This is my first post here. Apologies, if it is not in right place.

This is a POE situation where the cable resistance is 4.5 ohms for each distance of about 40 meters.
Power required at each point is 12VDC 1A

We need power at 6 locations with total distance of about 250 meters.

Initially, I tried with 30V DC but I could not get power beyond second point.

Currently, I am trying with 60VAC 50Hz as input & getting a power circuit designed by local guy that will support input between 20VAC to 60VAC

My guy is unable to calculate the power requirements correctly, we are going on trial & error basis.

I thought I could post here to get directions.

My requirements are 12VDC 1A at 6 locations with resistance of cable given as in the image.

What is the best power input (Is 60VAC 50Hz Okay?) and what (circuit) should be at each location.

What will be voltage at each location?

My guy can design basic power circuit but cannot calculate.

Thanks a ton.

 

To get 12V at that last location, and taking that each location is drawing 1A, you would need to apply 1304V at the input
I fear you are going to have to re-think this system. Perhaps run an individual supply cable to each location. That would need a 66V source.

 

Dear Albert Hall,

Thank you for your reply.

Unfortunately, in this context, I cannot run another cable.

I have couple of queries.
1. For 60V AC how many locations would be supported?
2. Could you calculate voltage requirements for 2, 3, 4 or 5 locations?

Thx

 

1. If you have 60V AC (RMS?) input, what is the voltage requirement at each location (Peak or RMS)?
Will you need a rectifier, in which case we would need to subtract the diode voltages?

2. DC or AC?

If you have 6A total current flowing then the first run of cable will dissipate 324W. Will your ethernet cable support that current and amount of heat? Is the cable going to be in any sort of trunking which would restrict the cooling of the cable?

 

From: https://en.wikipedia.org/wiki/Power_over_Ethernet#Power_capacity_limits
"Category 5 cable uses 24 AWG conductors, which can safely carry 360 mA at 50 V according to the latest TIA ruling. The cable has eight conductors (only half of which are used for power) and therefore the absolute maximum power transmitted using direct current is 50 V × 0.360 A × 2 = 36 W. Considering the voltage drop after 100 m (330 ft), a PD would be able to receive 31.6 W. "

 

Well, for a guy not from the industry, and an end user, I will try to answer.

You are right about the CAT5 cable power carrying capacity.

60V AC with 6A is scary scenario.

I took few readings during our first trial.

Input is 33V AC for this trial
for 1 device -- 0.12A
for 2 devices -- 0.3A (voltage reading was 22V)
for 3 devices -- 0.41A (voltage reading 18V)
for 4 devices -- 0.57A (volrage reading 11.5V) (the device was not working & rebooting regularly)

My logic (being an engineer in a different discipline) is that maybe input voltages are not enough.

So, I asked the local guy to make 60V AC input and make a splitter that can take from 10V to 60V.

The peak usage is 12 watts. Nominal usage is 4-8 watts.

My guess is that 60V AC setup will give me 4 devices with overall current of about 0.5 A.

After first trial, I am hopeful that we will get at least 4 devices working.

We are going for another trial on this Saturday. I will post my results here. But I needed a theoretical confirmation on how many devices should this support.

"Will you need a rectifier, in which case we would need to subtract the diode voltages?"
Little out of my league But rectifier is required, because my local guys keeps talking about it.
(I dont know about power beyond voltage, current, resistance, watts and ohms law that I studied when I was a kid)


Note: we can have CAT5 cable custom manufactured to our specification.