fuse blowing on power supply

[Holty]

Hi
My first thread in this section. I am not knowledgeable in electronics, so thought you could give me some help.
I have an Antelope Audio Voltikus power supply that powers a dac, which is 18 volts. The power supply has two fuses and it looks like only one of them is blowing, roughly every three to four weeks. I have kept a log of times and which one blows. When i power it down the light goes out slowly, but it is on power up there is nothing, when the fuse blows.

It has been back to the manufacturer once and now it looks like it will be going again. The fuses were changed from 0.8a-250v time delay to 0.5a-250v time delay when it was last back.

Thanks Jim.

[AndrewT]

keep returning it till the retailer decides to refund or replace.

Make sure they pay postage both ways.

[Triodethom]

Originally Posted by AndrewT

keep returning it till the retailer decides to refund or replace.

Make sure they pay postage both ways.

Totally agree let them fix it or replace it .

[Osvaldo de Banfield]

Try running this apparatus on a series with an incandescent light bulb of about ten times the power drained from this power supply. Observe the filament bright each time the supply is turned on. There may be a short overload at turn on, or the fuse is too close to the initial current surge.

[AndrewT]

A T rated fuse (or any fuse) passes a short term current that is many times the rated current.

I would expect the equipment to draw a start up current that far exceeds the normal operating current. The correct fuse would be to allow operation during times of maximum demand. This size of fuse would then allow the larger start up pulse.

An example of this is the use of soft start for transformers.
A 240VA 240Vac transformer will run on a T1A fuse. This fuse will pass 10Apk for a very short period. It will even pass 50Apk if the period is short enough.
This transient pass ability is what allows equipment to start. Match the start current to the start period and the fuse survives, many hundreds of restarts. A 100r resistor will probably allow the T1A fuse to survive using a soft start circuit. The maximum start transient current can't be higher than about 3.4Apk and that can only last a few tens of ms.

[Triodethom]

1. the manual states .8a t fuse but the factory used .5a t fuse .
2. Do both fuses blow or just one and is it always the same one ?
3. Given the slow turn off of the light there may be a problem with the bled (drain) resistor.
4. Have you monitor the ac line voltage at the time of the problem given only every 3 to 4 weeks what time of the day does it happen ?

[DF96]

The bleed resistor is unlikely to be the problem. Slow turn off means high value, which means less load.

If the unit works OK then try a 1A fuse. Triodethom's idea of checking mains voltage is also worth doing, as this seems to vary more than it used to in many countries.

[Osvaldo de Banfield]

Originally Posted by AndrewT

A T rated fuse (or any fuse) passes a short term current that is many times the rated current.

I would expect the equipment to draw a start up current that far exceeds the normal operating current. The correct fuse would be to allow operation during times of maximum demand. This size of fuse would then allow the larger start up pulse.

An example of this is the use of soft start for transformers.
A 240VA 240Vac transformer will run on a T1A fuse. This fuse will pass 10Apk for a very short period. It will even pass 50Apk if the period is short enough.
This transient pass ability is what allows equipment to start. Match the start current to the start period and the fuse survives, many hundreds of restarts. A 100r resistor will probably allow the T1A fuse to survive using a soft start circuit. The maximum start transient current can't be higher than about 3.4Apk and that can only last a few tens of ms.

It is the so called "I²t", of fuses and thyristors.

[AndrewT]

Originally Posted by Osvaldo de Banfield

........................ or the fuse is too close to the initial current surge.

Originally Posted by Osvaldo de Banfield

It is the so called "I²t", of fuses and thyristors.

If you know the second, then why suggest the first?

[Osvaldo de Banfield]

Originally Posted by AndrewT

If you know the second, then why suggest the first?

Depending on the load type (Capacitive or inductive), a initial current sourge can appear on the input line, as in the case of mains rectifier in SMPS, PC monitors, motor inverters, etc, and if the fuse rating may be overloaded if, for example, the set is used in 110 or 220V mains, as the peack is bigger as mains voltage is bigger. Also, some old sets has a auto 110/220 switching arround AVS08 ST CI and TRIAC, and if this circuit is malfunctioning, it can cause sporadic fuse blown (By example, if the low voltage smooting cap for this IC is dry).

This is the reason for suggest the series lamp test.