Almost certainly a dumb question.

I have 6V cycle lights which came with a chunky 4.5Ah lead acid battery.

Now I can get a replacement for under £10 (or more - not sure what the
difference is although those targeted at security alarms seem to carry a
premium).

However there are USB backup devices which offer 3.2Ah or more at 5v at a
fraction of the weight.

So I had the passing thought that running 6v lights at 5v might give a
reasonable light level and much lightness.

However I have no real grasp of what the effect of under volting a DC
light could be - in fact 12V car systems are probably running at 13-14V at
times so the whole idea may be a non starter.

Almost certainly not worth buying a 5V battery (although I already have a
backup battery for phone/tablet) so I was just idly wondering.....

Cheers

Dave R

--
Windows 8.1 on PCSpecialist box

On Tue, 07 Apr 2015 17:19:08 +0000, David wrote:

However I have no real grasp of what the effect of under volting a DC
light could be

A big reduction in light output

in fact 12V car systems are probably running at 13-14V at times so the
whole idea may be a non starter.

Yep, alternator output is typically 14-14.5v, so you should see close to
that at the bulbs at all times the engine's running.

On 7 Apr 2015 17:19:08 GMT, David wrote:

Almost certainly a dumb question.

I have 6V cycle lights which came with a chunky 4.5Ah lead acid battery.

Now I can get a replacement for under £10 (or more - not sure what the
difference is although those targeted at security alarms seem to carry a
premium).

However there are USB backup devices which offer 3.2Ah or more at 5v at a
fraction of the weight.

So I had the passing thought that running 6v lights at 5v might give a
reasonable light level and much lightness.

However I have no real grasp of what the effect of under volting a DC
light could be - in fact 12V car systems are probably running at 13-14V at
times so the whole idea may be a non starter.

Almost certainly not worth buying a 5V battery (although I already have a
backup battery for phone/tablet) so I was just idly wondering.....

Presuming E over I still equals R, I think you are just going to get a
dull orangey glow that won't be much use to anybody.

Years ago, I built a contraption around my hub-dynamo which gave me
lights, signalling and a battery back-up which cut in when stationary.
Nowadays, I think I'd do it completely differently and use LEDs and
rechargeable AA cells.

Nick

David wrote:
Almost certainly a dumb question.

I have 6V cycle lights which came with a chunky 4.5Ah lead acid battery.

Now I can get a replacement for under £10 (or more - not sure what the
difference is although those targeted at security alarms seem to carry a
premium).

However there are USB backup devices which offer 3.2Ah or more at 5v at a
fraction of the weight.

So I had the passing thought that running 6v lights at 5v might give a
reasonable light level and much lightness.

While you /can/ do it, bulb systems have been almost completely wiped out by
LEDs these days - you get more light output for less battery usage and not
much money (unless you want to). So retrofitting to a bulb system seems to
be to be a waste of time.

The one thing bulbs are still good at is non-directional lighting (eg all
round rear light visibility), but clusters of LEDs or reflectors do a decent
job at approaching this.

If you insist, though, one thing you could try is replacing the bulb with a
lower voltage. IIRC, back in the day it was common for 2-cell torches to
take either a 3.5V or a 2.5V bulb - the latter would be brighter but take
more battery and burn out more quickly. So maybe you could run a 4.5V bulb
in your lights?

Theo
(wondering whether torch bulbs will go the way of the valve and the
photographic film...)

On 07 Apr 2015 18:43:18 +0100 (BST), Theo Markettos
wrote:

David wrote:
Almost certainly a dumb question.

I have 6V cycle lights which came with a chunky 4.5Ah lead acid battery.

Now I can get a replacement for under £10 (or more - not sure what the
difference is although those targeted at security alarms seem to carry a
premium).

However there are USB backup devices which offer 3.2Ah or more at 5v at a
fraction of the weight.

So I had the passing thought that running 6v lights at 5v might give a
reasonable light level and much lightness.

While you /can/ do it, bulb systems have been almost completely wiped out by
LEDs these days - you get more light output for less battery usage and not
much money (unless you want to). So retrofitting to a bulb system seems to
be to be a waste of time.

The one thing bulbs are still good at is non-directional lighting (eg all
round rear light visibility), but clusters of LEDs or reflectors do a decent
job at approaching this.

If you insist, though, one thing you could try is replacing the bulb with a
lower voltage. IIRC, back in the day it was common for 2-cell torches to
take either a 3.5V or a 2.5V bulb - the latter would be brighter but take
more battery and burn out more quickly. So maybe you could run a 4.5V bulb
in your lights?

Theo
(wondering whether torch bulbs will go the way of the valve and the
photographic film...)

Oy! Less of the doomsaying about photographic film if you don't mind!
Today I took my 35mm SLR in for an overhaul.

Nick

On 07/04/2015 18:19, David wrote:
Almost certainly a dumb question.

