How hot do hotwires get?

As the title explains how hot do higher power 25W+ hotwires get eg a ROP high or a philips 5761

The reason I ask is I'd like to build one with decent amount of runtime but if its too hot to handle after 5 mins then it seems a bit of a pointless exercise

Hot enough to start fires! Runtimes for these tend to be very short when they generate 'blinding" levels of light. Go HID for a more user-friendly high power, long(er) runtime light.


Karl

I recently put together a 6D Mag with an ROP high, I used a Kai reflector and still had the stock lens in, I had a salvaged NiCad pack in it. I did not intend to run it long, just wanted to check it out for now.

Having it on for several seconds, it was nice and bright, the finnish on the reflector started to grey, and the center of the lens was begining to melt.

This was definately less than 60 seconds.

ROP low bulbs are fine in that, had used them a bit already. If you are going to go 25W or more, get good parts.

More to your question though, I have used the ROP low and simmilar for several minutes at a time without having temperature problems. They get pretty warm but can still be handled safely. (maybee not by a little child though, keep out of reach of )

These have beeen I think around 20W. Double the power may not be too bad, more will chime in.

Hope that helps.

As long as you stay below 35 watts, you won't have any problems. More than this, and heat in the flashlight head and body can become an issue. Note this well, however: the ability of the incandescent beam to start fires does NOT mean that the head itself is hot enough to start fires! The infrared from the filament is what is starting the fire--like a heat lamp in a bathroom or radiating from a hot woodstove. If all that head had to stay in the head, then a 35W hotwire would be a heatsinking nightmare.

The 100W USL light that I designed and Bill produced (is still trying to finish producing, that is) is a 100W incan, and the head will get hot enough to cause minor burns on skin after only 10 minutes of continuous running.

In your case, as long as you have a metal reflector and lamp holder and head, you should be fine.

It depends on the wattage, degree of overdrive, duration of run time, bulb filament construction, glass envelope size (& subsequent proximity to reflector edge), brand/model (i.e. Osram IRC bulbs have coating to reflect back infrared radiation and increase efficiency of lumen output at a given wattage--and with less ambient heat radiation), type of reflector (some like FiveMega's have heat fins; then there are different shapes & size diameter & surfaces), type of head (some are finned to dissipate heat), glass lens quality. In short it is not an easy question to answer.

You may find some examples of actual temps I took with my Fluke 179 while doing destructive testing (link in my sig). Remember these temps were taken with probe a few mm from bottom of glass envelope, and without being enclosed in a metal head. The heat would be higher in actual enclosed flashlight.

Over 300deg is my guess.

Just build yourself one of the "smaller" hotwires. I can run my Mag11 for a long dog walk with no problems.

Also, try building a multi-level hotwire for lower temps and longer runtimes.

My 2 "C" Li-ion ROP gets warm if you use it for a while, but it's not too hot to carry. The head might be able to burn you though if you left it on for the whole 40 minute runtime in one shot. You can also melt the plastic tower that holds the bulb socket with a ROP though if you leave it on for long periods of time. I replaced the tower in my 2 "C" with a metal MagCtower so that's not an issue.

I have two ROP's (one 2 "C" and one 6AA -> 2D) and my Kai Domain reflectors in them haven't had any issues.

Ta for the replies, The wattage range I had in mind was 20-35 watts and it seems its not going to be a major problem.

I'm holding off for AW to finish his regulated mag D switches so I may go for a 5761 so i can have different usable levels.

soupdragon said:

As the title explains how hot do higher power 25W+ hotwires get eg a ROP high or a philips 5761

Click to expand...

I'll measure a hotwire when I collect all parts to build one, probably in a month or so.

FYI: Fenix L0D on high mode heats to ~39C/102F after a few minutes (ambient was 27C/80F). It feels warm, but not hot. On lower modes it's ~32C/90F. As a point of reference: tea cup around 50C/122F starts to feel hot (at least for me), around 60...70C/140..160F begins to be too hot to hold comfortably.

A 5761 in a SureFire M4 off two Li-ions...

1. Run continuously for a minimum of five minutes...
2. Held in the hand during the duration of the run and probing...
3. With an outdoor ambient temperature of 65°F....

