Fuse Question

[RSLancastr]

It's not a computer question, but I didn't know a better place for it. Actually, since it's about my computer lamp, there's my justification for posting it here. :)

I have a desk lamp which stopped working a while ago. I bought a replacement bulb for it, but that didn't make it work.

At that point I noticed there was a compartment on the bottom of the lamp's base marked "2A Fuse Maximum." I pulled out the fuse, which was a little (20mm) cylindrical amp(glasscylinder with metal-capped ends). It was marked "2A 125V".

I haven't been able to find an identical fuse, but found some the same size which are 2A, 250V.

On the back of the box which these 2A 250V fuses came in, it says

Before replacing a fuse, check manufacturer's recommendations to insure that the amperage rating on the fuse is the same as the circuit requirement and the voltage rating is equal to or greater than the circuit voltage.

Emphasis mine.

So, should it be safe to use this fuse in the lamp?

Editred to add: lamp will be plugged into standard US AC 110 house current.

[stormer]

Yes

[tsg]

Yes. You don't want to put in a fuse rated for less than the voltage that will be applied to it, but greater than is fine. Don't, however, replace the fuse with one rated for a higher amperage than the old one.

To simplify:
Higher voltage rating = ok
Higher amperage rating = not ok.

[Alareth]

Yes, that fuse will work fine. Your question is one of the top 10 most commonly asked questions in my job at RadioShack.

Here in the US voltage ratings on fuses aren't a concern usually because the smallest you find is 125V and we run 120V electrical. There are a few lower voltage fuses outthere, but they are normally limited to automotive 12V system applications

[RSLancastr]

Thanks, all.

Unforunately, the fuse wasn't the problem either. Brand new bulb and fuse, and still no light. Looks like I'll need to buy another desk lamp.

Yes, that fuse will work fine. Your question is one of the top 10 most commonly asked questions in my job at RadioShack.

Well, someone should train the woman I spoke to at the Radio Shack where I bought the fuse. She kept telling me that I could "burn out the device" that way. I decided to believe what was on the back of the package the fuses came in, but wanted to confirm it here.

I'm now going to give my lamp a decent burial... :(

[Skeptic Guy]

Well, it didn't work...maybe you DID burn it out!!!! :D

[gnome]

Radio shacks are of mixed quality. In one that I go to, they're clueless and just are useful for selling you what you've picked out. In another one they actually give useful electrical advice.

[Alareth]

I should get paid more for my skills.

[RSLancastr]

I should get paid more for my skills.
Your mad Radio Shack skillz.

[gnome]

You see me roll on my Segway...

[bruto]

I should get paid more for my skills.If you actually do have a clue about what you're talking about, indeed you should. I have always suspected that Radio Shack has a special policy, perhaps a special education program as well, to teach all RS employees to answer any question authoritatively whether they know anything or not. I have never been any place where so much total BS and downright incorrect information was so freely offered (and by place I mean many different Radio Shack stores). So yes, indeed, if you work at a Radio Shack, you should get a bonus for every true answer you give. You should also tell us where your store is, so that we can go there when we are looking for something for which we do not already know all the answers ourselves. It might be worth the extra trip.

[ThatSoundAgain]

Regarding the lamp: It may have a broken wire or a short-circuit that blew the second fuse as well. Do you have a way of testing this, like a multimeter?

Both a broken wire and a short could very likely be fixed if you were to put ten minutes into it.

[RSLancastr]

Regarding the lamp: It may have a broken wire or a short-circuit that blew the second fuse as well. Do you have a way of testing this, like a multimeter?

Nope, no multimeter. Not even a single meter. :(

Actually, I bought two identical (cheap) lamps more than a year ago. One went through this failure about six weeks ago, and I replaced it with the other, which subsequently went out about two weeks ago.

I'm guessing that purchasing a multimeter would probably cost about as much as buying a new cheapo lamp.

[ThatSoundAgain]

Yes, probably, but it's a handy tool to have.

I've used an old analog one for a long time, thinking it would be expensive to get a digital one with all the fancy stuff it can do (like testing transistors) - and then it turns out that my local paint & home improvement shop has been selling them for ~ $10 all htis time.

Sounds like your lamps had a just-out-of-warranty-self-destruct-system. Sucks.

[illogical]

yes, the only ones most people will ever see are 12, 125, 250 V and similar. esp that size.

#14, they have dropped in cost. sometimes i see Flukes at pawn shops. you might be able to get a good deal if the seller doesn't look up the value.

ideally, one would have analog, digital, and an interface for PC.

[illogical]

i like the fluorescents that screw into the regular sockets. they are ok for background light and don't put out heat in the summers.

