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nagylzs
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RB260GSP, short circuit error

Fri Jul 09, 2021 10:29 pm

Hello, I have a network with these devices connected:

24V power supply --> sw01 (RB260GSP) -- (wire1)---> sw02 (RB260GSP) --(wire2)--> r01 (HAP-AC2)

Very strange thing is happening. The web interface of sw02 displays 22.6V on passive poe-in (on ether1). If I connect r01 (HAP-AC2) to it, then the red led light flashes for a moment, and then the switch displays "short circuit". If I connect the HAP-AC2 to (wire1) directly (e.g. without sw02), then it works! Also, if I connect them all of them the same way but with a much shorter (wire1), then all of them work again.

First I thought that wire1 might be too long and it has too much resistance. But I checked, and that is not the case. First of all, the link on wire1 is stable 1Gbps full duplex, and the length of wire1 is about 10 meters. Voltage drop on that wire is about 1V. If I connect HAP-AC2 directly to sw01 on the same wire1, then I measure 4.3W load on the wire, and the voltage is still well above 20V. It means that the wire has low resistance. It is true that HAP-AC2 requires at least 18V on its POE-IN, but I cannot imagine that sw02 would drop 5 volts between its poe in and poe out. Even if it drops 2V (which would be ridiculous), the HAP-AC2 would still get more than 20V input. But I wanted to be sure, so I also tried to put a passive POE splitter on the output of sw02, and power up the HAP-AC2 from that. The result is the same: sw02 displays "short circuit".

I have also tried to manually set the output of the sw02 to "on", and also to "calib". None of them work. Also tried to use a different POE-OUT port on sw02, with the very same result: sw02 displays "short circuit" and just stops working.

Any idea what the problem is?

Thanks
Last edited by nagylzs on Sat Jul 10, 2021 4:23 pm, edited 1 time in total.
 
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Re: RB260GSP, sort circuit error

Fri Jul 09, 2021 10:33 pm

I just measured again. Input voltage on sw01 is 23.5V. Input voltage on sw02 is 22.7V. That is 0.8V voltage drop, and it includes the (supposed) power FET inside sw01 and the 10m long wire1. We can safely suppose that sw02 won't drop more than 2V, so the HAP-AC2 must be getting more than 20V on its poe-in port. And it does not work.

BTW, I have tested both wire1 and wire2 cables with a cable tester. They are normal patch cables (not cross cables), and all 8 wires are conducting.
 
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Re: RB260GSP, sort circuit error

Sat Jul 10, 2021 12:00 am

Max power consumption of hAP ac2 is rated at 16W (21W with attachments whatever that means) and I guess that it really can draw that much power at some stage during boot time. Add 5 Watts of power consumption of the cascaded RB260GSP to get total power draw of 21W. And with supply voltage around 22 Volts that's uncomfortably close to the PoE out max current of 1A. Mind that it might happen during a really short period of time, too short for a multimeter to notice, but long enough for PoE out protection circuitry to trip.

I wouldn't run my devices on such a tight power budget. You can use a RBGPOE passive injector on the wire1 near to sw01, those injectors have rated max current of 2A. The only drawback is use of two power adapters.
 
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Re: RB260GSP, sort circuit error

Sat Jul 10, 2021 7:33 am

You are probably right, I'll try with RGBPOE, and also a splitter before sw01.

But I'm still not sure if that will help. You say that RB260GSP has 5W power consumption, but that is the max. I have measured and this one actually draws 1.1W. Nothing else is connected to it, it does nothing just sits there. Also, the difference between a 1 meter wire and a 10 meter wire can't be that big. I have tried with a 1 meter wire, and I could power two HAP devices at the same time without any problem. (I understand that I should not do that, I only did that to find the problem.) Maybe the problem is with wire1 itself? I did not install it, it is inside the walls. I'll also try with a 15m brand new cable, just to see what happens.
 
