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Author Topic: Help request with noob circuit XD  (Read 1287 times)

Phil22

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Help request with noob circuit XD
« on: August 14, 2019, 06:22:02 AM »


Hi All,


We’d like to ask which of the 2 setups below (or possibly neither) would work fine.
We don’t have any experience of electronics so assistance and advice is sincerely welcomed.


For our Banckert’s lighting, the plan is: 2 navigation lights, 1 internal bridge light and 2 mast lights. 

Additional to the 9V battery on the circuit will be a fuse and a 3 position sliding switch like this:

(The extra functionality might be used in future - for now it'll be only used for ON/OFF)



For the 2 navigation lights, they’ll be largely contained inside 3mm brass housings so a flash of red and green marker pens over the LED surface should suffice for colour.

LEDs: 5 | Size: 3mm |
Colour: white | Voltage: 3.4V (max 72V) | Amps: 20mA (max 30mA)

Suggestions below came from this resource:http://led.linear1.org/led.wiz


Setup A 20mA





Setup B 22mA





Goal:
We want the LEDs to be bright (subjective lol) but nowhere near max.

Questions:
1. Will the switch and/or fuse also take away current resulting in less brightness?
2. Would the ohme value of the resistors need to be adjusted taking point 1 into account?
3. What would be the recommended fuse in terms of holding current and trip limit?
4. Are there any other things that need to be accounted for?

Thanks in advance =)
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malcolmfrary

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Re: Help request with noob circuit XD
« Reply #1 on: August 14, 2019, 09:50:32 AM »

Quote
1. Will the switch and/or fuse also take away current resulting in less brightness?
2. Would the ohme value of the resistors need to be adjusted taking point 1 into account?
3. What would be the recommended fuse in terms of holding current and trip limit?
4. Are there any other things that need to be accounted for?


1  No
2  No
3  1A, smallest value you are likely to find, not really needed with a PP3 supplying the current.
4a  Unless it is a very large boat with long wiring runs, the thinnest wire you can find will be fine
4b  If using a PP3, a fuse will probably not be needed, the battery will provide its own current limiting.
4c  Different colour LEDs have different efficiencies, yellow need nore current than red or green, their resistor value will therefore need to be different.  Using red and green, typical Vf and If would be 1.9V and 10mA, adjusted by fitting appropriate resistors and reducing the total current.  See 4e.
4d  LEDs are pre-coloured unless you get white ones.  White are the least efficient. 
4e  The switch shown "should" be OK, but might be a bit near its limit for 100mA.  If a specification is available, that should help.

A lot of models have eye wateringly bright nav lights.  On real ships and boats, they are usually just above the legal minimum required.  Deck lights are much brighter.
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Phil22

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Re: Help request with noob circuit XD
« Reply #2 on: August 15, 2019, 12:57:36 AM »

Spot on Malcolm - thank you for the detailed answer, it answered more of our questions as a result.
Thinking of the switch limit we are going to try out the 20mA setup  ;)

After trimming down the LED anode and cathode (legs), are there any recommended methods for sealing and insulating these points in the circuit? I've read that some people will cover the underside of an LED with epoxy (after the wires have been soldered). 2 of our LEDs will sit in holes on the V-shaped bracket (funnel section) so the undersides will be exposed.




Cheers!
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malcolmfrary

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Re: Help request with noob circuit XD
« Reply #3 on: August 15, 2019, 09:36:10 AM »

Spot on Malcolm - thank you for the detailed answer, it answered more of our questions as a result.
Thinking of the switch limit we are going to try out the 20mA setup  ;)

After trimming down the LED anode and cathode (legs), are there any recommended methods for sealing and insulating these points in the circuit? I've read that some people will cover the underside of an LED with epoxy (after the wires have been soldered). 2 of our LEDs will sit in holes on the V-shaped bracket (funnel section) so the undersides will be exposed.




Cheers!
Thats 20mA per element, so "alot" of them = 20 times "alot" mA.  5X20 = 100mA, which is often the rated limit on small slide switches which were originally intended to switch very low currents as in changing waveband on a radio.  Exceeding the limit by a mild degree won't do any noticeable harm, but going well over will result in reduced switch life.  Nothing dramatic, it will just stop working.
Insulating the exposed metal?  Paint. Or yacht varnish, or a dab of epoxy, obviously after soldering.  Varnish is the stuff used to insulate the winding wires in motors. 
A common trick is to have the LEDs on the negative side of the circuit, using the metal of the mast as a common return, or, if not a metal mast, a common wire.  Still needs a resistor for each LED and a wire from resistor to LED +.
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Phil22

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9V Parallel Circuit Mockup
« Reply #4 on: August 16, 2019, 04:16:03 PM »

Thank you once again Malcom for helping us out.  {-)
Bought some parts for the build this week. Still unsure of how to wire in the slider switch.
It has six terminals (prongs) but no markings. Internet searches mention "positive out" and "negative out" so now a bit stumped.

Here is the mockup with all white LEDs




Again many thanks!
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Phil22

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Re: Help request with noob circuit XD
« Reply #5 on: August 17, 2019, 04:03:40 AM »

Result!!

Put together a test circuit and after trying a couple of positions on the slide switch terminals. It works.
(+) wire to the end (ON position) and the (-) wire in the centre (OFF Position) within the same row.




