The Second 12v DC light keeps blowing - yet the first is fine.

**GT250** · 07-08-13, 04:21 PM

Hi all,
Driving me f*ing crazy this one! I've ran out of ideas and now down to the last globe.

For years (maybe 4), i've had two 12v DC CFL's in the kitchen ceiling. All working fine - but in hindsight the second one has glowed 'dimmer' or took longer to fire up.
These globes are around the house in general and over time they have gone. So i bought some new ones off ebay.

Over the last 2 months, every globe i have placed in the kitchen 'second' light housing has blown!

And i can't work out why. One lasted 1 week. One lasted 3 switch's on.

I originaly had the wiring (from a normal household light switch 4 gang), whereby the + and - ran from the switch to the first globe and then off that housing to second globe.
So after all these blowings, i decided to run a seperate + - to the second globe. No good.

Thinking that the length/thickness of the cable was not allowing enough current through and these 'new' globes were more sensitive. I used a much thicker + cable from the light switch to both globes and used a thicker cable - from the first globes -.
No good.
Might work for 3 days or 5. Might blow on the 2nd switch on.

Next i wired from the light switch a seperate + and - directly to the second globe. No good. After 3 on/offs - gone. I even had the housing dangling down to 'see' what happens and i saw a little puff of smoke from the 8th globe i had...

Now i have one globe left ($78 for 10qty).

In all cases with the new globes, they fired up straight away together. With the old (4yr ones), the second one always came on last - in a series power configuration [+/- from switch to first globe, then off the first globe to the second globe] so i assumed the first globe took the first hit and the second caught up!

But now with these new globes (much brighter btw), they seem to fire up at the same time, not matter the cabling layout.

I've checked the housing/connections etc of the second light and it all feels ok. Jeeze! It's just + and - terminals...!

Just over 13v at the terminals when i flick the light switch.
Yet the first light has not blown at all....

What is going on?

Is there some sort of feedback from the electronics not talkign to each other?
Going crazy!!!

**mtv** · 07-08-13, 04:32 PM

Unless I missed it, you haven't described the power supply... what it is and where it is.

Is it regulated?

Are both lamps powered from the same DC power supply?

Are there any electronic components in the lamp holders?

Have you used any of the ebay lamps in the fitting that isn't blowing lamps?

EDIT: Hmmm.... just noticed you said the two lamps are wired in series.

I suspect that's the problem... if they are 12 VDC, they should be wired in parallel with a DC power supply with sufficient current capacity (plus a bit in reserve) for the load.

**Uncle Fester** · 07-08-13, 05:17 PM

MTV, I think he mains daisy chaining from one globe to the next not actually series. On one picture you can see both red and black going in and out of the socket.These globes would not work on 6V at all.

GT250 It would not be the first time somebody(like me) bought a batch of Chinese made lamps and most of them turned out to be faulty.

**Skepticist** · 07-08-13, 11:32 PM

Is there a significant temperature difference between the 2 locations?
EG 1 of the lamps is directly above the hotplates or something like that (just a thought because temperature really cuts down the life expectancy of CFLs - the inverter capacitors suffer badly especially if not good quality high temp rated types)

**Reschs** · 08-08-13, 12:26 AM

First test should have been, remove first lamp and store. Fit both lamp holders with identical lamps. Does the same scenario apply?
If not you have shitty lamps. If the scenario remains the same put the stored lamp in the second position to see if it blows.
If it blows and the new one in the First position survives, we have a mystery.

**GT250** · 08-08-13, 05:30 AM

Thank you for the replies guys.

Just a quick post as got to head out (Hate getting up at 4:00!).

THe power supply is from an Invertor that has 12v outputs.

I've even put the 1st light globe (that has never blown), into the the second light postion and it lasted a few day!!

The only common denominator left is to change the light socket housing - but surely it can't be that? I've checked the cabling, nothing loose. If the globe is inserted the wrong way it doesn't fire up (DC), put the right way, it fires up..

Going crazy..

**Uncle Fester** · 08-08-13, 09:41 AM

Originally Posted by GT250

Thank you for the replies guys.

Just a quick post as got to head out (Hate getting up at 4:00!).

THe power supply is from an Invertor that has 12v outputs.

I've even put the 1st light globe (that has never blown), into the the second light postion and it lasted a few day!!

The only common denominator left is to change the light socket housing - but surely it can't be that? I've checked the cabling, nothing loose. If the globe is inserted the wrong way it doesn't fire up (DC), put the right way, it fires up..

Going crazy..

Check that there are no insulation batts or anything that could be blocking the airflow when the lamp holder is inserted in the ceiling.
Might just be a coincidence that the old bulb died shortly after you swapped it.

**Tiny** · 08-08-13, 11:11 AM

Originally Posted by GT250

THe power supply is from an Invertor that has 12v outputs.

Going crazy..

That link is to a Regulator, not an inverter?
The Plasmatronics Regs are top range so it should be good (I have one as well).
One output from the regulator is for charging batteries from the solar input.
Another output is for 12v load, that is your power supply from your battery via the regulator if you wish to use the regulators logging & battery protection features.
The regulator listed has a max load of 30A, if you get close to or past this limit you may get blackouts or possibly current fluctuations that could damage lights.
If you're not using close to its limit then that isn't a problem, just thought I'd mention that as a possibility.

