LEAST-efficient automotive bulb

[Alaric Darconville]

(Probably not really a "transportation lighting" function since it's not even designed to produce lighting, but...)

Yes, that's right-- I'm looking for the automotive bulbs with the lowest luminous efficacy possible, because I have this silly, wacky, goofy, nutty idea to make a 12V automotive space heater that uses miniature bulbs for the heat (sorta like an EZ-Bake™ oven uses a 60W bulb to bake brownies). The bulbs will be semi-sealed up within an opaque container so there will be no light emitted (beyond what might leak out of edges or where the cord comes out).

I plan on using it in a 10A fused cigar lighter socket, so I figure I need to keep the total operating current below 10A so I don't pop the fuse every time I plug it in (even with a slo-blo fuse, inrush current on too many bulbs could trip it). Probably, then, it would be wiser to use fewer, but higher-wattage, bulbs than more, but lower-wattage, bulbs-- but I could also be wrong on that.

What bulb, due to its inefficiency, would give me the most BTU/hr?

 

[-Virgil-]

What an interesting question. Any incandescent bulb produces mostly heat and not much light. I wonder if the best thing might be 24v bulbs, underdriven at 12v. Can't say whether you'd have better results with something small like a 24v P21W or something big like a 24v 70w H1 or H3. Or maybe use 2-filament 12v bulbs (9007, H4, H13) with the filaments in series with each other. Doing some quick calcs with the standard power exponent (1.6) a bulb rated 70w at 24v would consume 23w at 12v, so you could have 5 such bulbs and probably still be OK with your 10A limit. Or a 21w 24v bulb would take about 7w at 12v, so you could have 16 of those. It gets tougher to calculate the power draw of unequal filaments powered in series with each other; probably have to drag out the clamp ammeter and see for yourself.

 

[Alaric Darconville]

What an interesting question.

Isn't it, though?

Any incandescent bulb produces mostly heat and not much light. I wonder if the best thing might be 24v bulbs, underdriven at 12v. Can't say whether you'd have better results with something small like a 24v P21W or something big like a 24v 70w H1 or H3. Or maybe use 2-filament 12v bulbs (9007, H4, H13) with the filaments in series with each other. Doing some quick calcs with the standard power exponent (1.6) a bulb rated 70w at 24v would consume 23w at 12v, so you could have 5 such bulbs and probably still be OK with your 10A limit. Or a 21w 24v bulb would take about 7w at 12v, so you could have 16 of those. It gets tougher to calculate the power draw of unequal filaments powered in series with each other; probably have to drag out the clamp ammeter and see for yourself.[/QUOTE]

I think the big problem is still inrush current-- a 15A household wall plug still only allows 600W of incandescent lighting, which on the face of it seems like a 5A limit, but this buffer is needed due to the cold filaments allowing much higher current to flow, even if momentarily. According to Incandescent Lamps, Publication Number TP-110 (General Electric), the resistance of a cold filament is 1/15th that of a hot one.

The 24V, 70W H3 has an 8.22 ohm filament resistance, the 12V has a resistance of 2.62 ohm -- I'm not sure if those are hot or cold numbers, but if both reflect the same, maybe the 24V would be better, after all.

I also thought using 1M CP spotlight with light-opaque, IR-passing filter on it (fully exposed film negatives could be a Q&D proof-of-concept), or make such a filter for a spotlight I already have (a Stanley* 35W HID handheld spotlight), as I recall once I used it to help defrost a windshield (but the light was rather annoying, and I was rather afraid to crack the glass by concentrating a lot of heat in one place).




*Stanley, the hardware company, not the automotive light bulb company.

 

[dogshome]

Why not use a 15R ceramic 100W resistor for about £7 from Radio Spares?

 

[spencer]

If you are enclosing the bulbs in an opaque container then the efficiency of the bulbs does not matter as an additional light will also be converted to heat. Buy the cheapest bulbs you can find that will work with your application. You could use an LED running at the same wattage as a incandescent bulb and as long as no light escapes, they will produce the same amount of heat.

 

[Alaric Darconville]

Why not use a 15R ceramic 100W resistor for about £7 from Radio Spares?

For some reason, the thought of the resistor being the only thing on the circuit would act like a short circuit, since I'm not all that up with electrical theory at times.

If you are enclosing the bulbs in an opaque container then the efficiency of the bulbs does not matter as an additional light will also be converted to heat.

But perhaps not as quickly as existing as heat right away (but I could be wrong about that).

 

[-Virgil-]

For some reason, the thought of the resistor being the only thing on the circuit would act like a short circuit

Light bulb filament = resistor.

 

[Alaric Darconville]

Light bulb filament = resistor.

Well, I *know* that. But I'm not used to seeing a light bulb used where a normal resistor would be used-- and aside from resistive heating elements and ballast resistors to test batteries (or just doing calibration functions), I just don't conjure images in my head of people putting a resistor as the sole load on a circuit.

