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Other Vintage Household Electrical or Electromechanical Items For discussions about other vintage (over 25 years old) electrical and electromechanical household items. See the sticky thread for details. |
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18th Jan 2024, 8:29 pm | #1 |
Triode
Join Date: Nov 2014
Location: Leominster, Herefordshire, UK.
Posts: 25
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Christmas light problems - help please !!!
Hi - I know it’s not the right season but ….. I have a love of vintage lights not so much Father Christmas etc just strings of old bulbs dotted around the house.
I have a string of 1960’s 20v bulbs which I under run by having 16 bulbs on and they are much admired and are no trouble. So I have slowly been collecting early milk glass bulbs to do something similar with. I have 16 various 16v bulbs and have made a string of 18 so as to under run them as before however I am 2 bulbs short so I put in a couple of 20v bulbs thinking they would just be a bit dimmer ….. what actually happens is every time I try the lights, one of the 20v bulbs blows. I am at a loss now and don’t want to keep wasting bulbs …. Is it the voltage rating ? Different wattage ? Help please !!! Last edited by Tinker1966; 18th Jan 2024 at 8:36 pm. |
18th Jan 2024, 8:43 pm | #2 |
Moderator
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,787
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Re: Christmas light problems - help please !!!
They probably have a much lower current rating than the rest of the string. This will cause them to be overvoltage and one of them will fail.
A power diode (1N4007 or similar) in series with the string is usually a better way of preserving bulb life, though it may cause visible flicker. Sensitivity to this varies between individuals. |
18th Jan 2024, 9:38 pm | #3 | |
Triode
Join Date: Nov 2014
Location: Leominster, Herefordshire, UK.
Posts: 25
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Re: Christmas light problems - help please !!!
Quote:
I know most of the more modern bulbs tend to be 3w and that some of the earlier ones are 7w as some of them are stamped with both voltage and wattage. I have just found some plain bulbs rated at 7w and added them in and hey presto nothing is blowing ! However now, once they’ve been on for a minute or so they all flash in unison - I am now beyond confused …… |
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18th Jan 2024, 9:43 pm | #4 | |
Moderator
Join Date: Dec 2010
Location: Exeter, Devon and Poole, Dorset UK.
Posts: 6,824
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Re: Christmas light problems - help please !!!
Quote:
They have a Bi metallic strip near the filament. Perhaps a picture of the inside of the bulb will confirm? Cheers Mike T
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Invisible airwaves crackle with life or at least they used to Mike T BVWS member. www.cossor.co.uk |
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18th Jan 2024, 11:44 pm | #5 |
Dekatron
Join Date: Jan 2012
Location: Brentwood, Essex, UK.
Posts: 5,316
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Re: Christmas light problems - help please !!!
After I had extended a string of twelve 20V 3W bulbs to 16 and had no spares when one blew, I used a 12V bulb of the same current rating until I was able to get some 20V replacements.
If you have a string of higher current bulbs and replace one by a lower current bulb, the higher current bulbs behave like a constant current source that attempts to force the higher current through the lower current bulb, causing the voltage across it to rise to a high value in excess of its voltage rating and making it blow. Conversely, when replacing a bulb in a low current string by a high current one, the constant current provided by the string will result in a low voltage appearing across the replacement, making it glow dimly. |
19th Jan 2024, 2:44 pm | #6 | |
Triode
Join Date: Nov 2014
Location: Leominster, Herefordshire, UK.
Posts: 25
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Re: Christmas light problems - help please !!!
Quote:
Now I am understanding more about the different bulbs I have. |
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19th Jan 2024, 9:51 pm | #7 |
Nonode
Join Date: Jan 2016
Location: Stafford, Staffs. UK.
Posts: 2,529
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Re: Christmas light problems - help please !!!
This reminds me of a discussion when I worked in Woolies. Someone brought back some tree light bulbs, saying they all failed very quickly, though they were the correct voltage for their string. I did query whether they were the correct wattage and they got quite stroppy telling me they had some random qualification, and that only the voltage was important, so what did I know. Store manager decided he knew better. Maybe he did, as it probably wasn't worth the argument, and maybe I should have known better myself.
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20th Jan 2024, 11:21 pm | #8 |
Triode
Join Date: Apr 2020
Location: Northallerton, North Yorkshire, UK.
Posts: 36
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Re: Christmas light problems - help please !!!
I have a large collection of used low voltage filament bulbs salvaged from Christmas fairy lights donated by friends and relatives when almost all of the rest of the world went led. In the annual December get the lights working session I have found a bench variable power supply invaluable in determining the power rating as well as the voltage rating of individual bulbs. Before I owned the power supply I used to use a simple rheostat and measure the voltage and current with two multimeters. As others have said matching the power rating is important to get even illumination and avoid blows.
Chris |
20th Jan 2024, 11:53 pm | #9 |
Dekatron
Join Date: Aug 2016
Location: Colchester, Essex, UK.
Posts: 4,081
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Re: Christmas light problems - help please !!!
...and just occasionally, a sealed packet of NOS spares will be found to have a rogue lamp of the wrong voltage or wattage, a situation exacerbated by the fact that some (and the push-ins in particular) have no markings. Reputation means nothing, i found one in a packet of Woolies lamps!
Dave |
22nd Jan 2024, 1:16 am | #10 |
Heptode
Join Date: May 2010
Location: Warminster, Wiltshire, UK.
Posts: 682
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Re: Christmas light problems - help please !!!
Ii always used to find the Woolworths bulbs were always a bit on the bright side and hence didn’t used to last as long as other makes.
Probably we shouldn’t of mixed different makes. Maybe if you used all of one make this wouldn’t happen. I assume between makes there is a slight wattage difference Andy
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22nd Jan 2024, 11:49 am | #11 |
Dekatron
Join Date: Aug 2003
Location: near Reading (and sometimes Torquay)
Posts: 3,086
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Re: Christmas light problems - help please !!!
Slow starting helps. I started doing that (with variac) to ours when I ran out of spares.
It's the same issue as series valve heater chains - if you have differing thermal inertias then during the startup some lamps are overloaded until it all reaches the operational current - the reason they added thermistors in TVs. I am considering adding a capacitor dropper but I need to recheck what happens during the startup with that. |
22nd Jan 2024, 4:06 pm | #12 |
Triode
Join Date: Nov 2014
Location: Leominster, Herefordshire, UK.
Posts: 25
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Re: Christmas light problems - help please !!!
Well thank you to everyone who commented. Both issues are now sorted out.
Firstly I was mixing my voltage and wattages which as everyone clearly explained leads to blown bulbs … I now have a string of 3w 20v bulbs and a string of 7w 16v bulbs. And secondly I found one of the milk glass bulbs was indeed a flasher bulb causing the whole string to flash ! I hadn’t ever realised these flash bulbs were around at the time of milk glass bulbs! So now they’re up and running so thanks to all. |
22nd Jan 2024, 9:38 pm | #13 |
Dekatron
Join Date: Jan 2006
Location: Ramsbottom (Nr Bury) Lancs or Bexhill (Nr Hastings) Sussex.
Posts: 5,814
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Re: Christmas light problems - help please !!!
I had two sets of twenty 12v bulbs. I thought those were too bright and when some failures occured I built a chain of thirty which worked out at 8 volts each. It wasn't a very sophisticated set-up but [to my surprise] it was quite bright enough and lasted about thirty years. They were only replaced out of family members wanting a change in the end
Dave W |