Advertisement
12 VDC Lighting Failure Mode
My Instrument Trailer is equipped with 12V DC incandenscent lamps overhead in each compartment. The bath & vanity gets more switching than any other and a failure mode has become critical. Swapping cooler LED arrays in is appropriate.
>>
Switching Direct Current is _always_ detrimental to switch contacts and burns holes in the copper straps inside the switch itself.
(Alternating Current has a self-quenching property because of the periodic zero crossing in the AC sine wive, and the problem is not usually severe.)
>>
Consequently I am in a position to repair the problem and have a couple of things in mind. First, of course will be to replace the switch itself with a snap-action with contacts rated for DC (no quench loads.)
The decision to convert _now_ to LED lighting is clear, and I have experimented already with the automotive replacements for brake/turn signal bulbs and side markers. I am comfortable with the Amber, but Red is considerable also. Of course I would prefer White light.
The dig is the fact that sockets for the incandescent bulbs that are stock in the lamp holder and lens assembly, are fitted for bulbs with ONE contact other than the metal can base. The turn signal and brake auto LED replacements have TWO contacts other than the metal can base.
The first modification to improve is to replace the lamp base sockets with TWO-plus-the-metal-can-base contacts, and wire them together. So rather than switching one bulb or two, both sides are either dim or bright at the same time, depending on the switch position.
I expect much better performance and life cycling.
The second modification will be to include a large current capable NPN bipolar transistor, so that the switch contacts will handle much less current, while the 12VDC power is still available to the contacts in the new sockets. (I am prefering 20A collector current devices with a CE breakdown over 120V, beta is on the order of >20.) With the opportunity to further set up for automation, I will keep the motion detector and dimming circuits to myself.
Anyhow. Be cautious about switching DC. The contacts are always much more vulnerable to burns.
My Instrument Trailer is equipped with 12V DC incandenscent lamps overhead in each compartment. The bath & vanity gets more switching than any other and a failure mode has become critical. Swapping cooler LED arrays in is appropriate.
>>
Switching Direct Current is _always_ detrimental to switch contacts and burns holes in the copper straps inside the switch itself.
(Alternating Current has a self-quenching property because of the periodic zero crossing in the AC sine wive, and the problem is not usually severe.)
>>
Consequently I am in a position to repair the problem and have a couple of things in mind. First, of course will be to replace the switch itself with a snap-action with contacts rated for DC (no quench loads.)
The decision to convert _now_ to LED lighting is clear, and I have experimented already with the automotive replacements for brake/turn signal bulbs and side markers. I am comfortable with the Amber, but Red is considerable also. Of course I would prefer White light.
The dig is the fact that sockets for the incandescent bulbs that are stock in the lamp holder and lens assembly, are fitted for bulbs with ONE contact other than the metal can base. The turn signal and brake auto LED replacements have TWO contacts other than the metal can base.
The first modification to improve is to replace the lamp base sockets with TWO-plus-the-metal-can-base contacts, and wire them together. So rather than switching one bulb or two, both sides are either dim or bright at the same time, depending on the switch position.
I expect much better performance and life cycling.
The second modification will be to include a large current capable NPN bipolar transistor, so that the switch contacts will handle much less current, while the 12VDC power is still available to the contacts in the new sockets. (I am prefering 20A collector current devices with a CE breakdown over 120V, beta is on the order of >20.) With the opportunity to further set up for automation, I will keep the motion detector and dimming circuits to myself.
Anyhow. Be cautious about switching DC. The contacts are always much more vulnerable to burns.
posted by:
|
Nevada
|
Advertisement
Advertisement
-
Re: 12 VDC Lighting Failure Mode
Wed, July 29, 2009 - 1:31 PMSwitching to LEDs will mean less current draw which will also help with your switches. -
-
Re: 12 VDC Lighting Failure Mode
Wed, July 29, 2009 - 6:13 PMnice one b. i was just thinking that -
-
Re: 12 VDC Lighting Failure Mode
Thu, July 30, 2009 - 2:57 AMAs was I, however, transistorizing is an interesting touch.
I would point out that transistorizing it is likely to introduce a leakage current, though, which may negate the benefit of having an efficient light by using electricity when the light is actually off.
-
-
Re: 12 VDC Lighting Failure Mode
Tue, August 18, 2009 - 7:58 AMgreetings, I'm new to the tribe(however I haven't been to the tattoo parlor yet...)
fascinating read on LED lights. I hope to design some LED fixtures and systems for architectural lighting and wonder if you have any experience with or desires in how to connect/wire them and transitioning from the Edison medium base, which will be obsolete in a few years.
I am also curious about the Leakage Current and how much power that will waste; have you got some numbers to share?
thanks,
Geoff -
-
Re: LED Leakage Current
Tue, August 18, 2009 - 10:51 AMleakage current in Light Emitting Diodes is _extremely_ low.
diode reverse bias leakage current is actually lowest in LEDs compared to any other rectifier technology
it is prefered in some high-performance low-noise amplifier designs for that reason only -
-
Re: LED Leakage Current
Wed, August 19, 2009 - 2:37 AMI think maybe it was in reference to the transistorized solution suggested earlier in this thread.
-
-
-
-
-
-
Re: 12 VDC Lighting Failure Mode
Wed, July 29, 2009 - 8:16 PMWent into a local Home Depot the other day and was surprised that they are now selling a selection of LED lighting from Philips. They have coll and warm white bulbs with various AC bases. I bought a 7 watt cool white that I'm using in a swag lampshade above my kitchen table. I'm really happy with the soft diffusion of the 4 LED's and their 25 degree spread. It replaced a 60 watt daylight spot and the LED gives off a brighter beam. It cost me $30 canadian. I'm going back for more. -
-
Re: 12 VDC Lighting Failure Mode
Thu, July 30, 2009 - 3:00 AMAs I sit here typing, I am basking in the glow of a 2.25W LED lamp purchased from Lowe's for $20 US. It was made by Utililight, and has nine 3-chip packages (i.e. 3 LEDs in one lens, making a total of 27 LEDs), and a native operating voltage of 12V. In addition to coming with a wall wart to plug it in, it comes with a "link cable" which would normally be used to link several of these together on one power supply, but which could also be sacrificed to the hardware hacker gods in order to send it power from an already 12VDC supply.
-