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Re: RB260GSP, sort circuit error

Sat Jul 10, 2021 8:10 am

More thinking. The power output of sw01 equals the power consumption of sw02 + r01, plus losses on the wire. The power output of sw02 equals to the power consumption of r01. So sw01 will always output more power than sw02. Despite this fact, sw01 never complains about short circuit, but sw02 always does. Something is not right. The "short circuit" message is probably not related to the 1A/port limit, because that would cause sw01 to shut down its output sooner.

(Maybe I'll test the actual voltage vs time curve with a scope, but that requires adding multiple POE injectors and splitters.)
 
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Re: RB260GSP, sort circuit error

Sat Jul 10, 2021 12:43 pm

Can second that cascading PoE with RB260GSP did not work for me. When powered with the power supply the RB260GSP did support mutiple SXTsq ac,wAP ac,hAP ac2 and cAP ac. When powered over PoE_in even just powering a single mAP lite failed. The PoE_in seems to be limited in total power input (PoE_in resistors ???? 'short circuit" triggered by low PoE_out voltage??? PoE Input is limited by the PoE_out of other RB260GSP anyway !!)

Cascading with Powerbox Pro (using PoE_in for PoE_out) on the other hand works fine.

"For the best PoE output functionality, please use the power jack to power the CSS unit." <- https://help.mikrotik.com/docs/display/UM/RB260-series
 
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Re: RB260GSP, sort circuit error

Sat Jul 10, 2021 1:15 pm

One example, not the truth:
If power source provide exactly 24V, what are the max Watt or Ampere?
That info is provide when no device are attached, the internal resistance/use cause Ampere increase and Voltage drop.

Just using PoE circuit on 1st RB260GSP, the internal "diods" drop volts from 0,5 to 1 (depends on type and model)

The cable from 1st RB260GSP to 2nd for Ohm effect drop Voltage again 0,8V as you wrote
@bpwl say: and is limited to 1A by the 1st RB260GSP PoE_out per port limit

The cable from 2st RB260GSP to hAP ac^2 drop Voltage again of 0,8V for example
@bpwl say: have same limit to 1A

If RB260GSP use 5W, on 1st the Ampere are 5/(24 - 1) ~ 0,22 A
the seconds still 5W, but with less Volt, Ampere have a little increase: 5/(24-1-0,8) ~ 0,23 A
on the third device than use 16W, Ampere increase again: 16/(24-1-0,8-0,8) ~ 0,75 A
@bpwl say: and 0,23 + 0,75 = 0,98, close to the MAX 1A

When powered the hAP ac2 cause Voltage drop on source because is used,
more power are drained, then Voltage go low, Ampere increase.
With hAP for example, if the Voltage drop on power source are 1V, the Ampere again increases:
16/(24-1-0,8-0,8-1) ~ 0,784A ~20,4V
@bpwl say: and at this point 0,23 + 0,784 = 1,014, over the MAX 1A

Ethernet cable (assuming that the plastic insulation is perfect) can transport also 100.000V
But is really poor to transport Ampere due to diameter size.

But on all of that device the peak current when start are unreported.
For example, if the hAP has 40W peak current, 40/(24-1-0,8-0,8) ~ 1,87A
and 1,87 + 0,23 = 2,1 A
@bpwl say: the double supported MAX 1A for out and over the MAX 2A of total of outs

This is why is better to directly power all PoE out switch type and do not use on cascade.

If this setup must be used because is not alternatives,
use 30V as power source, less request of Amperes on cables
Last edited by rextended on Sat Jul 10, 2021 2:13 pm, edited 8 times in total.
 
