mrpackethead
Full time elf
Heres my problem,
The front end of most SMPS is a bridge rectifier and a set of caps. When you first turn them on, the "inrush" current to charge the caps can be 10-20x times the normal run time current.. Typically just for the first half wave of AC. So, a 350W supply might be as much as 30A.. If you turn on 20 of these together, you've got 600A, and it will trip your circuit breakers for sure.
What i need is a way to "soft-start" the power supply; so that i can reduce the load;
Options I can see.
(1) Stagger the turn on.. so, that they are just turning on one at a time; thuse reducing the total inrush current to a point where its probably ok.
(2) Use power supplies with "soft start" on them.. Typically seem to be much more expensive.
(3) Use A NTC device in series with the power supply. The theory behind this is that the NTC ( negetive temperture co-efficent ) resistor has a high resistance when cold, and a low reistance when hot. When you first turn on, its cold, so it effectively limits the current to a low value, as it warms up ( because its dumping power ), its reistance drops ( to a very low value ).. The effect of using this, is that the current draw on turn on is drastically reduced. .( it does mena that the power supply will also take longer to "turn on", but thats not really a bit problem ( we are taking 1-2 seconds rather than .05 sec ).
There is a problem however, with these.. If you turn the power off, the NTC is still hot for up to 60 seconds.. If the power comes on during this period, they offer no in-rush protection.. ( becuase they are in their low reistance state ).
So, i need a "power lock out". if the power goes off, its got to stay off untill i manaully reset it..
Does anyone have any practical experience around this problem?
The front end of most SMPS is a bridge rectifier and a set of caps. When you first turn them on, the "inrush" current to charge the caps can be 10-20x times the normal run time current.. Typically just for the first half wave of AC. So, a 350W supply might be as much as 30A.. If you turn on 20 of these together, you've got 600A, and it will trip your circuit breakers for sure.
What i need is a way to "soft-start" the power supply; so that i can reduce the load;
Options I can see.
(1) Stagger the turn on.. so, that they are just turning on one at a time; thuse reducing the total inrush current to a point where its probably ok.
(2) Use power supplies with "soft start" on them.. Typically seem to be much more expensive.
(3) Use A NTC device in series with the power supply. The theory behind this is that the NTC ( negetive temperture co-efficent ) resistor has a high resistance when cold, and a low reistance when hot. When you first turn on, its cold, so it effectively limits the current to a low value, as it warms up ( because its dumping power ), its reistance drops ( to a very low value ).. The effect of using this, is that the current draw on turn on is drastically reduced. .( it does mena that the power supply will also take longer to "turn on", but thats not really a bit problem ( we are taking 1-2 seconds rather than .05 sec ).
There is a problem however, with these.. If you turn the power off, the NTC is still hot for up to 60 seconds.. If the power comes on during this period, they offer no in-rush protection.. ( becuase they are in their low reistance state ).
So, i need a "power lock out". if the power goes off, its got to stay off untill i manaully reset it..
Does anyone have any practical experience around this problem?