Fuse in a Bosch battery charger

[^woody^]

My Bosch 10.8v charger stopped working, and it seems that the fuse soldered to the board has blown. Google says it might be a 1.25 A.

It's hard to tell, but would this be a normal fast or slow blow fuse?

I plan to bridge it with a fuse in a fuse holder (blade car type or a glass type), is there anything wrong with this plan?

 

[omega015]

Does the fuse not have markings on the side saying what rating it is?

https://www.swe-check.com.au/pages/learn_fuse_markings.php

Nothing wrong with your plan but instead of the blade style fuses I would add a pcb mount fuse holder, probably can make it fit the existing holes or small hole drilled at one end and bit of solid wire to bridge the gap.

 

[SFK]

Woody,
I guess you mijht have already seen this, but see here for someone who had similar issue with Bosch 10V Charger -> failed fuse and capacitors. Unfortunately they did not detail what fuse is needed, and they failed to fix it in the end as the fuse re-failed after replacing capacitor. Perhaps they had multiple failed capacitors.
http://www.ultimatehandyman.co.uk/forum1/bosch-10-8v-charger-dead-t78214.html

Nothing wrong with your plan to use Wire-fuse holder, and likely to be best option as can do quick test and no issue with getting product with correct pitch to match existing fuse holder.
sfk

 

[ericmark]

I would also say a fuse normally fails for a reason, and unless you know why it failed, you are likely wasting your time. In the days before switch mode you may have been able to easy trace the fault, today it's mainly buy new.

 

[securespark]

If it is soldered onto a PCB, I would guess it is not user serviceable.

 

[bernardgreen]

The lump in the middle suggests it was a slow blow fuse.

However it is not that simple as many "slow" blow fuses are :-
slow blow at say 10 times rated current for a short duration of two or three mains cycles allowing capacitors to charge up at switch on.
slow blow at say 5 times rated current after a longer duration over load
fast blow at say 20 times rated current to interrupt supply to a short circuit fault

The thermal charactoristics ( hence the time to blow ) of PCB mounted fuses are affected to some extent by the way the fuse is mounted to the PCB

http://www.littelfuse.com/~/media/f..._application note slow vs fast auto fuses.pdf

 

[333rocky333]

What are the codes stamped on the end
caps of the fuse

 

[endecotp]

I think that the blob of metal that you can see at the middle of the fuse wire is the thing that makes it "slow blow".
I'm not certain though...

 

[^woody^]

Woody,
I guess you mijht have already seen this, but see here for someone who had similar issue with Bosch 10V Charger -> failed fuse and capacitors. Unfortunately they did not detail what fuse is needed, and they failed to fix it in the end as the fuse re-failed after replacing capacitor. Perhaps they had multiple failed capacitors.
http://www.ultimatehandyman.co.uk/forum1/bosch-10-8v-charger-dead-t78214.html

Nothing wrong with your plan to use Wire-fuse holder, and likely to be best option as can do quick test and no issue with getting product with correct pitch to match existing fuse holder.
sfk

Thanks for that link. I did the usual google search and all I found was some schematic which might be the charger I have , but I never thought of the UHM site.

 

[^woody^]

Righty then. Thanks for the replies, I'll try and answer all the posts in one.

The markings on the fuse are very difficult to see. They are covered in solder or not very indented to make out. A google search led me to a foreign site with what seemed to be the board's schematic which indicated a 1.25A fuse. Why a fuse should be hard-soldered instead of replaceable I'll never know. Further reading indicates that the blob in the fuse means that it is a slow blow type.

I can't see any burn or blown bits on the board or components. The charger was happily working with a battery that had been fully charged inserted and I left it plugged in (as I have done all the time previously). The supply was turned off in the house I was working in for the sparks to do something or other, and I suspect that must have done something to the charger (?) as it was not working afterwards then the power was put back on.

I had to order a new charger today, as I need it before I will have chance to get and change the fuse, but it will annoy me to throw this away for the sake of a fuse, so I will have to have a go at a repair. If the fuse does blow again, then anything else will be beyond my capabilities.

 

[endecotp]

Why a fuse should be hard-soldered instead of replaceable I'll never know.

"The benefit of using axial leaded fuses is that they are typically cost-effective and easy to install whereas the primary negative factor is that they are not so easy to replace in the field."​

http://www.optifuse.com/blog/p090921.php

 

[^woody^]

"The benefit of using axial leaded fuses is that they are typically cost-effective and easy to install whereas the primary negative factor is that they are not so easy to replace in the field."​

http://www.optifuse.com/blog/p090921.php

Hmm, yes cost. But surely a fuse by its nature is designed to be an easily replaceable component? Of all the electronic gear I've looked in over the years where a fuse has been present, its been an easily removeable one.

 

[endecotp]

But surely a fuse by its nature is designed to be an easily replaceable component?

No, not really. It's intended to blow and make the device stop safely instead of catching fire when some other component fails. It shouldn't blow unless the product is already broken.

In the past, components including transistors and integrated circuits were often fitted in sockets because they might not survive the temperature in a wave-soldering machine. I imagine that some care is needed to make a fuse that doesn't fail - either the fuse wire or the glass - when exposed to those temperatures.

 

[ban-all-sheds]

I can't see any burn or blown bits on the board or components.

Replace the fuse with a bit of thick wire, and power the thing up.

Watch for smoke etc coming out of the bits which are broken.

 

[Mikefromlondon]

Looking at the fuse, it seems it has blown due some overloading rather than some short or part failure, as that would have caused the fuse wire to disintegrate completely in a flash with blackened glass cover. You could try a 1amp quick blow fuse or since it is a charger you can even try a 250mA anti-surge fuse.

You asked why anyone would want to solder a fuse on a pcb directly, this is for cost reasons and is there to protect against people replacing blown fuse in a 3 pin plug to a much larger size like 13Amps. You can buy a wire ended fuse too, often a 10 ohm wire wound resistor is used instead of a fuse as that would also blow up but they are designed for this purpose so that they don't catch a flame. So they are made of fire and flame retardant materials or coatings on them.

You could solder another glass fuse on top of that, but won't be easy as the end caps start to push out with soldering heat, so you need to keep them pressed in whilst soldering, after soldering test fuse continuity with a meter.