Which bayonet type is this?

[mascip]

Hi, in a bayonet socket I have tried a 12V BA15D light bulb (LED), but it doesn't work.

Trying the light bulb with a battery, I found out that one of the two pins at the bottom is for the positive, whilst the other pin is useless, as the negative must be applied to the light bulb metal body.

The bayonet socket provides positive and negative on the two pins at the bottom, but the metal body is not connected to the negative.

So that's why this light doesn't work: the negative given by the socket is not in the same place as what the light bulb expects.

This tells me that it's not a BA15D bulb that I need.

So, which type of bayonet fitting is it, that I must get?

 

[Darkwood]

Hi mascip, welcome to the forum.

Thread will be relocated to DIY section and you will be given access when admin' is next online.

 

[Spoon]

Usually these types of lamps have a Bright and Dim mode. Hence the two contacts at the bottom. The body is the negative.
A toggle switch is used for selecting which mode. If you are testing the socket then you will get 12V on one contact and nothing on the other, due to the switch.
Have you tried another type of lamp rather than a LED?

 

[mascip]

Thank you

I measured 12.7v between the two contacts at the bottom of the socket, but nothing between its body and the contacts. I also checked that connecting the light bulb directly to the battery did make the light glow (negative on the bulb's body, positive on a contact at its bottom), which confirms that in the socket, the negative was not connected to the body; because it would have made the light glow.

My guess is that this socket is wired for a different type of light bulbs, which has the negative on one of the two contacts, instead of the body. Does/did such a socket type exist? (it might be up to 30 years old, and quite possibly not intended for LEDs?)

Or did I miss something somewhere? I measured it three times to double check, but it's so easy to miss something simple.

 

[Barry White]

They do a bulb/lamp with the power supplied by the pins old cars and lorries had them and they were used on buses as interiour lights see
TO CLEAR - Ring 12v 24w SBC BA15d Bus Bulb - R810 | eBay.

You either have a faulty or dual "fillament/led" bulb .I suspect its a stop n tail bulb for a car

 

[mascip]

So this "bus" bulb would get power supplied by the pins? How do you understand this by reading its description?
Would it exist as LED, to use less power?

I tried this same thing with 3 different LED bulbs (different makes), all BA15D, and all with the same result so it's not a faulty bulb.

 

[Deleted member 26818]

BA15 is the size of the lamp, i.e. it has a diameter of 15mm.
The lamp may have one or two contacts on the bottom (single or twin filliment).
Both contacts usually are positive and the body negative
One contact will be low wattage the other higher wattage, i.e. as with stop tail light bulbs, one will be 5W the other 21W.
You need to check whether your lamp holder is for a single or twin filliment bulb.
Another thing you should be aware of, is that the two pins which stick out from the side of the body are off set with twin filliment bulbs. One pin higher than the other.
This is to ensure the bulb is inserted correctly.
If it is attempted to insert the bulb incorrectly, then either the bulb cannot be inserted or sometimes it inserted but does not locate correctly, and the lamp does not work.
Some bulbs have the pins off set round the circumference of the body, both are at the same height, just not opposite one another.

 

[mascip]

Thanks for the explanation spinlondon!

I inserted the bulbs correctly: the two pins that stick out were each on their correct side.

How do I check whether the lamp holder is for a single or twin filament bulb?

 

[Barry White]

So this "bus" bulb would get power supplied by the pins? How do you understand this by reading its description?
Would it exist as LED, to use less power?

I tried this same thing with 3 different LED bulbs (different makes), all BA15D, and all with the same result so it's not a faulty bulb.

because I have fitted them in the past in 12v and 24v options and you can clearly see a single filament.
link us to the bulb you bought ?

or contact these guys for leds

http://www.dynamoregulatorconversions.com/online-shop-for-led-bulbs-and-light-boards-etc.php

 

[mascip]

Here are the three LED bulbs I tried:
- LED 1
- LED 2
- LED 3

The socket is part of a Navigation light for a boat from the 70s or 80s, so it's probably quite old.

 

[Barry White]

led 2 and 3 are dual fillament stop and tail bulbs (well dual led) the negative to the outer metal case and positive to either or both pins on the base to illuminate the bulb either dim or bright or even both sets.
suspect led 1 is the same but carnt be sure with the info supplied.

 

[mascip]

I'm guessing I won't find a LED that suits this lamp socket, so I should just get a new socket, probably. Or in this case, a new navigation light.

Thanks for your help

 

[Barry White]

you will get a led a quick search of ebay produces these 2x MG TRIUMPH JAGUAR AUSTIN HEALEY MORGAN LED BULBS GLB209 BA15D 5W BAYONET | eBay
depends on how bright you need them at a guess these are equivalent to a 5w incandesent lamp.

 

[mascip]

What is the difference is between these light bulbs and the ones I bought? Does GLB209 mean that the negative connects through the second contact at the bottom?

 

[Barry White]

Older bayonet bulbs were double contact and powered the the fillament through just the pins and polarity did not matter. later bulbs used single pin and the"outer can" to power the bulb. Then along came the dual fillament bulb (used for the stop and tail lights on cars) its basically 2 bulbs in one so each pin powers up an individual fillament using the outer can as a return.
some leds are polarity conscious if so just insert and if it dont work turn it around 180 degrees and reinsert.

the bulbs you bought are 2 bulbs in one used for stop and tail on cars the description is written in chinese then changed to english and hence the confusion both bulb types have the same size and number of pins.The pins are just connected differently.

 

[mascip]

Very clear explanation, thank you!

"Double contact" is the key word I needed to find the appropriate LED bulb. Great!

 

[Marvo]

Re: Reported Post by darkwood

If it's a single filament BA15D and the bayonet pins aren't at different heights then the holder (base) will obviously accept the lamp in two possible directions.

With an old fashioned filament lamp this wasn't a problem because it would work equally well in both directions. With new LED type lamps polarity is a big issue, it will only work one way around in the fitting and it could be damaged the other way around.

It's very possible you've already damaged the lamp already by accident so test it on a bench with a battery first. Then you'd need to establish which side of the lamp holder is positive and preferably mark it so you can ensure when the lamp is inserted its positive side is in contact with the positive side of the lamp holder before putting power on it.

 

[Richard Burns]

Lamp designations are like this

B a 15 d
Bulb, all purpose shape, 15mm diameter, double contact
also known as SBC small bayonet cap

B A 15 s
single contact
also known as SCC single centre contact

B a u 15 s
120° off set pins single contact
B a y 15 d
different height pins double contact double filament (can be single filament)
B a z 15 d
120° off set pins double contact double filament

However some manufacturers are a bit lax about this and may not specify correctly.

You were originally correct with the bulb designation, the supplier was not.

 

[BroadReach]

Please bear in mind if this is for use in a boat Nav Light, the filament used in old nav lights were specially designed for a pin point source. i.e. the filament is in a straight line up and down not curled round like a domestic lamp.

This is required to ensure the light is only visible through the correct angle of view.

Normal LED replacement bulbs may not give the correct light pattern.

 

[Marvo]

Please bear in mind if this is for use in a boat Nav Light, the filament used in old nav lights were specially designed for a pin point source. i.e. the filament is in a straight line up and down not curled round like a domestic lamp.

This is required to ensure the light is only visible through the correct angle of view.

Normal LED replacement bulbs may not give the correct light pattern.

Good point, some of those old navigation lights had a coloured fresnel type lenses in which case the exact position of the light source would be critical.