[gnome]

If you actually do have a clue about what you're talking about, indeed you should. I have always suspected that Radio Shack has a special policy, perhaps a special education program as well, to teach all RS employees to answer any question authoritatively whether they know anything or not. I have never been any place where so much total BS and downright incorrect information was so freely offered (and by place I mean many different Radio Shack stores). So yes, indeed, if you work at a Radio Shack, you should get a bonus for every true answer you give. You should also tell us where your store is, so that we can go there when we are looking for something for which we do not already know all the answers ourselves. It might be worth the extra trip.

I consider it another good possibility that the management has no idea whether their employees are giving out good information or not, and so the employees have learned not to say "I don't know"...

[slyjoe]

I worked at RS many years ago (ok, more than 2 decades) and was working on my EE degree. When the manager heard me give technical advice, he basically told me to never do that. They were worried about liability if advice was wrong.

ETA: he suggested I try to sell them a book about how electronics works.

[Rob Lister]

I'd just wrap the old fuse in tinfoil and be done with it.

[illogical]

I'd just wrap the old fuse in tinfoil and be done with it.

good idea. the light will be 5% brighter that way.

[illogical]

don't knock Radio Shack. i used to play with a 200 in 1 kit, and now i'm a gainfully employed salesman at Bestbuy.

[Grimoire]

I'd just wrap the old fuse in tinfoil and be done with it.
I once had to convince someone that it was a bad idea to replace the main fuse in his car with a bolt. He figured he was saving money, because he kept blowing the fuse. :eye-poppi To this day, I don't know if he actually found the real cause of the problem, or if he kept the bolt in place.

[triviaace]

I have an architectural lamp with the same problem. I checked the bulb with an ohmmeter and it appeared to be good. Then I opened the lamp and checked the fuse and it was blown. I bought a package of Littlefuse 250VAC 5 Amp fast acting fuses and they keep getting blown. When I observed the wiring, it looks like the opposite ends of the fuse connection are to the arms of the lamp and read 0 Ohms without a fuse inserted. The wiring looks like the lamp will never work. Can anyone help with a wiring schematic or other assistance for this type of lamp. It uses a 12V 50W max Halogen bulb, p/n GY 6.35.

[MortFurd]

Your halogen lamp has a transformer. The bulb is in the low voltage side. I'd be surprised if there were a fuse there, though I might be wrong. The fuse and the switch are normally on the high voltage side - connected to the power cable.

Unplug the lamp from AC.

Check to be sure which side the fuse is in.

If it is on the high voltage side, remove the fuse and check continuity across the fuse. If you get a short, there's something massively wrong.

If the fuse is in the low voltage side, then when you remove the fuse you will get continuity across the fuse connections. Remove the bulb and it should go away. This would be normal.

[This Guy]

Good ole Radio Shack!

Once overheard one of their salesmen explaining the "memory chip" that is inside ni-cad batteries, that makes them go bad. I debated stopping him, and giving the poor lady he was talking to a better understanding, but decided to keep my mouth shut.

They have been handy stores though! When I was a teen, I use to buy tubes for our old TV set at RS. Over the years I've spent more than a few dollars there. Even had one of their old TRS-80s (a model 1, with a whopping 16k of Ram!).

Great stores, if you know what you want ;)

As for the lamp, the switch may be the problem.

[MortFurd]

Good ole Radio Shack!

Once overheard one of their salesmen explaining the "memory chip" that is inside ni-cad batteries, that makes them go bad. I debated stopping him, and giving the poor lady he was talking to a better understanding, but decided to keep my mouth shut.

They have been handy stores though! When I was a teen, I use to buy tubes for our old TV set at RS. Over the years I've spent more than a few dollars there. Even had one of their old TRS-80s (a model 1, with a whopping 16k of Ram!).
Great stores, if you know what you want ;)

As for the lamp, the switch may be the problem.
Ha! I've got you beat. I had a TRS-80 Model I, Level II with 48K on board. Normally you had to have the expansion box to get 48K, but a company named Holmes Engineering sold a little module that plugged in in place of the original RAM and added 32K for a total of 48K.

Woohoo!

[This Guy]

Ha! I've got you beat. I had a TRS-80 Model I, Level II with 48K on board. Normally you had to have the expansion box to get 48K, but a company named Holmes Engineering sold a little module that plugged in in place of the original RAM and added 32K for a total of 48K.

Woohoo!

hehe cool!

Mine had the level II basic also.

Do any other mods to it?

