E14 Lamp Keeps Coming Unscrewed

[paul_g_787]

Hi All.

The lamp in my oven recently blew, so I replaced it with a new one but it keeps coming unscrewed every few days. I have done it up as tight as I dare and don't want to risk damaging the lamp by overtightening it.

Any tips on how to prevent this?

It is a crap brand oven - Bush and doesn't use a BC lamp like our old Bosch oven did, it is an E14 lamp instead which I don;t see many of these days.

I found it fairly hard to find one of these E14 lamps at 300°C rating as most are 100°C, but CPC came up trumps as always.

[Ian.M]

Is it actually coming unscrewed or is the solder pip on the base flattening out?

[paul_g_787]

Yea it is actually coming unscrewed. One time I took the cover off and the lamp had fallen out the socket and was in the glass cover.

[Monkeh]

Fan oven? You may have a vibration problem. Clean the fan and make sure nothing is loose.

[Ian.M]

That's not good.  Crappy bulbholder with minimal contact spring tension  + vibration from the fan I assume.  If Monkeh's suggestion doesn't help, there's not much you can do short of changing the bulbholder.  Anything to make the screw thread fatter or stop it turning has to stand up to 300 deg C and *never* shed conductive particle inside the bulbholder while you are screwing it in, so far from easy.

[james_s]

Wouldn't surprise me if it's a cheap lamp with a sloppy base that doesn't fit tightly in the socket. You could try putting a piece of polyamide tape on part of the threads to increase the friction. As long as you leave enough exposed metal to make the electrical contact that shouldn't be a problem. Another possible fix is a dab of high temperature RTV sealant at the top of the socket after the bulb is screwed in to glue it in place. That will peel off easily enough when it's time to replace the lamp again.

[amyk]

I wonder if thermal expansion/contraction  is enough to make it unscrew itself...

[paul_g_787]

Fan oven? You may have a vibration problem. Clean the fan and make sure nothing is loose.

Yes it is a fan oven. Good suggestion, will see if I can get to the fan and check that.

Although the old lamp never came loose. However I think it was glued in with the grease that had built up. I cleaned it with contact cleaner before fitting the new lamp.

[langwadt]

That's not good.  Crappy bulbholder with minimal contact spring tension  + vibration from the fan I assume.  If Monkeh's suggestion doesn't help, there's not much you can do short of changing the bulbholder.  Anything to make the screw thread fatter or stop it turning has to stand up to 300 deg C and *never* shed conductive particle inside the bulbholder while you are screwing it in, so far from easy.

squeeze the threaded part (lightly) to make it slightly oval?

[paul_g_787]

That's not good.  Crappy bulbholder with minimal contact spring tension  + vibration from the fan I assume.  If Monkeh's suggestion doesn't help, there's not much you can do short of changing the bulbholder.  Anything to make the screw thread fatter or stop it turning has to stand up to 300 deg C and *never* shed conductive particle inside the bulbholder while you are screwing it in, so far from easy.

squeeze the threaded part (lightly) to make it slightly oval?

No, as it is a high temperature lamp it is ceramic filled between the glass and metal base. If you do this it will crack the ceramic and the glass bit will fall out.

[Ian.M]

I *THOUGHT* Langwadt meant squeeze the bulbholder, which would work if its (a) accessible, and (b) a formed metal shell rather than something like ceramic with a spring side contact.  Personally, I thought the odds were pretty low so I didn't bother suggesting that.

[SeanB]

The holders also are available with an integrated lamp, so all you do is replace the holder with the integrated lamp version. I have a good collection from scrapped ovens that I use, so never really have to actually buy a lamp for them, but the easiest solution is to take a small flat blade screwdriver and slightly deform the top turn of the socket, so it has a lot of resistance to the lamp screwing loose, keeping it in place.

[paul_g_787]

Well it turns out that the JEGS brand lamps were the problem. I bought a Status branded one from Tesco and no issue with the lamp unscrewing.

So I think I will steer clear of the JEGS brand lamps.

[Alti]

I do not think this is a problem of particular brand. These type of threads are not intended to be used in environment where vibration is a factor. If you take a look at E40 sockets used for street lighting, these have a spring just to prevent that (clearly an afterthought). If you want vibration-proof, use mating that is designed for such environment (look automotive).

[james_s]

It's entirely possible that one particular brand of lamp has slightly smaller bases than others, everything seems to get smaller and thinner and cheaper all the time.

[paul_g_787]

I mean, both brands of lamp are sold as an oven lamp suitable for fan ovens at 300°C, so I would think that they must have had vibration in mind.

Having a look again, the base of the JEGS lamp is very very thin and I believe nickel or something??, it is obviously very cheap and flimsy and can be crushed with your thumb and finger with hardly any force and it just falls off the glass part of the lamp.

The Status branded lamp however the base is very chunky and is brass. I gave it a scratch to see and it is not just plated it is actual brass. It has no flex in it at all.

In addition, the glass is unnoticeably thicker on the Status compared to the JEGS brand lamp and the Status lamp is noticeably heavier.

It has been a number of weeks now and the Status brand lamp is still working perfectly!!

So I think it is safe to conclude the JEGS lamps are overall of very poor quality and I do not think it unreasonable to avoid this brand JEGS in future.

[exe]

I think we had bulbholders and incadecent bulbs that would unscrew by themselves every few months or so. The worst part is that intermittent contact created sparks. I remember hearing that sound that intermittent contacts produce... I didn't figure out what was wrong. I tried to bend the spring contact, tried to screw it harder, nothing helped.

[paul_g_787]

Yes, the JEGS lamp was making cracking noises like your ones due to poor contact too. It actually has made holes in the metal base due to it being so thin.

No such issue with the Status brand lamp.

I liked our old Bosch oven which had a BC lamp and holder instead of Edison Screw.

[james_s]

You could change the lampholder, ceramic BC lampholders suitable for high temperature are readily available.