Hi all
I just have a question.
I plan to use a regulated power supply capable of delivering 4.5A at 12v.
I will then add a 4A fuse, then a serious amount of additional capacitance at the output. At least 20,000uF, but divided into multiple various value electrolytic and ceramic caps.
I just need to know how I can add as much capacitance at the output without blowing the fuse any time I switch it on.
Is there anything I can do to counter the startup surge?
I just have a question.
I plan to use a regulated power supply capable of delivering 4.5A at 12v.
I will then add a 4A fuse, then a serious amount of additional capacitance at the output. At least 20,000uF, but divided into multiple various value electrolytic and ceramic caps.
I just need to know how I can add as much capacitance at the output without blowing the fuse any time I switch it on.
Is there anything I can do to counter the startup surge?
try a slow blow fuse
if you are worried about rasing the output impeadence of the regulator, the fuse should be in front of the regulator.
I have worked on tons of industrial equipment and there was always several layers of protection.
A breaker or fuse on the AC input side,
A large fuse usually 50% or 100% larger than the rated power supply ie 7 or 10 amp fuse for a 5 amp power supply,
A smaller fuse very close to the rated power supply,
sometimes a combination of slow blow and fast blow fuses,
the power supply and all of its electronic protection if any,
and an output fuse.
For very large currents 25 to 150 amps or more there was generally no output fuse.
if you are worried about rasing the output impeadence of the regulator, the fuse should be in front of the regulator.
I have worked on tons of industrial equipment and there was always several layers of protection.
A breaker or fuse on the AC input side,
A large fuse usually 50% or 100% larger than the rated power supply ie 7 or 10 amp fuse for a 5 amp power supply,
A smaller fuse very close to the rated power supply,
sometimes a combination of slow blow and fast blow fuses,
the power supply and all of its electronic protection if any,
and an output fuse.
For very large currents 25 to 150 amps or more there was generally no output fuse.
Thanks for your help multisync.
I do plan to put the fuse at the front of the regulator. I will keep the unit switched on most of the time, to minimize the number of times I have to charge up the output caps. A 4A slow blow fuse may work, the regulator can deliver 4.5A, so I won't be putting it at risk.
I do plan to put the fuse at the front of the regulator. I will keep the unit switched on most of the time, to minimize the number of times I have to charge up the output caps. A 4A slow blow fuse may work, the regulator can deliver 4.5A, so I won't be putting it at risk.
Is this a linear type PSU or a "laptop type" smps ? If the latter then it may well limit or go into some foldback limiting automatically if the capacitance appears more like a short to it. If the former, then adding a limiter within the feedback loop of the regulator would take care of any problems.
well if Ic = C * dV / dT you know how fast (or slow) you should let the voltage get to final value. 4A fuse dictates: dT = 20 000uF * 12V / 4A which is 60ms. Your regulated supply may not let you slow it down that much, if any at all. ?
So to be safe add some limiting series element that you short out after a short time, say a few seconds to be conservative.
So to be safe add some limiting series element that you short out after a short time, say a few seconds to be conservative.
btw. your PS probably handles short bursts of overcurrent so in practice there may not be any issues. But what if it's output rises to 12V in 1ms? The required current will be: Ic= 20 000uF * 12V / 1ms = 240A... But in reality you wont see that much, the risetime will be slowed down by the PS' current limit / internal resistance.
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