IR lamp resistance - Page 1
Forum section: electronics / general

author: Faringdon
author_rank: Super Contributor
timestamp: May 18, 2023, 02:25:31 pm
content: Hi,We are doing a Coffee shop outdoor heater.We worry about the inrush into the IR lamp even though we turn on at zero cross. The lamp's resistance could be so low.https://www.lamps2udirect.com/infra-red-heating-bulbs/infra-red-118mm-500-watt-slim-ruby-r7s-patio-heater-light-bulb/70605For a 500W IR lamp, would you expect its resistance to be 115R?.....(when warmed up)....what would be the lowest resistance at say 10degC?...just before turning it ON?Also, do you know where you can buy the holders for these lamps?...they are R7S holders.

author: bdunham7
author_rank: Super Contributor
timestamp: May 18, 2023, 02:44:26 pm
content: About 10 ohms. But surely you can just obtain one and measure it?

author: Faringdon
author_rank: Super Contributor
timestamp: May 18, 2023, 05:26:53 pm
content: Thanks yes, ours is 8.3R....but for how many mains cycles is the resistance that low?...how does res increase with time?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: May 18, 2023, 05:56:02 pm
content: Quote from: Faringdon on May 18, 2023, 02:25:31 pmDo you have a multimeter?QuoteDo you have Google ? "R7S Holder" would be a good start

author: Gyro
author_rank: Super Contributor
timestamp: May 18, 2023, 07:34:28 pm
content: Quote from: Faringdon on May 18, 2023, 05:26:53 pmIR lamps have much heavier filaments than ordinary incandescents. Why don't you measure it and get an actualrealanswer rather than guesses!

author: Someone
author_rank: Super Contributor
timestamp: May 18, 2023, 11:31:33 pm
content: Quote from: Gyro on May 18, 2023, 07:34:28 pmWould you agree forum goers expect pithy replies?I have not come up with a pithy reply and am worried that the answers I have would not be funny enough. Relying on puns can be difficult when the reader translates to another language. Could you suggest a better pithy reply?

author: james_s
author_rank: Super Contributor
timestamp: May 18, 2023, 11:55:59 pm
content: Quote from: Faringdon on May 18, 2023, 05:26:53 pmWhy don't you get an oscilloscope, a current transformer and one of the lamps in question and find out? How is anyone here supposed to give you this information?

author: dmills
author_rank: Super Contributor
timestamp: May 19, 2023, 08:19:47 am
content: Also run it until it fails and look at the transient as the filament parts, been my experience that things which are essentially TH lamps will do wild things as they fail and it is not uncommon for lamp failure to eat semiconductors.50A semiconductor, 10A TH load, and watch the semi fail short as the lamp fails. I think it is the arc in the lamp that tends to short circuit the filament, but I never did really get to the bottom of it.

author: Gyro
author_rank: Super Contributor
timestamp: May 19, 2023, 09:38:13 am
content: Quote from: Someone on May 18, 2023, 11:31:33 pm[ Edit after PM conversation with Someone]Pithy replies are unfortunately lost on the OP but we can only hope that he will take the hint and do some basic measurement himself, rather than coming straight here and asking pointless questions that can only be answered by gathering his own data.

author: jonpaul
author_rank: Super Contributor
timestamp: May 19, 2023, 10:22:45 am
content: FTTS: Incandescent lamp filaments are well documented since 1920s.See General Electric, Thorn, GEC, Sylvania app notes and sepcs for the IR lamps halogen, inc lmapsjPS: usual FTTS garbage time waster as outdoor radiant heaters electric/IR or gas are already or soon to be banned by the enviro-nuts

author: james_s
author_rank: Super Contributor
timestamp: May 19, 2023, 06:00:58 pm
content: Quote from: dmills on May 19, 2023, 08:19:47 amThis is exactly what happens. You know that bright flash that you get sometimes when an incandescent lamp fails? That is an arc that forms in the gas fill, it quickly jumps to the wires that connect the filament and creates a very low impedance, your incandescent lamp becomes a gas discharge lamp without a ballast to limit the current. If you look closely at a bulb that has failed this way you'll usually notice the ends of the lead wires are melted off. Nearly all lamps are fused, either in the stem or via foil at the pinch seals of tubular lamps. This will usually prevent the protection device on the branch circuit from popping but it's notoriously difficult to protect semiconductors from large transient overloads.

