Author Topic: Current shunt output smoothing  (Read 420 times)

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Offline Robert Smith Eco Warrior

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Current shunt output smoothing
« on: April 19, 2021, 08:15:54 am »
Hi All,
I am just doing a bit of temporary wiring in my battery shed to put a 100A/100mV current shunt between my charge controller and batteries. I still have my additional winter solar panels laid out on the ground and I shall soon put them away for the summer. I just wanted to pop the shunt in so I can see what current I am getting from the panels.
I am making up a circuit for monitoring but just want to measure the shunt output with my Fluke 77 mk II (I think) multimeter.
I am wondering if the PWM switching of the charge controller will give nonsense readings on the multimeter and can I filter the shunt output with a capacitor of some value?
 

Offline Gyro

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Re: Current shunt output smoothing
« Reply #1 on: April 19, 2021, 08:43:26 am »
Good luck with finding a capacitor that will directly smooth a 1m \$\Omega\$ source impedance. You could use an RC filter though, placing a higher value series resistor between the shunt and the capacitor. for instance 1k resistor and 100uF capacitor would give you a -3db frequency of about 1.5Hz.
Chris

"Victor Meldrew, the Crimson Avenger!"
 

Offline Robert Smith Eco Warrior

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Re: Current shunt output smoothing
« Reply #2 on: April 19, 2021, 12:03:14 pm »
Ah, yes, I see what you mean.
I shall try those values you suggested.
I am waiting for Covid lockdown rules to allow me to go and collect an ocilloscope I have bought. Then I might have a chance of seeing what is going on.
 

Offline Gyro

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Re: Current shunt output smoothing
« Reply #3 on: April 19, 2021, 01:21:24 pm »
Those are hopefully worst case values. If possible try to stay down to 10uF or lower as you could do that with a film capacitor, preventing potential leakage current issues with an electrolytic cap (or use a Tantalum bead). The limiting factor on the series resistor is inaccuracy caused by the input resistance of the DMM, normally 10Meg. I am probably being a bit over cautious there too, a 10k resistor would still only affect the reading by 0.1%, your shunt is almost certainly less accurate than that anyway.
Chris

"Victor Meldrew, the Crimson Avenger!"
 
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Offline Robert Smith Eco Warrior

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Re: Current shunt output smoothing
« Reply #4 on: April 22, 2021, 06:57:18 pm »
Thanks for that.
I have a few threads going and I missed your reply for a while.
 

Offline David Hess

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Re: Current shunt output smoothing
« Reply #5 on: April 23, 2021, 10:03:20 am »
The charge controller should have decoupling on its input and the multimeter should not care anyway.
 


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