LED bulbs

On Thursday, in article
<[email protected]>
[email protected] "Austin Shackles" wrote:

> On or around Thu, 03 Aug 2006 09:49:02 +0100, Steve Taylor
> <[email protected]> enlightened us thusly:
>
> >Austin Shackles wrote:
> >> fackinell. you could dispense with the battery and the engine...
> >>
> >> 10 Farad is enough energy to power a small bomb.
> >
> >I didn't slip up. You can buy 2500 FARAD capacitors, albeit at only
> >2.6v. 12V 10F caps are /used to be available from Maplin, for sub woofer
> >in car freaks.
>
> it's still a lot of energy. does the amount of energy depend on voltage? I
> don't think it does.

Power is Volts times Amperes.

Energy is power times time (seconds).

1 Ampere is 1 Coulumb per second.

So Power is Volts times Coulombs divided by seconds.

And Energy is Volts times Coulombs. (time cancels out)

Since one Farad is one Coulomb at one Volt, the energy in a capacitor is
proportional to the square of the voltage. Something like 10 Farads at
15 Volts will run a 1-bar electric fire for just over 2 seconds, which,
while pretty fierce in terms of current, is only 66 Amperes.

Of course, if you had a capacitor rated at 1500 Volts (which is the
voltage at which nasty things will happen inside the capacitor) you
could stuff 22 megaJoules into it, and that is a things-go-boom event
when you dead short the terminals (or the insulation inside the
capacitor fails).

So don't do that.

--
David G. Bell -- SF Fan, Filker, and Punslinger.

"I am Number Two," said Penfold. "You are Number Six."

David G. Bell wrote:

> Of course, if you had a capacitor rated at 1500 Volts (which is the
> voltage at which nasty things will happen inside the capacitor) you
> could stuff 22 megaJoules into it, and that is a things-go-boom event
> when you dead short the terminals (or the insulation inside the
> capacitor fails).
>
> So don't do that.
>

...or at least be sporting enough to invite us to watch.
Steve

On or around Thu, 03 Aug 2006 15:56:21 +0100 (BST), [email protected]
("David G. Bell") enlightened us thusly:

>Since one Farad is one Coulomb at one Volt, the energy in a capacitor is
>proportional to the square of the voltage. Something like 10 Farads at
>15 Volts will run a 1-bar electric fire for just over 2 seconds, which,
>while pretty fierce in terms of current, is only 66 Amperes.
>
>Of course, if you had a capacitor rated at 1500 Volts (which is the
>voltage at which nasty things will happen inside the capacitor) you
>could stuff 22 megaJoules into it, and that is a things-go-boom event
>when you dead short the terminals (or the insulation inside the
>capacitor fails).

22 megajoules... hmmm. joules/sec are watts, ain't they?

so you could get 22Kw for 1000 s... bit more than quarter of an hour. So
you can't quite replace the engine with it.


Just been thinking back... we had a period at school of making booby-trapped
not-light-bulbs using small low-voltage electrolytic capacitors wired into a
240V bayonet socket. Make a lovely bang, they do
--
Austin Shackles. www.ddol-las.net my opinions are just that
"Brevis esse laboro, Obscurus fio" (it is when I struggle to be
brief that I become obscure) Horace (65 - 8 BC) Ars Poetica, 25

Austin Shackles wrote:

> 22 megajoules... hmmm. joules/sec are watts, ain't they?
>

Yep.
> so you could get 22Kw for 1000 s... bit more than quarter of an hour. So
> you can't quite replace the engine with it.

It'll happen.

Steve

Liam wrote:

> So fitting a capacitor may help, I may experiment with that, how exactly
> would that be wired in?

In parallel with the light clusters, there's not a heck of a lot of
point doing it near the battery.

Could there be any other side effects fitting one?
> What size capacitor would it be worth fitting?

Seriously, a 10 Farad one, as used by car hi-fi freaks, for similar reasons.

If you want to try per-cluster, then a 470uF would be bearable.

Steve

Austin Shackles wrote:

>
> Just been thinking back... we had a period at school of making booby-trapped
> not-light-bulbs using small low-voltage electrolytic capacitors wired into a
> 240V bayonet socket. Make a lovely bang, they do

Must be a global phenomenon - we did the same.


--
EMB

Steve Taylor wrote:
> Liam wrote:
>
> > So fitting a capacitor may help, I may experiment with that, how exactly
> > would that be wired in?
>
> In parallel with the light clusters, there's not a heck of a lot of
> point doing it near the battery.
>
> Could there be any other side effects fitting one?
> > What size capacitor would it be worth fitting?
>
> Seriously, a 10 Farad one, as used by car hi-fi freaks, for similar reasons.
>
> If you want to try per-cluster, then a 470uF would be bearable.
>
> Steve

Car Hi Fi uses massive capacitors in order to get very good low
frequency performance from the power amps rather than to get rid of
spikes (for the same reason as using very heavy gauge wiring).

