One sidelamp lights with very low brightness compared to the other.
The sidelamp bulbs are silvered, which I have not seen before.
One bulb is silvered on front half & clear at back.
The other bulb is silvered front & back, which must be giving the very low brightness, which I'm not sure is correct.
Is this correct or is the bulb silvered front & back manufactured wrong or do I just have the wrong bulb ??
Looking on ebay I see there are lots of types of W5W coloured bulbs, so I'm not sure.
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Both the bulbs need replacement. I believe the silver is the filament deteriorating
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Silvering on a bulbis usually an indication of an air leak. Only a matter of time before the bulb(s) fail.
Replace them both now. From memory i thinkthey are 207 12v5w scc bulbs but any car shop will confirm.
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If any other bulbs are showing similar effects; checking the charging voltage might be worthwhile.
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Too low a voltage and the filaments can carbonise up, hence you'll get a metallic looking appearance on the glass if this happens.
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I've just replaced battery in last few weeks, as it went flat on 2 different occasions, days after 150 mile roundtrip, which was strange.
Checked charging voltage with the old battery & it was around 14V at idle, maybe 13.5V at higher rev.
Edited by peter973 on 05/09/2008 at 23:18
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That's pretty ballpark; so maybe the bulbs were just getting old?
Worth keeping an eye on though.
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Checked charging voltage with the old battery & it was around 14V at idle maybe 13.5V at higher rev.
Try checking the voltages at the bulb sockets.
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As a former vehicle sparky I have never come across this appearance on a bulb with too low voltage. If you were to reduce the rated voltage of a bulb by say 5% then the bulb will last about 50% longer. This silvery appearance is common on old bulbs, due to the filament materials burning off over an extended period and being deposited on the inside of the glass. This is common on side/tail bulbs as they are used the most, compared against brake and indicator bulbs which have intermittant use.
Seeing a bulb in this condition means its right at the end of its life, and any shock like a flick with a finger will usually finish them off. If air gets into a bulb it leaves a white deposit, then it will only live for a few seconds before blowing.
I used to work in a bus workshop for a major operator, and on a vehicle which was up for its MOT I would regularly check all the side/tail bulbs for this sympton, because one blowing on test-day would be a failure and major grief, with points deducted from the Operators Licence. The Spanish Inquest had nothing on it.
It would pay to have a look at your bulbs once in a while for this sign. Often the side lamps fitted in head light units can be viewed by simply looking through the glass, turned off of course.
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and any shock like a flick with a finger will usually finish them off.
I had a look at these silvered bulbs, took out the lampholder from the headlamps & tested the bulbs.
Was surprised that the filament actually shone through the silvered coating, as I thought it was being reflected out of the back of bulb where it was not so silvered.
Saw that the bulb silvered at front/back was very dim indeed.
Tried flicking the bulbs to see if they died, but they kept going !!
Will have to replace them.
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I have 4 spare capless bulbs like my sidelamp bulbs, the print label on the bulbs has rubbed off.
I assumed they would be 5W bulbs.
My calculation says a 5W bulb should have a resistance around 28.8 ohms.
I checked the 4 spare bulbs, 2 are 3 ohms, 1 is 5 ohms, 1 is around 25-30 ohms.
Does that make sense, where would these 3 & 5 ohm bulbs be used ??
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dash display bulbs on earlier vauxhalls, but also other models i would expect
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Cold resistance is not going to identify the bulb. Take your 3 ohm bult thats 48/50 watts, so that would melt the fitting. Use the mater in the current range in series with the bulb and light it up across the battery and measure the current, or go and buy two new bulbs from a motor factors. Regards Peter
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Cold resistance is not going to identify the bulb. Take your 3 ohm bult thats 48/50 watts so that would melt the fitting. Use the mater in the current range in series with the bulb and light it up across the battery and measure the current or go and buy two new bulbs from a motor factors. Regards Peter
I agree a 3 ohm 12 volt bulb would rate it at 48 watts.
That's how the bulbs work, the filament resistance draws the current which burns at 5 watts.
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That's how the bulbs work the filament resistance draws the current which burns at 5 watts.
Yes, but the current decreases significantly once the bulb heats up. When cold, there should be a low resistance between the terminals, so what you're getting is correct. Resistors on the other hand don't get hot hence increase resistance, so you can measure these any time.
The only way to measure a bulb's resistance is to measure the current and voltage and divide.
Edited by mfarrow on 09/09/2008 at 14:46
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dash display bulbs on earlier vauxhalls but also other models i would expect
I'm pretty sure they're sidelight bulbs as I got them when I was looking for lights for my 1988 Nissan Micra at a scrapyard.
I don't understand how what I assume must be 5W bulbs can measure 3 ohms, it doesn't make sense. 3 ohms is a massive difference from 28 ohms.
Edited by peter973 on 09/09/2008 at 14:15
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Peter
If these are capless sidelight bulbs, then they'll be 501s. [They only come in 1.2w to 5w variants anyway and all sidelights use the 5w ones.]
Don't bother messing about with an Ohmmeter; pointless with bulbs, as they'll all read differently cold.
Just stick them in - if they work, you're sorted; if not, try/buy another. This is a couple of blackened sidelight bulbs, not an engine swap.
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The resistance of the bulb varies by a factor or >10 depending on filament temperature- see 'electrical characteristics' part :-
en.wikipedia.org/wiki/Incandescent_light_bulb
The only way I can think of to estimate the wattage using a DMM is to find a bulb you know has the wattage you are looking for and comapre the 'cold' resistance of the unknown bulb with that.
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No, it varies make to make. The OP is even testing used old bulbs. Just plug one in and see how bright it is, the max in that size is 5W. And don't bother with used old bulbs. Regards Peter
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Peter
Go the local motor factors, or even better Vauxhall tell what car you have and buy some nice new ones. you dont need to worry about poking them with a mulitmeter then and trying to guess what they are.
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"you dont need to worry about poking them with a mulitmeter then and trying to guess what they are."
But where's the fun in that!!
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But where's the fun in that!!
Exactly, I was just curious, thought I'd test them.
From the Wiki article looks like my understanding wasn't up to scratch.
I've bought some new bulbs, but looks like I could have used the the spare ones I had.
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Tested the new bulbs I bought, they come in at 3.5 ohms.
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They'll be 41 watt bulbs then. A domestic 60 bulb bas a nominal value of 30 ohms so that has an initial output of 822 watts and people wonder why they pop when you turn them on. Mass Shock, excuse the pun. So now you know. Regards Peter
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Typo Sorry 70 not 30
They'll be 41 watt bulbs then. A domestic 60 bulb bas a nominal value of 70 ohms so that has an initial output of 822 watts and people wonder why they pop when you turn them on. Mass Shock, excuse the pun. So now you know. Regards Peter
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give me you email adresse and i will send you some new ones!
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They'll be 41 watt bulbs then. A domestic 60 bulb bas a nominal value of 70 ohms so that has an initial output of 822 watts and people wonder why they pop when you turn them on. Mass Shock excuse the pun. So now you know. Regards Peter
That must be for milli or micro seconds, interesting.
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