I have 6V cycle lights which came with a chunky 4.5Ah lead acid battery.

Now I can get a replacement for under £10 (or more - not sure what the
difference is although those targeted at security alarms seem to carry a
premium).

However there are USB backup devices which offer 3.2Ah or more at 5v at a
fraction of the weight.

So I had the passing thought that running 6v lights at 5v might give a
reasonable light level and much lightness.

However I have no real grasp of what the effect of under volting a DC
light could be - in fact 12V car systems are probably running at 13-14V at
times so the whole idea may be a non starter.

Almost certainly not worth buying a 5V battery (although I already have a
backup battery for phone/tablet) so I was just idly wondering.....

Cheers

Dave R

A chunky 4.5AH 6V battery implies something like a 10W incandescent
halogen bulb, so a running current of 1.7A and a startup surge of
several times that. I would be surprised if a USB backup battery would
supply that, and a 6V bulb on 5V will be not very bright and rather
orangey. In any event, the claimed capacity of a USB battery is likely
to be a lie.

If you don't hang about, LIDL have some LED lights for £6 at the moment,
and they're pretty good. If they're the rechargeable ones get two sets.

Cheers
--
Syd

On 07/04/2015 18:28, Adrian wrote:
On Tue, 07 Apr 2015 17:19:08 +0000, David wrote:

However I have no real grasp of what the effect of under volting a DC
light could be

A big reduction in light output

Yes for filament bulbs, though not quite as much as you would think
because at the lower temperature the resistance will also be lower, so
you get more than 5/6ths of the current, so the power dissipated will be
more than the 69% predicted by a simple minded calculation. The light
will be less "white".

For LED maybe no perceptible difference.

The "USB" power packs may well be regulated to provide no more than
about 1 amp.


in fact 12V car systems are probably running at 13-14V at times so the
whole idea may be a non starter.

Yep, alternator output is typically 14-14.5v, so you should see close to
that at the bulbs at all times the engine's running.

On 07/04/2015 18:19, David wrote:
Almost certainly a dumb question.

I have 6V cycle lights which came with a chunky 4.5Ah lead acid battery.

Now I can get a replacement for under £10 (or more - not sure what the
difference is although those targeted at security alarms seem to carry a
premium).

However there are USB backup devices which offer 3.2Ah or more at 5v at a
fraction of the weight.

So I had the passing thought that running 6v lights at 5v might give a
reasonable light level and much lightness.

However I have no real grasp of what the effect of under volting a DC
light could be - in fact 12V car systems are probably running at 13-14V at
times so the whole idea may be a non starter.

Almost certainly not worth buying a 5V battery (although I already have a
backup battery for phone/tablet) so I was just idly wondering.....

Cheers

Dave R


This raises quite a few questions.

How many lights are you powering (presumably 2?) and what is the power
of each bulb? If you work out the total power and divide by 6, that will
tell you how many amps of current you need. How many amps can this USB
device deliver? You say that it's 3.2 Ah - but that's the capacity, not
the current. For example, it may be able to deliver 3.2 amps for a
period of hour, or 0.32 amps for 10 hours - or something in between. If
it can't deliver the current required by the lamps, you're going to get
a very dim glow at best.

Assuming that it *can* deliver the required current, reducing the
voltage from 6 to 5 means that the bulbs will only run at 69% of their
rated power - because power is proportional to V squared. Worse than
that - because the lamps will run a lot cooler, the colour temperature
of the light emitted will change, with white light becoming yellower,
and more of the radiation being in the infra-red part of the spectrum
and less visible light.

In summary - a pretty bad idea!
--
Cheers,
Roger
____________
Please reply to Newsgroup. Whilst email address is valid, it is seldom
checked.

On 07 Apr 2015 18:43:18 +0100 (BST), Theo Markettos
wrote:

David wrote:
Almost certainly a dumb question.

I have 6V cycle lights which came with a chunky 4.5Ah lead acid battery.

Now I can get a replacement for under £10 (or more - not sure what the
difference is although those targeted at security alarms seem to carry a
premium).

However there are USB backup devices which offer 3.2Ah or more at 5v at a
fraction of the weight.

So I had the passing thought that running 6v lights at 5v might give a
reasonable light level and much lightness.

While you /can/ do it, bulb systems have been almost completely wiped out by
LEDs these days - you get more light output for less battery usage and not
much money (unless you want to). So retrofitting to a bulb system seems to
be to be a waste of time.

The one thing bulbs are still good at is non-directional lighting (eg all
round rear light visibility), but clusters of LEDs or reflectors do a decent
job at approaching this.

If you insist, though, one thing you could try is replacing the bulb with a
lower voltage. IIRC, back in the day it was common for 2-cell torches to
take either a 3.5V or a 2.5V bulb - the latter would be brighter but take
more battery and burn out more quickly. So maybe you could run a 4.5V bulb
in your lights?

