Under Cupboard Halogen Lamps don't last long

[TheCorner]

Hi,

We had a new kitchen fitted about 2 year ago and part of this was under cupboard 12W Halogen Lamps - There are a set of 3 on one side and set of 5 on the other, each set going into a transformer which I expect goes to a socket behind cupboards. They are activated by a switch on the wall obviously.

If I have lamps in all of them one of the lamps will blow pretty quickly, followed by another after a couple of weeks.

I'm guessing there is some sort of overload problem, but why and how do I fix it please?

Thanks

 

[Taylortwocities]

Did you mean 12volt, not 12watt lamps?

Usually its cheap lamps that cause this problem, or cr@p fittings. They don't like being in steamy places, or where there is any vibration.

I do not fit these any more as they are always trouble.
LED strips are far better and last an advertised average of 25,000 hours!

 

[Porque223]

Lamp life is proportional to voltage to the 12th or 14th power so if you can slightly reduce voltage with a resistor or by using thinner wires you may find a good compromise between brightness and lifetime.
Scrapped TV sets and receivers have power resistors ideally suited to this kind of thing.
You could use a diode but this changes the color temperature substantially, as would putting two bulbs in series. For my installation I used a small fluorescent lamp ballast as a series inductor but you can also use a capacitor but run all this by the sparkies on this site.

 

[333rocky333]

I would propose locating the transformers, possibly there sitting on top of the unit with the wires dropping down behind them.

Some are poor quality and the plug in connectors low grade, it would also allow you to check lamp wattage is within there designed operating range

As TTC said there is more reliable led stuff nowadays, some examples can be seen on displays at B+Q, wickes etc, though may entail modification to the wiring

 

[RF Lighting]

It's usually either carp lamps, or lampholders.

I too only fit LED these days.

 

[JohnW2]

Lamp life is proportional to voltage to the 12th or 14th power

In the UK, supply voltage is allowed to vary from 216.2V to 253V, the main determinant being the distance from transformer to consumer (and, of copurse, the loading). If what you say were correct, someone with a supply voltage at the bottom end of the range would enjoy a lamp life roughly 6.6 - 9.0 times the lamp life experienced by someone whose voltage was at the top of the permitted range. Do you believe that is the case?

Kind Regards, John

 

[333rocky333]

John, can you explain what the 12 to 14 power thing means please

 

[Porque223]

If what you say were correct, someone with a supply voltage at the bottom end of the range would enjoy a lamp life roughly 6.6 - 9.0 times the lamp life experienced by someone whose voltage was at the top of the permitted range. Do you believe that is the case?

Kind Regards, John

Over here it's 120 +/- 5% or +/- 10% depending on what state you live.
I can't personally confirm or disprove it but the people who study this stuff would, I guess, say yes.

Look it up, decide for yourself.

BTW, the brightness is supposed to vary with V^3.5 and insulation lifetime halves for each 10C additional along with many other chemical reactions that double in speed for each 10C increase.

I was having 40w bulbs in the front burning out frequently so I wired two in series. It's a very pleasing light and they are holding but this is of course anecdotal evidence.

I also had a friend whose auto voltage regulator went out so all the lights got whacked with probably 17vdc. The headlights burned out immediately but the smaller lights were still working so it also must depend on bulb wattage.

 

[JohnW2]

John, can you explain what the 12 to 14 power thing means please

Given a number, say N, squaring is 'to the power 2' (i.e. N x N), cubing is 'to the power 3' (i.e. N x N x N), so 'N to the power 12' would be:
N x N x N x N x N x N x N x N x N x N x N x N

If, as Porque suggested, the life of a lamp is inveresely (he forgot to say that) proportional to the 12th power of voltage, then the ratio of lamp life for two voltages, say P and Q would be:

P x P x P x .... x P (12 of them)
divided by
Q x Q x Q x .... x P (12 of them)

Rather than do those massive multiplications and then divide one by another, on can just do it in 'pairs', namely

(P/Q) x (P/Q) x (P/Q) x .... x (P/Q) [again, 12 of them]

If, per my example of UK voltages P is 253 and Q is 216.2, the (P/Q) is approximately 1.17, hence the ratio of lamp lives would be:

1.17 x 1.17 x 1.17 x .... x 1.17 (12 of them)

... which works out as about 6.6. You can just do the multiple multiplications on a calculator, but if your calcuator offers an "x^y" function, you can just do it directly by entering 1.17, then press x^y, then enter 12, then press 'equals'.

A bit difficult to express in prose (it's really a 'blackboard job'!), but I hope the above makes some sense!

Kind Regards, John

 

[seasickstevie]

I've got a headache

 

[JohnW2]

Over here it's 120 +/- 5% or +/- 10% depending on what state you live.

Here its 230V -6% +10%. That arises largely for historical/political reasons. The nominal UK voltage used to be 240V (and that in the rest of Europe 230V or whatever). When they decided to 'harmonise' voltrages across Europe, AFAIAA no country actually changed their voltages, but they 'tweaked' the acceptance limits so that everyone complied!

I can't personally confirm or disprove it but the people who study this stuff would, I guess, say yes. Look it up, decide for yourself.

If I ever have some spare moments, I might. Although what you say is obviously qualitatively correct, I would find it rather surprising if there were a 6-fold to 9-fold difference in life expectancy just within the range of permitted supply voltages.

Kind Regards, John

 

[JohnW2]

I've got a headache

I'm not surprised, and don't imagine that you are alone - but he did ask

Kind Regards, John

 

[EFLImpudence]

Given a number, say N, squaring is 'to the power 2' (i.e. N x N), cubing is 'to the power 3' (i.e. N x N x N), so 'N to the power 12' would be:
N x N x N x N x N x N x N x N x N x N x N x N

If, as Porque suggested, the life of a lamp is inveresely (he forgot to say that) proportional to the 12th power of voltage, then the ratio of lamp life for two voltages, say P and Q would be:

P x P x P x .... x P (12 of them)
divided by
Q x Q x Q x .... x P (12 of them)

Rather than do those massive multiplications and then divide one by another, on can just do it in 'pairs', namely

(P/Q) x (P/Q) x (P/Q) x .... x (P/Q) [again, 12 of them]
If, per my example of UK voltages P is 253 and Q is 216.2, the (P/Q) is approximately 1.17, hence the ratio of lamp lives would be:

1.17 x 1.17 x 1.17 x .... x 1.17 (12 of them)

... which works out as about 6.6. You can just do the multiple multiplications on a calculator, but if your calcuator offers an "x^y" function, you can just do it directly by entering 1.17, then press x^y, then enter 12, then press 'equals'.

A bit difficult to express in prose (it's really a 'blackboard job'!), but I hope the above makes some sense!

Kind Regards, John

 

[JohnW2]

As I wrote to SNM, it's not my fault - I was merely reply to a specific request!

Kind Regards, John

 

[333rocky333]

Thanks john,
I knew if anyone can explain, it would be you and as he is in usa maybe hes in bed.
I do beleive it prolongs the lamp life, possibly not that much though and do promote people to use there dimmers at 90% but have no facts it works, only what dimmer firms claim, and some claim 50% extra lamp life with just 10% dimming, but i suppose they would be biased.

Some even claim lamps are made for euro market and designed for 220 volt and over that has effects on the lamps.

I do recall in the 80's significant problems with the short life of 12v halogens this was caused by the torrodial trans giving out 13 volt plus.