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wesleyna
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Power loss on PowerboxPro ports

Tue Oct 30, 2018 8:59 am

Hi There,

We have a new High site that we have put up, units installed are as follows:
Powerbox Pro
LHG5AC
LHG5XL AC
MANTBOX15
The Cable run is a estimated between 50-60meters, we have used shielded CAT5 cable and powering with the original 24V 2.5A PSU and the gigabit POE injector.

The issue is, if we put a large amount of traffic on either of the LHG units, all three devices on the powerbox go off. If the Sector is switched off, we dont get any drops. I have checked the voltage and this is what we get:
1 device switched on: 22V
2 devices switched on: 18.5V
3 devices switched on: 15V

If I do a bwtest download test from the tower, the voltage drops to around 14V before all 3 units switch off again.

What are our options to resolve this? Run the powerbox directly on the DC jack? use CAT6 shielded cable? I considered 48V PSU, but that would pop the LHG's and the Sector.
 
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mohannad
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Re: Power loss on PowerboxPro ports

Tue Oct 30, 2018 10:01 am

Hello
First Try To Use a Good Quality Copper cable Cat6 second if the issue still the same change the adapter try to use 4A or more if you have it should be solved and the most important of all keep update the RB
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vecernik87
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Re: Power loss on PowerboxPro ports

Tue Oct 30, 2018 10:17 am

9W (Powerbox Pro)
8W (LHG5AC)
8W (LHG5XL AC)
13W (MANTBOX15)

Total = 9+8+8+13 = 38W
If your PSU supplies 24V, it will be 38/24= 1.5A flowing through 50 meters of wire (does not matter if Cat or DC)
to achieve less than 10V loss on such wire, you would need 10/1.5 = 6 Ohm or less over 2*50 meters (you must count both ways as the voltage loss happens on both branches of circuit). That is max 18 Ohm per 1000ft or 60 Ohm per 1000m.

Also, keep in mind this calculation is for perfect PSU which will give 24V all the time. Real PSU will decrease voltage when you increase current due to internal resistance so your devices might actually draw even more amps...

So, do not blindly install cat6 cable because cat6 does not guarantee low resistance. You need to find cable which will fit your requirements with low resistance.
With that in mind, you will find that you got not much choice - If I remember correctly typical Cat6 cable is 23AWG or more which has around 20 Ohms per 1000 feet (if it is pure copper, cheaper copper/aluminium versions would be around 30 Ohm per 1000 feets).
As you suggested, running from DC jack would be an option because it is easy to get normal DC wire with 20AWG or less.
Another option might be:
- running separate cable with full AC voltage and put your PSU up on tower.
- running 48V passive/af/at or to the tower and convert it down to 24V but that will cause another loss of power...
not sure if there are other options
 
mistry7
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Re: Power loss on PowerboxPro ports

Tue Oct 30, 2018 10:27 am

9W (Powerbox Pro)
8W (LHG5AC)
8W (LHG5XL AC)
13W (MANTBOX15)

Total = 9+8+8+13 = 38W
If your PSU supplies 24V, it will be 38/24= 1.5A flowing through 50 meters of wire (does not matter if Cat or DC)
to achieve less than 10V loss on such wire, you would need 10/1.5 = 6 Ohm or less over 2*50 meters (you must count both ways as the voltage loss happens on both branches of circuit). That is max 18 Ohm per 1000ft or 60 Ohm per 1000m.

Also, keep in mind this calculation is for perfect PSU which will give 24V all the time. Real PSU will decrease voltage when you increase current due to internal resistance so your devices might actually draw even more amps...

So, do not blindly install cat6 cable because cat6 does not guarantee low resistance. You need to find cable which will fit your requirements with low resistance.
With that in mind, you will find that you got not much choice - If I remember correctly typical Cat6 cable is 23AWG or more which has around 20 Ohms per 1000 feet (if it is pure copper, cheaper copper/aluminium versions would be around 30 Ohm per 1000 feets).
As you suggested, running from DC jack would be an option because it is easy to get normal DC wire with 20AWG or less.
Another option might be:
- running separate cable with full AC voltage and put your PSU up on tower.
- running 48V passive/af/at or to the tower and convert it down to 24V but that will cause another loss of power...
not sure if there are other options
@ vecernik87

Thats not the real usage Power draws.....

Powerbox takes 2,5-3,5W
LHG (both Models) about 3-4W, Mantbox the same (with SFP in use more)

But the Problem is the Bad cable, we often use 40-50m for passive POE, but not with low cost cables.......
 
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mohannad
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Re: Power loss on PowerboxPro ports

Tue Oct 30, 2018 10:32 am

Bro Try What i Recommended and feed me back
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vecernik87
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Re: Power loss on PowerboxPro ports

Tue Oct 30, 2018 11:13 am

@mistry7
I know that real power consumption will be most of the time lower than maximum. But thats how you design electrical circuits. Not by real usage but by maximum. Those devices are certified for some power and you need to accept that under some circumstances, they MAY reach that power consumption. You don't want your tower to die randomly. (Or maybe you want, in that case ignore my recommendation)
I fully agree that bad cable makes things worse and getting better cable may make it better. What I am trying to point out is simple physics which you can't avoid - bad vs good cable in networking technology usually focus only on attenuation, interference etc... But in this case you need to focus on resistance which is practically irrelevant for networking. If you get some fancy Cat6 with 30AWG, I guarantee it will work worse than Cat5 with 22AWG in terms of POE. That is not something "bro trust me". That is physics. To transfer energy, you need low resistance. To achieve low resistance you need to have good material (pure copper instead of cu/al mix) and increase wire cross-sectional area. To increase cross-sectional area you need wider diameter. Wider diameter = lower number on AWG scale. Cat5/5e/6/6a/7 has nothing to do with it because category does not specify resistance or wire gauge.

I meant just good advice. Final decision will be on you anyway.
 
wesleyna
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Re: Power loss on PowerboxPro ports

Tue Oct 30, 2018 11:48 am

Bro Try What i Recommended and feed me back
Thanks, I've contacted my local suppliers now to see if that have any cable that will work. If not I think I might just end up running direct power up to the top of the building.

The other issue is that we running next to alot of other cables(power I think, Cell tower cables( not sure what) and network cabling) over 6 stories. I suspect that could also be playing a role?
 
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vecernik87
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Re: Power loss on PowerboxPro ports

Tue Oct 30, 2018 12:17 pm

The other issue is that we running next to alot of other cables(power I think, Cell tower cables( not sure what) and network cabling) over 6 stories. I suspect that could also be playing a role?
Other cabling (AC/DC/networks/antennas) can interfere with your ethernet (thats why shielded cable would be better) but not with POE/DC. The inducted power is not that strong to overpower several watts of power from your PSU
 
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mohannad
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Re: Power loss on PowerboxPro ports

Tue Oct 30, 2018 1:37 pm

If its high voltage it might make interference but if they are normal power cables electrical cables there effect is neglected
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garlicbulb
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Re: Power loss on PowerboxPro ports

Tue Oct 30, 2018 4:49 pm

We just installed a similar setup although our run is shorter.. 24V is not the "golden rule:. We used a 30V supply for the POE We thought about 48V. The PowerboxPro is rated to 57V but our radios (non Mikrotik) couldn't take that much.

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