Simple wiring question, I'm 99 44/100ths % sure I'm right, but I have to ask

[theblooms]

OK, I have a situation at work where I have to light a rather large
area, but the lights have to be very bright and extremely impact and
shock proof. So that pretty much rules out conventional incandescent
light bulbs and fluorescent tubes. Plus, I have to do this on kind of
the cheap.


So this is what I came up with: Wire 8 automotive clear fog lamps in
series. The lenses are rated for rock strikes and road debris at
70MPH, perfect. They are absolutely vibration proof, being off-road
lights, and because of the lenses, they are bright at hell. As a
bonus, I can get them for $12 each.

That said, they are rated 55 watts at 12VDC, but of course they easily
go to 14.4V: the output of a car alternator. And being light bulbs,
they couldn't care less if they are seeing AC or DC current. So,
according to Ohm's Law, 8 wired in series, assuming 14.4V, they should
now want for 115.2V. Perfect for plugging into a standard wall
outlet.

Am I right, or am I going to electrocute myself?

 

[Spehro Pefhany]

OK, I have a situation at work where I have to light a rather large
area, but the lights have to be very bright and extremely impact and
shock proof. So that pretty much rules out conventional incandescent
light bulbs and fluorescent tubes. Plus, I have to do this on kind of
the cheap.


So this is what I came up with: Wire 8 automotive clear fog lamps in
series. The lenses are rated for rock strikes and road debris at
70MPH, perfect. They are absolutely vibration proof, being off-road
lights, and because of the lenses, they are bright at hell. As a
bonus, I can get them for $12 each.

That said, they are rated 55 watts at 12VDC, but of course they easily
go to 14.4V: the output of a car alternator. And being light bulbs,
they couldn't care less if they are seeing AC or DC current. So,

They'll be a bit happier off of AC.

according to Ohm's Law, 8 wired in series, assuming 14.4V, they should
now want for 115.2V. Perfect for plugging into a standard wall
outlet.

Am I right, or am I going to electrocute myself?

Both, perhaps.


Best regards,
Spehro Pefhany

 

[[email protected]]

They'll be a bit happier off of AC.



Both, perhaps.

Best regards,
Spehro Pefhany

You know what... regarding that 56/100% that's not so sure... does
anyone know how the resistance of a light bulb filament varies from
room temperature to operating temperature? (All within one second, of
course...)

Resistances could theoretically vary from light bulb to light bulb...
theoretically this could kill some light bulbs prematurely... ???

When in doubt, run the experiment! (With full safety goggles...)

Michael

 

[Homer J Simpson]

OK, I have a situation at work where I have to light a rather large
area, but the lights have to be very bright and extremely impact and
shock proof. So that pretty much rules out conventional incandescent
light bulbs and fluorescent tubes. Plus, I have to do this on kind of
the cheap.

I would use low or high pressure sodium in reflectors with guards.

 

[budgie]

OK, I have a situation at work where I have to light a rather large
area, but the lights have to be very bright and extremely impact and
shock proof. So that pretty much rules out conventional incandescent
light bulbs and fluorescent tubes. Plus, I have to do this on kind of
the cheap.


So this is what I came up with: Wire 8 automotive clear fog lamps in
series. The lenses are rated for rock strikes and road debris at
70MPH, perfect. They are absolutely vibration proof, being off-road
lights, and because of the lenses, they are bright at hell. As a
bonus, I can get them for $12 each.

That said, they are rated 55 watts at 12VDC, but of course they easily
go to 14.4V: the output of a car alternator. And being light bulbs,
they couldn't care less if they are seeing AC or DC current. So,
according to Ohm's Law, 8 wired in series, assuming 14.4V, they should
now want for 115.2V. Perfect for plugging into a standard wall
outlet.

Am I right, or am I going to electrocute myself?

Things that will probably bring you unstuck:

1. Lamps in your series strings won't necessarily share the volt drop equally.
Sooner or later - probably sooner - one will go O/C and the rest will
extinguish.

