Model Boat Mayhem - Forum

Technical, Techniques, Hints, and Tips => The "Black Arts!" ( Electrics & Electronics ) => Topic started by: triumphjon on April 01, 2012, 09:38:49 PM

Title: leds for nav lighting ?
Post by: triumphjon on April 01, 2012, 09:38:49 PM
having a few issues regarding the fitment of some L E D  for my navigation lights , all leds are wired +ve & -ve through the model to a power distribution point , all of the +ve are grouped together into a chocoblock , which is then connected to a resistor & to the +ve terminal on my 4.8 volt battery the -ve are divided to the individual switch outlets on my graupner smx switcher unit . i now cannot get all of the lights working together ? jon
Title: Re: leds for nav lighting ?
Post by: HawkEye on April 01, 2012, 11:14:08 PM
From what i can see the sxm switcher only has N/O outputs giving output to A or B or C or D ( I may be wrong ), some other switchers ( Electronize as an example ) have change over relays allowing them to be wired for concurrent operation - i.e. Output A+B+C+D depending on the control signal.

Therefore you may have to connect all your lights to one output in order to have them all on at once.

Hope that's some help.

hawkEye
Title: Re: leds for nav lighting ?
Post by: triumphjon on April 02, 2012, 07:58:34 AM
ive used another two of the switchers in other models and we can have all of the functions operating at once ! this one has been wired so that ive got all four nav lights together ie port/ star + mast head/ stern from one output , the search is another and the blue is on another . if i pull the stick to operate the navs i get just one lamp illuminateing of the four !
Title: Re: leds for nav lighting ?
Post by: malcolmfrary on April 02, 2012, 09:55:50 AM
What do the instructions on the switcher say?

BTW a resistor can only supply a set load - either one LED or all of them, depending on the value.  If you want to combine / permutate the load, you will need to wire each through its own resistor.  A resistor good for one LED might not pass enough current for several, one that will pass enough for several will possibly give too much for one.  In the first case, they glow faint, in the second, it will glow very brightly, but briefly.  Wiring several LEDs that might well have differing forward voltage drops will result in the one with the lowest drop winning, and starving the others of operating voltage.
Title: Re: leds for nav lighting ?
Post by: triumphjon on April 02, 2012, 06:32:16 PM
the switcher works on the -ve side of the battery , hence ive connected all of the +ve wires together and placed a resister between them and the battery wire !
Title: Re: leds for nav lighting ?
Post by: malcolmfrary on April 02, 2012, 06:49:22 PM
the switcher works on the -ve side of the battery , hence ive connected all of the +ve wires together and placed a resister between them and the battery wire !

Not being familiar with that particular switcher, I don't know whether it selects between outputs or whether any combination is possible, but I assume that you have the instructions that will tell you.  One common resistor with a variable load is asking for problems, like I said in my previous post.  Using a voltmeter to check which outlets are switched on for any given setting should give the required clues,  Connect the + side of the meter to batt +, look at each outlet in turn, on will show full voltage, off will (or should, provided that there are no stray supplies) show no volts.
Title: Re: leds for nav lighting ?
Post by: triumphjon on April 02, 2012, 07:00:46 PM
the switcher will switch any combination i require , using a small jumper it can also flash lights , dont think the switcher has anything to do with the problem , can i fit resistors on the -ve side of the leds or must they only be on the +ve ?
Title: Re: leds for nav lighting ?
Post by: malcolmfrary on April 02, 2012, 08:46:30 PM
Considering each LED, they don't care where the resistor is, as long as it's in series. 
The important thing is that each LED only gets the current it needs. A single LED can have its appropriate resistor calculated.  Two in parallel would require a different value, so in this case, forget the commoning of the LEDs, and the single resistor.
Rather use a separate resistor for each, common the other end of the resistors to the supply.  Either that, or a resistor between the LED and switcher and common the LED + sides to power supply. 
With that sorted, it becomes possible to sort the rest of the circuit operation, if needed.
Title: Re: leds for nav lighting ?
Post by: triumphjon on April 02, 2012, 09:46:28 PM
what ive done is sent individual wires from each " lamp " back down into the forward cabin ( ie a +ve &-ve to each ) all of the navigation lamps have been connected together ie 4 x +ve & 4x -ve  , at the moment when i connect my test power unit ( an ex 3v battery box with small resistor on the +ve side of the switch (( parasol lights ) )) the green led illuminates while the red wont ?
Title: Re: leds for nav lighting ?
Post by: HawkEye on April 02, 2012, 10:09:01 PM
what ive done is sent individual wires from each " lamp " back down into the forward cabin ( ie a +ve &-ve to each ) all of the navigation lamps have been connected together ie 4 x +ve & 4x -ve  , at the moment when i connect my test power unit ( an ex 3v battery box with small resistor on the +ve side of the switch (( parasol lights ) )) the green led illuminates while the red wont ?

