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Common mode inductance is "king" at SMPS input in Robot applications?

zenerbjt

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Dear Engineers,
I beleive that in equipments like battery powered robots, where the power bus is obviously shared by nothing else, its purely for use by the robot alone....then diff mode inductance needs only to be very small...just enough to filter off those high frequency switching harmonics which could otherwise radiate out of their supply cables. Would you agree, that the best filtration in robot applications, is a common mode choke upstream of every DCDC SMPS module?.....because common mode noise pertains to the RF emissions which could interfere with the signal circuitry on the robot.

So on a battery powered robot, for input filters to the SMPS's on the robot.....common mode inductors are order of the day....diff mode inductors are needed , but only tiny ones, just enough to filter out those highest harmonics....would you agree?
 

Carry for cents bazar

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No. There are many different robots for different conditions. There are robots for which you need to filter even the smallest interferences which come from a light bulb. What is the application of the robot? There are robots on which simple filter capacitors are enough.
 

zenerbjt

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The robot is a warehouse robot, for carrying products from one place to another in a warehouse. At the end of the day, the SMPS switching frequency isn't high enough to radiate out of a cable. The high harmoinics of the switching frequency could radiate out, but only tiny amounts of diff mode filter inductance are needed to filter those out. So this is why i say that only tiny amounts of diff mode filter inductance are needed. I hope i can be prooven wrong?
 

Carry for cents bazar

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This is a smart AGV. I have worked on such robots for 1 ton and 2 tons. The power supply used was an LM2578 switching power supply with a 52kHz switching frequency. Filter capacitors are enough in this case, unless the datasheet specifies an inductance or you have some special conditions in your factory. This was the circuit.
1600760756128.png

I have all the circuits, but I wont make it that easy for you. At 1 ton, with 1x12V battery, the AGV was working 8 hours. It was moving very slow, it had a sensor to prevent someone from being crushed. It was moving on a black line. The problem was that when the battery is deeply discharged, it lasts a year. I recommend a smaller discharge percentage, depending on the battery you choose. A sample(maybe not for your battery) graph is like this:
at 80% discharge the battery lasts 5 years
at 30% discharge the battery lasts 2-3 years

The battery must never fall under 30% and under 12.2V.

I recommend if possible to use a rail for power supply, instead of a black line. This will solve the problems with the battery being damaged and charged. It was taking 2 hours for the battery to get charged, which is wasted time or you need more batteries for the AGV to work continuously. You can put a rail on the sides of the factory and run a rail in the middle. If you put it high, the only danger becomes the electrical current if it falls, this is solved by isolating the cable and putting a good isolated connector on both ends, or you can put a glass wall with doors on the middle lane and only stop the AGV on certain positions, in order for it to unload.
 

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