2. Those lamps *may* go to 14v4, BUT in the automotive scenario the typical
volt drop between source (that 14v4) and lamp is at least 1v. If you manage to
get 14vanything at the lamps, their life will shorten - and see #1 above for the
consequences of failure of one lamp in a series string. Careful selection of
cabling will help drop the voltage at each lamp.

 

[theblooms]

Sodium lights won't work because of three problems:
1. quality of light. I need it to be as white as possible.
2. physical size. Looking back, I didn't mention this as a
requirement, but the bulbs and housings also need to be as compact as
possible.
3. cost. Sodium lights ain't cheap. Not in the slightest.

Thanks anyway for the reply. I REALLY DO appreciate it.

 

[John Fields]

You know what... regarding that 56/100% that's not so sure... does
anyone know how the resistance of a light bulb filament varies from
room temperature to operating temperature? (All within one second, of
course...)

---

 

[John Fields]

You know what... regarding that 56/100% that's not so sure... does
anyone know how the resistance of a light bulb filament varies from
room temperature to operating temperature? (All within one second, of
course...)

 

[GregS]

Fog lamps are suppose to have a shield in front of the lamp, so you don't see the
lamp, and the coverage is limited. if it does not have this, then its not a true fog lamp.
A driving or passing lamp does not have a shield in front of the lamp so coverage is bigger.
A standard auto headlamp does have a shield over the low beam lamp, but not
necessarily over the high beams. Small halogen lamps with sockets are prone to socket failure in the long run.
Just try to get a lamp with a wide coverage preferably with a seald beam system. Think
about total blackout when one fails.

greg

 

[Fred Bartoli]

Spehro Pefhany a écrit :

They'll be a bit happier off of AC.

How's that? Electronic wind?
I remember an interesting report about aircraft incandescent lamps
failure mode analysis used as some info source about aircraft crash...
(I think it was you that posted this).

 

[kell]

Things that will probably bring you unstuck:

1. Lamps in your series strings won't necessarily share the volt drop equally.
Sooner or later - probably sooner - one will go O/C and the rest will
extinguish.

2. Those lamps *may* go to 14v4, BUT in the automotive scenario the typical
volt drop between source (that 14v4) and lamp is at least 1v. If you manage to
get 14vanything at the lamps, their life will shorten - and see #1 above for the
consequences of failure of one lamp in a series string. Careful selection of
cabling will help drop the voltage at each lamp.- Hide quoted text -

- Show quoted text -

Maybe use nine. And you could rig up a second series that comes on
automatically when the lights black out. Something as simple as a
current transformer that holds a relay in the open circuit position:
when the lights black out, current stops, the relay closes and the
second series comes on.

 

[RST Engineering \(jw\)]

They are also "assumed" to be in relatively free air and/or have an induced
breeze on them from the forward speed of the vehicle. Don't put them into a
hot box and expect them to last very long.



Bogey value for lead-acid "automotive" style power sources is 13.4 volts.
14.4 for very long will boil the battery dry. I'd use 9 lamps in series.
If I wanted them to last forever, or if I was going to be switching them on
and off a lot, I'd use an input surge limiter that could handle your four
amps of steady state current.



Yes, probably.


Jim

 

[Rich Grise]

On 22 May 2007 18:05:47 -0700, the renowned theblooms


They'll be a bit happier off of AC.

Ah, the joys of the ambiguities of the English language!

By "off of AC", do you mean they'll be happier being powered by AC,
or they'll be happier if they get off the AC like getting off the sauce,
i.e., don't let AC near them?

I suspect you mean "running powered by AC", because the filament
evaporation will be symmetrical.

Both, perhaps.

Personally, I'd use more like 9 or 10 in series - 14.4 is probably pushing
it for an incandescent.

And, of course, we assume that OP knows about double-insulation.

Good Luck!
Rich

 

[Rich Grise]

You know what... regarding that 56/100% that's not so sure... does
anyone know how the resistance of a light bulb filament varies from room
temperature to operating temperature? (All within one second, of
course...)

