4.8v Bulb in 6v/12v Lantern?

[jimnms]

I have a lantern that can be powered by 4 D-cell batteries or by plugging it into a 12v accessory socket. I have two re-chargeable jumper boxes that can be used to jump off a car, which also have a 12v accessory socket on them. I keep one in the car and one in the house.

I bought the lantern to have in case of a power outage so that I can plug it into the jumper box and it should power the light for days. So far we've only had three power outages since I bought it. The first time it went out, it was only out for about 15 minutes, so I hardly got to use it. The second time the power went out, it was out for several hours. The lantern worked perfect. The lantern has a 10ft cord, so I set the power box at the foot of the bed, and placed the lantern on the bedside table. I laid in the bed and read a book for a couple of hours. The power came on shortly after I turned the lantern off to go to sleep.

A few days ago the power went out again. I plugged the lantern up and it came on for a few seconds then went out. It turned out to be a blown bulb. I have a 2 D-cell LED Maglite, but it also came with a krypton bulb. The lantern's bulb looked like it was the same size as the Maglite's bulb, so I fetched the bulb from the bottom of my Maglite. It fit, and worked fine in the lantern, though the power was only out for about half an hour.

The bulb on the lantern says 4.8v 0.75amp (it also says that on the bottom of the lantern), but the Maglite's bulb only says Maglite 2-D or something like that. I went to get a replacement bulb a couple of days ago because we were expecting some bad storms. I forgot the voltage but I remembered the 0.75amp part, so I bought the only 0.75amp bulb I saw. It was labeled as a replacement for a 3 D-Cell Maglite and was rated 3.6v 0.75amp.

I didn't feel like going back to exchange it, and luckily our power didn't go out. I went back today to return the bulbs and get the right one. I found the right bulb, it was labeled 6v Lantern 4.8v 0.75amp. I also found an LED "bulb" that says it will replace any bulb in any C or D cell flash light up to 9 cells, so I figured I'd give that a shot too.

When I got home I checked each bulb in the lantern. I turned off the lights and turned the lantern on with the 2 D-cell Maglite bulb still in it. It was pretty bright, but it had a blueish color to it. I put in the 4.8v 0.75amp bulb. I appears to only be slightly brighter, but it gives off a more natural white/yellow color. The LED bulb was not as bright, and had that blue/white LED color. I put the 4.8v bulb back in, and I figure I'll keep the LED handy in case the krypton bulb blows again.

Now here's the part I'm confused about. If it uses 4 D-cell batteries, that is 6v, but I plugged it into the 12v DC power box and used a multi-meter to test the voltage going to the bulb and it is putting 12v into the bulb, it doesn't step it down to 6v. What is that doing to the 4.8v bulb by pumping 12v of power into it?

 

[FILIPPO]

first :welcome:

second:
I think that is impossible to push at 12V a 4,8v designed bulb...it'll insta-flash immediately.

so I'm sure that the lantern drive the bulb at about 6V.

do the lantern have 2 bulbs that work at the same time?? if yes they may be connected in serial s an they are 6+6= 12V
have you tested the voltage at the bulb socket??

 

[jimnms]

It uses just one bulb. I can't actually test the voltage at the bulb socket. The bulb sits half-way down in a reflector thing, so to remove the bulb you have to unscrew the top, then twist the bulb holder and pull it out. I tested the voltage at the connectors that make contact with the bulb holder. There are no resistors inside the bulb holder (it is transparent), so I don't see how it would step the voltage down to 6v.

I'll post some pics if it will help.

 

[FILIPPO]

maybe some pics will help but I keep thinking that isn't possible tu run a 4.8V bulb at 12V....:thinking:

 

[Gunner12]

maybe some pics will help but I keep thinking that isn't possible tu run a 4.8V bulb at 12V....:thinking:

It's possible, but the 4.8v bulb would be extremely inefficient and would pretty much last forever. There are no bulbs now that can do that.

The light might have a driver/resistor to control the voltage so the bulb doesn't pop.

