinking it is not the clamp. This is with BNC connector and amplifier, 50A Tektronix probe.

--- End quote ---
Oh, OK, so the amplifier is not measured. Did you take care about ground loops then?

Also, the current clamp are not "broken", they just are not made to handle this situation well. It is combination of the core characteristics, and the hall effect sensor's characteristics, and the surrounding circuit's with their own problems.

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