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  • 1.  Why can I not mix power supplies in the EX4300(-32F)? I want DC and AC!!!

    Posted 04-02-2024 12:09

    The subject says it all: Why can I not mix power supplies in the EX4300(-32F)? I want DC and AC!!!

    The hardware guide says one can only use AC or DC, but from an electrical (and my) point of view, the secondary side (the one facing the switch) should be identical regardless of the input power type. What is the problem here, really? Has anyone run the AC-DC combo in the EX4300 or similar switch? I'd be wiling to try myself, but cannot recommend it to a customer without more info.



  • 2.  RE: Why can I not mix power supplies in the EX4300(-32F)? I want DC and AC!!!

    Posted 04-03-2024 02:09

    Well, here it is clearly stated that you should avoid mixing AC and DC power in the same chassis - 

    https://www.juniper.net/documentation/us/en/hardware/ex4300/topics/topic-map/ex4300-power-system.html

    I believe there are very specific reasons why AC+DC setup is not recommended for any other equipment, not only this model.



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    FARID AKHUNDOV
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  • 3.  RE: Why can I not mix power supplies in the EX4300(-32F)? I want DC and AC!!!

    Posted 04-03-2024 05:43

    Yes, it is clearly documented, so no issues there, but I guess I'm a bit frustrated since I cannot see an electrical problem mixing the two. Grounding and cabling could be one issue, but hardly on modern hardware. There are other switch brands that allow this in certain models but not in other (Nokia SAS-S does not, SAS-Mxp does).

    Electrically, an AC feed to a switching power supply (which all are today in this product segment) is rectified to DC the first thing that happens in the PSU, so from there on, it is a DC PSU anyway, just with a higher voltage than a -48 VDC PSU.

    As I said, perhaps more frustrated than expecting Juniper to change their policy... If anyone with real hard core electronics knowledge can shed some light, I'm all ears!




  • 4.  RE: Why can I not mix power supplies in the EX4300(-32F)? I want DC and AC!!!

    Posted 04-03-2024 05:54

    Surely, from electronics point of view nearly all the circuitry inside the switch is fed from DC. I think other vendors also have similar policies.



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    FARID AKHUNDOV
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  • 5.  RE: Why can I not mix power supplies in the EX4300(-32F)? I want DC and AC!!!

    Posted 04-23-2024 17:42

    Have you had any clarification on this yet?  

    I'm interested in this as well.  I have a scenario where I'm switching over from an EX3300 to EX3400.  Ideally, I'd like to power up the EX3400 with a single AC power supply, then swap out all the connections from the old.  Once I've confirmed everything is working properly, I would install a DC power supply, then move the DC power over from the old to the new , remove the AC power supply and install the second DC.

    If this works, it would minimize downtime.  If I had to revert to the old, I could have both switches powered up at the same time without having to wait for reboot.  Also, the DC power connections are different. The EX3300 is ring terminal vs the EX3400, which requires me to cut out the old terminal and wire up to a molex type terminal - not easy if I have to revert back.  

    Other than Juniper stating that it should not be done, I don't see why this wouldn't work, but would like to know if there's something I'm not thinking about.



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    Erik von Boltenstern
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  • 6.  RE: Why can I not mix power supplies in the EX4300(-32F)? I want DC and AC!!!

    Posted 04-24-2024 02:53

    Interestingly, the EX3400 hardware guide has no warnings (that I can find) regarding mixing AC and DC! You can compare the EX4300 and EX3400 hardware guides yourself. In the EX4300 power section, warnings are there, but not for the EX3400.

    https://www.juniper.net/documentation/us/en/hardware/ex3400/topics/topic-map/ex3400-power-system.html

    https://www.juniper.net/documentation/us/en/hardware/ex4300/topics/topic-map/ex4300-power-system.html

    I've asked one of our SEs, so hopefully we'll get some clarity on this one. My customer is still interested in AC+DC for the EX4300-32F.

    To be 100% sure and only use DC in the new chassis, you could buy a cheapish 48 VDC power supply so you can use AC power to feed this power supply and DC from that to the switch. You should get a professional 350 W 48 V DC PSU for under 50 USD. Example: https://www.digikey.se/en/products/detail/mornsun-america-llc/LM350-22B48R2/18108256




  • 7.  RE: Why can I not mix power supplies in the EX4300(-32F)? I want DC and AC!!!

    Posted 04-25-2024 06:38

    Erik,

    I just replied to the main message on this thread, but to address you specific question - while I would not recommend mix-and-match AC/DC power configuration for long-term deployment in a customer production network, if this is a short-term bridge to get the customer transitioned over from EX3300 to EX3400, then it might be okay to consider it.

    You will need to do some unit testing yourself first, to make sure it works and SW does not complain about the mix-and-match and will actually bring up the first DC supply, when you insert it into the EX3400 powered by single AC supply. Assuming all of that passes, and assuming this is a very temporary configuration on your way to a full DC deployment, it should be okay to use this to speed up the transition from EX3300 to EX3400. 

    Thanks,



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    Maitreya Sengupta
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  • 8.  RE: Why can I not mix power supplies in the EX4300(-32F)? I want DC and AC!!!

    Posted 04-25-2024 06:38

    I would caution against recommending this to a customer as a solution.

    There is more to power supplies than just input and output. There are system level considerations ranging from power redundancy / load sharing dependencies to thermal, grounding and EMC compliance considerations. The power supplies were not designed for AC/DC (great name for a band, BTW! :)) mix-and-match configuration. Nor is the EX4300 system tested and qualified with this power configuration. It may appear to work when it is first set up, but over time and across scale, there may be unpredictable corner case issues that come up. 

    Furthermore, it will be difficult for Juniper support teams to support any customer who deploys this unsupported power configuration. JTAC and support labs will not have this configuration available for testing. 

    If there is a significant business case / need for supporting mix-and-match on EX4300, I would suggest kindly reach out to EX-Seies PLM / Product Management leads. With their backing, it might be possible to define a JVD for the mix-and-match case and have that fully tested by Juniper Test teams. This will give us a chance to find and fix any corner case issues before it hits the customer. 

    Thanks!



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    Maitreya Sengupta
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  • 9.  RE: Why can I not mix power supplies in the EX4300(-32F)? I want DC and AC!!!

    Posted 04-25-2024 10:55

    Thank you very much for your reply, Maitrya. I do agree that there may well be more than just static electrical characteristics that determine if a PSU combo is usable or not. I'm just curious as to why Juniper along with many other vendors cannot offer the compatibility in some product lines. We also have a few special cases where customers need AC and DC feeds for their systems (typically AC direct line feed with DC UPS), so the requirement from customers are there.