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alabandical
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hAP AC PoE-Out Limits?

Fri May 07, 2021 8:56 am

I'm trying to use my hAP AC (962UiGS-5HacT2HnT) to pass PoE through to a fiber converter.

I had it working for a few hours, but after a reboot to upgrade from 6.48.1 to 6.48.2 the converter got stuck in a "brown-out" cycle where the power light just flickers continuously during boot. To be clear, I don't think the firmware itself is responsible; "/interface ethernet poe monitor 0" shows nothing while this is happening, and forcing PoE on also doesn't make any difference. The power draw of the converter shouldn't be excessive: its usual power supply is only rated at 12V 0.5A.

Are there any limits on PoE out that might cut power without showing in the monitor?

To illustrate more concretely, this is the setup I want and had temporarily working:
                48V PSU                                   -----------12V------->
                   |                                      |                    |
hEX | 2 ----- PoE Injector ----- 1 | hAP AC | 5 ----- PoE Splitter ----- Fiber Converter
Powering the hAP AC directly also causes the power to flicker:
                  48V PSU             -----------12V------->
                     |                |                    |
hEX | 2 ----- 1 | hAP AC | 5 ----- PoE Splitter ----- Fiber Converter

In contrast, removing the hAP AC works as expected and everything powers on:
                48V PSU              -----------12V------->
                   |                 |                    |
hEX | 2 ----- PoE Injector ----- PoE Splitter ----- Fiber Converter
I also verified that powering the hAP AC and injector from the same PSU works, to make absolutely sure it could handle the combined load:
                     ------48V PSU-----                  -----------12V------->
                     |                |                  |                    |
hEX | 2 ----- 1 | hAP AC | 5 ----- PoE Injector ----- PoE Splitter ----- Fiber Converter
 
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rextended
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Re: hAP AC PoE-Out Limits?

Fri May 07, 2021 10:23 am

Just read Specifications:

https://mikrotik.com/product/RB962UiGS-5HacT2HnT

Max out with input 30-57V is 0,350A
 
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mkx
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Re: hAP AC PoE-Out Limits?

Fri May 07, 2021 1:19 pm

What kind of PoE splitter is it? All MT devices will output same voltage as they are powered with ... which is, as per your diagram, 48V. If PoE splitter is not active device (e.g. reducing voltage to 12V), fiber converter is getting 48V on it's power input.
 
alabandical
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Re: hAP AC PoE-Out Limits?

Fri May 07, 2021 8:44 pm

The splitter does have a buck converter, so it's not a case of providing the incorrect voltage.

I manged to get an ammeter inserted on the 12V side of the connection, but it doesn't have a fast enough sampling rate to catch the inrush current while it's failing. It just stays pegged to zero while the LED flickers.

When I then tried measuring current on the lower 250mA range... everything worked. The meter's protection seems to limit the inrush enough to enable it to start.

Still, shouldn't the PoE monitor have reported a fault?

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