author: Faringdon
author_rank: Super Contributor
timestamp: May 21, 2023, 09:52:40 am
content: Thanks, this is an issue because we are driving it with a zero cross switched D2PAK triac.I reckon high initial inrush will reduce its lifetime, making the failure you describe come sooner.Its going to be a problem if when the lamp fails, the whole product becomes unuseable.Its going to be difficult to fuse, --to find a fuse which pops before the TRIAC will pop from that "gaseous discharge" incident.The customers wont be happy when they go to replace their IR bulb, and the product doesnt work because the PCB fuse has blown.Sounds like the Triac will need snubbering well...and i may need to put in some active current sense and limitation.Otherwise they who sip their coffee in the cold London night, on the street cafe table, will shiver.

author: Siwastaja
author_rank: Super Contributor
timestamp: May 21, 2023, 12:41:17 pm
content: Quote from: james_s on May 19, 2023, 06:00:58 pmIt is not uncommon at all to actually blow a 16A gG fuse when an incandescent bulb fails - either because it's a crappy bulb without an internal fuse wire, or is in a poor orientation so that the filament drops and bypasses the fuse. And I2t to blow a 16A gG fuse is massive - it's a true engineering feat to design a semiconductor based general purpose mains incandescent bulb driver which is reliable and never fails.

author: bdunham7
author_rank: Super Contributor
timestamp: May 21, 2023, 02:12:55 pm
content: Quote from: Siwastaja on May 21, 2023, 12:41:17 pmHow do bog-standard incandescent light dimmers like the ones in my house go on for decades without any issues?As for the 'engineering feat', the only obstacle I can think of to making a bullet-proof bulb driver would be convincing the boss to spend a bit more on properly overrated parts. Of course it probably almost always ends up being easier to just use a relay, but if you wanted to solve the OP's issue with a semiconductor solution I think you'd just need a 35A 'alternistor', a 1R power resistor and an MDL-4-R (or possibly a bit larger) fuse. The resistor would dissipate ~4W, but the device is a heater anyway, right? If the OP would like to to a bit of actual engineering he could add in a soft-start feature.https://www.mouser.com/new/littelfuse/littelfuse-q6035nah5-alternistor-triac/https://www.mouser.com/datasheet/2/87/eaton-mdl-time-delay-glass-tube-fuses-data-sheet-1608815.pdfhttps://www.mouser.com/ProductDetail/YAGEO/SQP10AJB-1R?qs=sGAEpiMZZMtTURnxoZnJAO1Jgj9enrz2HrnDRO4M1%252BC9baHhvXYD0w%3D%3D

author: Siwastaja
author_rank: Super Contributor
timestamp: May 21, 2023, 02:31:29 pm
content: OK, maybe I was exaggerating a bit. When efficiency does not matter, easiest way to improve SOA is just adding series resistance, which will limit peak current. But I have seen a few blown triac dimmers, to be fair.

author: Alti
author_rank: Frequent Contributor
timestamp: May 21, 2023, 07:08:42 pm
content: These IR bulbs work like ordinary incandescent bulbs powered with voltage lowered than rated. That is what makes them emit less energy in visible light spectrum. Rest is IR, as in GLS bulb. On top of that there is a red/amber filter that decreases visible spectrum intensity even further because in some applications visible light has a detrimental effect (like when you would like to fall asleep heated by such lamp). However, in a coffee shop I do not see the point of filtering visible spectrum and then adding light from other light sources. The light incandescent bulbs produce is very pleasant.The r7s bulbs do not come with reflector so I am not sure how you plan to arrange that but it might be tricky to focus the beam on some distant target (customer). I think for such application you would either need a massive panel of r7s bulbs surrounding/overhanging coffee space, or you need a beam that focuses on some area. I would say that BR125 or PAR125 might be better choices from economic point of view (unless that customer has infinite energy source nearby to power array of 500W r7s).If starting current is a problem you can also consider r7s IR bulbs with carbon fiber. These lamps do not have inrush current.

author: Faringdon
author_rank: Super Contributor
timestamp: May 22, 2023, 03:44:51 pm
content: Thanks, how about dimming the output of the IR lamp?Presumably at 200-500W, the PFC regs mean that phase cut dimmers are out of the question?Even symmetrical leading/trailing edge dimmers would fail harmonics at these power levels?Also, for inrush when turned on at low temperatures, we need an NTC...are there any which are say 10R at -10degC, and then 0.1R at 50degC?.....there doesnt seem to be. We only need an NTC for those freakk occasions when someone turns the product on in really cold temperatures.

author: dmills
author_rank: Super Contributor
timestamp: May 22, 2023, 10:57:47 pm
content: Firstly, forget D2Pak, not going to happen if you want reliability.Think old school theatrical dimming here, a honking great triac hard fired in Q3, with significant snubber and a fairly large interference suppression choke, it is possible to make this **reasonably** reliable (But every theatre chief tech has had to replace dimmer output devices on occasion). Mind you those things are often fed from a grid feed good for hundreds of amps per phase so the supply impedance is generally lower then what you see at the end of a bit of house wiring in a beer garden.There is usually a carve out in the harmonics rules for high power lighting dimmers, these are NOT viewed as power supplies in the regs so power factor rules for power supplies do not apply.The other approach that is worth a look is an IGBT with a driver that senses desaturation and can shut it down quickly enough to protect the power device, you still want to be looking at a butch power device, but this is how the reverse phase control dimmers tend to work it. You will need a few volts of negative bias to get it to switch off fast enough to not die. SiC might be a more modern approach here for smallish loads where I^2R < I*Vce(sat).

