E14 Lamp Keeps Coming Unscrewed - Page 1
Forum section: electronics / projects

author: paul_g_787
author_rank: Frequent Contributor
timestamp: March 07, 2021, 09:41:55 pm
content: 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.

author: Ian.M
author_rank: Super Contributor
timestamp: March 07, 2021, 09:45:47 pm
content: Is it actually coming unscrewed or is the solder pip on the base flattening out?

author: paul_g_787
author_rank: Frequent Contributor
timestamp: March 07, 2021, 10:39:46 pm
content: 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.

author: Monkeh
author_rank: Super Contributor
timestamp: March 07, 2021, 10:49:05 pm
content: Fan oven? You may have a vibration problem. Clean the fan and make sure nothing is loose.

author: Ian.M
author_rank: Super Contributor
timestamp: March 07, 2021, 10:52:26 pm
content: 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.

author: james_s
author_rank: Super Contributor
timestamp: March 07, 2021, 10:54:55 pm
content: 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.

author: amyk
author_rank: Super Contributor
timestamp: March 07, 2021, 11:30:31 pm
content: I wonder if thermal expansion/contraction is enough to make it unscrew itself...

author: paul_g_787
author_rank: Frequent Contributor
timestamp: March 07, 2021, 11:33:41 pm
content: Quote from: Monkeh on March 07, 2021, 10:49:05 pmYes 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.

author: langwadt
author_rank: Super Contributor
timestamp: March 07, 2021, 11:33:47 pm
content: Quote from: Ian.M on March 07, 2021, 10:52:26 pmsqueeze the threaded part (lightly) to make it slightly oval?

author: paul_g_787
author_rank: Frequent Contributor
timestamp: March 08, 2021, 06:51:39 pm
content: Quote from: langwadt on March 07, 2021, 11:33:47 pmNo, 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.

author: Ian.M
author_rank: Super Contributor
timestamp: March 08, 2021, 07:30:58 pm
content: 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.

author: SeanB
author_rank: Super Contributor
timestamp: March 08, 2021, 08:12:01 pm
content: 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.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: June 07, 2021, 07:56:22 pm
content: 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.

author: Alti
author_rank: Frequent Contributor
timestamp: June 07, 2021, 08:28:33 pm
content: 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).

author: james_s
author_rank: Super Contributor
timestamp: June 07, 2021, 10:33:18 pm
content: 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.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: June 14, 2021, 02:56:34 pm
content: 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.

author: exe
author_rank: Unknown
timestamp: June 14, 2021, 03:23:42 pm
content: 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.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: June 14, 2021, 03:58:02 pm
content: 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.

author: james_s
author_rank: Super Contributor
timestamp: June 14, 2021, 09:35:49 pm
content: You could change the lampholder, ceramic BC lampholders suitable for high temperature are readily available.