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Re: RB260GSP, sort circuit error

Sat Jul 10, 2021 2:01 pm

The cable from 1st RB260GSP to 2nd for Ohm effect drop Voltage again 0,8V as you wrote
and is limited to 1A by the 1st RB260GSP PoE_out per port limit

PoE-out Details
PoE-out ports	 Ether2-Ether5
PoE out	         Passive PoE
Max out per port output (input 18-30 V)	1 A
Max total out (A)	                2 A
 
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Re: RB260GSP, sort circuit error

Sat Jul 10, 2021 2:08 pm

edited, please check if is ok what you mean ;)
 
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Re: RB260GSP, sort circuit error

Sat Jul 10, 2021 2:24 pm

One example, not the truth:
If power source provide exactly 24V, what are the max Watt or Ampere?
That info is provide when no device are attached, the internal resistance/use cause Ampere increase and Voltage drop.
I'm not sure what you mean. The power supply is rated 24V 2.5A DC, that is about 60W.
Just using PoE circuit on 1st RB260GSP, the internal "diods" drop volts from 0,5 to 1 (depends on type and model)
I would be suprised if it used BJTs. I believe it uses a mosfet with low Rdson value (0.1 ohm or less).
The cable from 1st RB260GSP to 2nd for Ohm effect drop Voltage again 0,8V as you wrote
@bpwl say: and is limited to 1A by the 1st RB260GSP PoE_out per port limit
That 0.8V drop includes voltage drop between sw01 input-output, and drop on wire1. I'm not sure how it is distributed between the two.
The cable from 2st RB260GSP to hAP ac^2 drop Voltage again of 0,8V for example
@bpwl say: have same limit to 1A

If RB260GSP use 5W, on 1st the Ampere are 5/(24 - 1) ~ 0,22 A
That is the maximum possible power consumption. In my concrete setup it was consuming 1.1W, that is about 0.4A. (And there was almost no network traffic on the wire.)

I understand your calculations, but you are always calculating with max power consumption and worst case scenarios. The peak current does not reach 1A in my case (that would be at least 20W). I did not measure but I'll. (But I'm confident about this.)
This is why is better to directly power all PoE out switch type and do not use on cascade.
If this setup must be used because is not alternatives,
use 30V as power source, less request of Amperes on cables
Unfortunately none of these are alternatives. I have to drive other devices and they cannot withstand 30V.

I have a solution that is far from perfect, but it would probably work:

1. send power with RGBPOE instead of sw01.
2. use a gigabit POE splitter to get the power at sw02. (but that is a problem in its own, because I have to purchase a gigabit passive poe splitter, and that is not easy)
3. use the output of the splitter to drive sw02 AND the HAP AC too.
4. if this still does not work, then increase voltage to 48V on the sender side, and use a buck converter on the receiver side to convert it to 24V or maybe even less - but that requires DIY solutions, soldering etc.
 
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Re: RB260GSP, sort circuit error

Sat Jul 10, 2021 2:46 pm

"One example, not the truth" and "(depends on type and model)" are here for prevent those questions...

you are always calculating with max power consumption and worst case scenarios
Must be done on that way!!!

The peak current does not reach 1A in my case
You must use a professional tester capable to analyze & memorize values on microseconds interval.


RGBPOE can be used on both directions....
 
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Re: RB260GSP, sort circuit error

Sat Jul 10, 2021 2:57 pm

"One example, not the truth" and "(depends on type and model)" are here for prevent those questions...
you are always calculating with max power consumption and worst case scenarios
Must be done on that way!!!
The peak current does not reach 1A in my case
You must use a professional tester capable to analyze & memorize values on microseconds interval.
I have a 100Mhz digital scope but... probably I'll just use a POE injector and a splitter instead. Much easier solution. It would be very interesting to see the results though... but it is too much trouble.
RGBPOE can be used on both directions....
Really? I did not know that! Are you saying that it has no galvanic isolation between its input and output ethernet ports?
 
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Re: RB260GSP, sort circuit error

Sat Jul 10, 2021 2:58 pm

Nono, I talk about power on RGBPOE, can be injected and can be... extracted!!!

You can use 2 PoE: one at the start with power provided from jack, the other at the end (in reverse direction) to extract power from female jack
 
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Re: RB260GSP, sort circuit error

Sat Jul 10, 2021 3:36 pm

Nono, I talk about power on RGBPOE, can be injected and can be... extracted!!!

