# Cambium 670 electrical power usage

We are building a wind turbine backup power supply for our Cambium 670 microwave links located on towers here in Hawaii. I've researched the Cambium 670 manual and cannot find any refererence to the actual wattage used by the 670 powered by the enhanced AC/DC power supply. I need this info to complete the turbine specs. Any help in this matter would be greatly appreciated.

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The PTP 50670 ODU uses about 30 W.

You need to add the power disspated in the cable. The power used to heat the cable depends on the supply voltage, the resistance per unit length, and the length of the cable. If the length is only a few feet, you can ignore cable losses.

If you're powering the AC+DC Enhanced Power Injector (EPI) from DC, then no power is lost in the EPI. On the other hand, if you're powering from AC, you need to allow for the 90% efficiency of the power converter.

As an example, consider AC power to the EPI, and 50 m of standard Cat5e cable at 6.25 ohms/100 m:

EPI output voltage = 57 V
Cable resistance = 0.0625 ohms/m
Cable length = 50 m
Total cable resistance = 0.0625 x 50 = 3.13 ohms
Current = 0.542 A
ODU voltage = 55.30 V
ODU power = 0.542 x 55.3 = 30.00 W
Cable power = 0.542 x 0.542 x 3.13 = 0.92 W
Power output of EPI = 30 + 0.92 = 30.92 W
Efficiency 90%
Power input to EPI = 30.92/0.9 = 34.36 W

If you allow 35 W input to the EPI, this should be sufficient. You will need more power for cables longer than 50 m.

By the way, the only tricky bit of the calculation is the current, where you need to solve a quadratic.

Please let us know how the project progresses!

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