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issue with running two MM420

9/16/2010 5:06 PM	Rate (0)
dauriat Posts: 3 Rating: (0)	Dear experts, I have troubles with the following installation : I have two MM420 (3 and 7.5 kW) mounted side by side in an electrical case driving two pumps. When the bigger MM420 is offline I have no problem with the smaller one. But when the second MM420 is powered and (I think but not sure) even not running, I have, some time to time, the smaller MM420 crashing with the BOP displaying "P----" and not responding. No communication is possible on USS and the only issue is a power off/on cycle. I can precise that both MM420 are wired on the same USS bus. Any idea ? Thanks,
dauriat Posts: 3 Rating: (0)	Last edited by: dauriat at: 9/16/2010 5:59 PM
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9/17/2010 12:12 AM	Rate (0)
Graeme Platinum Expert Joined: 6/4/2008 Last visit: 8/5/2025 Posts: 1518 Rating: (327)	Hi, please read this manual Micromaster 4 EMC Guidelines and check that your installation follows the manufacturers recommendations, this problems sounds exactly like the advice in this manual has not been followed. Also, check the correct terminations of the USS bus are installed. I see this problem on many different sites. Cheers, Graeme

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9/17/2010 1:21 PM	Rate (0)
dauriat Posts: 3 Rating: (0)	Hi, thanks for your reply. I also suspected EMC being the cause of my problem. But would you know where to look first ? is it because of data cables getting interference, or the Micromaster itself through power cables or others? radiated or conducted interferences ? I believed micromasters were designed to be relatively immune to EMC, what bothers me most is the fact that i have no error messages to tell me which part to look at. Thanks,
dauriat Posts: 3 Rating: (0)
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9/18/2010 9:53 PM	Rate (0)
Graeme Platinum Expert Joined: 6/4/2008 Last visit: 8/5/2025 Posts: 1518 Rating: (327)	Hi, disconnect the USS from the smaller drive and then start the larger one, does the BOP still crash? Reconnect the USS and repeat. If the cause is the USS, try changing the route of this comms cable. Also, make sure the power cables are routed well away from ANY signal or comms cables. Most panel builders wire power in single cores, for considerable distances, however, none of them run the power in trefoil configuration (Trefoil is a three wire crossover configuration not unlike a hair plait) This configuration reduces the emissions from the power wires. Hope this gives you some more ideas. Cheers, Graeme

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9/28/2010 5:52 PM	Rate (0)
dauriat Posts: 3 Rating: (0)	For information if it can help someone : I improved the general earthing of all the components but I still had the problem. I then disconnected the USS bus and since then the system is running fine. I didn"t figure out a solution yet to get it working with the uss wired.
dauriat Posts: 3 Rating: (0)
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