|
Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
|
Thread Tools |
18th Feb 2020, 12:17 am | #21 | |
Octode
Join Date: May 2007
Location: Liss, Hampshire, UK.
Posts: 1,873
|
Re: Replacement bulbs with LED question
Quote:
|
|
18th Feb 2020, 12:35 am | #22 |
Nonode
Join Date: Jan 2010
Location: North Somerset, UK.
Posts: 2,129
|
Re: Replacement bulbs with LED question
If all four bulbs are run in series from an 18 volt supply, then a supply current of about 280ma is reasonable.
|
18th Feb 2020, 12:42 am | #23 |
Nonode
Join Date: May 2004
Location: Halifax, West Yorkshire, UK.
Posts: 2,587
|
Re: Replacement bulbs with LED question
I'll take your word for it 'broadgage' as I'm not prepared to try and do the maths but it seems an odd way to go about things. Also I'm not entirely sure from the pictures whether or not the bulbs are connected across the DC or AC output which will make a difference if switching to LEDs.
Alan Last edited by ajgriff; 18th Feb 2020 at 1:11 am. |
18th Feb 2020, 1:23 am | #24 |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,535
|
Re: Replacement bulbs with LED question
The pictures clearly show the lamps connected across one of the two 18V transformer secondaries. The other secondary feeds a bridge for the electronics dc supply. It may be "odd" but it looks deliberate. The underrun bulbs would give a fairly gentle yellowish light which would be quite in keeping for the application. Lower current 6V bulbs could of course just be fitted if required.
If LEDs are seriously favoured, it looks like with a little modification another bridge and capacitor could be fitted to provide a suitable dc supply!
__________________
....__________ ....|____||__|__\_____ .=.| _---\__|__|_---_|. .........O..Chris....O |
18th Feb 2020, 1:30 am | #25 |
Nonode
Join Date: May 2004
Location: Halifax, West Yorkshire, UK.
Posts: 2,587
|
Re: Replacement bulbs with LED question
Makes sense Chris although it wasn't clear to me. Must be getting tired as it's late - that's my excuse anyway.
Alan |
18th Feb 2020, 3:37 am | #26 |
Nonode
Join Date: Oct 2010
Location: Tintinara, South Australia, Australia
Posts: 2,339
|
Re: Replacement bulbs with LED question
If you are doing the LED fitting yourself (as opposed to buying LED replacement units), there is no need to to rectify the AC.
All you need to do is use two LEDS per each bulb location, connected in anti parallel to each other with a capacitor dropper. You can even use the MES globe bases by carefully breaking out the glass and soldering the LEDS in. |
18th Feb 2020, 10:59 am | #27 | |
Tetrode
Join Date: Aug 2009
Location: Derbyshire, UK.
Posts: 50
|
Re: Replacement bulbs with LED question
Quote:
That could be true I suppose. I've never seen the lamps work you see as it came to me a few weeks ago. Definately all of the bulbs are blown. |
|
18th Feb 2020, 11:01 am | #28 | |
Tetrode
Join Date: Aug 2009
Location: Derbyshire, UK.
Posts: 50
|
Re: Replacement bulbs with LED question
Quote:
|
|
18th Feb 2020, 11:26 am | #29 |
Hexode
Join Date: Jun 2018
Location: Buckinghamshire, UK.
Posts: 387
|
Re: Replacement bulbs with LED question
It's rather diificult to imagine four bulbs wired in series all failing simultaneously. I would think it more likely that one has failed causing all four to extinguish?
Surprise has been expressed at the lamp power, but they would have be running at well under a watt each. In a car application the illumination of the smallest dashboard instrument would have used a 2W bulb or sometimes more. I think it'll be difficult to match the pleasant warm glow of an under-run filament using LEDs. I'd simply replace all four bulbs and move on. They'll last for many, many years running at 4.5v. Cheers |
18th Feb 2020, 12:14 pm | #30 | ||
Dekatron
Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 5,761
|
Re: Replacement bulbs with LED question
Quote:
The attached sketch shows the physical appearance of an LED and the theoretical symbol. LEDs have one leg longer than the other - that is the positive (anode) connection. (The negative connection also has a small 'flat' on the rim of the lens, but not very obvious.) Hope that helps a bit.
__________________
David. BVWS Member. G-QRP Club member 1339. |
||
18th Feb 2020, 2:06 pm | #31 |
Tetrode
Join Date: Aug 2009
Location: Derbyshire, UK.
Posts: 50
|
Re: Replacement bulbs with LED question
Thanks David. And many thanks to all with this so far. This place is brilliant.
Thanks, Tirgon. I think they must have blown over time. No idea if all blew at the same time. They might even be the original bulbs. The unit looks like it's from the 80's. I think I'll just get some normal bulbs first and see if they work. Who knows, they might have been replaced with the wrong type and they all went at the same time and never replaced. https://internationallamps.co.uk/pro...0-6-5v-300ma/] But do you think these would work as a replacement? once I've established the ones above work properly? https://internationallamps.co.uk/pro...e10-mes-white/ ...Or do LED bulbs need to be wired up differently? BTW. I do have a multimeter. I could check the voltage of the bulb fittings but which setting would be best to use on the multimeter? |
18th Feb 2020, 4:23 pm | #32 | |
Hexode
Join Date: Jun 2018
Location: Buckinghamshire, UK.
Posts: 387
|
Re: Replacement bulbs with LED question
Quote:
Cheers |
|
18th Feb 2020, 5:06 pm | #33 |
Tetrode
Join Date: Aug 2009
Location: Derbyshire, UK.
Posts: 50
|
Re: Replacement bulbs with LED question
Ahh... okay.
Well, just checked all the bulbs again and they are definitely dead. So maybe someone kept swapping them round, maybe? I've ordered some identical bulbs so I'll update when I get them. |
18th Feb 2020, 5:09 pm | #34 |
Dekatron
Join Date: Nov 2011
Location: Surrey, UK.
Posts: 4,394
|
Re: Replacement bulbs with LED question
Just occasionally, I've noticed series arrangements of bulbs all being open circuit- I wondered if the first to go open circuit goes briefly into low-impedance metal-vapour arc mode, giving the remaining old and weak filaments a final kick-up that fractures them. This particular case is a low-voltage, low-energy situation though, so that seems unlikely.
More prosaically, a string of weary and time-served filaments might simply fracture if the device is dropped or heavily knocked. |
18th Feb 2020, 7:15 pm | #35 | |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,535
|
Re: Replacement bulbs with LED question
Quote:
__________________
....__________ ....|____||__|__\_____ .=.| _---\__|__|_---_|. .........O..Chris....O |
|
18th Feb 2020, 8:26 pm | #36 |
Guest
Posts: n/a
|
Re: Replacement bulbs with LED question
18V AC unloaded may go up to 24V, ideal for 4 x 6.3V bulbs. And as it is raw AC I would stick to filament lamps. As to the 0.28A output being overloaded I bet the other side has very little taken from it, all will be well.
|