...Hit 195°F when probed directly in the center of the lens. Radiant heat was obviously reflected back into the reflector assembly by the probe and its leads, so figure somewhere in the neighborhood of 175-195°F. The exterior section of the bezel parallel to the filament started at 90°F after five minutes and topped off at 105°F. The body was noticeably warm after a full ten minute run, particularly the tailcap region.

a mag85 become warm in about 10 minutes...with this bulbs heat isn't a big iusse...with 50/100w bulbs heat is a serious problem!:devil:

Anecdotally, I went for a long walk on the beach with my Kai ROP-lo - finned reflector and 5 amp hour li-ion D cells. I wasn't poking at the window or head ... no wait, that's a lie. I was futzing with focus all the way through the walk, and it never was uncomfortable to touch. I never poked the window, but I could feel heat coming off it when I got back.

(Remember: ROP-lo is an overdriven 11-watt bulb, and two li-ion cells drive it rather hard. I'd guesstimate around 15 watts, since I don't know how much current it draws - nominal voltage is 7.4, but li-ions come off the charger at up to 4.2 volts a pop, giving me an estimate of slightly over 15 watts. I fudged it down to account for running somewhere between 3.7 and 4.2 volts, and back upwards because I don't know how many more amps it pulls. I also may have gone over all that twice, but it's 1:42 AM here and my memory's getting hazy.)

A Mag85 with 9 full Ni-Mh's (AA) will burn paper when you have a minute :naughty:

Just tried it yesterday with my just-new Mag85. Didn't get the same result today, but that's because I was using a set of eight plus one garbage battery what in the last 20 hours has emptied from +1.25 Volts to -0.55 Volts. Gonna trash that battery now...

Well the conclusion I draw from this is that hotwires in the region of 30w do get warm they dont get to hot to handle after 5-10 mins.

It seems to be an aim of a few hotwire builds to get a 30W bulb to run for more than an hour I still have my doubts that a constant hour long run would be wise.

I've just got the reflector to finish off a classic 4D ROP so I'll have a go myself and see althou as the pack I'm using is an ancient 1400mah RC nicad pack I doubt i'll get more than 20 mins runtime

Has anyone done a long ie 30 mins+ test of a 25W+ bulb I do remember reading about a warped bulb tower in a ROP

Well, run it and test what??? Temperature? That varies depending on humidity and roomtemperature and the speed of the light moving trough the fresh air.

A 4D ROP? How do you get 7,2 Volt out of a 4D? Wasting a lot of space? Using 6x 1/2 D + spacer? Using 2S2P AW 'C'?

The 4D ROP is the original recipe that uses 6 Sub-C cells. It is quite inefficient space wise but I had an old Radio Control Nicad pack sitting around so i thought i'd use it to test it out.

I understand that there are plenty of variables regarding the temperature

My query relates to the temperature of the body of the light and any possible risk in using one for longer runtimes. Additionally the problems that heat might cause to internal parts I.E bulb pottings, plastic switch parts or batteries

soupdragon said:

The 4D ROP is the original recipe that uses 6 Sub-C cells. It is quite inefficient space wise but I had an old Radio Control Nicad pack sitting around so i thought i'd use it to test it out.

I understand that there are plenty of variables regarding the temperature

My query relates to the temperature of the body of the light and any possible risk in using one for longer runtimes. Additionally the problems that heat might cause to internal parts I.E bulb pottings, plastic switch parts or batteries

Click to expand...

with 1400mah you'll never get 1 hr of runtime...

go and visit Cheapbatterypacks website (or contact CPF member LuxLuthor) and buy a 4700mah SC battery pack...

IMO, you can run an hotwir for more than 1 hr but not a ROP, for the simly reason that is a potted bulb and will melt down the mag thower....

my suggestion? get a KIU socket and a WA1111 bulb (same battery/host set up but longer runtime, less powerful ... just a little...)

happy modding! :wave:

Filippo the 4D ROP i've built was more as stopgap from bits and pieces I had (apart from the reflector) and I know that the 1400maH Nicad isnt gonna cut it runtime wise. It got used in the build as it was an 15 year old RC battery pack that wasnt up to much for RC use

I'm waiting on AW to finish the regulated version of his D mag switch with some e-moli cells and a WA1111 or the similar Phillips 7388 (little brother to the 5761)

soupdragon said:

As the title explains how hot do higher power 25W+ hotwires get eg a ROP high or a philips 5761

The reason I ask is I'd like to build one with decent amount of runtime but if its too hot to handle after 5 mins then it seems a bit of a pointless exercise

Click to expand...

Hot enough to melt the stock M@g reflector, lens and anything you leave to close to it whilst running... the body of the M@g regulates heat pretty well so you won't be getting a hot hand after 5 minutes runtime

I run my Hotwire in overdriven 20w/50w configurations and haven't experienced overheating issues to date, without a laser thermometer I can't be anymore specific than that :thumbsup: