Electrical puzzle

[pwfl]

I liked the idea of having nice bright nav lights so big ships wouldn't bump into us.

But we were finding running a 25 watt bulb all night every night on long passages was taking so much amp hrs out of our batteries, that on clear nights we found ourselves thinking about running with no lights (I HATE using the engine to charge the batteries, & we weren't keeping up with our other means of charging).

We decided it would be better to have 10 watt bulbs & be able to run them without worrrying so much about draining the batteries, than have brighter lights that we kept off half the time to save power.

OK, so here's the mystery: we have a battery monitor which seems to be quite accurate. ie we turn on something that's supposed to draw, say 1.4 A, & it says we're drawing 1.4 A, etc..

Now with the 25 W bulbs, the current draw should be got by Power = Volts x Current - ie Current = 25W/12V = 2.1Amps. Which is pretty much what the battery monitor said.

But with the 10 Watt bulbs, where the current should be 10W/12V = 0.8Amps, instead it reads 1.6 A!!

Apart from the fact that this is not giving me anywhere near the savings in amp hours that I was hoping for, what I want to know is HOW is this possible???

I have about 10 spare 10 Watt bulbs. By 2 different manufacturers. Bought from 2 different chandlers, in different parts of the country.

The bulbs are stamped 12V 10W on the bulbs themselves (ie it is not that they have been put in the wrong boxes).

They all give the same reading.

Any ideas???





<hr width=100% size=1>

 

[jfkal]

To make sure there is nothing else influencing it I would test them on the bench with a handheld ammeter (Just Battery, Ammeter and bulb) and take it from there.
There could be a bad connection i.e. high resistance short somehwere up the mast which comes into the picture more prominent when you use a lower wattage bulb.

<hr width=100% size=1>

 

[Robin]

You mention bulbs implying more than one so are you talking about changing the bulb in (one) masthead tricolour lamp or in say a pulpit bicolour plus a stern light (total two) or 2 separate bow lights plus sternlight (total three). It sounds to me that your meter is reading the output from TWO 10w bulbs.

<hr width=100% size=1>

 

[AndrewJ]

Not a direct response to your question, but when I bought my boat, the previous owner had taken a small 12v light bulb (from an automobile taillight etc.) and put it in a glass salt shaker (the kind with the serrated sides (square cut)). It's really astounding the amount of light this puts out, the square cuts seem to amplify the light and the current draw is minimal. I tried one better and put a 12v LED, one of the "brilliant" ones and this worked almost as well, with even less current draw. I use it for an anchor light at "eye" level. (mounted outside the cockpit). I have a "cigarette lighter" socket in my cockpit and plug the light into that.


<hr width=100% size=1>

 

[tcm]

Re: dim sailing

um, regardless, surely it is best to run the engines for a while if that's what is needed for decently bright lights? Sorry. Very worrying to think that some (or are there several?) purist loonies might use no lights cos they "really hate running the engine". Different matter if lights temporarily don't work, of course. Getting a bigger battery, or an additional battery in parallel, would seem much wiser.

<hr width=100% size=1>

 

[pwfl]

Sorry Robin, I meant bulb - the masthead tricolour, so I don't think there were any other bulbs in the circuit that could have been influencing things.

Either way, I'm looking at the difference in total current draw between replacing 1 25 watt bulb with 1 10 W bulb, regardless of whatever else is running.

<hr width=100% size=1>

 

[pwfl]

Re: dim sailing

Yes, TCM, it was worrying - hence our decision to try 10 W bulbs, rather than find ouselves in the position that we were thinking such things.

In my defence, I would say that this was on ocean passages, with no traffic seen for some time, & on clear, moonlit nights with good vis all the way to the horizon.

We are a small boat & already have 2 110 Ah batteries, which is about as much as we can stand (we've already lost sight of our boot stripe). We also carry limited fuel, & so prefer to keep it for when we really need it. We have a towed generator, but when we haven't been making great speed, that 25 W bulb really starts chewing into your amp hrs.

<hr width=100% size=1>

 

[tcm]

Re: back to the o-level physics

i still can't get away from the idea that the bulbs must be wrong, somehow. But 2 different chandlers/mauf? Best as another says to testem with a handheld mulitmeter.

cheers.

<hr width=100% size=1>

 

[tome]

Is your masthead a combined tricolour/all round white? If so, the all round white will be 10W whilst the tricolour should be 25W. Have you looked at the masthead when you power it up (usually have to get some distance away to observe it)?

It could be that you have a wiring fault and that both bulbs are coming on.

You can check the 10W bulbs by temporarily wiring one straight across the domestic battery whilst observing the current draw, this will at least tell you whether there is a fault.

<hr width=100% size=1>

 

[steve_cronin]

I think maybe your answer is....

...that a 10watt bulb tends to get labelled rather in accordance with the expected light output than it's actual power consumption.

Since most are automotive related, the actual power consumption isn't all that critical. For example two "21watt" stop lamp bulbs in parallel actually draw 4.1amps at 12 volts and four 5 watt sidelights draw 2.1 amps. You will also discover that a 60 watt mains bulb doesn't draw 0.25 amps at 240 volts as you might expect otherwise 24 such bulbs on at the same time would trip your 6amp lighting circuit breaker. They have all become nominal values over time, the lower voltage and power ones being much further "off the curve" than the higher ones.

