Component confirmation

General discussion of using Roboclaw motor controllers
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Ultravis
Posts: 2
Joined: Wed Feb 17, 2021 6:50 pm

Component confirmation

Post by Ultravis » Wed Feb 17, 2021 6:53 pm

Hi I would like some confirmation on my pre charge resistor selection on my 2x60A Robclaw running at 24 volts. I know a lot of people ask this question but I would like know for sure before I fry a high end controller.
Website says 2x60A Roboclaw is 1080uF changed to farad is 0.00108f
for 1 second start-up time 1 / 3 = 0.3333333333333333
0.3333333333333333 / 0.00108 = 308.641975308642

So this is around 309 ohms then I can just round it up to say a 330 ohm ¼ watt Resistor. Is that correct ?

Also for the Bypass Diode A power diode rated for 1 to 3 amps. Does this mean a 1N5408 3A 1000V Diode will do the job. https://www.jaycar.com.au/1n5408-3a-100 ... e/p/ZR1018


Thank you very much.

Paul

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Basicmicro Support
Posts: 1543
Joined: Thu Feb 26, 2015 9:45 pm

Re: Component confirmation

Post by Basicmicro Support » Thu Feb 18, 2021 10:59 am

309ohms is a reasonable calculation. You can go lower of course. Even limiting the pre-charge time to 1/10th of second will limit the surge current enough to prevent a significant ground bounce. That ground bounce is what causes negative spikes on power up which can kill electronics. We are very conservative in the manual but dont have to go with a 1 second pre-charge time.

Ultravis
Posts: 2
Joined: Wed Feb 17, 2021 6:50 pm

Re: Component confirmation

Post by Ultravis » Thu Feb 18, 2021 3:11 pm

Thank you for the fast response yes I may go with a lower ohm resistor to speed things up a little. You did not say anything about the bypass diode so I'm guessing it's ok or not overly important, I wasn't sure about the voltage rating on it I guessed the higher the better. Thank you again

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Basicmicro Support
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Re: Component confirmation

Post by Basicmicro Support » Wed Feb 24, 2021 11:47 am

Yes you can, but the lower you go the larger the resistor needs to be(eg 1/4watt 1 watt 5 watts etc... to deal with the power dissipation. Also I don't recommend anything smaller than a 6ohm resistor. This will limit Di/Dt to something reasonable.

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