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Old 19th Nov 2021, 3:04 pm   #1
SiriusHardware
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Default Ballast in halogen lamps (sometimes)

I noticed my Dad's floor standing halogen uplighter (with 400W 118mm R7 halogen bulb) was at times consuming half of all the power being used by his house, according to his smart meter. This light is on every day from dusk until bedtime.

I've bought a 30W LED equivalent. It says in the instructions with the new LED assembly that if there is a 'ballast' in series with the original bulb it has to be removed (shorted out) before this new bulb is fitted.

I've often heard of ballasts in the context of flourescent lights, but in the context of Halogen lights, what are they (inductor, resistor?) and what is their original purpose? It appears that not all halogen light fittings have them because the instructions are to remove them IF fitted.
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Old 19th Nov 2021, 3:27 pm   #2
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Default Re: Ballast in halogen lamps (sometimes)

I think that is to cope with fluorescent fittings too.
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Old 19th Nov 2021, 3:40 pm   #3
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Default Re: Ballast in halogen lamps (sometimes)

Yes, I think the manufacturer's have copied and pasted from their instructions for their fluorescent-replacement products.
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Old 19th Nov 2021, 3:51 pm   #4
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Default Re: Ballast in halogen lamps (sometimes)

Lower voltage halogen bulbs last a lot longer than mains voltage ones. Some parts of the lighting industry refer to anything other than a switch between mains and bulb as a ballast.

Is there a dimmer?

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Old 19th Nov 2021, 4:38 pm   #5
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Default Re: Ballast in halogen lamps (sometimes)

Metal halide discharge fittings have ballasts and some take linear, double-ended lamps. Your LED might be intended to replace either tungsten or metal halide, hence the possibility of there being a ballast or not.
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Old 19th Nov 2021, 5:13 pm   #6
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Default Re: Ballast in halogen lamps (sometimes)

This is a mains powered bulb / led replacement. Yes, there is a dimmer but the LED replacement is specifically sold as dimmable. There remains the possibility that it might not be the 'right sort' of dimmer, but that was a gamble I took.

The replacement bulb is also colossal compared to the original thin tubular bulb so it remains to be seen whether it will physically fit into the space available. It won't be possible to fit the protective glass over the top but that is mainly there to stop people from touching the dangerously hot halogen bulb. The replacement should run cooler.

This is your typical domestic floor standing uplighter with a secondary gooseneck reading lamp, the main lamp takes tubular Halogen bulbs which look like this:

https://www.diy.com/departments/dial...2669241_BQ.prd

Cheap to buy, but definitely not cheap to run.
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Old 19th Nov 2021, 5:39 pm   #7
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Default Re: Ballast in halogen lamps (sometimes)

(-Almost certainly the new lamp won't like the old dimmer, they usually flicker then expire.
Not an issue of course, just lock it at 100% or if sequential switching, bypass it or swap connections.)
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Old 19th Nov 2021, 5:47 pm   #8
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Default Re: Ballast in halogen lamps (sometimes)

Apparently it will be OK with a trailing-edge dimmer, so say the instructions with the new LED replacement bulb. Do I know whether the dimmer circuit is leading edge or trailing edge? Of course not. I bought dimmable because my Dad does occasionally turn it down to, oh, only 200W or so, so I do ideally need that feature to work.

The lamp is I would say about 15 years old - apologies but I thought I had posted this in 'Modern Technology' since it concerns a relatively new lamp and a LED replacement.
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Old 19th Nov 2021, 7:52 pm   #9
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Default Re: Ballast in halogen lamps (sometimes)

Quote:
Originally Posted by SiriusHardware View Post
The replacement bulb is also colossal compared to the original thin tubular bulb so it remains to be seen whether it will physically fit into the space available. It won't be possible to fit the protective glass over the top but that is mainly there to stop people from touching the dangerously hot halogen bulb. The replacement should run cooler.
I don't think the glass is to protect from heat. Pretty sure the glass would also be hot enough to cause a nasty burn.

I would think that the glass is there to absorb UV light that can cause damage to skin. Not all halogen lamps emit this (depends on the glass they are made of) but the manufacturer can't be sure you would replace it with a UV safe one.

There was a particular product manufactured by various companies. Some protected the plastic lens against potential damage from non UV protected lamps. Others used UV protected lamps but then customers got upset when they didn't buy the 'right' lamps from the original manufacturer and the lenses yellowed.
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Old 19th Nov 2021, 9:11 pm   #10
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Default Re: Ballast in halogen lamps (sometimes)

I confess I had not thought of that. I've come across quite a few of these where the user / owner asked me to look because there was a horrible smell like burning hair coming from the lamp. Usual cause: No glass shade and an unfortunate moth lured to its doom. I've always thought the shade (if fitted) at least gives the moth a bit of a chance.

If the LED replacement works they should hopefully survive for long enough for me to rescue them and put them outside.
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Old 21st Nov 2021, 12:19 pm   #11
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Default Re: Ballast in halogen lamps (sometimes)

The protective glass is to prevent hot glass shards from flying across the place should the halogen bulb explode, modern LED replacements don't require the glass.
The only issue I can see is the dimmer causing the bulb to behave erratic, apart from that, the bulb should be compatible.
EDIT: check the lamp dimmer for it's minimum wattage, most halogen dimmers go down to 60w min loading.
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Last edited by Glowing Bits!; 21st Nov 2021 at 12:22 pm. Reason: Added more info
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Old 21st Nov 2021, 7:22 pm   #12
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Default Re: Ballast in halogen lamps (sometimes)

Metal halide lamps make explicit mention of the need to cover them with safety glass to mitigate the risk of explosion upon failure. As Lucien Nunes mentions, some metal halide lamps fit in the same or similar sockets but do require a ballast.
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Old 21st Nov 2021, 7:33 pm   #13
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Default Re: Ballast in halogen lamps (sometimes)

Quote:
Apparently it will be OK with a trailing-edge dimmer
A trailing edge dimmer is one generally aimed at LED bulbs although they will drive an incandescent bulb as well.