You can use 2 PoE: one at the start with power provided from jack, the other at the end (in reverse direction) to extract power from female jack
RGBPOE has female barrel jack only.

If I can use RGBPOE on both ends, then it means that RGBPOE has no galvanic isolation between its ethernet ports. Does it, or does it not?
 
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Re: RB260GSP, sort circuit error

Sat Jul 10, 2021 3:38 pm

RGBPOE has female barrel jack only.
Yes, and you have one pair of scissor?
Or one dead transformer?

galvanic isolation between its ethernet ports
I do not know and really I do not understand why matter if is used to "extract" current than "inject"
Last edited by rextended on Sat Jul 10, 2021 3:42 pm, edited 2 times in total.
 
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Re: RB260GSP, sort circuit error

Sat Jul 10, 2021 3:41 pm

edited, please check if is ok what you mean ;)
The 1A max comes from the specs of the RB260GSP ( https://mikrotik.com/product/RB260GSP )
There is no power diagram, and no information on short burst overcurrent that is allowed. (What usually is the case.)
I only was thinking on the non-linearity of the voltage drop that a current limiter would introduce once you get near or at the current limit.

There seems to be some "logic" in the overcurrent protection, as some posts on this forum suggest to play with the "PoE Priority" to avoid some glltches in the PoE out of the port you want to protect, by allowing the PoE out interrupt on lower priority ports first, and gain some overcurrent trigger time.
(Lost the reference to the posts, could have been for Power Pro also !))

If there is no room for a power unit at Switch2, then a PoE injector near Switch1 on the line to the Switch2 might just give that little extra current to the PoE input.(2.5A versus 1A in extremis). But the comment in the UM suggests that the PoE_in to PoE_out connection is not as good as the power jack to PoE out. So at the end, you might need to extend the power cable of your second power supply with 10 meter. (Small power cable diameter will easily outperform UTP) There is also "thicker" UTP cable, as it works on a shorter cable, this could matter. https://www.broadbandbuyer.com/advice/3 ... net-cables
Last edited by bpwl on Sat Jul 10, 2021 4:04 pm, edited 2 times in total.
 
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Re: RB260GSP, sort circuit error

Sat Jul 10, 2021 3:45 pm

I do not know and really I do not understand why matter if is used to "extract" current than "inject"
I matters, because if it does not have isolation then it will also go into POE-IN port of any connected device - and in my case, it means that I cannot use this trick with devices that cannot withstand 30V.
 
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Re: RB260GSP, sort circuit error

Sat Jul 10, 2021 3:49 pm

(duplicate)
Last edited by rextended on Sat Jul 10, 2021 3:56 pm, edited 2 times in total.
 
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Re: RB260GSP, sort circuit error

Sat Jul 10, 2021 3:51 pm

The 1A max comes from the specs of the RB260GSP ( https://mikrotik.com/product/RB260GSP )
There is no power diagram, and no information on short burst overcurrent that is allowed. (What usually is the case.)
I only was thinking on the non-linearity of the voltage drop that a current limiter would introduce once you get near or at the current limit.
I'm not sure if that matters, but it does the same thing in forced "on" mode. Maybe the short circuit protection cannot be disabled by setting POE mode to "on". I do not see this documented anywhere, I'm just guessing.

This still does not explain why sw02 turns off its output, instead of sw01. The biggest difference is that sw01 is powered on the jack, and sw02 is powered on poe-in.
There seems to be some "logic" in the overcurrent protection, as some posts on this forum suggest to play with the "PoE Priority" to avoid some glltches in the PoE out of the port you want to protect, by allowing the PoE out interrupt on lower priority ports first, and gain some overcurrent trigger time.
(Lost the reference to the posts, could have been for Power Pro also !))

