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Author Topic: changing voltage on lights  (Read 2233 times)

irishcarguy

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changing voltage on lights
« on: March 29, 2013, 11:18:44 PM »

I know this may be a stupid question to some but I want to reduce the voltage to my mast lights to 6v from 12v, can I do it with a resistor & what resistor will I require. I wish to reduce my cabin light to 3 volts,  from 12 volts,same question, How do I do it(a very dumb electrician)Mick B.
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Mick B.

dreadnought72

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Re: changing voltage on lights
« Reply #1 on: March 30, 2013, 12:12:00 AM »

Check out Maplins for voltage regulators. A quid'll get you something that'll put out 6V and up to 1amp from a supply of up to 35V.

Andy
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Re: changing voltage on lights
« Reply #2 on: March 30, 2013, 02:40:22 AM »

What your looking for is a 7806 voltage regulator and a small heatsink.
Its not so much the load but the load and difference in potential.. so grab a small heat sink..
 
Its easy to wire up ..looking at the front face  its  pin1=volt in, pin2=ground pin3 = out .. double check with a voltmeter and you on your way..
http://www.engineersgarage.com/electronic-components/7806-ic
 
Should cost you under a buck at most electronic component stores ..Watch radio shack and those type places prices are ridiculous
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irishcarguy

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Re: changing voltage on lights
« Reply #3 on: March 30, 2013, 02:47:38 AM »

Thank you both, I had been looking too at fleabay & the low prices that are unbelievable from China, they even offer free shipping & the units have a display too both for voltage & current, Mick B.
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Mick B.

inertia

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Re: changing voltage on lights
« Reply #4 on: March 30, 2013, 08:33:26 AM »

This is probably the UK's most expensive electronics retailer, and this is an adjustable voltage regulator............. Heat-sink mandatory for full power capability  http://www.maplin.co.uk/lm317-3-terminal-adjustable-voltage-regulators-8067
You don't need a built-in voltage and current display; buy a digital multimeter for about $C10 and you can learn all about model boat electrics with it!
DM
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malcolmfrary

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Re: changing voltage on lights
« Reply #5 on: March 30, 2013, 09:28:51 AM »

The LM7806 is a rare bird, but available, I found one googling - http://www.amazon.com/LM7806-Voltage-Regulator-6v-TO-220/dp/B008PS8VYQ
The LM7805 is much more common, and a 5 volt supply will work lights almost as well, the main difference being that the lights will last longer.  At 1A, they will be trying to lose a little over 7 watts each, so a substantial heatsink will be needed.  When the heatsink is considered, it might be simpler and lighter to just use a 6 volt battery.  There are such things as voltage regulators that don't act as automatic self adjusting resistors, but they are not yet cheap.
For the 3 volt lighting, I would try to arrange things so that the lamps were in series pairs, making them effectively 6 volt lamps.
The problem with trying to calculate the resistor required is that filament bulbs have a very different value when hot than when cold, so the only way really is to either read the manufacturers data sheet or calculate the current from the known voltage and wattage or measure it.  Then you can calculate the value of the resistor to make the full circuit pull the required current off 12 volts.  Or if its a fully charged battery, 14.5 volts.  Thats where a regulator is useful, it adjusts itself to the correct value for the voltage its outputting. 
For 6 volts off a charged battery, 14.5-6 = 8.5 volts.  At 1A, thats 8.5 watts.  If you want to keep the regulator within its temperature limits, you will be looking for a heatsink rated at better than 4 degrees centigrade per watt, and that is going to be a substantial lump of aluminium to give the needed surface area without fan assistance.  And that assumes that there is somewhere to transfer the unwanted heat away from the insides of the boat to the outside world.
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787eng

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Re: changing voltage on lights
« Reply #6 on: March 30, 2013, 09:36:23 AM »

Why make life complicated and having to get rid of all that heat?
As far as I see it you have two simple options

1 Wire lights in a series/ parallel option to get your 3/6/12 Volt requirements.
2 If you are using a 2.4GHz radio
http://www.technobotsonline.com/switching-variable-regulator-3a.html

Mark
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grendel

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Re: changing voltage on lights
« Reply #7 on: March 30, 2013, 09:52:26 AM »

surely it would be easy to drill a small aluminium block to attach to the chip, run a copper or brass tube through it with heat sink paste and water cool as you would a motor with a scoop under the hull, seems to me the simplest method of disposing of unwanted heat in a hull.
Grendel
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787eng

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Re: changing voltage on lights
« Reply #8 on: March 30, 2013, 10:12:04 AM »

And not producing any heat to start with isn't  %% .
I guess he could boil the water in the heatsink when he is not moving forward for coffee ok2
 
Mark.
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inertia

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Re: changing voltage on lights
« Reply #9 on: March 30, 2013, 10:17:30 AM »

It's a damn sight easier to either follow the wiring diagram which has been done for you (Mr Burke...........!!!) OR use separate batteries OR wire the lights in series e.g. 2 x 6v bulbs = 12v supply etc. Resistors and regulators always involve wasting energy.
Of course, if you're as rich as Croesus and you don't mind wasting energy and charging a BIG battery then you could always buy one of these    http://www.harbormodels.com/site08/main_pages/power_distribution_panel.htm
That fan on the top is not there for decoration.
DM
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787eng

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Re: changing voltage on lights
« Reply #10 on: March 30, 2013, 10:28:11 AM »

You need to read up on switching regulators. {-)  Read the text in the link I originaly sent "the regulator can be up to 96% efficient."
A switching regulator is in essence what you were selling for years after "Bobs boards" were considerd out of the ark
 
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malcolmfrary

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Re: changing voltage on lights
« Reply #11 on: March 30, 2013, 10:35:56 AM »

From the technobots link -
Quote
Price Ex VAT: 16.92(20.30 inc tax)
A passive regulator costs about 0.30, as opposed to 20.30.  To halve the voltage for a lamp, the correct resistor is another identical lamp in series.  The wiring is a little more complicated different.  To quarter the voltage, 3 more identical lamps.Just add to the complexity, cost and weight of a cooling system, a water cooled one, unless fitted with a pump, will only work when the boat is moving in water.  It doesn't work out of water, say on a display stand or when being checked on the bench.
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Circlip

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Re: changing voltage on lights
« Reply #12 on: March 30, 2013, 10:43:45 AM »

Can you still get Rotary converters from Arthur Sallis?
 
 It's a  TOY  boat{-)
 
  Regards  Ian.
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oldiron

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Re: changing voltage on lights
« Reply #13 on: March 30, 2013, 10:47:57 AM »

Mick

  Send me your address  via PM and I'll send you a voltage regulator. I use them in my boats to power my receivers instead of a seperate battery pack. Mount it on a bit of aluminum and you're good to go.

John
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inertia

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Re: changing voltage on lights
« Reply #14 on: March 30, 2013, 01:29:26 PM »

You need to read up on switching regulators. {-)  Read the text in the link I originaly sent "the regulator can be up to 96% efficient."
A switching regulator is in essence what you were selling for years after "Bobs boards" were considerd out of the ark

And here's me thinking it was all done with smoke and mirrors..........or magic............
DM
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irishcarguy

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Re: changing voltage on lights
« Reply #15 on: March 30, 2013, 03:58:57 PM »

Hi Dave,(inertia)what prompted this is that I have made the mast in my Smit Nederland from brass tube, I use the mast as one wire & join all 7 of the other wires into a single wire.Because the bulbs are in their brass lamps they seem to get very hot. I thought (wrong or right) that if I reduced the power to the bulbs to 6 volts they will not get as hot if only 6 volts (dimmer) & also last longer. It was a hard job getting all the wires inside the mast together with strobe wiring as well & the thought of having to replace one of the bulbs boggles the mind. I just want to know what is the best way to make the setup as it is now more reliable & long lasting.Mick B.
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Mick B.

inertia

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Re: changing voltage on lights
« Reply #16 on: March 30, 2013, 04:21:24 PM »

PM sent, Mick.
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Re: changing voltage on lights
« Reply #17 on: March 31, 2013, 03:08:05 AM »

Why not just make up a voltage divider ,easiest in a pinch  only watch the wattage of the resistor's.Really. Switching regulators..why would anyone want to get involved with Mosfets for simple reduction in running voltage..
The LM317 while adjustable is still only rated at 1.5A ,LM350 will get you 3Amp..
The L7806 isn't all that rare , They can easily be had for 5 at a time for under $2 Can.
A heatsink doesn't have to be a large block of anything..it could be done with a couple or three pennies clamped on with a small paper clamp..get crafty and you'll probably find a little metal something to pop it on ..
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