OOOOoooos and smiles broke out like turning on the xmas tree  {-) {-) {-) {-) {-)









Plan to dim down the bridge light in some way, maybe add some kind of shade for it. We will continue to add more updates to our build thread: https://www.modelboatmayhem.co.uk/forum/index.php?topic=63135.msg667222#msg667222

This is a massive step for us as we have never done any electronics before. Thank you to @Malcolm and @Subculture. We are very grateful, your guidance got us this far.
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malcolmfrary

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Re: Help request with noob circuit XD
« Reply #6 on: August 17, 2019, 09:15:14 AM »

Quote
Plan to dim down the bridge light in some way, maybe add some kind of shade for it.
...........higher value resistor, if the existing is 330 ohms, go for 390.  Saves a few mA as well.
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JimG

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Re: Help request with noob circuit XD
« Reply #7 on: August 17, 2019, 10:57:45 AM »

Result!!

Put together a test circuit and after trying a couple of positions on the slide switch terminals. It works.
(+) wire to the end (ON position) and the (-) wire in the centre (OFF Position) within the same row.



Unless you are planning to switch a second circuit it is best to bridge both halves of the terminals with the wiring. This way both sides of the slide   are being used for the switching giving some redundancy in case of corrosion caused by dampness.
Jim
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Phil22

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Re: Help request with noob circuit XD
« Reply #8 on: August 19, 2019, 11:55:19 AM »

Thanks very much Jim! Do you mean split the positive wire and add it the the remaining terminal in the row?
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JimG

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Re: Help request with noob circuit XD
« Reply #9 on: August 19, 2019, 12:35:29 PM »

Just push the +ve wire through both end terminals (same end) and solder then the black wire through both middle terminals and solder. This way both halves of the slide are switching together.
Jim
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Phil22

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Re: Help request with noob circuit XD
« Reply #10 on: August 19, 2019, 01:25:17 PM »

Gotcha. Will do!! Appreciate the advice Jim.

Now that we have a benchmark for the brightness, we've decided to run with stronger resistors with about 15mA output.
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Phil22

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Re: Help request with noob circuit XD
« Reply #11 on: August 19, 2019, 02:06:23 PM »

In your experience is it okay to heat wrap 1/4W resistors? Various sites online are for and against. One line of answers we see is that 1/4W resistors don't get very hot anyhow so it's acceptable (dependent on how much current is being handled). Our new aim is with 5 x 3.4W LEDs @ 14mA/470 ohmes each on 9V. Would this setup be considered acceptable for heat wrapping? Going on the guideline of operating at less than 60% of the rated power.
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malcolmfrary

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Re: Help request with noob circuit XD
« Reply #12 on: August 20, 2019, 08:59:43 AM »

Depends on the heat wrap (presumably heat shrink sleeve) and how close to the power limit of the resistor and how many are packed close to each other.  Then you need to consider the heat transferring ability of the sleeve. 
A resistor has a maximum power rating because going above that in free air at an ambient temperature of 25C will cause the resistor to heat above its maximum safe temperature, whatever that might be. 
Going above that in free air will cause the paint on it to bubble and possibly char off.  It usually results in the wires detatching from the actual resistor. 
Enclosing it in an insulating sleeve will reduce its ability to dissipate heat, which will cause it to run hotter.  What this will do to either the resistor or the plastic of the sleeve is anybody's guess, but a move to half watt resistors would improve likely reliability.  The process is called "de-rating", and is normal practice when designing for reliability in uncertain environments.
Is there a reason for wanting to sleeve them?
Design tip - try not to have hot resistors too near to stuff that melts like wire insulation or structural plastic.  If they had been handing out tee shirts for that kind of thing back then, I would have added them to my collection.

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Phil22

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Re: Help request with noob circuit XD
« Reply #13 on: August 21, 2019, 01:14:07 AM »

Hi Malcolm,
Many thanks for the reply and detailed information.
As electronics is a brand new area for us we have a lot of questions as you can see. Googling various aspects of the build invariably leads to differences of opinion (exp. to heat wrap resistors or not). Being able to ask MBM forum members with experience is invaluable at our level.

"Is there a reason for wanting to sleeve them?"
As most of the circuit we be installed inside the plywood deck cabins, we're thinking how to affix and protect the resistors/wires internally?

Related to moving to 1/2W resistors from 1/4W (with the same 470 ohme value), would this change give us the same LED brightness while in turn provide a better reliability margin?

Cheers,
Phil
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malcolmfrary

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Re: Help request with noob circuit XD
« Reply #14 on: August 21, 2019, 09:03:09 AM »

It the value of the resistance in ohms that determines the brightness of the LED.  The power rating determines whether the resistor will survive or not with the current going through it.  Resistors are generally covered with a built in layer of insulation, it is just the leads that are live and might benefit from insulation which is where heatshrink comes in useful.
For a good introduction to electronics at a component level, have a look at - https://archive.org/details/PracticalElectronicsHandbook - download and read at leisure.  There are several later editions of the book (worth paying money for) because electronics moves on rapidly, but the basics remain.  Unlike most text books, its written in English rather that technical.
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Phil22

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Re: Help request with noob circuit XD
« Reply #15 on: August 23, 2019, 12:57:18 AM »

Outstanding! Cheers Malcolm!!!!
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