author: james_s
author_rank: Super Contributor
timestamp: May 22, 2023, 11:47:39 pm
content: Quote from: bdunham7 on May 21, 2023, 02:12:55 pmImpedance of the wiring I suspect. I've had them fail, but not very often. They may be more prone to failure in 240V regions.

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 23, 2023, 01:37:33 pm
content: You could soft start it with phase angle control, the peak voltage will be low at low power settings so the inrush would also be low. That combined with limiting the maximum power setting would make it last a really long time.

author: bdunham7
author_rank: Super Contributor
timestamp: May 23, 2023, 02:16:38 pm
content: Quote from: Faringdon on May 22, 2023, 03:44:51 pmHow many 'engineers' does it take toreplaceturn ona light bulb?So here's a few relevant observations about turning on an incandescent light bulb.First, if you limit the current to the amount that the bulb will draw when warmed up--in your case about 2 amps--the bulb will turn on a bit slower but typically not enough to matter. You might not even notice in the case of smaller bulbs. So if you had a huge bulb or bulbs in parallel that drew current that was a large fraction of your circuit breaker or fuse ampacity, inrush limiting might not be totally insane, although I personally haven't seen it done on anything short of large commercial devices like theatre lighting where they soft-start via dimmers. A single IR-heater that draws 2A on a 16A circuit really shouldn't need anything at all. I have 500W (250W x 2) IR heaters in my bathrooms that run off of a 15A 120V circuit (not dedicated) so they draw ~4.5A when on.Second, if your bulb does fail at turn-on and even if it goes short, those faults clear very quickly--at least the ones I've seen. Also, I think the IR bulbs like the one you mention aren't all that likely to fail short and they typically have pretty long lifetimes. If you still want to incorporate short protection without blowing your fuse (and you absolutely need a fuse...) you'll need to passively limit the current to something below what would blow your fuse in less then 1 cycle and then have an overcurrent detection system that will shut the power off at the end of the current half-cycle. That's assuming you are using a triac.Third, bulbs like that have fairly long thermal time constants. Both soft-starting and dimming could be accomplished by cycle-skipping rather than phase control. Perhaps a 5-cycle (100ms) period with dimming levels from 1 to 5.

author: Faringdon
author_rank: Super Contributor
timestamp: May 24, 2023, 07:27:37 pm
content: Thanks, i dont suppose anyone knows offhand what is the stray inductance of the IR lamp in the top post...there will be some stray L which will need dealing with if turned ON/OFF with high current.Will get the LCR on it when i can find it.The LCR45 isnt going to measure it too well unfortunatelyhttps://uk.farnell.com/peak-electronic-design/lcr45/impedance-meter-hh-10h-10000uf/dp/2917879?CMP=KNC-GUK-GEN-KWL-RLSA-PUR-TEST-921&mckv=_dc|pcrid|610187754228|&gclid=EAIaIQobChMI852Sh9iO_wIVmrbtCh1QdQAyEAAYASAAEgLl-fD_BwE

author: dmills
author_rank: Super Contributor
timestamp: May 25, 2023, 04:33:17 pm
content: An old HP 4192A is what you want for these sorts of measurements, or an old gen rad or HP impedance bridge, but if you are dimming then you will need a honking great series inductor anyway, so the lamp inductance becomes insignificant in comparison.

author: Faringdon
author_rank: Super Contributor
timestamp: May 25, 2023, 06:53:32 pm
content: Thanks, we are hoping to do symetrical phase cut dimming, with no series inductor added.

author: jonpaul
author_rank: Super Contributor
timestamp: May 26, 2023, 09:54:30 pm
content: Just another nonsense post by FTTS. Of course there is no "We" who are "doing" anything for a "customer" its just FTTS imagination to waste our time.1/ IR lamp filament resistance is function of filament temperature and PTC so cold/hot R is perhaps 5..25 :1 ratio.See 1930s..1950s General Electric IR lamp data.2/ IR lamps are never dimmed, no reason. On or off.3/ Outdoor /restaurant/patio space heaters gas or electric are banned in many parts of EU and surely soon in UK, USA, CA, AU etc by environazis laws and regs.Moot project.Another 5 min lost to FTTS toilet bowl of time.Thanks again!j