I assumed that the original contributor's contribution was meant to be
10uF, not 10F! A 10F capacitor would be a bit expensive in relation to
the bulb!!!

What you do when you use a capacitor to get rid of spikes is
effectively to use it as a low pass filter, where the R or L component
of the filter is formed by the output impedance of the voltage source
(i.e. the alternator, battery, wiring). The effect of the capacitor in
removing the voltage spike thus depends on this impedance, which is
very low for a car battery and associated wiring. Thus, a large
capacitor is needed to get rid of spikes in car electrics.

If you want to go down the capacitor route, rather than use a massive
capacitor, it would be more economical to use an inductor (coil) in
series with the +12V power to the +12V on the bulb as well as the
capacitor across the bulb, thus forming a conventional LC filter.

+12V --------| coil |--------------------------
| |
Capacitor Bulb
| |
GND--------------------------------------------

Another alternative would be to look at using a semiconductor spike
suppressor across the bulb. Have a look at Rapid Electronics (
http://www.rapidelectronics.co.uk/ ) part number 26-3812. A bit
cheaper, too!

Going back to the capacitor size issues, a simple capacitor consists of
two conducting plates separated by an insulating material (called the
dielectric). The capacitance is proportional to the area of the plates
but inversely proportional to the thickness of the dielectric. Real
life capacitors are made in a number of different ways (usally by
rolling up the "plates" and dielectric to get a big area in a small
volume). The capacitance for a given physical size thus gets higher
with a thinner dielectric, but, of course, a thinner dielectric breaks
down at a lower voltage. Hence the tradeoff between capacitance and
maximum working voltage for a given physical size.

ArthurC wrote:
> If you want to go down the capacitor route, rather than use a massive
> capacitor, it would be more economical to use an inductor (coil) in
> series with the +12V power to the +12V on the bulb as well as the
> capacitor across the bulb, thus forming a conventional LC filter.

The capacitor is the quickest and simplest tryout. Your inductor has to
carry the lamp DC without saturating, and you need one with each cluster.

Personally, I'd scope the 12V supply and see what's happening, but you
have to have access to a scope....

> Another alternative would be to look at using a semiconductor spike
> suppressor across the bulb. Have a look at Rapid Electronics (
> http://www.rapidelectronics.co.uk/ ) part number 26-3812. A bit
> cheaper, too!
That's a good way to do it.

> Hence the tradeoff between capacitance and
> maximum working voltage for a given physical size.


2.5 V 2500 Farad is the biggest I've found so far.

Steve

On or around 4 Aug 2006 04:31:41 -0700, "ArthurC" <[email protected]>
enlightened us thusly:

>Car Hi Fi uses massive capacitors in order to get very good low
>frequency performance from the power amps rather than to get rid of
>spikes (for the same reason as using very heavy gauge wiring).

newly-acquired motor here has an interesting glitch - if you turn the stereo
(quite a nice JVC with 12-disc changer) up too high, it cuts out, then in
again, then out again...

I speculate that the power supply into the head unit isn't up to it - too
much volume = too much current from the supply, leading to voltage drop
which makes the unit think the ignition's been turned off. Then the voltage
recovers, and it turns back on again, voltage drops...

--
Austin Shackles. www.ddol-las.net my opinions are just that
"You praise the firm restraint with which they write -_
I'm with you there, of course: They use the snaffle and the bit
alright, but where's the bloody horse? - Roy Campbell (1902-1957)

On or around Fri, 04 Aug 2006 13:11:25 +0100, Steve Taylor
<[email protected]> enlightened us thusly:

>ArthurC wrote:
>> If you want to go down the capacitor route, rather than use a massive
>> capacitor, it would be more economical to use an inductor (coil) in
>> series with the +12V power to the +12V on the bulb as well as the
>> capacitor across the bulb, thus forming a conventional LC filter.
>
>The capacitor is the quickest and simplest tryout. Your inductor has to
>carry the lamp DC without saturating, and you need one with each cluster.
>
>Personally, I'd scope the 12V supply and see what's happening, but you
>have to have access to a scope....
>
>> Another alternative would be to look at using a semiconductor spike
>> suppressor across the bulb. Have a look at Rapid Electronics (
>> http://www.rapidelectronics.co.uk/ ) part number 26-3812. A bit
>> cheaper, too!
>That's a good way to do it.
>
> > Hence the tradeoff between capacitance and
>> maximum working voltage for a given physical size.
>
>
>2.5 V 2500 Farad is the biggest I've found so far.
>
>Steve

There was one at the school I went to some years ago (1977-1984) which was
part of the emergency lighting system I think. 0.5F and presumably about
24V.
--
Austin Shackles. www.ddol-las.net my opinions are just that
"You praise the firm restraint with which they write -_
I'm with you there, of course: They use the snaffle and the bit
alright, but where's the bloody horse? - Roy Campbell (1902-1957)

On Thursday, in article
<[email protected]>
[email protected] "steve" wrote:

> David G. Bell wrote:
>
> > Of course, if you had a capacitor rated at 1500 Volts (which is the
> > voltage at which nasty things will happen inside the capacitor) you
> > could stuff 22 megaJoules into it, and that is a things-go-boom event
> > when you dead short the terminals (or the insulation inside the
> > capacitor fails).
> >
> > So don't do that.
> >
>
> ..or at least be sporting enough to invite us to watch.