I used a couple tricks from the ole 80Micro mag, and used an unused NOR gate (if I recall correctly) on the motherboard to allow me to reverse the video (black to white/white to black). Also routed the clock to the Z80 processor through a switch, and another unused component (I forget now exactly how I did it), so I could switch the clock rate to about double, using either the switch (which would sometimes cause the Z80 to hang up) or with an "OUT" command via software/keyboard. Basically took one of the higher outputs, available, but unused, from the timing chip, and made it available to the Z80.

I loved that computer :)

[MortFurd]

hehe cool!

Mine had the level II basic also.

Do any other mods to it?

I used a couple tricks from the ole 80Micro mag, and used an unused NOR gate (if I recall correctly) on the motherboard to allow me to reverse the video (black to white/white to black). Also routed the clock to the Z80 processor through a switch, and another unused component (I forget now exactly how I did it), so I could switch the clock rate to about double, using either the switch (which would sometimes cause the Z80 to hang up) or with an "OUT" command via software/keyboard. Basically took one of the higher outputs, available, but unused, from the timing chip, and made it available to the Z80.

I loved that computer :)
No other mods. I was only 14, and my dad wasn't about to let me start soldering on the insides of that thing.

Nothing like a really primitive machine to teach about how things work, and how to get the most out of the least.

[This Guy]

No other mods. I was only 14, and my dad wasn't about to let me start soldering on the insides of that thing.

Nothing like a really primitive machine to teach about how things work, and how to get the most out of the least.

I was.., let's just say past 14 when I was playing with mine ;)

Your right about learning from the old stuff though. :)

[Dan O.]

As for the lamp, the switch may be the problem.

If it's blowing the fuse, it's probably not a problem in the switch.

If you have an ohm meter you can make your own schematic. Just unplug the lamp, turn the switch off, remove the bulb and fuse, then use the meter to figure out which points are still connected and draw the map as you go.

The Primary (high voltage side) of the transformer should show up as a small resistance on your meter. The secondary side will show a much smaller resistance that may be difficult to see with your meter.

You should get something like:

line (hot) ---- fuse ---- switch ---- transformer (primary) ---- line (neutral)

bulb ---- fuse (optional) ---- transformer (secondary) ---- bulb

The chassis may be isolated or connected to the AC ground. The chassis may also be connected to one side of the secondary circuit. There should be no connection to the chassis on the primary side.

You might have a short circuit on the secondary side, probably where a wire goes through the frame or on the bulb socket. This will need to be found and fixed.

For a 50W lamp, the fuse on the primary side should only be about 1.5A. If there is a secondary fuse, 50W/12V=4.2A. But this doesn't consider the lower resistance of the cold bulb. Measure the bulb with your meter and divide 12V by the cold bulb resistance to get the starting current.

ETA: Always try to replace fuses with the same size and type as the product was originally engineered to use.

[This Guy]

If it's blowing the fuse, it's probably not a problem in the switch.

SNIP

I was talking about RSL's lamp, from the OP. Sorry, I should have clearified.

I don't think he said the fuse was blowing on his, just that replacing the bulb and the fuse didn't fix it. That would leave the wiring or the switch. Other's mentioned the wiring, but I don't think anyone mentioned the switch. Some lamps are made with cheap switches that tend to fail (crappy contact material that pits or falls off and what have you).

[illogical]

i'll add that there are different types of fuses. some are made to blow quickly, others don't.

[Dan O.]

I was talking about RSL's lamp, from the OP. Sorry, I should have clearified.

It there is a fuse, there is almost always more than a switch and bulb in the lamp. I suspect the OP's is another 12V lamp with a transformer. Sometimes the transformers have a built-in thermal fuse.

ETA: I never throw anything away without smashing it apart first to find out how it works and why it failed.

[ThatSoundAgain]

ETA: I never throw anything away without smashing it apart first to find out how it works and why it failed.

You and me both. Plus, I always try to salvage parts to mess around with. I also make a point of going through the electronics / furniture trash from the block where I live, if the stuff there doesn't work I can almost always salvage some useable parts. I've found functional a webcam once (with the optics glued in place), stereo equipment and lots of working computer parts. Nothing like being able to help your friends out with some RAM or a PSU when their computers fail.

[bruto]

It there is a fuse, there is almost always more than a switch and bulb in the lamp. I suspect the OP's is another 12V lamp with a transformer. Sometimes the transformers have a built-in thermal fuse.

ETA: I never throw anything away without smashing it apart first to find out how it works and why it failed.

If it is a 12 volt lamp and it blew the fuse, there's a really good possibility that it blew the transformer as well. I've had rather bad luck with those lamps, especially the cheap chinese ones that look (but do not behave) like those expensive yuppie halogen desk lamps.