Theo
(wondering whether torch bulbs will go the way of the valve and the
photographic film...)

And spinning-rust harddrives.



--

Graham.

%Profound_observation%

On 07/04/2015 22:03, Roger Mills wrote:

snip

Assuming that it *can* deliver the required current, reducing the
voltage from 6 to 5 means that the bulbs will only run at 69% of their
rated power - because power is proportional to V squared.

The lamp resistance isn't fixed though, it varies significantly with
temperature. Light output is roughly V^3.4, so for a 6V lamp on 5V
you'd get about 54% of the 'rated' light. Power goes at roughly V^1.6
so you'd use about 75% of the rated power. So about half the light for
three quarters the power.

Worse than
that - because the lamps will run a lot cooler, the colour temperature
of the light emitted will change, with white light becoming yellower,
and more of the radiation being in the infra-red part of the spectrum
and less visible light.
S'true.

In summary - a pretty bad idea!
Indeed.

Cheers
--
Syd

On 07/04/15 18:19, David wrote:
Almost certainly a dumb question.

I have 6V cycle lights which came with a chunky 4.5Ah lead acid battery.

Now I can get a replacement for under £10 (or more - not sure what the
difference is although those targeted at security alarms seem to carry a
premium).

However there are USB backup devices which offer 3.2Ah or more at 5v at a
fraction of the weight.

So I had the passing thought that running 6v lights at 5v might give a
reasonable light level and much lightness.

However I have no real grasp of what the effect of under volting a DC
light could be - in fact 12V car systems are probably running at 13-14V at
times so the whole idea may be a non starter.

Almost certainly not worth buying a 5V battery (although I already have a
backup battery for phone/tablet) so I was just idly wondering.....

Cheers

Dave R

5 X 1.2v NiCd or NiMh cells will give you a very decent 6V.

Lithium polymer sadly will do 7-8v on full charge for a 2 cell.

But LiFePo is about 3v per cell so two of those....




--
Everything you read in newspapers is absolutely true, except for the
rare story of which you happen to have first-hand knowledge. €“ Erwin Knoll

Well I guess the answer is, it very much depends on the light source. If you
are going to use filament bulbs, then the light might well be a bit dimmer
than on 6V, but if you are saying the lights ran on 4.5V, then I'd hazzard a
guess they will be a little brighter and last less long. I thought these
days most cycle stuff used LED lights, and as these are current limited
internally you will notice no difference as the extra disipation by the
current limiting system would be able to cope I'm sure.


Brian

--
From the Sofa of Brian Gaff Reply address is active
"David" wrote in message
...
Almost certainly a dumb question.

I have 6V cycle lights which came with a chunky 4.5Ah lead acid battery.

Now I can get a replacement for under £10 (or more - not sure what the
difference is although those targeted at security alarms seem to carry a
premium).

However there are USB backup devices which offer 3.2Ah or more at 5v at a
fraction of the weight.

So I had the passing thought that running 6v lights at 5v might give a
reasonable light level and much lightness.

However I have no real grasp of what the effect of under volting a DC
light could be - in fact 12V car systems are probably running at 13-14V at
times so the whole idea may be a non starter.

Almost certainly not worth buying a 5V battery (although I already have a
backup battery for phone/tablet) so I was just idly wondering.....

Cheers

Dave R

--
Windows 8.1 on PCSpecialist box

On Tue, 07 Apr 2015 18:50:20 +0100, Nick Odell
wrote:

On 07 Apr 2015 18:43:18 +0100 (BST), Theo Markettos
wrote:

Theo
(wondering whether torch bulbs will go the way of the valve and the
photographic film...)

Oy! Less of the doomsaying about photographic film if you don't mind!
Today I took my 35mm SLR in for an overhaul.

Which reminded me of the last time I used my film SLR's, for a roll of
Kodachrome 64, which got sent via Kodak UK (and maybe via Kodak Switzerland) to
the last processing facility in the USA.

I know it was sent only a few days before the final deadline, a quick google
suggests this would have been the end of 2010 but I seem to recall the UK / Euro
cutoff might have been a month or two earlier.

--

On Tue, 07 Apr 2015 18:55:13 +0100, Syd Rumpo wrote:

On 07/04/2015 18:19, David wrote:
Almost certainly a dumb question.

I have 6V cycle lights which came with a chunky 4.5Ah lead acid
battery.

Now I can get a replacement for under £10 (or more - not sure what the
difference is although those targeted at security alarms seem to carry
a premium).

However there are USB backup devices which offer 3.2Ah or more at 5v at
a fraction of the weight.

So I had the passing thought that running 6v lights at 5v might give a
reasonable light level and much lightness.

However I have no real grasp of what the effect of under volting a DC
light could be - in fact 12V car systems are probably running at 13-14V
at times so the whole idea may be a non starter.

