Buffalo power Adapters : Buffalo Technology
12-volt power adapter onto

Buffalo power Adapters

When I was looking for a new hard disk for my Network-attached storage (aka NAS), I found the startup current of Seagate ST2000DM001 (aka Barracuda or Desktop HDD) in my Buffalo HD-LX2TU3 is 2.5A and output current of the adapter is 1.5A. It requires 67% higher than the adapter could offer. Is it safe use of electricity usage and okay to my hard disk?

I didn’t know and decide to research.

Back to basic, let’s begin from knowing Ac adapter.

Originally, most AC/DC adapters were linear power supplies, containing a transformer to convert the mains electricity voltage to a lower voltage, a rectifier to convert it to pulsating DC, and a filter to smooth the pulsating waveform to DC, with residual ripple variations small enough to leave the powered device unaffected… Wiki: AC Adapter

An AC adapter has fix amount of capacitor, the main purpose of it is to provide fix and steady voltage. If the capacitor is dead, the power adapter won’t be able to provide steady voltage.

Also according to , it may provide lower than the calculate current with fix voltage.

if you were to use a scope on a motor you would see why we say inrush and startup are not the same. Stick a scope on your motor…pull in the contactor…wham …very high current with very short duration. Afterall…a motor winding is just a short circuit until current causes a magnetic field to build. But the motor isn’t even spinning yet, is it? Now comes startup current and time that is different from inrush and must be dealt with differently. Take a 1hp motor at 480 without anything attached to the shaft. Measure it with a scope. You have inrush ..then the motor spins up to speed and during that period decreasing curve current flows until at rated speed. Now put a load on. Inrush current/time stays exactly the same…but your overall starting current/time curve is totally different and is load based… Switchman from IHS GlobalSpec CR4: Inrush Current and StartUp Current

When an UPS is switched from Line to battery (and yes it can take several millisectons) the Inrush current is not a factor. The reason is that durning this switch over time the computer Power is not switched off. The Capacitors inside the PSU will supply the power for this duration. You might see some perabations on the output lines but they would be small. Inrush currents are normally due to the capacitance in the load charging being at 0 Volts and appears as a short circuit decreasing to an open in 5 time constants.

Even with a PFC circuit, the inruch current amplitute and duration is depentent on the load characteristics. Setting the MAX rating to 3 to 4 times rated is not abnormal… RetiredChief in Tom’s Hardware: Forum: How Many Amps for This Power Supply?

When components needs more current (aka inrush current), because the watt is fixed at design time, the voltage needs to be decrease. The temperature also increase immediately due to the inrush current according to EXTENDING THE LIFE OF POWER FACTOR CAPACITORS by John Houdek.

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