 

[dogshome]

If you look in any electric fire or kettle, the heater is a wire wound or stamped metal resistor. An aluminium clad wirewound resistor from RS (also Ebay I guess) mounted on a suitable piece of aluminium (perhaps an aluminium box) would make a very safe electric heater. Fuse it or go belt and braces and fit a high temperature switch in the box too.

http://www.resistorsonline.com/gifs/aluminium-housed.jpg
https://encrypted-tbn3.gstatic.com/...KO6p59NHx2hPb3ONFZ0LEuvJINDH9UgZHyGUo-_uSxf2h

Image tags removed see Rule #3 Do not Hot Link images. Please host on an image site, Imageshack or similar and repost – Thanks Norm


P.S 100W isn't going to warm you up, but it would take the chill out of a frozen car if left switched on a while. 10A is a large battery drain though. A hot heater needs to be carefully placed also!

 

[-Virgil-]

Wait, this is to heat up the interior of a car? Why reinvent the wheel to get a half-job done? Buy a coolant heater instead and it will not only give you instant cabin heat but also pay for itself in reduced fuel consumption. They're available as in-line units (radiator or heater hose) in case your engine's core plugs aren't easily accessed.

 

[Alaric Darconville]

http://www.resistorsonline.com/gifs/aluminium-housed.jpg
https://encrypted-tbn3.gstatic.com/...KO6p59NHx2hPb3ONFZ0LEuvJINDH9UgZHyGUo-_uSxf2h
(hotlinked images changed to URL references)

P.S 100W isn't going to warm you up, but it would take the chill out of a frozen car if left switched on a while. 10A is a large battery drain though. A hot heater needs to be carefully placed also!

Just to get a head start on clearing the windshield (and only while the engine is running). I doubt that 340BTU/hr would really make the car that much more comfortable.

Buy a coolant heater instead and it will not only give you instant cabin heat but also pay for itself in reduced fuel consumption. They're available as in-line units (radiator or heater hose) in case your engine's core plugs aren't easily accessed.

Not so much the interior, but to put heat on the windshield to get a head start on removing snow, frost, or ice. It takes a while for the engine to warm up if the car isn't being driven-- but it's not safe to drive if the windshield isn't clear. In this case, only the immediate heat of electric heat will do. I'm also looking into getting a freeze plug heater, because that *certainly* alleviate a lot of winter time problems-- cold, underlubricated starts, long warmup time, and terrible emissions/fuel economy. I looked at many of the inline ones but they don't list the Previa on the "application guide", so a 400W freeze plug heater seems to be my best bet.

 

[dave_b]

Hey Alaric, I just have a 750 Watt Motomaster Car Warmer. It sits on the thick rubber floor mat on the floor of the back seat area. I ran an extension chord through the firewall. I plug it on when frost is likely or even when its snowing, and it keeps my windows clear. Combine this with a block heater/frost plug heater and you will be ready to go no matter what the weather.

Alternatively, if supplemental electric heat only while the engine is running is your goal, they make 12V car warmers something like this http://www.canadiantire.ca/en/pdp/12v-window-defogger-0303402p.html#.UppTPeImtUY

Sorry I don't know what your local equivalent of Canadian Tire is.

 

[Alaric Darconville]

Dave,

I've looked at those cigar lighter plug heaters (Atwood's even has a bunch in stock pretty cheap), but thought building my own might be slightly cheaper (and kindof fun, in a way).

As far as the freeze plug heaters-- Kat's or Zerostart? Those seem to be the two big brands (and probably still made in the same factory with the same dispassion as each other).

 

[-Virgil-]

Then again, if you want to really blow big money on the project (ha), you could spend four figures on a Webasto gasoline-powered engine heater with timer and everything.

Kat's is a very old brand; their heaters used to be quite good but I have no idea if they still are. I also have no idea how good or bad Zerostart's heaters might be.

Have you considered checking to see if there's an option available from Toyota?

 

[dave_b]

Sorry AD, given my location every car I have ever bought has always had some form of block heater installed, so I don't know whats good.

I totally get the appeal of an off the wall project though. Scheme away!

 

[SemiMan]

I think you may find that a 100 watts is almost useless depending on where you live. As you are only using with the engine running I expect that if is so cold outside you need to wait much for the engine to heat up to clear the windshield, then 100 watts will not provide any meaningful window clearing. 500 watts maybe, 100 watts no.

Semiman

 

[inetdog]

How about the not inexpensive but straightforward solution of an inverter and small hair dryer?
Has anyone seen a 12V hair dryer or heat gun?
Too high a wattage to power from the cigarette lighter socket (aux DC power outlet these days) in either case.
Don't create too great a localized temp difference and shatter the glass. More likely to happen with side or back windows than with the windscreen.
Tapatalk...

 

[SemiMan]

Need to direct wire to the battery for that sort of current.

 

[Alaric Darconville]

Good suggestions, all. I suppose this thread oughta be moved out of the automotive lighting subforum, as it was a tenuous connection to this at best.

Or, it may be closed if there's no real good place to put it.

 

[Hamilton Felix]

FWIW, those little 12V defrosters that Harbor Freight is always putting on sale can help a bit. But they have inadequate cords. And after you replace the cord with adequate wiring, you find that it cooks lighter plugs (sockets and their wiring too, if you aren't careful) and is generally not an extended or continuous use item. But if you place it on the rear shelf and start down the road, it will help defog the back window. Just remember to unplug it as soon as it's no longer needed.

In general, the idea of electric heat in a car is a non-starter. Even 30 amps isn't going to get you a lot of heat. But even a very small heater core with hot coolant from the engine running through it, will get you plenty of heat. I wish more vehicles had two heaters, like my 1996 Suburban (or Dad's old 1953 Buick).