Products > Test Equipment
Include a NTC Current Limiter in my DIY AC PSU Chain?
t1d:
I am building my DIY AC PSU chain. It consists of:
1) Emergency All Stop Button to
2) Isolation Transformer to
3) Variable Autotransformer to
4) Dim Bulb Current Limiter (Multi-Bulb) to
5) DUT.
Each piece is independent, so that it can be used separately, if need be, for other purposes.
Might it be helpful to include a NTC Current Limiter? Advantages/Disadvantages? If so, which component should I add it to? The input on the Dim Bulb Current Limiter? It sort of seems redundant, unless all the bulbs are bypassed...
Thank you for your help.
Randall:
Bump !
I'm very interested in this question ????
Lookin' forward to a response.....
thm_w:
The bulb is already going to limit current, I wouldn't bother.
If you need to ramp up the voltage then you have an autotransformer that can be turned slowly.
srb1954:
--- Quote from: thm_w on October 06, 2022, 09:38:06 pm ---The bulb is already going to limit current, I wouldn't bother.
--- End quote ---
The dim bulb will eventually limit the current but it will let through quite a high surge or fault current until the filament has come up to temperature. An extra NTC resistor can compensate for this behaviour by ensuring that there is sufficient initial circuit resistance to limit the peak surge current.
--- Quote ---If you need to ramp up the voltage then you have an autotransformer that can be turned slowly.
--- End quote ---
That doesn't always work well with equipment incorporating switch-mode PSUs. These typically have an under-voltage lock-out and won't start until the mains supply reaches a certain level. At which point the switcher will suddenly become active and draws its maximum rated current as it attempts to deliver its rated power to the load. Or, if there is a fault in the PSU, the current draw is only limited by the relatively low impedance of the auto-transformer windings. A dim bulb tester is often better in this situation as it will allow the switch-mode PSU to start up quickly but limit the total current draw to safe levels if there is a fault condition in the PSU.
coppercone2:
you might find this thread useful
https://www.eevblog.com/forum/repair/current-limiter-box-for-repairs/
I stopped working on it because I just have not needed one
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