tcvt
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Posts: 4
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Post by tcvt on Aug 19, 2020 10:10:09 GMT -5
We have two LakeShore625 magnetic power supplies (MPS) connected in *parallel* to a 14T liquid-cooled superconducting magnet. When energizing the magnet, we set the ramp rate and current outputs of the two supplies to be equal. Maximum field is reached when both supplies output ~54.3A. For both, the compliance limit is set to 5V. Recently, we have started to experience the following issue: One of the MPS (the top one from the attached image) seems to be working fine and has no problem ramping up to 54.3A. The other however, seems to not be able to ramp beyond 43A. When this current value is reached, it actually starts to drop, even though it is instructed to ramp further. The output voltage of both supplies is ~1.5V, well below the compliance limit of 5V. What could be the cause of this issue? Thanks! Attachments:
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tcvt
New Member
Posts: 4
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Post by tcvt on Aug 19, 2020 10:24:11 GMT -5
EDIT: When ramping down, the output current of the top one decreases as it should, but the output current of the bottom one actually increases beyond 43A.
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Post by Lake Shore Cosmin on Aug 19, 2020 19:52:35 GMT -5
Please contact us at service@lakeshore.com with your name, address, institution/company contact info and the serial number of the misbehaving power supply. We'll open a service case and will forward the symptoms and other relevant information to our engineer in charge with this product line. If a repair is needed, we will inform you of the steps to follow. For testing purpose, we may ask you to run your power supplies on a short instead of the actual magnet. We would also ask you to run the unit under test, alone, on a short instead of the magnet.
Generally speaking, the Model 625 is a current source and the current sources should only be connected in parallel. I guess you are not actually connecting them in series; maybe was a typo.
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tcvt
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Post by tcvt on Aug 20, 2020 5:09:49 GMT -5
Thanks for the reply! Indeed I meant in parallel. I will contact the service department.
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tcvt
New Member
Posts: 4
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Post by tcvt on Aug 20, 2020 8:13:26 GMT -5
UPDATE: I shorted the outputs of the misbehaving power supply and was able to ramp it up to 60A without problems (0.2 A/s). I then shorted the output of the two power supplies connected in parallel (see the attached images) and ramped up the current to the maximum values (60A). It seemed to work just fine. The only difference is that this configuration constitutes a smaller load compared to when it is actually connected to the magnet. With a slower ramp rate (0.0064A/s) it also worked. Curious to hear your thoughts. Attachments:
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Post by Lake Shore Cosmin on Aug 20, 2020 12:16:54 GMT -5
These tests and details are very useful! I will consult with our engineers and then respond to you, most likely by-email.
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