When using an RB750UP or OmniTik UPA with the stock 2.5A power supply, we often see a voltage drop to as low as 20V on some of our installations with longer Cat5 runs, and it appears to be affecting the stability of some of our point-to-point links.
Are there any caveats to using a 24V/3A (or 4A or 5A) power supply in these situations? Is there much risk to overheating the Cat5 (24 AWG solid-conductor, foil-shieded CMX) at those power levels?
one caveat - voltage at the end of the line will be the same as with lower amperage PSU, what you need is - higher voltage PSU, something like 28V - 30V so one longer leads when voltage drops over line - you get usable voltage of MAX 28V for RB750UP (it will work also with 30V at the router, but that is not recommended for prolonged use of hardware)
With higher current availability, wouldn’t the voltage drop be reduced?
no, only side effect might be that there are less fluctuation of voltage due to power consumption/loss patterns, but that depends highly on PSU and properties of the cable you are using.
Higher voltage on the other hand will reduce current over cable and thus, reduce losses, since losses are only there due to current becoming higher.
In that case, I’ll look through a pile of laptop chargers for something around 28V/3A.
Voltage drop is mostly consistent over the same distance given the same input voltage and wire. There is a minimal impact of current consumed but it is really insignificant. Higher voltage will have less of a drop, and less loss energy loss due to resistance of high gauge wire.
Better explained here.
http://www.calculator.net/voltage-drop-calculator.html
http://beyond-wifi.com/poe/poe-calc.html
What is not shown is the conversion deficiencies of the on board voltage regulator of the routerboards.
Use a PSU with batteries , less drop on the psu side and also a higher voltage of 27.6V
What length is ..longer Cat5 runs..?
Also as a test you could simply attach two 12volt batteries in series = 24V close to RB750UP or OmniTik UPA and check stability of the link,
If stability is the same then you don’t have a issue with power supply voltage drop,
If using the batteries you have no stabilty issues then I would check AC voltage and are you using a UPS to give a clean AC supply to the dc power supplies.
Around 100’ to the OmniTik UPA, then another 100’ to the most distant unit (the others are 20-80’ away).
Is that 100 ft about 30meters or 100 meters?
30m (100ft.)
Do you use AWG24 cable ?
Patchcables are only AWG26 and with 30 meters of cable you will get problems..