Most traditional dimmers are leading-edge, aimed solely at incandescent bulbs and the sort that contain a triac. A very few 'dimmable' led's will work with either leading or trailing edge but they are few and far between, Osram/LEDvance do one that works great but it's hit and miss with the others.

Even winding a leading edge dimmer up to full and plugging an led bulb in is no guarantee it will work. HWMBO has a leading edge dimmer in an ornamental lamp and there's been a supermarket LED in there for some time. It tends to have a little flicker every so many minutes, sometimes just a blip, but I know its happening and it will get a halogen bulb in there as soon as I can find one.
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Old 23rd Nov 2021, 5:15 pm   #14
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Default Re: Ballast in halogen lamps (sometimes)

Is there a 'bush electrician' trick I can use to determine whether a dimmer circuit is trailing edge or leading edge? I don't really want to be hanging a scope across the feed to the bulb.

We can assume that the manual for the lamp went the distance years ago and even if it had not it would be unlikely to have emphasised what sort of dimming technique it used since the only compatible bulbs available at the time would have been halogen filament types.
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Old 23rd Nov 2021, 7:12 pm   #15
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Default Re: Ballast in halogen lamps (sometimes)

I wonder if some kind of inductive loop held near the lamp, connected to your 'scope' might pick up enough to see the waveform? I guess you could always look at the PCB of the controller, too.

I think part of the reason for the switch, is that newer controllers aren't simply controlling the power (leading edge dimmers essentially wait for the half cycle to get to a certain voltage before switching on using a diac and triac) where newer stuff often has some kind of microcontroller, probably with some kind of RF link (either wifi or just a receiver) that means they actually need power. The thing is with that, that you can't simply use any kind of normal power supply. That's because in the vast majority of UK installations, the Neutral isn't available in the light switch. There's only phase, switched phase, and earth. So the only way for the electronics to get power is by 'stealing' it from the trailing edge switch off.

I'm not sure why this method is used trailing edge, and can't be done leading edge, but it does seem to be why the change has happened. It does mean, though, you can never get 100% because there has to be an off period, however small, for the electronics to steal the power.

LED compatibility with dimmers to be honest is a nightmare. I have a few replacement lightswitches so they can be remote controlled. They are trailing edge to steal power as described. Because of the issues the manufacturer of the dimmers / switches published a compatibility list. The wall lights use a total of 6 lamps, the ceiling light 3 lamps. Apart from the supplier sending some wrong versions in a couple of orders, and some not working straight out of the box, the wall lights (6 lamps) work fine and the fade up and down as they come on and off is no problem (though I strongly suspect they would be significantly brighter on a straight switched supply, given how bright they are at the first flicker of power) but the 3 lamps in the ceiling sometimes have a bit of a fit until they get switched off and on again.
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Old 23rd Nov 2021, 8:07 pm   #16
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Default Re: Ballast in halogen lamps (sometimes)

Hmm, maybe I can locate the 'dimmed live' wire going to the top lamp fitting and wrap some turns of a pickup loop around it to see if I can see which part of the half-cycle is being knocked out, the leading part or the trailing part. One thing for sure, there is no shortage of current whizzing back and forth along the wires to the lamp.

Being a standalone floor lamp, this particular unit does have the neutral available within the unit so the dimmer circuit, if required, could have full time, full fat mains and only needs to act on the downstream feed to the bulb fitting. It doesn't necessarily have to be an inline (series) dimmer like the ones used in wall switches.
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Old 23rd Nov 2021, 8:42 pm   #17
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Default Re: Ballast in halogen lamps (sometimes)

Is this one of those lamps where the dimmer is a separate unit integrated into the flex? If so, I would simply replace it with one suitable for the new LED.
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Old 23rd Nov 2021, 9:32 pm   #18
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Default Re: Ballast in halogen lamps (sometimes)

I have direct personal experience of two of these lamps in detail. The first is one we had that had a single uplight, and had an in flex dimmer. That could have been easily replaced or bypassed.

The latter, which my parents still have has a 240v uplighter and a 12v task light on a gooseneck, both halogen incandescents. The dimmers are very built in, and in the case of the 12v lamp must also be some kind of switching supply.

I got them a replacement LED for the 240v linear bulb but lockdown prevented me fitting and trying it. I couldn't find a 12v LED that would physically fit at the time.
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Old 23rd Nov 2021, 9:56 pm   #19
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Default Re: Ballast in halogen lamps (sometimes)

I'm also personally acquainted with two of the first type and one of the second type which unfortunately sounds like the one under discussion, although I don't know if the reading lamp is 12V. (We've never had to replace that bulb).

I think it's going to be a case of: Find out what sort of dimming is used for the 240V linear bulb and if it turns out to be trailing-edge, try the LED bulb. If it's not then I'll have to try to talk my Dad into replacing it with an economic equivalent - maybe my offering to buy it for Xmas will soften the blow.
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Old 23rd Nov 2021, 10:06 pm   #20
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Default Re: Ballast in halogen lamps (sometimes)

Just going further on my quoted experience of such lamps. Somebody posted that the glass cover might protect moths. In my experience I can't say it wouldn't but can say it didn't help bluebottles who smelled rather badly when they decided to visit.
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