Although to be really safe you could never turn the amp on 
A 5 year old who's been specifically told not to.
And yes, it happens. Happened to a build I did for a friend. I said that's the one thing that could not be done and that's exactly what his kid did.
I usually hand out a set of spare fuses just in case. Turns out, one was needed.
That approach seems to be the most conservative and safest of all. Unlike an NTC, a power resistor can be cycled five or ten times in rapid succession, and provide inrush protection each time. (An NTC would remain hot, thus low resistance, allowing huge inrush on power cycles #2 thru #10). If the relay fails, the power resistor heats both itself and the thermal fuse, so the thermal fuse opens, protecting the amplifier and giving you a chance to replace the bad relay and the popped thermal fuse.
Would you please draw a big red arrow on your photograph, showing the location of the thermal fuse? I can't seem to find it.
I use a thermistor which I then short out with a relay. Thermistors designed for mains protection can handle very high energies for short periods and they are compact.
Personally, I would not just rely on a thermistor on its own for an application like an audio amplifier. Thermistors work best where the load is very well defined and you can guarantee that after some period the thermistor resistance would have reduced to the point where the dissipation would be acceptable.
These guys have some useful products and information Inrush Current Limiters - Thermistors | Ametherm
Personally, I would not just rely on a thermistor on its own for an application like an audio amplifier. Thermistors work best where the load is very well defined and you can guarantee that after some period the thermistor resistance would have reduced to the point where the dissipation would be acceptable.
These guys have some useful products and information Inrush Current Limiters - Thermistors | Ametherm
The datasheets usually only give two or three points on the (X=current, Y=resistance) plot. It's up to you to interpolate or to measure it yourself in the lab.
Here are a couple of examples
https://www.mouser.com/datasheet/2/600/SL1560002-276470.pdf
https://www.mouser.com/datasheet/2/18/AAS-920-325D-Thermometrics-NTC-Inrush-031814-web-1315885.pdf
_
Here are a couple of examples
https://www.mouser.com/datasheet/2/600/SL1560002-276470.pdf
https://www.mouser.com/datasheet/2/18/AAS-920-325D-Thermometrics-NTC-Inrush-031814-web-1315885.pdf
_
Last edited:
We really need to look at what's happening with the peak currents into the transformer to decide whether its DC on the mains, or the core is possibly saturating on the peaks.
Seems to me just slapping a 2 ohm in series with the primary to reduce noise is hardly a robust way to solve this issue.
You could try getting hold of a current transformer and monitoring the output on a scope for example.
Seems to me just slapping a 2 ohm in series with the primary to reduce noise is hardly a robust way to solve this issue.
You could try getting hold of a current transformer and monitoring the output on a scope for example.
A low inductance in series with a rectifier reduces charging current spikes and widens them. As said, the initial inrush current can be controlled with a wirewound resistor that is shorted as soon as system reaches stability. This can be done using a thyristor if an inductor is used after a rectifier bridge. If not, a triac or mechanical relay can be used.
I bought it on eBay. It's a Chinese made kit. In the working principle, it says, "When the power is turned on, power is supplied to the load through a negative temperature coefficient thermistor, as the thermistor temperature increases, the resistance drops, the voltage rises slowly, thus effectively inhibiting the inrush current impact on the line and other electrical appliances. About 2 seconds after the relay ttracts gathers, short circuit thermistor, the power supply through the relay contacts directly to the load, the load into the normal working condition."
Funny, I thought it was "Is inrush current limiter responsible for quieter power transformer?"
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.