Resistances could theoretically vary from light bulb to light bulb...
theoretically this could kill some light bulbs prematurely... ???

When in doubt, run the experiment! (With full safety goggles...)

They've been running series strings of Xmas tree bulbs for almost a
century now. (not continuously, of course, I mean at Xmas, you drag
out your series string of bulbs & stuff.) I don't foresee voltage-sharing
as a problem - the one with the least resistance will, of course, drop the
lowest voltage; they will reach equilibrium, much like series LEDs do.

Cheers!
Rich

 

[Rich Grise]

Sodium lights won't work because of three problems:
1. quality of light. I need it to be as white as possible.
2. physical size. Looking back, I didn't mention this as a
requirement, but the bulbs and housings also need to be as compact as
possible.
3. cost. Sodium lights ain't cheap. Not in the slightest.

Thanks anyway for the reply. I REALLY DO appreciate it.

You could also use a low-voltage system, like those yard lights that
you see all over the place.

The stumbling block, of course, is the cost of the transformer, and the
need for really fat wire. At the transformer output, it has to carry
ALL of the current for every bulb - 10X 4A bulbs would be 40 amps -
#6 or #4 wire should be happy with that amount of current. Or, you
could run individual pairs to each lamp.

Good Luck!
Rich

 

[Spehro Pefhany]

Ah, the joys of the ambiguities of the English language!

By "off of AC", do you mean they'll be happier being powered by AC,
or they'll be happier if they get off the AC like getting off the sauce,
i.e., don't let AC near them?

The former.

I suspect you mean "running powered by AC", because the filament
evaporation will be symmetrical.

Less notching effects, so the filaments should last somewhat longer.

Personally, I'd use more like 9 or 10 in series - 14.4 is probably pushing
it for an incandescent.

And, of course, we assume that OP knows about double-insulation.

Good Luck!
Rich

Nature has a way of reminding us of such things every now and then.


Best regards,
Spehro Pefhany

 

[Homer J Simpson]

Sodium lights won't work because of three problems:
1. quality of light. I need it to be as white as possible.

We used high pressure sodium for color matching with good results.

2. physical size. Looking back, I didn't mention this as a
requirement, but the bulbs and housings also need to be as compact as
possible.

You can buy 12 V 50 W tungsten halides with reflector at the dollar store.
You could try matching them for use in series strings, however if one burns
out you will apply 115 VAC across that lamp and they may arc over since they
are not designed for this service.

 

[krw]

Fog lamps are suppose to have a shield in front of the lamp, so you don't see the
lamp, and the coverage is limited. if it does not have this, then its not a true fog lamp.

I guess the fog lamps on any of my cars haven't been true. Fog lamps
simply are mounted lower so they don't reflect off the fog directly
back. They're usually pointed more down so they illuminate the road
directly in front.

A driving or passing lamp does not have a shield in front of the lamp so coverage is bigger.

High beams are simply pointed straight forward.

A standard auto headlamp does have a shield over the low beam lamp, but not
necessarily over the high beams.

Not here. Low beams are simply pointed down and to the right so they
aren't in the opposing driver's eyes.

Small halogen lamps with sockets are prone to socket failure in the long run.

Never had one fail.

Just try to get a lamp with a wide coverage preferably with a seald beam system. Think
about total blackout when one fails.

That's why I have two. ;-)

<stuff snipped because top posting makes no sense>

 

[krw]

They've been running series strings of Xmas tree bulbs for almost a
century now. (not continuously, of course, I mean at Xmas, you drag
out your series string of bulbs & stuff.) I don't foresee voltage-sharing
as a problem - the one with the least resistance will, of course, drop the
lowest voltage; they will reach equilibrium, much like series LEDs do.

The series Xmas bulb strings have an internal structure that will
short the bulb when the filament burns out, allowing the string to
stay alive.

 

[Marra]

What will probably happen is one light will be lower resistance than
the rest and take a lot of current and blow itself up as it lights
first and the others remain almost a short circuit.

I know they do this with xmas tree lights but they are usually run
well below 12 volts each.