I have noticed that some manufacturers are actually quoting light output now on their boxes. Maybe the notional consumption values might disappear altogether soon. I bought some "150watt" mushroom bayonet fit bulbs in a supermarket in Athens ( I tried in vain to get over 100watt in similar outlets in the UK). They had the "Lumens" very prominently displayed on the box but I had to look quite hard to find the wattage.

Steve Cronin

<hr width=100% size=1>

 

[dickh]

I would be very wary about reducing the wattage of nav lights. If I remember correctly the Tricolour must be 25watts to be compliant, and even then only has a range of 2 miles. White lamps are better, 10 watts will also give 2 miles. With only 10watts in a tricolour, I would doubt if you get barely 1 mile range. All coloured lamps should be 25watts but white stern and steaming lights can 10watts to give same range(I may be out on the above ranges but you get the idea)
Is your mast head wiring correctly sized? You have to add up both the wires, to and from the lamp and the refer to the tables to get minimum voltage drop. If I remember corectly, you should use at least 1.5mm² tinned flexible cable, which very few manufacturers fit as standard - it always seems to be 0.75mm² or smaller.

<hr width=100% size=1>dickh
I'd rather be sailing... /forums/images/icons/smile.gif

 

[AlanPound]

If there was significant resistance in the wiring (and there certainly will be at least a little), the the brightness of the lamp will decrease, and the overall current consumed will also decrease (ohms law).

... If the overall current *increased* (for whatever reason) then the light would actually get brighter....

<hr width=100% size=1>

 

[tcm]

Re: series resistance

agreed, cept his first reading with the 25 w bulb shows that the resistance in the wires is minimal, doesn't it?

<hr width=100% size=1>

 

[Ivy]

you could stick with the 25w lamps, put a second switch in series with the first with a resistor across it, with the second switch off the resistor will cause the light to shine less brightly ( for clear nights), switch it on to by-pass the resistor for full brightness. it will save your batteries but it won't keep you up with the col-regs.

Use a varyable restistor to make it more adjustable.

<hr width=100% size=1>

 

[AlanPound]

weeeell, using white (or deliberately red/green - white is actually the more difficult) LEDs, one of the tricks you can pull is to pulse them... as long as the pulsing is quick enough, the 'retention of vision' makes the human eye perceive the pulsed light as continuous (rather than strobed), but the average current consumed is maybe halved by pulsing.... *plus* LEDs produce pretty much 'cold' light - I mean, little energy is wasted in the form of heat (compared with the incandescent bulb)...

.... ok - problems,

i) LEDs tend to be fairly directional, so you would need a circular array of them..., plus a little bit of circuitry to pulse them - however, the result would have almost indefinite life (apart from the vagaries of a salt-laden atmosphere, and it *could* be completely encapsulated in resin)

ii) apart from the perceived brightness, there are regulatory lumens to meet, and those were never written for even 20th century illumination (let alone 21st...), despite the fact that ordinary bulbs and lamp units (in all probablilty) only ever meet the regs when a) newly manufacturered, not salt encrusted, nor faded b) in a lab, and c) under ideal, fresh battery conditions...

I mean, the point about this is that a good, resin potted LED array, probably emits 99% of its original design light output, even after 20 years... (my tricolour doesn't look that good after even 1 year....)

I think there are companies introducing products like this (is it Hella?) .....none too soon as far as I am concerned - the fewer excuses I have to go up the mast, the happier I will be..


<hr width=100% size=1>

 

[Ivy]

Some good points there alan, but, the Idea of pulsing the LEDs would seem a bit "over the top" as they draw such a small amount of current anyway.

I've seen these Led clusters advertised, but, I haven't yet tried one, I don't think they are much good for a nav light, as they wouldn't stand high enough inside the fitting for the lens to focus the beam if light.

<hr width=100% size=1>

 

[dickh]

I did see some from another post on this forum a few weeks ago - an american site which will purpose make them, but they were talking LOTS of $!! See
<A target="_blank" HREF=http://www.deepcreekdesign.com>http://www.deepcreekdesign.com</A> only replacement 'bulbs' so you still need the original Aquasignal or similar tricolour - but still not officially approved.
So at the moment uneconomic for the average cruiser.
Hella do make some but I believe are only approved in the US - and they are expensive. You can see them on their website. Do a search on this forum on LED nav lights.

<hr width=100% size=1>dickh
I'd rather be sailing... /forums/images/icons/smile.gif<P ID="edit"><FONT SIZE=-1>Edited by dickh on 10/09/2003 11:42 (server time).</FONT></P>

 

[tome]

Ivy

To reduce a 25W bulb to 10W you would need a series resistor of around 8 ohms. You would lose around 6W energy across the resistor, so would end up consuming 16W which is not a terribly efficient way of doing it. Better to go with a 10W bulb in the first place though I'll stick with my 25W and put up with the occasional charge to keep the batteries going.

Regards
Tom

<hr width=100% size=1>

 

[Ivy]

I quite agree with you. I hadn't worked out the details although I no it's not a very efficient method it would work. Improving the charging system would be better, maybe a solar panel for instance.

I'll be sticking with my 25w tri-col, just the same.

<hr width=100% size=1>

 

[AlanPound]

I have a feeling we have been here before... but can't remember the outcome...

<Hella do make some but I believe are only approved in the US>

... do they need actual approval - is there an official testing/approval authority (in the UK), or is it simply the case that they have to meet the minimum illumination standards as set out in candelas etc...?

<hr width=100% size=1>