Ah ! It's not good to have different led's in parallel with just one resistor shared between them, you'll find that they require slightly different voltages and only the lowest voltage LED will light, it can be achieved with identical led's but for the cost of a few resistors not worth it, give each one it's own resistor and all should be fine.

HawkEye
Title: Re: leds for nav lighting ?
Post by: malcolmfrary on April 03, 2012, 10:02:22 AM
Ah ! It's not good to have different led's in parallel with just one resistor shared between them, you'll find that they require slightly different voltages and only the lowest voltage LED will light, it can be achieved with identical led's but for the cost of a few resistors not worth it, give each one it's own resistor and all should be fine.

HawkEye
Pretty much what I said in reply #3 "Wiring several LEDs that might well have differing forward voltage drops will result in the one with the lowest drop winning, and starving the others of operating voltage."
Title: Re: leds for nav lighting ?
Post by: HawkEye on April 03, 2012, 12:47:52 PM
Pretty much what I said in reply #3 "Wiring several LEDs that might well have differing forward voltage drops will result in the one with the lowest drop winning, and starving the others of operating voltage."

Yup ! - pretty much,  sorry I must of skipped that post, if it cures the problem then all's good though  :-))

HawkEye
Title: Re: leds for nav lighting ?
Post by: Circlip on April 03, 2012, 01:03:07 PM
Been on before but worth a repost :-

   http://ledz.com/?p=zz.led.resistor.calculator


   Regards  Ian.
Title: Re: leds for nav lighting ?
Post by: barriew on April 03, 2012, 05:29:23 PM
This one is also useful for when you have more than 1 LED - it works out the best arrangement of an array of LEDs in series or parallel with the appropriate resistors

Barrie

http://led.linear1.org/led.wiz
Title: Re: leds for nav lighting ?
Post by: triumphjon on April 03, 2012, 06:28:32 PM
ive been into my local maplins today , they have advised a resistor per led  they have made a calculation and supplied me with the cxorrect item , will see if it works later
Title: Re: leds for nav lighting ?
Post by: balders on April 04, 2012, 10:10:08 PM
You could always do as I have done,CHEAT!! After messing about on various projects sorting out resistor values and soldering in etc. I came across an advert in Railway Modeller for a company called MICROMINIATURES .CO.UK  They do a range of L E D's in 6v and 12 v in every colour we are likely to need and each one as a very neatly soldered in resistor.

You simply connect all to a single choc. box connector and from there a single wire to each battery terminal and the jobs a good'un.

O.K so they will cost around 6 for 10 but I think it's well worth it for the time and effort they will save.


                                                                                                                Andy
Title: Re: leds for nav lighting ?
Post by: triumphjon on April 04, 2012, 10:22:26 PM
having soldered resisters  to all of the +ve wires , then onto a small peice of vero board and connected a +ve red wire back to a battery , the bonus is that ive finally got a full set of navigation lamps working , allbeit the port lamp is very dim !
Title: Re: leds for nav lighting ?
Post by: emlra on April 04, 2012, 11:25:27 PM
All the ends either +ve or _ve can be fed from a single common point, the other ends need the appropriate resistor to be soldered in each each individual 'return line' and then via swich/switches back to the other battery terminal,
The reason for this being that each colour needs a different current (number of wiggley Amps) for it to work possibly'explains your weak red.

http://led.linear1.org/led.wiz should be of some assistance.

You will know the parameters...colour
supply voltage and max current I that the device will handle in mA (find out from your LED supplier)

Bob's your uncle and Fannies his significant other!

Rex
Title: Re: leds for nav lighting ?
Post by: Umi_Ryuzuki on April 05, 2012, 05:50:23 AM

Using the LED wiz, you will probably come up with info like this...

LED Resisitors for 6v
Yellow/Red    220ohm 1/8watt
White/Green   150ohm 1/8watt

LED Resisitors for 12v
Yellow/Red    560ohm 1/2watt
White/Green   470ohm 1/2watt

I usually include this info when I send out any LED lights.

Quote

Do not hook up any LED without the
resistors in place.

Yellow and red
Forward Voltage 1.8v-2.2v
Forward Current 18 mA

White and Green
Forward Voltage 3.2-3.4v
Forward Current 20mA

Source voltage will be the battery or
the power supply voltage.


 8)


Title: Re: leds for nav lighting ?
Post by: triumphjon on April 05, 2012, 08:36:04 AM
sorted the dim red , ive replaced it with a new one , its now working as it should ! i was advised at the local maplin store to only fit the resisters on the +ve side of the circuit , which is what ive done , the very small GRAUPNER SMX  switcher i use only switches from the neg side of the power supply , very clever little unit as it allows both solid , monentry and plusating switching and gives four outputs  from a single channel on the radio , on this boat its being used just for lighting , another boat weve got it controlling nav lights , a pair of flashing blue beacons , a search light plus a windscreen washer pump to operate a fire monitor