Alternatively your 12v power supply can also be direct from your battery via a fuse or fuse box. Only load restrictions are wiring, fuses & battery limitations.

BTW I live on a standalone power supply & have had countless CFL failures on 12v lights, they just don't seem to make them with any quality control.
Part of the problem could be that they can't cope with the voltage fluctuations from approximately 12V to 14.5V depending on if the batteries are under heavy load or being Boost charged.
I've tried several different brands from expensive to not so expensive (there isn't any cheap ones in 12v DC) & have some that lasted months to some that are still going after years in service.
I can't find any correlation to position of light fitting in house or brand of light globe, it is just a lottery which ones will live or die.
I even changed from using Bayonet fittings to Edison Screw fittings, with the same results, poor life expectancy for some lights & not others, in my opinion due to poor quality in manufacturing of lights.
I am currently thinking of rewiring for 240v lights as everything else in house now is 240v from my Selectronic Sinewave inverter, so I say why not, the 240v CFL lights are at least a little better priced & a much better range.

**mtv** · 08-08-13, 11:19 AM

I know this doesn't solve the mystery, but if you are considering replacing a fitting, why not replace both with LED lamps?

**GT250** · 08-08-13, 02:06 PM

Yes I have thought about the LED ones.
But I've never found them that bright (did try some in a bedroom ages ok), but some of the individual LEDs have gone.

Can anyone recommend some 12v Bayonet and Edission LED lights that are very bright and give off 'sunlight' light, or close to? Good quality, don't mind paying extra if I don't have to faff around like these things.

**Tiny** · 08-08-13, 04:45 PM

Originally Posted by GT250

Yes I have thought about the LED ones.
But I've never found them that bright (did try some in a bedroom ages ok), but some of the individual LEDs have gone.

Can anyone recommend some 12v Bayonet and Edission LED lights that are very bright and give off 'sunlight' light, or close to? Good quality, don't mind paying extra if I don't have to faff around like these things.

not only are they not that bright but they are mostly narrow spot beam so you need heaps of them to properly light a room.

**mtv** · 08-08-13, 05:14 PM

I've been using these and found them to be quite good.

I'd only compare brightness to the same value of a CFL though.

They have a very soft diffused light with an extremely wide beam of 270°.

They are mains powered though, not 12V.

Most of the 12V LED's I've seen are more of the MR16 type but there are quite a few on the market now with diffusers.

Check some of the lighting places as they are becoming more popular and with increased output.

**Tiny** · 08-08-13, 06:12 PM

Thanks mtv, I have been looking at those as well as these
That's why I'm contemplating switching over to 240v lighting.
I guess the bulk of the market is 240v, so that's where the best products are.

For 12v the best place to shop these days is ship chandlers, although they are not necessarily stocking lights for lighting large areas like a house.

**GT250** · 09-08-13, 08:54 AM

Hi mtv,
Thanks to you and everyone else for your replies.

I've actually put those 240v 10w and 5w's throughout the house.

Just that from ages ago i laid 2x pure 12v feeds from the regulator (not inverter

), through the house.

I'll do some research into 12v LED lighting.

**GT250** · 06-09-13, 06:58 PM

Sorry for the delay. Wanted to make sure.

I bought some of these;

or; 9W LED Corn Light Bulb Lamp

Had them in for 3 weeks now and all working fine. Been turning them on and off. Left them on for 8 hours and then flicked them on and off repeatedly...
All working fine.

Surely, must have been some freq issue with the other CFL's?

Anyway. $12 each (ow!), but give out great light. 9W as against the CFL's at 11w or 13w.

Thanks for everyones help and advise.

Cheers,
GT250.

**Downunder35m** · 07-09-13, 12:36 AM

There is one very common problem when using a lot of CLF at once:
Power spikes and the lack of the correct voltage to fire up.
Less of a problem in 240V but in 12V DC the electronics are often dirt cheap.
If you still have the CLF's you might be able to replace the Mosfet inside (about 80 cents each and they should work fine again.
A very common problem is overheating due to cheap and only most basic components.
CLF'a are actually designed to be used with the fitting down, so no ceiling mount.
I had a few in the shed when it was still solar powered and the ones mounted the right way are still in use, all of the ones mounted on the ceiling died within a few weeks.
Repaired most of them with better parts but got fed up in the end and got 240V put in the shed now.

**typan** · 07-09-13, 08:36 AM

What I would do is wire each lamp holder back to the power supply, that would stop any voltage drop & any spikes if any.

**Downunder35m** · 07-09-13, 07:00 PM

From within the resistance of the cable, yes.
But not caused by the power supply itself.
If you check with an old styly oscilloscope you will the spikes I mean.
Keep in mind that your system has to deliver a lot of power instantly when the lamps are switched on, it will drop once they are at operating temp.
LED drivers work in a different way and can compensate "bad" things a bit easier than the CFL electronics.
For those interested: a 12V CFL chops the DC to about 400V AC, this again is pumped up to reach the about 1000V to fire the lamp up,
once on the voltage drops to around 200V.
A 240V CFL only makes 400V DC and this is pumped to the necessary voltage directly through the driver.
So the system is much simpler in design with only half of the power mosfets.
A different system is used for those flouro work lights, the 18W lamp is driven directly by about 600V DC from a converter similar to what is used charge the flash on your camera.
If you still use those CFL's it might be worth to check their temp after about 2 hours of use, if above 60° you have a clear indicator why they give up so fast.