I want to place capacitor(s) in my circuit to help stabilize the current spikes and reduce the amount of noise on the power lines (without adding another power supply). I just don’t know which capacitor I need and where to place them.
Is placing 2 separate 470uf capacitors to each servo correct, like the photo? Or do I need 1 470uf capacitor directly after the battery? Maybe a combination of both? Or with another capacity?
What is the max current for the servos?
Then you must know what the rise time is for the noise you are interested in. Capacitors do not perform magic. 470uF capacitors will only have effect on very slow changing noise pulses.
You will need to experiment with placement. Watching the noise on your oscilloscope will tell you if the noise id reduced or not.
According to the servo data sheet, the servo stall current is around 800 mA. I’ve learnt that I need to allow 1A for each servo. So the max current will be 2A in total.
You will need low value ceramic capacitors in parallel with the large value capacitors so that high frequency noise is suppressed as well as the low frequency stuff.
Favourite is to use a 0.1uF ceramic capacitor across a 470uF to 1000uF capacitor for each servo. But nothing beats the batteries being able to be able to supply the peak current in the first place.what sort of batteries are you using?
Thanks for the advice! I thought there was a standerd way to add capacitors with this setup. But will check the noise with an oscilloscope like you mentioned!
Electrolytic capacitors might be added to the output of the power supply if you can see sag in the voltage. But while they will limit the voltage sag, they also lengthen the time of the sag because the capacitors also need to be recharged!
The capacitors may not be needed.
Does everything work without the capacitors?
Why do you suspect spikes and noise?
I have a hexapod robot with two servos and 4AAs work perfectly without capacitors.
Was thinking about 4x Duracell Plus 100 AA 2900 mAh Alkaline 1.5 V. May I ask if I correctly applied your advice to this new design?
My version works without them. However, since I use a single power source to supply power to both the Arduino and servos, I thought it would be good practice to add capacitors to keep the supply line noise limited. Adding them would be more of an extra safety measure, just to be on the safe side. But I happily follow your advice that in this case it’s an unnecessary addon.
Not really. They don't prevent overvoltages or overcurrents from occuring. The regulator on the Nano 33 should take care of any power fluctuaions on it's input.
If it ain't broke why try to fix it.
Good point! Thank you for the help and the extra explanation! Much appreciated.
Glad I could help
Have a nice day!
Yes that is the way to apply what I said.
It is important to know the maximum input discharge current for these batteries. I found this at voltage - How many amperes can an alkaline AA battery supply? - Electrical Engineering Stack Exchange
However, I would consider other types of battery like a rechargeable Lithium-ion battery otherwise, as Jim said it functions without them so there is only a need to have them if you are getting noise from them. You are more likely to get current dips than current spikes.
Thank you for the confirmation and the extra info you provided! It helps a lot.
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