KRC2 mains filter

    A colleague has recently procured an ex BMW KR140L120-B2 with KRC2 05 SR AK9 BMW L6 cabinet EU version. His workshop is not equipped with 3-phase power so he is utilizing a proprietary phase converter using a 3-phase idle motor as ballast to produce 400v delta 3-phase from 230v single phase. The problem is the RCD (residual current device) supplying the building trips when switching on the robot when the phase converter is already powered up. Even though the RCD has been exchanged for a higher tripping current version (300mA), the switch on tripping still occurs. He has found that if the PE (ground) connection to the robot cabinet is disconnected, the robot powers up without tripping the RCD.

    Looking through some old training documentation, I found that on the KRC2 specification page it says:- "Mains filter leakage current approx. 300 mA". Apparently this RCD tripping phenomenon is a known issue with KRC2 but I suspect it is worse in this case, due to the asymmetric-to-ground 3-phase supply. Is there a straightforward solution, perhaps by exchanging the mains filter for another type? What would be the consequence of isolating the ground connection to the filter? Of course an isolating transformer might also be the answer, but a simpler solution is preferred.

    Edited once, last by Razzzhead (November 14, 2019 at 3:18 PM).

    Quote from panic mode

    well, you may not like this but one straight forward solution is get proper 3-phase service...

    If only that were possible! The rented workshop is on a farm and the cost of running 3-phase to the premises would be prohibitive. The only other commercial solution would be to change premises which is not feasible.

    Since the original post, the mains filter has been isolated from ground and the robot can now be powered up without tripping the RCD. However there is now an undervoltage error when running at more than 50% override.

    "Undervoltage" suggests that, at higher speeds, the robot is drawing more current than the supply can provide without losing voltage. You might have to use a higher-capacity power converter. Unless the bottleneck is on the single-phase mains side, in which case... well, you're probably stuck with the generator option, in that case. I've never done it myself, but I've seen KRCs run directly from generators in the past -- however, the power capacity has to be sufficient (plus margin), and the power supply needs to be fairly "clean" of harmonics, spikes, non-sinusoidal waveforms, etc.

    The other posters on this thread are right, you are likely seriously under-powered.

    Also, full-sized KUKA controllers are spec'ed for 400V Wye type 3-phase power, not Delta.

    If you don't have a transformer in the bottom of your cabinet (which BMW robots typically don't) you should look into using a transformer that will make this change for you.

Advertising from our partners