Power supply for little halogen light popped

[bushtech]

Fuse rating = (watts/volts) x 1.25
20/230x1.25=0.108A
150mA fuse?

 

[bertus]

Hello,

You could have a look at the littelfuse selection guides.

Bertus

 

[bushtech]

Thanks Bertus
Interesting reading

Gaat je wel

Dries

 

[73's de Edd]

NO . . . . .that 1 ohm resistor is being your fuse item.

 

[bushtech]

St Edd
Duh. So there is no difference between a fusible resistor and a normal resistor?

 

[bushtech]

I have found a 1/4W 1.2Ω resistor at Mantech that I'll order. Metal film though

 

[WHONOES]

Yes there is. A fusible resistor is designed to...……..fuse. An ordinary resistor is not. The fact that it may go open circuit is because of abuse in use and is not its intended function.

 

[bushtech]

Now I'm confused.

 

[Tha fios agaibh]

If you cant find a replacement, I'd just replace it with a delay type .2a fuse.
I sometimes solder leads on the ends a glass fuse, then cover it with shrink tube to insulate it.

I don't think 1 Ω makes any difference here.

 

[bushtech]

Thanks @Tha fios agaibh

Have ordered some 1.5Ω 1/4W resistors and 0.15A fast blow fuses. Will install in seriies. Due to space constraint the fuse will end up outside the little box, so judicious application of heatshrink will be applied so that state of fuse can be seen

 

[Tha fios agaibh]

Very good Bushtech, although I suspect a fast acting .15 might be a wee bit small.

 

[bushtech]

Ah, we'll see. Need some practice with making the smoke escape

 

[Martaine2005]

I don't think 1 Ω makes any difference here.

Yes John, I am inclined to agree with you. Especially as St Edd mentions that the resistor IS the fuse. I, like @bushtech am a tad confused too. Why place a heat(shrunk)? Fusible 1 ohm resistor instead of a suitable fuse or why not both?. It probably has something to do with the lamp and transformer being an inductive and resistive load. A fuse may blow and the fusible resistor will tolerate?. Just a guess.

Martin

 

[Tha fios agaibh]

I agree. If a replacement fusable resistor can't be found, it's better to use a fuse than a standard resistor that won't blow.
I would guess that a fast acting fuse would instantly pop due to inductance of the halogen light. Even my slow blow .2A suggestion is probably too small.

I would probably just jumper out the spot where the fusable resistor was and use an in-line fuse holder where you can change out the fuse easily.

Presumably a fusable resistor is like an extra slow blow fuse?

Not a bad idea to measure the line current.

 

[bushtech]

Yes , when the parts arrive, will do a bit of sleuthing to see whats happening, measure the current etc.

 

[bushtech]

This lamp worked for upwards of ten years in our pantry with 2 other identical ones. I surmise the little fusible resistor just gave up. The combination of our electrical supply company ineptitude combined with the ferocity of thunder storms is a formidable opponent that keeps me busy trying to fix the growing list of broken electrical equipment. And the I always wonder how the older equipment copes with the 220V now being 238V

 

[73's de Edd]

Sir bushtech . . . . .

INITIALLY . . . .

Yes , when the parts arrive, will do a bit of sleuthing to see whats happening, measure the current etc.

ALSO be SURE to test that power supply after replacing the power transistors, with a 60 watt incandescent lamp in series with the AC power input to see if you get a full brilliance lighting up of it . . . . .if so . . .thats then BAAAAAAAAADDDDD . . . . news . . . .back to the drawing board.

SECONDARILY . . . . .

My real forte is not exactly being with fusible / ( confusible) resistors . . .but . . . . just refer to as many of these patents as is required.


https://patents.google.com/patent/US3887893A/en

Particular interest is made to the left column, as the right column is chock full of lawyerese " said " barriers.

In your resistors situation, the 3 should be ~1/2 ohm and the 3a ~ 1/2 ohm with the thermally fusible link being deposited in the 10 sector.


" It should be apparent to those skilled in the art that the fusible resistor may be manufactured in a number of ways. For example, the resistive film 3 and 3a may be applied as two separate sections which are spaced apart to form a gap therebetween and in which the fusible link 10 is deposited. "

REFERENCE MARKUP . . . . .






73's de Edd . . . . .

My last Turkey Day, Christmas and New Year meals ( yum-yummy ! ) certainly taught me one thing . . . . Never eat more than you can lift !



.

 

[Martaine2005]

ALSO be SURE to test that power supply after replacing the power transistors, with a 60 watt incandescent lamp in series with the AC power input to see if you get a full brilliance lighting up of it . . . . .if so . . .thats then BAAAAAAAAADDDDD . . . . news . . . .back to the drawing board.

This is great information and every DIY bench should have One. Mine is swtchable from 100w to 200w.

Martin

 

[bushtech]

Parts finally arrived, sigh.
Replaced the 13005's and installed a 1.5Ω resistor and then measured the current after the resistor.Light came on and dim bulb tester stayed off (60W globe)
This is what the ammeter shows:


Could it really be drawing 14.5μA

 

[Tha fios agaibh]

Could it really be drawing 14.5μA

So its working now?
Where are you measuring? You should have 150ma or more on the incoming line, but if you were measuring current across (parallel) the 1.5Ω resistor you wouldn't read much.

Try reading voltage drops across it instead of inline current measurements.