Inrush current circuit
- Thread starter Wayne
- Start date
My friend Rod in Australia says you should only use a thermistor or resistor in the power supply line if you have a relay to take them out of the circuit after they do their job of limiting current for a few cycles (in rush). The reason for this is heating cycles will cause degradation of the device over time, causing spectacular failure. This goes along with Joe's comment above about added resistance, which would be eliminated with a relay.
He shows a few circuits using a charging capacitor to time the cycles, but there are other ways to do this, as mentioned above.
He shows a few circuits using a charging capacitor to time the cycles, but there are other ways to do this, as mentioned above.
In my research if found Rod Elliot doesn’t like that stand alone idea at all he says
“ Many people like the idea of using NTC (negative temperature coefficient) thermistors for inrush limiting, with a common claim being that no additional circuitry is needed. For any product that does not draw consistent high power at all times, in a word, don't. Controversial? Not really - just because they are used by a number of major manufacturers doesn't always mean they'll be alright. If used in a switched system as described here, they are safe and reliable, but I have personally seen (yes, with my very own eyes) NTC thermistors explode mightily if there is a fault. Resistors can also fail, but the failure is (usually) contained - there are exceptions of course. In general, NTC thermistors are designed for very high peak current, but as noted earlier, you will see many different ways to describe the same thing, with almost no commonality between makers. To be genuinely useful, thermistors must be bypassed after the inrush event has ended.
You may enjoy Reading his tread on the subject I value a lot what he has amalgamated on his web site. Not everything is in line with my ideas but most is.
https://sound-au.com/articles/soft-start.htm
I am building a triple toroidal transformer amp with total 1950va. So limit the inrush and deal with bussing in the core created by DC in the core I have ordered this combo PCB for Combined Soft Start (inrush current limiter) & DC Blocker (trap, filter)
It uses wire wound resistors of which I will likely switch the NTC thermistors
Let you know if it works next year
It uses wire wound resistors of which I will likely switch the NTC thermistors
Let you know if it works next year
Attachments
Toroids are different from EI transformers since Toroids lack the inherent gapping of the core which exists in EI laminations. The remanence of a toroid core can be very high, depending on where the last turn off cycle ended with respect to the AC line. Thus at startup, you also have that random chance that the core was left in a remanence state that aligns with the first startup cycle and it drives the core into saturation. This presents an effective short to the line on the first half cycle before later recovering.
Soft starts are effective in this situation.
Soft starts are effective in this situation.
- Joined
- Jan 14, 2011
- Messages
- 74,216
- Location
- Gillette, Wyo.
- Tagline
- Halfbiass...Electron Herder and Backass Woof
- Joined
- Jan 14, 2011
- Messages
- 74,216
- Location
- Gillette, Wyo.
- Tagline
- Halfbiass...Electron Herder and Backass Woof
- Joined
- Jan 14, 2011
- Messages
- 74,216
- Location
- Gillette, Wyo.
- Tagline
- Halfbiass...Electron Herder and Backass Woof