Measuring output current (%load) of DC Power Supply

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Naveed

We have three parallel power supplies (output: 20Vdc/20A each). Some new consumers will also use this power supply. We have to calculate current output current for each power supply to know loading on each power supply on a running system.

Please advise how to calculate / measure load on DC power supply. We have three SL20.100 (PULS) supplies in parallel configuration. Each power supply rated 24Vdc / 20A. Since new consumers have to be connected to these power supplies with total load of about 3A. We don't know what is the current load on these supplies and will they be able to handle additional load.

Please advise how it can be measured without shutting down any power supply or removing any wiring.
 
S
Typically a DC supply will measure its own current internally for control and display purposes, with a shunt, which is essentially a resistor of very small but very precisely calibrated ohm value. Typically, they'll produce a voltage drop of either 50 or 100mv at the nameplate rating of the shunt, which will obviously be the same as or somewhat larger than the nameplate rating of the DC supply.

The supply may already be equipped with interface electronics to give you a signal proportional to amps in a more customary usable format such as 0-10V or 4-20ma, often isolated from its internal electronics. If not, you can purchase a signal isolator with an appropriate mv scaled input and either use their shunt wiring or add your own in parallel. By its nature the shunt is a very stiff signal source and you adding your wiring will not change the signal going to the control electronics of the supply, as long as you use the isolator.

If you just need to make a one time measurement, you can just get an accurate, calibrated DMM and measure the shunt drop directly, assuming the voltage to ground is safe for you to do so, and do the calculations yourself. You'll still need to know the shunt full-scale ratings for mv and amps.
 
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