| Electronics > Beginners |
| Question about start up current |
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| Electro Fan:
Is there any general trend or rule of thumb for circuit design with respect to accommodating startup (or "in rush") current? For example, if a given circuit requires 1 Amp maximum on a normal basis after turn-on, is there some reason to design the power supply to support 2x (2 Amps) of current during startup? Is there really a need or reason to build a power supply to handle some excess current capacity (beyond the normal current consumed after startup)? If so, what is happening to the excess current during startup? Charging capacitors? Something else? I'm sure it's somewhat circuit specific but any general guidance would be helpful. PS, these questions are driven mostly by an interest in DC circuits powered by an AC to DC power supply (typically in the 5 - 30V DC range), so maybe the startup considerations are different for AC, or motors, etc. For starters, I'm just trying to understand the need to power relatively simple DC circuits. Thx Thanks |
| soldar:
No. Each circuit is different and has to be considered on its own. Some circuits can have no inrush current (over normal operating current) and soe can have tens or hundreds times ore and mainly be limited by the resistance of the wires feeding it. Are you thinking of any circuit in particular? |
| Zero999:
There really isn't enough information here to say. A large DC motor will draw an enormous current on start-up. An LED rope light will draw no more current on start up, than it does in normal operation. |
| David Hess:
Safe power supplies are designed to start into any load without damage. One place there can be trouble however is if a power supply uses fold-back current limiting, it may not be able to start into a heavy load. Most loads however do not draw high current at low voltages so this is rarely a problem. If it is a problem, then the fold-back current limiting circuit needs to be adjusted to take this into account. |
| Electro Fan:
--- Quote from: soldar on June 01, 2019, 09:27:03 pm ---No. Each circuit is different and has to be considered on its own. Some circuits can have no inrush current (over normal operating current) and soe can have tens or hundreds times ore and mainly be limited by the resistance of the wires feeding it. Are you thinking of any circuit in particular? --- End quote --- What got me thinking about it is was a GPSDO that I saw spec'd as having 2.5A inrush current but only needing about 0.3 - 0.6A normal operating current. I realize motors are likely different than non-motorized electronics but I'm trying to understand what are typical non-motorized reasons that startup (inrush) requirements might be higher than normal operating current requirements. No big project here, just trying to understand the types of things (other than motors and mechanical devices) that would dictate additional current overhead capability in a DC power supply. |
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