I am tempted to suggest it to one of those stupid science tricks
programmes on TV.



--
David G. Bell -- SF Fan, Filker, and Punslinger.

"I am Number Two," said Penfold. "You are Number Six."

David G. Bell wrote:

> I am tempted to suggest it to one of those stupid science tricks
> programmes on TV.

Course, have you seen these mega-amp current pulse jobbies used to
shrink metal objects.

Steve

I'm using LEDs from both the manufacturers on my boat which has no charging
system other than small solar panels.
So far I have had no problems with the bulbs running at 12v direct from a
battery.

TonyB

TonyB wrote:
> I'm using LEDs from both the manufacturers on my boat which has no charging
> system other than small solar panels.
> So far I have had no problems with the bulbs running at 12v direct from a
> battery.

You're laughing then, because there won't be any nasty horrors coming
from an alternator/engine combination.

Steve

"ArthurC" <[email protected]> wrote in message
news:[email protected]...
>
> Steve Taylor wrote:
>> Liam wrote:
>>
>> > So fitting a capacitor may help, I may experiment with that, how
>> > exactly
>> > would that be wired in?
>>
>> In parallel with the light clusters, there's not a heck of a lot of
>> point doing it near the battery.
>>
>> Could there be any other side effects fitting one?
>> > What size capacitor would it be worth fitting?
>>
>> Seriously, a 10 Farad one, as used by car hi-fi freaks, for similar
>> reasons.
>>
>> If you want to try per-cluster, then a 470uF would be bearable.
>>
>> Steve
>
> Car Hi Fi uses massive capacitors in order to get very good low
> frequency performance from the power amps rather than to get rid of
> spikes (for the same reason as using very heavy gauge wiring).
>
> I assumed that the original contributor's contribution was meant to be
> 10uF, not 10F! A 10F capacitor would be a bit expensive in relation to
> the bulb!!!
>
> What you do when you use a capacitor to get rid of spikes is
> effectively to use it as a low pass filter, where the R or L component
> of the filter is formed by the output impedance of the voltage source
> (i.e. the alternator, battery, wiring). The effect of the capacitor in
> removing the voltage spike thus depends on this impedance, which is
> very low for a car battery and associated wiring. Thus, a large
> capacitor is needed to get rid of spikes in car electrics.
>
> If you want to go down the capacitor route, rather than use a massive
> capacitor, it would be more economical to use an inductor (coil) in
> series with the +12V power to the +12V on the bulb as well as the
> capacitor across the bulb, thus forming a conventional LC filter.
>
> +12V --------| coil |--------------------------
> | |
> Capacitor Bulb
> | |
> GND--------------------------------------------
>
> Another alternative would be to look at using a semiconductor spike
> suppressor across the bulb. Have a look at Rapid Electronics (
> http://www.rapidelectronics.co.uk/ ) part number 26-3812. A bit
> cheaper, too!
>

Thanks for that.
The transient voltage suppressors sound like the easiest idea to try. Would
I need one for each bulb or could one be used for a few bulbs? I have the
side lights on the Land Rover wired in three circuits, LH side, RH side and
dashboard.
Also I see there are Unidirectional and bidirectional ones available, would
the unidirectional ones be more suited to DC voltage?
Just had a thought would these suppressors be suitable to replace the
regulator unit for the fuel gauge? mine is working fine, just for future
referance.

Thanks
Liam

--
www.sumpoil.pwp.blueyonder.co.uk

Austin Shackles wrote:
> On or around 4 Aug 2006 04:31:41 -0700, "ArthurC" <[email protected]>
> enlightened us thusly:
>
>> Car Hi Fi uses massive capacitors in order to get very good low
>> frequency performance from the power amps rather than to get rid of
>> spikes (for the same reason as using very heavy gauge wiring).
>
> newly-acquired motor here has an interesting glitch - if you turn the stereo
> (quite a nice JVC with 12-disc changer) up too high, it cuts out, then in
> again, then out again...
>
> I speculate that the power supply into the head unit isn't up to it - too
> much volume = too much current from the supply, leading to voltage drop
> which makes the unit think the ignition's been turned off. Then the voltage
> recovers, and it turns back on again, voltage drops...
>
Check how it's been earthed - I've seen a few that are "earthed" onto a
wire that isn't an earth and that leads to this sort of problem.

--
EMB