If there is no room for a power unit at Switch2, then a PoE injector near Switch1 on the line to the Switch2 might just give that little extra current to the PoE input.(2.5A versus 1A in extremis). But the comment in the UM suggests that the PoE_in to PoE_out connection is not as good as the power jack to PoE out.
I suspect the same. But it is not documented. Only option left is to try this. :-) I can only test this tomorrow, will come back with the results.

Thank you for your time!
Last edited by nagylzs on Sat Jul 10, 2021 4:35 pm, edited 1 time in total.
 
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Re: RB260GSP, sort circuit error

Sat Jul 10, 2021 3:56 pm

Ah, now I understand what you mean....
The male lan plug are isolated from power source.

Think, on normal way, if not isolated, are no matter on what side you put the device, or provide current to the standard "switch" or PC ethernet port...

Please find a time to correct topic title from sort to short... tanks... ;P
 
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Re: RB260GSP, short circuit error

Sat Jul 10, 2021 4:41 pm

The power drop on (wire1) (actually any wire) depends on the current. So at peak times the power drop may be significantly higher than in a steady state. Now, the overcurrent protection is likely implemented by monitoring (rapid) voltage drops (instead of current peaks). Which means a long (relatively high resistance) wire that is feeding power to your sw02 may lead to false-positive overcurrent events on the output ports.

Regarding RBGPOE "pairing" - check this post out: viewtopic.php?f=2&t=120841
 
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Re: RB260GSP, short circuit error

Sat Jul 10, 2021 4:45 pm

Regarding RBGPOE "pairing" - check this post out: viewtopic.php?f=2&t=120841
Fantastic!
 
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Re: RB260GSP, short circuit error

Sat Jul 10, 2021 8:22 pm

I wrote that 5 time (post #11, #13, #15, (#18) and #20),
And now is "Fantasctic" just because someone add a photo?

Work also on "smart PoE-out capable device" if the out on "smart PoE-out capable device" is forced,
because the "internal resistance" of the RBGPOE is not recognized from standard values.
 
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Re: RB260GSP, short circuit error

Sun Jul 11, 2021 4:28 pm

As I promised, I'm back with the results. I have tested the RB260GSP input/output characteristics in a lab.

Test environment:
  • Power supply is a precision laboratory power supply that is able to output 24V 20A. It also has adjustable overcurrent protection and adjustable output voltage.
  • I have added a variable resistor in series with the power supply, and then it went into the DC input jack of the RB260GSP switch. This resistor was simulating a longer ethernet cable on the POE-in line.
  • The test load on the POE-out side of the switch was a HAP-AC2 router.
Here are the results:
  • If the resistor is very small (<0.5 Ohm), then everything works fine
  • When the resistor reaches about 2Ohms, then the switch will detect "short circuit" and shut down its POE output.
  • This behaviour seems to be independent of the static voltage level. Does not matter if you use 12V input or 24V input or even 30V input. I have tried all of them.
  • It is clearly not a power supply problem - the lab power supply produced exactly the adjusted voltage, and it could have given 10 times the required power
  • I have also tired to add a 22000uF capacitor in paralel to the power input jack of the switch. This was helping a bit - then I could increase the resistance to about 3Ohms before it started to shut down its outputs.
  • When I circumvented the whole thing with POE injectors and splitters, then I could power up both devices. In fact, I could add another load resistor and I could easily power another 20W of load. I have also tried to turn off/on this load resistor periodically to see how it affects the switch and the router. Not suprisingly, the voltage was fluctuating, but the devices had no problem with that.
The conclusion is that RB260GSP measures the derivative of the power supply voltage. If it goes below a certain negative value, then it shuts down its power output. I strongly believe that the short circuit detection is faulty. It only works if the input power supply has very low internal resistance. When you are using POE-in to power the device, then the power supply will always have a higher internal resistance. (Well not always, but in all cases when POE input is needed anyway...)