 

[FILIPPO]

There are no bulbs now that can do that.

so, at least, at the moment this is impossible :thumbsup:

 

[ginaz]

how is it possible for that bulb to handle 12v? and last forever at that voltage? and if that one can do it, why are there no bulbs now that can do it? i'm probably just reading you wrong but i can't get a handle on that

 

[jimnms]

Here are some pics. This is the top of the lantern with top cap removed. The bulb is in inside the holder and locked into place. The switch is located in the top that unscrews, it has a metal "bridge" that swings over to make contact with the metal tabs at 10 o'clock and 4 o'clock position. The multimeter is connected to the two metal rods that run up from the bottom of the lamp where the batteries are located and make contact with the metal tabs under the bulb holder. You can see the multimeter reading 11.93v.



This is the same view, but with the bulb holder removed.



Last is a closeup of the bulb holder.



You can click any of the pictures to see the full size original where you can zoom in for better detail.

 

[Gunner12]

jimnms

Sorry, can't help you with the bulb since I haven't hung out in the Incan section long enough.

how is it possible for that bulb to handle 12v? and last forever at that voltage? and if that one can do it, why are there no bulbs now that can do it? i'm probably just reading you wrong but i can't get a handle on that

I've been in the Incan forum long enough to explain this though(somewhat).

If the bulb had a life of a long enough time(pretty migh forever for an incan bulb), the filament would be thick enough to handle 12v overdrive without popping.

There are no bulbs now that can do that because there is no need for such a bulb and it would be pretty much useless(or really inefficient) at it's rated voltage of 4.8v.

 

[Mr Happy]

There are no bulbs now that can do that because there is no need for such a bulb and it would be pretty much useless(or really inefficient) at it's rated voltage of 4.8v.

Well there are bulbs now that can do that of course -- they are 12 V or higher rated bulbs. I have a 14.4 V bulb for DeWalt lights that will certainly run almost forever on 4.8 V.

jimnms: It really isn't possible to run a 4.8 V bulb on 12 V. The bulb will flash immediately. There is most likely some kind of resistor or regulator inside the lantern that controls the current to the bulb. When you measure the voltage at the bulb terminals as you show, it is important to measure it with the bulb connected and illuminated. The voltage you measure with the bulb disconnected is not necessarily the voltage that the bulb sees.

By the way, the 2D cell bulb will not last very long at all in that lantern. It is amazing that it even survived without instaflashing. The bright blue color you saw is the bulb being overdriven to within an inch of its life. You need a 4D cell bulb for matching with the lantern.

 

[FILIPPO]

Well there are bulbs now that can do that of course -- they are 12 V or higher rated bulbs. I have a 14.4 V bulb for DeWalt lights that will certainly run almost forever on 4.8 V.

jimnms: It really isn't possible to run a 4.8 V bulb on 12 V. The bulb will flash immediately. There is most likely some kind of resistor or regulator inside the lantern that controls the current to the bulb. When you measure the voltage at the bulb terminals as you show, it is important to measure it with the bulb connected and illuminated. The voltage you measure with the bulb disconnected is not necessarily the voltage that the bulb sees.

By the way, the 2D cell bulb will not last very long at all in that lantern. It is amazing that it even survived without instaflashing. The bright blue color you saw is the bulb being overdriven to within an inch of its life. You need a 4D cell bulb for matching with the lantern.

+1 good explanation!:thumbsup:

 

[jimnms]

I found a way to hook up the multi meter while the light is on, it wasn't easy since I only have two hands and I couldn't use the clips. It does step the voltage down, but it's different depending on the input voltage. On the 12v jump start box which puts out 12v, it drops to 4.5v when I turn the light on. I plugged it into another DC power source which was putting out 14v and the power was dropped to 5.5v.

I didn't think it should be possible to put 12v into a 4.8v bulb, but I was wondering since the bulb blew out after only three uses. I guess I'll just see how long this one lasts, I've got the LED replacement to fall back on if it blows the next time the power goes out.

:thanks:

 

[TorchBoy]

It does step the voltage down, but it's different depending on the input voltage. On the 12v jump start box which puts out 12v, it drops to 4.5v when I turn the light on. I plugged it into another DC power source which was putting out 14v and the power was dropped to 5.5v.

Sounds like it does use a resistor.