Almost certainly not worth buying a 5V battery (although I already have
a backup battery for phone/tablet) so I was just idly wondering.....

Cheers

Dave R

A chunky 4.5AH 6V battery implies something like a 10W incandescent
halogen bulb, so a running current of 1.7A and a startup surge of
several times that. I would be surprised if a USB backup battery would
supply that, and a 6V bulb on 5V will be not very bright and rather
orangey. In any event, the claimed capacity of a USB battery is likely
to be a lie.

If you don't hang about, LIDL have some LED lights for £6 at the moment,
and they're pretty good. If they're the rechargeable ones get two sets.

Cheers

Hmm....didn't know they had rechargeable.

{Nips out the the bike bits stock to check}

Crivit ones I just bought (for another bike) are rechargeable.
Hadn't even clocked that.

I still like my old CatEye twin head lamps though - outdated and non-LED
as they are.

Sadly I think our local Lidl is out of stock now - will check though.

Anyway, proper lead acid battery it is.

Cheers

Dave R



--
Windows 8.1 on PCSpecialist box

On Tuesday, 7 April 2015 18:50:24 UTC+1, Nick Odell wrote:
On 07 Apr 2015 18:43:18 +0100 (BST), Theo Markettos
wrote:

David wrote:
Almost certainly a dumb question.

I have 6V cycle lights which came with a chunky 4.5Ah lead acid battery.

Now I can get a replacement for under £10 (or more - not sure what the
difference is although those targeted at security alarms seem to carry a
premium).

However there are USB backup devices which offer 3.2Ah or more at 5v at a
fraction of the weight.

So I had the passing thought that running 6v lights at 5v might give a
reasonable light level and much lightness.

While you /can/ do it, bulb systems have been almost completely wiped out by
LEDs these days - you get more light output for less battery usage and not
much money (unless you want to). So retrofitting to a bulb system seems to
be to be a waste of time.

The one thing bulbs are still good at is non-directional lighting (eg all
round rear light visibility), but clusters of LEDs or reflectors do a decent
job at approaching this.

If you insist, though, one thing you could try is replacing the bulb with a
lower voltage. IIRC, back in the day it was common for 2-cell torches to
take either a 3.5V or a 2.5V bulb - the latter would be brighter but take
more battery and burn out more quickly. So maybe you could run a 4.5V bulb
in your lights?

Theo
(wondering whether torch bulbs will go the way of the valve and the
photographic film...)

Oy! Less of the doomsaying about photographic film if you don't mind!
Today I took my 35mm SLR in for an overhaul.

You should have taken it to be euithanised ;-)

On Wed, 08 Apr 2015 10:04:56 +0000, David wrote:

On Tue, 07 Apr 2015 18:55:13 +0100, Syd Rumpo wrote:

On 07/04/2015 18:19, David wrote:
Almost certainly a dumb question.

I have 6V cycle lights which came with a chunky 4.5Ah lead acid
battery.

Now I can get a replacement for under £10 (or more - not sure what the
difference is although those targeted at security alarms seem to carry
a premium).

However there are USB backup devices which offer 3.2Ah or more at 5v
at a fraction of the weight.

So I had the passing thought that running 6v lights at 5v might give a
reasonable light level and much lightness.

However I have no real grasp of what the effect of under volting a DC
light could be - in fact 12V car systems are probably running at
13-14V at times so the whole idea may be a non starter.

Almost certainly not worth buying a 5V battery (although I already
have a backup battery for phone/tablet) so I was just idly
wondering.....

Cheers

Dave R

A chunky 4.5AH 6V battery implies something like a 10W incandescent
halogen bulb, so a running current of 1.7A and a startup surge of
several times that. I would be surprised if a USB backup battery would
supply that, and a 6V bulb on 5V will be not very bright and rather
orangey. In any event, the claimed capacity of a USB battery is likely
to be a lie.

If you don't hang about, LIDL have some LED lights for £6 at the
moment,
and they're pretty good. If they're the rechargeable ones get two
sets.

Cheers

Hmm....didn't know they had rechargeable.

{Nips out the the bike bits stock to check}

Crivit ones I just bought (for another bike) are rechargeable.
Hadn't even clocked that.

Further check shows previous Crivit light supports recharging but didn't
come with charger or rechargeable batteries.

However I now have a charger.

Looks like a double result :-)





--
Windows 8.1 on PCSpecialist box

On Wed, 08 Apr 2015 09:51:14 +0100, The Natural Philosopher
wrote:

5 X 1.2v NiCd or NiMh cells will give you a very decent 6V.

Lithium polymer sadly will do 7-8v on full charge for a 2 cell.

So put it through one of these for a stable 6v, just 99p and a few minutes
tweaking the output pot.

www.ebay.co.uk/itm/221541272222

--