exploding fuses ??

[Buhl]

I dont know if this question should have been in the solid state forum, bute its related to my zen 4 amp.....

Im in the proces of assembling the powersupply, and when i connect the toroidial transformer to the mains, my fuse between mains and the transformer blows, with a 3,15 amp fuse it explodes with a loud bang !

I have not connected the secondarys of the transformer, so there is no shorting there.

I measure about 1 ohm across the trafos primarys - that should be ok ?
It also seems that the secondaries ate mesuring properly - i have close to 0 ohms acros two pairs of secondaries.

What is wrong - anybody ??

Thanx alot in advance !

Cheers !

Hans Houmøller

[Hans B]

Hi Hans

There are two types of fuses - fast blowing fuses (in danish "flinke") and slow blowing fuses (in danish "træge"), and I think that you might be using the fast blowing fuse. I had the same problem with my torodial in the beginning - but then switched to a slow blowing fuse (a torodial transformer has a big starting current).

The 1 Ohm or so in the torodial seems fine and if none of the secondaries are connected in any way I see no problem.

Good luck with the project

Hans Bjergegaard

[Buhl]

Hej Hans
Thnx for the reply - i have just checked the fuses im using, and they are labeld "T3,15A" wicth should mean slow or "træg" in danish ?

hmm - should i try to skip the fuse, and hope that the 10 amps mains fuse will take it ??


1000 tak for hjælpen !


/Hans

[Netlist]

Originally posted by Buhl

hmm - should i try to skip the fuse, and hope that the 10 amps mains fuse will take it ??

With no load at the secondary side the 3.5AT fuse can't blow.
You probably made the wrong connection with the four(?) wires of the primary.
Check that first.
Do you have a variac?

/Hugo

[Buhl]

No, sadly I dont have a variac - but couldnt the turn-on surge be great enough to blow a 3 amp fuse ??

Theres only two primary windings, so I dont think I could connect anything wrong ?


/Hans

[Netlist]

Strange, how big is your trafo?
I mean VA-rating.
You could also put a 60W lamp in series with one primary wire.

/Hugo

[Buhl]

The trafo is 750 VA, toroidial - the strange thing is that I have a 1,6 KV that measures exactly the same dc resistance - but it will start with a 1,6 amp fuse - but ofcourse inductance and the way the trafo is winded has a lot to say....

I try the lamp thing....



/Hans

[kropf]

1 ohm for the primary seems quite low. I have a couple of toroids at home for this project and I'll measure them this evening.

The other possibility is that you have a shorted loop connected through the center of the toroid. That would act as a shorted secondary and will always blow the primary fuse.

Jeremy

[Netlist]

Normally, a 3.15AT fuse connected the way you did
shouldn’t ‘explode with a loud bang’.
If perhaps the fuse is too small, it rather should just melt.
That's what worries me.
Now, if a 3.15At fuse blows, a 1.6AT fuse will certainly blow.

/Hugo - still wondering what could be wrong

[Buhl]

Its working now - I put a ligth bulb in series, and the big dounot is alive

I have another trafo exactly like the first, and they measures the same.

I have 18 volt AC on both secondarys now.
But, I need to couple them in series to get the 36 volts needed for the Z4 - is it just shorting any two wires from each fase, and then I have 36 volts on the remaining two ?
Or should i short live from one fase and zero from the other ?



Thanx for the help - its greatly appreciaeted !!!


/Hans