It is very natural to have some voltage drop on longer POE cable. In fact, this should be expected! The short circut detection should be designed in a way that allows to use power supplies with higher internal resistance. POE works that way, by design. I understand that this would require current measurement on the POE-out ports, instead of voltage drop measurement over time. Such protection circuit would be more difficult to implement, and it would cost more.

Anyway, RB260GSP can only be cascaded only if its power supply (including the POE-in line) has a very low resistance (<0.5Ohm), e.g. connected with a very short ethernet cable. This is a fact. The use cases are very narrow. When you need to use POE to power a device, then almost always you will have a longer ethernet cable and that precludes cascading of these devices.

The rumours about using a different circuit for its DC input jack and POE-in jack are untrue. I have measured that too. There is no apparent difference between the two power inputs. The root of this myth is probably the way we are using DC input jacks - we tend to plug in a local power supply with a short cable, and that has a low internal resistance. So it would seem that the DC input jack behaves differently, but it is not.

The second sentence on the main product page ( https://mikrotik.com/product/RB260GSP ):

> Ports 2-5 can power other PoE capable devices with the same voltage as applied to the unit (passive PoE over datalines only).

The specification also says that the unit can be powered from POE-in. What it does not say is that you cannot do both. Technically you can, but only in very special, rare cases.

I think that this should be documented! In my concrete case, I have bought this device because - according to the specification - I was confident that I could cascade two of these devices. But in practice, I had to create this abnomination:

https://imgur.com/a/hxm0Xdx

Using the cables above, I can power 3-4 devices without problems. The power supply is fine. The power lines are fine. The power consumers are also fine and they are stable. The problem is clearly with the switch. In fact, I'm not using the POE part of the switch at all, simply because it does not work as it should.

I think that MikroTik should at least add a note about this in the product specification. I think that I'm not the only one who had problems with this. I really think that adding such note would be benefical for both MikroTik and for the customers.
 
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Re: RB260GSP, short circuit error

Sun Jul 11, 2021 5:14 pm

Do you know there should be a "Port1 PoE In Long Cable" setting on the System tab? See:
- https://wiki.mikrotik.com/wiki/SwOS/CSS106#System (for the current RB260GSP / CSS106 boxes)
- https://wiki.mikrotik.com/wiki/SwOS/RB2 ... SP_only.29 (for the older/original RB260GSP boxes)
 
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Re: RB260GSP, short circuit error

Sun Jul 11, 2021 5:56 pm

Do you know there should be a "Port1 PoE In Long Cable" setting on the System tab?
I did not know about that. I'll definitely try this, just I'm not sure when. (Probably tomorrow?) Then I'll come back with the test results again.

By the way, the input voltage sensor has at least 5% error. I have measured an actual input voltage of 13.2V (with a multimeter), but the switch displays 12.5V. I think that 5% is too much.

If this "long cable" setting works, then I'll be a happy camper! :-)
 
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Re: RB260GSP, short circuit error

Sun Jul 11, 2021 11:24 pm

The long cable setting works!
 
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Re: RB260GSP, short circuit error

Mon Jul 12, 2021 1:12 am

Nice laboratory checks @nagylzs.
And happy end txs to @andiys suggestion.

Not what one would expect by intuition ... :-) , but logical if compared to the experiments. (but not by the MT hint to prefer the DC plug)

Port1 PoE In Long Cable If enabled, it will turn off short detection on all PoE out ports to allow use of longer ethernet cables. This is potentially dangerous setting and should be used with caution. (CSS106-1G-4P-1S model)
 
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Re: RB260GSP, short circuit error

Sat Jul 17, 2021 3:13 pm

I wanted to share another interesting thing. When I connected the two switches with two RGBPOE on both sides, then I could only get a 100M full duplex link. When I removed one of the injectors, then I got 1Gbps link. I was experimenting this for a while. Always got 1Gbps link, except when there was an RGBPOE on both sides.

The "solution" was a workaround: I have used on of the spare POE output ports on the switch to extract power...

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